Supported heteropolyacid (HPW) catalysts for the continuous alkylation of isobutane with 2-butene: The benefit of using MCM-41 with larger pore diameters

12-Tungstophosphoric acid (HPW) has been supported on three different carriers: a commercial silica, a high surface area amorphous aluminosilicate (MSA), and an all-silica mesoporous MCM-41; and their catalytic properties have been determined for the alkylation of 2-butene with isobutane at 33°C and 2.5 MPa. A maximum in activity, selectivity to TMP and stability with time on stream was found for the HPW/SiO2 catalyst with 40 wt% acid loading, despite the higher acid dispersions achieved with the high surface area MCM-41 and MSA supports. The lower activity of the HPW/MSA samples is due to a stronger interaction of HPW with the surface sites of the aluminosilicate, which in turn decreased both the number and the average acid strength of the Brönsted acid sites of the heteropolyacid. When the HPW was supported on MCM-41 a continuous decrease of the catalytic activity with the HPW content was observed. This fact, together with the characterization results, suggests a partial blockage of the monodimensional pores of MCM-41, which decreased the accessibility of the reactants to the Brönsted acid sites of the heteropolyacid located inside the pores. We show that this pore blockage can be decreased, and the catalytic activity of HPW/MCM-41 catalysts increased, by using a MCM-41 sample with larger pore diameter.