Optimizing Active Sites for High CO Selectivity during CO₂ Hydrogenation over Supported Nickel Catalysts

Abstract

Controlling the selectivity of CO2 hydrogenation catalysts is a fundamental challenge. In this study, the selectivity of supported Ni catalysts prepared by the traditional impregnation method was found to change after a first CO2 hydrogenation reaction cycle from 100 to 800 °C. The usually high CH4 formation was suppressed leading to full selectivity toward CO. This behavior was also observed after the catalyst was treated under methane or propane atmospheres at elevated temperatures. In situ spectroscopic studies revealed that the accumulation of carbon species on the catalyst surface at high temperatures leads to a nickel carbide-like phase. The catalyst regains its high selectivity to CH4 production after carbon depletion from the surface of the Ni particles by oxidation. However, the selectivity readily shifts back toward CO formation after exposing the catalysts to a new temperature-programmed CO2 hydrogenation cycle. The fraction of weakly adsorbed CO species increases on the carbide-like surface when compared to a clean nickel surface, explaining the higher selectivity to CO. This easy protocol of changing the surface of a common Ni catalyst to gain selectivity represents an important step for the commercial use of CO2 hydrogenation to CO processes toward high-added-value products.

Tuning product selectivity in CO2hydrogenation over metal-based catalysts

“…As well, they are promising for CO 2 hydrogenation because of the dual-function of H 2 dissociation and C═O bond scission. [109][110][111][112] Porosoff et al 18 reported the CO 2 hydrogenation on defined Mo 2 C surfaces, which are highly active and selective for CO production. The Mo 2 C catalyst shows CO 2 conversion of 8.7% and CO/CH 4 ratio of 14.5 for CO 2 hydrogenation at 300 °C, which outperforms noble metal bimetallic catalysts.…”

“…In addition to the Mo 2 C, other carbides such as Ni 3 C and InNi 3 C 0.5 were explored for CO 2 hydrogenation. 111,112 Although Ni is highly selective for methanation, both of Ni 3 C and InNi 3 C 0.5 with carbide structures exhibit superior RWGS feature. Chen et al 111 reported that the InNi 3 C 0.5 supported on Al 2 O 3 /Al-fiber shows over 97% CO selectivity in CO 2 hydrogenation under wide reaction conditions.…”

“…Carbide phases, such as Ni 3 C, easily forms in Ni catalysts at high reaction temperature, because carbon is highly miscible on the Ni surface. 118 Galhardo et al 112…”

CO2 Hydrogenation on NixMg1−xAl2O4: A Comparative Study of MgAl2O4 and NiAl2O4

“…The role played by nickel in CO 2 hydrogenation is well understood in terms of particle size [10] and metal-reactant intermediate reactions [19]. It has also been reported that oxygen vacancies in NiAl 2 O 4 promote the dissociation of CO 2 to CO [20] and facilitate the hydrogenation of adsorbed CO to atomic carbon.…”

Metal Nanoparticles Wrapped on Defective Nitrogen-doped Graphitic Carbons as Highly Selective Catalysts for C02 Hydrogenation

“…Catalysts such as Fe, Co, Ni and Cu supported on silica and carbon materials have been comprehensively investigated in CO2 hydrogenation. [78] Among them, Fe and Co-based catalysts are widely used in the CO2 modified FTS, due to the significant selectivity to C2+ hydrocarbons. [79] These active transition metal in the form of small nanoparticles or even clusters and single atom supported on metal oxides with large surface areas, such as γ-Al2O3, [80] ZrO2, [81] TiO2 [82] and CeO2 [83] have been frequently reported as solid catalysts for CO2 hydrogenation.…”