Theoretical study of CO adsorption and oxidation on Au3–5 clusters supported on silico-aluminophospates

The Au3-5 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 Au3/SAPO-11, Au4/SAPO-11, Au5/SAPO-11, CO–Au3/SAPO-11, CO–Au4/SAPO-11 and CO–Au5/SAPO-11 aggregates to analyze the geometries of small clusters of Au3, Au4 and Au5 on SAPO-11 support. Au3 cluster presents 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 a less stable structure. Au5 cluster displays a “pentagon shaped” structure as the most stable. The CO interaction with Au3, Au4 and Au5/SAPO-11 is studied; this CO adsorption is different from that reported in the literature. The formation energy ΔEF of the aggregates, the CO adsorption energy ΔEads on them and the change of energy of the oxidation reaction are presented. Some relevant charges and bond indexes were calculated. On supporting all Au3-5 there is a charge transfer from the Au cluster to the binding O atoms. On CO adsorption in all Au3-5 clusters there is a charge transfer from the cluster to the CO.