Synthesis of solid superacids and their activities for reactions of alkanes

Our recent works on synthesis of solid superacids are reviewed. For evaluation of the surface acidity, temperature-programmed desorption of argon is proposed. For elucidation of the preparative conditions determining the catalytic activity, sulfated zirconias were prepared under different preparative conditions. The conditions varied were type of hydrated zirconia gel, drying temperature before sulfation, calcination temperature after sulfation. Although the optimum drying temperature and calcination temperature were different depending on the type of zirconia gel, the attainable activities were independent of the type of zirconia gel. We also modified sulfated zirconia by addition of Pt, Ru, and Fe to see the effects of the modification on the catalytic activity. The addition of Pt to sulfated zirconia resulted in an increase of the catalytic activity. The optimum amount of Pt-added was 7.5 wt.%. The optimum amount of Pt could be reduced to 3 wt.% when the catalyst was prepared by the double calcination method in which calcination procedures were performed both before and after impregnation with platinate solution. The role of Pt in enhancement of the catalytic activity is suggested to be caused by enhancement of the acid strength due to the coordination of PtO to S=O groups. The catalytic activity of sulfated zirconia was also markedly enhanced by mechanically mixing with sulfated iron oxide. The enhancement was suggested to be caused by Fe3+ acting as a reservoir for H- formed during the reaction. (C) 2003 Elsevier Science B.V. All rights reserved.