Insights into Bimetallic Oxide Synergy during Carbon Dioxide Hydrogenation to Methanol and Dimethyl Ether over GaZrO_x Oxide Catalysts

Abstract

Hydrogenation of CO2 to methanol and dimethyl ether (DME) is one strategy to tackle the global climate change and meet the portable fuel demand simultaneously. The bimetallic oxide synergy is known to boost the yields of methanol and DME from CO2 hydrogenation. However, the origin of this synergy is still unclear. We synthesized a series of GaZrO x catalysts by the evaporation-induced self-assembly method. The GaZrO x (27%) catalyst displays superior activity than admixtures of the (Ga2O3 + ZrO2) oxides. We propose that the Zr3+–OV–Ga–O species (OV represents the oxygen vacancy) on the GaZrO x catalyst is the active site. Our results demonstrate that the synergistic effect stems from neighboring Ga–O sites and Zr3+–OV sites, as revealed by complementary X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, in situ diffuse reflectance infrared Fourier transform spectroscopy, electron paramagnetic resonance spectroscopy, and solid-state NMR spectroscopy results. We demonstrate that H2 is dissociated on polarized Ga–O sites to produce Ga–H and −OH species, while CO2 is trapped by the oxygen vacancies and activated by electron transfer from the Zr3+ ions. The whole picture of the CO2 hydrogenation reaction mechanism on the GaZrO x catalyst is presented. The atomic- and electronic-levels understanding of the active sites and the origin of the synergistic effect open up a new avenue for the rational design of highly active catalysts for CO2 hydrogenation.

Mn-Doped Highly Dispersed RuO2 Catalyst with Abundant Oxygen Vacancies for Efficient Decarboxylation of l-Lysine to Cadaverine

“…The surface carboxylate species (RCOO-Mn), where the character R represented NH 2 (CH 2 ) 4 CH­(NH 2 )– group, with a conjugate structure was formed after releasing one molecule of H 2 O. It was taken as the intermediate in decarboxylation process as previous studies described. , The similar conjugate structure was also observed in carbon dioxide hydrogenation to methanol catalyzed by Ga-doped ZrO x oxide . The surface carboxylate species can undergo two cycles to give different products.…”

“…16,66 The similar conjugate structure was also observed in carbon dioxide hydrogenation to methanol catalyzed by Ga-doped ZrO x oxide. 67 The surface carboxylate species can undergo two cycles to give different products. In Cycle 1, it was hydrated to form methyl species (RCH 2 O−Mn).…”

Highly Efficient Decarboxylation of L-Lysine to Cadaverine Catalyzed by RuO2 Encapsulated in FAU Zeolite

“…After the dehydration process, the surface carboxylate species (Ru-COOR) with a conjugate structure was formed, where the character R represented NH 2 (CH 2 ) 4 CH(NH 2 )-group. This conjugated chemical was believed to be the intermediate in the decarboxylation process [48,49]. Thirdly, the decarbonylation process occurred to form active R species while releasing one CO molecule.…”

Impacts of the Catalyst Structures on CO2 Activation on Catalyst Surfaces

“…On the most stable CO 2 adsorption configuration, one of the oxygen atoms of the adsorbed CO 2 occupied the oxygen vacancy site with low adsorption energy (−0.31 eV). Feng et al [167] synthesized a series of GaZrO x catalysts by the evaporation-induced self-assembly (EISA) method and proposed the Zr 3+ -O V -Ga-O species (O V represents the oxygen vacancy) on the GaZrO x surface as the active site (Figure 10c). The synergistic effect stems from neighboring Ga-O and Zr 3+ -O V sites.…”

“…Copyright 2016 American Chemical Society (c) Proposed mechanism for the hydrogenation of CO 2 to methanol and DME on the GaZrO x catalyst. Reproduced with permission from the authors of[167]. Copyright 2021 American Chemical Society.…”