Bulk mixed metal oxides find wide application as selective oxidation catalysts, electro-catalysts, sensors, etc. In spite of the extensive use of bulk mixed metal oxides in numerous applications, there is only a limited amount of information available in the literature about their surface compositions and cation oxidation states in different environments since prior studies focused on characterizing the bulk structures of mixed oxides with techniques such as XRD, TEM and XAS. With modern surface science techniques, it is now possible to determine the elemental composition of the outermost surface layer (High Sensitivity-Low Energy Ion Scattering (HS-LEIS) Spectroscopy) and cation oxidation states in different environments (Near Atmospheric Pressure (NAP)-XPS). Recent examples from selective oxidation reactions (e.g., methanol oxidation to formaldehyde and propylene oxidation to acrolein) by bulk molybdate and vanadate mixed oxide catalysts will be presented. These findings provide insights into the nature of the surfaces of bulk mixed oxides and exhibit surface segregation of the redox components (VOx and MoOx) and their dynamic redox behavior in response different environmental conditions. The new findings are in contrast to the catalysis models by mixed oxides in the literature based on the bulk structures with the assumption that the surface is just a termination of the bulk structure. The new insights are causing a paradigm shift in catalysis by bulk mixed metal oxides that require establishing new catalysis models.

Nature of surfaces for bulk mixed metal oxides

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.