Surface properties and catalytic activity of TiO2-ZrO2 mixed oxides in dehydration of methanol to dimethyl ether

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 degrees 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.