Abstract
We have studied the structure of mononuclear gold supported on acidic form of faujasite zeolite in two oxidation states, namely, 0 and +1, using density functional theory. The binding of the gold monomer to the zeolite support is stronger in the oxidation state +1 than in the oxidation state 0. For the oxidation state 0, the hydrogenated clusters AuH/(2H)-FAU, AuH2/H-FAU generated by stepwise reverse hydrogen spillover from bridging OH groups of zeolite are energetically preferred over the Au/(3H)-FAU structure. Reverse hydrogen spillover of all the three acidic protons from the zeolite to the Au monomer did not lead to a stable structure. The calculated reverse hydrogen spillover energy per hydrogen atom for zeolite supported AuH and AuH2 clusters are −10.2 and −5.1 kJ/mol, respectively, in the oxidation state 0, while in the oxidation state +1 it is 20.9 kJ/mol for zeolite supported Au+H cluster.
Highlights
Oxide-supported transition metal clusters form an important class of system both for theoretical and experimental investigations mainly due to their very important applications as catalysts
The activity of supported metal clusters is found to be higher than bare clusters and these metal-support interfaces are believed to act as active sites for catalysis
In an earlier investigation [11] of Au6 cluster supported on faujasite zeolite, we found that the Journal of Catalysts hydrogenated clusters generated by stepwise reverse hydrogen spillover from the support to the cluster are more stable than the bare supported clusters
Summary
Oxide-supported transition metal clusters form an important class of system both for theoretical and experimental investigations mainly due to their very important applications as catalysts. The common metal oxide supports used for gold cluster catalysis are MgO, Al2O3, SiO2, TiO2, and so forth It has been found by Vayssilov and Rosch [7] that transition metal clusters M6 with hydrogen impurity adsorbed on a zeolite support have more nearest neighbour M-O contacts than the corresponding bare adsorbed clusters indicating that the presence of hydrogen in the adsorbed cluster leads to higher stability. In view of the catalytic importance of the gold monomer for CO oxidation reaction, we were motivated to investigate the possibility of reverse spillover of hydrogen from the faujasite zeolite support to the gold monomer, by transferring hydrogen atoms, one at a time, from the support to the gold. As the activity of supported nanoparticles depends greatly on the oxidation state of the metal, we shall perform this investigation in two oxidation states, 0 and +1
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