Catalytic Activity For CO2 Reduction Research Articles

Transition-Metal-Doped CeO2 for the Reverse Water-Gas Shift Reaction: An Experimental and Theoretical Study on CO2 Adsorption and Surface Vacancy Effects.

Transition metal-doped ceria (M-CeO2) catalysts (M = Fe, Co, Ni and Cu) with multiple loadings were experimentally investigated for reverse water gas shift (RWGS) reaction. Density functional theory (DFT) calculations were performed to benchmark the properties that impact catalytic activity of CO2 reduction. Temperature-programmed desorption (TPD) was conducted to study the CO2 binding strength on doped CeO2 surfaces; the trend of the energy along increasing metal loading agrees with the DFT calculations. Notably, CO2 dissociative adsorption energy and oxygen vacancy (OV) formation energy are key descriptors obtained from both DFT and experiments, which can be used to evaluate catalytic performance. Results show the effectiveness of transition metal doping in enhancing CO2 adsorption and reducibility of the surfaces, with Fe showing particularly promising results, i.e., CO2 conversion higher than 56% at 600 °C and 100% selectivity to CO. Cu exhibits 100% selectivity to CO but low CO2 conversion, while Co and Ni showed notable ability of methanation, particularly at high loadings. This study finds that an effective CeO2 based RWGS catalyst corresponds to OV sites that have low OV formation energies for surface reduction, and moderate CO2 adsorption energies for strong interaction with the surface to promote C-O bond scission.

Harnessing the electrocatalytic potential of in-situ exsolution of Ni nanoparticles on lanthanum and calcium co-doped strontium titanate for CO2 reduction in solid oxide electrolysis cells

The exsolution phenomenon of metal nanoparticles from a perovskite oxide involves the creation of oxygen vacancies, contributing to improved catalytic activity for CO2 reduction. In this context, a B-site Ni-doped and A-site La, Ca co-doped strontium titanate, denoted as La0.20Sr0.25Ca0.45Ni0.05Ti0.95O3-δ (Ni-LSCT), is synthesized with the aim of serving as a highly efficient cathode in conjunction with LSM as the anode and YSZ as the electrolyte for CO2 reduction via solid oxide electrolysis process. The incorporation of 5 mol% Ni doping at the B-site of the perovskite is successfully achieved, leading to the subsequent release of highly dispersed nanoparticles upon exposure to a reducing environment. YSZ-electrolyte-supported SOECs featuring the Ni-LSCT cathode demonstrate a notable current density of 0.93 A/cm2 at an applied voltage of 2.5 V at 800 °C in pure CO2. Moreover, at the same temperature, the reduction current density measures 1.21 A/cm2 when the Ni-LSCT serves as the cathode in a 70/30 molar ratio (CO2/H2) environment and 1.73 A/cm2 with a 50/50 molar ratio of the feed gas, both at an applied voltage of 2.5 V. This suggests an enhanced CO2 reduction performance in a reducing atmosphere. The introduction of Ni doping into LSCT enhances the electrochemical activity of the cathode by augmenting oxygen vacancies, while the presence of Ni nanoparticles on the cathode surface intensifies the active sites. Collectively, this innovative electrocatalyst configuration presents promising prospects for CO2 electrolysis within the SOEC framework.

Enhanced CO2 photoreduction to CO by small-size NH2-UiO-66 nanoparticles immobilization on Mo2C

The small-size and efficient charge separation of MOFs catalysts are essential for improving photocatalytic performance. In this work, a series of small-size NH2-UiO-66 nanoparticle-modified Mo2C photocatalysts were successfully prepared by hydrothermal synthesis with in situ growing NH2-UiO-66 on the surface of Mo2C. The addition of Mo2C can not only obtain small-size NH2-UiO-66 nanoparticles, but also significantly increase the separation efficiency of photo-generated carriers and prolongs the carrier lifetime, thereby promoting the photoreduction of CO2 in water vapor with excellent stability. The resulting 11-Mo2C/NH2-UiO-66 (11-MCNU) exhibits excellent catalytic activity for CO2 reduction to CO product at room temperature and atmospheric pressure. The yield of CO can reach 11 μmol g−1 in the absence of organic solvents, sacrifice agents and photosensitizers, which is much higher than that of the isolated NH2-UiO-66 and Mo2C.

Synergistic effect of phthalocyanine and pyrochlore-type oxide catalysts to enhance activity of electrochemical carbon dioxide reduction

Abstract Electrochemical CO2 reduction has been attracting attention due to its potential to improve the environment. In this study, we found that the combination of Co-phthalocyanine and pyrochlore-type Bi2Sn2O7 catalyst gave high catalytic activity for CO2 reduction, and devised a new electrocatalyst that combines them for their synergistic effects.

Silicon‐Doped Graphene as a Catalyst for Hydrogenation of Carbon Dioxide: A Molecular Simulation Study

AbstractThe catalytic effect of Si‐doped graphene nanoflakes (NFs) on CO2 reduction with molecular hydrogen was explored theoretically at the TPSS/def2‐SVP+D3BJ level of theory. Substituting carbon with silicon generates defects in the NF structure, which leads to a polyradical ground state of the NF. The silicon defect enhances the reactivity towards the substrates. Si‐doped graphene NFs exhibit higher catalytic activity for CO2 reduction to formic acid than silicene. Notably, Si‐doped graphene favors formic acid over carbon monoxide, which is similar to silicene. Formic acid to formaldehyde and formaldehyde to methanol conversions have also been studied, sometimes showing improved efficacy of Si‐doped graphene over silicene. The final reduction step, the methanol to methane reaction, occurs in four steps, with the rate‐determining step involving hydrogen transfer from silicon to methyl, whose activation energy is lower than that of silicene. Si‐doped graphene NFs act as better catalysts with lower activation energies than those of silicene. Overall, silicon‐doped graphene enhanced the catalytic activity while maintaining the environmental stability of the graphene.

Mechanistic insights of electrocatalytic CO2 reduction by Mn complexes: synergistic effects of the ligands.

The electrocatalytic mechanisms of CO2 reduction catalyzed by pyridine-oxazoline (pyrox)-based Mn catalysts were investigated by DFT calculations. In-depth comparative analyses of pyrox-based and bipyridine-based Mn complexes were carried out. C-OH cleavage is the rate-determining step for both the protonation-first path and the reduction-first path. The free energy of CO2 activation (ΔG1) and the electrons donated by CO ligands in this step are effective descriptors in regulating the C-OH cleavage barrier. The reduction of carboxylate complex 6 (E6) is the potential-determining step for the reduction-first path. Meanwhile, for the protonation-first path, the initial generation (E2) or the regeneration (E8) of active catalyst might be potential-determining. Hirshfeld charge and orbital contribution analysis indicate that E6 is definitely based on the heterocyclic ligand and E2 is related to both the heterocyclic ligand and three CO ligands. Therefore, replacement of the CO ligand by a stronger electron donating ligand can effectively boost the catalytic activity of CO2 reduction without increasing the overpotential in the reduction-first path. This hypothesis is supported by the mechanism calculations of the Mn complex in which the axial CO ligand is replaced by a pyridine or PMe3.

A first-principles study of electro-catalytic reduction of CO2 on transition metal-doped stanene.

Employing first-principles calculations based on density functional theory, this work examines the activity of 3d transition metal-doped stanene for electro-catalytic CO2 reduction through the first two electron transfer steps to CO. Our results related to CO2 activation, the first and a crucial step of the reduction process revealed that, among the entire 3d transition metal row studied, only Ti- and Fe-doped stanene can bind and significantly activate the CO2 molecule, while the rest of the TM single atoms are inert in activating the molecule. The activation of the CO2 molecule on Ti- and Fe-doped stanene has been observed in the presence of water as well. In addition, the formation of OCHO has been observed to be energetically preferred over COOH formation as a reaction intermediate, indicating the preference for the formate path of the reduction reaction. Furthermore, despite the strong adsorption of H2O on the catalyst surface, the presence of water seems to enhance CO2 adsorption on the catalysts, contrary to what has been observed recently in graphene-based catalysts. Finally, our difference charge density and the Bader charge calculations reveal that the ability of Ti- and Fe-doped stanene in activating the CO2 molecule and their potential catalytic activity for CO2 reduction is to be attributed to the charge transfer between the catalyst and the molecule, providing new insights into the rational design of 2D catalysts beyond graphene.

Bi/2 H-MoS2−x composite for efficient photo-thermal synergistic catalytic CO2 reduction

The high carrier recombination rate and poor photocorrosion resistance of intrinsic MoS2 lead to a poor photocatalytic CO2 reduction activity. Here, the photocatalytic CO2 reduction performance of 2 H-MoS2 was significantly enhanced by constructing Bi/2 H-MoS2−x composite and photo-thermal synergy strategy. Under the optimal conditions of 200 °C and 42 mW·cm-2 of 420 nm irradiation, Bi/2 H-MoS2−x exhibited an excellent photo-thermal synergistic catalytic activity of CO2 reduction with a CO production rate of 34.42 μmol-1·g-1·h-1. Mechanistic studies showed that the introduction of Bi greatly improved the light absorption ability, generated S vacancies as electron capture centers for rapid separation of photocarriers, and promoted the generation of key intermediates. The involvement of heat led to a photo-thermal synergistic effect, which accelerated the charge migration and surface reaction rate. Our work provides new insights into the development of efficient catalysts for CO2 reduction and the mechanism study of photo-thermal synergistic catalysis.

Catalytic reduction of CO2 in the interface formed by monolayer graphene and metal atom (Pt, Ni, Pd, Co) doped Cu-nanoclusters: A theoretical design and investigation

In this study, pristine Cu13 nanocluster and a series of metal atoms (Pt, Ni, Pd and Co) doped Cu12X were designed and placed on the top of a monolayer graphene to form novel catalysts for CO2 reduction. Based on the designed catalysts, we studied the reaction mechanisms of five catalysts for CO2 reduction leading to three different products: CH4, CH3OH and HCOOH. By comparing the activation energies of different reaction channels of different catalysts, we obtained the three different product rate-determining steps of CO2 reduction of CH4, CH3OH and HCOOH. The selectivity order of CO2 reduction products catalyzed by graphene-supported Cu13/G and doped Cu12X/G catalysts is CH4>CH3OH>HCOOH. The order of catalyst activity is Cu12Co/G>Cu12Ni/G>Cu12Pd/G>Cu12Pt/G>Cu13/G. The doping of the four metals Pt, Ni, Pd and Co are all beneficial for improving the catalytic activity of CO2 reduction, and the catalytic activity of metal Co doping is the optimal. These results agree well with the observed phenomena. Our study reveals a correlation between the CO2 reduction catalytic activity of graphene-supported Cu13/Cu12X nanoclusters and their physical properties.

Preparation of Highly Conductive Phthalocyaninato-Cobalt Iodide at the Interface between Aqueous KI Solution and Organic Solvent and Catalytic Properties for Electrochemical Reduction of CO2

Abstract For the industrial practical use of cobalt phthalocyanine (CoPc) as a catalyst for CO2 reduction, the effect of improving conductivity of CoPc crystal on the catalytic activity was investigated. Focusing on (phthalocyaninato) cobalt iodide (CoPcI), which is a highly conductive charge-transfer complex, a simple method for synthesizing CoPcI by simply mixing at an interface between aqueous KI solution and CH2Cl2 solution containing CF3COOH and CoPc was developed by applying the CoPc crystal phase transformation method. The X-ray diffraction pattern of the obtained powder at the interface of CoPc organic and potassium iodide aqueous solutions revealed that the powder is composed of one-dimensional columns of CoPc and a linear array of triiodide ions (I3−). UV-vis absorption spectra showed that iodide ions (I−) change to triiodide ions (I3−) at the interface between aqueous KI solution and organic solvent under acidic conditions. The catalytic property of CoPcI was investigated by polarization measurement and electrochemical impedance spectroscopy using a gas diffusion carbon electrode. CoPcI showed high catalytic activity for CO2 reduction with high CO production selectivity.

Theoretical study on the reduction mechanism of CO2 to HCOOH on Pd3Au: an explicit solvent model is essential

The work function and d-band center of a catalyst together determine the catalytic activity of CO2 reduction to formic acid. And it is necessary to consider the solvation effect using an explicit solvent model.

HCOOH Electrosynthesis via Coelectrolytic Processes of CO2 Reduction and CH3OH Oxidation

Electrochemical coconversion of CO2 at the cathode and CH3OH at the anode to produce HCOOH provides a sustainable route for low-cost HCOOH production and efficient utilization of CO2. Catalysts play an important role in electrochemical reactions. However, there are still few efficient matched catalysts for CH3OH oxidation to HCOOH and CO2 reduction to HCOOH (CO2RR-to-HCOOH). Herein, metal-doped LaMnO3 (Ag-LMO, Sn-LMO, and Sr-LMO) for CH3OH oxidation to produce HCOOH at the anode and Cu–M (M = Pd, Pb, Bi, Sn, and In) bimetal catalysts for CO2RR-to-HCOOH at the cathode are exploited. The results indicate that metal-doped LaMnO3 could directly facilitate CH3OH oxidation by reducing the overpotential. The B-site metal-doped effect is better than the A-site metal-doped effect on CH3OH oxidation. B-site metal-doped Ag-LMO exhibits a better CH3OH oxidation performance, which can reduce the ΔGPLS by 43.08% compared to LMO. Pb@Cu shows an excellent catalytic activity for CO2 reduction to HCOOH. The overpotential is 0.08 V for CO2 reduction to HCOOH. This study shed light on the application of Cu-based bimetal materials and La–Mn perovskites in the electrocatalytic field.

Unravelling the Multiple Synergies in MOF/CMP Supramolecular Heterojunction for Enhanced Artificial Photosynthesis

AbstractMetal–organic framework (MOF) and conjugated microporous polymers (CMP) are two groups of supramolecular structures with potential applications for artificial photosynthesis though their catalytic activities are yet to be improved. A MOF/CMP hybrid photocatalyst NU@FNBZ with markedly higher catalytic activity for CO2 reduction to CO is hereby reported. The hybrid catalyst benefits from the high CO2 adsorption capacity of NU and the high visible light response of FNBZ. Moreover, the covalent bonding facilitates the formation of type II heterojunction that allows electron transfer from FNBZ to NU, leading to improved catalytic activity in the electron rich NU and enhanced CO2 adsorption in the electron depleted FNBZ. This work manifests that multiple synergy effects can be achieved by rational design of hybrid supramolecular photocatalysts.

Ti/Ni co-doped perovskite cathode with excellent catalytic activity and CO2 chemisorption ability via nanocatalysts exsolution for solid oxide electrolysis cell.

Carbon dioxide (CO2) gas is the main cause of global warming and has a significant effect on both climate change and human health. In this study, Ni/Ti co-doped Sr1.95Fe1.2Ni0.1Ti0.2Mo0.5O6-δ (SFNTM) double perovskite oxides were prepared and used as solid oxide electrolysis cell (SOEC) cathode materials for effective CO2 reduction. Ti-doping enhances the structural stability of the cathode material and increases the oxygen vacancy concentration. After treatment in 10% H2/Ar at 800°C, Ni nanoparticles were exsolved in situ on the SFNTM surface (Ni@SFNTM), thereby improving its chemisorption and activation capacity for CO2. Modified by the Ti-doping and the in situ exsolved Ni nanoparticles, the single cell with Ni@SFNMT cathode exhibits improved catalytic activity for CO2 reduction, exhibiting a current density of 2.54 A cm−2 at 1.8 V and 800°C. Furthermore, the single cell shows excellent stability after 100 h at 1.4 V, indicating that Ni/Ti co-doping is an effective strategy for designing novel cathode material with high electrochemical performance for SOEC.

Changing your tune on catalytic efficiency: Tuning Cr concentration in La0.3Sr0.7Fe1-xCrxO3-δ perovskite as a cathode in solid oxide electrolysis cell

Solid Oxide Electrolysis Cell (SOEC) are in the focus of interest for many years, due to their ability to convert CO2 emissions to CO fuel, and thus, regenerate fuels and diminish environmental pollution. A perovskite structure (ABO3) electrode La0.3Sr0.7Fe1-xCrxO3-δ (LSFCr, A = La, Sr, B = Fe, Cr) with x = 0, 0.1, 0.2 and 0.3, was found to be a proper candidate for SOEC performance, and was tested experimentally for various properties under various environments. It has been showed that the optimal trade-off is present when x = 0.3 (La0.3Sr0.7Fe0.7Cr0.3O3-δ) and the SrCrO4 phase was found when x > 0.33. It was also reported that Cr dopants can improve the structural stability of La0.3Sr0.7FeO3-δ in reducing atmospheres. The current work investigates by the density functional theory (DFT) method the effect of Cr stoichiometry on La0.3Sr0.7Fe1-xCrxO3-δ perovskite on the electronic properties, mechanical properties, and surface catalytic activity of CO2 reduction. This work is based on our previous experimental and DFT+U study that revealed that surface models with two surface oxygen vacancies are necessary for describing CO2 reduction. Here the calculations showed that Cr atoms have an impact on the electronic behavior of LSFCr, since the bandgap depends on Cr concentration. According to the bulk modulus values, La0.3Sr0.7Fe1-xCrxO3-δ perovskite may be mechanically stable under applied stress. Moreover, the mechanical bulk modulus lowering, when SrCrO4 is present, may be an indication of possible lower stability and degradation. The calculations showed that more Cr atoms near the active site “changes your tune” on CO2 reduction by improving the reaction thermodynamically through dictating the reducing and oxidizing roles to the participating atoms in the catalysis. The low +3 oxidation state of Cr has an impact on reaction progress by creating more reductive environment.

Bridge Sites of Au Surfaces Are Active for Electrocatalytic CO2 Reduction.

Prior in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) studies of electrochemical CO2 reduction catalyzed by Au, one of the most selective and active electrocatalysts to produce CO from CO2, suggest that the reaction proceeds solely on the top sites of the Au surface. This finding is worth updating with an improved spectroelectrochemical system where in situ IR measurements can be performed under real reaction conditions that yield high CO selectivity. Herein, we report the preparation of an Au-coated Si ATR crystal electrode with both high catalytic activity for CO2 reduction and strong surface enhancement of IR signals validated in the same spectroelectrochemical cell, which allows us to probe the adsorption and desorption behavior of bridge-bonded *CO species (*COB). We find that the Au surface restructures irreversibly to give an increased number of bridge sites for CO adsorption within the initial tens of seconds of CO2 reduction. By studying the potential-dependent desorption kinetics of *COB and quantifying the steady-state surface concentration of *COB under reaction conditions, we further show that *COB are active reaction intermediates for CO2 reduction to CO on this Au electrode. At medium overpotential, as high as 38% of the reaction occurs on the bridge sites.

Curious Effect of Isotope-Labelled Substrate/Co-Enzyme on Catalytic Activity of CO2 Reduction by Formate Dehydrogenase from Candida Boidinii

Abstract The effects of isotope-labelled NADH and CO2 on formate dehydrogenase from Candida boidinii (CbFDH)-catalyzed CO2 reduction activity were investigated. It was found that the rate of CO2 reduction to formate with CbFDH decreased by using deuterium-labelled NADH (NADH-d4) as a co-enzyme. In contrast, the rate of CbFDH-catalyzed CO2 reduction to formate was unchanged in the use of 13CO2 as a substrate. In the substrate 12CO2 and 13CO2 is mixed, however, curious phenomenon on CbFDH-catalyzed CO2 reduction activity decrease was observed.

An in-situ spectroscopic study on the photochemical CO2 reduction on CsPbBr3 perovskite catalysts embedded in a porous copper scaffold

Photocatalytic CO2 reduction is a technology which converts carbon dioxide into high value-added chemicals, simultaneously resulting in a reduction of carbon dioxide and the production of useful chemicals. To increase the conversion efficiency and product selectivity, various parameters such as the light absorption efficiency, catalytic reaction activity on the electrode surface, and charge separation efficiency must be considered. In this study, photocatalytic CO2 reduction was investigated using an inorganic halide perovskite-based photocatalyst with a copper scaffold as a co-catalyst. We found that, when the two catalyst materials are used together, the photosensitized perovskite-based photocatalyst efficiently delivers excited electrons to the copper scaffold and produces a higher variety of products (for example, CH4, C2H4, and C2H6) than that without the copper scaffold. During photo-irradiation, a multi-scattering process occurs in the copper scaffold, which generates more photo-induced carriers, resulting in an enhanced light harvesting ability compared to that of the planar structure without the porous scaffold. Therefore, the CsPbBr3 perovskite catalysts embedded in a porous copper scaffold exhibit superior photocatalytic performance toward CO2 reduction. In the photocatalytic reduction reaction of CO2 on the perovskite photocatalyst with a copper scaffold, ethylene (C2H4, 46.5 μmol/g) was a major product and methane (CH4, 18.9 μmol/g), ethane (C2H6, 17.1 μmol/g), and propane (C3H8, 11.3 μmol/g) were additionally detected. On the other hand, the planar perovskite photocatalyst has very low catalytic activity for CO2 reduction and only methane (CH4, 17.2 μmol/g) was observed as a main conversion product from CO2 after light irradiation. Additionally, in this work, in-situ ATR-IR analysis was performed to understand the photocatalytic CO2 reduction mechanism.

The Z-scheme g-C3N4/3DOM-WO3 photocatalysts with enhanced activity for CO2 photoreduction into CO

The catalytic performance of light-derived CO2 reduction with H2O is strongly dependent on the separation efficiency of photogenerated carriers. Herein, the direct Z-scheme catalysts (g-C3N4/3DOM-WO3) of graphitic carbon nitride (g-C3N4) nanosheets decorated three-dimensional ordered macroporous WO3 (3DOM-WO3) were successfully fabricated by using the in-situ colloidal crystal template method. The slow light effect of 3DOM-WO3 photonic crystals expands the absorption of visible light and improves the utilization of light energy. The Z-scheme structure of g-C3N4/3DOM-WO3 catalysts is able to upgrade the separation efficiency of photogenerated electron-hole pairs. The g-C3N4/3DOM-WO3 photocatalyst, whose formation rate of CO product is 48.7 μmol g−1 h−1, exhibits the excellent catalytic activity for CO2 reduction. The transfer pathway of stimulated electrons over the g-C3N4/3DOM-WO3 photocatalyst is proposed and discussed. The present approach provides unique insights into the rational development of high-performance photochemical systems for efficient CO2 reduction into valuable carbon-containing chemicals and energy fuels.

Theoretical insights into the selective and activity of CuAu catalyst for O2 and CO2 electroreduction

By using first principles calculations, CuAu alloy catalysts were shown to exhibit a high catalytic activity at low overpotential. The proposed approach is promising for explorations of the selectivity of both the oxygen reduction (evolution) reaction (ORR/OER) and the carbon dioxide reduction reaction (CO2RR) via the low-index (100) and (110) facets on the CuAu grain boundary (GB) surface, leading to a high selectivity toward CH4 on CuAu (110) and indicating that the CuAu is a highly efficient catalyst that can improve the catalytic performance of CO2 reduction to generate hydrocarbon fuels. The CO2 reduction reaction refers to the transfer of a series of successive protons/electrons (H+/e−) from the CuAu surface by different reaction mechanism pathways. We found that CuAu exhibits a promising catalytic activity for CO2 reduction that can be used for CH4 selective conversion energy storage. The results predicted that intermediate species form during the hydrogenation steps by spontaneous reactions. The atomic level can be used to gain insight into the high-performance catalysts and electrochemical mechanisms involved in the reduction of CO2 to different hydrocarbon fuels, which is an important method of revealing the reaction mechanism of the elementary steps for CO2RR and should be examined in future studies.