Surface and acidic properties of some mixed oxide catalysts in relation to their catalytic activities

Abstract

A series of silica-alumina catalysts were prepared to contain different proportions of alumina. The catalysts were calcined at 773–973 K. Another series of silica-titania catalysts of different chemical compositions were prepared and calcined between 773 and 973 K. The textural properties (surface area and pore structure) of the catalysts were determined by low-temperature nitrogen adsorption at 77 K. The surface acidity (acid amount and acid strength) was determined for each catalyst by thermal programmed desorption (TPD) of pyridine. The catalytic cracking of cumene at 673–773 K and the catalytic conversion of isopropanol at 473–593 K were investigated using microcatalytic technique. Cracking of cumene is a first-order catalytic reaction which takes place on relatively strong acid sites and the reaction is structurally sensitive. Dehydration of isopropanol on mixed oxide catalysts is a zero-order reaction and proceeds on most of the acid sites. Dehydration of isopropanol is related to the surface acid density and is structurally insensitive.