One-Step Synthesis of Nitrogen-Doped α-MoC Supported on SBA-15 with Enhanced Catalytic Activity for the Reverse Water–Gas Shift Reaction

Abstract

The reverse water–gas shift reaction (RWGS) has been regarded as an essential route for CO₂ utilization, and molybdenum carbides show promise as efficient RWGS catalysts. Herein, we investigate the evolution of MoO₃ to α-MoC in a mixture of CH₄/NH₃/H₂ (5/1/15 by volume) and how the nitrogen dopant modulates the catalytic activity of α-MoC for the RWGS reaction. It is found that the MoO₃ evolution in the mixture follows a path: MoO₃ → MoO₂ → MoO_zN_yC_x → MoN_yC_x → N-doped α-MoC. The moderate nitrogen-doped content favors the α-MoC activity due to enhanced CO desorption. As a result, the optimized N-doped α-MoC synthesized at 680 °C exhibited 39% CO₂ conversion with 98.5% CO selectivity at 400 °C, 24,000 mL g^–1 h^–1 space velocity, and 0.1 MPa, which is close to the equilibrium conversion (40.3%). In situ Fourier transform infrared (FTIR) spectroscopy reveals that the adsorbed formic acid, carboxyl, and formate species were identified as intermediates of the RWGS reaction. The enhanced CO desorption makes the conversion of the intermediates to CO smoother and the activity more stable at lower reaction temperatures. This work develops a simple method for the preparation of cubic α-MoC and the role of N doping in the RWGS reaction.