ACIDITY AND REACTIVITY OF SULFATED ZIRCONIA AND METAL-DOPED SULFATED ZIRCONIA

Since its discovery, sulfated zirconia and metal-doped sulfated zircon ia have been the subject of numerous reports on their catalytic activi ty, Their ability to perform low-temperature hydrocarbon isomerization s has led to claims that sulfated zirconia and metal-doped sulfated zi rconia are superacids or at least very strong acids. This has led to m any investigations on the acid strength of sulfated zirconia and metal -doped sulfated zirconia producing varying results, We report the use of cal-ad (which uses combined information from calorimetry and adsorp tion of pyridine onto the solid acid) to determine the acidity of sulf ated zirconia and metal-doped sulfated zirconia. We find that sulfated zirconia has two types of acid sites: 24 mu mol of a strong site, whi ch has a strength of 31.2 kcal/mol, and 52 mu mol of a weaker site of 25.8 kcal/mol, which places the acidity of sulfated zirconia lower tha n that of HZSM-5 (41 kcal/mol) and about the same as that of HY (34 kc al/mol), Doping sulfated zirconia with 0.2 wt % Pt does not change the acidity, but doping with iron and manganese (which increases the cata lytic activity) results in a lower measured acidify, indicating that i ron and manganese have occupied the strongest acid sites.