Tailored Brønsted and Lewis surface acid sites of the phosphotungstic Wells Dawson heteropoly-acid

Abstract

The synthesis of transition metals Wells Dawson heteropoly salts along with their elemental composition, water content, structure and specific surface area were thoroughly investigated. Additionally, the use of a molecular probe such as pyridine allowed the quantification of Lewis and Brønsted surface acid sites. The transition metals counter-cations provide both Lewis and Brønsted acid sites. The concentration of Brønsted acid sites is influenced by the crystallization water associated with the heteropoly anion. Additionally, the dispersion of the phosphotungstic Wells Dawson heteropolyacid over transition metal oxides evidenced the presence of both Brønsted and Lewis surface acid sites. The concentration of these sites is related to the surface dispersion of the crystals of the HPA over the oxide supports and the degree of hydration of the HPA.