Tuning CO₂ Hydrogenation Selectivity by N-Doped Carbon Coating over Nickel Nanoparticles Supported on SiO₂

Abstract

Controlling the selectivity of CO2 hydrogenation is a challenge for the application of earth-abundant-based metal catalysts. Herein, we show that a high-temperature pyrolysis protocol can be applied to prepare a nickel catalyst embedded in N-doped carbon (Ni@NC), which provides an enhanced selectivity to CO in the nickel-catalyzed CO2 hydrogenation reaction under atmospheric pressure. The nitrogen-containing carbon overlayer was obtained through controlled pyrolysis of the nickel–1,10-phenanthroline complex impregnated on SiO2. The Ni@NC/SiO2 catalyst is more selective for CO, following the reverse water-gas shift reaction pathway, while an analogous “naked” Ni catalyst was more selective toward CH4, following the CO2/CO complete hydrogenation pathway. Although the Ni@NC/SiO2 catalyst has larger particle sizes than the naked Ni/SiO2 catalyst, the binding strength of CO to the Ni@NC surface is significantly weaker. Consequently, the CO intermediate easily desorbs instead of being converted into methane. Hence, selectivity toward CO, which is an important intermediate to methanol and C2+ products, or CH4 can be modulated by a simple modification of the Ni surface through controlled carbon deposition.