The role of carbonaceous deposits and support impurities in the selective hydrogenation of ethyne

Selective acetylene detection through surface modification of metal–insulator–semiconductor sensors with alkanethiolate monolayers

“…Interestingly, the activity and selectivity for acetylene hydrogenation on supported Pd catalysts has been found to be partly determined by the coverage of a carbonaceous layer that accumulates under operating conditions on the surface. It has been suggested that this carbonaceous layer functions by modifying the active site environment at the Pd surface to (in some cases) favor reaction of acetylene [17,18]. Although this study is focused on hydrocarbon functionalities bound to the surface through a sulfur atom, a similar phenomenon-the modification of active sites by a layer that in other contexts could be considered a catalyst poison-may be responsible for the observed sensing behavior.…”

Surface-level mechanistic studies of adsorbate–adsorbate interactions in heterogeneous catalysis by metals

“…Ponec and colleagues noted that the formation of carbonaceous deposits on a Pd/SiO 2 catalyst simultaneously decreased activity while improving ethylene selectivity. However, when this experiment was performed using a catalyst with a SiO 2 support from a different source ethylene selectivity decreased [54]. Similarly, Monte Carlo modeling of acetylene hydrogenation catalysts in industrial conditions suggests acetylene hydrogenation activity may be either promoted or poisoned by varying the concentration of polymeric carbonaceous deposits [56].…”

“…Similar to any catalyst performing hydrocarbon chemistry, acetylene hydrogenation catalysts operate with a large number of carbonaceous deposits on the metal surface [26]. Although the stronger binding of acetylene over ethylene is largely responsible for the observed selectivity in ethylene-rich feed streams [39], it has been suggested that acetylene binds too tightly on the clean metal surface to be reactive, and that a carbonaceous overlayer is necessary for good activity [54]. This assertion is supported by DFT studies which show the presence of carbonaceous deposits can destabilize acetylene adsorption by up to 150 kJ/mol [55].…”

Propyne hydrogenation over alumina-supported palladium and platinum catalysts

“…Al-Ammar and Webb subsequently developed a three-site model that identified two active sites for ethyne adorption [11,12]. Ponec and co-workers suggested a different perspective, notably that the carbonaceous deposits were inactive and acted as a selectivity modifier, by preferentially diminishing metal sites active for the full hydrogenation of ethyne with respect to discrete metal ensembles active for partial hydrogenation of the ethyne [13,14]. Sárkány et al examined a range of catalysts concentrating on ageing phenomena and linked the role of a surface polymer in the promotion of spillover processes that affected ethene selectivity [15].…”