Thermokinetic and Spectroscopic Mapping of Carbon Monoxide Adsorption on Highly Dispersed Pt/γ-Al2O3

The understanding and quantification of the CO adsorption modes and strength on ultradispersed platinum catalysts supported on gamma-Al2O3 is of prominent importance for analytic and catalytic purposes. We report a multiscale experimental (AEIR, CO-TPD) and theoretical approach to provide vibrational properties, adsorption enthalpies, and desorption behaviors. First principles calculations on Pt-13(CO)(m)/gamma-Al2O3 and Pt(111) surface models (using various exchange-correlation functionals) provide a complementary view to experimental approches. Adsorption enthalpies computed with the RPBE functional appear to be the most compatible with the AEIR results. The occupation of top sites by CO dominates the behavior of supported Pt clusters. CO coverage reaches higher values in comparison to Pt(111) for similar operating conditions, and considerable cluster reconstruction is observed at high coverage. First principles calculations also confirm the IR assignment related to the various adsorption modes on top and bridge sites and demonstrate a particle size effect, lowering the frequency of linear adsorption at top sites with respect to extended Pt(111) surfaces. Finally, first principles-based microkinetic modeling of CO-TPD experiments shows that the adsorption strengths predicted on the small-size cluster by DFT are compatible with the experimental values. We discuss possible reasons for the experimental desorption pattern to be much broader than the computed pattern.

Automated summary

The study investigates the adsorption modes and strength of CO on platinum catalysts supported on gamma-Al2O3, revealing that CO primarily occupies top sites on supported Pt clusters. Compared to Pt(111), CO coverage is higher on supported Pt clusters and cluster reconstruction is observed at high coverage.