Direct C–C Coupling of CO₂ and the Methyl Group from CH₄ Activation through Facile Insertion of CO₂ into Zn–CH₃ σ-Bond

Abstract

Conversion of CO2 and CH4 to value-added products will contribute to alleviating the green-house gas effect but is a challenge both scientifically and practically. Stabilization of the methyl group through CH4 activation and facile CO2 insertion ensure the realization of C-C coupling. In the present study, we demonstrate the ready C-C coupling reaction on a Zn-doped ceria catalyst. The detailed mechanism of this direct C-C coupling reaction was examined based on the results from density functional theory calculations. The results show that the Zn dopant stabilizes the methyl group by forming a Zn-C bond, thus hindering subsequent dehydrogenation of CH4. CO2 can be inserted into the Zn-C bond in an activated bent configuration, with the transition state in the form of a three-centered Zn-C-C moiety and an activation barrier of 0.51 eV. The C-C coupling reaction resulted in the acetate species, which could desorb as acetic acid by combining with a surface proton. The formation of acetic acid from CO2 and CH4 is a reaction with 100% atom economy, and the implementation of the reaction on a heterogeneous catalyst is of great importance to the utilization of the greenhouse gases. We tested other possible dopants including Al, Ga, Cd, In, and Ni and found a positive correlation between the activation barrier of C-C coupling and the electronegativity of the dopant, although C-H bond activation is likely the dominant reaction on the Ni-doped ceria catalyst.

One‐Step Reforming of CO2 and CH4 into High‐Value Liquid Chemicals and Fuels at Room Temperature by Plasma‐Driven Catalysis

“…Recently, Ge and co‐workers investigated the direct C−C coupling of CO 2 and CH 4 to form acetic acid on a Zn‐doped ceria catalyst by density functional theory (DFT) modeling;1 this is an attractive route as the direct conversion of CO 2 and CH 4 into acetic acid is a reaction with 100 % atom economy [Equation (1)]. However, this reaction is thermodynamically unfavorable under practical conditions.…”

Direct Conversion of Methane with Carbon Dioxide Mediated by RhVO3−Cluster Anions

“…The co-conversion of methane and carbon dioxide to valueadded chemicals represents an important subject in C 1 chemistry from energy and environmental perspectives, [1] but it is very difficult because of the inherent stability of both CH 4 and CO 2 .D ry reforming of methane (DRM) with CO 2 has been developed for generation of syngas (CO + H 2 ) [2] that can be converted to desired products by either alcohols synthesis or Fischer-Tropsch processes. [3] However,s uch indirect route is highly energy intensive.T he design of catalysts that can achieve the direct co-conversion of CH 4 and CO 2 thus becomes appealing driven by the economical consideration. [4] There have been several attempts at direct production of chemicals from CH 4 and CO 2 using heterogeneous catalysts including Cu/Co metal oxides, [5] oxide-supported noble metals (Rh, Pd, and Pt), [6] and metal-exchanged zeolites.…”

“…[3] However,s uch indirect route is highly energy intensive.T he design of catalysts that can achieve the direct co-conversion of CH 4 and CO 2 thus becomes appealing driven by the economical consideration. [4] There have been several attempts at direct production of chemicals from CH 4 and CO 2 using heterogeneous catalysts including Cu/Co metal oxides, [5] oxide-supported noble metals (Rh, Pd, and Pt), [6] and metal-exchanged zeolites. [7] These direct processes still suffer from high temperature (> 700 K) or poor selectivity and low yield.…”

Supported Porous Nanomaterials as Efficient Heterogeneous Catalysts for CO2 Fixation Reactions

“…Zn-doped ceriaw as found to be av ery efficient catalyst in activating the CÀHb ond of methanei nt he presence of CO 2 to form the CÀCc ouplingp roduct acetic acid. [206] Here the Zn sites stabilized the ÀCH 3 moiety through the formationo fa ZnÀCb ond, whereas ceria activated the CO 2 molecules and thus CÀCc oupling proceeded smoothly.I nav ery recent article Park et al reported the synthesis of acetic acid by simultaneous co-activation of CH 4 and CO 2 over Cu-loaded Li/Na/K/Ca-ZSM-5 materials [207] in am icro-reactor at 425-525 8Cw ith slow feeding of these gas mixtures. Here the Cu NPs facilitates the CÀHa ctivation, whereas the alkali anda lkaline earth metal sites promote the activation of CO 2 molecules so that the CÀC bond formation reactionoccurs, leading to the selectiveformation of CH 3 CO 2 H. Chen et al have also reportedt he synthesis of ethanol (C 2 H 5 OH)bypassing CO 2 into an aqueous dispersion of bimetallico xysulfides of Cu/Ni, Cu/Co,a nd Cu/Sn as heterogeneous catalyst under ambient conditions.…”

“…Zn‐doped ceria was found to be a very efficient catalyst in activating the C−H bond of methane in the presence of CO 2 to form the C−C coupling product acetic acid . Here the Zn sites stabilized the −CH 3 moiety through the formation of a Zn−C bond, whereas ceria activated the CO 2 molecules and thus C−C coupling proceeded smoothly.…”