PT SPECIES IN ZEOLITE-X - CATALYTIC ACTIVITY IN O-18 EXCHANGE OF O-2 WITH ZEOLITIC OXYGEN, O-18(2)-O-16(2) EQUILIBRATION, H-2-D-2 EQUILIBRATION, AND THE CO-NO REACTION

Pt-0, Pt2+ and Pt-ox were prepared by different treatments of platinum tetrammine complexes in alkali faujasites. The observed behavior of P t, especially in TPR experiments, provided evidence that the decomposi tion of ammine complexes in an oxygen stream yields predominantly Pt c ations, which following reduction by hydrogen leads to the formation o f small metallic clusters, whose reoxidation gives Pt-ox in zeolite ca vities. The activity of both latter species was markedly higher than t hat of Pt2+ in the reaction studied, i.e., in the isotopic exchange of gaseous oxygen with the oxygens of the zeolite framework, in the equi libration of hydrogen and oxygen molecules (D-2 + H-2 and O-18(2) + O- 16(2) reaction, respectively), and in the NO reduction by CO. The cata lytic reactions were studied over NaX and KX zeolites. Isotopic exchan ge of O-18(2) With zeolitic oxygen occurred even below 400 degrees C, oxygen activated on Pt centers (3Pt per unit cell) being spilled over to the oxygen of the zeolite skeleton. The equilibration of the gaseou s oxygen molecules began above 300 degrees C, while that of hydrogen m olecules was easily measured at -78 degrees C. (C) 1997 Academic Press .