Characterization of Pt/SiO2 Model Catalysts at UHV and Near Atmospheric Pressures

Abstract

Pt/SiO 2 model catalyst samples, prepared under UHV conditions in a contiguous high pressure reactor cell surface analysis chamber, have been characterized via CO oxidation reaction kinetics under elevated pressure conditions (approaching 1 atm). Reaction kinetics are studied as a function of Pt coverage (h Pt = 1-10 mL), along with measurements on a Pt(110) single crystal for direct comparison. CO desorption measurements and STM measurements on Pt/SiO 2 films at T = 300 K have been obtained at various h Pt . Kinetic results show agreement between observations on single crystal and catalyst samples, and general agreement and correlation is obtained for site calculations across the various methods. Results demonstrate the utility of well characterized model catalyst samples in obtaining qualitative and quantitative reactivity data at elevated pressures.

Catalysis with Supported Size-selected Pt Clusters

“…Similar sized catalysts were investigated under near atmospheric pressures (in a reaction cell) and supported by UHV characterization. TOF and activation energies were extracted and the results were extrapolated to single crystal data, suggesting no size effects in 2 − 3 nm particles [92,19]. Catalysts synthesized by colloidal methods and tested in flow reactors, at elevated temperatures, support these findings [46,94] and the assumption of structure insensitivity.…”

“…This means, its turnover rate is essentially independent of metal dispersion, even though the structure and coordinative unsaturation of exposed metal atoms are known to differ among clusters of different size [46,7]. However, several examples for insensitivity are known [92] (and herein) for very small sizes and is correlated to the higher binding strength of CO on step sites present on these small particles, which contain a higher fraction of CO bound to step sites.…”

“…These model catalyst surfaces have significantly contributed to a better understanding [43,183,184,9,185,11,186,5]. Beside these supported particles, prepared in UHV usually by means of deposition by evaporation processes [92], other means of preparing model catalyst surfaces are know, e.g. using lithography [187,175,188,189].…”

“…Therefore, by using these more sophisticated materials, two mapressure gap jor strategies towards bridging the pressure gap have been pursued. On one hand there is the popular approach of adapting conventional surface science techniques to work at elevated/high pressures for inadapting in − situ techniques to higher pressures situ measurements [90,92]. This has been successfully achieved for a wide variety of instruments, i.e.…”

“…In either case, good knowledge of the stability of the catalyst is a prerequisite for the study of its reactivity, however, often catalyst reactivity is probed [19,92,91], with addressing little attention to its stability.…”