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Carbon formation on nickel and nickel‐copper alloy catalysts
Author(s) -
Alstrup I.,
Tavares M. T.,
Bernardo C. A.,
Sørensen O.,
RostrupNielsen J. R.
Publication year - 1998
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/(sici)1521-4176(199805)49:5<367::aid-maco367>3.0.co;2-m
Subject(s) - nickel , disproportionation , catalysis , chemistry , dehydrogenation , chemisorption , copper , hydrogen , carbon fibers , alloy , inorganic chemistry , materials science , organic chemistry , composite material , composite number
Equilibrium, kinetic and morphological studies of carbon forma‐ tion in CH 4 + H 2 , CO, and CO + H 2 gases on silica supported nickel and nickel‐copper catalysts are reviewed. The equilibrium deviates in all cases from graphite equilibrium and more so in CO + CO 2 than in CH 4 + H 2 . A kinetic model based on information from surface science results with chemisorption of CH 4 and possibly also the first dehydrogenation step as rate controlling describes carbon formation on nickel catalyst in CH 4 + H 2 well. The kinetics of carbon formation in CO and CO + H 2 gases are in agreement with CO disproportionation as rate determining step. The presence of hydrogen influences strongly the chemisorption of CO. Carbon filaments are formed when hydrogen is present in the gas while encapsulating carbon dominates in pure CO. Small amounts of Cu alloying promotes while larger amounts (Cu : Ni ≥ 0.1) inhibits carbon formation and changes the morphology of the filaments (“octopus” carbon formation). Adsorption induced nickel segregation changes the kinetics of the alloy catalysts at high carbon activities. Modifications suggested in some very recent papers on the basis of new results are also briefly discussed.