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Nickel catalysts supported on rice husk ash-alumina (Ni/RHA-Al 2 O 3 ) were prepared by an incipient wetness impregnation method. Characterization included TGA, DSC, TPR, XRD, and BET. Results show that the decomposition of the nickel compound to nickel oxide was complete above 500• C. The TPR analysis revealed a strong interaction between nickel and support, and a decrease in reducibility of NiO with increasing calcination temperature. The XRD analysis of Ni/RHA-Al 2 O 3 catalyst precursors demonstrated the presence of spinel. It also showed that the size of crystallites in the supported NiO first decreased with increase in calcination temperature up to 700• C, and then increased due to phase transformation of nickel oxide to spinel. The pores are mesopores and their meshy surface structure was not affected by calcination temperature in the range investigated. The catalytic activity was tested by CO 2 hydrogenation with an H 2 /CO 2 ratio of 4/1 at 500• C. The CO 2 conversion and CH 4 yield for CO 2 hydrogenation over 15 wt% Ni/RHA-Al 2 O 3 catalyst were almost independent of calcination and reduction temperatures.

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The faujasite framework structure and the morphological properties of Co 2þ -exchanged NaX zeolite were maintained when samples were treated at a temperature 600 C, but were distorted at higher temperature. The cobalt (II) exchange and thermal treatment processes significantly improved the H 2 S adsorption capacity of the NaX zeolite and the highest values were 4.24 mg g À1 for 0.10-CoX-600 and 4.42 mg g À1 for 0.15-CoX-600. Moreover, the firstorder adsorption kinetic showed a relatively good fit when applied to the experimental data for the H 2 S adsorption process.

The cobalt (II) ion-exchange process followed the Freundlich and Langmuir adsorption models as well as the pseudo-second-order kinetic model. The cobalt-exchanged contents increased when the initial Co(NO3)2solution concentration increased up to 0.14 mol L−1at the optimal pH of 6.05. The N2adsorption isotherms are mixed types I/II isotherms and H3 type hysteresis. Both the micropore and mesopore adsorptions occurred during the adsorption process. The modification, which is both the cobalt (II) exchange and thermal treatment, significantly improved the surface properties of NaX zeolites. Accordingly, the optimal temperature range is 500 to 600°C for a thermal treatment. This is consistent with the results of XRD analysis.