Reaction mechanisms of methanol synthesis from CO/CO 2 hydrogenation on Cu 2 O(111): Comparison with Cu(111)

Theoretical study of the effects of surface Cu coordination environment on CO2 hydrogenation to CH3OH

The coordination environment of Cu (the coordination number and arrangement of surface atoms) plays an important role in CO2 hydrogenation to CH3OH. Compared with the extensive studies of the effects of coordination number, the comprehensive effects of coordination number and arrangement of surface atoms were seldom explored in literature. To unravel the effects of surface Cu coordination environment on CO2 hydrogenation to CH3OH, the adsorption and reaction behaviors of H2 and CO2 on Cu(111), (100), (110) and (211) with different coordination numbers and arrangement of surface Cu were systematically calculated by density functional theory (DFT) and kinetic Monte Carlo (kMC) simulation. It was found that the adsorption energies of intermediates in CO2 hydrogenation on Cu surfaces increase with the decrease of coordination number. When the Cu coordination numbers are similar, the charge density on the open surface derived from the different atom arrangement becomes larger and leads to stronger interaction with intermediates than that on the compact one. DFT calculation and kMC simulation indicate that methanol formation pathway follows CO2*→HCOO*→HCOOH*→H2COOH*→H2CO*→CH3O*→CH3OH* on four Cu facets; CO formation is via CO2 direct dissociation on Cu(111), (100) and (110) but COOH* dissociation on (211). The low-coordinated surface Cu with more openness on Cu(211) is the highly active site for CO2 hydrogenation to CH3OH with high turnover of frequency (3.71 × 10-4 s-1) and high selectivity (87.17 %) at 600 K, PCO2 = 7.5 atm and PH2 = 22.5 atm, which is much higher than those on Cu(111), (100) and (110). This work unravels the effects of coordination environment on CO2 hydrogenation at the molecular level and provides an important insight into the design and development of catalysts with high performance in CO2 hydrogenation to CH3OH.

Sustainable methanol production from carbon dioxide: advances, challenges, and future prospects

The urgent need to address global carbon emissions and promote sustainable energy solutions has led to a growing interest in carbon dioxide (CO2) conversion technologies. Among these, the transformation of CO2 into methanol (MeOH) has gained prominence as an effective mitigation strategy. This review paper provides a comprehensive exploration of recent advances and applications in the direct utilization of CO2 for the synthesis of MeOH, encompassing various aspects from catalysts to market analysis, environmental impact, and future prospects. We begin by introducing the current state of CO2 mitigation strategies, highlighting the significance of carbon recycling through MeOH production. The paper delves into the chemistry and technology behind the conversion of CO2 into MeOH, encompassing key themes such as feedstock selection, material and energy supply, and the various conversion processes, including chemical, electrochemical, photochemical, and photoelectrochemical pathways. An in-depth analysis of heterogeneous and homogeneous catalysts for MeOH synthesis is provided, shedding light on the advantages and drawbacks of each. Furthermore, we explore diverse routes for CO2 hydrogenation into MeOH, emphasizing the technological advances and production processes associated with this sustainable transformation. As MeOH holds a pivotal role in a wide range of chemical applications and emerges as a promising transportation fuel, the paper explores its various chemical uses, transportation, storage, and distribution, as well as the evolving MeOH market. The environmental and energy implications of CO2 conversion to MeOH are discussed, including a thermodynamic analysis of the process and cost and energy evaluations for large-scale catalytic hydrogenation.

Preparation of catalyst for CO2 hydrogenation reaction based on the idea of element sharing and preliminary exploration of catalytic mechanism

Under the background of the continuous rise of CO2 annual emissions, the development of CO2 capture and utilization technology is urgent. This study focuses on improving the catalytic capacity of the catalyst for CO2 hydrogenation, improving the efficiency of CO2 conversion to methanol, and converting H2 into chemical substances to avoid the danger of H2 storage. Based on the concept of element sharing, the ASMZ (Aluminum Shares Metal Zeolite catalysts) series catalyst was prepared by combining the CuO-ZnO-Al2O3 catalyst with the ZSM-5 zeolite using the amphoteric metal properties of the Al element. The basic structural properties of ASMZ catalysts were compared by XRD, FTIR, and BET characterization. Catalytic properties of samples were measured on a micro fixed-bed reactor. The catalytic mechanism of the catalyst was further analyzed by SEM, TEM, XPS, H2-TPR, and NH3-TPD. The results show that the ASMZ3 catalyst had the highest CO2 conversion rate (26.4%), the highest methanol selectivity (76.0%), and the lowest CO selectivity (15.3%) in this study. This is mainly due to the fact that the preparation method in this study promotes the exposure of effective weakly acidic sites and medium strength acidic sites (facilitating the hydrogenation of CO2 to methanol). At the same time, the close binding of Cu-ZnO-Al2O3 (CZA) and ZSM-5 zeolite also ensures the timely transfer of catalytic products and ensures the timely play of various catalytic active centers. The preparation method of the catalyst in this study also provides ideas for the preparation of other catalysts.

Carbon Dioxide Conversion on Supported Metal Nanoparticles: A Brief Review

The increasing concentration of anthropogenic CO2 in the air is one of the main causes of global warming. The Paris Agreement at COP 21 aims to reach the global peak of greenhouse gas emissions in the second half of this century, with CO2 conversion towards valuable added compounds being one of the main strategies, especially in the field of heterogeneous catalysis. In the current search for new catalysts, the deposition of metallic nanoparticles (NPs) supported on metal oxides and metal carbide surfaces paves the way to new catalytic solutions. This review provides a comprehensive description and analysis of the relevant literature on the utilization of metal-supported NPs as catalysts for CO2 conversion to useful chemicals and propose that the next catalysts generation can be led by single-metal-atom deposition, since in general, small metal particles enhance the catalytic activity. Among the range of potential indicators of catalytic activity and selectivity, the relevance of NPs’ size, the strong metal–support interactions, and the formation of vacancies on the support are exhaustively discussed from experimental and computational perspective.

Differences in Deterioration Behaviors of Cu/ZnO/Al2O3 Catalysts with Different Cu Contents toward Hydrogenation of CO and CO2

The deterioration behaviors of Cu/ZnO/Al₂O₃ (CZA) catalysts upon different Cu contents were elucidated. The fresh and spent catalysts after being used in CO and CO₂ hydrogenation at 250 °C under atmospheric pressure were properly characterized using various techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy, and temperature-programmed reduction for the changes of metal sites, while the textural and chemical properties and carbon deposition on spent CZA catalysts were analyzed by N₂ physisorption, energy-dispersive X-ray spectroscopy, and temperature-programmed oxidation. During the hydrogenation reaction for both CO and CO₂, the unstable Cu⁰ site on the spent CZA catalyst having a low Cu loading (sCZA-L) was oxidized to CuO and the aggregation of metal crystallite sites (Cu-ZnO and ZnO) was observed. Moreover, the amount of carbon deposition on sCZA-L (ca. >2%) is higher than the spent CZA catalyst having a high Cu loading (sCZA-H, ca. <0.5%). These phenomena led to a decrease in the surface area and the blockage of active sites. These findings can be determined on the catalytic deactivation and the obvious decrease in the catalytic activity of the CZA catalyst having a low Cu content (CZA-L, Cu:Zn = 0.8).

Conversion of carbon dioxide to methanol: A comprehensive review

This review explains the various methods of conversion of Carbon dioxide (CO₂) to methanol by using homogenous, heterogeneous catalysts through hydrogenation, photochemical, electrochemical, and photo-electrochemical techniques. Since, CO₂ is the major contributor to global warming, its utilization for the production of fuels and chemicals is one of the best ways to save our environment in a sustainable manner. However, as the CO₂ is very stable and less reactive, a proper method and catalyst development is most important to break the CO₂ bond to produce valuable chemicals like methanol. Litertaure says the catalyt types, ratio and it surface structure along with the temperature and pressure are the most controlling parameters to optimize the process for the production of methanol from CO₂. This article explains about the various controlling parameters of synthesis of Methanol from CO₂ along with the advantages and drawbacks of each process. The mechanism of each synthesis process in presence of metal supported catalyst is described. Basically the activity of Cu supported catalyst and its stability based on the activity for the methanol synthesis from CO₂ through various methods is critically described.

Recent advances in the routes and catalysts for ethanol synthesis from syngas

Ethanol, as one of the important bulk chemicals, is widely used in modern society. It can be produced by fermentation of sugar, petroleum refining, or conversion of syngas (CO/H₂). Among these approaches, conversion of syngas to ethanol (STE) is the most environmentally friendly and economical process. Although considerable progress has been made in STE conversion, control of CO activation and C-C growth remains a great challenge. This review highlights recent advances in the routes and catalysts employed in STE technology. The catalyst designs and pathway designs are summarized and analysed for the direct and indirect STE routes, respectively. In the direct STE routes (i.e., one-step synthesis of ethanol from syngas), modified catalysts of methanol synthesis, modified catalysts of Fischer-Tropsch synthesis, Mo-based catalysts, noble metal catalysts and multifunctional catalysts are systematically reviewed based on their catalyst designs. Further, in the indirect STE routes (i.e., multi-step processes for ethanol synthesis from syngas via methanol/dimethyl ether as intermediates), carbonylation of methanol/dimethyl ether followed by hydrogenation, and coupling of methanol with CO to form dimethyl oxalate followed by hydrogenation, are outlined according to their pathway designs. The goal of this review is to provide a comprehensive perspective on STE technology and inspire the invention of new catalysts and pathway designs in the near future.

Photocatalytically-assisted oxidative adsorption of As(III) using sustainable multifunctional composite material - Cu2O doped anion exchanger

The purpose of the presented study was to explore the photocatalytic activity of Cu₂O-supported anion exchangers and to explain the mechanism of their action in water purification processes. The functionality of this type of material was studied in the process of As(III) removal from water. As a result of the reactivity of cuprous oxide and functional groups of the polymer, the obtained composite exhibited complex activity towards arsenic(III) species. The adsorption studies were conducted under various conditions: dark, UV-VIS irradiation, VIS irradiation, under aerobic and anoxic conditions. The results from chemical analyses were supported by instrumental analyses - X-ray photoelectron spectroscopy, and FTIR and Raman spectroscopy. These studies showed that the mechanism of As(III) oxidative adsorption is based on the coupling of several reaction pathways: 1) photocatalytic oxidation involving Cu₂O as a photocatalyst, and photogenerated holes and ROS as oxidative agents, 2) chemical oxidation on the surface of CuO (being a result of the ageing process) with a re-oxidation of the produced Cu₂O to CuO by ROS and oxygen present in water, and 3) photochemical oxidation of As(III) in solution under UV light irradiation and subsequent adsorption of arsenates in the functional groups of the polymer.

Catalytic Hydrogenation of CO2 to Methanol: A Review

High-efficiency utilization of CO2 facilitates the reduction of CO2 concentration in the global atmosphere and hence the alleviation of the greenhouse effect. The catalytic hydrogenation of CO2 to produce value-added chemicals exhibits attractive prospects by potentially building energy recycling loops. Particularly, methanol is one of the practically important objective products, and the catalytic hydrogenation of CO2 to synthesize methanol has been extensively studied. In this review, we focus on some basic concepts on CO2 activation, the recent research advances in the catalytic hydrogenation of CO2 to methanol, the development of high-performance catalysts, and microscopic insight into the reaction mechanisms. Finally, some thinking on the present research and possible future trend is presented.

Comparative study on the effect of different copper loading on catalytic behaviors and activity of Cu/ZnO/Al2O3 catalysts toward CO and CO2 hydrogenation

The ternary Cu/ZnO/Al₂O₃ (CZA) catalysts having different Cu loading were prepared by the co-precipitation method. Then, they were used in CO and CO₂ hydrogenation to produce methanol under atmospheric pressure at 250 °C. The high Cu loading CZA catalyst (CZA-H) resulted in the enhancement of structural features and textural properties (e.g., BET surface area and the crystallite size of copper species). Furthermore, the conversion of CO and CO₂ over CZA-H catalyst was apparently higher than that of the CZA-L (low Cu loading) catalyst. The major product of CO hydrogenation obtained from both catalysts was methanol, whereas in CO₂ hydrogenation, the main product was CO. Deactivation of catalysts was also crucial during CO and CO₂ hydrogenation. Therefore, the spent catalysts were determined to identify the nature of carbon formation. It revealed that amorphous and graphitic cokes were present. These cokes have different mechanisms in the elimination from the surface leading to influencing the deactivation process. The spent CZA-L was found to have higher carbon content, which was around 2.3% and 3.1% for CO and CO₂ hydrogenation, respectively. Besides the amorphous coke, the graphitic coke was also observed in CZA-L after time on stream for 5 h.

In Situ IR Studies on the Mechanism of Dimethyl Carbonate Synthesis from Methanol and Carbon Dioxide

The synthesis of dimethyl carbonate (DMC) from methanol and Carbon dioxide (CO2) has been investigated over 5% Rh/Al2O3 catalyst. Diffuse Reflectance Infrared Fourier Transfer Spectroscopy (DRIFTS) was used to probe the reaction adsorbates which showed that activation of methanol and CO2 involves generation of intermediate methoxy species and formate ingredients, participating in elementary steps of DMC formation. Formation of DMC involves parallel routes comprising interaction of the OH group of Al2O3 through an acid/base mechanism and formate pathway with participation of metal sites. DMC in acid/base pathway is formed via methoxy species to form methoxy carbonate (CH3O)CO2 (active adsorbate), which then reacts with the methyl species to form DMC. The pathway involving metal Rh sites generates an additional elementary step for the involvement of CO2 in the reaction through active formate species. The synergy of parallel pathways determines the performance of the 5% Rh/Al2O3 catalyst. Further improvement of catalyst performance should be based on such a feature of the reaction mechanism.

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.

DFT study the water-gas shift reaction over Cu/α-MoC surface

Cu-based catalysts have been widely used for water-gas shift reaction (WGS, CO + H₂O → CO₂ + H₂), and α-MoC support also shows the good performance for the reaction. Therefore, WGS reaction is systematically studied over Cu/α-MoC by using density functional theory (DFT). DFT result shows the strong metal-support interaction between Cu and α-MoC(111) support. As a result, an extensive tensile strain is introduced in the Cu lattice due to α-MoC support, and Cu 3d band center shifts to Fermi level. However, the strong metal-support interaction does not lead to significant polarization of the Cu/α-MoC surface due to the less charge transfer from Mo to Cu. For the WGS reaction, small Cu particles on α-MoC(111) are likely to facilitate the reaction. At the interface of Cu-α-MoC(111), oxygen stabilizes the dissociated *H, which is benefit of H₂O scission. Then, the activity increases compared with Cu(111) surface. In general, small Cu particles on α-MoC support also have good activity for WGS reaction compared with Au deposition on α-MoC. Graphical abstract.

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.

Study on the Adsorption and Activation Behaviours of Carbon Dioxide over Copper Cluster (Cu4) and Alumina-Supported Copper Catalyst (Cu4/Al2O3) by means of Density Functional Theory

The adsorption and activation of carbon dioxide over copper cluster (Cu4) and copper doped on the alumina support (Cu4/Al2O3) catalytic systems have been investigated by using density functional theory and climbing image nudged elastic band. The adsorption energies, geometrical configurations, and electronic properties are analysed. The results show the strong chemical interaction between the copper cluster and the alumina support. Both the Cu4 cluster and Cu4/Al2O3 systems have a high adsorption ability for CO2, and the adsorption process is of chemical nature. The role of the alumina support in the adsorption and activation of CO2 has been addressed. The calculated results show that the “synergistic effect” between Al2O3 and Cu4 is the key factor in the activation of CO2.

Interaction of CO, O, and CO2 with Cu cluster supported on Cu(1 1 1): a density functional theory study

We performed density functional theory (DFT) based calculations to investigate the interaction of CO₂ and its dissociated species (CO and O) on Cu₃ cluster supported on Cu(1 1 1) (Cu₃/Cu(1 1 1)) surfaces. Similar investigations were conducted on Cu(1 1 1) for purpose of comparison. In general, adsorption of CO and O are stronger on the cluster region than on the terrace region of Cu₃/Cu and on the flat Cu surface. CO₂, on the other hand, is weakly adsorbed on the surfaces. With reference to CO₂ dissociation on Cu(1 1 1), we found that the cluster lowers the activation barrier and provides a more stable adsorption of the dissociated species. The presence of co-adsorbed CO in the cluster, however, will increase the activation energy. The variation in the activation barrier with the amount of CO is influenced by the stability of the O atom from the dissociated CO₂. We further found that the adsorption energy of O atom is a possible descriptor for CO₂ dissociation on the cluster region. The Cu cluster supported on Cu surface could be a promising catalyst for CO₂ related reactions based on the lower activation energy for CO₂ dissociation on the system than on Cu(1 1 1).

DFT and microkinetic investigation of methanol synthesis via CO2 hydrogenation on Ni(111)-based surfaces

A DFT study of methanol production via CO2 hydrogenation reactions on clean Ni(111) and Ni(111)-M (M = Cu, Pd, Pt, or Rh) surfaces has been performed. The reaction network of this synthesis reaction has been determined using energy profiles. The competing reaction network between the formate-mediated route and the carboxyl-mediated route is also presented. Both routes are equally possible in mediating the overall synthesis reactions. A simple selectivity analysis based on the energy barrier shows that methanol synthesis is more preferred rather than formic acid (HCOOH) or carbon monoxide (CO) production. A mean-field kinetic analysis is also employed to determine the kinetic performance of all catalytic surfaces. The formate-mediated route is found to be energetically and kinetically more dominant than the carboxyl-mediated route. Cu, Pd, and Pt dopants are successful in increasing the kinetic performance of the clean Ni(111) surface in the formate route and Cu, Pt, and Rh dopants in the carboxyl route.

Surface Segregation in CuNi Nanoparticle Catalysts During CO2 Hydrogenation: The Role of CO in the Reactant Mixture

Surface segregation and restructuring in size-selected CuNi nanoparticles were investigated via near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at various temperatures in different gas environments. Particularly in focus were structural and morphological changes occurring under CO₂ hydrogenation conditions in the presence of carbon monoxide (CO) in the reactant gas mixture. Nickel surface segregation was observed when only CO was present as adsorbate. The segregation trend is inverted in a reaction gas mixture consisting of CO₂, H₂, and CO, resulting in an increase of copper concentration on the surface. Density functional theory calculations attributed the inversion of the segregation trend to the formation of a stable intermediate on the nanocatalyst surface (CH₃O) in the CO-containing reactant mixture, which modifies the nickel segregation energy, thus driving copper to the surface. The promoting role of CO for the synthesis of methanol was demonstrated by catalytic characterization measurements of silica-supported CuNi NPs in a fixed-bed reactor, revealing high methanol selectivity (over 85%) at moderate pressures (20 bar). The results underline the important role of intermediate reaction species in determining the surface composition of bimetallic nanocatalysts and help understand the effect of CO cofeed on the properties of CO₂ hydrogenation catalysts.

A DFT study of the catalytic pyrolysis of benzaldehyde on ZnO, γ-Al2O3, and CaO models

The catalytic pyrolysis pathways of carbonyl compounds in coal were systematically studied using density functional theory (DFT), with benzaldehyde (C₆H₅CHO) employed as a coal-based model compound and ZnO, γ-Al₂O₃, and CaO as catalysts. The results show that the products of both pyrolysis and catalytic pyrolysis are C₆H₆ and CO. However, the presence of any of the catalysts changes the reaction pathway and reduces the energy barrier, indicating that these catalysts promote C₆H₅CHO decomposition. Graphical abstract The presence of catalysts changes the reaction pathway and the energy barrier decreases in the order Ea (no catalyst)> Ea (CaO)> Ea (γ-Al₂O₃)> Ea (ZnO), indicating that these catalysts promote C₆H₅CHO decomposition.