Theoretical study of the CO catalytic oxidation on Au/SAPO-11 zeolite (original) (raw)
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Quantum chemistry calculations were carried out, using ONIOM2 methodology, to investigate the CO adsorption and oxidation on gold supported on Silicoaluminophospates (SAPO) molecular sieves Au/SAPO-11 catalysts. Two models were studied, one containing one Au atom per site (AuASAPO-11), and the other with two Au atoms per site (Au2ASAPO-11). The results reveal that the CO adsorption and oxidation are exothermic on Au/SAPO11 with an DE of �41.0 kcal/mol and DE ¼ �52.0 kcal/mol, for the adsorption and oxidation, respectively. On the Au2ASAPO-11 model, the CO adsorption and oxidation reaction occur, with a DE of �29.7 kcal/mol and �52 kcal/mol, respectively. According to our results, the oxidation reaction exhibits an Eley-Rideal type mechanism with adsorbed CO. The theoretical calculations reveal that this type of material could be interesting to disperse Au and consequently to strengthen its catalytic use for different reactions. VC 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:...
Theoretical study of the water effect on CO adsorbed over Au/SAPO-11 catalysts
Journal of Computational Methods in …, 2009
In this study, we carried out two-layer ONIOM calculations to determine the energy changes for the gold-exchanged silicoaluminophospate (Au/SAPO-11) catalysts interaction with CO, H _ {2}, and H _ {2} O molecules, and the formation of possible intermediate species, such ...
Theoretical study of small clusters Au 3−4 on Au/SAPO-11 catalysts and their interactions with CO
Quantum chemistry calculations were done, using the ONIOM2 methodology at two different levels of calculation, B3LYP for the high level and UFF for the low level. These calculations were performed on Au3/SAPO-11, Au4/SAPO-11, CO-Au3/SAPO-11 and CO-Au4/SAPO-11 aggregates to analyze the geometries of small clusters of Au3 and Au4 on SAPO-11 support. Au3 cluster present a triangle structure in Au3/SAPO-11. Au4 cluster shows a "Y shaped" structure in Au4/SAPO-11. Au4 as a rhombus structure is also studied but it is an unstable intermediate to the "Y shaped" structure. The CO interaction with Au3 and Au4/SAPO-11 is studied, this CO adsorption is different from reported in the literature. The formation energy ΔEF of the aggregates and the CO adsorption energy ΔE ads on them are presented.
Computational and Theoretical Chemistry, 2014
The Au 3-5 clusters supported on silico-aluminophospates (SAPO-11) were studied using quantum chemistry calculations, by means of the ONIOM2 methodology at two different levels of calculation, B3LYP for the high level and UFF for the low level. These calculations were performed on Au 3 /SAPO-11, Au 4 /SAPO-11, Au 5 /SAPO-11, CO-Au 3 /SAPO-11, CO-Au 4 /SAPO-11 and CO-Au 5 /SAPO-11 aggregates to analyze the geometries of small clusters of Au 3 , Au 4 and Au 5 on SAPO-11 support. Au 3 cluster presents a triangle structure in Au 3 /SAPO-11. Au 4 cluster shows a ''Y shaped'' structure in Au 4 /SAPO-11. Au 4 as a rhombus structure is also studied but it is a less stable structure. Au 5 cluster displays a ''pentagon shaped'' structure as the most stable. The CO interaction with Au 3 , Au 4 and Au 5 /SAPO-11 is studied; this CO adsorption is different from that reported in the literature. The formation energy DE F of the aggregates, the CO adsorption energy DE ads on them and the change of energy of the oxidation reaction are presented. Some relevant charges and bond indexes were calculated. On supporting all Au 3-5 there is a charge transfer from the Au cluster to the binding O atoms. On CO adsorption in all Au 3-5 clusters there is a charge transfer from the cluster to the CO. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m p t c
The Journal of Physical Chemistry B, 2006
Although Au catalysts can be readily prepared on titania via the deposition-precipitation (DP) method, the direct application of the method similar to the preparation of silica-supported Au catalysts only results in diminished success. This paper reports a novel, efficient method to synthesize highly active Au catalysts supported on mesoporous silica (SBA-15) through a gold cationic complex precursor [Au(en) 2 ] 3+ (en) ethylenediamine) via a wet chemical process. The gold cationic precursor was immobilized on negatively charged surfaces of silica by a unique DP method that makes use of the deprotonation reaction of ethylenediamine ligands. The resulting mesoporous catalyst has been demonstrated to be highly active for CO oxidation at room temperature and even below 273 K, the activity of which is much superior to that of silica-supported Au catalysts previously prepared by various solution techniques. The pH value of the gold precursor solution plays a key role in determining the catalytic activity through the regulation of [Au(en) 2 ] 3+ deprotonation reaction and the surface interaction of silica with the gold precursor. This mesoporous gold silica catalyst has also been shown to be highly resistant to sintering because of the stabilization of Au nanoparticles inside mesopores.
Theoretical study of small clusters Au 5−6 on Au/SAPO-11 catalysts and their interactions with CO
Journal of Computational Methods in Sciences and Engineering
Quantum chemistry calculations were done, using the ONIOM2 methodology at two different levels of calculation, B3LYP for the high level and UFF for the low level. These calculations were performed on Au5/SAPO-11, Au6/SAPO-11, CO-Au5/SAPO-11 and CO-Au6/SAPO-11 aggregates to analyze the geometries of small clusters of Au5 and Au6 on SAPO-11 support. Au5 cluster presents a pentagonal structure in Au5/SAPO-11. Au6 aggregate shows a "multi triangular" structure (as from a trapezoidal "W shaped" Au5) in Au6/SAPO-11. Au5 is also obtained as an "X shaped" structure. Similarly another Au6 aggregate configuration is obtained also multi triangular but as from X shape Au5 cluster. The CO interaction with Au5 and Au6/SAPO-11 is studied. The formation energy ΔEF of the aggregates, the CO adsorption energy ΔE ads on them and CO frequency are presented.
Physical Chemistry Chemical Physics, 2011
Supported gold nanoparticles have generated an immense interest in the field of catalysis due to their extremely high reactivity and selectivity. Recently, alloy nanoparticles of gold have received a lot of attention due to their enhanced catalytic properties. Here we report the synthesis of silica supported AuCu nanoparticles through the conversion of supported Au nanoparticles in a solution of Cu(C 2 H 3 O 2 ) 2 at 300 1C. The AuCu alloy structure was confirmed through powder XRD (which indicated a weakly ordered alloy phase), XANES, and EXAFS. It was also shown that heating the AuCu/SiO 2 in an O 2 atmosphere segregated the catalyst into a Au-CuO x heterostructure between 150 1C to 240 1C. Heating the catalyst in H 2 at 300 1C reduced the CuO x back to Cu 0 to reform the AuCu alloy phase. It was found that the AuCu/SiO 2 catalysts were inactive for CO oxidation. However, various pretreatment conditions were required to form a highly active and stable Au-CuO x /SiO 2 catalyst to achieve 100% CO conversion below room-temperature. This is explained by the in situ FTIR result, which shows that CO molecules can be chemisorbed and activated only on the Au-CuO x /SiO 2 catalyst but not on the AuCu/SiO 2 catalyst.
Journal of the American Chemical Society, 2002
Gold-based catalysts have been of intense interests in recent years, being regarded as a new generation of catalysts due to their unusually high catalytic performance. For example, CO oxidation on Au/TiO2 has been found to occur at a temperature as low as 200 K. Despite extensive studies in the field, the microscopic mechanism of CO oxidation on Au-based catalysts remains controversial. Aiming to provide insight into the catalytic roles of Au, we have performed extensive density functional theory calculations for the elementary steps in CO oxidation on Au surfaces. O atom adsorption, CO adsorption, O 2 dissociation, and CO oxidation on a series of Au surfaces, including flat surfaces, defects and small clusters, have been investigated in detail. Many transition states involved are located, and the lowest energy pathways are determined. We find the following: (i) the most stable site for O atom on Au is the bridge site of step edge, not a kink site; (ii) O 2 dissociation on Au (O2f2Oad) is hindered by high barriers with the lowest barrier being 0.93 eV on a step edge; (iii) CO can react with atomic O with a substantially lower barrier, 0.25 eV, on Au steps where CO can adsorb; (iv) CO can react with molecular O 2 on Au steps with a low barrier of 0.46 eV, which features an unsymmetrical four-center intermediate state (O-O-CO); and (v) O2 can adsorb on the interface of Au/TiO2 with a reasonable chemisorption energy. On the basis of our calculations, we suggest that (i) O2 dissociation on Au surfaces including particles cannot occur at low temperatures; (ii) CO oxidation on Au/inactive-materials occurs on Au steps via a two-step mechanism: CO+O2fCO2+O, and CO+OfCO2; and (iii) CO oxidation on Au/active-materials also follows the two-step mechanism with reactions occurring at the interface.
Molecules, 2012
O 2 adsorption is a key process for further understanding the mechanism of selective CO oxidation (SCO) on gold catalysts. Rate constants related to the elementary steps of O 2 adsorption, desorption and surface bonding, as well as the respective activation energies, over a nanosized Au/γ-Al 2 O 3 catalyst, were determined by Reversed-Flow Inverse Gas Chromatography (RF-IGC). The present study, carried-out in a wide temperature range (50-300 C), both in excess as well as in the absence of H 2 , resulted in mechanistic insights and kinetic as well as energetic comparisons, on the sorption processes of SCO reactants. In the absence of H 2 , the rate of O 2 binding, over Au/γ-Al 2 O 3 , drastically changes with rising temperature, indicating possible O 2 dissociation at elevated temperatures. H 2 facilitates stronger O 2 bonding at higher temperatures, while low temperature binding remains practically unaffected. The lower energy barriers observed, under H 2 rich conditions, can be correlated to O 2 dissociation after hydrogenation. Although, H 2 enhances both selective CO reactant's desorption, O 2 desorption is more favored than that of CO, in agreement with the well-known mild bonding of SCO reactant's at lower temperatures. The experimentally observed drastic change in the strength of CO and O 2 binding is consistent both with well-known high activity of SCO at ambient temperatures, as well as with the loss of selectivity at higher temperatures.
Materials (Basel, Switzerland), 2018
In this work we report the effects of support structural properties and its modification with some metal oxides modifiers on the catalytic behavior of Au catalysts in the total CO oxidation at 20 °C. Au catalysts were supported on mesoporous silica materials (MSM) having different structural properties: Channel-like (SBA-15), cage-like (SBA-16), hexagonal (HMS), and disordered (DMS-1) structures. The effect of the modifier was evaluated by comparison of the catalytic response of the SBA-15-based catalysts modified with MgO, Fe₂O₃, TiO₂, and CeO₂. The chemical, structural, and electronic properties of the catalysts were investigated by a variety of techniques (metal content analysis by ICP-OES, N₂ physisorption, XRD, UV-vis DRS, DRIFTS of adsorbed CO and OH regions, oxygen storage capacity (OSC), HR-TEM, and XPS). The activity of calcined catalysts in the CO oxidation reaction were evaluated at steady state conditions, at 20 °C, atmospheric pressure, and when using, as feed, a 1%CO/1...