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Reaction of cyclopropane, methylcyclopropane and propylene with hydrogen on the (111) and (110)-(1x2) surfaces of iridium

Engstrom, J. R. and Goodman, D. W. and Weinberg, W. H. (1990) Reaction of cyclopropane, methylcyclopropane and propylene with hydrogen on the (111) and (110)-(1x2) surfaces of iridium. Journal of Physical Chemistry, 94 (1). pp. 396-409. ISSN 0022-3654. doi:10.1021/j100364a067.

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The hydrogenation, isomerization, and hydrogenolysis of cyclopropane, methylcyclopropane, and propylene have been investigated on the (111) and (110)-(1X2) single-crystalline surfaces of iridiium at reactant partial pressures from 0.4 to 10 Torr of hydrocarbon (P_(HC)) and between 20 and 500 Torr of hydrogen (P_H2) and at surface temperatures from 375 to 700 K. Both the kinetics of the reaction (activation energies and preexponential factors) and the dependences of the rates of reaction on the reactant partial pressures (apparent reaction "orders") were examined in detail. Postreaction surface analysis revealed the presence of a carbonaceous residue, the coverage of which was found to vary with the reaction conditions. The reaction of cyclopropane and hydrogen resulted in both hydrogenation to propane and the hydrogenolysis to methane and ethane, with the hydrogenation channel dominating for temperatures below 500 K. The Ir(110)-(1X2) surface was found to be more active than the (111) surface for both the hydrogenation and the hydrogenolysis of cyclopropane. In both cases, the specific activity (per metal surface atom basis) on Ir(110)-(1X2) was greater by a factor between approximately 2 and 10. The hydrogenation of methylcyclopropane on both the Ir(111) and Ir(110)-(1X2) surfaces was found to be dominated by the production of n-butane. This result was interpreted qualitatively by invoking parallel reaction mechanisms for the production of n-butane and isobutane, with then-butane channel exhibiting a higher apparent activation energy, thus, dominating at the higher temperatures. The hydrogenolysis of methylcyclopropane was found to be similar to that of cyclopropane on both surfaces. However, a selectivity difference was observed between the two surfaces for hydrogenolysis, the product distributions for the major reaction channels were CH_4 + C_3H_8 on Ir(111) and CH_4 + C_2H_6 + C_3H_8 on Ir(110)-(1X2). The absence of ethane in the major hydrogenolysis channel on the Ir(111) surface can be explained on a stereochemical basis if formation of the appropriate intermediate proceeds through an "edge complex", the formation of which is forbidden sterically on the Ir(111) surface. The Ir(110)-(1X2) surface was found to possess a greater specific activity compared to the Ir(111) surface for the hydrogenation of propylene.

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Alternate Title:Reaction of cyclopropane, methylcyclopropane and propylene with hydrogen on the (111) and (110)-(1 times 2) surfaces of iridium
Additional Information:© 1990 American Chemical Society. Received: March 13, 1989; In Final Form: July 11, 1989. This work was performed at Sandia National Laboratories and supported by the U.S. Department of Energy under Contract DE-AC04-76DP00789. We acknowledge the partial support of the Office of Basic Energy Sciences, Division of Chemical Science (D.W.G.), and National Science Foundation Grant No. CHE-8617826 (W.H.W.). Registry No. Ir, 7439-88-5; cyclopropane, 75-19-4; methylcyclopropane, 594-11-6; propylene, 115-07-1.
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Department of Energy (DOE)DE-AC04-76DP00789
Issue or Number:1
Record Number:CaltechAUTHORS:20171106-160039436
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Official Citation:Reaction of cyclopropane, methylcyclopropane and propylene with hydrogen on the (111) and (110)-(1 .times. 2) surfaces of iridium J. R. Engstrom, D. W. Goodman, and W. H. Weinberg The Journal of Physical Chemistry 1990 94 (1), 396-409 DOI: 10.1021/j100364a067
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83007
Deposited By: Tony Diaz
Deposited On:07 Nov 2017 15:58
Last Modified:15 Nov 2021 19:54

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