The Influence of Textural and Compositional Characteristics of Nafion/Silica Composites on Isobutane/2-Butene Alkylation

Nafion/silica composites of different surface areas and polymer contents were prepared using a sol–gel technique. Their catalytic behavior was measured for the liquid phase alkylation of isobutane with 2-butene. A maximum initial (TOS=1 min) activity and selectivity to trimethylpentanes as well as slower decay were detected for the sample with the smallest surface area (10 m2 g−1) and a Nafion content of 20 wt%. Catalysts with the same polymer content but a larger surface area showed a considerably lower initial activity and selectivity; deactivation was faster. This can be explained by the fact that, in composites with a greater surface area—highly dispersed Nafion—the sulfonic groups of the polymer interact to a greater extent with the silanol groups of the silica, resulting in a decrease in the activity of the sulfonic groups. In the same way, when the Nafion content is varied in those composites with a large and similar BET area, the rates of deactivation are inversely proportional to the amount of resin in the sample. Moreover, a silica-supported Nafion catalyst, prepared by impregnation, has given results as good as those obtained with the more active Nafion/silica composite. The effect of the process variables (TOS, temperature, and isoparaffin/olefin molar ratio) on the activity and selectivity of these catalysts was studied as well. Comparison of these catalysts with other solid acid materials, such as an H-Beta zeolite and a sulfated zirconia, shows that the Nafion/silica samples behave more like H-Beta than like the sulfated zirconia catalyst.