Carbon deposition behaviors in dry reforming of CH4 at elevated pressures over Ni/MoCeZr/MgAl2O4-MgO catalysts

Abstract

Carbon deposition is a major bottleneck for the development of durable catalysts applicable for the dry reforming of CH4 (DRM). In this work, the carbon deposition behaviors in dry reforming of CH4 at elevated pressures over Ni/MoCeZr/MgAl2O4-MgO catalysts which exhibited a durable stability and excellent coking resistance at atmospheric pressure DRM reaction in our previous report were examined. The differences in the types and sources of carbon deposition under atmospheric pressure and elevated pressure were clarified by XRD, TPO, TEM and Raman spectroscopy as well as the comparative experiments conducted in CH4, CO and CH4/CO atmospheres. It was found that the stability of the catalyst declined rapidly at elevated reaction pressure, and the sources and types of carbon deposition in DRM reaction under atmospheric pressure and pressurized conditions were significantly different at temperatures above 800 °C, but barely differed at temperatures below 700 °C. Under atmospheric pressure, the filamentous carbon (carbon nanotubes, CNTs) was produced by CH4 decomposition reaction and CO disproportionation reaction at 500 and 600 °C, the encapsulated graphitic carbon was generated by CH4 decomposition reaction at 800 and 850 °C, and the filamentous carbon and encapsulated graphitic carbon deriving from CH4 decomposition reaction and CO disproportionation reaction coexisted at 700 °C. Under high pressure, CH4 decomposition reaction and CO disproportionation reaction were jointly involved in the formation of carbon deposition. The filamentous carbon was formed regardless of the reaction temperature, and accompanied by the encapsulated graphitic carbon at 700, 800 and 850 °C. It is concluded that stable DRM catalysts at atmospheric pressure may not be competent for the pressurized DRM because the sources and types of carbon deposition at pressurized conditions are different and the methods of carbon removal and suppression at atmospheric pressure are not fully applicable, thus further study is needed to develop durable catalysts at pressurized DRM.