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Using the dispersion-corrected density functional theory (DFT-D3) method, we systematically studied the adsorption of 15 kinds of transition-metal (TM) clusters on pristine graphene (Gr) and N-doped graphene (N-Gr). It has been found that TM n (n = 1–4) clusters adsorbed on the N-Gr surface are much stronger than those on the pristine Gr surface, while 3d series clusters present similar geometries on Gr and N-Gr surfaces. The most preferred sites of TMs migrate from hollow to bridge to the top site on the Gr surface along the d series in the periodic table, while the preferred sites of TMs migrate in a much more complex manner on the N-Gr surface. It has also been found that charge transfer decreases along the d series for adsorbed clusters on both surfaces, but adsorbed clusters present less charge transfer on the N-Gr surface than on the Gr surface. What is more interesting is that some TM (Tc, Ru, and Re) clusters change the growth mechanism from the three-dimensional (3D) growth mode on the Gr surface to the two-dimensional (2D) growth mode on the N-Gr surface. At last, it has been found that adsorbed clusters are more dispersed on the N-Gr surface than on the pristine Gr surface due to growth and average aggregation energies.

As a pure combustible gas with a high calorific value, methane has long been favored, and that is why the CO2 methanation reaction is attracting more and more attention. However, it is still challenging for this reaction due to the chemical inertness of CO2 molecules, poor reaction efficiency at low temperatures, catalyst sintering at high temperatures, and carbon monoxide toxicity. Herein, the ammonia evaporation method was utilized to synthesize a series of Zn-modified Ni/SiO2 catalysts with high surface area and high dispersity of active metals. The 80Ni-Zn/SiO2 catalyst with an appropriate Ni/Zn molar ratio of 80:1 exhibited a high-performance breakthrough with a CO2 conversion greater than 80% at 300 °C, good stability for 40 h at 310 °C, and a gas hourly space velocity of 18,000 mL·g–1·h–1. These catalysts were further characterized by using a series of methods like in situ diffuse reflectance infrared Fourier transform spectroscopy to investigate the structural properties and potential reaction pathways. The effect of the Zn promoter on the Ni/SiO2 catalyst for CO2 methanation has been well investigated, namely, improving Ni dispersion and enhancing the H2 adsorption. The findings demonstrate the broad availability, affordability, and remarkable high-performance practicability of the raw ingredients for the production of Ni-based catalysts for commercial applications.

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