Catalytic Methane Decomposition to Hydrogen over a Surface‐Protected Core‐Shell Ni@SiO₂ Catalyst

Abstract

Methane decomposition is a promising method to obtain CO x -free hydrogen. The main difficulty of this process is that the produced carbon would deposit on the active phase of the catalyst, leading to catalyst deactivation. In this study, a coreshell-structured composite catalyst comprising highly active Ni nanoparticles (NP) as core and mesoporous silica as shell is introduced. The silica shells were synthesized by using cetyltrimethylammonium bromide as template and tetraethyl orthosilicate as precursor. Ni NP and Ni@SiO 2 were examined as catalysts for hydrogen production by methane decomposition at different temperatures and gas hourly space velocities. The results show that the core-shell catalyst exhibited much better stability in methane decomposition than Ni NP without silica shell and a traditional supported catalyst.

Methane decomposition into CO x ‐free hydrogen over a Ni‐based catalyst: An overview

“…By varying the GHSV from 5000 to 24 000 mL g −1 hour −1 , a significant reduction in methane conversion is not observed. The porous silica support used in their study is concluded to effectively adsorb methane, permitting a sufficient contact time for the decomposition of methane even under varied GHSV conditions 113 . Moreover, at a higher GHSV, the deactivation rate increases 114,142 .…”

“…As oxide supports, metal oxides such as Al 2 O 3, 21,80,97,107 TiO 2, 108,109 SiO 2, 79,110‐114 MgO, 101,115 CeO 2, 100,116 ZrO 2, 23,94 and zeolite 22,104 are frequently used for a Ni‐based catalyst. In practice, active metal particles must be dispersed onto the oxide support surface.…”

“…Synthesis methods that can produce an active and a stable Ni‐based catalyst for the CMD reaction include impregnation, 19,21‐23,60,77‐80,84,96,100,101,103,104,109‐111,114,127‐130 precipitation, 76,87,95,105,112,131‐134 and the sol‐gel method 67,68,94,97,108,116 . In addition, polyol reduction, 113,118,135 EISA, 85,115 fusion, 82 and emulsion 136 are employed. Impregnation and precipitation are among the most common preparation methods used to prepare Ni‐based catalysts in studies published from 2015 to 2020 (Figure 7) due to their cost‐effectiveness and relatively simple preparation steps.…”

Unveiling the Roles of Precursor Structure and Controlled Sintering on Ni-Phyllosilicate-Derived Catalysts for Low-Temperature Methane Decomposition

“…The effects of active metal (primarily Fe, Ni, Co, and combinations thereof), catalyst support (e.g., SiO 2 , , Al 2 O 3 , , MgO, ZrO 2 , TiO 2, CeO 2 , , La 2 O 3 ), promoters (e.g., noble metals, group VIB metals, and base-metal alloys), and preparation methods (e.g., impregnation, , solid-state fusion, evaporation-induced self-assembly, and sol–gel) on reaction rates, catalyst stability and product morphology have all been studied extensively in recent years. In contrast, few studies ,− have investigated low-temperature (<500 °C) CMD despite the potentially significant reduction in operating costs and heating-related carbon emissions from milder operating conditions. Importantly, the unfavorable effect of lower temperatures on the equilibrium conversion can be mitigated by continuously separating H 2 using H 2 -permeable membranes. − As carbon diffusion and precipitation rates with different temperature sensitivities must be carefully balanced for optimal catalyst activity and stability, catalysts that are optimized for higher-temperature CMD may not perform equally well at lower temperatures.…”

Direct Nonoxidative Conversion of Methane to Higher Hydrocarbons over Silica-Supported Nickel Phosphide Catalyst

“…The Ni/SiO 2 catalyst showed a good conversion of methane but less yield of hydrocarbons. Methane is decomposed to H 2 and C on the Ni/SiO 2 catalyst, as previously reported. ,− When earlier d-block metals than Ni (Mn, Fe, Co) were added as a second element to Ni on SiO 2 , the selectivity to hydrocarbons and yields were as low as those observed for Ni/SiO 2 catalyst. However, methane conversions of these d-block metals were higher than that of Ni/SiO 2 .…”