Study on the mechanism of hydrogen production by methane decomposition catalyzed by activated carbon loaded by carbon black for increasing defect sites

Abstract

Under the background of the “dual carbon goal” era, hydrogen production from methane decomposition is considered to be a promising high-purity hydrogen production technology due to no CO2 emissions. The research on carbon catalyst modification is a hot spot in related fields. To improve the stability of activated carbon (AC) catalysts, the new catalysts prepared by coconut shell activated carbon supported with carbon black (CB) ketjen black EC300J was proposed and prepared. And its characterization test analysis, catalytic methane cracking experiment and molecular simulation calculation were carried out. The results show that the catalyst prepared when the amount of dispersant was 1 g and the AC and CB mass ratio was 8∶2 had better catalytic performance, the initial activity at 1 000 ℃ was up to 85%, the deactivation was delayed for 15 min, and the methane conversion in the middle stage of the reaction was about 8% higher than that in AC. This is because that CB is loaded on the surface of AC and generates deposited carbon with defect sites through reaction. The results of molecular simulation calculations show that the main reason is that the existence of topological defects increases the nonlocality of its s and p orbitals, which improves the adsorption performance of methane and promotes the reaction. In addition, the micropores on the surface of AC and oxygen-containing functional groups such as carboxyl, carbonyl, and hydroxyl groups also have different degrees of promotion on the adsorption of methane molecules. The heat of adsorption is the greatest when the pore size is 0.8 nm, which means that the presence of micropores is conducive to methane adsorption on AC, especially small micropores. All three functional groups can promote the adsorption of methane on the surface of AC, among which the carboxyl group promotion effect is better, and the carbonyl and hydroxyl effects are not much different.

Keywords

• methane decomposition
• activated carbon
• carbon black
• defective structure