Catalysts For CO2 Hydrogenation Research Articles

Flame Spray Pyrolysis Synthesis of Ultra-Small High-Entropy Alloy-Supported Oxide Nanoparticles for CO2 Hydrogenation Catalysts.

The synthesis of high-entropy alloys (HEAs) with ultra-small particle sizes has long been a challenging task. The complex and time-consuming synthesis process hinders their practical application and widespread adoption. This study presents the novel synthesis of TiO2 nanoparticles loaded with a quinary high-entropy alloy through flame spray pyrolysis (FSP) for the first time. The extremely fast heating rate of flame combustion makes the precursor fast pyrolysis gasification, high temperature in the flame field promotes the metal vapor mixing uniformly, and the fast quenching process can reduce the particle aggregation sintering, the ultra-small particle size of HEA firmly attached to the TiO2 surface. The catalysts prepared via this gas-to-particle pathway exhibit excellent performance in CO2 hydrogenation, achieving a conversion rate of 62% at 450°C, and maintaining their activity for over 220h without significant particle agglomeration. This finding provides valuable insights for the future design of catalytically active materials with enhanced activity and long-term stability.

Zn promoted GaZrOx ternary solid solution oxide combined with SAPO-34 effectively converts CO2 to light olefins with low CO selectivity.

We proposed a new strategy for CO2 hydrogenation to prepare light olefins by introducing Zn into GaZrOx to construct ZnGaZrOx ternary oxides, which was combined with SAPO-34 to prepare a high-performance ZnGaZrOx/SAPO-34 tandem catalyst for CO2 hydrogenation to light olefins. By optimizing the Zn doping content, the ratio and mode of the two-phase composite, and the process conditions, the 3.5%ZnGaZrOx/SAPO-34 tandem catalyst showed excellent catalytic performance and good high-temperature inhibition of the reverse water-gas shift (RWGS) reaction. The catalyst achieved 26.6% CO2 conversion, 82.1% C2=-C4= selectivity and 11.8% light olefins yield. The ZnGaZrOx formed by introducing an appropriate amount of Zn into GaZrOx significantly enhanced the spillover H2 effect and also induced the generation of abundant oxygen vacancies to effectively promote the activation of CO2. Importantly, the RWGS reaction was also significantly suppressed at high temperatures, with the CO selectivity being only 46.1% at 390°C.

Construction of nanoflower cobalt-based catalyst for methane-free CO hydrogenation to hydrocarbon reaction.

Methane and its oxidation product (i.e., CO2) are both greenhouse gases. In the product chain of CO hydrogenation to hydrocarbon reaction, methane is also an unwanted product due to its poor added value. Herein we investigated the effect of structure-directing agent urotropine on cobalt-based catalyst supported on Al-O-Zn type carrier and achieved an initial and pioneering exploration of methane-free CO hydrogenation to hydrocarbon reaction at mild CO conversion range. The catalyst modified by urotropine has a nanoflower micromorphology and can significantly change the reaction performance, almost completely eliminating the ability of the catalyst to inhibit C-C coupling within a mild CO conversion range, that is, it can produce no or less C1-C4 gaseous hydrocarbons, while rich in condensed hydrocarbons (i.e., C5+ hydrocarbon selectivity can reach as high as 92.8%-100.0%).

Catalytic hydrogenation of CO2 to DME on surface Cu via highly efficient electron redistribution at the Cu0/Cu+ interface

The activity of copper-based bifunctional catalysts for CO2 hydrogenation to dimethyl ether (DME) is generally constrained by the loss of Cu0 sites during the reaction. Previous studies have focused on introducing additional elements to improve the stability of active sites. In this study, an electron redistribution of the Cu/Cu2O interface was constructed. Surface Cu0 provides active sites for H2 adsorption and dissociation, and the Cu0/Cu+ interface sites are more beneficial for the activation and hydrogenation of CO2. The Ointer–H moieties that form at interface sites reduce the reaction energy barrier of CH3OH synthesis, and the decomposition of H2COOH* to CH2O* species is the rate-limiting step. In addition, the Cu0/Cu+ interface restricts the migration of copper species and protects the weak acid sites of HZSM-5 during the reaction. The present work provides an atomic-level description of H2 dissociation and CO2 activation by Cu0/Cu+ surface and interface sites.

Utilizing in situ construction of N-doped hierarchical porous carbon to achieve electronic control of highly dispersed Pd nanoparticles for efficient catalytic hydrogenation of CO2 to formic acid

Hydrogenation of CO2 to produce formic acid/formate is a significant pathway for future energy storage and utilization. The development of heterogeneous catalysts with high activity and stability for this process is still a challenge. In this work, the in-situ N-doped hierarchical porous carbon derived from distiller's grains was used as a support for Pd-based catalysts (Pd/NC) to convert CO2 into valuable chemicals while making high-value use of waste biomass. The optimum catalyst, Pd/NC-800, shown exceptional catalytic performance, achieving a turnover frequency (TOF) of 2060h-1 at 100℃, 4MPa in the catalytic CO2 hydrogenation to formate reaction. Comprehensive experimental results and density functional theory calculations indicate that the electronic effect between the pyridine N in the support and the Pd nanoparticles (NPs) can make the Pd surface reach the state of electron enrichment and enhance the metal-support interaction. Moreover, the synthesized material has hierarchical pore structure, which provides abundant Pd anchor location sites and improves mass transfer efficiency. The results not only provide a feasible strategy for the preparation of efficient CO2 hydrogenation catalysts, but also break a new and effective avenue for the resource utilization of distiller's grains.

The copper size effect of CuZn/CeO2 catalyst in CO2 hydrogenation to methanol

The escalating emission of CO2 has caused a significant environmental impact. Hydrogenation of CO2 to methanol stands as the primary objective in the liquid sunlight vision, aiming to mitigate CO2 emissions. CuZn-based transition metal catalysts, known for their cost-effectiveness, demonstrate commendable catalytic performance at moderate temperatures and pressures, showcasing considerable potential in industrial applications. Consequently, a series of catalysts, composed of CuZn-based species supported on CeO2 with strategically introduced appropriate oxygen vacancies, were meticulously prepared. It worth to noting that the size of Cu was precisely tuned, along with the enhanced ability to the adsorption and activation of CO2 and H2. As a result, the optimal CuZn/CeO2 catalyst exhibits high methanol formation rate, recording at 433.4 gMeOH kgcat−1 h−1 with selectivity of 68.5% at 260 °C and 3 MPa. Simultaneously, the reaction path and the evolution of intermediates in CO2 hydrogenation was thoroughly delineated.

Detection and Characterization of Hydride Ligands in Copper Complexes by Hard X-ray Spectroscopy.

Transition metal complexes, particularly copper hydrides, play an important role in various catalytic processes and molecular inorganic chemistry. This study employs synchrotron hard X-ray spectroscopy to gain insights into the geometric and electronic properties of copper hydrides as potential catalysts for CO2 hydrogenation. The potential of high energy resolution X-ray absorption near-edge structure (HERFD-XANES) and valence-to-core X-ray emission (VtC-XES) is demonstrated with measurement on Stryker's reagent (Cu6H6) and [Cu3(μ3-H)(dpmppe)2](PF6)2 (Cu3H), alongside a non-hydride copper compound (Cu-I). The XANES analysis reveals that coordination geometries strongly influence the spectra, providing only indirect details about hydride coordination. The VtC-XES analysis exhibits a distinct signal around 8975 eV, offering a diagnostic tool to identify hydride ligands. Theoretical calculations support and extend these findings by comparing hydride-containing complexes with their hydride-free counterparts.

Revealing the Interaction between Cu and MgO in Cu/MgO Catalysts for CO Hydrogenation to CH3OH

Revealing the Interaction between Cu and MgO in Cu/MgO Catalysts for CO Hydrogenation to CH₃OH

Highly selective CuO-ZnO@Cu-MOR catalysts prepared by ultrafast solid processing for carbon dioxide hydrogenation to methanol

The conversion of CO2 into methanol has emerged as a promising strategy for addressing climate change and optimizing the utilization of carbon resources. Conventional synthesis methods for Cu-based catalysts, such as co-precipitation, necessitate the consumption of substantial amounts of solvent and meticulous control over preparation conditions, while also being susceptible to deactivation by water during hydrogenation. Therefore, it is crucial to develop a catalyst that can be readily synthesized and exhibits outstanding performance and durability. In this study, we present an ultrafast (only 20 min), solid-phase grinding approach to fabricate CuO-ZnO@Cu-MOR catalysts for CO2 hydrogenation to methanol. The resulting catalysts were comprehensively characterized using XRD, XPS, H2-TPR, NH3-TPD, SEM, HRTEM, and In-situ-FTIR techniques. Notably, the CuO-ZnO@Cu-MOR catalysts with a distinctive capsule-like structure displayed a high catalytic performance for CO2 hydrogenation. The byproducts of methane and water produced by the CO2 hydrogenation process were able to be further converted to methanol through Cu-MOR, leading to a significant enhancement of the methanol selectivity (95.6 %) and CO2 conversion (22.8 %). Moreover, a long-term test lasting 300 h demonstrated constant catalytic performances and superior durability.

Development of Fe-based catalysts for CO2 hydrogenation to higher hydrocarbons for operating in slurry reactor

The development of CO2 hydrogenation catalysts for hydrocarbon production is a challenging and relevant task as it can contribute to solving of the CO2 emission problem. In the present work, we describe our journey in the development of catalysts for operating in a slurry reactor. The screening of the preparation methods and catalyst composition yielded an active and highly selective CO2 hydrogenation catalyst with catalytic performances comparable to the best ones reported in the literature. The most perspective catalysts were successfully evaluated in CO2 hydrogenation using a slurry reactor. The supported catalysts were found to have a lower ability to form higher hydrocarbons compared to bulk catalysts. This could be correlated with the particle sizes of the active component of the respective catalysts. This insight may be useful in preparing tailor-made Fe-based catalysts with high chain growth probability. The important issue of mechanical strength for slurry operation was highlighted.

Deciphering Local Structural Complexity in Zn/Ga-ZrO2 CO2 Hydrogenation Catalysts.

In the last few decades, massive effort has been expended in heterogeneous catalysis to develop new materials presenting high conversion, selectivity, and stability even under high-temperature and high-pressure conditions. In this context, CO2 hydrogenation is an interesting reaction where the catalyst local structure is strongly related to the development of an active and stable material under hydrothermal conditions at T/P > 300 °C/30 bar. In order to clarify the relationship between catalyst local ordering and its activity/stability, we herein report a combined laboratory and synchrotron investigation of aliovalent element (Ce/Zn/Ga)-containing ZrO2 matrixes. The results reveal the influence of similar average structures with different short-range orderings on the catalyst properties. Moreover, a further step toward the comprehension of the oxygen vacancy formation mechanism in Ce- and Ga-ZrO2 catalysts is reported. Finally, the reported results illustrate a robust method to guide local structure determination and ultimately help to avoid overuse of the "solid solution" definition.

Thermally stable Ni foam-supported inverse CeAlOx/Ni ensemble as an active structured catalyst for CO2 hydrogenation to methane

Nickel is the most widely used inexpensive active metal center of the heterogeneous catalysts for CO2 hydrogenation to methane. However, Ni-based catalysts suffer from severe deactivation in CO2 methanation reaction due to the irreversible sintering and coke deposition caused by the inevitable localized hotspots generated during the vigorously exothermic reaction. Herein, we demonstrate the inverse CeAlOx/Ni composite constructed on the Ni-foam structure support realizes remarkable CO2 methanation catalytic activity and stability in a wide operation temperature range from 240 to 600 °C. Significantly, CeAlOx/Ni/Ni-foam catalyst maintains its initial activity after seven drastic heating-cooling cycles from RT to 240 to 600 °C. Meanwhile, the structure catalyst also shows water resistance and long-term stability under reaction condition. The promising thermal stability and water-resistance of CeAlOx/Ni/Ni-foam originate from the excellent heat and mass transport efficiency which eliminates local hotspots and the formation of Ni-foam stabilized CeAlOx/Ni inverse composites which effectively anchored the active species and prevents carbon deposition from CH4 decomposition.

Titania-crystal-phase-engineered strong metal-support interactions and catalysis in CO2 hydrogenation

Tailoring strong metal-support interactions (SMSIs) have been verified to become an efficient strategy for developing novel heterogeneous catalysts. Here, both TiO2 supports (anatase (A) and rutile (R)) were employed to prepare the Pd/TiO2 catalysts and strongly titania-crystal-phase-dependent Pd-TiO2 SMSIs and catalysis in CO2 hydrogenation were observed. A-TiO2 is more facile to undergo Pd-TiO2 SMSIs than R-TiO2, which could be relevant to better reducibility over calcined Pd/A-TiO2C catalyst. Catalytic performance of the Pd/TiO2-R (reduced) catalysts in CO2 hydrogenation are sensitive to the Pd-TiO2 structures, among which the Pd nanoparticles mostly encapsulated by TiO2-x overlayers over Pd/A-TiO2-R catalyst with more prominent SMSIs is more intrinsically active. This could be ascribed to both stronger H-spillover and hydrogenation property and better CO2 activation capacity over Pd/A-TiO2-R catalyst. However, its catalytic activity is seriously restricted by the number of intrinsically active sites due to less exposed Pd atoms to block H2 activation sites. These results clearly demonstrate the crystal-phase engineering as an efficient strategy to tailor the SMSIs for developing improved heterogeneous catalysts.

Gas-phase continuous synthesis of metal-organic framework-derived hybrid catalysts for combined CO2 and CO hydrogenation to methanol

Aerosol-based continuous synthesis for metal–organic framework (MOF) derived catalyst materials, in combination with real-time gas-phase electrophoresis for material characterization, is demonstrated for methanol production via combined CO2 and CO hydrogenation. Cu-based and Zn-based MOF colloids were prepared as the templates for the synthesis of Cu-ZnO catalysts supported on either Al2O3 or CeO2. The results showed the incorporation of real-time gas-phase electrophoresis enabled traceability of continuous catalyst production. Optimal selectivity of 90.52 %, and space–time yield of 7.50 mmol gcat−1h−1 were achievable in the methanol production. Interestingly, the space–time yield of methanol was shown to be linearly proportional to metal surface area of the catalyst. This study demonstrated significant advances in the continuous production of MOF-derived hybrid catalysts through aerosol-phase synthesis with real-time characterization. The high catalytic performance of the developed materials in the combined CO2 and CO hydrogenation to methanol bears promise for applications in the field of CO2 utilization.

Unlocking the Potential of Cu/Ti3C2Tx MXene Catalyst in Plasma Catalytic CO2 Hydrogenation

Plasma catalytic CO2 hydrogenation has emerged as a promising approach for converting CO2 into valuable chemicals such as CO, offering a potential solution to mitigate greenhouse gas emissions. In this study, we investigate the synergistic effect between plasma and a Cu/Ti3C2Tx MXene catalyst for CO2 hydrogenation via the reverse water gas shift (RWGS) reaction in a dielectric barrier discharge (DBD) reactor. Our findings reveal a significant enhancement in CO2 conversion (33.1%) and CO yield (31.9%) when using the Cu/Ti3C2Tx catalyst compared to plasma alone or with a Ti3C2Tx foam. Plasma treatment creates unsaturated Ti sites on the Ti3C2Tx surface, dramatically improving CO2 adsorption and activation, while Cu NPs significantly enhances the activation and dissociation of H2 molecules on the catalyst surface. These surface adsorbed hydrogen species readily hydrogenate adsorbed CO2 molecules through the Langmuir-Hinshelwood mechanism. Furthermore, these surface hydrogen species can also participate in the conversion of gas-phase CO2 molecules through the Eley-Rideal pathway. This work sheds light on the synergistic plasma catalytic mechanism and provide insights for optimizing CO2 hydrogenation processes using MXene catalysts.

Regeneration of copper catalysts mediated by molybdenum-based oxides

Cu catalysts, known for their unparalleled catalytic capabilities due to their unique electronic structure, have faced inherent challenges in maintaining long-term effectiveness under harsh hydrogenation conditions. Here, we demonstrate a molybdenum-mediated redispersion behavior of Cu under high-temperature oxidation conditions. The oxidized Cu nanoparticles with rich metal-support interfaces tend to dissolve into the MoO3 support upon heating to 600 °C, which facilitates the subsequent regeneration in a reducing atmosphere. A similar redispersion phenomenon is observed for Cu nanoparticles supported on ZnO-modified MoO3. The modification of ZnO significantly improves the performance of the Cu catalyst for CO2 hydrogenation to methanol, with the high activity being well maintained after four repeated oxidation-reduction cycles. In situ spectroscopic and theoretical analyses suggest that the interaction involved in the formation of the copper molybdate-like compound is the driving force for the redispersion of Cu. This method is applicable to various Mo-based oxide supports, offering a practical strategy for the regeneration of sintered Cu particles in hydrogenation applications.

Selectivity control between reverse water-gas shift and fischer-tropsch synthesis in carbon-supported iron-based catalysts for CO2 hydrogenation

CO2 hydrogenation to chemicals and fuels has the potential to alleviate CO2 emissions and displace fossil resources simultaneously via consecutive RWGS and FTS reactions, also known as CO2-FTS. As Fe-based catalysts are active and selective for both reactions, their bifunctionality requires a delicate balance between the RWGS and FTS. In this work, we investigated the thermodynamic constraints of RWGS and CO2-FTS, the influence of CO2 conversion on selectivity and the influence of Fe nanoparticle size within the range of 4.7 to 10.3 nm. An inert carbon support was selected to rule out metal-support interaction and promoting effects of the support. Catalytic performance was evaluated at 300 °C, 11 bar, H2/CO2/Ar = 3/1/1, 600 to 72000 mL·gcat−1·h−1. At a CO2 conversion level below RWGS equilibrium conversion of 23 %, RWGS was found to be the primary and dominant reaction. No primary Sabatier reaction was observed. At higher CO2 conversion till the CO2-FTS threshold of 42 %, the secondary FTS reaction became dominant. Notably, a non-linear relation between CO2 conversion and CO selectivity was discovered. Comparing two catalysts with identical 5 wt% Fe loading but different average Fe nanoparticle size (6.6 and 8.4 nm), the 8.4 nm Fe catalyst was at least two times more active than the 6.6 nm Fe catalyst. In situ Mössbauer spectroscopy suggested a positive correlation between particle size, carburization and selectivity towards long-chain hydrocarbons. For these potassium-promoted carbon-supported Fe-based catalysts, nanoparticles of at least 8 nm are required for the formation of Fe carbides and improved reactivity.

Hydrogen Spillover Mechanisms on Copper on Zinc Oxide-Based Catalysts for Carbon Dioxide Hydrogenation to Methanol

This literature review examines the hydrogen spillover mechanisms on copper on zinc oxide (Cu/ZnO)-based catalysts for CO2 hydrogenation to methanol. The production of methanol from CO2 is an attractive process for mitigating greenhouse gas emissions and producing a valuable chemical feedstock. Cu/ZnO-based catalysts are known to exhibit high activity and selectivity towards methanol production and the hydrogen spillover effect is believed to play a crucial role in their performance. The review discusses the current understanding of the hydrogen spillover mechanism, including the nature of the active sites and the factors that affect spillover efficiency. It also summarises recent advances in catalyst design, such as the use of promoters and dopants, to enhance the hydrogen spillover effect and improve catalytic performance. This article provides a comprehensive overview of the hydrogen spillover mechanism on Cu/ZnO-based catalysts for CO2 hydrogenation to methanol, highlighting the potential of this technology for sustainable methanol production.

Developing Multifunctional Fe-Based Catalysts for the Direct Hydrogenation of CO2 in Power Plant Flue Gas to Light Olefins

The hydrogenation of carbon dioxide (CO2) to produce light olefins is one of the most promising ways to utilize CO2 in power plant flue gas. However, the low concentration of CO2 (~10%) and the existence of water steam in the flue gas pose great challenges for the catalyst design. To address these problems, we introduced a Mg promoter and hydrophobic component into the Fe-based catalyst to improve the CO2 adsorption capacity and weaken the negative effects of water. The yield of light olefins on an optimized multifunctional Fe-based catalyst increased by 37% in low-concentration CO2 hydrogenation with water steam. A variety of characterizations proved that the Mg promoter played critical roles in regulating the adsorption capacity of CO2, increasing the surface electron density of Fe species, and promoting the formation of iron carbide active sites. The hydrophobic component mainly contributed to constraining the oxidation of iron carbides via water steam. It benefited from the rational design of the catalyst, showing how our multifunctional Fe-based catalyst has great potential for practical application in CO2 utilization.

Modulating selectivity in CO2 Methanation through Rhodium catalysts supported on Zirconia-Chemically grafted SBA-15

This study presents the impact of ZrO2 incorporation on Rh-supported SBA-15 catalysts for CO2 hydrogenation. ZrO2 was chemically grafted onto the SBA-15 surface, varying concentrations of ZrO2 from 5 to 20 wt.%. The ZrO2-free catalyst favored CO production, leaning towards the reverse water gas shift reaction. The addition of ZrO2 notably enhanced catalytic activity and led to a significant shift in selectivity towards methane production. The selectivity modulation is linked with the modified surface of SBA-15, covered with a ZrO2 phase. The FTIR characterization under reaction conditions evidenced Rh-carbonyls formation in all samples. However, in catalysts materials with ZrO2, formate species are also formed, probably promoted by the Zr-OH groups. A linear relation between formate species and the CH4 selectivity suggests that the methane formation could be associated with the hydrogenation of formate species, while the desorption of carbonyls on Rh can explain the CO generation.