Surface Properties and Catalytic Activity of TiO₂–ZrO₂ Mixed Oxides in Dehydration of Methanol to Dimethyl Ether

Abstract

A series of TiO₂–ZrO₂ mixed oxides with varying molar ratio of TiO₂ to ZrO₂ were prepared by the co-precipitation method. The crystalline phases of the oxides were characterized by XRD and their acid–base properties by TPD of NH₃ and CO₂ and IR of adsorbed pyridine. The catalytic activities were investigated for the vapor phase dehydration of methanol to dimethyl ether (DME) in a fixed-bed reactor under atmospheric pressure. The mixed oxides are highly amorphous in nature. The acid–base properties and CH₃OH conversion activity are increasing with TiO₂ content and an optimum value is achieved for a molar ratio of Ti/Zr in the vicinity of 1/1. At lower reaction temperature (<300 °C), the selectivity for DME is nearly 100%. A good correlation is observed between dehydration activity and the acid–base properties of the TiO₂–ZrO₂ catalysts. It is significant to note that TiO₂–ZrO₂ catalysts show high stability against water during dehydration reaction. Based on our results, a surface mechanism involving both acid–base sites has been proposed for DME formation.