CO₂ reduction with green H₂ is an attractive way to produce fuels or chemicals. CO and CH₄ are the main products for CO₂ hydrogenation under atmospheric pressure while CH₃OH and C₂₊ hydrocarbons/alcohols can be produced at high pressure. Unveiling the origin of tunable CO and CH₄ selectivity is very important to rationally design CO₂ hydrogenation catalysts as there are a lot of similarities between the atmospheric-pressure and high-pressure reactions in the reaction mechanism of CO₂ hydrogenation. Here, a unique doping-segregation method based on Ni-based spinel is developed to precisely control the size of supported Ni nanoparticles from 1 nm to 12 nm, which strongly affects the product selectivity for CO₂ hydrogenation reactions. Based on the in-situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) combined with transient response experiments, the reverse water-gas shift (RWGS) followed by H₂-assisted CO dissociation and hydrogenation pathway is determined as the primary pathway for CO₂ hydrogenation over Ni-based spinel catalysts. The activation energy of the rate-determining step (i.e., H₂-assisted CO dissociation) and the activation temperature of CO in a hydrogen atmosphere are then identified as quantitative descriptors of CO₂ hydrogenation selectivity. The generality of these descriptors is also demonstrated over various Ni-supported catalysts including Ni/SiO₂, Ni/ZrO₂, Ni/CeO₂, and Ni/Al₂O₃. These results will guide the design of superior catalysts with a desired selectivity and bring new insight into Sabatier's principle for better understanding of the structure-performance relationship in heterogeneous catalysis.

<b>Figure 1</b> <b>Descriptor identification for CO<sub>2</sub> hydrogenation selectivity</b> (a) CO signal of CO hydrogenation TPSR, and (b) the plot of CO activation temperature and as a function of CH<sub>4</sub> selectivity for CO<sub>2</sub> hydrogenation over Ni-based catalysts

Figure 1 Descriptor identification for CO₂ hydrogenation selectivity (a) CO signal of CO hydrogenation TPSR, and (b) the plot of CO activation temperature and as a function of CH₄ selectivity for CO₂ hydrogenation over Ni-based catalysts

Jiaming Tian

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