Ligand/cluster/support catalytic complexes in heterogeneous ultrananocatalysis: NO oxidation on Ag3/MgO(100)

Abstract

In the present work we explore via first-principles simulations whether the ligand/cluster/support catalytic complex generated by CO oxidation over silver trimers deposited on the regular MgO(100) surface – i.e. a Ag₃/carbonate or Ag₃(CO₃)/MgO(100) species – can be used as a catalyst in a different reaction: the selective oxidation of NO to NO₂ (or NOox). The Ag₃(CO₃)/MgO(100) complex is first shown to be reasonably stable at room temperature in terms of both disaggregation and sintering, and that it can be generated from Ag₃ adsorbed onto an oxygen vacancy defect of the regular MgO(100) surface under oxidation conditions. It is then found that the Ag₃(CO₃)/MgO(100) species transforms under NOox conditions into an even more complex aggregate, a mixed carbonate/double-nitrite Ag₃(CO₃)(NO₂)₂/MgO(100) species, which can then act as an efficient catalyst of NOox. It is noteworthy that under NOox reaction conditions a different ligand/cluster/support catalytic complex is formed with respect to the original COox one. These findings prove the diversity of the catalytic chemistry of subnanometer (or ultranano) metal clusters deposited on oxide substrates, associated with the formation of many different ligand/cluster/support aggregates, the vast amount of combinatorial possibilities thus opening, and the need for computational approaches to perform systematic structural and stoichiometric searches in order to cope with such a multiform diversity.