Characterization of H4PMo11 VO40 heteropolyacid on SiO2 and SiC supports

Abstract

Heteropolyacid H₄PMo₁₁VO₄₀ has been deposited in different amounts on the surface of SiO₂(Aerosil) and SiC supports. The samples were characterized by surface potential, ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS) techniques. The thermal stability of the acid increases at a low acid content corresponding to ca. 0.1–0.75 theoretical monolayers for the SiO₂ support and up to 2.5 monolayers for the SiC support. At higher acid content it is lower (SiO₂) or the same (SiC) as that of the unsupported acid. On the basis of the XPS and ISS data, a model of the acid dispersion has been proposed. The deposited phase forms blocks which cover maximally 20% of the SiO₂ and 50–60% of the SiC surface, even when the acid content is equal (SiO₂) or exceeds (SiC) the theoretical monolayer coverage.