Hydrogenation of CO 2 over nickel catalysts on rice husk ash-alumina prepared by incipient wetness impregnation

Abstract

Nickel catalysts supported on rice husk ash-alumina (Ni/RHA-Al 2O 3) were prepared by the incipient wetness impregnation method. Characterizations were investigated by TPR, XPS, XRD, SEM, and BET techniques. The catalytic activities of nickel catalysts were tested by CO 2 hydrogenation with H 2/CO 2 ratio of 4:1 for temperatures between 400 and 800 °C. The XPS analysis of Ni/RHA-Al 2O 3 demonstrated the presence of spinel. The TPR analysis indicated that the interaction between nickel and support was strong and difficult to reduce with more than one nickel oxide compound, such as bulk NiO and two NiAl 2O 4-like species. The results of N 2-adsorption by BET indicated that the maximum surface area was found at 15 wt.% nickel loading with mesopores. The XRD analysis of samples suggested that the crystallite sizes of supported NiO increased with the increase in nickel loading. The CO 2 conversion and CH 4 yield for CO 2 hydrogenation were found to depend on the nickel loading. The reaction temperature of 500 °C might be the optimum temperature for CO 2 hydrogenation to give the maximum yield and selectivity of CH 4. Furthermore, the hydrogenation tests showed that the performance of Ni/RHA-Al 2O 3 is better than that of Ni/SiO 2-Al 2O 3.