INTERACTION OF CO WITH PLATINUM SPECIES IN ZEOLITES - EVIDENCE FOR PLATINUM CARBONYLS IN PARTIALLY REDUCED ZEOLITE PTNAX

The decomposition of Pt(NH3)42+ in zeolite NaX both in vacuo and in flowing oxygen (T(max)=630 K) yields a variety of ionic species, which appear in IR spectra as PtO-, Pt(delta+)-, Pt2+-CO and [Pt(CO)2]+ complexes formed after the adsorption of CO at 300 K. Subsequent reduction with hydrogen results in characteristic particle size distributions, which are reflected in distinct vibration frequencies of adsorbed CO, i.e., ca. 2010 cm-1 for d almost-equal-to 1.2 nm (supercage size) and ca. 2070 cm-1 for d almost-equal-to 4 nm. A hydrated precalcined sample treated with CO shows unusual low platinum carbonyl bands at 1930-1950 and 1720-1740 cm-1, assigned to [Pt3 (CO)6]2- clusters, supported on Pt2+/PtO. The appearance of these Chini complexes is most probably connected with the occurrence of the low temperature water gas shift reaction.