Multiscale Investigation of the Mechanism and Selectivity of CO2 Hydrogenation over Rh(111)

CO2 hydrogenation over Rh catalysts comprises multiple reaction pathways, presenting a wide range of possible intermediates and end products, with selectivity toward either CO or methane being of particular interest. We investigate in detail the reaction mechanism of CO2 hydrogenation to the single-carbon (C1) products on the Rh(111) facet by performing periodic density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations, which account for the adsorbate interactions through a cluster expansion approach. We observe that Rh readily facilitates the dissociation of hydrogen, thus contributing to the subsequent hydrogenation processes. The reverse water-gas shift (RWGS) reaction occurs via three different reaction pathways, with CO hydrogenation to the COH intermediate being a key step for CO2 methanation. The effects of temperature, pressure, and the composition ratio of the gas reactant feed are considered. Temperature plays a pivotal role in determining the surface coverage and adsorbate composition, with competitive adsorption between CO and H species influencing the product distribution. The observed adlayer configurations indicate that the adsorbed CO species are separated by adsorbed H atoms, with a high ratio of H to CO coverage on the Rh(111) surface being essential to promote CO2 methanation.

Hybrid Prediction-Driven High-Throughput Sustainability Screening for Advancing Waste-to-Dimethyl Ether Valorization

Assessing the prospective climate preservation potential of novel, innovative, but immature chemical production techniques is limited by the high number of process synthesis options and the lack of reliable, high-throughput quantitative sustainability pre-screening methods. This study presents the sequential use of data-driven hybrid prediction (ANN-RSM-DOM) to streamline waste-to-dimethyl ether (DME) upcycling using a set of sustainability criteria. Artificial neural networks (ANNs) are developed to generate in silico waste valorization experimental results and ex-ante model the operating space of biorefineries applying the organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS). Aspen Plus process flowsheeting and ANN simulations are postprocessed using the response surface methodology (RSM) and desirability optimization method (DOM) to improve the in-depth mechanistic understanding of environmental systems and identify the most benign configurations. The hybrid prediction highlights the importance of targeted waste selection based on elemental composition and the need to design waste-specific DME synthesis to improve techno-economic and environmental performances. The developed framework reveals plant configurations with concurrent climate benefits (-1.241 and -2.128 kg CO2-eq (kg DME)-1) and low DME production costs (0.382 and 0.492 € (kg DME)-1) using OFMSW and SS feedstocks. Overall, the multi-scale explorative hybrid prediction facilitates early stage process synthesis, assists in the design of block units with nonlinear characteristics, resolves the simultaneous analysis of qualitative and quantitative variables, and enables the high-throughput sustainability screening of low technological readiness level processes.

CO2 Activation and Hydrogenation on Cu-ZnO/Al2O3 Nanorod Catalysts: An In Situ FTIR Study

CuZnO/Al2O3 is the industrial catalyst used for methanol synthesis from syngas (CO + H2) and is also promising for the hydrogenation of CO2 to methanol. In this work, we synthesized Al2O3 nanorods (n-Al2O3) and impregnated them with the CuZnO component. The catalysts were evaluated for the hydrogenation of CO2 to methanol in a fixed-bed reactor. The support and the catalysts were characterized, including via in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The study of the CO2 adsorption, activation, and hydrogenation using in situ DRIFT spectroscopy revealed the different roles of the catalyst components. CO2 mainly adsorbed on the n-Al2O3 support, forming carbonate species. Cu was found to facilitate H2 dissociation and further reacted with the adsorbed carbonates on the n-Al2O3 support, transforming them to formate or additional intermediates. Like the n-Al2O3 support, the ZnO component contributed to improving the CO2 adsorption, facilitating the formation of more carbonate species on the catalyst surface and enhancing the efficiency of the CO2 activation and hydrogenation into methanol. The synergistic interaction between Cu and ZnO was found to be essential to increase the space–time yield (STY) of methanol but not to improve the selectivity. The 3% CuZnO/n-Al2O3 displayed improved catalytic performance compared to 3% Cu/n-Al2O3, reaching a CO2 conversion rate of 19.8% and methanol STY rate of 1.31 mmolgcat−1h−1 at 300 °C. This study provides fundamental and new insights into the distinctive roles of the different components of commercial methanol synthesis catalysts.

A computational study of direct CO2 hydrogenation to methanol on Pd surfaces

The reaction mechanism of direct CO₂ hydrogenation to methanol is investigated in detail on Pd (111), (100) and (110) surfaces using density functional theory (DFT), supporting investigations into emergent Pd-based catalysts. Hydrogen adsorption and surface mobility are firstly considered, with high-coordination surface sites having the largest adsorption energy and being connected by diffusion channels with low energy barriers. Surface chemisorption of CO₂, forming a partially charged CO₂^δ-, is weakly endothermic on a Pd (111) whilst slightly exothermic on Pd (100) and (110), with adsorption enthalpies of 0.09, -0.09 and -0.19 eV, respectively; the low stability of CO₂^δ- on the Pd (111) surface is attributed to negative charge accumulating on the surface Pd atoms that interact directly with the CO₂^δ- adsorbate. Detailed consideration for sequential hydrogenation of the CO₂ shows that HCOOH hydrogenation to H₂COOH would be the rate determining step in the conversion to methanol, for all surfaces, with activation barriers of 1.41, 1.51, and 0.84 eV on Pd (111), (100) and (110) facets, respectively. The Pd (110) surface exhibits overall lower activation energies than the most studied Pd (111) and (100) surfaces, and therefore should be considered in more detail in future Pd catalytic studies.

Hydrogenation of carbon dioxide (CO2) to fuels in microreactors: a review of set-ups and value-added chemicals production

A review of CO2 hydrogenation to fuels and value-added chemicals in microreactors.

Synergetic effect of metal–support for enhanced performance of the Cu–ZnO–ZrO2/UGSO catalyst for CO2 hydrogenation to methanol

Novel Cu–ZnO–ZrO2/UGSO catalysts for CO2 hydrogenation to methanol were developed using a metallurgical residue as catalytic support, focusing on (i) the synergy of Cu/Zn/Zr and UGSO composition and (ii) UGSO modification, on catalytic activity and stability.

On the Effect of Cobalt Promotion over Ni/CeO2 Catalyst for CO2 Thermal and Plasma Assisted Methanation

In recent years, carbon dioxide hydrogenation leading to synthetic fuels and value-added molecules has been proposed as a promising technology for stabilizing anthropogenic greenhouse gas emissions. Methanation or Sabatier are possible reactions to valorize the CO2. In the present work, thermal CO2 methanation and non-thermal plasma (NTP)-assisted CO2 methanation was performed over 15Ni/CeO2 promoted with 1 and 5 wt% of cobalt. The promotion effect of cobalt is proven both for plasma and thermal reaction and can mostly be linked with the basic properties of the materials.

CO2 Hydrogenation to Olefin-Rich Hydrocarbons Over Fe-Cu Bimetallic Catalysts: An Investigation of Fe-Cu Interaction and Surface Species

Previously, we reported a strong Fe-Cu synergy in CO2 hydrogenation to olefin-rich C2+ hydrocarbons over the γ-Al2O3 supported bimetallic Fe-Cu catalysts. In this work, we aimed to clarify such a synergy by investigating the catalyst structure, Fe-Cu interaction, and catalyst surface properties through a series of characterizations. H2-TPR results showed that the addition of Cu made both Fe and Cu easier to reduce via the strong interaction between Fe and Cu. It was further confirmed by X-ray absorption spectroscopy (XAS) and TEM, which showed the presence of metallic Fe and Fe-Cu alloy phases in the reduced Fe-Cu(0.17) catalyst induced by Cu addition. By correlating TPD results with the reaction performance, we found that the addition of Cu enhanced both the moderately and strongly adsorbed H2 and CO2 species, consequently enhanced CO2 conversion and C2+ selectivity. Adding K increased the adsorbed-CO2/adsorbed-H2 ratio by greatly enhancing the moderately and strongly adsorbed CO2 and slightly suppressing the moderately and strongly adsorbed H2, resulting in a significantly increased O/P ratio in the produced hydrocarbons. The product distribution analysis and in situ DRIFTS suggested that CO2 hydrogenation over the Fe-Cu catalyst involved both an indirect route with CO as the primary product and a direct route to higher hydrocarbons.

Active Sites and Interfacial Reducibility of CuxO/CeO2 Catalysts Induced by Reducing Media and O2/H2 Activation

The development of a highly efficient and stable catalyst for preferential oxidation of CO for the commercialization of proton-exchange membrane fuel cells has been a result of continuous effort. The main challenge is the simultaneous control of abundant active sites and interfacial reducibility over the catalyst Cu_xO/CeO₂. Here, we report a strategy to modulate porosity, active sites, and O-vacancy sites (O_V) by reducing media and O₂/H₂ activation. O₂-pretreated CeO₂-supported Cu catalysts unequivocally demonstrate the low-temperature activity owing to the excess concentrations of Cu⁺ and Cu²⁺ as well as the relative population of Ce³⁺ and O-vacancy sites at the surface. O₂ activation improves the Cu²⁺ diffusion into the CeO₂ lattice to generate the synergistic effect and induces the formation of electron-enriched Cu²⁺-O_V-Ce³⁺ sites, which accelerate the activation and dissociation of CO/O₂ and the formation of reactive oxygen species during catalysis. Density function theory (DFT) calculations reveal that CO adsorbs on Cu₂O {110} and CuO {111} with relatively optimal adsorption energy and longer C-Cu lengths in contrast to that on Cu {111}, favoring the adsorption and desorption of CO. These are crucial for ongoing CO oxidation, producing CO₂ by the Mars-van Krevelen mechanism.

CO2 reduction and ethane dehydrogenation on transition metal catalysts: mechanistic insights, reactivity trends and rational design of bimetallic alloys

Reactivity trends of transition metal catalysts, studied for the ethane dehydrogenation reaction using CO₂ as a mild oxidant.

Recent advances in hydrogenation of CO2 into hydrocarbons via methanol intermediate over heterogeneous catalysts

This review provides recent advances in the conversion of CO₂ to methanol, methanol to hydrocarbons, and direct conversion of CO₂ to hydrocarbons via methanol intermediate over various monofunctional and bifunctional solid catalysts.

Selectivity controlled transformation of carbon dioxide into a versatile bi-functional multi-carbon oxygenate using a physically mixed ruthenium–iridium catalyst

The efficiency of supercritical CO₂ (scCO₂) as a reactant was successfully unfolded in the synthesis of a high-value C₂₊ oxygenate via hydrogenation and C–C bond formation under comparatively mild conditions.

Surface reaction kinetics of the methanol synthesis and the water gas shift reaction on Cu/ZnO/Al2O3

Detailed modeling of the methanol synthesis combining theoretical surface kinetics, catalyst structural changes, and a broad experimental validation.

Trends and Outlook of Computational Chemistry and Microkinetic Modeling for Catalytic Synthesis of Methanol and DME

The first-principle modeling of heterogeneous catalysts is a revolutionarily approach, as the electronic structure of a catalyst is closely related to its reactivity on the surface with reactant molecules. In the past, detailed reaction mechanisms could not be understood, however, computational chemistry has made it possible to analyze a specific elementary reaction of a reaction system. Microkinetic modeling is a powerful tool for investigating elementary reactions and reaction mechanisms for kinetics. Using a microkinetic model, the dominant pathways and rate-determining steps can be elucidated among the competitive reactions, and the effects of operating conditions on the reaction mechanisms can be determined. Therefore, the combination of computational chemistry and microkinetic modeling can significantly improve computational catalysis research. In this study, we reviewed the trends and outlook of this combination technique as applied to the catalytic synthesis of methanol (MeOH) and dimethyl ether (DME), whose detailed mechanisms are still controversial. Although the scope is limited to the catalytic synthesis of limited species, this study is expected to provide a foundation for future works in the field of catalysis research based on computational catalysis.

How Size Matters: Electronic, Cooperative, and Geometric Effect in Perovskite-Supported Copper Catalysts for CO2 Reduction

In heterogeneous catalysis, bifunctional catalysts often outperform one-component catalysts. The activity is also strongly influenced by the morphology, size, and distribution of catalytic particles. For CO2 hydrogenation, the size of the active copper area on top of the SrTiO3 perovskite catalyst support can affect the activity, selectivity, and stability. Here, a detailed theoretical study of the effect of bifunctionality on an important chemical CO2 transformation reaction, the reverse water gas shift (RWGS) reaction, is presented. Using density functional theory computation results for the RWGS pathway on three surfaces, namely, Cu(111), SrTiO3, and the Cu/SrTiO3 interface between both solid phases, we construct the energy landscape of the reaction. The adsorbate-adsorbate lateral interactions are taken into account for catalytic surfaces, which show a sufficient intermediate coverage. The mechanism, combining all three surfaces, is used in mesoscale kinetic Monte Carlo simulations to study the turnover and yield for CO production as a function of particle size. It is shown that the reaction proceeds faster at the interface. However, including copper and the support sites in addition to the interface accelerates the conversion even further, showing that the bifunctionality of the catalyst manifests in a more complex interplay between the phases than just the interface effect, such as the hydrogen spillover. We identify three distinct effects, the electronic, cooperative, and geometric effects, and show that the surrounded smaller Cu features on the set of supporting SrTiO3 show a higher CO formation rate, resulting in a decreasing RWGS model trend with the increasing Cu island size. The findings are in parallel with experiments, showing that they explain the previously observed phenomena and confirming the size sensitivity for the catalytic RWGS reaction.

CO2 Hydrogenation to Methanol over La2O3-Promoted CuO/ZnO/Al2O3 Catalysts: A Kinetic and Mechanistic Study

The hydrogenation of CO2 to methanol has been investigated over CuO/ZnO/Al2O3 (CZA) catalysts, where a part of the Al2O3 (0, 25, 50, 75, or 100%) was substituted by La2O3. Results of catalytic performance tests obtained at atmospheric pressure showed that the addition of La2O3 generally resulted in a decrease of CO2 conversion and in an increase of methanol selectivity. Optimal results were obtained for the CZA-La50 catalyst, which exhibited a 30% higher yield of methanol, compared to the un-promoted sample. This was attributed to the relatively high specific surface area and porosity of this material, the creation of basic sites of moderate strength, which enhance adsorption of CO2 and intermediates that favor hydrogenation steps, and the ability of the catalyst to maintain a large part of the copper in its metallic form under reaction conditions. The reaction mechanism was studied with the use of in situ infrared spectroscopy (DRIFTS). It was found that the reaction proceeded with the intermediate formation of surface formate and methoxy species and that both methanol and CO were mainly produced via a common formate intermediate species. The kinetic behavior of the best performing CZA-La50 catalyst was investigated in the temperature range 190–230 °C as a function of the partial pressures of H2 (0.3–0.9 atm) and CO2 (0.05–0.20 atm), and a kinetic model was developed, which described the measured reaction rates satisfactorily.

Ni–Zn–Al-Based Oxide/Spinel Nanostructures for High Performance, Methane-Selective CO2 Hydrogenation Reactions

Abstract

In the present study, NiO modified ZnAl2O4 and ZnO modified NiAl2O4 spinel along with pure Al2O3, ZnAl2O4 and NiAl2O4 for comparison in the CO2 hydrogenation reaction have been investigated. It was found that NiAl2O4, NiO/ZnAl2O4 and ZnO/NiAl2O4 catalysts exhibited outstanding activity and selectivity towards methane even at high temperature compared to similar spinel structures reported in the literature. NiO/ZnAl2O4 catalyst showed CO2 consumption rate of ~ 19 μmol/g·s at 600 °C and ~ 85% as well as ~ 50% of methane selectivity at 450 °C and 600 °C, respectively. The high activity and selectivity of methane can be attributed to the presence of metallic Ni and Ni/NiO/ZnAl2O4 interface under the reaction conditions as evidenced by the XRD results.

Graphic Abstract

High performance Ni–Zn–Al-based oxide/spinel nanostructures is synthesized and NiO/ZnAl2O4 catalyst exhibited higher catalytic activity in the CO2 hydrogenation reaction due to the presence of metal support interaction between Ni and ZnAl2O4 support.

Analysis of Mass Transport through Anisotropic, Catalytic/Bio-Catalytic Membrane Reactors

This paper investigated the steady-state mass transport process through anisotropic, composite membrane layers with variable mass transport coefficients, such as the diffusion coefficient, convective velocity, or chemical/biochemical reaction rate constant. The transfer processes can be a solution-diffusion model or diffusive plus convective process. In the theoretical part, the concentration distribution as well as the inlet and outlet mass transfer rates’ expressions are defined for physical transport processes with variable diffusion or solubility coefficients and then that for transport processes accompanied by first- and zero-order reactions, in the presence of diffusive and convective flow, with constant and variable parameters. The variation of the transport parameters as a function of the local coordinate was defined by linear equations. It was shown that the increasing diffusion coefficient or convective flow induces much lower concentrations across the membrane layer than transport processes, with their decreasing values a function of the space coordinate. Accordingly, this can strongly affect the effect of the concentration dependent chemical/biochemical reaction. The inlet mass transfer rate can also be mostly higher when the transport parameter decreases across the anisotropic membrane layer.