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Activation of Alkanes by Transition Metal Nitrides and Carbides

Published online by Cambridge University Press:  15 February 2011

C. A. Bennett ,
M. K. Neylon ,
H. H. Kwon ,
S. Choi ,
K. E. Curry  and
L. T. Thompson
C. A. Bennett
Affiliation:
Department of Chemical Engineering, University of Michigan, Ann Arbor, M1 48109
M. K. Neylon
Affiliation:
Department of Chemical Engineering, University of Michigan, Ann Arbor, M1 48109
H. H. Kwon
Affiliation:
Present Address: Department of Chemistry, Lehigh University, Bethlehem, PA 18015
S. Choi
Affiliation:
Present Address: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352
K. E. Curry
Affiliation:
Union Carbide Corporation, South Charleston, WV 25303
L. T. Thompson
Affiliation:
Department of Chemical Engineering, University of Michigan, Ann Arbor, M1 48109
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Abstract

Group V and VI nitrides and carbides were synthesized by the temperature programmed reaction of metal oxides with ammonia or an equimolar mixture of methane/hydrogen. The synthesis protocols were developed using thermogravimetric techniques. The resulting nitrides and carbides were primarily mesoporous and possessed surface areas in the range of 11 – 81 m2/g. Their alkane activation rates were comparable to a Pt-Sn/AL20 3 dehydrogenation catalyst and the surface area normalized reaction rates decreased in the following order: Mo2N > W2C > WC > W2N > WC1−x > VCoa0.05N > MO2C > VN = VC > NbMo0.01 N > NbMo0.05 > NbN = NbC. The activities measured at 450°C ranged between 1011 – 1013 molecules/cm2/s for n-butane and 1012 – 1013 molecules/cm2/s for n-hexane. The Group VI nitrides and carbides were far more active than the Group V materials. The Group VI materials catalyzed the hydrogenolysis and dehydrogenation reactions with similar activities whereas the Group V materials were more than 98% selective to dehydrogenation. While the metal atom type had the most significant effect on the catalytic properties, the lattice structure of the material also played a role. In particular, we observed that WC (hex) was almost twice as active as WC1-x (fcc). Nitrides and carbides of the same metal and lattice structure possessed similar catalytic properties, implying that the effect of the non-metal atom type was minimal. The W2N catalyst was found to be highly selective towards n-butane isomerization. The multimetallic nitrides each demonstrated some form of synergy.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 549: Symposium FF – Advanced Catalytic Materials - 1998 , 1998 , 45
Copyright
Copyright © Materials Research Society 1999

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