Re-promoted Ni-Mn bifunctional catalysts prepared by microwave heating for partial methanation coupling with water gas shift under low H2/CO conditions

Abstract

Re-promoted Ni-Mn bifunctional catalysts were prepared by microwave and conventional heating separately, and tested for partial methanation coupling with water gas shift (WGS) of simulated biomass gas in a fixed bed reactor. A series of characterization techniques including N2 isothermal adsorption, XRD, H2-TPR, H2-TPD, SEM, TEM and XPS were employed to examine the physico-chemical properties of the catalysts. With the reaction condition of 350 °C, H2/CO = 0.8 and H2O/CO = 1, 82.6% CO conversion, 70.0% CH4 selectivity and 82.8% CO2 growth rate were obtained on the Ni-Mn/Re-Al2O3 (MV) catalyst, which indicated its excellent synergetic effect on partial methanation coupling with WGS. According to the characterization results, it was found that microwave heating was beneficial to increase the dispersion of Ni species in comparison with conventional heating and the addition of Re promoter elevated the catalytic performance from both structural and electronic aspects, which was proven by the lowered reduction temperature of β-type NiO and the intensified electron cloud density of active Ni atoms, respectively. In addition, the sequence of Re impregnation also had impact on the catalytic performance. Step impregnation prepared Ni-Mn/Re-Al2O3 (MV) exhibited larger turnover frequency (TOF) than co-impregnation prepared Ni-Mn-Re/Al2O3 (MV) in the H2/CO range of 0.6–1.0, owing to the larger electron cloud density and better anti-coking ability of the former catalyst. The 110-h lifetime test further demonstrated the potential of stable Ni-Mn/Re-Al2O3 (MV) catalyst in industrial application.