Theoretical study of small clusters Au_(5-6) on Au/SAPO-11 catalysts and their interactions with CO

摘要

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 Au_5/SAPO-11, Au_6/SAPO-11, CO-Au_5/SAPO-11 and CO-Au_6/SAPO-11 aggregates to analyze the geometries of small clusters of Au_5 and Au_6 on SAPO-11 support. Au_5 cluster presents a pentagonal structure in Au_5/SAPO-11. Au_6 aggregate shows a "multi triangular" structure (as from a trapezoidal "W shaped" Au_5) in Au_6/SAPO-11. Aus is also obtained as an "X shaped" structure. Similarly another Au_6 aggregate configuration is obtained also multi triangular but as from X shape Au_5 cluster. The CO interaction with Au_5 and Au_6/SAPO-11 is studied. The formation energy △E_f of the aggregates, the CO adsorption energy △E_(ads) on them and CO frequency are presented.