THE STATE OF ZIRCONIA SUPPORTED PLATINUM CATALYSTS FOR CO2 CH4 REFORMING/

In Pt/ZrO2 catalysts used for CO2/CH4 reforming to syngas, not all acc essible Pt contributes equally to the activity of the catalyst. The ca talytic activity is determined by the accessibility of Pt on the Pt-Zr O2 perimeter. This is explained in terms of the CO2 activation via car bonate species on the support which must be in the proximity of the Pt particles to react with the methane activated on the metal. The signi ficance of the support is also emphasized by the low activity of Pt bl ack and Pt/SiO2, which were incapable of forming carbonates on the sup port. The perimeter concentration of Pt/ZrO2 can be changed by changin g the Pt concentration in the catalyst or by increasing the calcinatio n temperature which causes sintering of the Pt particles. In contrast to the calcination temperature, the reduction temperature did not infl uence the activity although the hydrogen chemisorption capacity was ma rkedly decreased by increasing the reduction temperature. As sintering was excluded on basis of particle size determination from EXAFS resul ts a SMSI state on Pt/ZrO2 during high temperature reduction is conclu ded to exist. This state does not persist under reaction conditions du e to the presence of adsorbed oxygen from CO2 dissociation. (C) 1997 A cademic Press.