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

Abstract

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 to compare the reactivity in this pressure range to the known model catalytic acetylene reactivity in ultrahigh 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 of acetylene, ANPs on both surfaces catalyze the formation of ethylene and benzene, with ethylene as the more probable product. The ANPs on bilayer SiO2/Ru­(0001) were highly selective toward ethylene formation, with an ethylene/benzene ratio of more than 2 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.

100% selective cyclotrimerization of acetylene to benzene on Ag(111)

“…In order to probe the robustness of Ag, we examined if the acetylene trimerization reaction poisoned the Ag(111) surface since catalyst deactivation was common in previously reported trimerization systems like Ni/SiO 2 , SiO 2 /Si(100) and uorine on alumina. 17,38,59 Specically, we performed ve consecutive cycles of TPD experiments without cleaning the Ag(111) in between as shown in Fig. 3.…”

“…Previous work has shown that it is possible to produce benzene from acetylene on a variety of metal surfaces under both ultra-high vacuum (UHV) and reaction conditions. 9–35 For example, Tysoe et al showed acetylene forms benzene and ethylene on a Pd(111) surface and that increasing the surface acetylene coverage increased the yield of benzene. 36 In addition, the authors observed a threshold acetylene coverage of 0.3 ML, below which benzene formation does not occur.…”

Two-Dimensional Ultrathin Silica Films

“…Sorek et al. have recently studied the support effects on Pd–Cu alloy NPs for selective acetylene hydrogenation by using a BL silica/Ru(0001) substrate and native silicon dioxide substrate. , The Pd–Cu alloy NPs (5 ± 2 nm) with different Pd/Cu composition ratios were deposited on both substrates via the water buffer layer-assisted growth method . It was found that the Pd–Cu alloy NPs on BL silica/Ru(0001) have much higher thermal stability and sintering resistance than the ones on SiO 2 /Si­(100) even under 0.2 mbar acetylene at 600 K, which presumably benefited from the charge transfer through the thin silica bilayer to the ruthenium substrate. , …”

“…(d) Schematic diagram of the acetylene hydrogenations on Pd–Cu NPs on SiO 2 /Si­(100) and silica/Ru(0001). Reproduced with permission from refs and . Copyright 2019 and 2020 American Chemical Society.…”

“…In addition to the UHV studies, the acetylene hydrogenation was also conducted at near ambient pressure conditions (0.5 mbar acetylene) in order to correlate the reactivity/selectivity in both pressure regimes and therefore to better understand the pressure-gap issue in the model catalytic reactions (Figure c,d) . Interestingly, the results are similar to those found under UHV conditions.…”