Phase transformation of ZrO2 by Si incorporation and catalytic activity for isopropyl alcohol dehydration and dehydrogenation

Abstract

The synthesis of metal oxides under basic conditions can yield unexpected experimental errors, such as contamination by impurities. Here, we clarified the influence of Si on the physicochemical properties of ZrO2 by comparing intentionally synthesized silica–zirconia (SZ) with accidentally synthesized Si-containing ZrO2. While pure monoclinic ZrO2 with a low surface area (20 m2 g−1) and acidity was synthesized without Si addition, SZ was structurally transformed to a tetragonal phase with a high surface area (140 m2 g−1) and acidity with the incorporation of Si. The ZrO2 synthesized by precipitation and digestion at pH 10.0 for different periods (24 − 240 h) using glassware equipment was found to have up to 26% dissolved Si; the mixture exhibited physicochemical properties similar to those of SZ catalysts with equivalent amounts of Si. The crystallization temperature of amorphous ZrO2 increased with increasing Si content, whereas the crystal size decreased with the amount of Si in the structure. The stabilization of the tetragonal phase by the incorporation of Si was theoretically investigated using density functional theory. The catalytic performance of the SZ catalysts toward the dehydration/dehydrogenation of isopropyl alcohol (IPA) was studied and compared with that of ZrO2 catalysts prepared by the precipitation method. The Brønsted acid sites originating from Si incorporation were more advantageous for the dehydration of IPA to propylene than Lewis acids.