CO Hydrogenation Reaction Research Articles

Ru-Catalyzed Reverse Water Gas Shift Reaction with Near-Unity Selectivity and Superior Stability

Cascade catalysis of reverse water gas shift (RWGS) and well-established CO hydrogenation holds promise for the conversion of greenhouse gas CO2 and renewable H2 into liquid hydrocarbons and methanol under mild conditions. However, it remains a big challenge to develop low-temperature RWGS catalysts with high activity, selectivity, and stability. Here, we report the design of an efficient RWGS catalyst by encapsulating ruthenium clusters with the size of 1 nm inside hollow silica shells. The spatially confined structure prevents the sintering of Ru clusters while the permeable silica layer allows the diffusion of gaseous reactants and products. This catalyst with reduced particle sizes not only inherits the excellent activity of Ru in CO2 hydrogenation reactions but also exhibits nearly 100% CO selectivity and superior stability at 200–500 °C. The ability to selectively produce CO from CO2 at relatively low temperatures paves the way for the production of value-added fuels from CO2 and renewable H2.

CO2 Hydrogenation to Methanol over Partially Reduced Cu-SiO2P Catalysts: The Crucial Role of Hydroxyls for Methanol Selectivity

The involvement of surface hydroxyl species in controlling methanol selectivity for a CO2 hydrogenation reaction was investigated over Cu-phyllosilicate (Cu-SiO2P) catalysts prepared by a urea-assisted hydrothermal synthesis method. The role of hydroxyls involvement was investigated by treating the Cu-SiO2P catalyst between 225 and 350 °C in H2 gas. The presence of Cu-containing phyllosilicate structures in Cu-SiO2P catalysts was confirmed through TEM and XPS analyses. As evidenced by in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and X-ray absorption spectroscopy, Cu+ centers are dominant surface species for Cu in Cu-SiO2P catalysts during the hydrogenation reaction. Also, bidentate formate species are the prominent intermediates to direct methanol formation via methoxy intermediate species. The hydroxyl intervention in CO2 hydrogenation for a hydroxyl-abundant Cu-SiO2P catalyst reduced at 225 °C is confirmed by the appearance of a new band at 2944 cm–1 (−C–H) by high-pressure in situ DRIFTS CO2 hydrogenation experiments. H2/CO-TPR revealed the uniformity and presence of surface hydroxyls in Cu-SiO2P catalysts. The best catalyst Cu-SiO2P reduced at 225 °C gave a stable CO2 conversion of 3.5% and a methanol yield of 140 mg MeOH/g-cat.h (a methanol selectivity of 77%) at 225 °C and 3 MPa pressure for a 24 h reaction time. The presence of hydroxyls generated due to partial reduction of the Cu-SiO2P catalyst and surface enriched with Cu+ species could be the reasons for its superior catalytic performance.

Elucidating the layer-number impact of MoS2 on the adsorption and hydrogenation of CO

MoS2 is an attractive sulfur-resistant catalyst for directly converting sulfur-containing syngas to high value-added chemicals. However, the effect of the layered structure on the catalytic activity for CO hydrogenation reactions is far from clear. Herein, MoS2/carbon composite catalysts with 1–8 stacking layers in MoS2 crystallites are synthesized, and the impact of the layer numbers on the catalytic performance is probed for the low-temperature methanation of sulfur-containing syngas. The results indicate that the turnover frequency of CO methanation increases from 2.4 × 10-3 to 3.7 × 10-3 s−1 with decreasing layer numbers of MoS2 crystallites from 8.3 to 1.1. This result is thoroughly explained by the fact that the higher ratio of rim sites in MoS2 crystallites with fewer layer numbers enhances the catalytic activity, which originates from the facilitated activation of CO and H2. These understandings are important for the rational design and development of more efficient MoS2-based catalysts for CO hydrogenation.

Biohydrogen production by glycerol Aqueous-Phase Reforming: Effect of promoters (Ce or Mg) in the NiAl2O4 spinel-derived catalysts

Biohydrogen production by Aqueous-Phase Reforming (APR) of glycerol was studied over nickel aluminate spinel-derived catalysts modified by Ce or Mg. As reference, an alumina supported nickel catalyst was also investigated. Catalysts were characterised by a sort of techniques in order to elucidate any structure-activity relationship, and tested for the WGS and CO hydrogenation reactions. It was concluded that the spinel catalyst allowed a better dispersion of the metallic Ni, and led to a more APR active and more hydrogen-selective catalyst. Mg and Ce doping further increased the nickel dispersion and increased basicity what could be related to their higher WGS relative reaction rate. Also, Mg doping hindered nickel reduction due to Ni-Mg interactions. Both promoters improved the stability of the textural properties under APR conditions, minimizing the formation of boehmite. Leaching of Ni was found, at lesser extent after Mg doping.

Ternary Fe–Zn–Al Spinel Catalyst for CO2 Hydrogenation to Linear α-Olefins: Synergy Effects between Al and Zn

Direct conversion of CO2 into linear α-olefins with Fe-based catalysts is promising both technically and economically. Al as a widely employed structural additive to Fe-based CO/CO2 hydrogenation catalysts is known to exhibit a side effect of shifting the selectivity from olefins to undesirable methane. Here, we report that by doping Zn into a binary Fe–Al spinel, a ternary Fe–Zn–Al spinel catalyst could be obtained with a high space–time yield with respect to linear α-olefins of 150.8 mmolC·gFe–1·h–1 in CO2 hydrogenation reactions. Multiple in situ/ex situ characterizations combined with DFT calculations illustrate that active Fe5C2 nanoparticles are wrapped with Fe–Al spinel overlayers with the introduction of Al alone, which is responsible for facilitating hydrogenation and inhibiting C–C coupling over the Fe–Al catalysts. Extra doping of Zn allows redistribution of Al to alleviate undesirable strong interactions between Fe5C2 and spinel phases, rendering a high selectivity to higher olefins. The revelation of a subtle synergy effect between Al and Zn underscores the pivotal role of precise tuning of multiple catalyst additives in optimizing the overall catalytic performance.

Revealing the dependence of CO2 activation on hydrogen dissociation ability over supported nickel catalysts

AbstractIn the present work, we demonstrate that the mechanism and kinetics of CO2 activation, as the first step of its hydrogenation, over supported nickel catalysts is particle size sensitive owing to the distinct H2 dissociation ability over nickel particles with various sizes. Large nickel nanoparticles facilitate H2 dissociation, enabling CO2 activation via a kinetically favored redox mechanism compared to small nickel nanoparticles that activate CO2 via the formate mechanism. The elucidation of the dependency of the catalytic reaction pathway on particle size will guide the rational design of supported nickel catalysts for selective CO2 hydrogenation. This work demonstrated in the CO2 hydrogenation reaction, CO2 is activated through different mechanisms due to different H2 dissociation capabilities over supported Ni catalysts with different particle sizes, which provides a convincing experimental explanation for the structural sensitivity of nickel‐based catalysts.

The effect of process parameters on catalytic direct CO2 hydrogenation to methanol

The direct CO2 hydrogenation to methanol is an attractive route to actively remove CO2 and to promote sustainable development. Herein, the performance of Cu-Zn-Mn catalyst supported on mesoporous silica KIT-6 (hereafter, CZM/KIT-6) for methanol synthesis by direct CO2 hydrogenation reaction was investigated by varying the process parameters, which included the weight-hourly space velocity, reaction temperature and reaction pressure. The CO2 conversion was found to decrease with the increase of WHSV. On the other hand, CO2 conversion increased with reaction temperature and pressure. Meanwhile, the methanol selectivity increased with WHSV and reaction pressure but decreased with the increase of reaction temperature. The apparent activation energy of methanol production at low reaction temperature (160 - 220 °C) was 10 kcal/mol. Non-Arrhenius behaviour of methanol formation was observed at high reaction temperature (220 - 260 °C). The performance of CZM/KIT-6 was maintained at high level, with the average methanol yield of 24.4 %, throughout the stability experiment (120-hour time-on-stream). In post-reaction XRD analysis, the copper crystallite growth was found to be 53.5 %, thus, resulting in 35.3 % loss of copper surface area.

Microstructure and catalytic properties of Fe3O4/BN, Fe3O4(Pt)/BN, and FePt/BN heterogeneous nanomaterials in CO2 hydrogenation reaction: Experimental and theoretical insights

Hexagonal boron nitride (h-BN) nanosheets are a promising material for various applications including catalysis. Herein, h-BN-supported Fe-based catalysts are characterised with respect to CO2 hydrogenation reaction. Heterogeneous Fe3O4/BN, Fe3O4(Pt)/BN, and FePt/BN nanostructures are obtained via polyol synthesis in ethylene glycol. The sizes of Fe3O4 nanoparticles and their distributions over h-BN surfaces depend on the amount of H2PtCl6 added to the synthesis media. Bimetallic FePt nanoparticles are formed when Pt content is high enough. In situ TEM analysis shows the formation of core–shell h-BN@FePt nanoparticles during heating that prevents FePt NPs from further sintering during the catalytic process. The mechanism of Fe and Pt interaction is elucidated based on the molecular dynamic simulations. The FePt/BN nanomaterials show significantly higher CO2 conversion rate compared to the Fe3O4/BN and Fe3O4(Pt)/BN heterogeneous nanomaterials and exhibit almost 100% selectivity to carbon monoxide. The Fe3O4/BN and Fe3O4(Pt)/BN nanomaterials show better selectivity to hydrocarbons. The possible reaction pathways are discussed based on the calculated sorption energies of all reactants, intermediate compounds, and reaction products. The study highlights pronounced catalytic properties of the developed system and reveals a unique interaction mechanism between its components increasing their stability.

Effect of Na and K impurities on the performance of Ni/CeZrOx catalysts in DBD plasma-catalytic CO2 methanation

Carbon dioxide hydrogenation to synthetic fuels and value-added molecules has been lately proposed as a promising technology to stabilize anthropogenic greenhouse gas emissions. Alkali compounds are often present in biomass pyrolysis/gasification syngas or can remain on the surface of the catalyst upon its synthesis. Their presence conditions the performance of the catalyst used in the CO2 hydrogenation reaction. This extends to plasma-activated catalysis since alkali compounds can moreover alter the electric features of the catalytic material. In the present work, non-thermal plasma (NTP)-assisted CO2 methanation was performed over alkali metal (Na and K)-containing Ni/CeZrOx catalysts. The influence of the presence of such alkali compounds on the physicochemical, dielectric and catalytic behavior of these materials during the on-plasma operation was assessed. The presence of Na and K impurities resulted in decreased CO2 conversions, lower selectivity to CH4 and increased power consumption. Their interaction with both the support and the active phase led to a more difficult reduction of the Ce-species, as well as to an increase in the dielectric constant of the packed bed. Higher dielectric constant contributed to increased energy dissipation and favored the strong ionization of the gas contained in the reactor gap, resulting in CO formation as a consequence of direct CO2 splitting. Finally, the impeeded reducibility of the Ce-species led to CO2 adsorption in the form of polydentate and bridged carbonates which were not able to participate in the catalytic cycle, resulting in poorer overall catalytic performance and in the accumulation of O and C-species within the support.

CO hydrogenation reaction on Fe–Co–Mn nanocatalyst: impact of support and process conditions on performance and structure

AbstractThe hydrothermal method was used in order to prepare Fe–Co–Mn nanocatalysts. The prepared specimens were evaluated for the CO hydrogenation reaction. The impact of different kinds of supports such as Al2O3, SiO2, ZSM5, TiO2, MgO, ZSM5–Al2O3, ZSM5–TiO2, Al2O3–TiO2, Al2O3–SiO2, SiO2–ZSM5 and Al2O3–MgO on the behavior and structural characteristics of the Fe–Co–Mn ternary nanocatalysts was investigated. Evaluation of these various supported samples was performed under the same process conditions. Al2O3‐supported sample showed better performance for light olefin production chosen as an optimum sample. Furthermore, the influence of a change of support type on the rate of surface reactions was studied. The impact of operating parameters was also investigated, with the conditions of T = 623 K, P = 2 bar and H2/CO = 2 determined as the optimum reaction conditions. Catalyst characteristics were defined using a variety of methods. © 2021 Society of Chemical Industry (SCI).

Synthesis of few-layered graphene sheets as support of cobalt nanoparticles and its influence on CO hydrogenation

We prepared few-layered reduced graphene oxide (rGO) as support in CO hydrogenation reaction. We investigated the graphene structure, mostly its electron donation effects to the cobalt particles, exploring the CO dissociation and the reaction results. Some modifications in the graphene synthesis method allowed the obtaining of a few-layered structure. No crystalline areas were detected. The prepared reduced graphene oxide was decorated with cobalt nanoparticles using the precipitation-deposition method (15% wt) in an alcoholic media. The catalyst was characterized before and after reaction by several techniques. XPS results revealed a higher concentration of Co2+ species at the surface and electrostatic interaction with the support. Diffuse Reflectance Infrared Fourier Transform Spectroscopy analysis (DRIFTS) suggested formate species formation on the catalyst surface and the absence of bridge-bonded adsorbed CO. The electronic interaction between cobalt nanoparticles and graphene affected carbon monoxide dissociation, preventing the electron backdonation from the active metal NPs to CO molecules.

Hydrogenation of CO2 on NiGa thin films studied by ambient pressure x-ray photoelectron spectroscopy

Successful catalytic conversion of carbon dioxide into high-value chemicals, as a means of abating global CO2 emissions is a pressing challenge. Herein, we report on an ambient pressure x-ray photoelectron spectroscopy study of CO2 hydrogenation reaction using a mixed gas of CO2 and H2 at a pressure up to 0.1 mbar on polycrystalline nickel-gallium thin films prepared by vacuum co-deposition that are compositionally equivalent to Ni, Ni3Ga, Ni5Ga3 and NiGa2, which are some noted low pressure methanol synthesis catalysts. Ni film is very reactive at 300 K, with the reaction sequence initiated by facile CO2 dissociation, yielding C2O4 −2, CO3 −2, CO2 − and CO, but little HCOO− and HCO3 −. The product species observed on NiGa alloy films are not generally different from those observed from using Ni film but are now of different proportions. The NiGa2 film, with the highest Ga content, is the least reactive, as judged by a dominant molecular adsorption feature of CO2. Interestingly, the NiGa alloys are found to undergo composition change and surface restructuring induced by the reactant gas and heating during the reaction. A surface depletion of Ni and a surface enrichment of oxidic Ga are found to occur and continue unabated toward high temperature. For example, for the alloy film with a composition similar to that of Ni5Ga3 when exposed to the mixed gas at 500 K for the duration of measurements (a few h), the near surface region delimited by an XPS probing depth (3λ) of 36 Å is composed of 29% Ni, 24% Ga, and 47% oxidic Ga vs. 62% Ni, 34% Ga, and 4% oxidic Ga for the freshly prepared film at 300 K. Our study demonstrates that a complex interplay exists between the surface reactivity and the evolving chemical makeup as the alloy films are exposed to the reactive gas at elevated pressure and temperature.

Optimization of Calcination Conditions for Cu/ZnO/Al2O3-ZrO2 Catalyst

Promoted Cu/ZnO catalyst was synthesized on Al2O3-ZrO2 support. Effects of calcination conditions on the catalytic performance in a CO2 hydrogenation reaction were studied systematically using the response surface methodology (RSM). The application of RSM with rotatable central composite design (RCCD) for optimization on the influence of catalyst’s calcination variables on the CO2 conversion and methanol selectivity is presented. The calcination variables studied include temperature, A (181–518 °C), ramping rate, B (1–30 °C/min), and duration, C (1–7 h). From the RSM-generated model, the optimum calcination condition for this catalyst was 350 °C with 17.5 °C/min ramping rate for a 4 h duration. At the optimum calcination condition, the catalyst exhibited a Brunauer–Emmett–Teller (BET) surface area of 147 m2/g, a pore volume of 0.31 cm3/g, and a pore diameter of 8.1 nm.

The active sites of Cu\u2013ZnO catalysts for water gas shift and CO hydrogenation reactions

Cu–ZnO–Al2O3 catalysts are used as the industrial catalysts for water gas shift (WGS) and CO hydrogenation to methanol reactions. Herein, via a comprehensive experimental and theoretical calculation study of a series of ZnO/Cu nanocrystals inverse catalysts with well-defined Cu structures, we report that the ZnO–Cu catalysts undergo Cu structure-dependent and reaction-sensitive in situ restructuring during WGS and CO hydrogenation reactions under typical reaction conditions, forming the active sites of CuCu(100)-hydroxylated ZnO ensemble and CuCu(611)Zn alloy, respectively. These results provide insights into the active sites of Cu–ZnO catalysts for the WGS and CO hydrogenation reactions and reveal the Cu structural effects, and offer the feasible guideline for optimizing the structures of Cu–ZnO–Al2O3 catalysts.

Revamping SiO2 Spheres by Core–Shell Porosity Endowment to Construct a Mazelike Nanoreactor for Enhanced Catalysis in CO2 Hydrogenation to Methanol

AbstractBeyond the catalytic activity of nanocatalysts, the support with architectural design and explicit boundary could also promote the overall performance through improving the diffusion process, highlighting additional support for the morphology‐dependent activity. To delineate this, herein, a novel mazelike‐reactor framework, namely multi‐voids mesoporous silica sphere (MVmSiO2), is carved through a top‐down approach by endowing core‐shell porosity premade Stöber SiO2 spheres. The precisely‐engineered MVmSiO2 with peripheral one‐dimensional pores in the shell and interconnecting compartmented voids in the core region is simulated to prove combined hierarchical and structural superiority over its analogous counterparts. Supported with CuZn‐based alloys, mazelike MVmSiO2 nanoreactor experimentally demonstrated its expected workability in model gas‐phase CO2 hydrogenation reaction where enhanced CO2 activity, good methanol yield, and more importantly, a prolonged stable performance are realized. While tuning the nanoreactor composition besides morphology optimization could further increase the catalytic performance, it is accentuated that the morphological architecture of support further boosts the reaction performance apart from comprehensive compositional optimization. In addition to the found morphological restraints and size‐confinement effects imposed by MVmSiO2, active sites of catalysts are also investigated by exploring the size difference of the confined CuZn alloy nanoparticles in CO2 hydrogenation employing both in‐situ experimental characterizations and density functional theory calculations.

Insights on the Catalytic Active Site for CO2 Reduction on Copper-based Catalyst: A DFT study

• CO 2 RR reaction mechanism on cu and CuO was studied by DFT. • The favorable pathways for CO 2 RR into CH 3 OH production were determined. • Surface h on CuO has significant effect on CO hydrogenation reaction kinetics. • New fundamental insights on CO 2 RR mechanism were unveiled. Cu oxide and Cu are widely used catalyst in CO 2 reduction reaction (CO 2 RR) for methanol (CH 3 OH) production. However, due to the complexity of the oxidation states on catalyst surfaces, the active sites of Cu-based catalysts for CO 2 RR are still unclear. In this study, density functional theory (DFT) calculations were performed to investigate the active sites for CO 2 RR reduction into CH 3 OH on Cu (111) and CuO (111) surface. The most favored adsorption sites and reaction energetics involved in CO 2 activation and sequent CO hydrogenation steps for CH 3 OH formation were determined. It has been found that, for CO 2 reduction, the CO 2 →COOH*→CO* pathway prefers to occur on both Cu (111) and CuO (111) surfaces. More importantly, the analysis reveals that, compared with Cu (111) and clean CuO (111), sequent CO hydrogenation into CH 3 OH is promoted by the H pre-covered CuO (111), on which the surface H is set on Cu site (H Cu ). That is, in CO 2 RR, the catalytic active sites for CH 3 OH production are the H-covered Cu sites on CuO (111) surface. These new insights on the catalytic active sites for CH 3 OH production on Cu-based catalyst would potentially guide the design of efficient CO 2 RR catalysts.

A Versatile Ambient‐to‐High‐Pressure Reaction Transmission Cell for in situ/operando Infrared Spectroscopic Investigations

AbstractInvited for this month's cover is the group of Angelika Brücker at the Leibniz Institute for Catalysis in Rostock (Germany). The cover picture shows a self‐developed stainless‐steel reaction cell for operando transmission FTIR studies of heterogeneous catalytic gas‐phase reactions at pressures up to 30 bar and temperatures up to 300°C, which is connected to a mass spectrometer for online product analysis. The performance of the cell has been tested in three types of CO2 hydrogenation reactions (CO2 Fischer‐Tropsch synthesis, CO2 methanation, CO2 conversion to dimethyl ether) on various solid catalysts implemented as self‐supporting wafers. Catalytic data obtained with this cell showed the same trends as those measured in a fixed‐bed plug‐flow reactor, thus confirming their reliability. Read the full text of their Full Paper at 10.1002/cmtd.202100024.

A Versatile Ambient‐to‐High‐Pressure Reaction Transmission Cell for in situ/operando Infrared Spectroscopic Investigations

AbstractDesign and applications of an in‐house developed high pressure/high temperature transmission FTIR reaction cell are presented. By coupling with a mass spectrometer online analysis of product formation is possible enabling operando FTIR spectroscopic studies. The cell, made of stainless‐steel, has been designed to be operable at pressures up to 30 bar and temperatures between 22 °C and 300 °C. Long‐time tests, with no signs of damage of the cell and windows have been conducted at 15 bar and 250 °C. The performance of the cell was tested by studying three types of CO2 hydrogenation reactions (CO2 Fischer‐Tropsch synthesis, CO2 methanation, CO2 conversion to dimethyl ether) on selected catalyst systems by varying temperature and pressure. The operando spectroscopic measurements revealed reliable data which reflect the same trends as found by respective catalytic tests.

Cover Picture: A Versatile Ambient‐to‐High‐Pressure Reaction Transmission Cell for in situ/operando Infrared Spectroscopic Investigations (Chemistry ‐ Methods 7/2021)

The Front Cover shows a self-developed stainless-steel reaction cell for operando transmission FTIR studies of heterogeneous catalytic gas-phase reactions at pressures up to 30 bar and temperatures up to 300°C, which is connected to a mass spectrometer for online product analysis. The performance of the cell has been tested in three types of CO2 hydrogenation reactions (CO2 Fischer-Tropsch synthesis, CO2 methanation, CO2 conversion to dimethyl ether) on various solid catalysts implemented as self-supporting wafers. Catalytic data obtained with this cell showed the same trends as those measured in a fixed-bed plug-flow reactor, thus confirming their reliability. More information can be found in the Full Paper by Jane Weiß et al.

Hydrogen spillover-driven synthesis of high-entropy alloy nanoparticles as a robust catalyst for CO2 hydrogenation

High-entropy alloys (HEAs) have been intensively pursued as potentially advanced materials because of their exceptional properties. However, the facile fabrication of nanometer-sized HEAs over conventional catalyst supports remains challenging, and the design of rational synthetic protocols would permit the development of innovative catalysts with a wide range of potential compositions. Herein, we demonstrate that titanium dioxide (TiO2) is a promising platform for the low-temperature synthesis of supported CoNiCuRuPd HEA nanoparticles (NPs) at 400 °C. This process is driven by the pronounced hydrogen spillover effect on TiO2 in conjunction with coupled proton/electron transfer. The CoNiCuRuPd HEA NPs on TiO2 produced in this work were found to be both active and extremely durable during the CO2 hydrogenation reaction. Characterization by means of various in situ techniques and theoretical calculations elucidated that cocktail effect and sluggish diffusion originating from the synergistic effect obtained by this combination of elements.