[Show abstract][Hide abstract] ABSTRACT: Titania nanowires (NW) supported gold–copper (Au–Cu) bimetallic nanoparticles were synthesized and pretreated in hydrogen and air at 300, 500 and 700 • C, for the one-pot conversion of cellobiose to glu-conic acid. Catalyst samples were characterized by temperature-programmed desorption of NH 3 , Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy, Field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The structure and activity of Au–Cu/TiO 2 NW were highly affected by the pretreatment conditions. Catalyst samples reduced in H 2 and at higher temperatures resulted better catalytic performance as compared with those calcinated in air at the same temperature. The influence of support, calcination temperature and atmosphere as well as gold content on the catalytic performance of Au–Cu/TiO 2 NWs are investigated. The characterization results suggested high hydrogen reduction temperature created oxygen vacant sites on the titania NW support. This is consequently associated with the stabilization of highly reactive oxygen species at the periphery of the metal–support interface. Interactions between the metals and the titania NWs support and between the promoter and the active metal enhanced the formation of gluconic acid.
[Show abstract][Hide abstract] ABSTRACT: A carbon-based solid acid catalyst was prepared via hydrothermal method using glucose as carbon precursors and aqueous solution of H2SO4 as sulfonation agent. The as-synthesized solid acid catalyst was attempted in the catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF). The effects of acid site density, reaction time, solvents, catalyst amount, temperature and mole ratio of catalyst to substrate were investigated. Under the optimum reaction conditions, the HMF yield of 90% was achieved in dimethylsulfoxide (DMSO) solvent at 160 °C after 1.5 h reaction time duration. The solid acid catalyst can be separated from the reaction mixture after reaction and reused without substantial loss in catalytic activity.
[Show abstract][Hide abstract] ABSTRACT: The aerobic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) is one of the most attractive reactions to establish biomass-based sustainable chemical processes. Supported Au and Pt catalysts have mainly been reported for this reaction, but excess amounts of base additives are generally required, which makes the process less green. Here, we demonstrate that Pt nanoparticles loaded on functionalized carbon nanotubes (CNTs) can catalyze the aerobic oxidation of HMF to FDCA in water without any base additives. Kinetic studies suggest a tandem reaction mechanism via 2,5-diformylfuran and 5-formylfurancarboxylic acid intermediates. It has been clarified that the oxygen-containing functional groups, in particular carbonyl/quinone and/or phenol groups, on CNT surfaces play crucial roles in FDCA formation. These functional groups could enhance the adsorption of HMF as well as the reaction intermediates from water and might facilitate hydrogen transfer.
[Show abstract][Hide abstract] ABSTRACT: Anatase interim layer-stabilized rutile@CrxOy core–shell nanorod arrays as photoanodes of photoelectrochemical water splitting cell can output a four-fold enhanced and stabilized visible-light photocurrent, as reported on p. 1352 by J. L. long, X. X. Wang, B. Liu et al.
[Show abstract][Hide abstract] ABSTRACT: In order to reduce considerable emissions of N-containing pollutants from combustion of sewage sludge derived solid fuel, an integrated system of hydrothermal deamination and air stripping was developed to effectively remove and recover nitrogen from dewatered sewage sludge (DSS). Three characteristic hydrothermal regimes contributing to deamination were identified. Initial hydrolysis of inorganic-N and labile protein-N was responsible for ammonium (NH+ 4-N) released below 300 oC/9.3 MPa, whereas deamination of pyridine-N dominated when being raised to 340 oC/15.5 MPa. At 380 oC and 22.0 MPa, remarkable deamination of stable protein-N occurred, which was accompanied by formation of more heterocyclic-N compounds and resulted in 76.9% N removal from DSS and 7980 mg/L NH+ 4-N solution. As a result of catalytic hydrolysis and cracking, calcium oxide additive not only accelerated deamination of stable protein-N, pyrrole-N, and pyridine-N but also favored transformations of protein-N and quaternary-N to nitrile-N and pyridine-N, respectively, leading to 86.4% total N removal efficiency. The nitrogen transformation reactions and conversion pathways during hydrothermal deamination were proposed and elaborated in detail. Moreover, an efficient air stripping process was coupled to remove and recover ammonia from liquid fraction via ammonium sulfate. Consequently, this system achieved an overall N recovery rate of 62%.
[Show abstract][Hide abstract] ABSTRACT: Carbon nanotubes are promising materials for various applications. In recent years, progress in manufacturing and functionalizing carbon nanotubes has been made to achieve the control of bulk and surface properties including the wettability, acid-base properties, adsorption, electric conductivity and capacitance. In order to gain the optimal benefit of carbon nanotubes, comprehensive understanding on manufacturing and functionalizing carbon nanotubes ought to be systematically developed. This review summarizes methodologies of manufacturing carbon nanotubes via arc discharge, laser ablation and chemical vapor deposition and functionalizing carbon nanotubes through surface oxidation and activation, doping of heteroatoms, halogenation, sulfonation, grafting, polymer coating, noncovalent functionalization and nanoparticle attachment. The characterization techniques detecting the bulk nature and surface properties as well as the effects of various functionalization approaches on modifying the surface properties for specific applications in catalysis including heterogeneous catalysis, photocatalysis, photoelectrocatalysis and electrocatalysis are highlighted.
Chemical Society Reviews 04/2015; 44(10). DOI:10.1039/c4cs00492b · 33.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the present study, hydrothermal conversion (HTC) of dewatered sewage sludge (DSS) under sub- and near-critical water has been performed to investigate effects of reaction temperature and pressure, moisture content of DSS, and calcium oxide (CaO) additive on evolution profile and characteristics of gas, solid, and liquid products. Although energy recovery rate decreased with increasing temperature and pressure, significant decarboxylation and dehydration reactions led to hydrochars with best fuel quality at 320 °C. High moisture content favored decarboxylation reaction but reduced H2 and CH4 yields. Compared to that in the absence of additive, H2 yield increased almost 6-fold at 380 °C and Ca/C molar ratio of 0.2, resulting in 58% H2 and 26% CH4 in final fuel gas. The results suggested that mineralization of heteroatomic compounds and dissolution of metals or mineral elements occurred during HTC. Under higher temperature and pressure, heavy metals or mineral elements were prone to be immobilized whereas dehalogenation became more distinct. CaO additive not only facilitated hydrolysis and deamination of organic compounds but also accelerated further fixation of inorganic elements and anions.
International Journal of Hydrogen Energy 04/2015; 40(17):5776–5787. DOI:10.1016/j.ijhydene.2015.03.006 · 3.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The catalytic activity of gold supported on ZSM5 (Au/ZSM5) was investigated for the selective oxidation of ethanol in the presence of excess oxygen. Au/ZSM5 catalyst pretreated by nonthermal O2 plasma method showed the best oxidative activity compared to low-temperature calcination in air and high-temperature reduction in hydrogen atmosphere. Results from microscopy and X-ray diffraction characterizations proved that plasma pretreatment afforded a small Au particle size and a uniform dispersion of Au nanoparticles on ZSM5 surfaces. Characterization results further demonstrated that the residual ammonia adsorbed on ZSM5 surfaces during the precipitation can be oxidized to nitrate ions by nonthermal O2 plasma treatment, while it converted to NO+ by low-temperature oxygen calcination and was completely removed by high-temperature hydrogen reduction. Dissimilar surface/interface properties caused the tremendously different interaction between gold nanoparticles and zeolite support, and consequently the catalytic performances in ethanol oxidation. In particular, under the nonthermal O2 plasma pretreatment, the formed NO3− species lowered the acidity of ZSM5 surfaces as well as anchored the Au nanoparticles, resulting in nearly 100% selectivity toward selective oxidation instead of acid-catalyzed reactions even under high reaction temperature.
[Show abstract][Hide abstract] ABSTRACT: Ternary core–shell heterostructured rutile@anatase@Crx Oy nanorod arrays were elaborately designed as photoanodes for efficient photoelectrochemical water splitting under visible‐light illumination. The four‐fold enhanced and stabilized visible‐light photocurrent highlights the unique role of the interim anatase layer in accelerating the interfacial charge transfer from the Crx Oy chromophore to rutile nanorods. Driving light: Ternary core–shell heterostructured rutile@anatase@Crx Oy nanorod arrays are elaborately designed as photoanodes for photoelectrochemical water splitting under visible‐light irradiation. Thus, affording a novel strategy to extend the photoresponse of oxide array materials, and showing the promising application of rutile@anatase@Crx Oy photoanodes in the domain of photoelectrochemistry.
[Show abstract][Hide abstract] ABSTRACT: A novel microspherical composite with an Au@SiO2 core and mesoporous aluminosilica shell is synthesized and used as the heterogeneous catalyst in the aerobic epoxidation of cis-cyclooctene, exhibiting great catalytic activity and stability.
Chemical Communications 02/2015; 51(20). DOI:10.1039/c4cc09570g · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, multi-walled carbon nanotubes supported Pt and Pt-based bimetallic catalysts were prepared and their catalytic activities were investigated to screen effective and economical catalyst for H2 production in catalytic aqueous phase reforming (CAPR) of glycerol. Nickel promoted Pt catalyst with optimized Ni:Pt molar ratio afforded highest glycerol conversion rate (81.21%) and carbon conversion to gas (15.3%) although hydrogen gasification ratio (7.2%) was poorer than that of noble metals promoted Pt-based bimetallic catalysts. Adding CaO significantly enhanced the fraction and selectivity of H2 over Pt-Ni catalyst and those of CH4 were reduced to a negligible level, which was possibly attributed to the facilitated water-gas shift reaction and inhibited methanation through in-situ CO2 sorption via carbonation. Results suggested that Pt-Ni bimetallic catalysts improved dehydrogenation–decarboxylation and dehydration–hydrogenation reactions, leading to high glycerol conversions. Introducing CaO further favored C–C bond cleavage towards high H2 yield. The catalytic performance can be completely recovered after regenerating the catalyst and adding sacrificial CaO. In terms of reduced consumption of precious metal catalyst, excellent catalyst performance and hydrothermal stability, combination of Pt-Ni bimetallic catalyst and CaO additive was identified as an effective catalytic system for H2 production in CAPR of glycerol.
[Show abstract][Hide abstract] ABSTRACT: Biodiesels produced from renewable sources exhibit superior fuel properties and renewability and they are more environmentally friendly than petroleum-based fuels. In this paper, a three-step transesterification, catalyzed by a pyridinium-based Brønsted acidic ionic liquid (BAIL), for biodiesel production was investigated using density functional theory (DFT) calculations at the B3LYP/6-311++G(d) level. The DFT results elucidate the detailed catalytic cycle, which involves the formation of a covalent reactant–BAIL–(methanol)n (n = 1/3) intermediate and two transition states. Hydrogen bond interactions were found to exist throughout the process of the catalytic cycle, which are of special importance for stabilizing the intermediate and transition states. Thus, a mechanism involving cooperative hydrogen bonding for BAIL-catalyzed biodiesel production was established. The Gibbs free energy profile based on the above mechanism was validated by the subsequent kinetic study. The trend of activation energy from kinetic mathematical models was reasonably consistent with that obtained from the DFT calculations.
Green Chemistry 01/2015; DOI:10.1039/C5GC00976F · 8.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report here the composition optimization of ZnxFe3-xO4 hollow nanospheres for enhancing microwave attenuation. ZnxFe3-xO4 hollow nanospheres were synthesized through a simple solvothermal process. The maximum magnetization moment of 91.9 emu/g can be obtained at x=0.6. The composite filled with Zn0.6Fe2.4O4 exhibited the bandwidth of 3.21~8.33 GHz for RL< -10 dB and a maximum relative bandwidth (Wp,max) of 88.6% at optimized thickness t0=0.34 cm. The enhancement should be attributed to the enhanced permeability resonance at high frequency. This optimized hollow material is very promising to be used as a mass efficient and broadband microwave attenuation material.
[Show abstract][Hide abstract] ABSTRACT: A series of bimetallic catalysts Au-M (M = Cu, Co, Ru, Pd and Ni) were supported on TiO2 via deposition-precipitation (DP) method using urea as precipitating agent. The resulting catalysts were used in the catalytic oxidation of cellobiose into gluconic acid. The interactions between the metals in the bimetallic catalysts were carefully investigated in order to unravel the effect of the second metal on the chemical and electronic properties of the active sites and their impact on the catalytic performance. Cu and Ruwere found to be promising promoters for the oxidation of cellobiose into gluconic acid, promoting oxygen activation in gold-catalyzed oxidation reactions, while Co and Pd were found to enhance the retro-aldol condensation of fructose into glycolic acid. In this case, the catalytic activity is dominated by the second metal added to Au. Hence, Au behaves more like a promoter of the second metal, preventing over oxidation and poisoning by the reaction intermediates and products. Ni specifically promoted the C-C scission, yielding a mixture of lower carbon-containing compounds and glycolic acid as the main products.
The major reaction products obtained were gluconic acid, glycolic acid, ethylene glycol and erythritol. The catalytic activity of the catalysts followed the order: Au-Cu/TiO2 > Au-Pd/TiO2 > Au-Ru/TiO2 > Au-Co/TiO2 > Au/TiO2 > Au-Ni/TiO2. Upon comparison, Au-Ru/TiO2 was found to be an active and selective catalyst towards the formation of gluconic acid. The nature of the metal interactions in the bimetallic systems greatly influenced the product distribution.
[Show abstract][Hide abstract] ABSTRACT: Rapidly growing research interests surround heterogeneous nanocatalysis, in which metal nanoparticles (NPs) play a pivotal role as structure-sensitive active centers. With advances in nanotechnology, the morphology of metal NPs can be precisely controlled, which can provide well-defined models of nanocatalysts for understanding and optimizing the structure–reactivity correlations and the catalytic mechanisms. Benefiting from this, further credible evidence can be acquired on well-defined nanocatalysts rather than common multiphase systems, which is of great significance for the design and practical application of active metal nanocatalysts. Numerous studies demonstrate that enhanced structure-sensitive catalytic activity and selectivity are dependent not only on an increased surface-to-volume ratio and special surface atom arrangements, but also on tailored metal–metal and metal–organic–ligand interfaces, which is ascribed to the size, shape, composition, and ligand effects. Size–reactivity relationships and underlying size-dependent metal–oxide interactions are observed in many reactions. For bimetallic nanocatalysts, the composition and nanostructure play critical roles in regulating reactivities. Crystal facets favor individual catalytic selectivity and rates via distinct reaction pathways occurring on diverse atomic arrangements, both to low-index and high-index facets. High-index facets exhibit superior reactivities owing to their high-energy active sites, which facilitate rapid bond-breaking and new bond generation. Additionally, organic ligands may enhance the catalytic activity and selectivity of metal nanocatalysts via changing the adsorption energies of reactants and/or reaction energy barriers. Furthermore, atomically dispersed metals, especially single-atom metallic catalysts, have emerged recently, which can achieve better specific catalytic activity compared to conventional nanostructured metallic catalysts due to the low-coordination environment, stronger interaction with supports, and maximum service efficiency. Here, recent progress in shaped metallic nanocatalysts is examined and several parameters are discussed, as well as finally highlighting single-atom metallic catalysts and some perspectives on nanocatalysis. The integration of nanotechnology and nanocatalysis has been shaping up and, no doubt, the combination of sensitive characterization techniques and quantum calculations will play more important roles in such processes.
Small 10/2014; 11(3). DOI:10.1002/smll.201400847 · 8.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the absence of prior drying, dewatered sewage sludge (DSS) was directly converted to hydrochars with superior fuel characteristics in subcritical water. Hydrochar derived at 320 degrees C and 12.0 MPa (SHC-320) was screened for systematic cocombustion with different-rank coals. The results suggest that SHC-320 reduced the activation energy of the blends and altered the main combustion profiles. Meanwhile, blending of SHC-320 induced greater heat loss for higher-rank coals, whereas a higher portion of SHC-320 further improved the ignition reactivity of high-rank coal blends. In the high-temperature region, the value of the pre-exponential factor increased with increasing coal/SHC-320 ratio, resulting in more intense synergistic effects in blends. At a low coal/SHC-320 ratio (30:70), intense antisynergistic effects occurred in cocombustion with low- or high-rank coals. As a result of distinct synergistic interactions, cocombustion with moderate-rank coal achieved the best combustion efficiency among the blends. These findings benefit efficient utilization of DSS as a hydrochar solid fuel in existing cofiring power plants.
Energy & Fuels 09/2014; 28:6140-6150. DOI:10.1021/ef501386g · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Palladium nanoparticles supported on carbon nanotubes (CNT) functionalized with various organosilane modifiers have been prepared through a post-synthesis grafting method followed by a metal adsorption-reduction approach. The surface property, catalyst structure, electrochemical activity, and catalytic performance were tested in the selective aerobic oxidation of benzyl alcohol. The variation in type and amount of surface-functional groups played a key role in controlling catalytic behavior through fine tuning the surface basicity, metal nanoparticle size and size distribution, metal-support electronic interaction. In all these tested organosilane modifiers, 3-aminopropyl triethoxysilane exhibited the largest improvement in catalytic performance, with a remarkably high quasi-turnover frequency of 288,755 h(-1) based on the electrochemical active surface area.
Applied Catalysis B Environmental 09/2014; s 156–157:385–397. DOI:10.1016/j.apcatb.2014.03.043 · 7.44 Impact Factor