Study of the influence of the impregnation acidity on the structure and properties of molybdena–silica catalysts

Abstract

Three samples of 8 mol% MoO₃ supported on SiO₂ have been prepared using impregnating solutions with different acidity levels (pH 1, 6 and 11, respectively). The three products had different structures and behaved in a varied manner vis á vis pyridine adsorption. At pH 1 the active phase-support interaction was strongest and a silicomolybdate phase was formed, whereas at pH 6, where the interaction was weaker, MoO₃ islands were obtained on the silica surface. At pH 11 interaction was very low and simple coprecipitation of molybdena and silica took place.