BIFUNCTIONAL REACTIONS OF ALKANES ON TUNGSTEN CARBIDES MODIFIED BY CHEMISORBED OXYGEN

被引:146
作者
IGLESIA, E [1 ]
BAUMGARTNER, JE [1 ]
RIBEIRO, FH [1 ]
BOUDART, M [1 ]
机构
[1] STANFORD UNIV,DEPT CHEM ENGN,STANFORD,CA 94305
关键词
D O I
10.1016/0021-9517(91)90284-B
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Tungsten carbides modified by chemisorbed oxygen catalyze n-heptane isomerization with high selectivity. Kinetic, isotopic tracer, and deuterium-exchange measurements show that the reaction proceeds via sequential n-heptane dehydrogenation and heptene isomerization steps. At low temperatures, isomerization rates are limited by heptene rearrangements but dehydrogenation steps become increasingly rate-limiting as temperature increases. The isomer distribution in n-heptane and 3,3-dimethylpentane reaction products and the 13C distribution in isoheptanes formed from n-heptane-1-13C show that isomerization occurs predominantly by methyl migration steps typical of carbenium-ion rearrangements on acid sites. WOx species on carbide surfaces appear to introduce acid sites similar to those present in supported tungsten oxides. n-Heptane dehydrocyclization and hydrogenolysis reactions also require heptene intermediates. Dehydrocyclization occurs predominantly by (1, 6) ring closure while hydrogenolysis leads to random cleavage of carbon-carbon bonds in n-heptane. © 1991.
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页码:523 / 544
页数:22
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