Synthesis and characterization of several La3+ and Sr2+ vanadates, active as methanol oxidation catalysts

Substitution of Sr²⁺ for La³⁺ in strontium orthovanadates gives materials with interesting bulk and surface properties.

The results indicate that there are correlations between increasing selectivities to formaldehyde and (i) the decreasing crystallinity of the mixed vanadates, (ii) the increasing La migration from the surface towards the bulk, (iii) the decreasing initial temperature of reduction of V⁵⁺ in the catalysts.

The migration of the La³⁺ could leave the oxygen of the crystal structure more accessible to the reducing hydrogen (during TPR measurements) and to the reactants in the catalytic methanol oxidation. This La³⁺ migration into the bulk may also be the cause of the loss of the crystallinity. In addition the La³⁺ vacancies in the isostructural mixed vanadate catalysts should be responsible for their selectivities in the oxidation of methanol to formaldehyde.