A Brønsted acid strength hierarchy for zirconia—silica—sulfate aerogels

Abstract

Manipulation of sulfate content, silica content, and activation temperature provides the means for controlling the strength of surface Brønsted acid sites in the zirconia—silica—sulfate system. This capability allows a development of an acid strength hierarchy, based on the adsorption of pyridine and isomerization of 1-butene and n-butane, as a rational basis for acid catalyst design. Introduction of silica into zirconia—sulfate co-gels also provides insight into the activation behavior of this important class of materials. Silica retards sintering upon heat treatment, thereby delaying crystallization of the zirconia component to higher temperatures. Activation of sulfate to a form capable of catalyzing the isomerization of n-butane is also delayed to higher heat treatment temperatures, confirming the role of crystallization in initiating the activation sequence.