31P and 51V MAS-NMR Characterisation of Mixed Vanadium and Titanium Phosphates Prepared from Molecular Precursors

Abstract

Coprecipitation of mixed vanadium and titanium phosphates has been performed by reacting a mixed solution of vanadium alkoxide (VO(OPrn)3) and titanium alkoxide (Ti(OPrn)4) with anhydrous phosphoric acid (H3PO4). The goal is to obtain a mixture at a molecular level of phosphates with both acidic and redox properties. In protic solvents, such as propanol, the vanadium phosphate precipitation is slow, so, as indicated by the chemical analysis, the coprecipitation is not stoichiometric. The kinetics of precipitation of both vanadium and titanium phosphates are much faster in aprotic solvents such as tetrahydrofuran (THF) and result in homogeneous precipitates. 31P and 51V MAS-NMR experiments, have been used in order to characterise the homogeneity in these samples. Phase separation is observed upon heating at 700∘C.