Abstract
Reduced Pt/K-LTL has been studied with XAFS spectroscopy before and after CO admission at room temperature. The results of the EXAFS data-analysis show that after reduction very small platinum metal particles are present consisting of five to six atoms. CO admission at room temperature leads to complete decomposition of the platinum metal particles and the formation of a platinum carbonyl cluster most probably stabilised by the zeolite walls. Modelling shows that the platinum carbonyl cluster just fits inside the pores of the zeolite-LTL. Analysis of the white line intensities of platinum LII and LIII X-ray absorption edges reveals that after reduction and in the presence of chemisorbed hydrogen the platinum metal particles in Pt/K-LTL have 0.12% more d-band vacancies than bulk platinum metal. This value increases to 0.34% after CO admission implyingπ-backdonation from platinum to CO, a positive charge on Pt in the newly formed cluster or a combination of both. The results of this study have a large impact on the interpretation of existing literature FTIR CO data obtained on Pt/K-LTL. The results question the validity of CO chemisorption carried out to determine the dispersion of very small platinum particles.
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