Carbon deposition and methane steam reforming on silica-supported NiCu catalysts

Abstract

Methane decomposition and steam reforming were studied over silica-supported copper-nickel alloy catalysts. Hydrogen chemisorption and X-ray photoelectron spectroscopy (XPS) measurements showed copper surface segregation after reduction at 773 K. The carbon formation/gasification equilibrium was the same for the alloy catalysts as for monometallic nickel catalysts except at the highest copper concentration (80 at.% Cu). The rate of carbon formation, for more than 10 at.% Cu, was more strongly decreased by alloying with Cu than the rate of steam reforming, which followed approximately the decrease in hydrogen capacity. On samples with less than 80 at.% Cu the carbon was deposited mainly as filaments with a metal particle at the end and with approximately the same diameter as the metal particle. At 80 at.% Cu thinner filaments of a new type were observed. A kinetic expression describing the rate of methane decomposition at low hydrogen pressure over the catalysts with 10 at.% Cu or lower indicates that a surface reaction step is rate controlling.