CO Hydrogenation Activity Research Articles

Rational Design of N-doped Carbon Coated Cobalt Nanoparticles for Highly Efficient and Durable Photothermal CO2 Conversion.

The photothermal CO2 hydrogenation to high value-added chemicals and fuels is an appealing approach to alleviate the energy and environmental concerns. However, it still relies on the development of earth-abundant, efficient and durable catalysts. Here, we report the design of N-doped carbon coated Co nanoparticles (NPs) as a photothermal catalyst, synthesized through a two-step pyrolysis of Co-based ZIF-67 precursor. Consequently, the catalyst exhibits remarkable activity and stability for photothermal CO2 hydrogenation to CO with a 0.75mol gcat -1 h-1 CO production rate under the full spectrum of light illumination. The high activity and durability of this Co NPs are mainly attributed to the synergy of the attuned size of Co NPs, the thickness of carbon layers and the N doping species. Impressively, the experimental characterizations and theoretical simulations show that such a simple N-doped carbon coating strategy can effectively facilitate the desorption of generated CO and activation of reactants due to the strong photothermal effect. This work provides a simple and efficient route for the preparation of highly active and durable nonprecious metal catalysts for promising photothermal catalytic reactions. This article is protected by copyright. All rights reserved.

Effect of Different In2O3(111) Surface Terminations on CO2 Adsorption.

In2O3-based catalysts have shown high activity and selectivity for CO2 hydrogenation to methanol; however, the origin of the high performance of In2O3 is still unclear. To elucidate the initial steps of CO2 hydrogenation over In2O3, we have combined X-ray photoelectron spectroscopy and density functional theory calculations to study the adsorption of CO2 on the In2O3(111) crystalline surface with different terminations, namely, the stoichiometric, reduced, and hydroxylated surface. The combined approach confirms that the reduction of the surface results in the formation of In adatoms and that water dissociates on the surface at room temperature. A comparison of the experimental spectra and the computed core-level shifts (using methanol and formic acid as benchmark molecules) suggests that CO2 adsorbs as a carbonate on all three surface terminations. We find that the adsorption of CO2 is hindered by hydroxyl groups on the hydroxylated surface.

ZrO2 promoted Ru/In2O3 catalyst for selective hydrogenation of CO2 to methanol

With the strong metal-support interaction, In2O3 supported Ru catalyst has been confirmed to be active for selective hydrogenation of CO2 to methanol. Herein, we report that the addition of ZrO2 into Ru/In2O3 further improves the catalytic activity for CO2 hydrogenation to methanol. The catalyst characterization shows a formation of In2O3-ZrO2 solid solution, which is an excellent support for the highly dispersed Ru catalyst. Compared to Ru/In2O3, a significantly higher methanol selectivity is achieved over the Ru/In2O3-ZrO2 catalyst with 1 wt% Ru loading. The methanol space–time yield (STY) reaches 0.685 gMeOH h−1 gcat−1 at 300 ℃, 5 MPa, and 21000 cm3 gcat−1h−1. It has more than 20% increase compared to Ru/In2O3. The addition of ZrO2 optimizes the oxygen vacancies of In2O3, improves the CO2 adsorption and enables a more stable catalyst architecture, while the hydrogen spillover by the highly dispersed ruthenium improves the hydrogen activation ability of the catalyst. All these results in a high level of methanol yield.

Hydrogenation of CO2 to MeOH Catalyzed by Highly Robust (PNNP)Ir Complexes Activated by Alkali Bases in Alcohol.

Despite receiving significant attention, well-defined homogeneous complexes for hydrogenation of carbon dioxide (CO2) to methanol (MeOH) are scarce and suffer issues of low catalyst turnover numbers (TONs) at high catalyst concentrations and deactivation in the presence of CO and at elevated temperatures. Herein, we disclose a system deploying sterically demanded (PNNP)Ir complexes for a sustained activity for hydrogenation of CO2 to MeOH at temperatures ∼200 °C in an alcohol solvent. Through reaction optimization, we achieved a TON of ∼9000 for MeOH formation, which exceeds most active homogeneous systems reported to date, and robustness on par with or exceeding most reactive systems utilizing amine additives was demonstrated. The key to achieving sustained catalyst turnover for the system was utilizing a catalytic amount of an alkali base additive, which serves the dual purpose of facilitating more efficient outer-sphere reduction of CO2 and HCO2Et and enhancing the selectivity of MeOH over in situ formed CO.

Enhanced performance and stability of Cu/ZnO catalyst by hydrophobic treatment for low-temperature methanol synthesis from CO2

CO2 hydrogenation to methanol is an efficient way to utilize CO2 and store hydrogen. However, realizing high activity and methanol selectivity as well as excellent stability are still challenges due to the competitive reverse water-gas shift (RWGS) reaction and the accumulation of water on the catalyst surface. Herein, Cu/ZnO catalyst was prepared by oxalic acid-assisted solid-state grinding method and then was subjected to hydrophobic treatment using stearic acid as a functionalization agent. The effect of stearic acid concentration on the physicochemical properties of Cu/ZnO catalysts and the catalytic activity for low-temperature CO2 hydrogenation to methanol was investigated and discussed in detail. Detailed catalyst characterizations disclosed that hydrophobic treatment using suitable concentration of stearic acid removed residues from the decomposition of oxalic acid and also increased specific surface area, surface basicity, reducibility and hydrogen adsorption strength on Cu/ZnO catalysts, leading to the enhanced catalytic performance and methanol selectivity. Among all the catalysts, Cu/Zn-2 mM catalyst exhibited methanol selectivity and methanol space time yield (STY) of 78.8% and 87.17 g/kg·h−1 at 200 ℃, much higher than those of untreated Cu/ZnO catalyst (71.7% and 68.93 g/kg·h−1). The hydrophobic Cu/Zn-2 mM catalyst also exhibited outstanding stability for low-temperature CO2 hydrogenation to methanol, keeping its activity for 100 h without obvious deactivation when compared to untreated Cu/ZnO catalyst. This facile hydrophobic treatment using stearic acid not also enhanced catalytic activity, methanol selectivity and stability of Cu/ZnO catalysts for low-temperature methanol synthesis, but also enlightened the invention of more hydrophobic materials in the near future.

Dual Localized Surface Plasmon Resonance effect enhances Nb2AlC/Nb2C MXene thermally coupled photocatalytic reduction of CO2 hydrogenation activity

Nb2AlC/Nb2C MXene (NAC/NC) heterojunction photocatalysts with Schottky junctions were obtained by selective etching of the Al layer, resulting in 146.25 μmol·g−1 electrons and 15.28 μmol·g−1 holes stored in the heterojunction. The average conversion of NAC/NC thermally coupled photocatalytic reduction of CO2 under the simulated solar irradiation reached 110.15 μmol⋅g−1⋅h−1, and the CO selectivity reached over 92%, which was 1.49 and 1.74 times higher than that of pure Nb2AlC and Nb2C MXene, respectively. After light excitation, the localized surface plasmon resonance (LSPR) effect of holes distributed on the surface of Nb2C MXene crystals in the heterojunction will form high-energy thermal holes to dissociate H2 to H+ and reduce CO2 to form H2O at the same time. The high-energy electrons formed by the LSPR effect of Nb2C MXene and the conduction band electrons generated by the photoexcitation of Nb2C MXene can be migrated to Nb2AlC under the action of the interfacial Schottky junction to supplement the electrons needed for the LSPR effect of Nb2AlC, which continuously forms high-energy hot electrons to convert the adsorbed CO2 into *CO2−, b-HCO3, and HCOO. Subsequently, HCOO releases ⋅OH in a cyclic reaction to continuously reduce to form CO. The dual LSPR effect of Nb2AlC and Nb2C MXene is used to enhance the hydrogenation activity of thermally coupled photocatalytic reduction of CO2, which provides a new research idea for the application of MXene in thermally coupled photoreduction of CO2.

The structure-activity relationship of AlOOH for CO hydrogenation

In this paper, the structure-activity relationship of three AlOOH samples prepared using the complete liquid-phase, hydrothermal and precipitation methods is investigated. The structure of AlOOH samples is characterized by XRD, BET, FT-IR, and NH3/CO2/CO-TPD-MS techniques. The activity of CO hydrogenation is studied over AlOOH composite catalysts which are mechanically mixed with a methanol synthesis catalyst, in a fixed-bed reactor. The results demonstrate that the different preparation methods employed have a profound effect on the structure of AlOOH, which subsequently affects the catalytic performance, especially the product distribution. Particularly, the AlOOH prepared using the hydrothermal method exhibits high crystallinity, and possesses an integrated interlayer structure. This unique structure enhances the dissociative adsorption of CO molecules, facilitates the growth of the carbon chain, and results in a remarkable increase in the proportion of higher alcohols in the products. Therefore, these findings contribute not only to a better understanding of catalysts for higher alcohols but also broaden the research scope in the field of catalytic material.

Unraveling Anisotropic and Pulsating Etching of ZnO Nanorods in Hydrochloric Acid via Correlative Electron Microscopy.

Despite much technical progress achieved so far, the exact surface and shape evolution during wet chemical etching is less unraveled, especially in ionically bonded ceramics. Herein, by using in situ liquid cell transmission electron microscopy, a repeated two-stage anisotropic and pulsating periodic etching dynamic is discovered during the pencil shape evolution of a single crystal ZnO nanorod in aqueous hydrochloric acid. Specifically, the nanopencil tip shrinks at a slower rate along [0001̅] than that along the ⟨101̅0⟩ directions, resulting in a sharper ZnO pencil tip. Afterward, rapid tip dissolution happens due to accelerated etching rates along various crystal directions. Concurrently, the vicinal base region of the original nanopencil tip emerges as a new tip followed by the repeated sequence of tip shrinking and removal. The high-index surfaces, such as {101̅m} (m = 0, 1, 2, or 3) and {21̅ 1̅n} (n = 0, 1, 2, or 3), are found to preferentially expose in different ratios. Our 3D electron tomography, convergent beam electron diffraction, middle-angle bright-field STEM, and XPS results indicate the dissociative Cl- species were bound to the Zn-terminated tip surfaces. Furthermore, DFT calculation suggests the preferential Cl- passivation over the {101̅1} and (0001) surfaces of lower energy than others, leading to preferential surface exposures and the oscillatory variation of different facet etching rates. The boosted reactivity due to high-index nanoscale surface exposures is confirmed by comparatively enhanced chemical sensing and CO2 hydrogenation activity. These findings provide an in-depth understanding of anisotropic wet chemical etching of ionic nanocrystals and offer a design strategy for advanced functional materials.

Insight Understanding of Ultrathin Carbon-Deficient Molybdenum Carbide Catalytic Activity for CO2 Conversion into Hydrocarbon Fuels

The catalytic reduction of carbon dioxide (CO2) to produce methane (CH4) as a hydrocarbon fuel has attracted extensive attention for renewable energy. In this study, we investigate ultrathin carbon-deficient molybdenum carbide (MoC0.66) as a catalyst for CO2 capture and conversion. Our findings indicate that MoC0.66 possesses remarkable catalytic activity for CO2 hydrogenation to CH4. Interestingly, unlike conventional catalysts, the limiting step of the MoC0.66 catalyst is determined by the release of *OH species during the CO2 reduction reaction (CO2RR). Increasing the temperature can improve the release of H2O and CH4 as well as the selectivity of the CO2RR. Moreover, the increase of temperature promotes the CO2RR on MoC0.66 by increasing the reaction rate, as evidenced by both simulation and experimental results. These results provide a way for the understanding of insight mechanisms for the CO2RR to energy-rich fuels at the atomic level and guide experimental applications of carbon-neutral reactions.

Cu-based high-entropy two-dimensional oxide as stable and active photothermal catalyst

Cu-based nanocatalysts are the cornerstone of various industrial catalytic processes. Synergistically strengthening the catalytic stability and activity of Cu-based nanocatalysts is an ongoing challenge. Herein, the high-entropy principle is applied to modify the structure of Cu-based nanocatalysts, and a PVP templated method is invented for generally synthesizing six-eleven dissimilar elements as high-entropy two-dimensional (2D) materials. Taking 2D Cu2Zn1Al0.5Ce5Zr0.5Ox as an example, the high-entropy structure not only enhances the sintering resistance from 400 °C to 800 °C but also improves its CO2 hydrogenation activity to a pure CO production rate of 417.2 mmol g−1 h−1 at 500 °C, 4 times higher than that of reported advanced catalysts. When 2D Cu2Zn1Al0.5Ce5Zr0.5Ox are applied to the photothermal CO2 hydrogenation, it exhibits a record photochemical energy conversion efficiency of 36.2%, with a CO generation rate of 248.5 mmol g−1 h−1 and 571 L of CO yield under ambient sunlight irradiation. The high-entropy 2D materials provide a new route to simultaneously achieve catalytic stability and activity, greatly expanding the application boundaries of photothermal catalysis.

Hydrogenation of Carbon Dioxide to Formate by Noble Metal Catalysts Supported on a Chemically Stable Lanthanum Rod-Metal-Organic Framework.

The conversion of carbon dioxide to formate is of great importance for hydrogen storage as well as being a step to access an array of olefins. Herein, we have prepared a JMS-5 metal-organic framework (MOF) using a bipyridyl dicarboxylate linker, with the molecular formula [La2(bpdc)3/2(dmf)2(OAc)3]·dmf. The MOF was functionalized by cyclometalation using Pd(II), Pt(II), Ru(II), Rh(III), and Ir(III) complexes. All metal catalysts supported on JMS-5 showed activity for CO2 hydrogenation to formate, with Rh(III)@JMS-5a and Ir(III)@JMS-5a yielding 4319 and 5473 TON, respectively. X-ray photoelectron spectroscopy of the most active catalyst Ir(III)@JMS-5a revealed that the iridium binding energies shifted to lower values, consistent with formation of Ir-H active species during catalysis. The transmission electron microscopy images of the recovered catalysts of Ir(III)@JMS-5a and Rh(III)@JMS-5a did not show any nanoparticles. This suggests that the catalytic activity observed was due to Ir(III) and Rh(III). The high activity displayed by Ir(III)@JMS-5a and Rh(III)@JMS-5a compared to using the Ir(III) and Rh(III) complexes on their own is attributed to the stabilization of the Ir(III) and Rh(III) on the nitrogen and carbon atom of the MOF backbone.

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.

Boosting oxygen vacancies by modulating the morphology of Au decorated In2O3 with enhanced CO2 hydrogenation activity to CH3OH

CO2 hydrogenation to methanol has become one of the most promising ways for CO2 utilization, however, the CO2 conversion rate and methanol selectivity of this reaction still need to be improved for industrial application. Here we investigated the structure-activity relationship for CO2 conversion to methanol of In2O3-based catalysts by modulating morphology and decorating Au. Three different Au/In2O3 catalysts were prepared, their activity follow the sequence of Au/In2O3-nanosphere (Au/In2O3-NS) > Au/In2O3-nanoplate (Au/In2O3-NP) > Au/In2O3-hollow microsphere (Au/In2O3-HM). Au/In2O3-NS exhibited the best performance with good CO2 conversion of 12.7%, high methanol selectivity of 59.8%, and large space time yield of 0.32 gCH3OH/(hr·gcat) at 300°C. The high performance of Au/In2O3-NS was considered as the presence of Au. It contributes to the creation of more surface oxygen vacancies, which further promoted the CO2 adsorption and facilitated CO2 activation to form the formate intermediates towards methanol. This work clearly suggests that the activity of In2O3 catalyst can be effective enhanced by structure engineering and Au decorating.

Understanding surface structures of In2O3 catalysts during CO2 hydrogenation reaction using time-resolved IR, XPS with in situ treatment, and DFT calculations

The In2O3 catalyst has been shown to have a high activity for CO2 hydrogenation to methanol. For this high pressure process, reliable spectral assignment of surface species formed by interaction with CO2, H2O, and other major reaction ingredients, is the key step to achieve mechanistic understanding. In this study, in situ IR and XPS are performed to investigate the O1s binding energies of the adsorbates induced by CO2 and H2O treatments along with density functional theory (DFT) simulations to further correlate the calibrated assignments with surface structures. Time resolved IR indicates that carbonates formation induced by CO2 exposure replaces the original hydroxyl on In2O3, and XPS further reveals that these two oxygen species have very similar binding energies (532.0 ± 0.2 eV). Computational results using the In2O3(110) and (111) slab models give good agreement with the XPS experiments, further suggesting that the amount of oxygen vacancy concentration does not induce new lattice oxygen O1s binding energy, but resulting in a slight shift to a higher binding energy instead. Our results provide useful structure information for the In2O3 catalyst surface and shed light for further investigations into its kinetic behavior under methanol synthesis condition.

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.

CO2 Activation on Ni(111) and Ni(110) Surfaces in the Presence of Hydrogen

The structure sensitivity of CO2 activation in the presence of H2 has been identified by ambient-pressure X-ray photoelectron spectroscopy (APXPS) on Ni(111) and Ni(110) surfaces under identical reaction conditions. Based on the APXPS results and computer simulations, we propose that, around room temperature, the hydrogen-assisted activation of CO2 is the major reaction path on Ni(111), while the redox pathway of CO2 prevails on Ni(110). With increasing temperature, the two activation pathways are activated in parallel. While the Ni(111) surface is fully reduced to the metallic state at elevated temperatures, two stable Ni oxide species can be observed on Ni(110). Turnover frequency measurements indicate that the low-coordinated sites on Ni(110) promote the activity and selectivity of CO2 hydrogenation to methane. Our findings provide insights into the role of low-coordinated Ni sites in nanoparticle catalysts for CO2 methanation.

Highly Efficient CuPd0.1/γ-Al2O3 Catalyst with Isolated Pd Species for CO2 Hydrogenation to Methanol

CO2 hydrogenation is one of the most effective solutions for mitigating excessive CO2 emissions. In this work, CuPdx/γ-Al2O3 (x = 0.05–5.7 wt %) catalysts were prepared and applied in CO2 hydrogenation to methanol. The results showed CuPd0.1/γ-Al2O3 achieved excellent CO2 hydrogenation activity. It is demonstrated that the Pd species of CuPd0.1/γ-Al2O3 is highly dispersed on the γ-Al2O3 support at the atomic level and separated from Cu nanoparticles by AC-HAADF-STEM, rather than forming CuPd alloy. Part of the hydrogen species activated by isolated Pd atoms overflows onto γ-Al2O3 and influences the reduction of CuO, thus effectively increasing the Cu+/(Cu++Cu0) ratio which is correlated with the prominent CO2 hydrogenation performance. On the other hand, we found that CH3OH retained on catalyst surface can be further reformed into CO, which significantly reduces the selectivity of CH3OH. To limit CH3OH reforming, the activity test of CuPd0.1/γ-Al2O3 in a fixed bed at different weight hourly space velocity was performed, where the remarkable methanol yields of 5.9 mmol/gcat./h were obtained.

Construction of surface active centers on the mesoporous Co/CeO2-δ catalysts for CO2 hydrogenation

The surface active centers, which include metal Co, surface oxygen vacancies, and Co0–CeO2-δ interface structures, can be constructed on the mesoporous Co/CeO2-δ catalysts by wet impregnation method. And the surface active centers can be regulated by the Co species dosage. The interaction between the metal Co and CeO2-δ can promote surface oxygen vacancies and Co0–CeO2-δ interface structures to be formed and be conducive to inhibit the aggregation and sintering of Co species in high temperature environment. The prepared Co/CeO2-δ catalysts have better catalytic performances for CO2 hydrogenation than the single component Co and CeO2-δ catalysts, which can be attributed to the synergistic effect between Co0 active centers, surface oxygen vacancies, and Co0–CeO2-δ interface structures. Therefore, the Co/CeO2-δ catalysts have strong adsorption and activation ability for reactant CO2 and H2 molecules to improve the CO2 hydrogenation activity. At atmospheric pressure and 400 °C, the CO2 conversion and CH4 selectivity on the Co/CeO2-δ catalyst with Co loading of 12% could reach 59.7% and 95.7%, respectively, and maintained good stability in 9 cycles for CO2 hydrogenation reaction.

Zn-CdZrOx solid solution catalysts for hydrogenation of CO2 to methanol

CO2 is one of the members of greenhouse gases, and its capture, collection, and recycling have aroused widespread concern. Methanol is not only a basic organic chemical raw material, but also a high-quality clean fuel. The idea of CO2 hydrogenation to methanol can turn waste into treasure and realize the resource utilization of CO2 ultimately. Of course, the value of solving environmental and energy problems is immeasurable.Here, a series of y% Zn-doped CdZrOx catalysts are prepared and the 5.0% Zn-CdZrOx shows 80.82% methanol selectivity and 8.52% CO2 conversion rate at 320℃. Combining HRTEM images and XRD patterns, it is found that 5% Zn-CdZrOx shows the structure of the solid solution. CO2-TPD shows that the desorption peak area of 5.0% Zn-CdZrOx is large, which means more beneficial to CO2 adsorption and activation. H2-TPR indicates the existence of the strongly synergistic interaction between Zn, Cd, and Zr of 5.0% Zn-CdZrOx. From the in-situ DRIFTS, the peaks of HCOO* and H3CO* species are monitored, which is important to methanol formation.It is supposed there is a synergistic effect between Cd, Zn, and Zr in this catalyst and the structure of the solid solution is the decisive factor for the activity of CO2 hydrogenation to methanol.

Room-Temperature CO2 Hydrogenation to Methanol over Air-Stable hcp-PdMo Intermetallic Catalyst.

CO2 hydrogenation to methanol is one of the most promising routes to CO2 utilization. However, difficulty in CO2 activation at low temperature, catalyst stability, catalyst preparation, and product separation are obstacles to the realization of a practical hydrogenation process under mild conditions. Here, we report a PdMo intermetallic catalyst for low-temperature CO2 hydrogenation. This catalyst can be synthesized by the facile ammonolysis of an oxide precursor and exhibits excellent stability in air and the reaction atmosphere and significantly enhances the catalytic activity for CO2 hydrogenation to methanol and CO compared with a Pd catalyst. A turnover frequency of 0.15 h-1 was achieved for methanol synthesis at 0.9 MPa and 25 °C, which is comparable to or higher than that of the state-of-the-art heterogeneous catalysts under higher-pressure conditions (4-5 MPa).