CO Hydrogenation Reaction Research Articles

Formation of COMs through CO hydrogenation on interstellar grains

Context. Glycoaldehyde, ethylene glycol, and methyl formate are complex organic molecules that have been observed in dark molecular clouds. Because there is no efficient gas-phase route to produce these species, it is expected that a low-temperature surface route existst that does not require energetic processing. CO hydrogenation experiments at low temperatures showed that this is indeed the case. Glyoxal can form through recombination of two HCO radicals and is then further hydrogenated. Aims. Here we aim to constrain the methyl formate, glycolaldehyde, and ethylene glycol formation on the surface of interstellar dust grains through this cold and dark formation route. We also probe the dependence of the grain mantle composition on the initial gas-phase composition and the dust temperature. Methods. A full CO hydrogenation reaction network was built based on quantum chemical calculations for the rate constants and branching ratios. This network was used in combination with a microscopic kinetic Monte Carlo simulation to simulate ice chemistry, taking into account all positional information. After benchmarking the model against CO-hydrogenation experiments, simulations under molecular cloud conditions were performed. Results. Glycoaldehyde, ethylene glycol, and methyl formate are formed in all interstellar conditions we studied, even at temperatures as low as 8 K. This is because the HCO + HCO reaction can occur when HCO radicals are formed close to each other and do not require to diffuse. Relatively low abundances of methyl formate are formed. The final COM abundances depend more on the H-to-CO ratio and less on temperature. Only above 16 K, where CO build-up is less efficient, does temperature start to play a role. Molecular hydrogen is predominantly formed through abstraction reactions on the surface. The most important reaction leading to methanol is H2CO + CH3O → HCO + CH3OH. Our simulations are in agreement with observed COM ratios for mantles that have been formed at low temperatures.

Determining number of sites on ceria stabilizing single atoms via metal nanoparticle redispersion

Single atom catalysts have recently attracted interest due to their maximization of the utilization of expensive noble metals as well as their unique catalytic properties. Based on its surface atomic properties, CeO2 is one of the most common supports for stabilizing single metal atoms. Many single atom catalysts are limited in their metal contents by the formation of metal nanoparticles once the catalyst support capacity for single atoms has been exceeded. Currently, there are no direct measurements to determine the capacity of a support to stabilize single atoms. In this work we develop a nanoparticle-based technique that allows for quantification of that capacity by redispersing Ru nanoparticles into single atoms and taking advantage of the different catalytic properties of Ru single atoms and nanoparticles in the CO2 hydrogenation reaction. This method avoids complications in metal loading caused by counterions in incipient wetness impregnation and can eventually be applied to a variety of different metals. Results using this technique follow trends in oxygen vacancy concentration and surface oxygen content and show promise as a new method for quantifying support single atom stabilization capacity.

Recent Developments in the Modelling of Heterogeneous Catalysts for CO2 Conversion to Chemicals

AbstractDensity functional theory (DFT) of the CO2 behavior on the catalyst surface provides valuable insights about the C=O bond activation, information about adsorption and dissociation of CO2, understanding the elementary steps involved in the mechanism of the CO2 hydrogenation reaction. Nowadays, DFT computational studies for the catalytic hydrogenation of CO2 are becoming very popular. Therefore, this article is focused on a comprehensive review of the DFT studies in thermocatalytic hydrogenation of CO2 at the gas‐surface interface and discusses three aspects: 1) processes taking place on the surfaces and facets of transition metal heterogeneous catalysts, 2) adsorption of CO2 on surfaces of different transition metals; 3) current understanding of reaction mechanisms taking place on the catalytic surface for the production of different compounds. A detailed schematic overview of the possible CO2 hydrogenation mechanisms and DFT simulations presented here will enhance the current understanding of the CO2 catalytic hydrogenation.

Resolving CO2 activation and hydrogenation pathways over iron carbides from DFT investigation

In this work, periodic density functional theory (DFT) calculations were performed to investigate the CO2 activation mechanism over thermodynamically stable χ-Fe5C2 (510) and θ-Fe3C (031) facets. Four major pathways of CO2 activation were examined, including the direct dissociation of CO2 and the H-assisted intermediates of *COOH, *HCOO, and *CO + *OH. Both χ-Fe5C2 and θ-Fe3C have proven to be active for CO2 direct dissociation (Ea =0.17 eV). As for H assisted CO2 activation, the one-step formation of *CO + *OH is feasible on χ-Fe5C2 (Ea =0.24 eV). Furthermore, θ-Fe3C favors the *HCOO pathway (Ea =0.20 eV) and *CO + *OH formation (Ea = 0.11 eV), while neither phase favors the formation of *COOH. Both CO2 direct activation and H-assisted CO2 activation pathways are of vital importance under high ratio of H/C in CO2 hydrogenation reaction. This work sheds light on CO2 activation mechanism over iron carbides, improving the rational design of CO2 hydrogenation catalysts.

MOFs-Based Catalysts Supported Chemical Conversion of CO2.

The dramatic increase in atmospheric carbon dioxide (CO2) concentrations has attracted human attention and many strategies about converting CO2 into high-value chemicals have been put forward. Metal-organic frameworks (MOFs), as a class of versatile materials, have been widely used in CO2 capture and chemical conversion, due to their unique porosity, multiple active centers and good stability and recyclability. Herein, we focused on the processes of chemical conversion of CO2 by MOFs-based catalysts, including the coupling reactions of epoxides, aziridines or alkyne molecules, CO2 hydrogenation, and other CO2 conversion reactions. The synthesized methods and high catalytic activity of MOFs-based materials were also analyzed systematically. Finally, a brief perspective on feasible strategies is presented to improve the catalytic activity of novel MOFs-based materials and explore the new CO2 conversion reactions.

The next big thing for silicon nanostructures - CO2 photocatalysis.

Silicene is a relatively new member of the growing family of two-dimensional single-element materials. Both top-down and bottom-up approaches provide access to silicene, the former via vapor deposition on a substrate and the latter via exfoliation of the layered CaSi2 precursor. Most top-down research has been concerned with understanding the various electronic, optical, magnetic, mechanical, electrical, thermal transport and gas-adsorption properties of silicene. By contrast, the focus on bottom-up silicene has primarily been on its synthesis, structure and chemical properties as they relate to its function and utility. Herein, emphasis is placed on the bottom-up strategy because of its scalability and the ease of subsequent silicene modification, with both qualities being important prerequisites for heterogeneous catalysis applications. In this context, synthetic freestanding silicene exists as single sheets or multilayer assemblies, depending on the CaSi2 exfoliation synthesis conditions. The structure of a sheet comprises three connected chair-configuration silicon 6-rings. This connectivity creates buckled sheets in which the hybridization around the unsaturated silicon atoms is sp2-sp3. By adjusting the CaSi2 exfoliation synthesis conditions, either layered silane (Si6H6) or siloxene (Si6H3(OH)3) nanosheets can be obtained. In our studies, we have explored the nucleation and growth of different transition metal nanoparticles on and within the layer spaces of these nanosheets, and explored their thermochemical and photochemical reactivity in CO2 hydrogenation reactions. An overview of these findings, related works and a new-and-optimized catalyst are provided in this article.

Photocatalytic hot-carrier chemistry

Abstract

Shining light on CO2: from materials discovery to photocatalyst, photoreactor and process engineering.

Heterogeneous catalysis, a process in which the reaction of gaseous or liquid chemical reagents is facilitated at the surface of a solid material, is responsible for the majority of industrial-scale chemical and fuel production reactions. The energy required to drive these reactions has historically been derived from the combustion of non-renewable fossil fuels and carries an unavoidably large carbon footprint. More recently, the development of environmentally responsible and sustainable chemical industries is increasingly motivated by greenhouse gas-induced climate change, thus creating demand for eco-friendly heterogeneous catalytic processes. This includes innovative approaches enabled by renewable forms of energy, such as the electrification of chemical and petrochemical processes, utilization of CO2 as a feedstock and the incorporation of light into catalytic reactions. Herein we review the conversion of solar energy to chemical energy using CO2, and describe how the photophysical and photochemical properties of nanostructured metal oxide photocatalysts have been engineered to efficiently incorporate light into heterogeneous gas-solid CO2 hydrogenation reactions. Realizing high photonic and energy efficiencies in these systems has demanded innovation in not only photocatalyst engineering, but also photoreactor and process engineering. Rather than exclusively providing an in-depth discussion of the chemistry and science within each individual study, this Tutorial Review highlights the multidisciplinary character of photocatalysis studies by covering the four essential components of a typical research work in this field (materials engineering, theoretical modelling, reactor engineering and process development) via case studies of the archetypal indium oxide catalyst materials. Through advances in these four components, progress has been made towards the ultimate goal of industrializing the production of CO2-derived chemicals and fuels.

CO2 hydrogenation using bifunctional catalysts based on K-promoted iron oxide and zeolite: influence of the zeolite structure and crystal size

The influence of the zeolite structure and crystal size on bifunctional tandem catalysts combining K-promoted iron oxide (K/Fe3O4) with different zeolites has been studied for the CO2 hydrogenation reaction at 320 °C and 25 bar.

On the conversion of CO2 to value added products over composite PdZn and H-ZSM-5 catalysts: excess Zn over Pd, a compromise or a penalty?

Zn was found to possess a dual role in composite PdZn–H-ZSM-5 catalysts for CO2 hydrogenation reactions: it promotes methanol formation when alloyed with Pd, but inhibits hydrocarbon formation by ion exchange with Brønsted acid sites in H-ZSM-5.

Montmorillonite-catalyzed conversions of carbon dioxide to formic acid: Active site, competitive mechanisms, influence factors and origin of high catalytic efficiency

Design of heterogeneous catalysts for CO2 conversions to value-added chemicals is highly desirable. Montmorillonite and other clay minerals have been used widely in catalytic reactions including CO2 hydrogenation, while a molecular-level understanding remains lacking. In this study, periodic density functional theory calculations are employed and a comprehensive understanding about montmorillonite-catalyzed CO2 hydrogenation to formic acid is given, including active site, mechanism, influence factors, competitive reaction paths, and origin of superior catalysis. Catechol that is readily available and can also be considered as a fragment of abundantly distributed humic substances is an effective hydrogen source. The penta-coordinated M3+ (M2+) sites of edge surfaces are active sites, and reactions occur preferentially at M2+ rather than M3+ sites. The catalytic activities depend strongly on the identity of M2+ (M3+) cations, and all reaction paths follow the concerted mechanisms transferring two hydrogen atoms in one step, with those producing formate being highly preferred. M2+/Al3+ substitutions and substituent effects are two critical factors to affect catalytic activities, and with synergy of Mg2+/Al3+ substitutions and -NMe2 substituent, reactions are exergonic (−0.09 eV) and activation barriers are so low (0.48 eV) that formate can be facilely produced at ambient conditions. Edge surfaces of clay minerals are bifunctional catalysts, with M2+ cations showing Lewis acids and MOH groups playing similar effects as basic additives. Results provide new insights about heterogeneous catalysis of CO2 hydrogenation and other reactions.

Experimental research of oily sawdust air gasification

This article shows oily sawdust gasification research on countercurrent installation. Experimental research was on a laboratory scale. The main purpose of the experiment was combustible gas production with higher CH4 concentration. Gas concentrations like CO, CO2, CH4, H2, and CnHm determine syngas composition. The technological parameter’s value defines experimental conditions. Value of this was fuel to air ratio. With fuel to air ratio change, syngas composition was a differential phenomenon where it depended on the process parameters like temperature. Additionally, evaluation of methane formation from CO, H2, and CO2 was done. Methanization coefficients were based on CO and CO2 hydrogenation reactions. Component’s activity was in analogs way to syngas components changed.

Imaging Catalysis: Operando Investigation of the CO2 Hydrogenation Reaction Dynamics by Means of Infrared Thermography

Infrared thermography is a powerful tool to investigate the dynamic evolution of temperature in chemical reactions. The CO2 hydrogenation reaction is an ideal model reaction to assess the presented...

Unravelling the Promotional Effect of La2O3 in Pt/La‐TiO2 Catalysts for CO2 Hydrogenation

This work reports the preparation of a La2 O3 -modified Pt/TiO2 (Pt/La-TiO2 ) hybrid through an excess-solution impregnation method and its application for CO2 hydrogenation catalysis. The Pt/La-TiO2 catalyst is characterized by XRD, H2 temperature-programmed reduction (TPR), TEM, X-ray photoelectron spectroscopy (XPS), Raman, EPR, and N2 sorption measurements. The Pt/La-TiO2 composite starts to catalyze the CO2 conversion reaction at 220 °C, which is 30 °C lower than the Pt/TiO2 catalyst. The generation of CH4 and CO of Pt/La-TiO2 is 1.6 and 1.4 times greater than that of Pt/TiO2 . The CO2 temperature-programmed desorption (TPD) analysis confirms the strengthened CO2 adsorption on Pt/La-TiO2 . Moreover, the in situ FTIR experiments demonstrate that the enhanced CO2 adsorption of Pt/La-TiO2 facilitates the formation of the active Pt-CO intermediate and subsequently boosts the evolution of CH4 and CO. The cycling tests reveal that Pt/La-TiO2 shows reinforced stability for the CO2 hydrogenation reaction because the La species can prevent Pt nanoparticles (NPs) from sintering. This work may provide some guidance on the development new rare-metal-modified hybrid catalysts for CO2 fixation.

Ni\u2013Zn\u2013Al-Based Oxide/Spinel Nanostructures for High Performance, Methane-Selective CO2 Hydrogenation Reactions

In the present study, NiO modified ZnAl2O4 and ZnO modified NiAl2O4 spinel along with pure Al2O3, ZnAl2O4 and NiAl2O4 for comparison in the CO2 hydrogenation reaction have been investigated. It was found that NiAl2O4, NiO/ZnAl2O4 and ZnO/NiAl2O4 catalysts exhibited outstanding activity and selectivity towards methane even at high temperature compared to similar spinel structures reported in the literature. NiO/ZnAl2O4 catalyst showed CO2 consumption rate of ~ 19 μmol/g·s at 600 °C and ~ 85% as well as ~ 50% of methane selectivity at 450 °C and 600 °C, respectively. The high activity and selectivity of methane can be attributed to the presence of metallic Ni and Ni/NiO/ZnAl2O4 interface under the reaction conditions as evidenced by the XRD results.Graphic High performance Ni–Zn–Al-based oxide/spinel nanostructures is synthesized and NiO/ZnAl2O4 catalyst exhibited higher catalytic activity in the CO2 hydrogenation reaction due to the presence of metal support interaction between Ni and ZnAl2O4 support.

Mesoporous carbon as an effective support for Fe catalyst for CO2 hydrogenation to liquid hydrocarbons

Identifying highly efficient catalysts for direct CO2 hydrogenation to liquid hydrocarbons is crucial for CO2 utilization via chemical conversion using renewable resources, the so-called Power-to-Liquids. In this study, well-defined mesoporous carbon (MPC) of 6.9 nm pore size was synthesized as a support material for Fe oxycarbide nanoparticles, which serve as active sites for the CO2 hydrogenation reaction, combining reverse water-gas shift and Fischer-Tropsch reactions. The unique physicochemical properties of MPC favored the formation of an active carbidic Fe phase and the rapid diffusion of produced hydrocarbons which resulted in an enhanced CO2 conversion and long-chain hydrocarbon selectivity. As a result, the MPC supported Fe catalyst showed C5+ hydrocarbon selectivity of 44.5% with a CO2 conversion rate of 50.6% (300 °C, 2.5 MPa, H2/CO2 = 3).

A Comparative Study on C2 Hydrocarbons and Methanol Synthesis from CO Hydrogenation Catalyzed by M1/W6S8 (M = Ir and Ca) Single-Atom Catalysts

Exploring highly selective catalysts for CO hydrogenation reactions remains a significant challenge as a critical stage in the conversion of CO resources into chemicals or fuels. Here, we provide guidelines on this issue, exploring the generation of major production in the CO hydrogenation process of M1/W6S8 (M = Ir and Ca) single-atom catalysts, and performing density functional calculations. Calculate the reaction energy and barrier for each basic step. Calculations represent that the Ca1/W6S8 catalyst is very advantageous for methanol synthesis (CO* + 4H* → CHO* + 3H* → CH2O* + 3H* → CH3O* + H* → CH3OH*). On the other hand, the Ir1/W6S8 catalyst strongly favors the production of C2 hydrocarbons. We use the harmonic transition state theory to calculate the rate constant of the subsequent step of converting CH3O* species on M1/W6S8 (M = Ir and Ca). The results of the rate constants are consistent with our kinetic results. These results add new insights into the basic understanding of complex CO hydrogenation reactions. A series of reactions starting from CO on the (a) Ir1/W6S8, (b) Ca1/W6S8. The activation barriers and reaction energies of the elementary steps are all shown in kcal/mol.

High methane selective Pt cluster catalyst supported on Ga2O3 for CO2 hydrogenation

Abstract In heterogeneous catalysis, the CO2 hydrogenation reaction is an important class of reactions that has been widely studied for decades. Particularly, the particle size of the metal plays a crucial role in controlling the selectivity of the CO2 hydrogenation reaction. However, there have only been a few studies investigating the selectivity for sub-nanometer sized particles. Here, we report the effect of Pt particle size on the catalytic activity and selectivity of CO2 hydrogenation. The size of the Pt particles was tuned by changing the amount of loading. With low Pt loading on gallium oxide, Pt clusters were formed; however, Pt nanoparticles were synthesized with high Pt loading. The Pt clusters were mainly edge and step sites where CO2 adsorbs more strongly, while the Pt nanoparticles were mainly composed of terrace sites. The catalytic performance of the Pt catalysts was examined using CO2 hydrogenation. The Pt clusters showed a higher methane selectivity than that of the Pt nanoparticles. The reaction mechanism was analyzed by diffuse reflectance infrared fourier transform (DRIFT) spectroscopy at reaction conditions. The Pt clusters mainly showed the formate peak, while showing fewer carbonate peaks than the support. These results suggest that the formation of CH4 follows the formate route.

Capsule-Structured Copper-Zinc Catalyst for Highly Efficient Hydrogenation of Carbon Dioxide to Methanol.

To develop a new and efficient CO2 -to-methanol catalyst is of extreme significance but still remains a challenge. Herein, an innovative indirect two-step strategy is reported to synthesize a highly efficient capsule-structured copper-based CO2 -to-methanol catalyst (CZA-r@CZM). It consists of a structurally reconstructed millimeter-sized Cu/ZnO/Al2 O3 core (CZA-r) with intensified Cu-ZnO interactions, which is made by a facile hydrothermal treatment in an alkaline aqueous solution, and a Cu/ZnO/MgO (CZM) shell prepared by an ethylene glycol-assisted physical coating method. The CZA-r core displays 2.7 times higher CO2 hydrogenation activity with 2.0 times higher CO selectivity than the previously reported Cu/ZnO/Al2 O3 (CZA-p), whereas the CZM shell can efficiently catalyze hydrogenation of the as-formed CO from the CZA-r core to methanol as it passes through the shell. As a result, the developed capsule-structured CZA-r@CZM catalyst exhibits 2.4 times higher CO2 conversion with 1.8 times higher turnover frequency and 2.3-fold higher methanol space-time yield than the CZA-p catalyst (729.8 vs. 312.6 gMeOH kgcat -1 h-1 ). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) experiments reveal that the CO2 hydrogenation reaction proceeds through a reverse water-gas shift reaction followed by a CO hydrogenation pathway via an *H3 CO intermediate. This work not only produces an efficient CO2 -to-methanol catalyst, but also opens a new avenue for designing superior catalysts for other consecutive transformations.

Hydrogenation of CO2 to formates on ruthenium(III) coordinated on melamine polymer network

Catalytic hydrogenation of CO2 to formic acid is considered as a crucial transformation in regards to alleviating the harmful impacts of global warming and completing the carbon cycle. In this respect, a novel heterogeneous Ru (III) catalyst is prepared by the immobilization of RuCl3.xH2O onto a melamine polymer-network (MPN). MPN is employed based on its abundant nitrogen functional groups which can stabilize the ruthenium species by complex formation, which is confirmed by characterization results. Influence of reaction parameters on the catalyst activity is investigated and a high turnover frequency of 4964 h−1 is observed. This high activity of the catalyst is attributed to the stabilization of Ru(III). The basic nitrogen groups of the MPN support, electron donating basic sites, can play a role in stabilizing the active ruthenium (III) species. These results indicate the high potential of melamine-based polymers to be applied as catalyst support materials in the CO2 hydrogenation reaction.