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The Adsorption of Triethylenediamine on Al 2 O 3 -II: Hydrogen Bonding to Al−OH Groups
Abstract
The hydrogen bonding of the triethylenediamine (TEDA) molecule to isolated Al-OH groups on partially dehydroxylated high area gamma-Al(2)O(3) powder has been studied using transmission IR spectroscopy. It has been found that TEDA adsorbs both singly and as multiple species to single Al-OH groups in clearly separable equilibrium stages of adsorption at 300 K. The reversible adsorption of a single TEDA molecule to Al-OH fits the Langmuir adsorption isotherm well, and the enthalpy of adsorption is found to be -15.6 +/- 0.5 kJ mol(-1) in the range of fractional coverage of 0.5-0.6. Red shifts of the Al-OH frequency from approximately -200 cm(-1) to approximately -1000 cm(-1) are observed as a result of -OH bonding to the N lone pair in the TEDA molecule.
... Metal oxides and supported noble metals are active for many deep oxidations [7][8][9][10]. Metal oxides are easier to obtain compared with alloys and supported catalysts. ...
... Metal oxides are easier to obtain compared with alloys and supported catalysts. Recently, aluminum oxide has been widely used for eliminating many organic pollutants [8][9][10]. Decomposition of carbon tetrachloride by alumina was reported by Khaleel and Dellinger [8]. ...
... able reactive property. Kim [9,10] studied the adsorption of triethylenediamine (TEDA) on partially and highly dehydroxylated-Al 2 O 3 surfaces where Al-OH group and surface Lewis acid Al 3+ serve as the important adsorption sites for the decomposition of TEDA, respectively. Mawhinney [11] investigated the reaction of 2-chloroethylethyl sulfide with a high surface area Al 2 O 3 which served as a decontamination medium, and pointed out that the dehydroxylation process played a critical role during this reaction. ...
A method of decomposing hexachlorobenzene (HCB) by γ-alumina was investigated at low temperature of 300°C. It was found that HCB was rather quickly decomposed under such a condition. Decomposition efficiency (DE) increases with increasing the surface area of γ-alumina. Pretreated γ-alumina has a better performance for the decomposition reaction. A high decomposition efficiency within the short reactive time of 60min was achieved to be 94.2%, which was obtained by preheating γ-alumina with the surface area of 220m2g−1 at 450°C for 2h. High surface area and appropriate pretreatment temperature probably provide more reactive sites such as the isolated OH groups and Al3+ sites surrounded by O2− sites. These sites may induce the decomposition of HCB via a main ring-cracking process. The present study, hopefully, holds the promise for the eliminating of HCB contained hazardous materials in industrial application.
... As for the reason why Metal/Al 2 O 3 was selected as the co-milling regent of MCT of HCB, many previous studies demonstrated its effectiveness in the organic pollutants treatment from their excellent adsorption and chemical composition properties [48][49][50][51][52]. HCB was selected as the model pollutant due to its universality, typical symmetry and polysubstitution. ...
Recent researches indicate that mechanochemical treatment (MCT) is a promising method to degrade the environmental hazards, especially in the area of persistent organic pollutants (POPs) disposal. However, the mechanochemical dechlorination mechanism of POPs still needs to be further verified. In this mechanochemical process, hexachlorobenzene (HCB) was chosen as a model pollutant with aluminum and alumina (Al + Al2O3) powders as the co-milling regents. Both of the intermediate analysis and quantum chemical calculations were adopted to elucidate the free radical dechlorination mechanism of HCB. The solid residues were characterized by electron spin-resonance (ESR) spectroscopy, Fourier transform infrared (FTIR) spectra and X-ray photoelectron (XPS) spectra, which proposed that the radicals formed in the mechanochemical process were chlorinated phenoxyl radicals (CB-O). Four quantum chemical descriptors were selected in predicting the intermediates and reaction pathway: (i) atomic charge, (ii) electrostatic potential (ESP), (iii) frontier molecular orbitals (FMO) theory and (iv) dual descriptor. Then, a stepwise dechlorination mechanism based on CB-O was proposed. It was found that the intermediates and radical-related reactions in the mechanochemical dechlorination of HCB are quite different from that happen in a typical photocatalytic dechlorination process. Impacts of different radical reactions on the dechlorination of HCB were also compared at last.
A hierarchical leaf-like alumina-carbon nanosheet catalyst was prepared by a chelate-assisted co-assembly method to improve the catalytic behavior of ethanol dehydration reaction, based on the chemical etching effect of ammonia water. The uniformly dispersed leaf-like nanosheet structure possessed a relatively large specific surface area and exposed more active sites, which could promote the ethanol dehydration reaction. This catalyst was promising to obtain a higher catalytic behavior (conversion of 98.3 % and ethylene selectivity of 97.0 %) than the sample without ammonia water modification (conversion of 63.2 % and ethylene selectivity of 46.7 %) at 450 ℃. The addition of ammonia water played an essential role in influencing the formation of the leaf-like nanosheet structure and the generation of Brönsted acid active sites, which remarkably promoted the proceed of ethanol dehydration. Importantly, a direct relationship was observed between the nanosheet thickness and the alumina content. The best catalytic activity with TOF of 361.8 h⁻¹ was obtained when the Al loading of 13.9 wt%, attributed to the suitably balanced weak/moderate acidic active sites ratio of ∼ 4.37. In-situ FTIR spectra of ethanol dehydration reaction clearly confirmed that ethanol was first converted to the intermediate product diethyl ether and then subsequently decomposed to ethylene at a higher temperature. The catalyst also maintained a good recyclability upon time on stream of 144 h at 450 ℃. This work provides an alternative way of developing non-noble metal catalyzing ethanol dehydration to ethylene.
Three crystalline forms of Al2O3 featuring rod-like fibers are synthesized, to perform the gaseous degradation of 1-chloronaphthalene (CN-1), a model compound. The degradation efficiency (DE) decreases as follows: micro/nano-γ-Al2O3 > micro/nano-η-Al2O3 > regular α-Al2O3. The high DE of 92.2% attained over γ-Al2O3 is attributed to its specific defective spinel structure, resulting in its large surface area and pore volume, large amounts of surface-adsorbed oxygen species, and Bronsted and Lewis acid sites. The degradation products, naphthalene and 1,4/1,6-dichloronaphthalene (DiCN), with yield ratios of 7.3–13.3, are detected, indicating the occurrence of hydrodechlorination and side chlorination reactions. 1,6-DiCN is believed to be the most favored DiCN isomer product based on the calculated ΔHr and ΔGr. However, the percentage values of intermediates formed via these two reactions, in the degradation of CN-1, are 9.1%, 4.5% and 4.4%, over α-, η- and γ-Al2O3, respectively. The oxidative degradation pathway possibly dominantly occurs especially over micro/nano-γ-Al2O3 with oxidative species such as O2−, O− and O2−, following the Mars–van Krevelen mechanism. Oxidation intermediates containing –CH2–, –CH3, and C–O groups are produced, which can be subsequently oxidized to low-molecular-weight products, such as formic, acetic and propanoic acids, and eventually completely oxidized to CO2.
This study investigates the adsorption and thermal transformations of a bicyclic tertiary amine, triethylenediamine, on the clean Si(100)-2×1 surface. Below room temperature, triethylenediamine adsorption leads to the formation of a strong dative bond between one of the nitrogen atoms of this compound and the silicon surface. In contrast to previously studied amines, the datively adsorbed triethylenediamine features a second tertiary amine entity that is not bonded to the surface, with a lone pair orbital that is directed away from the surface and is available for further reactions. The thermal chemistry and electronic properties of triethylenediamine on silicon are studied using thermal desorption spectroscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy. Near-edge X-ray absorption fine structure measurements are utilized to clarify the geometry of the adsorbates at room temperature. Density functional theory calculations are used to describe the binding geometry and electronic properties of the resulting surface species, and the likely reaction paths at elevated temperatures.
The dissociation of NH3 on a Si(1 0 0) surface activated with Cl atoms was investigated using X-ray photoelectron spectroscopy. Gas phase UV-Cl2 (0.1 10 Torr Cl2 for 10 600 s under 1000 W Xe lamp illumination) completely replaced the H-termination on aqueous-cleaned Si(1 0 0) with 0.82 ± 0.06 ML of Cl at 298 K. A single spin-orbit split Cl 2p doublet indicated that the Cl atoms were bound to Si dimer atoms, forming silicon monochloride (Cl Si Si Cl). Exposing the Cl-terminated surface at 348 K to NH3 (1 1000 Torr for 5 60 min) replaced one Cl atom with one N atom up to a coverage of 0.33 ± 0.02 ML. Cl atoms lowered the activation energy barrier for reaction to form a primary amine (Si NH2). Oxygen was coadsorbed due to competition by H2O contamination. The presence of Cl on the surface even after high NH3 exposures is attributed to site blocking and electrostatic interactions among neighboring Cl Si Si NH2 moieties. The results demonstrate a low temperature reaction pathway for depositing N-bearing molecules on Si surfaces.
The influence of fluorination of microcrystalline γ-alumina on the acidity of Lewis sites was studied by quantum chemical cluster model approach. B3LYP and HF/6-31++G(d,p) levels of theory were employed, considering the standard and counterpoise-corrected potential energy surfaces (PESs). Explicit inclusion of dynamical electron correlation effects along with the elimination of the basis set superposition effects in geometry optimization and harmonic vibrational analysis were found to be crucial to reproduce the experimental trends in the shifts of the pyridine n19b and n8a modes upon fluorination. The acidity of surface-exposed Al-sites was found to increase upon fluorination, which is manifested as a ~ 10 % increase of the interaction energies, and also in the characteristics of the electronic density and density Laplacian at the intermolecular bond critical point. Bader analysis of the electronic density has shown
that pyridine adsorption on pure and fluorinated γ-alumina can be classified as non-covalent interaction.
Potassium chloride salt pre-treated titanium silicalite-1 (TS-1) zeolite (K-TS-1) was prepared via an ion-exchange method.
XRD, EDX and BET were used to identify the structure of the zeolite. The BET surface area and the adsorption/desorption cumulative
pore volume of the K-TS-1 catalyst were about 297 m2/g and 0.213 cm3/g, respectively. The average pore diameter of the K-TS-1 catalyst was 29.49 Å. The catalytic activity of K-TS-1 catalyst
was studied in the fixed-bed catalytic reactor. 1,4-Diazabicyclo (2.2.2) octane (DABCO) was prepared from ethylenediamine
(EDA) over the K-TS-1 zeolite catalyst. The influences of various reaction parameters such as reaction temperature, space
velocity and concentration of EDA were discussed. The conversion of EDA was more than 96% and the selectivity of DABCO and
PIP were up to 64 and 30%, respectively, in the temperature of 340 °C and weight hourly space velocity of 1.5 h−1 in the presence of water.
The effect of triethylenediamine (TEDA) (also named 1,4-diazabicyclo [2.2.2]octane, DABCO) on the adsorption of ClCN on a γ-Al2O3 absorbent has been investigated. Both Fourier transform infrared (FTIR) and theoretical studies indicate that no direct interaction between amine groups of TEDA and ClCN molecules takes place. Instead, we found that TEDA competes with ClCN for active surface sites on γ-Al2O3. In addition, the adsorption behavior of cyanogen chloride (ClCN) on a clean γ-Al2O3 surface has been studied. The sequence of the thermally activated processes of diffusion, adsorption, desorption, and decomposition of ClCN molecules on the clean γ-Al2O3 surface following icelike ClCN layer formation at lower temperature was observed. One of the decomposition products, Al−NCO, was assigned by using an Al−18OH labeled surface for reaction with ClCN. In addition, Al−CN and Al2−OCN species were also detected upon ClCN decomposition. Good correlation of the calculated vibrational frequencies for the adsorbed species with experimental data is found.
The ability to design nanoparticles size and shape through the addition of simple and commercially available organic molecules is of particular interest in the catalytic domain because huge amounts of very fine powders are needed. The origin of this effect is all the more difficult to elucidate because the involved interactions are weak. In this paper, we have investigated the shaping of boehmite AlO(OH) nanoparticles in the presence of polyols like xylitol (C(5) alditol) by a combined experimental and theoretical approach. Experimental techniques such as XRD, TEM, IEP measurements, adsorption isotherms measurements, and (13)C MAS NMR experiments demonstrate that the effect of xylitol has a thermodynamic origin and suggest weak interactions between xylitol and the surface. Furthermore, the strongest proportion of lateral faces ((100), (001), and (101)) that of basal face would be in agreement with a preferential adsorption upon lateral surfaces. These results were refined by a computational approach. DFT calculations of surface energies (taking into account temperature and solvation effects) and of NMR shielding constants corroborate that molecular adsorption mode is preferred over all adsorption modes involving exchanges with surface OH groups. The preferred adsorption on lateral surfaces is attributed to the nest effect induced by hydroxyl groups localized on the concavities of the (001) and (101) surfaces, able to stabilize the xylitol molecule by hydrogen-bonding, whereas the basal (010) surface is almost flat. This combined experimental and computational approach thus provides interesting rationalization for the morphology effects observed.
The rates of dissolution of calcitic Carrara marble have been reported to be significantly reduced in alkaline pH (pH 8.25) at 25 degrees C in the presence of (1-hydroxyethylidene)-1,1 diphosphonic acid (HEDP). The adsorption takes place at the calcite/water interface at the double layer through the interaction of charged surface species with the charged solution species of the adsorbate. The present work focused on obtaining a better understanding of the interaction of the calcite surface with HEDP. Calculations were performed according to the triple layer model, assuming the formation of surface complexes between the charged surface species of calcite and the species of HEDP dominant at pH 8.25. According to the model, the adsorbed species are located at the inner Helmholtz plane of the electrical double layer. Strong lateral interactions between the adsorbed species were suggested and were corroborated from the calculation of the respective energy, which was equal to 69 kJ mol(-1). The adsorption isotherm was consistent with the proposed model at low surface coverage values, while discrepancies between the values experimentally measured and the predicted were found at higher adsorbate concentrations. The deviations from the predicted values were attributed to the fact that HEDP adsorption on calcite resulted in the formation of multiple layers. The model explained adequately the changes in the zeta-potential values of calcite in the presence of HEDP in the solution which resulted in charge reversal upon adsorption.
The coadsorption of CO and triethylenediamine (TEDA) (also called 1,4-diazabicyclo[2.2.2]octane, DABCO) on a high-area gamma-Al2O3 surface has been investigated with use of transmission FTIR spectroscopy. It has been found that TEDA binds more strongly to both Lewis acid sites and to Brønsted Al-OH sites than does CO. Competition experiments indicate that TEDA displaces CO to less strong binding sites. Evidence for weak CO...TEDA interactions is found in which small nu(CO) redshifts are produced. Comparison between different amines such as triethylenemonoamine (TEMA) (also called 1-azabicyclo[2.2.2]octane, ABCO), trimethylamine (TMA), and ammonia indicates that the nu(CO) redshift increases with increasing amine polarizability, indicating that the redshift is mainly due to dipole image damping effects on the CO oscillator frequency. The direct bonding between the exposed N lone pair electrons of the TEDA molecule and CO does not occur. First principles theoretical studies have characterized the bonding of CO with gamma-Al2O3 Lewis acid sites of various types as well as TEDA bonding to both Lewis acid sites and to Al-OH groups. The theoretical studies also indicate that strong bonding of adsorbed CO with TEDA molecules does not occur, and that the observed decrease in the binding energy of CO when coadsorbed with TEDA on gamma-Al2O3 is expected.
The adsorption of triethylenediamine (TEDA) on Lewis acid (Al(3+)) sites of the highly dehydroxylated Al(2)O(3) surface has been observed by FT-IR spectroscopy. This was done by monitoring the competitive adsorption of TEDA and CO on the Al(3+) sites. A stoichiometric replacement of Al(3+)-CO species was observed as Al(3+)-TEDA surface species were formed.
A discussion covers the crystallographic structure of bulk ..gamma..- and g-aluminas and the configurations of alumina crystal faces; IR spectroscopic studies of surface hydroxyl groups; surface densities of hydroxyl groups, oxygen atoms, and anion vacancies as a function of dehydroxylation temperature; identifcation of active sites as special configurations of multiple vacancies or clusters of oxygen atoms; mechanisms of defect site generation during dehydroxylation; studies of carbon monoxide chemisorption as a surface probe for the nature of defect sites; and surface mechanisms of chemisorption of hydrogen, deuterium, olefins, and aromatics, and deuterium exchange with surface hydroxyls and adsorbed olefins or aromatics. Diagrams, graphs, spectra, tables, and 96 references.
The hydrogen bonding of the NH3+ groups in the crystal structures of the amino acids falls into three distinct classes. Of the 56 structures examined in this analysis, the distribution is as follows. In 10 structures, the NH3+ group forms three two-center (linear) hydrogen bonds, in 25, the NH3+ group forms two two-center bonds and one three-center bond, and in 14, the NH3+ group forms one two-center bond and two three-center bonds. There were no examples of three three-center bonds being formed. There are three examples of four-center (trifurcated) bonds. Two of the four structures with NH2+ and NH+ groups also had three-center hydrogen bonds. This relatively high proportion of three-center bonds is a consequence of a deficiency in the number of functional protons necessary to satisfy the normal acceptor coordination of the carboxylate oxygens, which is two per oxygen, and the chloride ions, which is four.
The reaction of 2-chloroethylethyl sulfide (CEES) with a high-area Al2O3 surface was investigated. Two different reactive sites were created by thermally pretreating the Al2O3 powder:? isolated hydroxyl sites and Lewis acid?base pair sites. The reaction of CEES with the isolated hydroxyl groups at 303 and 473 K produced a surface-bound species, which is characterized by a carbon?oxygen stretching mode near 1100 cm-1. This assignment was confirmed by isotopic substitution of 18O into the isolated hydroxyl groups prior to reaction with CEES. The other reaction product detected at 473 K was HCl. For a more highly dehydroxylated Al2O3 surface, the reaction of CEES with the Lewis acid?base pairs produced a surface?bound species also exhibiting a carbon?oxygen stretching mode near 1100 cm-1. This species is postulated to form at O2- Lewis base sites as Al3+?Cl- bonds form on adjacent Lewis acid sites. The adsorption of pyridine onto the Lewis acid sites prior to CEES exposure effectively closes this reaction
The interaction of the various hydroxyl groups on the Al2O3 surface with a bifunctional adsorbate, 2-chloroethylethyl sulfide, was studied by transmission infrared spectroscopy. Al2O3 has five unique Al?OH groups, differentiated by their coordination to the surface, which give independent AlO?H stretching modes. Monitoring intensity changes in these modes as 2-chloroethylethyl sulfide (CEES) molecules diffuse into the porous structure of alumina shows distinctly different stages of surface diffusion and reaction at the Al?OH groups. Three sequential steps have been separated by studies at low temperature, where the rate of the processes was kinetically retarded to allow observation. The final stage of the CEES interaction with the surface occur when the CEES molecules adsorbed on the surface via the sulfide moiety at Al3+ Lewis acid sites undergo a hydrolysis reaction with the neighboring basic Al?OH groups.
The physical adsorption of N2 on silica surfaces containing isolated hyroxyl groups at 87 K. results in the formation of a hydrogen-bonded complex OH ⋯ N2 which exhibits νN2 = 2330 cm−1 (very weak in intensity), and νOH = 3710 cm−1. This is accompanied by the disappearance of the band due to the isolated OH surface groups at 3743 cm−1. The addition of N2(g) to a system containing the analogous OH ⋯ CO complex causes a reversible conversion to the OH ⋯ N2 surface complex and a displacement of the CO into the gas phase. Both N2 and CO surface complexes are thought to be terminally bound to hydroxyl groups.
The physical adsorption of CO onto SiO2 surfaces containing isolated OH groups results in the formation of two types of physisorbed CO. The first, CO species A, exhibits vCO = 2158 cm−1 and is bound by hydrogen bonding to the SiOHδ+ groups to form a surface complex SiOHδ+ … CO. The strength of this interaction is about 2.7 kcal mol−. The second form of physisorbed CO, CO species B, exhibits vCO = 2140 cm−1, and has pronounced rotational wings. The degree of rotational freedom is determined by the extent of shielding by CO of the polar groups on the surface. At high coverages of physisorbed CO species B, solvent effects due to CO species B on both the OH and CO stretching modes of the SiOH … CO complex are observed to cause small downward shifts in stretching frequency.
The adsorption of triethylenediamine (TEDA) at 300 K is observed to occur via hydrogen bonding to isolated Al-OH groups on the surface of partially dehydroxylated high area gamma-Al(2)O(3) powder. This form of bonding results in +0.3 to +0.4% blue shifts in the CH(2) scissor modes at 1455 cm(-1) and a -0.4% red shift in the CN skeletal mode at 1060 cm(-1), compared to the gas-phase frequencies. Other modes are red shifted less than 0.1%. The isolated OH modes are red shifted by -200 to -1000 cm(-1) due to the strong hydrogen bonding association of Al-OH groups with an N atom in TEDA. Thermal desorption of adsorbed TEDA from the surface occurs in the range 300-700 K. Mass spectral and infrared studies indicate that the decomposition of TEDA occurs on Al(2)O(3) above 725 K, and that C-H bonds are broken, forming adsorbed species with N-H bonds which are stable to 1000 K or above. In contrast to adsorption at 300 K, adsorption of TEDA at 85 K results in the formation of a condensed ice of TEDA, which covers the outer surface of the porous Al(2)O(3) and which does not interact with Al-OH groups inside the porous powder due to immobility.