Kinetic Isotopic Effects in Oxidative Dehydrogenation of Propane on Vanadium Oxide Catalysts

Abstract Kinetic isotopic effects (KIEs) for oxidative dehydrogenation of propane were measured on 10 wt% V 2 O 5 /ZrO 2 . Normal KIEs were obtained using CH 3 CH 2 CH 3 and CD 3 CD 2 CD 3 as reactants for primary dehydrogenation (2.8) and combustion (1.9) of propane and for secondary combustion of propene (2.6), suggesting that in all cases C–H bond dissociation is a kinetically relevant step. CH 3 CH 2 CH 3 and CH 3 CD 2 CH 3 reactants led to normal KIEs for dehydrogenation (2.7) and combustion (1.8) of propane, but to a very small KIE (1.1) for propene combustion. These results show that the methylene C–H bond is activated in the rate-determining steps for propane dehydrogenation and combustion reactions. The rate-determining step in secondary propene combustion involves the allylic C–H bond. In each reaction, the weakest C–H bond in the reactant is cleaved in the initial C–H bond activation step. The measured propane oxidative dehydrogenation KIEs are in agreement with theoretical estimates using a sequence of elementary steps, reaction rate expression, and transition state theory. The much smaller KIE for propane oxidative dehydrogenation (2.8) than the maximum KIE (6) expected for propane thermal dehydrogenation indicates the participation of lattice oxygen. The different KIE values for propane primary dehydrogenation and combustion suggest that these two reactions involve different lattice oxygen sites.

[1]  G. Centi,et al.  Catalytic behavior of V-containing zeolites in the transformation of propane in the presence of oxygen , 1996 .

[2]  F. Cavani,et al.  Key Aspects of Catalyst Design for the Selective Oxidation of Paraffins , 1996 .

[3]  G. Keulks,et al.  The catalytic oxidation of propylene: VIII. An investigation of the kinetics over Bi2Mo3O12, Bi2MoO6, and Bi3FeMo2O12 , 1980 .

[4]  E. A. Mamedov,et al.  Oxidative dehydrogenation of lower alkanes on vanadium oxide-based catalysts. The present state of the art and outlooks , 1995 .

[5]  H. Kung.  Oxidative Dehydrogenation of Light (C2 to C4) Alkanes , 1994 .

[6]  Alexis T. Bell,et al.  Structure and Properties of Vanadium Oxide-Zirconia Catalysts for Propane Oxidative Dehydrogenation , 1998 .

[7]  Fundamental study of the oxidation of butane over vanadyl pyrophosphate , 1985 .

[8]  B. Andersson,et al.  Oxidative dehydrogenation of propane over VMgO: kinetic investigation by nonlinear regression analysis , 1996 .

[9]  Alexis T. Bell,et al.  Structure and Catalytic Properties of Supported Vanadium Oxides: Support Effects on Oxidative Dehydrogenation Reactions , 1999 .

[10]  T. Blasco,et al.  Oxidative dyhydrogenation of short chain alkanes on supported vanadium oxide catalysts , 1997 .

[11]  Alexis T. Bell,et al.  Isotopic Tracer and Kinetic Studies of Oxidative Dehydrogenation Pathways on Vanadium Oxide Catalysts , 1999 .

[12]  C. R. Adams,et al.  Mechanism studies of the catalytic oxidation of propylene , 1964 .

[13]  E. Iglesia,et al.  Kinetic coupling and hydrogen surface fugacities in heterogeneous catalysis: I. Alkane reactions on Te/NaX, H-ZSM5, and Ga/H-ZSM5 , 1992 .

[14]  C. R. Adams,et al.  Investigation of the mechanism of catalytic oxidation of propylene to acrolein and acrylonitrile , 1963 .

[15]  S. Andersson.  Kinetic study of the oxidative dehydrogenation of propane over vanadia supported on amorphous AlPO4 , 1994 .

[16]  W. M. Haynes.  CRC Handbook of Chemistry and Physics , 1990 .

[17]  尾崎 萃.  Isotopic studies of heterogeneous catalysis , 1977 .

[18]  E. Iglesia,et al.  Matrix method for correction of mass spectra in deuterium-exchange applications , 1989 .

[19]  R. C. Weast.  CRC Handbook of Chemistry and Physics , 1973 .