*3.1. Catalytic Activity*

5 wt% Ni supported over γ-Al2O3, Y-zeolite and H-ZSM-5 catalysts (for simplification, these catalysts are designated as NA, NY and NH, respectively) were studied for DRM reaction at different temperatures from 500 to 700 ◦C. Figure 1a,b shows activity performance in terms of CH4 conversion and H2/CO ratios versus temperature for the NA, NY, and NH catalysts, respectively. The activity results demonstrate an increase in CH4 conversion with increase in reaction temperature from 500 to 700 ◦C which confirms the endothermic nature of DRM reaction [30,31]. The ratios of H2 to CO show interesting trends for each catalyst. It is noteworthy that CH4 conversion is mainly responsible for H2 production while CO comes from CO2. Hence, H2/CO ratios less than unity clearly justifies CO2 conversions are higher than CH4 conversion and vice versa. CO2 conversions higher than CH4 conversions also proves the occurrence of reverse water gas shift reaction (CO2 + H2 ↔ CO + H2O) which consumes H2 and brings H2/CO ratios less than one. This also suggests that H2/CO ratios higher than one, resulting from higher CH4 conversions, lead to the catalysts being more prone to carbon deposition [31].

**Figure 1.** (**a**) CH4 and (**b**) CO2 conversion versus time on stream for Ni supported on alumina (NA), Ni supported on Y-zeolite (NY), and Ni supported on H-ZSM-5 (NH) catalysts.
