Ni-supported in Tailored Silica Catalysts for Dry Reforming of Methane

Abstract

The continuous dependence on and excessive use of fossil fuels has led to the emission of various greenhouse gases, causing serious environmental problems. Carbon dioxide (CO2) and methane (CH4) are considered the main drivers of climate change and global warming. While the atmospheric concentration of CO2 is much higher, CH4 has a significantly stronger greenhouse effect. Therefore, the need to efficiently convert these two gases into useful substances through chemical reactions has become increasingly important. Dry methane reforming (DRM) is an innovative technology that can simultaneously convert CH4 and CO2 into synthesis gas (H2 and CO). The process not only decreases greenhouse gas emissions but also enables the synthesis of environmentally friendly chemical products. Nickel (Ni)-based catalysts are mainly used in DRM processes due to their high activity and economic advantages. However, Ni-based catalysts have low resistance to coking and sintering, leading to catalyst deactivation during DRM process and significantly hindering their potential for industrial applications. Therefore, effective catalyst design is essential for process stability. In this study, we present two strategic approaches to enhance the performance of nickel catalysts supported on silica for dry methane reforming (DRM) reactions. Chapter 1 investigates the influence of the silica framework ligand length on the catalyst activity and stability. The catalysts were synthesized using silica framework precursors with C1~C4 carbon chain lengths, through a sequentially integrated sol-gel and re-precipitation method. The carbon chain length of the ligand influenced the reaction rate during the synthesis process and final physicochemical properties. The longest chain framework ligand (C4) formed small and uniform Ni particles and enhanced the interactions between Ni and silica. Also, it enhanced acid/base properties, resulting in improved catalyst performance. Chapter 2 explored an approach to control the chemical characteristics of the silica surface. To impart acidic and basic properties to the silica, it was synthesized by adjusting the molar ratio of tetraethoxysilane (TEOS) and 3-aminopropyltrimethoxysilane (APTES), followed by impregnation with nickel (Ni). The synthesized silica and Ni impregnated catalysts exhibited differences in porous structure, acidity/basicity, and Ni states depending on the molar ratio of the silica precursors. Among them, the catalyst with an intermediate ratio has the advantages of both TEOS and APTES-rich conditions, effectively overcoming the limitations of silica-based supports. Thus, the performance of Ni-based catalysts in DRM significantly improved. This research used two strategic approaches to improve silica supports and enhance the performance and stability of nickel catalysts in dry methane reforming (DRM) reactions. These strategies are expected to provide new directions for the design of efficient and sustainable silica-supported nickel catalysts for DRM.