Direct carbon dioxide hydrogenation to produce bulk chemicals and liquid fuels via heterogeneous catalysis

Methanol synthesis from catalytic recycling of CO2 is one viable route to produce fuel and a stock chemical from a greenhouse gas. Herein, hydrogenation of CO2 to CH3OH is investigated with density functional theory calculations combined with mean-field microkinetic modeling. The model explores the direct route for CO2 hydrogenation (HCOOH route) and the competing reverse water-gas shift (RWGS) reaction. The predicted temperature dependence of turnover frequencies, selectivities, and reaction orders are in good agreement with previous experimental results. The formation of methanol at relevant reaction temperatures (470-670 K) is found to be kinetically controlled by H2COOH dissociation to H2CO + OH, whereas the RWGS reaction is solely controlled by CO2 hydrogenation to COOH. An analysis of the kinetic behavior reveals that the stabilization of hydrogen adsorption should be one way to improve the catalyst performance.

A First-Principles-Based Microkinetic Study of CO 2 Reduction to CH 3 OH over In 2 O 3 (110)

Reaction mechanism and catalytic activities of methanol (CH3OH) and CO formations from CO2 hydrogenation at all the different surface oxygen vacancy (Ov) sites on the stable cubic In2O3 (c-In2O3) (111) flat surface and (110) flat and (110) step surfaces were thoroughly investigated in order to establish the structure-performance relationship using density functional theory calculations. For CH3OH formation, the R2 step for bidentate formate intermediate (bi-HCOO*) hydrogenation to the dioxymethylene intermediate (H2COO*), or the R3 step for H2COO* dissociation to the formaldehyde intermediate (CH2O*) and surface O atom, was calculated to be the rate-determining step (RDS), whereas for CO formation, the R1a step for bent CO2 adsorbate (bt-CO2*) protonation to the carboxylate intermediate (COOH*), was calculated to be the only RDS. Further data science analysis using the perceptron learning and decision tree algorithms shows that the RDS for CH3OH formation for a given Ov site can be determined by the stability of two key reaction intermediates (H2COO* and CH2O*) along with the formation energy of the Ov site. Linear regression analysis was also performed to establish linear relationships between the activation barriers and corresponding reaction energies for R2 and R3 steps, which can also be useful in determining the actual RDS for CH3OH formation. Although the adsorption energies of the linear CO2 configuration intermediate (ln-CO2*) and the bt-CO2* as well as the difference between the activation barriers of the RDS for CO and CH3OH formations are required for reliably predicting the catalytic activity and product selectivity, our studies suggest a simple and intuitive structure-performance relationship for the c-In2O3 catalyst that tri-coordinated Ov sites favor CH3OH formation, whereas bi-coordinated Ov sites favor CO formation.

Understanding the structure-performance relationship of cubic In2O3 catalysts for CO2 hydrogenation

Hydride species on oxide catalysts are widely involved in oxide-catalyzed reactions, and relevant fundamental understanding is important to establish reaction mechanisms and structure-performance relations of oxide catalysts. In this topical review, recent progresses on the formation and reactivity of hydride species on the surface or in the bulk of oxides are briefly summarized. Firstly, characterization techniques for hydride species are introduced. Secondly, formation of hydride species on the surface or in the bulk of various oxides and their reactivity in oxide-catalyzed hydrogenation and dehydrogenation reactions are reviewed. Finally, short summary and outlook are given.

Hydride species on oxide catalysts.

Abstract In2O3 has emerged as a promising catalyst for CO2 activation, but a fundamental understanding of its mode of operation in CO2 hydrogenation is still missing, as the application of operando vibrational spectroscopy is challenging due to absorption effects. In this mechanistic study, we systematically address the redox processes related to the reverse water‐gas shift reaction (rWGSR) over In2O3 nanoparticles, both at the surface and in the bulk. Based on temperature‐dependent operando UV/Vis spectra and a novel operando impedance approach for thermal powder catalysts, we propose oxidation by CO2 as the rate‐determining step for the rWGSR. The results are consistent with redox processes, whereby hydrogen‐containing surface species are shown to exhibit a promoting effect. Our findings demonstrate that oxygen/hydrogen dynamics, in addition to surface processes, are important for the activity, which is expected to be of relevance not only for In2O3 but also for other reducible oxide catalysts.

Elucidating CO2 Hydrogenation over In2O3 Nanoparticles using Operando UV/Vis and Impedance Spectroscopies

Reaction pathways and the role of the carbonates during CO2 hydrogenation over hexagonal In2O3 catalysts

Computer-assisted rational design of heterogeneous catalysts has become a central theme of computational studies on industrial catalysis, which may contribute significantly to our impending transition from a fossil fuel-based energy and chemical industry into a renewable energy-based one. To this end, integrated research efforts in mechanistic elucidation of the relevant catalytic reactions remain essential, but emphasis must be further placed on the development of effective approaches in the rational design of industrial catalysts, where traditional methodologies must be combined with the new information-based technologies.

Zhimin Zhou

Papers

Understanding the structure-performance relationship of cubic In2O3 catalysts for CO2 hydrogenation

Reaction pathways and the role of the carbonates during CO2 hydrogenation over hexagonal In2O3 catalysts

Mechanistic studies toward the rational design of oxide catalysts for carbon dioxide hydrogenation