The role of CO2 dissociation in CO2 hydrogenation to ethanol on CoCu/silica catalysts

Saeidi S., Najari S., Hessel V., Wilson K., Keil F.J., Concepción P., Suib S.L., Rodrigues A.E.

Climate change, global warming, fossil fuel depletion and rising fuel prices have created great incentives to seek alternative fuel production technologies. CO 2 transformation to value-added products using renewable H 2 has proven to be an emerging solution to enable this goal. In this regard, three different promising processes, namely methane, methanol and hydrocarbon synthesis via CO 2 hydrogenation are thoroughly discussed. In addition, the influential factors affecting process efficiencies such as catalyst design and mechanistic insight, operating conditions as well as reactor types are investigated, with key pathways that dictate catalyst activity and selectivity of the most promising materials described. Furthermore, a brief overview of the reactor configuration and its crucial role in the improving process viability is analyzed. Accordingly, fixed-bed, fluidized-bed, annular and spherical reactors along with H 2 O/H 2 perm-selective membrane reactors are disscussed for hydrocarbon production. In addition, different reactor configurations are compared to assess the best one that is adjustable depending on the reaction mechanism. Consequently, a corrugated-wall dual-type membrane reactor is proposed as an emerging alternative for CO 2 hydrogenation to value-added products.

Xu D., Wang Y., Ding M., Hong X., Liu G., Tsang S.C.

Summary Converting the greenhouse gas CO2 into higher alcohols (HAs) via hydrogenation reaction requires more attention in C1 chemistry because the C2+ alcoholic products are value-added chemicals as fuel additives, reaction solvents, and intermediates. However, the chemical inertness of CO2, complexity in various reaction routes, and uncontrollability of C–C coupling from untamed surface moieties in higher alcohol synthesis (HAS) make this approach very challenging to achieve. In this review, we summarize and analyze the recent advances in catalytic HAS from direct CO2 hydrogenation. The first section highlights the potential promising catalyst families, including a noble-metal class of catalysts, modified Co-based catalysts, modified Cu-based catalysts, and Mo-based catalysts with the roles of promoters and supports specified in each case. The second section reviews the possible reaction mechanisms based on previous experimental results. The rational design of ideal catalyst systems for this reaction is discussed in the third section.

Xu D., Ding M., Hong X., Liu G., Tsang S.C.

Higher alcohol (C2+) synthesis (HAS) from direct CO2 hydrogenation is a promising way to realize the fixation of CO2 to high-value chemicals; however, the identification of active catalysts to give...

Zhang S., Liu X., Shao Z., Wang H., Sun Y.

Direct CO 2 hydrogenation to ethanol is one of the promising and emerging routes for the transformation of CO 2 into value-added chemicals, but it remains a major challenge because of low ethanol selectivity and catalytic stability. In this work, Na-promoted cobalt catalysts supported on different materials (Al 2 O 3 , ZnO, AC, TiO 2 , SiO 2 , and Si 3 N 4 ) were evaluated to elucidate the effects of supports. The SiO 2 - and Si 3 N 4 -supported catalysts exhibited efficient generation of ethanol with 18% CO 2 conversion and 62% selectivity in the alcohol distribution at 250 °C, whereas CH 4 was predominantly produced on other supported catalysts. Characterization results indicated that the Co 2 C active phase only remained intact on SiO 2 and Si 3 N 4 supports during reaction and exhibited excellent durability for 300 h, which was attributed to the existence of a strong metal–support interaction (SMSI) obtained by Si[sbnd]O[sbnd]Co bond formation. In situ DRIFTS results revealed that CO produced on Co 2 C inserted into CH x intermediates to form ethanol. Moreover, CO as the reactive intermediate could induce the regeneration and reconstruction of decomposed Co 2 C on the surface for catalytic sustainability. © 2019 Elsevier Inc.

Wang L., He S., Wang L., Lei Y., Meng X., Xiao F.

Selective hydrogenation of CO2 into valuable ethanol proceeds by the coupling of appropriate C1 intermediates to form C2-oxygenates. Matching the different C1 intermediates is crucial for this proc...

Wang G., Luo R., Yang C., Song J., Xiong C., Tian H., Zhao Z., Mu R., Gong J.

Metal oxide-promoted Rh-based catalysts have been widely used for CO2 hydrogenation, especially for the ethanol synthesis. However, this reaction usually suffers low CO2 conversion and alcohols selectivity due to the formation of byproducts methane and CO. This paper describes an efficient vanadium oxide promoted Rh-based catalysts confined in mesopore MCM-41. The Rh-0.3VOx/MCM-41 catalyst shows superior conversion (~12%) and ethanol selectivity (~24%) for CO2 hydrogenation. The promoting effect can be attributed to the synergism of high Rh dispersion by the confinement effect of MCM-41 and the formation of VOx-Rh interface sites. Experimental and theoretical results indicate the formation of til-CO at VOx-Rh interface sites is easily dissociated into *CHx, and then *CHx can be inserted by CO to form CH3CO*, followed by CH3CO* hydrogenation to ethanol.

Lin T., Gong K., Wang C., An Y., Wang X., Qi X., Li S., Lu Y., Zhong L., Sun Y.

Cobalt carbide (Co2C) nanoprisms derived from CoMn composite oxides exhibit promising catalytic performance for Fischer–Tropsch to olefins (FTO) synthesis via H2-lean syngas conversion, but with ne...

Yang C., Liu S., Wang Y., Song J., Wang G., Wang S., Zhao Z., Mu R., Gong J.

Identification of the active structure under reaction conditions is of great importance for the rational design of heterogeneous catalysts. However, this is often hampered by their structural complexity. The interplay between the surface structure of Co3 O4 and the CO2 hydrogenation is described. Co3 O4 with morphology-dependent crystallographic surfaces presents different reducibility and formation energy of oxygen vacancies, thus resulting in distinct steady-state composition and product selectivity. Co3 O4 -0 h rhombic dodecahedra were completely reduced to Co0 and CoO, which presents circa 85 % CH4 selectivity. In contrast, Co3 O4 -2 h nanorods were partially reduced to CoO, which exhibits a circa 95 % CO selectivity. The crucial role of the Co3 O4 structure in determining the catalytic performance for higher alcohol synthesis over CuCo-based catalysts is demonstrated. As expected, Cu/Co3 O4 -2 h shows nine-fold higher ethanol yield than Cu/Co3 O4 -0 h owing to the inhibition for methanation.

An B., Li Z., Song Y., Zhang J., Zeng L., Wang C., Lin W.

Selective conversion of CO2 to ethanol is of great interest but presents a significant challenge in forming a C–C bond while keeping a C–O bond intact throughout the process. Here, we report cooperative CuI sites on a Zr12 cluster of a metal–organic framework (MOF) for selective hydrogenation of CO2 to ethanol. With the assistance of an alkali cation, the spatially proximate Zr12-supported CuI centres activate hydrogen via bimetallic oxidative addition and promote C–C coupling to produce ethanol. The Cs+-modified MOF catalyst, in 10 hours, produces ethanol with >99% selectivity and a turnover number (based on all Cu atoms) of 4,080 in supercritical CO2, with 30 MPa of CO2 and 5 MPa of H2 at 85 °C, or a turnover number of 490 at 2 MPa of CO2/H2 (1/3) and 100 °C. Our work highlights the potential of using MOFs as a tunable platform to design earth-abundant metal catalysts for CO2 conversion. The synthesis of ethanol via CO2 hydrogenation is a challenging process, often hampered by low selectivity. This work reports a Zr12 cluster-based metal–organic framework as support for cooperative Cu(i) sites that catalyse CO2 hydrogenation to ethanol with remarkable selectivity upon promotion with caesium. Credit: Cloud background, CC0 1.0 Universal Public Domain Dedication.

Li W., Zhang G., Jiang X., Liu Y., Zhu J., Ding F., Liu Z., Guo X., Song C.

Cobalt catalysts supported on TiO2 with different crystal forms (anatase and rutile) differ sharply in CO2 conversion and product selectivity for CO2 hydrogenation. The Co/rutile-TiO2 catalyst selectively catalyzed CO2 hydrogenation to CH4, while CO is the main product on the Co/anatase-TiO2 catalyst. In situ DRIFT (diffuse reflectance infrared Fourier transform) results have partially revealed the reaction pathway of CO2 hydrogenation on these two catalysts. On Co/rutile-TiO2, the reaction proceeds through the key intermediate formate species, which is further converted to CH4. Differently, the reaction on Co/anatase-TiO2 undergoes CO2 → *CO, which desorbs to form gas-phase CO instead of subsequent hydrogenation. The strongly bonded *CO is required to enhance the subsequent hydrogenation. By simply changing the calcination temperature of anatase TiO2, the product selectivity can be tuned from CO to CH4 with a significant increase in CO2 conversion due to the surface phase transition of the anatase to the...

Yang C., Mu R., Wang G., Song J., Tian H., Zhao Z., Gong J.

This paper describes the promotional effect of hydroxyl groups over RhFeLi/TiO2 catalysts for the ethanol synthesis via CO2 hydrogenation.

Singh J.A., Cao A., Schumann J., Wang T., Nørskov J.K., Abild-Pedersen F., Bent S.F.

Methanol is an important chemical compound which is used both as a fuel and as a platform molecule in chemical production. Synthesizing methanol, as well as dimethyl ether, directly from carbon dioxide and hydrogen produced using renewable electricity would be a major step forward in enabling an environmentally sustainable economy. We utilize density functional theory combined with microkinetic modeling to understand the methanol synthesis reaction mechanism on a model CoGa catalyst. A series of catalysts with varying Ga content are synthesized and experimentally tested for catalytic performance. The performance of these catalysts is sensitive to the Co:Ga ratio, whereby increased Ga content results in increased methanol and dimethyl ether selectivity and increased Co content results in increased selectivity towards methane. We find that the most active catalysts have up to 95% CO-free selectivity towards methanol and dimethyl ether during CO2 hydrogenation and are comparable in performance to a commercial CuZn catalyst. Using in situ DRIFTS we experimentally verify the presence of a surface formate intermediate during CO2 hydrogenation in support of our theoretical calculations.

Davidson M., Ji Y., Leong G.J., Kovach N.C., Trewyn B.G., Richards R.M.

Due to the uniform and stable pore structure, mesoporous silica has attracted increasing research attention as a catalyst support material. As a large family of mesoporous silica-supported materials, noble-metal nanoparticles supported on mesoporous silica catalysts have demonstrated desirable properties across a broad platform of reactions. In this review article, we first introduce systems of metal nanoparticles dispersed on mesoporous silica, and then, we focus on next generation systems, in which the noble metal is not supported on the mesoporous silica but rather entrapped/intercalated within the silica matrix, thus enhancing particle stability and in some cases, enhanced activity. Herein, research and future directions on both synthesizing hybrid noble-metal nanoparticles/mesoporous silica composite catalysts and their resultant properties will be discussed.

Ao M., Pham G.H., Sunarso J., Tade M.O., Liu S.

The gradual depletion of oil resources and the necessity to reduce greenhouse gas emissions portray a concerning image of our contemporary security of liquid transportation fuels in the event of a global crisis. Despite a vast amount of natural gas resources that we have and the huge economic incentive, the conversion of gas to liquid fuels or chemicals is still very limited because of the high technological complexity and capital cost for facilities. However, with the anticipated depletion of liquid petroleum and the soaring price of crude oil, the conversion of natural gas to liquid feedstock or fuels will become more and more important. Higher alcohols are important feedstocks for the chemical and pharmaceutical industries and have wide applications as potential fuel additives or hydrogen carriers for fuel cells for clean energy delivery. There is a long-standing interest in the synthesis of higher alcohols from syngas, an important Fischer–Tropsch technology for natural gas conversion. The purpose of ...

Wang L., Wang L., Zhang J., Liu X., Wang H., Zhang W., Yang Q., Ma J., Dong X., Yoo S.J., Kim J., Meng X., Xiao F.

Methods for the hydrogenation of CO2 into valuable chemicals are in great demand but their development is still challenging. Herein, we report the selective hydrogenation of CO2 into ethanol over non-noble cobalt catalysts (CoAlOx ), presenting a significant advance for the conversion of CO2 into ethanol as the major product. By adjusting the composition of the catalysts through the use of different prereduction temperatures, the efficiency of CO2 to ethanol hydrogenation was optimized; the catalyst reduced at 600 ° gave an ethanol selectivity of 92.1 % at 140 °C with an ethanol time yield of 0.444 mmol g-1 h-1 . Operando FT-IR spectroscopy revealed that the high ethanol selectivity over the CoAlOx catalyst might be due to the formation of acetate from formate by insertion of *CHx , a key intermediate in the production of ethanol by CO2 hydrogenation.

Ma Y., Liu Y., Huang Z., Han X., Ye L., Qin X., Xu H., Kong L., Li J., Zhang J., Pu X., Liu J.

Dong R., Wu C., Vo T., Lim S.H., Cao X., Zheng J., Xiao X., Chu W., Liu Y.

The homogeneously distributed Co and Cu bimetallic species act as active sites for CO2 hydrogenation reactions, achieving TOF of formate production at 625.2 h−1 under optimized reaction conditions.

Ahmed A.T., Sekac T., Altalbawy F.M., Al‐Hetty H.R., Ramachandran T., Chahar M., Chohan J.S., Singh K., Abosaoda M.K., Abbas J.M.

AbstractThis review provides a comprehensive overview of current progress in catalytic technologies for converting CO2 to ethanol, emphasizing the importance of sustainable and environmentally friendly alternatives. A range of methodologies is explored, including thermodynamic analysis, thermocatalytic, electrocatalytic, and photocatalytic approaches, while discussing fundamental reaction mechanisms and catalyst design strategies. Significant advancement has been made in the thermocatalytic hydrogenation of CO2, with mixed metal and metal oxide catalysts achieving selectivities exceeding 90%. However, challenges remain in optimizing catalyst performance for enhanced selectivity and conversion rates. Electrocatalytic reduction offers a promising pathway, focusing on alkaline electrolytes and innovative catalyst designs such as Cu/Au and Al‐Cu/Cu2O. Meanwhile, photocatalytic systems harness solar energy, with various novel photocatalysts showing potential for high efficiency. This review aims to elucidate the current landscape and future perspectives on CO2‐to‐ethanol conversion technologies, highlighting their potential role in sustainable energy solutions.

Liu L., Liu J., Li G., Shi X., Yin J., Zheng S., Yung K., Yang H.B., Lo T.W.

AbstractThe thermocatalytic hydrogenation of CO2 to ethanol has attracted significant interest because ethanol offers ease of transport and substantial value in chemical synthesis. Here, we present a state‐of‐the‐art catalyst for the CO2 hydrogenation to ethanol achieved by precisely depositing single‐atom Ir species on P cluster islands situated on the In2O3 nanosheets. The Ir1‐Px/In2O3 catalyst achieves an impressive ethanol yield of 3.33 mmol g−1 h−1 and a turnover frequency (TOF) of 914 h−1 under 1.0 MPa (H2/CO2=3 : 1) at 180 °C, nearly 8 times higher than that of the unmodified Ir1/In2O3 catalyst. Additionally, at a more industrially relevant pressure of 5.0 MPa, the TOF of the Ir1‐Px/In2O3 catalyst can reach up to 2108 h−1, surpassing previously reported catalysts. Combined in situ characterization and theoretical studies reveal that the hydrogenation process is significantly enhanced by the Ir1‐Px entities. Specifically, the Ir atom facilitates CO2 activation and C−C coupling, while the surrounding P island exhibits exceptional H2 dissociation ability. These three steps have been found crucial for the CO2 hydrogenation reaction. This discovery opens new opportunities for the regulation of the microenvironment of current catalysts by providing essential chemical functionalities that enhance intricate and complex reaction processes.

Liu L., Liu J., Li G., Shi X., Yin J., Zheng S., Yung K., Yang H.B., Lo T.W.

AbstractThe thermocatalytic hydrogenation of CO2 to ethanol has attracted significant interest because ethanol offers ease of transport and substantial value in chemical synthesis. Here, we present a state‐of‐the‐art catalyst for the CO2 hydrogenation to ethanol achieved by precisely depositing single‐atom Ir species on P cluster islands situated on the In2O3 nanosheets. The Ir1‐Px/In2O3 catalyst achieves an impressive ethanol yield of 3.33 mmol g−1 h−1 and a turnover frequency (TOF) of 914 h−1 under 1.0 MPa (H2/CO2=3 : 1) at 180 °C, nearly 8 times higher than that of the unmodified Ir1/In2O3 catalyst. Additionally, at a more industrially relevant pressure of 5.0 MPa, the TOF of the Ir1‐Px/In2O3 catalyst can reach up to 2108 h−1, surpassing previously reported catalysts. Combined in situ characterization and theoretical studies reveal that the hydrogenation process is significantly enhanced by the Ir1‐Px entities. Specifically, the Ir atom facilitates CO2 activation and C−C coupling, while the surrounding P island exhibits exceptional H2 dissociation ability. These three steps have been found crucial for the CO2 hydrogenation reaction. This discovery opens new opportunities for the regulation of the microenvironment of current catalysts by providing essential chemical functionalities that enhance intricate and complex reaction processes.

Salami R., Zeng Y., Han X., Rohani S., Zheng Y.

Kostyniuk A., Likozar B.

Gunerhan A., Altuntas O., Açıkkalp E.

Chen J., Zhao X., Shakouri M., Wang H.

AbstractThermocatalytic conversions of carbon dioxide (CO2) to value‐added products offer promising approaches to achieving net negative emissions. The catalysts for CO2 conversions, particularly for CO2 hydrogenation reactions, usually involve more than one catalytic sites working together. In this review, we first introduce the advanced characterization techniques used to identify the catalytic sites in CO2 hydrogenation catalysts, sites for hydrogen (H2) activation and CO2 adsorption/activation. We then discuss how the dual or multiple‐site configurations influence the catalytic activity and selectivity in reactions such as reverse water‐gas shift (RWGS), CO2 methanation, and CO2 hydrogenation for methanol (MeOH). We finally explain the Catalytic Sites Contiguity (CSC) concept that our research group developed from the work in CO2 reforming of methane and use it to understand the relationship between the spatial arrangement of catalytic sites and the efficiency of reactant activation and conversion in recent publications on MeOH synthesis from CO2 hydrogenation. We hope our insights into the impact of CSC on catalytic performance lead to a potential top‐down design method in optimizing the CO2 hydrogenation catalysts.

Yao R., Wu B., Yu Y., Liu N., Niu Q., Li C., Wei J., Ge Q.

The electronic property of a catalyst is crucial to the generation of key reaction intermediates for targeted synthesis. Herein, we reported a strategy by modifying iron catalysts with sulfate and alkali metal (Li, Na, or K) to regulate the electronic property and optimize the reaction pathways for CO2 hydrogenation to higher alcohols. The characterizations demonstrated the influencing relationship between the electronic property of iron catalysts and the catalytic capabilities for CO dissociation, non-dissociated CO activation and catalytic hydrogenation, which were critical to selective synthesis of higher alcohols. Na-S modification was proven more effective to balance the multiple capabilities required for higher alcohols synthesis and the NaS-Fe catalyst gave a higher C2+OH yield in CO2 hydrogenation. DFT calculations further validated the advantage of Na-S modification from the aspects of CO adsorption and C−C coupling. This strategy provides more flexibility in site regulation and applies to catalyst design for many reactions.

Pamei M., Sharma S.K., Das D., Vadivel S., Paul B., Puzari A.

Zhang Q., Wang S., Dong M., Wang J., Fan W.

CO2 hydrogenation to higher alcohols (C2+OH) is an effective way to realize carbon recycling, which can not only reduce the CO2 amounts in atmosphere and mitigate the greenhouse effect, but also provides a new route to synthesize important chemicals. However, this process is a challenge because the inert CO2 molecule is difficult to be activated and undergo C–C coupling. The key to achieve selective conversion of CO2 to C2+OH is to design high-performance catalytic systems and unravel the reaction mechanism. In this review, we report several typical CO2 hydrogenation-to-C2+OH catalyst materials, including noble-metal catalysts, Cu-based catalysts, Co-based catalysts and Mo-based catalysts, and evaluate the effects of various promoters on the catalytic performance and reaction mechanism. It will provide not only fundamental insights into the CO2 hydrogenation-to-C2+OH reaction mechanism, but also guidance for the development of related high-performance catalysts.

Wang X., Pan J., Wei H., Li W., Zhao J., Hu Z.

CO2 hydrogenation into valuable chemical compounds can effectively address the issues of greenhouse gas emissions and energy scarcity.

Zhang J., Fan Z., Wu D.

AbstractConverting the abundant biomass resources in nature into fine chemicals can not only reduce carbon emissions but also effectively deal with the depletion of fossil energy, which is of strategic significance for sustainable development. In this paper, by optimizing the content of bimetallic components, highly active co‐doped Co1Cu3 bimetallic silicate was designed and synthesized. After reduction, a highly dispersed and stable Co1Cu3/SiO2 catalyst was obtained, which was used to catalyze the aqueous phase hydrogenation of furfural (FFR) to cyclopentanone (CPO). Compared with the traditional supported catalyst, the Co1Cu3/SiO2‐ammonia evaporation (AE)‐300 catalyst prepared by AE has the best performance. Under the optimal reaction conditions, the conversion of FFR was as high as 95.1 % and the selectivity of CPO was 88.6 %. This high activity can be attributed to the formation of highly dispersed and uniform metal active sites with low content of Co. At the same time, the formation of flocculent silicate enhances the synergism between CoCu and SiO2 support and increases the specific surface area of the catalyst. In addition, the experimental results show that the reaction carbon balance will be destroyed with the high concentration of FFR solution.

Boretti A.

AbstractThis paper addresses the urgent challenge of CO2 emissions and the need for sustainable energy sources. It emphasizes CO2 hydrogenation as a promising solution for large‐scale long‐term energy storage, converting CO2 into valuable fuels using green hydrogen generated from renewable sources. The study concentrates on exploring pathways leading to oxygenated compounds, such as alcohols or ethers, for their utilization as sustainable fuels. The investigation encompasses methanol, dimethyl ether, ethanol, and higher alcohols. The paper investigates catalysts for CO2 hydrogenation, ranging from traditional metal‐based to advanced materials, aiming to identify efficient and stable catalysts for synthesizing oxygenated compounds. Catalysts are indispensable in CO2 hydrogenation for the synthesis of oxygenated compounds, contributing to improved reaction kinetics, selectivity, economic viability, reduced environmental impact, and the overall sustainability of the process. The goal is to contribute to a fully renewable, carbon‐neutral system powered by excess solar and wind electricity, where recycled CO2 and green hydrogen are used to produce fuels, to be stored and then used to produce energy, electricity, heat, or mechanical energy, on demand, with the capture of the CO2, in a system which is overall carbon neutral. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.