Mechanism of improving the stability of activated carbon catalyst by trace H2S impurities in natural gas for hydrogen production from methane decomposition

Abstract

Direct methane decomposition for hydrogen production is considered a clean technology with limited CO2 emission. However, catalysts usually suffer from deactivation due to carbon deposition. This study reported a method of improving the catalyst stability by using a trace amount of H2S which naturally exists in natural gas, and the action mechanism of H2S was discussed. Coconut shell activated carbon (AC) was used as the catalyst, the pure methane was mixed with 100, 200, and 300 ppm H2S and decomposed at high temperature. Results show that adding different concentrations of H2S can increase the methane conversion and delay the deactivation time of the AC catalyst. Through scanning electron microscopy characterization and Brunauer-Emmet-Teller analysis, it was found that the positive effect of H2S is achieved by changing the carbon deposition morphology which in turn changes the AC pore width distribution and the specific surface area. Under the action of H2S, AC has a relatively large number of micropores during the reaction, promoting the adsorption of methane molecules on AC. First-principles calculations show that H2S changes the reaction pathway of methane dehydrogenation and promotes methane decomposition.