Defective graphitic carbon as a high chlorine conversion catalyst for methyl chloride production from methane

Abstract

In the methane chlorination reaction, unreacted Cl2 is a cause of reactor corrosion and contamination, and thus research on catalysts with high Cl2 conversion is needed. In this study, carbon-based catalysts were used for the methane chlorination reaction. As carbon-based catalysts, commercially available amorphous carbons with sp3-dominant hybridized structures and graphitic carbons with sp2-dominant hybridized structures were investigated. Two different groups of carbons exhibited distinct catalytic performance in CH4 and Cl2 conversions and product selectivity. Amorphous carbons exhibited relatively low CH4 and Cl2 conversions, and an undesired product, CCl4, was largely generated. On the other hand, graphitic carbons exhibited relatively high conversions and CCl4 was not generated. In particular, a graphitic carbon with an optimum defect site exhibited almost 100% Cl2 conversion. These catalysts can be strongly affected by the adsorption phenomenon of the reactants and products. We propose reasons for the different catalytic performance and plausible reaction mechanisms for the carbon-based catalysts and verify them through experimental analyses: Raman spectroscopy, TGA-MS, XPS, XRD, and EDS and density functional theory (DFT) calculations.