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Medium Pressure Reactivity of Acetylene on Pd-Cu Alloy Nanoparticles Supported on Thin Silica Films.

The ability to correlate industrial high-pressure catalysis with high vacuum research has been of great interest for decades. We employed a double chamber vacuum system to study the self-hydrogenation of acetylene to ethylene and its trimerization to benzene at medium pressures, in order to compare the reactivity in this pressure range to the known model catalytic acetylene reactivity in ultra-high vacuum (UHV). We measured the reactivity of Pd-Cu bimetallic alloy nanoparticles (ANPs) with different elemental compositions deposited on top of native SiO2/Si(100) and on bilayer SiO2/Ru(0001) surfaces, where the latter was shown to contribute to ANP stability. Following exposure to 0.5 mbar acetylene, ANPs on both surfaces catalyze the formation of ethylene and benzene, with the former as the more probable product. The ANPs on bilayer SiO2/Ru(0001) were highly selective towards ethylene formation, with an ethylene/benzene ratio of up to three orders of magnitude, whereas on the native SiO2/Si(100) there was a significantly lower selectivity (about 5) at the same temperature range and catalyst elemental composition. Interestingly, these selectivity values are similar to those found under UHV conditions. In addition, ANPs grown on native SiO2/Si(100), unlike SiO2/Ru(0001), revealed an optimal temperature for ethylene and benzene formation due to the limited stability of the particles.