High-pressure cell to study the catalytic behavior of bulk samples and surface deposited mass-selected nanoclusters at atmospheric conditions

Abstract

A high-pressure reaction cell was developed to study the catalytic activity of supported subnanometer catalysts under atmospheric conditions. With the help of a capillary, the gas composition in the vicinity of the catalyst surface can be analyzed. First, the mean residence time of the gaseous components in the capillary was determined. The dependence of the partial pressures of the reactants on the vertical distance between the capillary and the catalyst was then characterized with the aid of a polycrystalline Pt sample. A Pt(111) surface was then used to validate the experimental setup concerning the CO oxidation under oxygen-rich conditions at a total pressure of 1000 mbar. The partial orders of reaction for CO and O2 agree with values from the literature. The change in the reaction mechanism, which was also described in the literature, could be observed from the temperature-dependent investigation of the CO oxidation. The obtained turn-over frequency and the activation energy at about 660 K agree well with the values obtained in the high-pressure CO oxidation studied in a batch reactor. The efficiency of the experimental setup is demonstrated by examining supported Pt10 clusters since the site density was reduced by a factor of 15 compared to the bulk samples. Taking the Pt site density into account, the sample with the decamers is approximately 5–6 times more active than the Pt(111) surface at a temperature of 673 K. Accordingly, the activation energy for the CO oxidation of 106 kJ mol−1 significantly decreased compared to the value of 132 kJ mol−1 for Pt(111). This finally proves that the high-pressure cell enables the systematic investigation of the size-dependent catalytic behavior of nanoclusters with low degrees of coverage in the future.