Synthesis of highly active sulfated zirconia by sulfation with SO3

Highly active sulfated zirconia (SZ) materials were prepared by sulfation of crystalline zirconia with gaseous SO3. This direct method circumvents the use of liquid sulfation agents, as well as a final calcination step. The amount of sulfur species retained by SO3-SZ samples was directly proportional to the fraction of monoclinic phase and the concentration of Brønsted acid sites. However, the catalytic activity in n-butane isomerization at 373 K was proportional to the concentration of labile chemisorbed SO3, most likely in the form of pyrosulfate species showing a characteristic IR band at 1404 cm−1. Tetragonal zirconia favors the formation of these labile sulfur species, playing a key role in light alkane activation.