Catalytic hydrolysis of methyl mercaptan and methyl thioether on hydroxyl-modified ZrO2: a density functional theory study

Abstract

The purification and removal of organic sulfur from natural gas is conducive to increasing the added value of natural gas and reducing environmental pollution. In this study, the adsorption properties of methyl mercaptan (CH₃SH), dimethyl sulfide (C₂H₆S) and H₂O on the surface of hydroxyl-modified ZrO₂ were investigated using density functional theory (DFT) calculations. Additionally, a reaction mechanism was proposed for hydroxyl-modified ZrO₂ catalyzing the hydrolysis of CH₃SH and C₂H₆S. The chemisorption of H₂O molecules on the catalyst surface is attributed to H–O and H–Zr bonds. The chemisorption of CH₃SH and C₂H₆S on the catalyst surface is attributed to Zr–S bonds. Competitive adsorption between the three gases exists only between CH₃SH and C₂H₆S. It reveals the water-resistant properties of hydroxyl-modified ZrO₂ in desulfurization. The adsorption energies of the three gas molecules on the hydroxyl-modified ZrO₂ surface are in the order of CH₃SH − (Zr) > C₂H₆S − (Zr) > H₂O − (OH). The natural hydrolysis of CH₃SH and C₂H₆S is a heat-absorbing process that cannot occur spontaneously. The rate-determining step for CH₃SH catalytic hydrolysis is the formation of CH₃O. The fracture of CH₃SHO is the rate-determining step for C₂H₆S catalytic hydrolysis. The depletion of the surface hydroxyl groups can be replenished by the dissociation of H₂O molecules. Hydroxyl-modified ZrO₂ facilitated the hydrolysis process of CH₃SH to a greater extent than that of C₂H₆S. This study provides theoretical guidance for industrial applications and the design of hydroxyl-containing hydrolysis catalysts.