Influence of Domain Size and Support Composition on the Reducibility of SiO2 and TiO2 Supported Tungsten Oxide Clusters

• Published in: Journal of physical chemistry. C 2024-08, Vol.128 (33), p.13864-13878
• Main Authors: Mamedov, Konstantin, Shrestha, Anukriti, Whitcomb, Colby A., Paolucci, Christopher, Davis, Robert J.
• Format: Article
• Language: English
• Subjects: C: Chemical and Catalytic Reactivity at Interfaces; Cluster chemistry; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Monomers; Oxidation state; Oxides; Redox reactions
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.4c03652

Supported tungsten oxides are widely used in a variety of catalytic reactions. Depending on the support, the cluster size, oxidation state, reducibility and speciation of the tungsten oxides can widely differ. When promoted with a platinum group metal, the resulting spillover of hydrogen may facilitate the reduction of supported tungsten oxide species, depending on the support. High resolution scanning transmission electron microscopy imaging showed nanometer scale WO x clusters were synthesized on SiO2 whereas highly dispersed species were formed on TiO2. Results from H2-temperature-programmed reduction showed the presence of Pd lowered the initial reduction temperature of SiO2-supported WO x species but interestingly did not affect that of TiO2-supported WO x . X-ray photoelectron and absorption spectroscopies showed the W atoms in SiO2-supported WO x species reduce from a +6 oxidation state to primarily +5 after thermal treatment in 5% H2, while the fraction of W in the +5 oxidation state was relatively unaffected by reduction treatment of TiO2-supported WO x . The unusual behavior of TiO2-supported WO x was explained by quantum chemical calculations that reveal the lack of change in the oxidation state of W is attributed to charge delocalization on the surface atoms of the titania support, which does not occur on silica. Moreover, modeling results at