Dry reforming of methane on nickel dispersed on mesoporous silica : effect of synthesis conditions

Abstract

The reduction of greenhouse gases utilization and emission is the main interest of the scientists all over the world. Dry reforming of methane (DRM) is gaining more attention, due to its consumption of two greenhouse gases, namely methane and carbon dioxide, and its production of syngas. Moreover, the products ratio (1:1) of H2: CO is suitable for Fishcher-Tropsch synthesis. DRM is highly endothermic and requires severe conditions to proceed thermodynamically. Thus, the main challenge is the design a catalyst that can maintain its activity and stability under the reaction conditions. Noble metals have showed great catalytic activity and stability when used as an active phase in DRM catalysts. However, their use is not favored to economic an accessibility reasons. Nickel-based catalysts are an affordable and available promising alternative for noble metals. Thus, Nickel was used as an active phase in this study. The mesoporous based silica support, Santa-Barbara Amorphous material (SBA-15), used as catalytic supports in DRM, provide good dispersion of the active phase and good prevention to sintering. Thus SBA-15 is chosen as a support for Nickel in this study. The main focus of this thesis is to study the effect of the modifications made during SBA-15 synthesis (acidity, stirring rate, hydrothermal treatment, etc) on the activity/stability performance of Ni-based catalyst. In this study, eight supports SBA-15(x) were prepared and characterized by N2 sorption and showed different textural properties. Then, all the samples were impregnated with 5wt % Nickel using the two solvent impregnation method. Finally, eight catalysts Ni5/SBA-15(x) are obtained. The calcined fresh samples are characterized by N2 sorption, TPR, TEM, SEM and XRD. The results suggest similar SBA-15 structures with a small difference in grains shape .In addition, differences in Nickel particles size and localization are observed. A good dispersion of the Nickel particles is noted for all the catalysts. Catalytic activities are measured with a GHSV of 3600mL.g-1.h-1 at temperatures ranging from 200 to 800°C and atmospheric pressure. Stability measurements are conducted with the same GHSV at a fixed temperature of 650°C for 12 hours. The catalysts showed high activity and selectivity toward DRM. No significant deactivation is observed throughout the stability test.The characterizations by SEM and XRD after the test indicate that no sintering took place. The main cause of the small deactivation is due to coke deposition. Further studies of the spent catalysts by TEM are required to determine the type of coke deposited.