Applied Catalysis B Environmental (APPL CATAL B-ENVIRON)

Publisher: Elsevier

Journal description

Applied Catalysis is divided into two sections, General and Environmental. Applied Catalysis B: Environmental covers the catalytic chemistry of polluting substances.- Catalytic elimination of known environmental hazardous effluents, nitrogen oxides, carbon monoxide, chlorinated and other organic compounds, used catalysts, etc. from stationary or mobile sources in air, water, soil, etc.- Catalytic combustion and catalytically assisted combustion- Basic understanding and characterization of the corresponding catalysts, their activity and selectivity.- Catalytic sensors used in monitoring the environment or industrial or automotive effluents.- Catalytic processes occurring in the environment itself.The journal will accept original letters, reviews, research papers and articles of general interest. Articles of general interest (feature articles) may cover regulations, overviews on strategies for pollution abatement, case studies, general policy for energy and natural resources conservation, global environmental issues, etc.A News Brief section will provide news and views relevant to environmental catalysis, together with meeting reports, project summaries, book reviews, and a calendar of forthcoming events.Since the scope of the Elsevier journals Applied Catalysis and Journal of Molecular Catalysis are complementary, an appropriate choice for submission to either journal could be borderline, in which case the advice of one of the editors should be sought.

RG Journal Impact: 10.72 *

*This value is calculated using ResearchGate data and is based on average citation counts from work published in this journal. The data used in the calculation may not be exhaustive.

RG Journal impact history

2019Available summer 2020
201810.72
20177.55
20167.66
20158.51
20147.89
20136.05
20125.69
20116.38
20104.96
20095.05
20084.57
20074.26
20063.50
20053.19
20043.58
20033.10
20022.29
20013.07
20002.67

RG Journal impact over time

RG Journal impact
RG Journal impact over timeGraph showing a linear path with a yearly representation of impact points of the journal

Additional details

Cited half-life5.30
Immediacy index2.54
Eigenfactor0.05
Article influence1.48
Websitehttp://www.sciencedirect.com/science/journal/09263373
Website descriptionApplied Catalysis B: Environmental website
Other titlesApplied catalysis
ISSN0926-3373
OCLC38523376
Material typeDocument, Periodical, Internet resource
Document typeInternet Resource, Computer File, Journal / Magazine / Newspaper

Publications in this journal

Under pH 7 - 10 conditions, the mesoporous silica supports proposed for use in water treatment are relatively unstable. In batch experiments conducted in pH 7 solutions, the commonly used support SBA-15 dissolved quickly, releasing approximately 30 mg/L of dissolved silica after 2 hours. In column experiments, more than 45% of an initial mass of 0.25 g SBA-15 dissolved within 2 days when a pH 8.5 solution flowed through the column. In a mixed iron oxide/SBA-15 system, the dissolution of SBA-15 changed the iron oxide reactivity toward H(2)O(2) decomposition, because dissolved silica deposited on iron oxide surface and changed its catalytic active sites. As with SBA-15, other mesoporous silica materials including HMS, MCM-41, four types of functionalized SBA-15, and two types of metal oxide-containing SBA-15 also dissolved under circumneutral pH solutions. The dissolution of mesoporous silica materials raises questions about their use under neutral and alkaline pH in aqueous solutions, because silica dissolution might compromise the behavior of the material.
Single-phase perovskite-like oxides NdSrCu1−xCoxO4−δ and Sm1.8Ce0.2Cu1−xCoxO4+δ (x = 0, 0.2, and 0.4) were prepared using the citric acid complexing method coupled with ultrasonic treatment. We characterized the materials by a number of analytical techniques. It was found that the NdSrCu1−xCoxO4−δ and Sm1.8Ce0.2Cu1−xCoxO4+δ catalysts possess T and T′ crystal structures, respectively. There are Cu3+/Cu2+ ions and oxygen vacancies in the former and Cu2+/Cu+ ions and extra (over-stoichiometric) oxygen in the latter. We examined the catalytic activity of the materials for methane combustion. Methane conversion increased with a rise in the amount of nonstoichiometric oxygen over the two series of catalysts. It is concluded that oxygen nonstoichiometry and Cu3+/Cu2+ or Cu2+/Cu+ redox couples facilitate the oxidation of methane over the NdSrCu1−xCoxO4−δ and Sm1.8Ce0.2Cu1−xCoxO4+δ catalysts.
This study reports the results obtained for the degradation of humic acid (HA) in aqueous solution, by electrochemical and photoelectrochemical oxidation. The experiments were carried out using electrolysis and photo-assisted electrolysis on a thermally prepared oxide electrode mounted in a flow cell reactor. Results showed that both process are effective for the degradation of humic acid. However, by assisting electrolysis with UV radiation, the total organic carbon (TOC) reduction rate was greatly improved. For instance, at 20 mA cm−2, electrolysis was responsible for 25% of TOC reduction after 180 min of reaction time. On the other hand, the decrease during the photo-electrolysis reached 65% at the same current density and processing time.
Chromium oxides dispersed on various supports by precipitation method were tested for the catalytic fluorination of HCFC-133a to HFC-134a. Catalytic activity decreased in the order of MgO>Al2O3>MgF2>TiO2>ZrO2. The most active Cr/MgO, when properly activated and pre-fluorinated before the reaction, shows superior activity to other catalysts that have been reported so far. Isolated (monomeric) Cr(VI) species that was formed during an optimized thermal activation were changed into fluoride (CrxFy) and oxyfluoride (CrxOyFz) form of monomeric and oligomeric Cr species during the pre-fluorination with HF, the latter of which are believed to be active sites for the reaction. High pre-fluorination temperature accelerates the formation of crystalline Cr2O3 due to the formation of crystalline MgF2 from MgO which anchors the isolated Cr(VI).
The transformation of CF3CH2Cl over bulk chromium(III) oxide, fluorinated or not, leads mainly to the fluorination product CF3CH2F and to the alkene CF2=CHCl. In the presence of HF, CF3CH2F is the main product. In absence of HF this product is also obtained with HF formed in the elimination reaction of CF3CH2Cl to CF2=CHCl. At the same time a part of HF is used for the fluorination of chromium oxide. The XPS analysis of fluorinated catalysts with HF gives surface fluorine atomic contents which correspond to a F/Cr ratio of 0.36. A survey of the effect of partial pressures of HF and of CF3CH2Cl shows a zero order for HF and a 0.6 order for CF3CH2Cl. The fluorination reaction could occur on a partially fluorinated chromium(III) oxide involving HF oligomer species previously postulated by Rowley et al. [L. Rowley, J. Thomson, G. Webb and J.M. Winfield, Appl. Catal. A, 79 (1991) 89–103].
It is shown that it is possible to produce 1,2-propanediol (a high demand commodity chemical) in high yields via the vapor-phase catalytic hydrogenation of biomass-derived lactic acid. This catalytic process provides an environment-friendly route for the production of 1,2-propanediol from renewable resources. Reaction kinetics measurements were conducted for the vapor-phase hydrogenation of lactic acid over silica-supported copper at total pressures between 0.10 and 0.72 MPa and temperatures between 413 and 493 K. Lactic acid is hydrogenated over Cu/SiO2 under these reaction conditions to predominately 1,2-propanediol, with formation of smaller amounts of 2-hydroxy propionaldehyde, propionic acid, and propyl alcohols. Deactivation of the Cu/SiO2 catalyst does not appear to be significant under these reaction conditions. The production of 1,2-propandiol is favored at higher hydrogen partial pressures. At 473 K and a hydrogen partial pressure of 0.72 MPa, complete conversion of lactic acid was observed, with 88 mol% of the lactic acid converted to 1,2-propanediol. A reaction scheme for lactic acid conversion is proposed involving the dissociative adsorption of lactic acid to form an adsorbed α-hydroxy acyl species that undergoes successive hydrogenation steps to form adsorbed 2-hydroxy propionaldehyde species and then adsorbed α-hydroxy alkoxy species. These alkoxy species react with surface hydrogen to form 1,2-propanediol. The formation of 2-hydroxy propionaldehyde appears to be in equilibrium with 1,2-propanediol at the reaction conditions of the present study.
The study of the influence of synthesis operating variables (nature and concentration of complexing silane, palladium percentage, temperatures of gelling, aging and vacuum drying of xerogels, molar ratio between the complexing silane and palladium, molar concentration of ammonia solution, and use of tetramethylammonium hydroxide as base instead of NH3) allows improving metal dispersion in Pd/SiO2 cogelled xerogel catalysts. The use of 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) or 3-(2-aminoethylamino)propyltriethoxysilane (EDAES) to complex palladium in an ethanolic solution containing tetraethoxysilane (TEOS) and an ammonia solution of 0.54 mol/l allows obtaining a Pd/SiO2 xerogel catalyst with a mean metal particle diameter of 2.4 nm located inside silica particles. Indeed, complexes Pd(EDA(E)S)xn+ induce a nucleation mechanism because of their higher reactivity compared to the network-reagent (TEOS). Although metal particles are located inside the silica particles, their complete accessibility, via the micropore network, has been shown. 1,2-dichloroethane hydrodechlorination over Pd/SiO2 catalysts mainly produces ethane and the specific hydrodechlorination rate per gram of palladium increases proportionally with palladium dispersion. Hydrodechlorination over Pd/SiO2 cogelled xerogel catalysts is a structure insensitive reaction with regard to the ensemble size concept.
The degradation of high phenol and 1,2-propylene glycol concentrations (1 g/l) in water solutions by TiO2-photocatalysis has been studied. Important differences between the degradation mechanism of both molecules have been observed. From the obtained data it may be suggested that degradation of phenol takes place onto the catalyst surface by means of formation of peroxo-compounds. At low phenol concentrations another mechanism, the insertion of OH radicals may be favored. At low or high 1,2-propilene glycol concentrations degradation seems not to be affected by the OH radical insertion process. These conclusions have been obtained by studying the effect of catalyst concentration and adding different OH radical precursors such as H2O2 and S2O82−. Degradation intermediates have been identified by HPLC and FTIR. The FTIR study of the catalyst surface has shown infrared bands attributable to different chemisorbed M–OC6H5 species, peroxo-compounds, formates, ortho-formates and carboxilates that can inactivate the catalyst.
Several Ni/Mg/Al and Ni/Al hydrotalcite-like precursors have been prepared to study their catalytic properties in the hydrodechlorination of 1,2,4-trichlorobenzene in the gas phase. All the samples were characterised by X-ray diffraction (XRD), BET, scanning electron microscopy (SEM), temperature-programmed desorption (TPD) and hydrogen chemisorption techniques.When the magnesium content increases in the catalysts, both the activity and selectivity to benzene greatly increases and the deactivation of the catalysts becomes slower. The highest TOF and selectivity to benzene values at 523 K (100%) are achieved by the catalyst which has the most content of Mg without any significant change in activity even at reaction times higher than 500 min. This catalytic behaviour can be explained because the MgO modifies the electronic properties of the nickel particle causing the hydrogen desorption at lower temperatures and also adsorbs the HCl produced during the hydrodechlorination reaction.
Three polycarboxylic (hemimellitic (Hem), trimellitic (Tri) and pyromellitic (Pyro)) acids, representative of industrial pollutants and of compounds from biomass, were degraded by heterogeneous photocatalysis. The three molecule disappearance rates followed the order Pyro > Hem > Tri. They obeyed a Langmuir–Hinshelwood mechanism. The two competitive initial steps of attack of the molecules corresponded (i) to a hydroxylation reaction induced by photogenerated OH radicals and (ii) by a decarboxylation (photo-Kolbe) reaction resulting from the direct attack of one carboxylic group by a positive photo-hole. A very careful analysis of the degradation intermediates was performed using high performance liquid chromatography (HPLC) and gas chromatograph/mass spectrometer (GC/MS), especially in the case of Tri. The loss of several carboxyl groups leading to benzoic acid formation was observed before the aromatic ring opening. Several aliphatic acidic fragments were detected, such as malonic and succinic acids. Interestingly, a condensation product was detected, which indicated that some carboxylic radicals could attack a Tri molecule and form a Pyr molecule. However, all these acid intermediates could be photodecomposed — in agreement with previous results from the laboratory — into CO2 with a complete carbon mass balance. A detailed degradation pathway could be proposed.Such a reaction demonstrated that complex aromatic water pollutants, originating either from industry or from biomass, could be totally mineralized and that they could produce clean water.
The photocatalytic degradation of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, a non-biodegradable nitrogenous organic compound) in water was optimised under UV radiation using titanium dioxide photocatalyst. The reactor used was a pilot scale cocurrent downflow contactor photocatalytic reactor (CDCPR), a system offering very high mass transfer efficiency. The effect of photocatalyst loading, initial substrate concentration, temperature, pH, and different combinations of UV, O2, H2O2 and TiO2 on the photocatalytic oxidation of DBU was investigated. The TiO2 photocatalyst used was Degussa VP Aeroperl P25/20, a granulated form of Degussa P-25, recently developed to ameliorate downstream catalyst separation problems. The CDCPR was fitted with an internally and vertically mounted 1.0 kW UV lamp. The reactions were carried out at 40–60 °C and 1 barg, with the reactor being operated in closed loop recycle mode and suspended photocatalyst being re-circulated. Optimisation of reaction conditions using a combination of TiO2, UV radiation and O2 gave the most rapid degradation and mineralisation of the DBU in comparison with other processes. Under optimised conditions, 100% degradation of DBU was achieved in 45 min, with a quantum yield of 7.39, using a 1 kW lamp, 0.5 g/dm3 TiO2, 100 mg/dm3 DBU, 1 barg, 50 °C and pH of 3.17. Investigating the reaction pathway and its modelling showed a first order dependency, incorporating the effect of first intermediates of degradation. The activation energy was found to be 54.68 kJ mol−1 showing a significant influence of temperature on the photocatalytic degradation of DBU.
Solutions of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) with concentrations up to near saturation at pH 3.0 and at 25 °C have been treated with ozone and ozonation catalyzed with Fe2+ and/or UVA light. Direct ozonation yields a slow depollution, while all contaminants are completely removed under UVA irradiation. The highest oxidizing power is achieved when Fe2+ and UVA light are combined, since greater amounts of oxidizing hydroxyl radical are generated and Fe3+ complexes are photodecomposed. The initial mineralization rate is enhanced when herbicide concentration increases and more hydroxyl radicals are produced by the catalyzed ozonation processes. The herbicide decay always follows a pseudo first-order reaction. Reverse-phase chromatography allows the detection and quantification of aromatic intermediates such as 2,4-dichlorophenol, 4,6-dichlororesorcinol and chlorohydroquinone. In all treatments, fast dechlorination reactions take place leading to chloride ion accumulation in the medium. The evolution of generated carboxylic acids such as glycolic, glyoxylic, maleic, fumaric and oxalic has been followed by ion-exclusion chromatography. Only oxalic acid remains stable in the O3 system, being quickly mineralized to CO2 by hydroxyl radicals formed in the O3/UVA one. A high stability of oxalic acid in the O3/Fe2+ system has also been found, since it yields Fe3+-oxalato complexes. These species are photodecarboxylated under UVA irradiation in the O3/Fe2+/UVA system. A possible reaction pathway for 2,4-D mineralization involving all intermediates detected is proposed.
Pd/C catalysts used for the Pd/C gas-diffusion cathodes were prepared by the hydrogen gas and/or formaldehyde reduction, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). The electrochemical degradation of 2,4-dichlorophenol was investigated in a diaphragm electrolysis system, feeding with hydrogen gas then with air, using three different self-made gas-diffusion cathodes. The results indicated that the Pd/C gas-diffusion cathodes can not only reductively dechlorinate 2,4-dichlorophenols by feeding hydrogen gas, but also accelerate the two-electron reduction of oxygen (O2) to hydrogen peroxide (H2O2) by feeding air. Therefore, both the removal efficiency and the dechlorination degree of 2,4-dichlorophenol all reached about 100% after 80 min by using Pd/C gas-diffusion cathode, which were better than that of the carbon/polytetrafluoroethylene (C/PTFE) gas-diffusion cathode (no catalyst). The Pd/C catalyst prepared by the hydrogen reduction method had higher stability and catalytic activity than that prepared by the formaldehyde reduction method. By high-performance liquid chromatogram (HPLC), the main intermediates of 2,4-dichlorophenol dechlorination in the cathodic compartment were identified as 4-chlorophenol and 2-chlorophenol, which could be further dechlorinated to form phenol. Hydroquinone was the first intermediate formed from the oxidation of phenol, which was subsequently dehydrogenated to benzoquinone. The further oxidation of benzoquinone, after benzene ring cleavage, led to the formation of aliphatic carboxylic acids such as maleic, fumaric, and oxalic acids.
Acid solutions of the herbicide 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP) of pH 3.0 at 25.0 °C have been treated with ozone and ozonation catalyzed with Fe2+, Cu2+ and/or UVA light. This herbicide is slowly degraded by ozonation alone, while its destruction is enhanced under UVA irradiation. In the presence of Fe2+, the initial mineralization rate is accelerated due to the generation of oxidizing hydroxyl radical (OH), but a large proportion of stable products are formed. These species are partially removed when Fe2+ and UVA light are combined, since greater amounts of OH are produced and Fe3+ complexes are photodecomposed. Addition of Cu2+ to this system does not significantly improve its oxidizing ability, since the Cu2+/Cu+ pair gives a low additional OH concentration. The herbicide decay always follows a pseudo first-order reaction. 2,4-Dichlorophenol, chlorohydroquinone and chloro-p-benzoquinone are detected as aromatic intermediates by reversed-phase chromatography. The initial chlorine is always transformed into chloride ion. Ion-exclusion chromatography allows the quantification of generated carboxylic acids such as lactic, pyruvic, maleic, fumaric, oxalic and acetic. These acids are completely removed, except the two latter ones. Acetic acid remains stable in all cases. Oxalic acid is stable in the O3 system, being partially mineralized to CO2 by the O3/UVA one. It also yields stable Fe3+-oxalato complexes in the O3/Fe2+ system, which are rapidly photodecarboxylated in the O3/Fe2+/UVA and O3/Fe2+ + Cu2+/UVA methods. Cu2+-oxalato complexes also formed in the latter procedure are slowly mineralized with OH. A possible reaction sequence for 2,4-DP degradation involving all intermediates detected is proposed.
2-Propanol and molecular H2 (in methanol (MeOH) and MeOH–water) were examined as reducing agents for the liquid phase hydrodechlorination (HDC) of dioxins over 2 wt.% Pd/γ-Al2O3. Different amounts of NaOH were added to the reaction mixtures. The 2-propanol and H2(g)/MeOH systems presented similar HDC activity. Notwithstanding, Pd sintering and graphitic carbon directly bonded to Pd on catalyst surface was observed on samples used with H2(g)/MeOH. The addition of water to H2(g)/MeOH decreased Pd sintering and favored dissolution of sodium compounds. However, dioxin degradation efficiency diminished. By contrast, 2-propanol acting both as reducing agent and solvent provided hydrogen to the HDC reaction, avoided metal sintering and Pd–C formation. Besides, almost complete dioxin degradation under mild reaction conditions was obtained. Kinetic experiments of dioxin HDC with 2-propanol showed a maximum net reaction rate and turnover frequency (TOF) for a given initial concentration of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). After that value, both reaction rate and TOF decreased. On the other hand, reaction rates and TOFs of dioxin-like polychlorinated biphenyls (DL-PCBs) linearly increased with concentration.
Layered double hydroxide pillared by Paratungstate A ion, Mg12Al6(OH)36(W7O24)·4H2O, was prepared via anion exchange reaction of the synthetic precursor, Mg4Al2(OH)12TA·xH2O (TA2−=terephthalate), and [W7O24]6− ion. Some physico-chemical properties were measured and the preparation conditions were studied. Trace aqueous organocholorine pesticide, hexachlorocyclohexane (HCH), was totally degraded and mineralized into CO2 and HCl by irradiating a Mg12Al6(OH)36(W7O24)·4H2O suspension in the near UV area. Disappearance of trace HCH follows Langmuir–Hinshelwood first-order kinetics. The model and mechanism for the photocatalytic degradation of HCH on the Mg12Al6(OH)36(W7O24)·4H2O were proposed, indicating that the interlayer space is the reaction field, and that photogeneration of OH radicals are responsible for the degradation pathway.
The cerium ion (Ce4+) modified titania sol and nanocrystallites were prepared by chemical coprecipitation–peptization and hydrothermal synthesis methods, respectively. XRD patterns show that Ce4+-TiO2 sol particles had anatase semicrystalline structure. And the calcined Ce4+-TiO2 powder was composed of predominant anatase titania and crystalline cerium titanate (11.18 wt.% CexTi(1−x)O2). AFM micrograph shows that ultrafine particles were well dispersed in sol system and average particle size was about 10 nm. Ce4+-TiO2 nanocrystallites have grown into 70 nm in mean size. The difference in calculated particle size (2.41 nm for sol particle and 4.53 nm for crystallite) by XRD Scherrer’s formula was mainly due to aggregation effect of nanoparticles. The experimental results exhibit that Ce4+-TiO2 sol and nanocrystallites can effectively photodegrade reactive brilliant red dye (X-3B) with the dye/Ce4+-TiO2/visible-light reaction system. Moreover, photocatalytic reaction also can carry out in hydrosol reaction system as well as in suspension reaction system. And Ce4+-TiO2 sol has shown higher efficiency than nanocrystallites in respect of photocatalytic activity. Meanwhile, dye photodegradation mechanisms involving photolysis, photocatalysis, photosensitized photocatalysis and interband photocatalysis were proposed regarding different photocatalytic reaction system.
The activities of Pt supported on various metal-substituted MCM-41 (V-, Ti-, Fe-, Al-, Ga-, La-, Co-, Mo-, Ce-, and Zr-MCM-41) and V-impregnated MCM-41 were investigated for the reduction of NO by C3H6. Among these catalysts, Pt supported on V-impregnated MCM-41 showed the best activity. The maximum conversion of NO into N2+N2O over this Pt/V/MCM-41 catalyst (Pt=1 wt.%, V=3.8 wt.%) was 73%, and this maximum conversion was sustained over a temperature range of 70 °C from 270 to 340 °C. The high activity of Pt/V/MCM-41 over a broad temperature range resulted from two additional reactions besides the reaction occurring on usual supported Pt, the reaction of NO with surface carbonaceous materials, and the reaction of NO occurring on support V-impregnated MCM-41. The former additional reaction showed an oscillation characteristic, a phenomenon in which the concentrations of parts of reactant and product gases oscillate continuously. At low temperature, some water vapor injected into the reactant gas mixture promoted the reaction occurring on usual supported Pt, whereas at high temperature, it suppressed the additional reaction related to carbonaceous materials. Five-hundred parts per million of SO2 added to the reactant gas mixture only slightly decreased the NO conversion of Pt/V/MCM-41.
A series of sulphated zirconia (SZ) catalysts supported on MCM-41 were prepared by the liquid-crystal template method (LCT), using cetyltrimethylammonium bromide (CTABr) as template. The effect of metal oxides promotion (Al2O3, Fe2O3 and Ga2O3) on structural and textural property was studied. These materials were characterized by ion chromatography (for the determination of sulphates content), nitrogen-adsorption measurements, X-ray diffraction, FT-IR spectroscopy, TG–DSC analysis and TPR–MS measurements. The catalytic performance of the catalysts in both gas and liquid phase reactions was investigated. A correlation between morphological and chemical physical features of the systems and their catalytic activity is here proposed.
The activity of 25% TiO2-loaded various amounts of Cr-incorporated MCM-41 (25%TiO2/Cr-MCM-41) was studied as a catalyst for photodegradation of 4-chlorophenol under visible light (400–800 nm). Cr-MCM-41 with different ratios of Si to Cr was synthesized by hydrothermal method and loaded with 25 wt.% TiO2 utilizing sol–gel method. The surface areas of Cr-MCM-41 and 25% TiO2/Cr-MCM-41 samples decreased with increasing the amount of Cr incorporated. XRD analysis showed that the MCM-41 structure was formed only in the samples with Si/Cr ratio larger than 20. Temperature program reduction (TPR) and UV–vis spectra results clearly indicated that only Cr6+ was present in the samples with the ratio of Si to Cr more than 20. Whereas the material with the ratio of Si to Cr less than 20 contained chromium with mixed oxidation states. It was found that the photodegradation ability of 25% TiO2/Cr-MCM-41 was highly related to the amount of Cr6+ which strongly interacted with TiO2; the optimum atomic ratio of Si to Cr was 20.
The selective catalytic reduction of NO by propene in the presence of excess oxygen over Cu-Al-MCM-41 catalyst has been studied by a number of catalytic techniques to characterize the structural, chemisorptive and reactive properties. The characterization using XRD and NMR revealed that the structure of Cu-Al-MCM-41 remained unchanged after the reaction. The active sites related to the reduction of NO and the reaction mechanism were explored based on the data of H2 temperature programmed reduction (TPR), NO temperature programmed desorption (TPD), X-ray spectrometry (XPS) and in situ FT-IR. The results showed that a redox of Cu ions in Cu-Al-MCM-41 between monovalent and divalent states happened during the selective catalytic reduction of NO, and the reduction seemed to proceed via the intermediate of organic nitro compounds produced by the reaction of propylene adspecies and NO2. In addition, the presence of oxygen is essential to the formation of NO2 intermediate and to the cycle of active center between Cu2+ and Cu+. However, it also caused the deep oxidation of propylene, leading to the depletion in reducing agent at higher temperature.
Influence of hydrocarbon structure on selective reduction of NO by hydrocarbons (HC-SCR) over Cu-Al2O3 catalyst was studied by using linear and branched alkanes with different carbon numbers. As the carbon number of linear alkanes increased, reaction rates of NO and hydrocarbon increased. Reaction rates of NO and hydrocarbon for branched alkanes were lower than for linear alkanes of the same carbon number. Structure of hydrocarbon had no influence on the selectivity. Both reaction rates of NO and hydrocarbon had good correlations with mean bond energy of the alkanes. These correlations were also confirmed for the other catalysts such as Ag-Al2O3, Cu-MFI and so on, indicating that the mean bond energy of a hydrocarbon is a useful parameter to estimate its ability as a NO reductant for HC-SCR in diesel emission containing various hydrocarbons.
Sulfamethoxazole (SMX), one pharmaceutical compound, has been treated in aqueous solutions with catalysts (copper and cobalt type perovskites and cobalt–alumina) and promoters (activated carbons). Hydrogen peroxide and saturated carboxylic acids were identified as intermediates. The effects of adsorption and pH have been investigated. Removal of the starting SMX accomplished with ozone alone is a fast process but catalytic or promoted ozonation is needed to significantly reduce the resulting organic carbon. SMX is, thus, mainly removed through direct ozone reaction while hydroxyl radical oxidation is the mechanism of removal the remaining TOC. The kinetics of the process has also been investigated. Perovskite catalytic ozonation resulted to be a chemical control process and apparent rate constants for homogeneous and heterogeneous ozonation were determined. For activated carbon ozonation, external diffusion of ozone to solid particles controlled the process rate.
Copper oxide supported on ZrO2 catalysts (CuOx/ZrO2) were prepared by impregnation of ZrO2 with aqueous solutions of Cu(NO3)2. Copper-sulphated zirconia catalysts were prepared by three different methods: (i) impregnation of ZrO2 with aqueous solutions of CuSO4, (ii) impregnation of sulphated-ZrO2 (SZ) with toluene solutions of Cu(acetylacetonate)2, and (iii) sulphation of CuOx/ZrO2 via the gas-phase. Samples were characterized by X-ray diffraction (XRD), UV–VIS diffuse reflectance (DRS), Fourier transformed infrared (FT-IR), and redox cycles with CO and O2. The reduction of NO with C3H6 in the presence of excess O2 was studied in a flow apparatus fed by a reactant mixture of NO:C3H6:O2=4000:2000:20,000 ppm in He.Irrespective of the preparation method (i) catalysts with the same sulphate content had the same covalent sulphates, and (ii) catalysts with the same copper content and with the same sulphate content were equally active and selective. Sulphated samples were far more selective than the correspondent unsulphated CuOx/ZrO2, particularly sulphated samples with higher copper content. The presence of sulphates (i) made Cu(II) less reducible than in CuOx/ZrO2 and (ii) prevented CuO segregation. The catalytic activity and selectivity of copper-sulphated catalysts depends on a cooperative effect of copper and sulphate. The role of copper is to determine the activity for the NO reduction, and that of sulphate to maintain high the selectivity.
Fe/ZSM-5 catalysts with high Fe loading (Fe/Al∼1) have been prepared by sublimation of FeCl3 onto H-ZSM-5 samples of different Si/Al ratios. They catalyze NOx reduction with hydrocarbons in an excess of O2 and H2O. TPR shows that the Fe in the zeolite cavities is different from Fe2O3 particles. Naked Fe3+ ions are absent; oxo-ions, which are equally well reducible by CO and H2, prevail. A minority of the Fe complexes lose oxygen upon mere heating to ∼500°C; some of the reduced sites are reoxidized only by N2O. The population of oxo-complexes that lose oxygen by heating depends on the Si/Al ratio, this dependence is in qualitative agreement with the model of (2+) charged binuclear ions [HO–Fe–O–Fe–OH]2+. Upon reacting with NO, the bridging O atom is transferred and NO2 is formed. This step is not rate limiting for active catalysts with high Al/Si ratio and high Fe loading, but it becomes critical with zeolites of low Al/Si ratio.
Several catalysts, including FeZSM-5, Co2AlO4, LaCoO3, and BaFeAl11O19, were evaluated for N2O decomposition under representative flue-gas conditions in fluidized-bed combustion (FBC). Closely related formulations proved active and stable catalysts for process-gas or tail-gas de-N2O in nitric acid plants. With this as starting point, their potential suitability for N2O abatement in stationary combustion was assessed. Tests were carried out in a fixed-bed reactor at ambient pressure and in the temperature range of 473–1123 K using mixtures of N2O, O2, NO, CO, SO2, and H2O. The mixed oxide catalysts were strongly inhibited by water and sulfur dioxide and experienced fast deactivation in the simulated mixture containing all the gases. Bulk sulfate phases were detected by X-ray diffraction in the used perovskite and hexaaluminate, revealing insufficient chemical stability in the presence of sulfur and discouraging installation in the freeboard of the combustor. In great contrast, the activity of steam-activated FeZSM-5 in the model and simulated mixtures was comparable, rendering very stable performance during 30 h on stream. The unique tolerance of this iron zeolite to the complex combination of feed components makes it prone to implementation after the cyclone of FBCs, where temperatures are typically 800–1100 K.
The abatement of NO with CH4 in the presence of oxygen ([NO] = [CH4] = 1000 or 4000 ppm, [O2] = 0 to 2%, by volume) was studied on Co-ZSM-5 catalysts (Co content 0.29 to 4.1 wt.-%), prepared from H-ZSM-5 or Na-ZSM-5 by the ion-exchange method. On all samples, the amount of CO and NO adsorbed at room temperature was proportional to the cobalt content (CO/Co⋍ 0.5 and NO/Co⋍ 1.6), with the exception of the Co-ZSM-5 sample with Co 4.1 wt.-%, on which the adsorption was only slightly higher than that on Co-ZSM-5 with Co 2.0 wt.-%. Infrared spectroscopy (FTIR) showed the formation of carbonyls (one type only, on cobalt equivalent sites), cobalt mononitrosyls (two types) and dinitrosyls (two types). The intensity of bands from carbonyls and nitrosyls was about proportional to the cobalt content, with the exception of the Co-ZSM-5 sample with Co 4.1 wt.-%, on which the bands were roughly as intense as in the sample with Co 2.0 wt.-%. In the Co-ZSM-5 sample with Co 4.1 wt.-%, after heating with O2 at 773 K, or after its use in catalysis, diffuse reflectance spectroscopy (DRS) showed the presence of Co3O4, not detected by X-ray diffraction. In the presence of O2, the NO reduction rate was proportional to the Co content, except for the sample containing Co 4.1 wt.-%. The CH4 oxidation rate was proportional to the Co content, in the entire range of Co concentrations. The selectivity of catalysts for NO abatement (selective catalytic reduction, SCR), was nearly independent of Co content but was markedly lower on the sample with Co 4.1 wt.-%. The results suggest that only CoII ions exchanged in the framework of the ZSM-5 matrix are active in CO and NO adsorption and in the SCR reaction, whereas also the cobalt of the dispersed Co3O4 phase contributes to CH4 oxidation with O2.
Samples CuOx/ZrO2 (0.1–8.4 Cu atoms nm−2) were prepared by adsorption or impregnation methods. The characterisation of samples by means of XPS, XRD, DRS, ESR, IR and volumetric adsorption of CO, showed copper dispersion up to 2.5 atoms nm−2, and the presence of CuO in samples with higher Cu content. The selective catalytic reduction of NO with propene or ammonia in the presence of excess oxygen, was studied in a flow apparatus with reactant mixtures of various composition (NO : C3H6 : O2 = 0–4000 ppm : 100–2000 ppm : 0–3.5%; and NO : NH3 : O2 = 0–700 ppm : 700 ppm : 3.6%). With both propene and ammonia, CuOx/ZrO2 catalysts containing up to 2.5 Cu atoms nm−2 were active, selective and stable as a function of the time on stream. On all catalysts, with ammonia as reducing agents, up to 523 K, NO conversion equalled NH3 conversion leading to 100% selectivity. With both propene and ammonia, NO molecules that were converted to N2 per Cu atom and per second were nearly independent of the Cu content up to 2.5 Cu atoms nm−2.
The present paper deals with the preparation of catalytic filters for Diesel particulate removal by developing an in situ solution combustion synthesis method. Lanthanum chromite perovskite catalyst has been deposited on silicon carbide and cordierite honeycombs with the aim to investigate the influence of the starting solution containing catalyst precursors on the coating characteristics. SEM, XRD and EDX analyses have been carried out in order to evaluate the homogeneity and the thickness of the catalyst layer. In particular, using concentrated solutions, a single combustion synthesis step was found to be sufficient to obtain a continuous catalyst film on the support.Pressure drop evaluations and adhesion tests have also been performed thus verifying the possibility to insert this kind of catalyzed traps on the diesel exhaust gas lines. The homogeneity and the high adherence of the deposited catalyst layer, as well as the simplicity and the rapidity of the method, prove its suitability for immediate technological applications.
The twist-like helix W,N-codoped TiO2 photocatalysts were prepared by a simple one-pot synthesis route to hydrolysis of titania tetrachloride using ammonium tungstate as tungsten and nitrogen sources. The morphology and microstructure characteristics of W,N-codoped titania photocatalysts with different amount of tungsten doping were characterized by means of BET, TEM, SEM, XPS, UV–vis DRS, PLS and XRD. The probable mechanism of codoping effect is proposed. It is presumed that cooperation of nitrogen and tungsten ions leads to produce new states and narrow the band gap between the valence band and conduction band effectively, which will greatly improve the photocatalytic activity in the visible light region. On the other hand, the tungsten ions with changing valences in the W,N-TiO2 samples are considered to act as trapping sites, which will effectively decrease the recombination rate of photo-induced electrons and holes and then increase the photo-oxidation efficiency of the catalysts. The metal and nonmetal codoped 1%-W,N-TiO2 sample shows the best photocatalytic activity, which is much superior to P25 under both visible and ultraviolet light irradiation. The superior activity of W,N-TiO2 photocatalysts can also be ascribed to the special twist-like helix structure with regular holes on the wall, high surface area, large pore volume and well-crystallized anatase phase.
A modeling and simulation study on Pt-catalyzed conversion of automotive exhaust gases is presented. The model is based on a newly developed surface reaction mechanism consisting of 73 elementary-step like reactions among 22 surface and 11 gas-phase species. Reactions for the conversion of the major pollutants CO, CH4, C3H6, and NOx are included. The mechanism is implemented in a two-dimensional flow field description of a single channel of the catalytic monolith. The model is evaluated by comparison with data derived from isothermal laboratory experiments in a flat bed reactor with platinum-coated monoliths using synthetic lean/rich cycling exhaust gas mixtures. The influence of CO and C3H6 at lean and H2 at rich conditions on NO conversion is investigated, both at steady-state conditions. Furthermore, the model is also applied for the simulation of emissions of hydrocarbons, CO, and NO from a gasoline engine (stoichiometric exhaust gas) in a dynamic engine test bench.
Titania nanotube arrays synthesized by the electrochemical oxidation of titanium foils have generated considerable interest as photocatalysts for their ordered nature and large surface area. Mixed-phase materials combining the anatase and rutile crystal phases of TiO2, however, have been much more widely studied due to their enhanced reactivity in comparison to pure phase materials. In this study, we seek to integrate these two lines of research and investigate the reductive and oxidative reactivity of TiO2 nanotube arrays (anatase phase) supported on TiO2 films of varying crystal phase composition. A series of TiO2 nanotubes 1.2 μm in length was synthesized, annealed at varying temperatures to control their crystallinity, and characterized by various physical techniques (e.g. XRD, diffuse reflectance, SEM). Photocatalytic CO2 reduction and acetaldehyde oxidation reactions were performed in the gas phase under UV and visible wavelengths. For CO2 reduction, reaction rates decreased with increasing rutile phase under UV. Rates increased with rutile phase ratio under visible and near visible light. For oxidation, the mixed-phase samples showed enhanced reactivity, with a maximum acetaldehyde destruction rate achieved at a 79:21 ratio of anatase to rutile. The samples were substantially less active under visible light, except for the 620 °C composite (77% rutile) which showed a slight rate increase. Nanotubes annealed at 680 °C collapsed to a random porous structure, but showed comparable reductive ability to the non-collapsed samples despite the loss of surface area. This is attributed to the creation of additional anatase–rutile crystallite interfacial area leading to the formation of unique active sites. Control of crystal phase composition through anneal temperature is found to be a simple way to tune the reactivity of these materials and enhance their ability to absorb visible light.
We have studied the conversion of nitric oxide and methane on several H- and Na-ZSM-5 zeolite catalysts in the absence of oxygen. Our results suggest that the NO-CH4 reaction can be explained in terms of a mechanism that starts with a nitric oxide decomposition step followed by the surface reaction of methane with the product oxygen regenerating the active site. We have found that reduced Pd/ZSM-5 catalysts are active for the nitric oxide decomposition reaction but deactivate rapidly due to self-poisoning by product oxygen. By contrast, in the presence of methane these catalysts can exhibit high activity and stability under certain conditions. For instance, when the nitric oxide decomposition and the reaction of methane with the surface oxygen proceed at comparable rates the catalyst is stable but when the methane conversion is lower than that required to remove all the oxygen produced (stoichiometric methane conversion) the catalyst rapidly deactivates. Under some conditions the methane conversion may be higher than the stoichiometric requirement leading to the deposition of carbonaceous species. These carbonaceous deposits can promote the reaction by helping to remove the product oxygen.
The formation of various species during the adsorption of NOx, issuing from a synthetic, Lean–Burn exhaust gas upon BaSnO3 was studied using FTIR and TGA. An exposure to CO2 does not lead to the formation of carbonates yet contact with NO2 does produce nitrates, which accounts for the high NOx capacity of such solids. N-bounded nitrate and bulk nitrate species were identified. These nitrates decompose upon heating with no loss of the perovskite structure. The process of absorption/desorption is reversible, repeatable and can be explained by the following equations:
Reported here is our recent investigation of the mechanism of the selective nitric oxide reduction by hydrocarbons on Cu-ZSM-5 catalysts in an oxygen-rich gas mixture. We studied the copper oxidation state change during the catalytic reaction using the X-ray Absorption Near Edge Structure (XANES) method. We observe that even under strongly net oxidizing conditions, a significant fraction of the copper ions in ZSM-5 is reduced to CuI at elevated temperature, when propene is present in the reactant stream. XANES spectra show that the CuI 1s → 4p transition intensity, which is proportional to cuprous ion concentration, changes with the reaction temperture in a pattern similar to the NO conversion activity. For comparison purposes, we also studied the CuI concentration change using a gas mixture in which propene was replaced by a stoichiometrically equivalent concentration of methane. Unlike propene, methane provides no NO selective reduction pathway over Cu-ZSM-5. No window of enhanced CuI concentration was observed using methane as the reductant. Our study indicates that, even in a strongly oxidizing environment, cupric ion can be partially reduced by propene to form CuI, possibly by way of allylic intermediate, which may be a crucial step for effective NO conversion through a redox mechanism.
NOx adsorption/desorption capacities of perovskites (ABO3) were measured under representative exhaust gas mixture conditions at temperatures below 550°C, with A=Ca, Sr, Ba and B=Sn, Zr, Ti. The solids exhibited good NO2 sorption capacities with a reversible adsorption to desorption process according to the sequence Ba>Sr>Ca for A, while for element B the sequence Sn>Zr>Ti is observed. In the case of alkaline earth metals, the absorption behaviour proved to be directly related to their electropositivity (Ba>Sr>Ca). The key factors which control the absorption of NO2 are the bonding energy between the element B and the oxygen atom on one hand and the electropositivity of the element A on the other. The best result was obtained with the perovskite BaSnO3. The absorption of NO2 is favoured at low temperature and in the presence of water. The addition of platinum has no significant influence upon any NO2 absorption.
Environmental concerns stemming from the use of conventional solvents and from hazardous waste generation have propelled research efforts aimed at developing benign chemical processing techniques that either eliminate or significantly mitigate pollution at the source. This paper provides an overview of heterogeneous and homogeneous catalysis in dense phase CO2, considered a green solvent. In addition to solvent replacement, the demonstrated advantages of using dense phase CO2 include the enhanced miscibility of reactants, such as O2 and H2 which eliminate interphase transport limitations, and the chemical inertness of CO2. Further, the physicochemical properties of CO2-based reaction media can be pressure-tuned to obtain unique fluid properties (e.g. gas-like transport properties, liquid-like solvent power and heat capacities). The advantages of CO2-based reaction media for optimizing catalyst activity and product selectivity are highlighted for a variety of reactions including alkylation on solid-acid catalysts, hydrogenation on supported noble metal catalysts and a broad range of homogeneous oxidations with transition metal catalysts and dioxygen as an oxidant. Through these examples, the need is emphasized for a systematic approach to research and development of supercritical carbon dioxide based processes, taking into account conventional multiphase reaction engineering principles, catalytic chemistry and phase behavior.
A novel regenerable Fe/activated coke (AC) desulfurizer prepared by impregnation of Fe(NO3)3 on an activated coke was investigated. Experiment results showed that at 200 °C the SO2 adsorption capacity of the Fe/AC was higher than that of AC or Fe2O3. Temperature-programmed desorption (TPD) revealed that H2SO4 and Fe2(SO4)3 were generated on the desulfurizer upon adsorption of SO2. Effect of desulfurization temperature was also investigated which revealed that with increasing temperature from 150 to 250 °C, the SO2 removal ability gradually increases. The used Fe/AC can be regenerated by NH3 at 350 °C to directly form solid ammonium-sulfate salts.
The hydrodechlorination of 4-chlorophenol with hydrogen in aqueous phase has been studied using different home-made Pd/active carbon catalysts. The active carbons employed were subjected to oxidation with nitric acid, hydrogen peroxide and ammonium persulfate and to thermal treatment under nitrogen atmosphere at temperatures ranging from 200 to 900 °C in order to modify their surface chemistry. High conversion values for 4-chlorophenol, well above 95%, were obtained working under mild conditions of temperature (50–75 °C) and pressure (2.4 bar). Modifications on the surface composition of the active carbon support upon oxidation and thermal treatment proved to affect to both conversion of 4-chlorophenol and selectivity towards cyclohexanol, the less toxic product in the reaction pathway. Increasing thermal treatment temperature showed to be detrimental in both respects whereas oxidation with nitric acid favored a higher selectivity to cyclohexanol. Those effects can be attributed more specifically to the relative presence of some oxygen groups on the surface of the support. Thus, the highest 4-chlorophenol conversions were obtained with the catalysts whose supports yielded higher amounts of CO2 upon temperature programmed desorption analysis. In particular, carboxylic acid and lactone groups where found to be relevant for a high conversion of 4-chlorophenol and their presence was also important to improve the selectivity to cyclohexanol. The presence of such groups can be related with a more homogeneous distribution of palladium on the catalysts surface.
The photocatalytic degradation of formetanate (FMT) was studied using titania Degussa P-25 as a catalyst. The disappearance of formetanate was proved to follow a half-order kinetics. This implies that two active sites are involved in the adsorption of one molecule of formetanate (dissociative adsorption). In our conditions, complete mineralization of 20 ppm of pure formetanate occurred within 125 min of UV-radiation. The presence of (i) formulation agents and (ii) of humic acids seemed to have an inhibiting effect on the initial rate. In all cases, mineralization of FMT led to a greater percentage of ammonium than of nitrate. Photocatalysis proved to be an excellent new advanced oxidation technology (AOT) to eliminate formetanate residues present in real surface and ground waters.
This study presents novel supported TiO2 catalysts able to mediate the photo-oxidation of cyanides with an acceptable kinetics. The catalyst preparation was optimized towards cyanide degradation using different TiO2 colloids on glass Raschig rings. The TiO2 during the photo-degradation of cyanides was activated by two different sources of UV light (366 nm). The catalyst used showed long-term stability and was able to degrade the cyanide solution within minutes in a repetitive fashion. The dependence of the cyanides oxidation rate was investigated as a function of: (1) catalyst preparation, (2) cyanide initial concentration, (3) applied light intensity, and (4) nature and concentration of the oxidant (O2 or/and H2O2). The Langmuir–Hinshelwood mechanistic model was used to fit the experimental data. The by-products observed in solution during the cyanide degradation were identified as cyanates and nitrites. The catalytic efficiency of the best catalyst was tested on real wastewater from the galvanic industry containing ∼400 mg/l of cyanides and 60–70 mg/l of Cu-ions.
In case of a severe (beyond design basis) accident in a nuclear power plant, a large amount of hydrogen could be generated by reaction of water of the primary coolant circuit with the fuel rods inside the reactor pressure vessel, and eventually released into the air-filled reactor building. For mitigating the risk of an explosion within the containment, a catalytic combustion of this hydrogen is considered as one of the most efficient counter-measure. The difficulty which is to be overcome is a possible poisoning of the catalyst by fission products and other components released by the damaged core, notwithstanding the fact that most of them enter the containment building as non-reactive large oxide particles. The main vapors which are suspected to have an inhibiting or poisoning effect are indeed di-iodine and methyl iodide, both potentially present in the containment atmosphere. We report on the possible effect of these molecules on Pt, Pd and Pt–Pd model catalysts at lower temperatures and somewhat higher iodine or iodide concentrations, as compared to inferred catalyst operational parameters in a reactor building during a severe accident. In these particular experimental conditions, platinum is substantially poisoned by both vapors. On the other hand, palladium, about 400 times less active than platinum, is much less altered by I2 and ICH3 vapors. A marked beneficial effect was found by alloying the two noble metals: the alloys show only a threefold decrease in activity with respect to platinum, and undergo a much weaker deactivation.
Photocatalytic oxidation (PCO) tests were carried out for toluene adsorbed on the activated carbon fibers (ACFs)-supported TiO2 photocatalyst in an environmental condition controlled chamber. TiO2/ACF catalyst was made and characterized by N2 adsorption isotherm for pore structure and scanning electron microscopy (SEM) for morphology, respectively. Through exploring the remnant of toluene and the accumulation of intermediates on the TiO2/ACF catalyst including species, amount and their change processes under different relative humidity (RH), this study aimed to explore the influence of RH on the PCO of toluene and the roles of water vapor in the PCO process: PCO reaction paths and the accumulation of intermediates on the TiO2/ACF catalyst. Results showed that (1) with the increase of RH in the chamber (15%, 30%, 45% and 60%) the PCO conversion rate of toluene was positive correlated and no catalyst deactivation was observed under all RH levels; (2) during the gas–solid PCO process of toluene, byproducts of aromatic ring oxidation including 2-methyl, p-benzoquinone and o(m, p)-cresol were observed on the TiO2/ACF catalyst which had not been reported, together with the intermediates of side chain oxidation including benzyl alcohol, benzaldehyde and benzoic acid which had been reported; (3) although benzaldehyde was the primary intermediate under all RH level, amounts of the byproducts of aromatic ring oxidation were increased with the increase of RH; and (4) elevated RH increased the accumulation of benzyl alcohol but assuredly decreased the accumulation of benzaldehyde. These results suggested that (1) RH affects both the PCO rate and the PCO reaction path of toluene; (2) although methyl group oxidation is the major path, aromatic ring oxidation, which is not the expected path for the PCO of toluene, is enhanced when the RH increases; (3) apart from the role of hydroxyl radical (OH) produced from water by TiO2, water molecule also directly takes part in the PCO process. A hypothesis has been suggested: transition species comprised of benzaldehyde, hydroxyl and water molecule exists in the PCO conversion process from benzaldehyde to benzoic acid, though the hypothesis has not been confirmed.
Samples CuOx/ZrO2 (0.1–8.4 Cu atoms nm−2) were prepared by adsorption or impregnation methods. The characterisation of samples by means of XPS, XRD, DRS, ESR, IR and volumetric adsorption of CO, showed copper dispersion up to 2.5 atoms nm−2, and the presence of CuO in samples with higher Cu content. The selective catalytic reduction of NO with propene or ammonia in the presence of excess oxygen, was studied in a flow apparatus with reactant mixtures of various composition (NO : C3H6 : O2 = 0–4000 ppm : 100–2000 ppm : 0–3.5%; and NO : NH3 : O2 = 0–700 ppm : 700 ppm : 3.6%). With both propene and ammonia, CuOx/ZrO2 catalysts containing up to 2.5 Cu atoms nm−2 were active, selective and stable as a function of the time on stream. On all catalysts, with ammonia as reducing agents, up to 523 K, NO conversion equalled NH3 conversion leading to 100% selectivity. With both propene and ammonia, NO molecules that were converted to N2 per Cu atom and per second were nearly independent of the Cu content up to 2.5 Cu atoms nm−2.
Several catalysts, including FeZSM-5, Co2AlO4, LaCoO3, and BaFeAl11O19, were evaluated for N2O decomposition under representative flue-gas conditions in fluidized-bed combustion (FBC). Closely related formulations proved active and stable catalysts for process-gas or tail-gas de-N2O in nitric acid plants. With this as starting point, their potential suitability for N2O abatement in stationary combustion was assessed. Tests were carried out in a fixed-bed reactor at ambient pressure and in the temperature range of 473–1123 K using mixtures of N2O, O2, NO, CO, SO2, and H2O. The mixed oxide catalysts were strongly inhibited by water and sulfur dioxide and experienced fast deactivation in the simulated mixture containing all the gases. Bulk sulfate phases were detected by X-ray diffraction in the used perovskite and hexaaluminate, revealing insufficient chemical stability in the presence of sulfur and discouraging installation in the freeboard of the combustor. In great contrast, the activity of steam-activated FeZSM-5 in the model and simulated mixtures was comparable, rendering very stable performance during 30 h on stream. The unique tolerance of this iron zeolite to the complex combination of feed components makes it prone to implementation after the cyclone of FBCs, where temperatures are typically 800–1100 K.
The abatement of NO with CH4 in the presence of oxygen ([NO] = [CH4] = 1000 or 4000 ppm, [O2] = 0 to 2%, by volume) was studied on Co-ZSM-5 catalysts (Co content 0.29 to 4.1 wt.-%), prepared from H-ZSM-5 or Na-ZSM-5 by the ion-exchange method. On all samples, the amount of CO and NO adsorbed at room temperature was proportional to the cobalt content (CO/Co⋍ 0.5 and NO/Co⋍ 1.6), with the exception of the Co-ZSM-5 sample with Co 4.1 wt.-%, on which the adsorption was only slightly higher than that on Co-ZSM-5 with Co 2.0 wt.-%. Infrared spectroscopy (FTIR) showed the formation of carbonyls (one type only, on cobalt equivalent sites), cobalt mononitrosyls (two types) and dinitrosyls (two types). The intensity of bands from carbonyls and nitrosyls was about proportional to the cobalt content, with the exception of the Co-ZSM-5 sample with Co 4.1 wt.-%, on which the bands were roughly as intense as in the sample with Co 2.0 wt.-%. In the Co-ZSM-5 sample with Co 4.1 wt.-%, after heating with O2 at 773 K, or after its use in catalysis, diffuse reflectance spectroscopy (DRS) showed the presence of Co3O4, not detected by X-ray diffraction. In the presence of O2, the NO reduction rate was proportional to the Co content, except for the sample containing Co 4.1 wt.-%. The CH4 oxidation rate was proportional to the Co content, in the entire range of Co concentrations. The selectivity of catalysts for NO abatement (selective catalytic reduction, SCR), was nearly independent of Co content but was markedly lower on the sample with Co 4.1 wt.-%. The results suggest that only CoII ions exchanged in the framework of the ZSM-5 matrix are active in CO and NO adsorption and in the SCR reaction, whereas also the cobalt of the dispersed Co3O4 phase contributes to CH4 oxidation with O2.
The present paper deals with the preparation of catalytic filters for Diesel particulate removal by developing an in situ solution combustion synthesis method. Lanthanum chromite perovskite catalyst has been deposited on silicon carbide and cordierite honeycombs with the aim to investigate the influence of the starting solution containing catalyst precursors on the coating characteristics. SEM, XRD and EDX analyses have been carried out in order to evaluate the homogeneity and the thickness of the catalyst layer. In particular, using concentrated solutions, a single combustion synthesis step was found to be sufficient to obtain a continuous catalyst film on the support.Pressure drop evaluations and adhesion tests have also been performed thus verifying the possibility to insert this kind of catalyzed traps on the diesel exhaust gas lines. The homogeneity and the high adherence of the deposited catalyst layer, as well as the simplicity and the rapidity of the method, prove its suitability for immediate technological applications.
The twist-like helix W,N-codoped TiO2 photocatalysts were prepared by a simple one-pot synthesis route to hydrolysis of titania tetrachloride using ammonium tungstate as tungsten and nitrogen sources. The morphology and microstructure characteristics of W,N-codoped titania photocatalysts with different amount of tungsten doping were characterized by means of BET, TEM, SEM, XPS, UV–vis DRS, PLS and XRD. The probable mechanism of codoping effect is proposed. It is presumed that cooperation of nitrogen and tungsten ions leads to produce new states and narrow the band gap between the valence band and conduction band effectively, which will greatly improve the photocatalytic activity in the visible light region. On the other hand, the tungsten ions with changing valences in the W,N-TiO2 samples are considered to act as trapping sites, which will effectively decrease the recombination rate of photo-induced electrons and holes and then increase the photo-oxidation efficiency of the catalysts. The metal and nonmetal codoped 1%-W,N-TiO2 sample shows the best photocatalytic activity, which is much superior to P25 under both visible and ultraviolet light irradiation. The superior activity of W,N-TiO2 photocatalysts can also be ascribed to the special twist-like helix structure with regular holes on the wall, high surface area, large pore volume and well-crystallized anatase phase.
A modeling and simulation study on Pt-catalyzed conversion of automotive exhaust gases is presented. The model is based on a newly developed surface reaction mechanism consisting of 73 elementary-step like reactions among 22 surface and 11 gas-phase species. Reactions for the conversion of the major pollutants CO, CH4, C3H6, and NOx are included. The mechanism is implemented in a two-dimensional flow field description of a single channel of the catalytic monolith. The model is evaluated by comparison with data derived from isothermal laboratory experiments in a flat bed reactor with platinum-coated monoliths using synthetic lean/rich cycling exhaust gas mixtures. The influence of CO and C3H6 at lean and H2 at rich conditions on NO conversion is investigated, both at steady-state conditions. Furthermore, the model is also applied for the simulation of emissions of hydrocarbons, CO, and NO from a gasoline engine (stoichiometric exhaust gas) in a dynamic engine test bench.
Titania nanotube arrays synthesized by the electrochemical oxidation of titanium foils have generated considerable interest as photocatalysts for their ordered nature and large surface area. Mixed-phase materials combining the anatase and rutile crystal phases of TiO2, however, have been much more widely studied due to their enhanced reactivity in comparison to pure phase materials. In this study, we seek to integrate these two lines of research and investigate the reductive and oxidative reactivity of TiO2 nanotube arrays (anatase phase) supported on TiO2 films of varying crystal phase composition. A series of TiO2 nanotubes 1.2 μm in length was synthesized, annealed at varying temperatures to control their crystallinity, and characterized by various physical techniques (e.g. XRD, diffuse reflectance, SEM). Photocatalytic CO2 reduction and acetaldehyde oxidation reactions were performed in the gas phase under UV and visible wavelengths. For CO2 reduction, reaction rates decreased with increasing rutile phase under UV. Rates increased with rutile phase ratio under visible and near visible light. For oxidation, the mixed-phase samples showed enhanced reactivity, with a maximum acetaldehyde destruction rate achieved at a 79:21 ratio of anatase to rutile. The samples were substantially less active under visible light, except for the 620 °C composite (77% rutile) which showed a slight rate increase. Nanotubes annealed at 680 °C collapsed to a random porous structure, but showed comparable reductive ability to the non-collapsed samples despite the loss of surface area. This is attributed to the creation of additional anatase–rutile crystallite interfacial area leading to the formation of unique active sites. Control of crystal phase composition through anneal temperature is found to be a simple way to tune the reactivity of these materials and enhance their ability to absorb visible light.

Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed.