Effect of the Rare Earth Metals (Tb, Nd, Dy) addition for the modification of nickel catalysts supported on alumina in CO2 Methanation

Abstract

In the current research, a group of rare-earth metals functionalized mesoporous Ni-M/Al2O3 (M = Tb, Dy, Nd) composite oxides were prepared by the one-pot sonochemical pathway and applied in the CO2 methanation procedure. Promoters can partially influence the textural and catalytic characteristics of Ni–Al2O3 catalysts. Physicochemical characteristics of the as-fabricated catalysts were identified utilizing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS), Temperature Programmed Reduction (H2-TPR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analyses. Among the specimens, the catalyst modified by Terbium (Tb) manifested better catalytic performance and CH4 selectivity, particularly at low temperatures (350–400 °C). The influence of reaction temperature (200–500 °C) was scrutinized below space velocity (GHSV) of 25,000 ml/gcath, atmospheric pressure, and stoichiometric ratio of CO2 to H2 (1: 4). The impact of the desired content of nickel and terbium was examined. The 25Ni–5Tb–Al2O3 operates the best function for CO2 methanation, which can attain the highest CO2 conversion of 66.93% at 400 °C at atmospheric pressure. The superior catalytic performance of 25Ni–5Tb–Al2O3 could be assigned to the appropriate fabrication method and the promotion effect of Terbium. The synthesis effect could be assigned to its large surface area, obtaining by the hot spot mechanism. The addition of Terbium promotes the Ni distribution on the supports as well as accelerates the positive reaction due to the oxygen vacancies of Terbium. Besides, these outcomes could be defined with the maximum distribution of active nickel sites on the catalyst and improvement in the catalyst reduction ability at low temperatures.