The dispersion state and NOx-SCR properties of VOx species on V2O5 catalysts with different preferentially exposed facets of TiO2 supports

Abstract

The V₂O₅/TiO₂ nanosheet (NS) catalyst with the {001} facet preferentially exposed for TiO₂ exhibits better NO_x-SCR reaction performance than V₂O₅/TiO₂ nanoplate (NL) and nanospindle (NP) catalysts with TiO₂ preferentially exposing the {111} and {101} facets, respectively. The experimental evidence indicates that the VO_x species mainly incorporate into the tetrahedral vacancies on TiO₂ (NP) with a highly polymerized state and higher reducibility, resulting in lower NO conversion and N₂ selectivity of the V₂O₅/TiO₂-NP{101} catalyst. In comparison, the VO_x species mainly incorporate into the octahedral vacancies on TiO₂ (NS) and TiO₂ (NL) with lower polymerization degree and lower reducibility, hence restraining the generation of N₂O and resulting in higher NO conversion and N₂ selectivity of V₂O₅/TiO₂-NS{001} and V₂O₅/TiO₂-NL{111} catalysts. Although the VO_x species in V₂O₅/TiO₂-NS{001} and V₂O₅/TiO₂-NL{111} catalysts have the same polymerization degree, the basicity of the O²⁻ ions in the {001} facet of TiO₂ is stronger than that of the {111} facet. As a result, the VO_x species dispersed in the V₂O₅/TiO₂-NS{001} catalyst have weaker acidity, and the adsorbed ammonia species (NH₄⁺ and NH₃) desorb easily from the surface of the catalyst, accounting for its best NO_x-SCR performance. This research paves a comprehensive insight to understand the facet–property relationships of oxide catalysts, which is helpful for providing interface information for SCR catalysts and constructing catalytic reaction systems with excellent performance.