Sulfated alumina and zirconia in isobutane/butene alkylation and n-pentane isomerization: Catalysis, acidity, and surface sulfate species

The catalytic behavior of sulfated alumina (SA) and zirconia (SZ) was compared for two acid-catalyzed reactions, i.e., isobutane/butene alkylation and isomerization of n-pentane. For the alkylation reaction, the SZ catalyst gave a higher C5+ alkane yield and much lower selectivity for trimethylpentanes (TMPs) at 2 h TOS. However, TMPs selectivity was comparable for both catalysts at 5.5 h TOS. For the isomerization, high n-pentane conversion was obtained on SZ at the reaction temperature of 100 °C when SA had no activity. Surface sulfate species were identified by IR spectroscopy. The acidity of sulfated oxides was compared by IR spectroscopy using pyridine and carbon monoxide as probe molecules and TPD–MS of ammonia. An effort was made to explain the difference between catalytic behavior of two sulfated oxides in terms of acidity, the nature of surface sulfate species and the formation of hydride species.