Influence of calcination procedure on the catalytic property of sulfated zirconia

Calcination parameters, such as atmosphere, duration and catalyst bed depth have a marked influence on the catalytic and spectroscopic properties of sulfated zirconia. Sulfated zirconia calcined in nitrogen or synthetic airflow, in deep bed, exhibited comparable activity in n-butane isomerization at 373 K, which suggests that oxygen is not necessary for formation of active sites. Catalysts calcined in shallow bed are catalytically inactive. Thus, the bed depth is concluded to be crucial for the formation of active sites. The samples calcined in shallow bed possessed lower sulfate content and the S=O stretching vibration was located at lower frequency. Calcination in the presence of water vapor also led to lower catalytic activity, sulfate content, and BET area. Extended calcination reduced gradually the activity and the sulfate content, which underlines the labile property of the active sites. A new interpretation of the function of the calcination step is proposed and compared with models described in the literature.