Characterization and Activity of K, CeO2, and Mn Promoted Ni/Al2O3Catalysts for Carbon Dioxide Reforming of Methane

Abstract

Reforming of methane with carbon dioxide into syngas over Ni/γ-Al2O3 catalysts modified by potassium, MnO, and CeO2 was studied. The catalysts were prepared by impregnation technique and were characterized by BET surface area, pore volume, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, temperature-programmed studies, and pulse chemisorption. The performance of these catalysts was evaluated by conducting the reforming reaction in a fixed-bed reactor. Results of the investigation suggested that stable Ni/Al2O3 catalysts for the carbon dioxide reforming of methane can be prepared by the addition of both potassium and CeO2 (or MnO) as promoters. The results of the various characterization techniques were used to relate the observed catalytic activity and stability to the catalyst property. The stability and lower amounts of coking on promoted catalysts were attributed to partial coverage of the surface of nickel by patches of promoters, strong metal−support interaction (TPR, H2 pulse chemisorption, H2-TPD), and their increased CO2 adsorption (CO2-TPD). For the stable 13.5Ni−2K/10CeO2−Al2O3 catalyst, the effect of reaction temperature and contact time on conversion and product yield was studied. It was found that the conversion and product yield increased with increasing reaction temperature and W/FCH4,0 and reached equilibrium at W/FCH4,0 = 1.7 kg-cat·h/kgmethane. The mechanism of the CH4/CO2 reaction has been proposed, based on which a kinetic model was developed to estimate the kinetic parameters. The estimated kinetic parameters predicted the product yields satisfactorily. CH4 activation to form CHx and CHxO decomposition are suggested to be the rate-determining steps of the CH4/CO2 reaction over the 13.5Ni−2K/10CeO2−Al2O3 catalyst. The activation energy for methane adsorption and dissociation (Ek1L), CHxO decomposition (Ek7L), and reverse water gas shift reaction (Ekr) were estimated to be 113.8 ± 5.5, 119.3 ± 4.7, and 155.3 ± 7.0 kJ/mol, respectively.