Surface states of MoO3 on ZrO2 and catalytic properties for the reaction of NO with H2
Abstract
The adsorption and reaction of nitric oxide on reduced molybdena–zirconia were studied by means of e.s.r., i.r. and u.v. spectroscopies. On the surface, at least two types of nitrosyl complex exist. At an early stage of reduction, a diamagnetic dinitrosyl complex with i.r. bands at ca. 1790 and 1690 cm–1 formed on NO adsorption and was ascribed to Mo4+(NO)2. After reduction at a higher temperature, a paramagnetic dinitrosyl species appeared upon NO adsorption and was tentatively assigned to Mo5+(NO)2. Nitric oxide can adsorb on Mo5+ in tetrahedral coordination, but not on Mo5+ in octahedral coordination. This can be explained by the coordination being limited. For the reaction of NO with H2, the species of Mo5+(NO)2 was concluded to be a main active complex in the catalytic cycle.