Steam Reforming of Hydrocarbons on Noble Metal Catalysts (Part 2)

Steam-reforming of n-heptane on rhodium catalysts was investigated under atmospheric pressure and in the temperature range from 550 to 800°C. The degree of dispersion of supported rhodium was determined from hydrogen chemisorption data measured at 25°C by a pulse technique.Rhodium supported on silica was found to sinter considerably on reduction in hydrogen flow, and its activity also decreased. On the other hand, γ-alumina support was found to keep the dispersion of rhodium unchanged on reduction in the temperature range from 550 to 800°C.The activity per weight of a catalyst increased with the concentration of rhodium supported on γ-alumina. The activity was correlated with the amount of hydrogen uptake when more than 0.2% of rhodium was supported.The product composition from reactions at 600°C was compared with the equilibrium composition determined by the following two reactions: i) CH4+H2O=CO+3H2, and ii) CO+H2O=CO2+H2. The composition was found to deviate considerably from the equilibrium at earlier stages of the reaction, but to approach it with increasing conversion of n-heptane. It was suggested that the rate of these equilibrating reactions, especially of the reaction ii), was smaller than that of the initial decomposition of the feed hydrocarbon.