Effect of surface acidity on the catalytic activity and deactivation of supported sulfonic acids during dehydration of methanol to DME

The influence of a catalyst's surface acidity on the catalytic activity and deactivation in the dehydration of methanol to DME was investigated. Different materials including propylsulfonic acid functionalized silica with different Bronsted acidities, silica-alumina, and propyl and phenylsulfonic acid functionalized silica-alumina catalysts were prepared. All the samples were characterized by XRD, TGA, XPS, N-2-sorption, ICP-OES and SEM analysis. It was found that the Bronsted and Lewis acidity of the SiO2/Al2O3-PhSO3H catalyst played a critical role in the performance of methanol to DME transformation. The grafting of sulfonic acid groups on silica-alumina enhanced the surface Bronsted acidity and also the reaction activity and selectivity for the dehydration of methanol to DME. In addition, the phenylsulfonic acid functionalized silica-alumina catalyst exhibited the highest activity and stability for the dehydration reaction at relatively low temperatures at which the gamma-Al(2)O(3)catalyst, commercial reference, displayed low dehydration activity. The effect of water was also investigated because in the indirect process to produce DME using acidic gamma-alumina, it had the most important effect on catalyst deactivation. As a result, water had a positive effect on methanol dehydration over the SiO2/Al2O3-PhSO3H catalyst in contrast to gamma-Al(2)O(3)which was rapidly deactivated. Thus, Bronsted and Lewis acid sites with suitable strength may be responsible for the effective conversion of methanol to DME with high stability and selectivity.