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 we re prepared using a sol-gel technique. Their catalytic behavior was measure d for the liquid phase alkylation of isobutane with 2-butene. A maximum ini tial (TOS = 1 min) activity and selectivity to trimethylpentanes as well as slower decay were detected for the sample with the smallest surface area ( 10 m(2) g(-1)) and a Nafion content of 20 wt%. Catalysts with the same poly mer content but a larger surface area showed a considerably lower initial a ctivity and selectivity; deactivation was faster. This can be explained by the fact that, in composites with a greater surface area-highly dispersed N afion-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 o f the sulfonic groups. In the same way, when the Nafion content is varied i n those composites with a large and similar BET area, the rates of deactiva tion are inversely proportional to the amount of resin in the sample. Moreo ver, a silica-supported Nafion catalyst, prepared by impregnation, has give n results as good as those obtained with the more active Nafion/silica comp osite. The effect of the process variables (TOS, temperature, and isoparaff in/olefin molar ratio) on the activity and selectivity of these catalysts w as studied as well. Comparison of these catalysts with other solid acid mat erials, such as an II-Beta zeolite and a sulfated zirconia, shows that the Nafion/silica samples behave more like H-Beta than like the sulfated zircon ia catalyst. (C) 1999 Academic Press.