Steam reforming of n-heptane using a Rh/MgAl: I. Support and kinetics 2O 4 catalyst

Abstract

A Rh/MgAl 2O 4 catalyst was found to be active for the steam reforming of n-heptane in the range 400–500°C. The MgAl 2O 4 support was prepared by calcining of a mixture of α-alumina and magnesia powders at 1420°C. The development of pore structure in MgAl 2O 4 support was examined with SEM, XRD and porosimetry before and during calcination. The pores are found to originate from voids among MgAl 2O 4 particles produced by solid reaction that magnesia was diffusing to alumina particles. Therefore, the pore size is able to control as a result of control of alumina particle size. In order to clarify the role of this support, a kinetic study on the reaction between n-heptane and steam was conducted at 500°C and 1 atm. The initial reaction rate, r 0 (mol g −1h −1), obtained experimentally is best expressed by the following equation: r 0=k( KP 0 C 7H 16 1+KP 0 C 7H 16 )( K′P 0 H 2O 1 +K′P 0 H 2O ) where k (0.071 mol/g h) is the apparent rate constant, p 0 j are the partial pressures of reactants j in the feed gas and K (111 atm −1) and K′ (0.712 atm −1) are the adsorption equilibrium constants for n-heptane and water, respectively. It is confirmed that steam reforming of n-heptane proceeds through the adsorption of n-heptane on rhodium metal and of steam on the support surface. The characteristics of the composition distribution of products shows that carbon monoxide is a primary product in the reaction system and both carbon dioxide and methane are the secondary products.