A XANES-TPR STUDY OF PTRE/AL2O3 CATALYSTS

We describe the measurement of X-ray absorption edges to determine the binding energy (chemical shift relative to metallic Pt and Re) to follow the temperature-programmed reduction (TPR) of PtRe/Al2O3 catalysts. Comparison of the derivative of the change in chemical shift with H-2 uptake (both as a function of temperature of reduction) on the reference catalysts, Pt/Al2O3 and Re/Al2O3, demonstrate that the two methods of following the reduction are quite similar. X-ray absorption chemical shifts allow the individual TPR of each metal component to be followed independently. When the was applied to a commercial 0.3 wt % Pt-0.3 wt % Re/Al2O3 catalyst calcined at 180, 250, 400, and 580-degrees-C, the lowest calcination temperature resulted in the coreduction of both Pt and Re. At progressively higher calcination temperatures, the reduction temperature of Re was increased, and after a 580-degrees-C calcination, a part of the Re is coreduced with the Pt and a part is reduced at a substantially higher temperature, probably producing a separate Re phase. While the chemical shift of Pt in Pt/Al2O3 is indistinguishable from bulk Pt, all bimetallic catalysts have a positive chemical shift, even though the reduction of Pt is likely to be complete.