The effect of sulfation conditions and activation temperature of sulfate-doped ZrO2, TiO2 and SnO2 catalysts during isobutane/2-butene alkylation

The activity, selectivity, and deactivation behavior of sulfated ZrO2, TiO2 and SnO2 catalysts during the liquid phase alkylation of isobutane with 2-butene at 32°C have been studied as a function of the sulfate source, i.e., sulfuric acid and ammonium sulfate, sulfate concentration, and calcination temperature. It has been shown that, for each metal oxide, the optimum calcination temperature giving maximum activity depends on both the source of sulfur and the sulfur concentration used during the impregnation step. Moreover, when the most active preparations of each sulfated oxide are compared, it is shown that the initial activity decreases in the order: SO4 2−/ZrO2⩾ SO4 2−/TiO2SO4 2−/SnO2, which is the expected trend of acid strength. However, owing to the higher strength of the acid sites, the former two catalysts present a very high initial cracking activity, thus affording low selectivities to the desired trimethylpentanes (TMP). It has also been shown that a certain loss of sulfates (between 0 and 30% of the initial sulfates for most of the preparations) takes place during the alkylation reaction on the three sulfated metal oxides. Sulfate decomposition is suggested to occur by chemical interaction of the butene molecules present in the feed with some surface sulfates.