Kohlenstoffbildung auf Nickel und Nickel-Kupfer-Legierungskatalysatoren

摘要

Equilibrium, kinetic and morphological studies of carbon formationin CH4+H2, CO, and CO+H2 gases on silica supported nickeland nickel-copper catalysts are reviewed. The equilibrium deviatesin all cases from graphite equilibrium and more so in CO+CO2than in CH4+H2. A kinetic model based on information from surfacescience results with chemisorption of CH4 and possibly alsothe first dehydrogenation step as rate controlling describes carbonformation on nickel catalyst in CH4+H2 well. The kinetics ofcarbon formation in CO and CO+H2 gases are in agreementwith CO disproportionation as rate determining step. The presenceof hydrogen influences strongly the chemisorption of CO. Carbonfilaments are formed when hydrogen is present in the gas whileencapsulating carbon dominates in pure CO. Small amounts ofCu alloying promotes while larger amounts (Cu : Ni ≥ 0.1) inhibitscarbon formation and changes the morphology of the filaments("octopus" carbon formation). Adsorption induced nickel segregationchanges the kinetics of the alloy catalysts at high carbon activities.Modifications suggested in some very recent papers on thebasis of new results are also briefly discussed.