Flame Synthesis of Cu/ZnO-CeO2 Catalysts: Synergistic Metal-Support Interactions Promote CH3OH Selectivity in CO2 Hydrogenation

Electron Transport Chains Promote Selective Photocatalytic Conversion of CO2 to Methanol

The photocatalytic conversion of carbon dioxide (CO2) into "liquid sunshine" methanol (CH3OH) using semiconductor catalysts has garnered significant attention. Increasing the number of effective electrons and regulating reaction pathways is the key to improving the activity and selectivity of CH3OH. Due to the electron transport properties of semiconductor heterojunctions and reduced graphene oxide (rGO), a CoS/CoS2-rGO nanocomposite was constructed and applied to the photocatalytic reduction of CO2 to CH3OH. The optimized CoS/CoS2-rGO-5 photocatalyst achieved a CH3OH production rate of 15.26 μmol·g-1 and a selectivity of 42%, which were higher than those of CoS and CoS/CoS2. This is mainly attributed to the fact that CoS/CoS2 and rGO jointly constructed efficient electron transport chains, which not only ensure that photogenerated electrons can achieve orderly and directional migration but also innovatively establish a dual reaction site mechanism, providing strong support for improving photocatalytic activity and selectivity of CH3OH. The design of composite catalysts by coupling of semiconductor heterojunctions with carbon material affords new territory for efficient photogenerated electron transport and provides alternative pathways for photocatalytic CO2 conversion.

Controlling Metal-Support Interactions to Engineer Highly Active and Stable Catalysts for COx Hydrogenation

This perspective focuses on the modulation of metal-support interaction (MSI) in catalysts for COx hydrogenation, highlighting their profound impact on catalytic performance. Firstly, it outlines different strategies, including the use of highly reducible oxides and moderate reduction treatments, which induce the classical strong metal-support interaction (SMSI) effect and the electronic metal-support interaction (EMSI) effect. Morphology engineering and crystalline phase manipulation of oxides presented as effective methods to control EMSI are also discussed. The discrimination of SMSI and EMSI can be achieved using oxides with low encapsulation tendencies, such as ZrO2, which supports electronic modifications without or minimizing the overgrowth issues, optimizing the catalytic performance for methanation. Then, the synergy between Cu and ZnO in methanol synthesis, enhanced by SMSI, is emphasized inside. Optimizing support oxides to control oxygen vacancies enhances the catalytic performance of CO2 hydrogenation to methanol. Perspectives for the future research on the fundamental understanding of structure-MSI-performance relationship for catalyst design is discussed.

Confinement Synthesis of Atomic Copper-Anchored Polymeric Carbon Nitride in Crystalline UiO-66-NH2 for High-Performance CO2-to-CH3OH Photocatalysis

Photocatalytic CO2 reduction to value-added fuels displays an attractive scenario to enhance energy supply and reduce global warming. We report herein the confinement synthesis of polymeric carbon nitride (PCN) incorporating with Cu single atoms (CuSAs) inside the crystalline UiO-66-NH2, which combines the merits of heterojunction photocatalysis and single-atom catalysis (SAC) to achieve high-performance CO2-to-CH3OH conversion. A series of spectral studies displays the formation of CuSAs@PCN inside the crystalline UiO-66-NH2. Remarkably, the ternary composite shows an excellent photocatalytic turnover frequency of 4.15 mmol ⋅ h-1 ⋅ g-1 for CO2-to-CH3OH conversion. Theoretical and experimental studies demonstrate the doping of CuSAs, as well as the formation of type-II heterojunction, are causal factors to achieve CH3OH generation. The study provides new insights designing high-performance photocatalyst for CO2 conversion to fuels at atomic scale.

Exploring carbon-based Cu-ZnO catalyst and substitutes for enhanced selective methanol production from CO2: An integrated experimental and computational study

Methanol, produced through the hydrogenation of carbon dioxide, is an essential intermediate compound that plays a crucial function in the production of various organic chemicals. Enhancing the design of copper-containing catalysts for the transformation of CO2 to methanol is a popular strategy in scientific literature, although challenges persist in advancing the efficiency of carbon dioxide transformation and the selectivity of methanol production. This research aims at creating CuZnO-M/rGO (M = Mg, Mn, and Cr) catalysts using an efficient method for selectively converting CO2 to methanol. By optimizing the operational parameters of this system, methanol productivity and CO2 conversion efficiency are enhanced. Under optimal conditions, a CO2 conversion rate of 23.5%, methanol selectivity of 90%, and a space-time yield of 0.47 gMeOH.gcat-1.h-1 were achieved with the CuZnO-MgO (5)/rGO catalyst. These levels were maintained over a 100-h period, demonstrating the stability of the catalyst system. These findings are highly consistent with the density functional theory (DFT) calculations, revealing that the CuZnO-MgO (5)/rGO catalyst possesses a -0.35 eV adsorption energy for CO2 and a favorable reaction pathway with the overpotential of 1.16 V towards methanol production emphasizing the high conversion and selectivity obtained.

Efficient reverse water gas shift reaction at low temperatures over an iron supported catalyst under an electric field

The development of high-performance Fe-based catalysts is attractive because Fe is a cost-effective and earth-abundant element. Application of an external electric field and an appropriate catalytic support to an Fe-based catalyst enabled the reverse water-gas shift reaction to proceed with high activity, selectivity, and durability even at the low temperature of 423 K. The Fe-supported catalyst showed superior CO selectivity (≈ 100%) compared to the Co- or Ni-supported catalyst. The apparent activation energy (5.9 kJ mol-1) over the Fe/Ce0.4Al0.1Zr0.5O2 catalyst under an electric field was much lower than that without an electric field (61.4 kJ mol-1).

Morphologically tuned CuO-ZnO-CeO2 catalyst for CO2 hydrogenation to methanol

Morphologically modified composite CuO-ZnO-CeO2 catalysts were synthesized using a single-step hydrothermal technique. The study highlights the influence of solvent on the structural and physico-chemical properties of the catalysts. Various techniques, such as XRD, FE-SEM, BET, XPS, and H2-TPR, were used to analyze the catalyst properties. Among the synthesized materials, the catalyst, prepared with a N,N-dimethyl formamide (DMF)-to-metal nitrates ratio of 20 (named as CZC-1), showed enhanced active sites in the form of surface features such as nanowire-like morphology, large surface area, low crystallite size, increased oxygen vacancies, and high CuO dispersion. A bench-scale fixed-bed flow reactor was used to examine the catalytic performance of the catalysts. At 225 °C reactor temperature, 30 bar reactor pressure, and with a space velocity of 6000 cm3 gcat-1 h-1, the CZC-1 catalyst showed 13.6% CO2 conversion and 74.1% methanol selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis confirmed the carbonate-formate-methoxy reaction pathway for methanol formation using the CZC-1 catalyst.

A Ce-CuZn catalyst with abundant Cu/Zn-OV-Ce active sites for CO2 hydrogenation to methanol

CO2 hydrogenation to chemicals and fuels is a significant approach for achieving carbon neutrality. It is essential to rationally design the chemical structure and catalytic active sites towards the development of efficient catalysts. Here we show a Ce-CuZn catalyst with enriched Cu/Zn-OV-Ce active sites fabricated through the atomic-level substitution of Cu and Zn into Ce-MOF precursor. The Ce-CuZn catalyst exhibits a high methanol selectivity of 71.1% and a space-time yield of methanol up to 400.3 g·kgcat-1·h-1 with excellent stability for 170 h at 260 °C, comparable to that of the state-of-the-art CuZnAl catalysts. Controlled experiments and DFT calculations confirm that the incorporation of Cu and Zn into CeO2 with abundant oxygen vacancies can facilitate H2 dissociation energetically and thus improve CO2 hydrogenation over the Ce-CuZn catalyst via formate intermediates. This work offers an atomic-level design strategy for constructing efficient multi-metal catalysts for methanol synthesis through precise control of active sites.

Dual active sites over Cu-ZnO-ZrO2 catalysts for carbon dioxide hydrogenation to methanol

CO₂ hydrogenation to methanol is a significant approach to tackle the problem of global warming and simultaneously meet the demand for the portable fuel. Cu-ZnO catalysts with various kinds of promoters have received wide attention. However, the role of promoter and the form of active sites in CO₂ hydrogenation are still in debate. Here, various molar ratios of ZrO₂ were added into the Cu-ZnO catalysts to tune the distributions of Cu⁰ and Cu⁺ species. A volcano-like trend between the ratio of Cu⁺/ (Cu⁺ + Cu⁰) and the amount of ZrO₂ is presented, among which the CuZn10Zr (the molar ratio of ZrO₂ is 10%) catalyst reaches the highest value. Correspondingly, the maximum value of space-time yield to methanol with 0.65 g_MeOH/(g_cat·hr) is obtained on CuZn10Zr at reaction conditions of 220°C and 3 MPa. Detailed characterizations demonstrate that dual active sites are proposed during CO₂ hydrogenation over CuZn10Zr catalyst. The exposed Cu⁰ takes participate in the activation of H₂, while on the Cu⁺ species, the intermediate of formate from the co-adsorption of CO₂ and H₂ prefers to be further hydrogenated to CH₃OH than decomposing into the by-product of CO, yielding a high selectivity of methanol.

Effect of glucose pretreatment on Cu-ZnO-Al2O3 catalyzed CO2 hydrogenation to methanol

A series of Cu-ZnO-Al₂O₃ catalysts (CZA) were prepared by glucose pretreatment and applied for methanol synthesis from CO₂ hydrogenation. The advantages of the glucose pretreatment and the effects of glucose content were investigated by XRD, N₂ physisorption, SEM, N₂O chemisorption, CO₂-TPD, H₂-TPR, TG, and XPS characterization techniques. The influence of glucose pretreatment on the average Cu particle size and the interaction between different components, as well as the effects of the amount of glucose on the Cu specific surface area, the ratio of Cu⁰/Cu⁺ and the performance of the catalysts were discussed. The results showed that the catalysts prepared by glucose pretreatment increased the number of basic sites and had a significant advantage in methanol yield. The optimum content of glucose was beneficial to improve the catalytic performance of the CZA catalyst. The maximum space-time yield of methanol was obtained by 2 wt% glucose pretreatments at 200 °C, which was 57.0 g kg^-1 h^-1.

Ultra-thin ZrO2overcoating on CuO-ZnO-Al2O3catalyst by atomic layer deposition for improved catalytic performance of CO2hydrogenation to dimethyl ether

An ultra-thin overcoating of zirconium oxide (ZrO₂) film on CuO-ZnO-Al₂O₃(CZA) catalysts by atomic layer deposition (ALD) was proved to enhance the catalytic performance of CZA/HZSM-5 (H form of Zeolite Socony Mobil-5) bifunctional catalysts for hydrogenation of CO₂to dimethyl ether (DME). Under optimal reaction conditions (i.e. 240 °C and 2.8 MPa), the yield of product DME increased from 17.22% for the bare CZA/HZSM-5 catalysts, to 18.40% for the CZA catalyst after 5 cycles of ZrO₂ALD with HZSM-5 catalyst. All the catalysts modified by ZrO₂ALD displayed significantly improved catalytic stability of hydrogenation of CO₂to DME reaction, compared to that of CZA/HZSM-5 bifunctional catalysts. The loss of DME yield in 100 h of reaction was greatly mitigated from 6.20% (loss of absolute value) to 3.01% for the CZA catalyst with 20 cycles of ZrO₂ALD overcoating. Characterizations including hydrogen temperature programmed reduction, x-ray powder diffraction, and x-ray photoelectron spectroscopy revealed that there was strong interaction between Cu active centers and ZrO₂.

A Review on Green Hydrogen Valorization by Heterogeneous Catalytic Hydrogenation of Captured CO2 into Value-Added Products

The catalytic hydrogenation of captured CO2 by different industrial processes allows obtaining liquid biofuels and some chemical products that not only present the interest of being obtained from a very low-cost raw material (CO2) that indeed constitutes an environmental pollution problem but also constitute an energy vector, which can facilitate the storage and transport of very diverse renewable energies. Thus, the combined use of green H2 and captured CO2 to obtain chemical products and biofuels has become attractive for different processes such as power-to-liquids (P2L) and power-to-gas (P2G), which use any renewable power to convert carbon dioxide and water into value-added, synthetic renewable E-fuels and renewable platform molecules, also contributing in an important way to CO2 mitigation. In this regard, there has been an extraordinary increase in the study of supported metal catalysts capable of converting CO2 into synthetic natural gas, according to the Sabatier reaction, or in dimethyl ether, as in power-to-gas processes, as well as in liquid hydrocarbons by the Fischer-Tropsch process, and especially in producing methanol by P2L processes. As a result, the current review aims to provide an overall picture of the most recent research, focusing on the last five years, when research in this field has increased dramatically.

Influence of Ag Metal Dispersion on the Catalyzed Reduction of CO2 into Chemical Fuels over Ag-ZrO2 Catalysts

Metal/metal oxide catalysts reveal unique CO₂ adsorption and hydrogenation properties in CO₂ electroreduction for the synthesis of chemical fuels. The dispersion of active components on the surface of metal oxide has unique quantum effects, significantly affecting the catalytic activity and selectivity. Catalyst models with 25, 50, and 75% Ag covering on ZrO₂, denoted as Ag₄/(ZrO₂)₉, Ag₈/(ZrO₂)₉, and Ag₁₂/(ZrO₂)₉, respectively, were developed and coupled with a detailed investigation of the electronic properties and electroreduction processes from CO₂ into different chemical fuels using density functional theory calculations. The dispersion of Ag can obviously tune the hybridization between the active site of the catalyst and the O atom of the intermediate species CH₃O^* derived from the reduction of CO₂, which can be expected as the key intermediate to lead the reduction path to differentiation of generation of CH₄ and CH₃OH. The weak hybridization between CH₃O^* and Ag₄/(ZrO₂)₉ and Ag₁₂/(ZrO₂)₉ favors the further reduction of CH₃O^* into CH₃OH. In stark contrast, the strong hybridization between CH₃O^* and Ag₈/(ZrO₂)₉ promotes the dissociation of the C-O bond of CH₃O^*, thus leading to the generation of CH₄. Results provide a fundamental understanding of the CO₂ reduction mechanism on the metal/metal oxide surface, favoring novel catalyst rational design and chemical fuel production.

Design of Aerosol Nanoparticles for Interfacial Catalysis

Interest in multifunctional nanoparticles is currently rising due to the increasing demand in green energy and environmental applications. The aerosol-based synthetic route emerges as a promising method for enabling the fabrication of multifunctional nanoparticles in a continuous and scalable manner. Meanwhile, interfacial catalysis is receiving great attention to enhance the performance of chemical reactions. In this regard, the utilization of aerosol nanoparticles is highly beneficial to the catalysis field by the creation of strong metal-support-promoter interactions for promoting interfacial catalysis. In this Perspective, aerosol-based synthesis of hybrid nanoparticles is briefly discussed. In addition, the interfacial catalysis of CO oxidation, methane combustion, CO₂ hydrogenation, and dry reforming of methane are discussed to provide fundamental insights and concepts for the rational design of nanocatalysts with efficient interfaces.

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.

Recent Advances of Photocatalytic Hydrogenation of CO2 to Methanol

Constantly increasing hydrocarbon fuel combustion along with high levels of carbon dioxide emissions has given rise to a global energy crisis and environmental alterations. Photocatalysis is an effective technique for addressing this energy and environmental crisis. Clean and renewable solar energy is a very favourable path for photocatalytic CO2 reduction to value-added products to tackle problems of energy and the environment. The synthesis of various products such as CH4, CH3OH, CO, EtOH, etc., has been expanded through the photocatalytic reduction of CO2. Among these products, methanol is one of the most important and highly versatile chemicals widely used in industry and in day-to-day life. This review emphasizes the recent progress of photocatalytic CO2 hydrogenation to CH3OH. In particular, Metal organic frameworks (MOFs), mixed-metal oxide, carbon, TiO2 and plasmonic-based nanomaterials are discussed for the photocatalytic reduction of CO2 to methanol. Finally, a summary and perspectives on this emerging field are provided.

Efficient CO2 catalytic hydrogenation over CuOx–ZnO/silicalite-1 with stable Cu+ species

Efficient and stable CuOx–ZnO/S-1 catalysts for CO2 hydrogenation were inexpensively prepared, in which the ZnO–Cu2O interface and silanol nests play key roles.

Exploring the Zn-regulated function in Co–Zn catalysts for efficient hydrogenation of ethyl levulinate to γ-valerolactone

A series of CoZn catalysts supported on N-doped porous carbon (CoxZny@NPC-T) prepared at different calcination temperatures are studied for catalytic hydrogenation of biomass-based ethyl levulinate to γ-valerolactone, in which Zn is introduced as a regulator.