Synthesis Gas Production via the Biogas Reforming Reaction Over Ni/MgO–Al2O3 and Ni/CaO–Al2O3 Catalysts

Abstract

The energetic utilization of biogas, a gas mixture consisting mainly of CH4 and CO2 via the reforming or the dry reforming of methane reaction is of enormous interest as it converts these two greenhouse gases into synthesis gas (H2/CO mixtures). Nickel based catalysts have been extensively studied for both reactions, as they are highly active, but they suffer from fast deactivation by coking that can even lead to reactor blocking. It is thus desirable to learn more about their coking behavior, and their structural and catalytic stability. In this work, un-promoted and promoted with 6.0 wt% MgO or CaO alumina supported nickel catalysts (8.0 wt% Ni) were studied for the biogas reforming reaction. Supported nickel catalysts were synthesized following the wet impregnation method. The as synthesized Ni/Al2O3, Ni/MgO–Al2O3, Ni/CaO–Al2O3 samples were characterized by various techniques such as XRD, SEM, ICP and BET. Catalytic testing experiments were performed in a fixed-bed reactor at temperatures ranging from 500 to 850 °C and a feed gas mixture with a molar CH4/CO2 ratio of 1.5 simulating an ideal model biogas. It was concluded that the Ni/MgO–Al2O3 and Ni/CaO–Al2O3 catalysts exhibit higher values for XCH4, XCO2, YH2 compared to the ones of the Ni/Al catalyst for temperature ranging between 550 and 750 °C, while the opposite is evidenced for T > 750 °C. It was also evidenced that the presence of magnesium or calcium oxide in the support ensures a quite stable H2/CO molar ratio approaching to unity (ideal for the produced syngas) even for low reaction temperatures.