Characterization and evaluation of mesoporous high surface area promoted Ni- Al2O3 catalysts in CO2 methanation

Abstract

In this research, mesoporous high surface area Ni-Al2O3 catalysts promoted with different transition metals (Cr, Fe, Mn, Cu, and Co) were synthesized via ultrasound-assisted co-precipitation method and their performance was explored in CO2 methanation process. The promoters can affect the textural and catalytic properties of the Ni-Al2O3 catalysts to some extent. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction with hydrogen (H2-TPR), and N2 adsorption-desorption (BET) were used for the characterization of the prepared samples. From the BET results, it was found that the incorporation of 5 wt% of the promoter into Ni-Al2O3 catalysts caused a decrease in the surface area, NiAl2O4 crystalline size and an increase in the mean pore diameter and total pore volume. Among the samples, the catalyst modified by Mn, exhibited the higher catalytic activity and selectivity towards CH4, especially at low temperatures (200–350 °C). These results could be explained by highest Ni active sites dispersion of this catalyst and enhancement of the catalyst reducibility at the low temperatures. The effect of Mn content was also evaluated and the results revealed that the Ni-Al2O3 sample modified with 3 wt% Mn with the highest BET surface area and the lowest crystalline size possessed the best catalytic performance. To further investigate the influence of ultrasonic irradiation, the optimal catalyst was prepared with a conventional co-precipitation method and its textural and catalytic properties were compared with those obtained for the catalyst prepared with the ultrasonic assisted coprecipitation method. Also, 25Ni-3Mn-Al2O3 catalyst showed a stable performance at 350 °C for 10 h in the CO2 methanation reaction.