Reduction of platinum dispersed on dealuminated beta zeolite

The Si/Al ratio of a commercial HB-25 beta zeolite sample was increased by treatment of dealumination and silicon-insertion. Platinum ions were subsequently dispersed onto the starting and the treated samples through impregnation of aqueous Pt(NH,),(NO,),. Chemical environments of dispersed platinum were characterized by temperature-programmed reduction (TPR) technique. The obtained TPR traces varied with extents of dealumination. Nevertheless, three major signals, in reduction temperature regions around - 50, 80 and 480 degrees C were distinguished from these TPR traces and characterized as reductions of platinum oxides dispersed on the external surface of zeolite (pt(e)O), platinum oxides occluded in channels ((PtOx)-O-o), and Pt-(-O-Si=)(y) complexes coordinated to external surface or defects of zeolite, respectively. From the variation in the contribution of the 480 degrees C peak in TPR traces, a formation of Si-OH silanol function groups on the zeolite surface during the dealumination treatment and a elimination of these groups during the silicon-insertion treatment are indicated. (C) 1998 Elsevier Science B.V. All rights reserved.