Catalysts For CO2 Hydrogenation Research Articles

Recent Progress in Nickel and Silica Containing Catalysts for CO2 Hydrogenation to CH4

The recent unusual weather changes occurring in different parts of the world are caused by global warming, a consequence of the release of extreme amounts of greenhouse gases into the atmosphere. Carbon dioxide (CO2) is one of these greenhouse gasses, which can be captured and reused to generate fuel through the methanation process. Nickel- and silica-based catalysts have been recognized as promising catalysts due to their efficiency, availability, and low prices. However, these catalysts suffer from metal sintering at high temperatures. Researchers have achieved remarkable improvements through altering conventional synthesis methods, supports, metal loading amounts, and promoters. The modified routes have enhanced stability and activity while the supports offer large surface areas, dispersion, and strong metal–support interactions. Nickel loading affects the formed structure and catalytic activity, whereas doping causes CO2 conversion at low temperatures and forms basic sites. This review aims to discuss the CO2 methanation process over Ni- and SiO2-based catalysts, in particular the silica-supported Ni metal in previously reported research works and point out directions for potential future work.

Exploiting the latency of carbon as catalyst in CO2 hydrogenation

The versatility of carbon has made it propitious for catalyst fabrication across various sectors of heterogeneous catalysis. Herein, a fundamental insight into the effects of carbon-supports in CO2 hydrogenation is established by facilely preparing and investigating diversely configured carbon supported Fe catalysts. Although the active component remains Fe, unique synergies attained over the Fe-carbon interfaces created an ambience disparate among the catalysts for enhanced activity and selective distribution. Generally, the carbons facilitated C–C coupling but more C5 + hydrocarbons are observed in the products when there is a stronger interaction between the carbon support and Fe phases. The selectivity for C5+ hydrocarbons reached the highest of ∼ 40 % in total hydrocarbon products when Fe and Na were encapsulated in carbon. Carbide formation was eased as a result of enhanced CO2 adsorption by the carbon supports whereas some surface functional groups attached to carbon surfaces improved C–C coupling to olefins and heavy hydrocarbons. The results presented maintains carbon as a promising catalytic material while the emphasis on structure, configuration, and surface properties reveal essentials in designing carbon-based catalysts in heterogeneous catalysis.

The influence of the compositions and structures of Cu-ZrO2 catalysts on the catalytic performance of CO2 hydrogenation to CH3OH

In this paper, Cu-ZrO2 catalysts were prepared and used for CH3OH synthesis through CO2 hydrogenation to clarify the influence of their compositions and structures on the catalytic performance. We mainly address the problem that how the oxygen vacancy and Cu-ZrO2 interface affect the catalytic performance jointly, because the previous articles only pay attention to the influence of the interface on CH3OH synthesis. Combined with experiments and various structural characterizations, we propose that oxygen vacancies play an essential role in CO2 activation instead of the interface; CH3OH selectivity is determined by the low-valence Cu species (Cu0 and Cu+) and ZrO2 interface (the main factor), and the pore size. The in-situ DRIFTS demonstrates that the conversion of *HCOO active intermediates to *CH3O on the optimal catalyst (CuZr-1) is faster. DFT calculations also shed light on the importance of oxygen vacancy in CO2 adsorption and the formate pathway. We believe this work provides useful insight for researchers to design highly efficient Cu-based catalysts for CO2 hydrogenation to CH3OH.

Improved copper-based catalysts for alcohol-assisted CO2 hydrogenation: A comparative study between novel nano-stabilized and deposition-precipitation method

A growing awareness of the need to control CO2 concentration in atmosphere spurs the demand for novel technologies to convert CO2 to useful chemicals. The conversion of CO2 into high-quality liquid fuel such as methanol is a primary focus, and using active catalysts is the key to achieving successful methanol synthesis from CO2 hydrogenation under mild conditions. A new way of synthesizing catalysts with highly dispersed nano copper particles, as well as the characteristics of the catalysts are reported in this study. This is the first instance of methanol catalysts being prepared using a combination of copolymer of polyethylene glycol and maleic acid (PEG-MA) as a stabilizer and layered hydrotalcite (HTC) as a support material. This resulted in a significant decrease in particle size and exhibited efficient catalytic performance in a 1-butanol promoted CO2 hydrogenation reaction at 170 °C, 3 MPa. The work also confirms the status of Zn as an influential factor for methanol synthesis. The application of ion-exchange process and stabilizers in catalyst preparation process effectively improves the CO2 conversion rate and methanol selectivity, which also inspires the development of catalysts in various fields.

Spatially resolved analysis of CO2 hydrogenation to higher hydrocarbons over alkali-metal promoted well-defined FexOyCz

A series of catalysts for CO2 hydrogenation to higher (C2+) hydrocarbons were prepared through controlled decomposition of iron (II) oxalate dihydrate impregnated with Li, Na, K, Rb or Cs carbonate. They consist of Fe3O4, Fe5C2, Fe3C and Fe. Their steady-state spatial phase distribution is, however, affected by the presence and the kind of the promoter. These structural characteristics determine catalyst activity and product selectivity. Fe3C seems to favor CH4 formation, while C2+-hydrocarbons are formed over Fe5C2. A positive relationship between the rate of C2+-hydrocarbons formation and the rate constant of dissociation of adsorbed CO2 was established, while an opposite dependence is valid for the rate of CO2 methanation. The rate constant of this reaction increases in the presence of alkali metal and with an increase in its atomic number. Therefore, CH4 is mainly formed over Rb- or Cs-doped catalysts through CO hydrogenation, while CO2 methanation prevails over the remaining catalysts.

Surface Redox Dynamics in Gold-Zinc CO2 Hydrogenation Catalysts.

Au-Zn catalysts have previously been shown to promote the hydrogenation of CO2 to methanol, but their active state is poorly understood. Here, silica-supported bimetallic Au-Zn alloys, prepared by surface organometallic chemistry (SOMC), are shown to be proficient catalysts for hydrogenation of CO2 to methanol. In situ X-ray absorption spectroscopy (XAS), in conjunction with gas-switching experiments, is used to amplify subtle changes occurring at the surface of this tailored catalyst during reaction. Consequently, an Au-Zn alloy is identified and is shown to undergo subsequent reversible redox changes under reaction conditions according to multivariate curve resolution alternating least-squares (MCR-ALS) analysis. These results highlight the role of alloying and dealloying in Au-based CO2 hydrogenation catalysts and illustrate the role of these reversible processes in driving reactivity.

Highly dispersed Fe/EG catalysts assisted by ammonium citrate and their application in CO2 hydrogenation to olefins

This study employed ammonium citrate as a small molecule additive to modulate the structure of the expanded graphite-loaded iron-based catalyst and its performance in CO2 hydrogenation to olefins. Through catalytic activity, the optimal performance was determined for a 1:1 M ratio of ammonium citrate to Fe salt precursor. The addition of ammonium citrate facilitated the dispersion of Fe particles by increasing the steric hindrance between Fe3+ and anchoring the Fe particles with amorphous carbon generated during calcination, resulting in a decrease in the particle size of iron particles from 20 to 45 nm to 12–27 nm. Furthermore, the nitrogen doping of the support was increased from 0.56% to 2.57%, which provided a strong electron-donating effect and facilitated the reduction and carbonization of iron species. The space time yield (STY) of light olefins was raised from 432.6 mg·gFe-1·h−1 to 604.1 mg·gFe-1·h−1, with a maximum O/P of 5.7. These results demonstrate the effectiveness of using ammonium citrate as an additive for improving the performance of expanded graphite-loaded iron-based catalysts in CO2 hydrogenation to olefins.

First-principles and microkinetic simulation studies of CO2 hydrogenation mechanism and active site on MoS2 catalyst

Molybdenum disulphide (MoS2) has attracted much attention as a promising non-precious metal catalyst for CO2 hydrogenation to energy-rich commodities. However, the exact reaction mechanism and active site on the MoS2 catalyst are still a matter of debate. Using density functional theory (DFT) calculations and microkinetic modeling, we study the competitive pathways leading to the formation of CO, methane and methanol at the S edge site in MoS2 catalyst, and the results are compared to those on the Mo edge and MoS2(001) in our previous work. It is found that CO is exclusively produced through redox mechanism on the S edge at 580–780 K, 1 bar and H2/CO2 ratio of 1, with the rate determining step of C-O bond scission in CO2. The rate of CO formation follows the order of Mo edge > S edge > MoS2(001), suggesting the Mo edge as the likely active site on the MoS2 catalyst. This work offers a mechanistic understanding toward CO2 hydrogenation on the MoS2 catalyst at the atomic level, and the insights gained can be used to design improved catalysts for the CO2 and CO hydrogenation and other important reactions of technological interest.

Tuning the content of S vacancies in MoS2 by Cu doping for enhancing catalytic hydrogenation of CO2 to methanol

Hydrogenation of CO2 to methanol is one of effective ways to promote "carbon neutrality". The activity of MoS2 as an efficient catalyst for the catalytic hydrogenation of CO2 to methanol is influenced by the content of in-plane S vacancies. Theoretically, the higher the density of in-plane S vacancies is, the better the performance of the catalyst is. In this work, a series of MoS2 nanosheets with different copper (Cu) dopant concentrations were prepared via hydrothermal method. It was found that the highest selectivity of MoS2-catalyzed CO2 hydrogenation to methanol along with the spatial-temporal yield was achieved at the Cu doping of 5%. Compared to the undoped MoS2 catalyst, the increase in methanol selectivity and spatial-temporal yield after doping was 13.37% and 2.27 times, respectively. This was due to the fact that Cu doping multiplied the number of S vacancies on MoS2, which altered the microstructure and chemical properties of the catalyst. However, a further increase in Cu dopant concentration reduced the S vacancy content on the MoS2 substrate, hindering the hydrogenation of the decomposed CO and thus decreasing the methanol yield. Therefore, a new technique to enhance MoS2-catalyzed CO2 hydrogenation to methanol was proposed.

Role of the structure and morphology of zirconia in ZnO/ZrO2 catalyst for CO2 hydrogenation to methanol

The global carbon dioxide (CO2) emission problem is getting increasingly severe nowadays. Hence a suitable CO2 hydrogenation technology to obtain methanol is an efficient way to achieve carbon neutrality. Zinc oxide (ZnO) nanoparticles were loaded on zirconium dioxide (ZrO2) with different morphologies via the impregnation method. This was followed by the investigation of the effect of zirconia structure and morphology on the interfacial synergy manifested in the catalysts and the catalytic performance in CO2 hydrogenation. The results showed that the CO2 conversion of the ZnO/ZrO2 catalyst possessing a hollow nanoframe-like morphology was significantly enhanced. This catalyst also exhibited the highest methanol space-time yield, which was 1.78 times higher than that of the ZnO/ZrO2 catalyst having an aggregate shape of irregular particles. The unique morphology effectively inhibited the transition of the metastable tetragonal ZrO2 (t-ZrO2) to the monoclinic ZrO2 (m-ZrO2) while forming a special interfacial structure with the loaded ZnO to strengthen the interfacial interaction. This enhanced the hydrogen activation capacity and generated more oxygen vacancies favorable to the activation of CO2.

Crucial Role of Surface FeOx Components on Supported Fe-Based Nanocatalysts for CO2 Hydrogenation to Light Olefins

Currently, Fe-based catalysts show excellent catalytic performance in the hydrogenation of CO2 to produce light olefins. Despite numerous studies, the identification of the role of catalytically active components over Fe-based catalysts for CO2 hydrogenation is not quite clear. In this work, a series of ZrO2-supported cobalt-doped Fe-based catalysts were fabricated by a microliquid film reactor-assisted coprecipitation method. It was demonstrated that appropriately strong interactions between Fe-containing species and the ZrO2 support in catalyst precursors could facilitate the generation of a defective FeOx component upon reduction treatment and inhibit the carburization of metallic iron during the reaction. Among all Fe-based catalysts, the catalyst bearing a (Co + Fe)/ZrO2 mass ratio of 3:7 and a Co/Fe molar ratio of 1:9 achieved a highest light olefins selectivity of about 38% at 49% CO2 conversion under reaction conditions (i.e., 320 °C, 2.0 MPa, and 4800 mL·gcat–1·h–1), along with a high Fe time yield to light olefins of 9.2 μmolCO2·gFe–1·s–1 and a low CO selectivity of 4.7%. Comprehensive structural characterization and catalytic CO2 hydrogenation experiments clarified that the surface-dominant defect-rich FeOx component as catalytically active species substantially played a crucial role in governing the hydrogenation of CO2, mainly owing to their enhanced adsorption and binding ability for CO2 and the CO intermediate. This study offers a new strategy to design Fe-based catalysts and provides deep insight into the role of iron oxide species for CO2 hydrogenation to produce light olefins.

CO2 hydrogenation to light olefins using In2O3 and SSZ-13 catalyst − Understanding the role of zeolite acidity in olefin production

With the aim to explore the effect of acidic properties of zeolites in tandem catalysts on their performance for CO2 hydrogenation, two types of SSZ-13 zeolites with similar bulk composition, but different arrangements of framework Al, were prepared. Their morphology, pore structure, distribution of framework Al, surface acid strength and density, were explored. The results showed that SSZ-13 zeolites with isolated aluminum distribution could be successfully synthesized, however, they contained structural defects. During calcination, the framework underwent dealumination, resulting in weaker Brønsted acidity and lower crystallinity. The morphologies were, however, well preserved. Compared with the SSZ-13 zeolites, synthesized conventionally, these low acidity SSZ-13 zeolites with isolated aluminum were good zeolite components in bifunctional catalysts for CO2 hydrogenation to light olefins. By combining with In2O3, they exhibited better catalytic performance for light olefin production during CO2 hydrogenation at low temperatures. Na+ cation exchange was used to adjust the Brønsted acid site (BAS) density with only minor changes to the cavity structure. Comparative experiments established that the BAS density of the zeolite, rather than the framework Al distribution (BAS distribution), overwhelmingly affected catalyst stability and product selectivity. A higher acid density reduced the selectivity for light olefins, while lower acid density tended to form inert coke species leading to rapid deactivation. The ideal amount of BAS density in the bifunctional catalyst was approximately 0.25 mmol/g, which exhibited 70% selectivity for light olefins among hydrocarbons, and 74% selectivity for CO without deactivation, after 12 h reaction at 325 ℃ and 10 bar.

Coverage effect of surface oxygen vacancy on In2O3-catalyzed CO2 hydrogenation revealed by first principles-based microkinetic simulations

Density functional theory (DFT) calculations and microkinetic simulations were performed to study the effect of the surface oxygen vacancy (OV) coverage on the In2O3 catalyst for methanol synthesis from CO2 hydrogenation, focusing on the In2O3(110) surface with a high OV coverage of 1 ML (In2O3(110)-allov) and compared with that with a low OV coverage of < 0.1 ML (In2O3(110)-vac). We find that the In2O3(110)-allov surface is less favorable for CO2 and H2 adsorptions than the In2O3(110)-vac surface, but the former has lower energy barriers for both the HCOO and COOH routes than the latter. Furthermore, the high OV coverage for the In2O3(110)-allov surface results in a significant lower CO2 reactivity, but gives surprisingly higher CH3OH selectivity. Our simulations may explain the experimentally observed deactivation of the In2O3 catalyst when over-reduced towards metallic In. Physical insights from this work should contribute to the rational design of efficient oxide-based CO2 hydrogenation catalysts.

Cu2In alloy-embedded ZrO2 catalysts for efficient CO2 hydrogenation to methanol: promotion of plasma modification.

Cu1In2Zr4-O-C catalysts with Cu2In alloy structure were prepared by using the sol-gel method. Cu1In2Zr4-O-PC and Cu1In2Zr4-O-CP catalysts were obtained from plasma-modified Cu1In2Zr4-O-C before and after calcination, respectively. Under the conditions of reaction temperature 270°C, reaction pressure 2MPa, CO2/H2 = 1/3, and GHSV = 12,000mL/(g h), Cu1In2Zr4-O-PC catalyst has a high CO2 conversion of 13.3%, methanol selectivity of 74.3%, and CH3OH space-time yield of 3.26mmol/gcat/h. The characterization results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed reduction chemisorption (H2-TPR) showed that the plasma-modified catalyst had a low crystallinity, small particle size, good dispersion, and excellent reduction performance, leading to a better activity and selectivity. Through plasma modification, the strong interaction between Cu and In in Cu1In2Zr4-O-CP catalyst, the shift of Cu 2p orbital binding energy to a lower position, and the decrease in reduction temperature all indicate that the reduction ability of Cu1In2Zr4-O-CP catalyst is enhanced, and the CO2 hydrogenation activity is improved.

Hydrogenation of CO2 to formic acid over efficient heterogeneous ruthenium oxide supported on cubic phase zirconium oxide catalyst

The development of active, cost-effective heterogeneous catalysts for the hydrogenation of CO2 to chemicals is currently progressing rapidly. In this study, we have demonstrated a significantly lower weight percentage (wt.%) RuO2/ZrO2 oxide catalyst that is effective for CO2 hydrogenation to formic acid (FA) synthesis. RuO2/ZrO2 was synthesized using a co-precipitation followed by a hydrothermal method. The X-ray diffraction pattern exhibits the cubic phase of ZrO2 with an average crystal size of 80.7 nm and tetragonal Ru oxide. Scanning electron microscopy and transmission electron microscopy confirmed that RuO2 was uniformly dispersed on the ZrO2 surface, with fringes measuring 0.22 and 0.25 nm corresponding to tetragonal Ru, which were incorporated in the ZrO2 oxide. XPS analysis showed that the Ru3/4+ chemical state strongly interacts with the ZrO2 facet, as confirmed via the Ru (110) and (211) planes. The outstanding performance of the 2.7 wt% RuO2/ZrO2 catalyst for CO2 hydrogenation yielded 40 mmol of FA with 39.7 TON. Based on the above investigations, we proposed a plausible mechanistic pathway for the hydrogenation of CO2 to FA over a RuO2/ZrO2 catalyst.

Precise tuning of the properties of MOR-type zeolite nanoparticles to improve lower olefins selectivity in composite catalysts for CO2 hydrogenation

CO2 utilization is a key technology for carbon neutrality and is in high demand worldwide; however, many challenges need to be overcome. Composite catalysts consisting of zirconia-based catalysts for CO2 hydrogenation and zeolite-based solid acid catalysts for methanol-to-olefins reaction have been realized one-pass synthesis of olefins from CO2. High selectivity for olefins is essential for utilizing this promising process, and in this work, we precisely tuned the properties of MOR-type zeolites using multiple-step post-synthetic treatments. Miniaturization by milling and recrystallization helped realize the optimization of the zeolite composition related to the acid strength as well as enhance gas diffusion. Defect-healing treatment recently developed by us was applied, and the defects generated in the framework during these processes were successfully removed. Finally, the optimized sample showed high catalytic activity in sequential CO2 hydrogenation to hydrocarbons with the olefin selectivity with an improvement in the olefin/paraffin ratio from 0.69 to 1.4.

Charge polarization-modulated Pd-Ni(OH)2 hybrids in mesoporous silica SBA-15 for efficient low-temperature CO2 hydrogenation to formate

Converting CO2 to formic acid/formate is a considerably significant pathway for future energy storage and utilization; however, it is critical to tailor high-performance catalysts for realizing the process. Herein, highly dispersed Pd-Ni(OH)2 hybrids were immobilized in ordered mesoporous silica SBA-15 via a facile impregnation method. The prepared SBA-15-supported Pd-Ni(OH)2 catalyst exhibited extraordinarily high catalytic performance and stability during the hydrogenation of CO2 toward formate. Significantly, Pd5Ni5/SBA-15, an optimized Pd5Ni5/SBA-15 catalyst afforded a superior formate generation rate of 150.5 molformate moltotalPd-1h−1 at a low temperature (40 °C), which was about 3-fold higher than that of monometallic Pd counterpart. Such a catalytic activity outperforms most of the previously reported catalysts because of its charge polarization action and synergy between bimetallic components as well as ultrasmall and well-dispersed metal species with increased accessible active sites. The relevant experimental observations were well supported by density functional theory (DFT) calculations. In addition, the catalytic activity of SBA-15-supported metal catalysts remained unchanged even after the 5th cycle, demonstrating excellent cycling durability due to the confinement effect of mesoporous silica. The facile synthesis strategy and excellent catalytic performance hold great potential applications of the prepared catalysts in CO2 hydrogenation to formate.

Facet-Controlled Cu-doped and K-promoted Fe2O3 nanosheets for efficient CO2 hydrogenation to liquid hydrocarbons

Hydrogenation of CO2 into liquid hydrocarbons is an attractive route for chemical utilization of CO2, but suffers from limited product selectivity. By controlling the exposed surface atoms of metal catalyst, purposefully enhancing the reaction rate of bottleneck steps for CO2 activation and C-C coupling is expected to solve this problem. Here, we tuned the exposed surface atoms of catalysts separately and simultaneously by facet control, doping and promoter modification; a nanosheet-shaped Fe2O3 rich in oxygen vacancies was first constructed to enhance the adsorption and activation of CO2. Cu doping and K promoter were further used to promote the formation of active χ-Fe5C2 phase and facilitate the coupling of C-C bond to form long chain fuels. The optimized K-promoted and Cu-doped Fe2O3 nanosheets (3 K/6Cu-Fe-S) exhibited high CO2 conversion (46.5%) and C5+ hydrocarbons selectivity (53.6%), accompanied with low CO (5.3%) and CH4 selectivity (12.2%) at 300 °C, outperforming other reported Fe-based catalysts significantly. Meanwhile, a 205 h on stream test indicated the excellent stability of 3 K/6Cu-Fe-S. The effects of each tuning method on catalytic activity and product selectivity were further studied by combining the change of the phase and surface electronic structure of the catalyst before and after the reaction. Cu doping and K promoter were verified to have a synergistic enhancement effect on the hydrogenation performance of CO2, rather than just the sum of the two. These findings would be beneficial for the rational design of CO2 hydrogenation catalysts.

Layered double hydroxides derived CuFe-based catalysts for CO2 hydrogenation to long-chain hydrocarbons

CO2 hydrogenation to yield long-chain hydrocarbons has attracted tremendous attention in both academic and industrial field. CuFe-based bimetal catalysts have been widely applied in CO2 hydrogenation owing to their low cost, facile preparation, and excellent performance. In this study, a series of CuFe-based catalysts with different Cu/Fe molar ratios have been synthesized from layered double hydroxide precursor. The optimized CuFe8-LDO catalyst with Cu:Fe=1:8 exhibits a C5+ selectivity of 45% at CO2 conversion of 9.5%. Through systematic characterizations including TEM, TPR, TPD, XPS, it is revealed the abundant and highly dispersed CuO favors the reduction of iron species, and enhances CO adsorption capacity of as-prepared catalysts. This study provides an in-deep understanding of Cu on CO2 hydrogenation performance of Fe-based catalysts.

Boosting the Production of Light Olefins from CO2 Hydrogenation over Fe–Co Bimetallic Catalysts Derived from Layered Double Hydroxide

CO2 hydrogenation to light olefins (C2–C4═) is especially attractive for the chemical utilization of CO2, and currently, effective catalysts are still under development. Herein, we report a succession of Fe–Co bimetallic catalysts derived from Fe–Co–Mg layered double hydroxides (LDHs) with different Fe/Co ratios [(c(Fe3+) + c(Co2+))/c(Mg2+) = 1] for converting CO2 to light olefins, which were also compared to MgO-supported Fe–Co prepared by the impregnation method. The best catalyst FeCo-9:1-LDH presented a high selectivity of C2–C4═ over 36% at a CO2 conversion higher than 40%. With ex/in situ characterization including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), we found that the Fe–Co–Mg LDH-derived catalyst (FeCo-9:1-LDH) is easily carburized to Co-modified iron carbide (Fe5C2), which is superior to the FeCo-9:1-I catalyst synthesized by impregnating Co and Fe onto MgO support. The former shows a higher CO2 conversion and higher C2–C4═ selectivity, while the latter produces more CH4. This work provides a series of catalysts for selective hydrogenation of CO2 to light olefins, as well as insights into the reaction pathway, favoring the rational design of CO2 hydrogenation catalysts.