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Cited by 73 publications
(4 citation statements)
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“…In addition to finding that multiple-exchange was more likely at high temperatures (consistent with Kemball’s work above), the authors also found that lower D 2 pressures and larger crystallites promoted multiple exchange; this was ascribed to having more open sites to activate additional C–H bonds . Allylic and pi-bonded intermediates have been proposed as intermediates, similar to studies above with the chiral alkanes, and the mechanism by which multiple exchange occurs has been studied in depth. More detailed studies on the exchange between cyclopentane and D 2 on Pd/alumina exhibited five product distributions, which the authors suggested indicate five distinguishable processes. , They assigned this distribution to different sets of surface sites; these results show that multideuteration, and thus the propensity to have a second C–H activation occur, is dependent not only on temperature, metal, and crystallite size but also on the facet and crystal termination (e.g., terrace, face, edge, step, corner) at which exchange occurs. This is not surprising because many catalysis studies show dependency of crystallite size and facet …”
Section: H/d Exchange On Metal Catalystssupporting
confidence: 66%
“…In addition to finding that multiple-exchange was more likely at high temperatures (consistent with Kemball’s work above), the authors also found that lower D 2 pressures and larger crystallites promoted multiple exchange; this was ascribed to having more open sites to activate additional C–H bonds . Allylic and pi-bonded intermediates have been proposed as intermediates, similar to studies above with the chiral alkanes, and the mechanism by which multiple exchange occurs has been studied in depth. More detailed studies on the exchange between cyclopentane and D 2 on Pd/alumina exhibited five product distributions, which the authors suggested indicate five distinguishable processes. , They assigned this distribution to different sets of surface sites; these results show that multideuteration, and thus the propensity to have a second C–H activation occur, is dependent not only on temperature, metal, and crystallite size but also on the facet and crystal termination (e.g., terrace, face, edge, step, corner) at which exchange occurs. This is not surprising because many catalysis studies show dependency of crystallite size and facet …”
Section: H/d Exchange On Metal Catalystssupporting
confidence: 66%
“…The catalytic conversion of olefins under reducing conditions is one of the simplest and most studied catalyzed reactions. When promoted by solid transition-metal catalysts, the ensuing hydrogenation, dehydrogenation, H−D exchange, and double bond isomerization reactions are accounted for by the so-called Horiuti−Polanyi mechanism (Scheme ). , This deceivingly simple scheme, which is based on a series of stepwise hydrogenation−dehydrogenation steps, can be used to explain many experimental observations, but also hides a number of complications associated with the regio- and stereospecificity of the β-hydride elimination step from the intermediate surface alkyl species. For instance, it has recently been pointed out by us that the exchange of the hydrogen atoms around a CC double bond by deuterium is accompanied by a cis−trans interconversion .…”
Section: Introductionmentioning
confidence: 99%
“…Some trends have been identified by past surface-science studies in connection with this issue, namely: (1) β-hydride elimination takes place preferentially from the more substituted β-carbons; (2) the desorption temperature of the resulting alkenes shifts to lower temperature with either decreasing chain length or increasing number of substitutions; and (3) the alkene yield is higher (relative to alkane production by the competing reductive elimination reaction) for branched alkyls compared to linear alkyls. Finally, there is the potential of a competing mechanism being operative in olefin conversion involving an initial dehydrogenation at an allylic position. , Indeed, some allyl intermediates are particularly stable, especially those based on cyclic species, and are therefore likely to be involved in either hydrogenation or selective oxidation catalytic processes.
1 Horiuti−Polanyi Mechanism
…”
Section: Introductionmentioning
confidence: 99%
“…Other workers have proposed concerted " hydrogen switch " mechanisms in which dissociative adsorption of olefin and hydrogen atom addition occurred simultaneously.~9 9 In 1962, it was reported that the dissociation of adsorbed olefin to give adsorbed n-allylic intermediates occurred readily as one of a series of consecutive dissociative steps in the exchange of substituted cyclopentanes with deuterium catalyzed by palladium films. 10 It was suggested that analogous processes might occur in other reactions, and butene isomerization was quoted as an example. Mechanism (2) shows how isomerization may proceed by an " abstraction-addition " mechanism, the abstraction step being the dissociative adsorption of olefin to give adsorbed hydrogen and an adsorbed .n-allylic species.19 11…”
mentioning
confidence: 99%