Formation of Ni Species Anchored on a Silicalite-1 Zeolite Framework as a Catalyst with High Coke Deposition Resistance on Dry Reforming of Methane

Dry reforming of methane (DRM), which converts the greenhouse gases methane and carbon dioxide to synthesis gas consisting of hydrogen and carbon monoxide, has attracted more and more attention. Various metal-supported catalysts have been developed for the DRM reaction, among which Ni nanoparticles are known to be the most effective for this reaction, due to their strong ability for CH4 adsorption and C–H decomposition. However, the problems of Ni sintering and carbon byproducts causing catalytic deactivation have hindered its practical application. Therefore, in this study, we synthesized Ni-anchored silicate-1 catalysts by a one-pot hydrothermal synthesis method and a dry gel conversion method and monitored their crystallization processes. In both methods, Ni species were anchored on the silicalite-1 zeolite frameworks at the early stage of crystallization. Thereafter, the content of Ni species decreased, suggesting that Ni-anchored silicalite-1 would be a metastable phase and the formation of pure silicalite-1 as a more stable phase would proceed with an increase of crystallization time. The anchored Ni species showed a reduction peak at a higher temperature in hydrogen temperature-programmed reduction (H2-TPR) than a conventional Ni-impregnated silicalite-1, indicating that the one-pot synthesis methods make it possible to form a Ni species strongly interacting with silicalite-1 supports. The obtained samples were applied to the DRM reaction. As a result, the samples prepared by the one-pot synthesis methods showed much better carbon deposition resistance (coke deposition: lower than 6%) than a conventional Ni-impregnated silicalite-1 (coke deposition: ca. 40%). It was also suggested that Ni species interacting strongly with the silicalite-1 framework is likely to be effective against Ni agglomeration and carbon deposition in the DRM reaction.