Catalytic Reduction Of CO2 Research Articles

Synergistic Coupling of Photocatalysis and Thermocatalysis for Efficient CO2 Conversion by Direct Z‐Scheme WO3/WS2

AbstractPhotothermal CO2 reduction using H2O combined with photocatalysis‐driven H2O splitting combined with thermal catalysis‐supported CO2 reduction has attracted rapid interest in artificial synthesis of solar fuel. With respect to extremely efficient photothermal catalysis, the photothermal impact of TMDCs (Transition Metal Dichalcogenides) facilitates CO2 reduction by activating lattice oxygen in oxide to enhance H2O oxidation. However, the fixed band gap of single photocatalyst is limited. The purpose of this work is to expand the band gap and improve the redox capacity. Hollow boxwood ball‐like WO3/WS2 Z‐scheme heterojunctions were prepared and used for photothermal catalytic CO2 reduction. DFT calculations and UV‐Vis spectra show LSPR effect in WOS heterojunctions, and the optical response extends to near infrared region. By comparison, the photothermal catalytic reduction of WO3/WS2 (9.717 μmol) by CO2 at 513 K is higher than that at 298 K (1.198 μmol) by a factor of 8. The formation of Z‐scheme heterojunction promotes rapid carrier transfer and lowers the reaction energy barrier. As well as the hollow structure improves light utilization and increases the interfacial area and number of active sites. In addition, the WO3/WS2 heterostructure utilizes its unique LSPR effect to generate heat through the photothermal effect, which can also promote molecular activation. This work reveals the important role of the LSPR effect in photothermal catalysis and demonstrates a TMDCs‐based photothermal‐driven catalysts, which presents a promising approach for designing of photothermal catalytic CO2 reduction.

Integrated CO2 capture and reduction catalysis: Role of γ-Al2O3 support, unique state of potassium and synergy with copper

Carbon dioxide capture and reduction (CCR) process emerges as an efficient catalytic strategy for CO2 capture and conversion to valuable chemicals. K-promoted Cu/Al2O3 catalysts exhibited promising CO2 capture efficiency and highly selective conversion to syngas (CO + H2). The dynamic nature of the Cu-K system at reaction conditions complicates the identification of the catalytically active phase and surface sites. The present work aims at more precise understanding of the roles of the potassium and copper and the contribution of the metal oxide support. While γ-Al2O3 guarantees high dispersion and destabilisation of the potassium phase, potassium and copper act synergistically to remove CO2 from diluted streams and promote fast regeneration of the active phase for CO2 capture releasing CO while passing H2. A temperature of 350℃ is found necessary to activate H2 dissociation and generate the active sites for CO2 capture. The effects of synthesis parameters on the CCR activity are also described by combination of ex-situ characterisation of the materials and catalytic testing.

CO2 electro/photocatalytic reduction using nanostructured ZnO and silicon-based materials: A short review

Reducing CO2 net emissions is one of the most pressing goals in tackling the current global warming emergency. Therefore, the development of carbon recycling strategies has resulted in the application of heterogeneous catalysts toward the electro/photocatalysis reduction of CO2 into hydrocarbons with potential reusability. Their morphology is among the properties that affect the performance and selectivity of catalysts towards this reaction. Nanostructuring methods offer popular strategies for catalytic applications since they allow an increase in the area/volume ratio and versatile control over surface physicochemical properties. In this review, we summarize studies that report the use of versatile synthesis techniques for obtaining nanostructured metallic and semiconductor materials with application in the electro/photocatalytic reduction of CO2. Enhancing mechanisms to the catalytic CO2 reduction yield, such as improved charge carrier separation efficiency, defect engineering, active site concentration, and localized plasmonic behavior, are described in conjunction with the control over the morphologies of the nanostructured platforms. Special attention is given to ZnO and silicon-based matrices as candidates for developing abundant and non-toxic catalytic materials. Therefore, this work represents a guide to the efforts made to design electro/photocatalytic systems that can contribute significantly to this field.

Hijacking the hydrogen atoms in photo-splitting of H2O2 for efficient reduction of CO2 to CH3OH

Photo-splitting of H2O2 in visible light is achieved by Cu-MOFs of Cu nodes and 1, 3, 5-benzene tricarboxylic acid (BTC) organic linkers (CuM) decorated with CdS (C) at varying concentrations of CdS in the CuMC composite. This process produces abundant nascent hydrogen atoms to promote the efficient catalytic reduction of CO2 to methanol (CH3OH) in visible light. The slow rate of recombination of the nascent hydrogen atoms produced by the H2O2 photo-splitting on the surface of the CdS quantum dots ensures a high steady-state concentration of hydrogen atoms with significantly reduced production of the less reactive hydrogen gas. With slow recombination of the photo-generated charges and the large surface areas for CO2 adsorption by the MOF, one of the CuMC composites is capable of convertingCO2 into CH3OH with a quantum efficiency approaching 80 %. A mechanism for the selective conversion of CO2 into CH3OH is proposed.

Pitfalls for POCOP-Type Palladium Pincer Complexes in Catalytic Reduction of CO2 with Catecholborane

Reduction of CO2 with catecholborane (HBcat) is known to be catalyzed by nickel hydride complexes supported by a bis(phosphinite)-based or POCOP-type pincer ligand. The objective of this research is to examine how changing the metal center from nickel to palladium would impact the outcome of CO2 reduction. Stoichiometric studies show that the palladium hydride complexes react rapidly with CO2, although the resulting palladium formate complexes can lose CO2 under reduced pressure or in chloroform. In the presence of HBcat, the formate complexes are converted back to the palladium hydride species while the formate group is reduced to CH3OBcat. This process is also accompanied by the formation of palladium bis(catecholato)borate complexes, which diverts some of the HBcat to yield B2(cat)3 and B2H6. For palladium hydrides stabilized by a POCOP-pincer ligand with relatively small phosphorus substituents (e.g., isopropyl or cyclopentyl groups), HBcat cleaves the P–O bonds in the ligand backbone to degrade the catalysts to secondary phosphine complexes. Without CO2, HBcat also undergoes H2 elimination with the Pd–H moiety to form palladium boryl complexes. These side reactions with HBcat and the palladium pincer complexes play profound roles in the catalytic reduction of CO2 with the borane.

Constructing Nanocaged Enzymes for Synergistic Catalysis of CO2 Reduction.

Promoting the activity of biological enzymes under in vitro environment is a promising technique for bioelectrocatalytic reactions, such as the conversion of carbon dioxide (CO2 ) into valuable chemicals, which is a promising strategy to address the environmental issue of CO2 in the atmosphere; however, this technique remains challenging. Herein, a nanocage structure for enzyme confinement is synthesized to enable the in situ encapsulation of formate dehydrogenase (FDH) in a porous metal-organic framework, which acts as a coenzyme and boosts the hybrid synergistic catalysis using enzymes. This study reveals that the synthesized FDH@ZIF-8 nanocage-structured hybrid (CSH) catalyst exhibits an improved catalytic ability of the enzymes and increases the hydrophobicity of the electrode and its affinity to CO2 . Thus, CSH can trap CO2 and control its microenvironments. The CSH catalyst boosts the conversion rate of CO2 to formic acid (HCOOH) to 28 times higher than that when using pure FDH. The in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) spectra indicates that OCHO* is the key intermediate. Density functional theory (DFT) calculations show that CSH has extremely low overpotential and is particularly effective for producing formate. This protection architecture for enzymes considerably promotes their biological application under in vitro environments.

Flow Characteristics of Electrochemical Catalytic Reduction of CO2 in Microchannel

Human beings need abundant material support and energy supply in their exploration of the universe. The sustainable supply of materials is an important condition for long-term space exploration. In situ resource utilization technology (ISRU) is an important way to realize the sustainable development of space exploration, which uses the abundant raw materials in outer space to transform energy and materials. In this paper, a microfluidic reaction device based on in situ resource utilization is designed, which converts H2O and CO2 into O2 and organic matter through photoelectrocatalysis. The flow and mixing process of gas-liquid two-phase flow was studied, and both the characteristics of mass transfer and the chemical reaction of fluids in the microchannel were studied. The dynamic process of the fluid-in-microchannel chemical reaction was expounded, and a prediction model of the volumetric mass transfer coefficient was proposed. The results show that the mass transfer coefficient of the chemical reaction is affected by the gas-liquid flow characteristics, and the mass transfer affects the rate of the chemical reaction. The material conversion of in situ resources by using the microchannel device can improve efficiency and accurately control the reaction products.

Fabrication of CNT encapsulated CuS/Ni3S4 nanohybrid for enhanced productions of solar fuels

The global warming and energy crisis are the two major problems for all the countries. To solve these two problems: The Photo catalytic reduction of CO2 into solar fuels one of the best solutions. Hence, we need efficient and stable photo catalyst for this conversion. In this work, we developed a novel photo catalyst of CNT decorated CuS/Ni3S4 hybrid composite prepared by the hydrothermal method. The XRD, UV-VIS, Raman, SEM, TEM and photo-luminescence studies were performed in order to get complete insight about phase, crystalline, band gap, size, purity and morphology of the prepared materials. All these results suggest that CNT decorated hybrid composites have benefits towards its photo catalytic activity. The photo catalytic activity of developed materials was investigated towards photo catalytic reduction of CO2 into CH3OH, CH4, C2H5OH, H2. The experiment results showed that 3 % CNT decorated CuS/Ni3S4 exhibited higher photo catalytic activity than other materials, which provided yield of 178.42 μmolg−1 methanol under irradiation of 6 h whereas, pristine CuS/Ni3S4 materials provided yield of 117.65 μmolg−1. It means that yield of methanol produced by hybrid composites 1.5 times higher than pristine chalcogen materials.

Silver Nanoparticle-Decorated Defective Zr-Based Metal–Organic Frameworks for Efficient Electrocatalytic Carbon Dioxide Reduction with Ultrahigh Mass Activity

Electrochemical reduction is considered to be a fascinating strategy to alleviate CO2 accumulation by converting it into value-added products. In this work, we used silver nanoparticle (Ag NP)-incorporated defective, thiol-functionalized UiO-66 metal–organic frameworks (MOFs) as a catalyst for the electrocatalytic conversion of CO2 to CO. We used a de novo defect engineering technique, coordination modulation, for defect incorporation as well as the functionalization of the MOF, where the introduced thiol moieties act as anchoring sites for the Ag NPs. Ag@UiO-66-SH catalyzed the CO2 reduction reaction to form CO with a Faradaic efficiency (FE) of 74% and a partial current density of 19.5 mA cm–2 at −1.1 V vs a reversible hydrogen electrode. This material showed remarkable catalytic stability, retaining the FE for CO without any significant loss in reduction current over 10 h and an excellent mass-specific activity of 218 A g–1. Density functional theory calculations further establish the enhanced catalytic CO2 reduction reaction (CO2RR) activity of Ag@UiO-66-SH compared to their pristine counterparts based on free energy calculations. This study demonstrates the use of metal NP–MOF composite materials with very less metal loading as an effective catalyst for CO2RR to CO.

Loading CuO on the surface of MgO with low-coordination basic O2− sites for effective enhanced CO2 capture and photothermal synergistic catalytic reduction of CO2 to ethanol

The higher capacity of CO2 adsorption on the surface of magnesium oxide (MgO) with low-coordination O2− sites would effectively enhance the catalytic reduction of CO2. Herein, a series of copper oxide (CuO) and MgO composites with different mass ratios have been prepared by hydrothermal method and used for photothermal synergistic catalytic reduction of CO2 to ethanol. The catalyst with CuO mass ratio of 1.6% shows the best yield (15.17 μmol·g−1·h−1) under 3 h Xenon lamp illumination. The improved performance is attributable to the loose nano-sheet structure, uniform dispersion of active sites, the increased specific surface area, medium-strengthbasicity, the high separation efficiency of electrons and holes, and the formation of Mg−O−Cu species. The synthesized CuO and MgO composites with loose nano-sheet structure facilitate the diffusion of reactants CO2, so an excellent CO2 adsorption performance can be obtained. Meanwhile, the introduction of CuO in the form of bivalence provides higher specific surface area and porosity, thus obtaining more active sites. Moreimportantly, the Mg−O−Cu species make the donation of electrons from MgO to CO2 easier, resulting in the breaking of the old Mg-O bond and the formation of C—O bond, thus promoting the adsorption and conversion of CO2 to ethanol.

High-performance photothermal catalytic CO2 reduction to CH4 and CO by ABO3 (A = La, Ce; B = Ni, Co, Fe) perovskite nanomaterials

The synthesis of renewable fuel by CO2 reduction is a promising research direction. The CO2 reduction reaction may be promoted using photothermal catalysis to achieve efficient CO2 conversion under mild conditions. In this context, designing efficient catalysts is urgent. In this work, ABO3 (A = La, Ce; B = Ni, Co, Fe) perovskite catalysts were prepared by coprecipitation and calcination. Experimental results show that the A-site ions and B-site ions in ABO3 perovskite nanomaterials have a great influence on their structure and photothermal catalytic performance. Among them, the LaNiO3 catalyst shows excellent photothermal catalytic performance in the conversion of CO2 to CO and CH4, which can generate 0.16 mmol g−1 h−1 CO and 1.38 mmol g−1 h−1 CH4 at low CO2 and H2 concentrations. For the LaNiO3 sample, its enhancement of catalytic performance mainly benefits from the largest number of active sites, the fastest carrier transport rate, and a relatively suitable band edge position compared with other catalysts. This study proposes a new method for improving the activity and selectivity of photothermal CO2 reduction and offers a new direction for the recycling of waste gas.

Bis-Imidazolium-Embedded Heterohelicene: A Regenerable NADP+ Cofactor Analogue for Electrocatalytic CO2 Reduction.

Biomimetic NAD(P)H-type organic hydride donors have recently been advocated as potential candidates to act as metal-free catalysts for fuel-forming reactions such as the reduction of CO2 to formic acid and methanol, similar to the natural photosynthesis process of fixing CO2 into carbohydrates. Although these artificial synthetic organic hydrides are extensively used in organic reduction chemistry in a stoichiometric manner, translating them into catalysts has been challenging due to problems associated with the regeneration of these hydride species under applied reaction conditions. A recent discovery of the possibility of their regeneration under electrochemical conditions via a proton-coupled electron-transfer pathway triggered intense research to accomplish their catalytic use in electrochemical CO2 reduction reactions (eCO2RR). However, success is yet to be realized to term them as "true" catalysts, as the typical turnover numbers (TONs) of the eCO2RR processes on inert electrodes for the production of formic acid and/or methanol reported so far are still in the order of 10-3-10-2; thus, sub-stoichiometric only! Herein, we report a novel class of structurally engineered heterohelicene-based organic hydride donor with a proof-of-principle demonstration of catalytic electrochemical CO2 reduction reaction showing a significantly improved activity with more than stoichiometric turnover featuring a 100-1000-fold enhancement of the existing TON values. Mechanistic investigations suggested the critical role of the two cationic imidazolium motifs along with the extensive π-conjugation present in the backbone of the heterohelicene molecules in accessing and stabilizing various radical species involved in the generation and transfer of hydride, via multielectron-transfer steps in the electrochemical process.

Spatially Separated Redox Cocatalysts on Ferroelectric Nanoplates for Improved Piezophotocatalytic CO2 Reduction and H2O Oxidation.

Utilizing solar and mechanical vibration energy for catalytic CO2 reduction and H2O oxidation is emerging as a promising way to simultaneously generate renewable energy and mitigate climate change, making it possible to integrate two energy resources into a reaction system for artificial piezophotosynthesis. However, the practical applications are hindered by undesirable charge recombination and sluggish surface reaction in the photocatalytic and piezocatalytic processes. This study proposes a dual cocatalyst strategy to overcome these obstacles and improve the piezophotocatalytic performance of ferroelectrics in overall redox reactions. With the photodeposition of AuCu reduction and MnOx oxidation cocatalysts on oppositely poled facets of PbTiO3 nanoplates, band bending occurs along with the formation of built-in electric fields on the semiconductor-cocatalyst interfaces, which, together with an intrinsic ferroelectric field, piezoelectric polarization field, and band tilting in the bulk of PbTiO3, provide strong driving forces for the directional drift of piezo- and photogenerated electrons and holes toward AuCu and MnOx, respectively. Besides, AuCu and MnOx enrich the active sites for surface reactions, significantly reducing the rate-determining barrier for CO2-to-CO and H2O-to-O2 transformation, respectively. Benefiting from these features, AuCu/PbTiO3/MnOx delivers remarkably improved charge separation efficiencies and significantly enhanced piezophotocatalytic activities in CO and O2 generation. This strategy opens a door for the better coupling of photocatalysis and piezocatalysis to promote the conversion of CO2 with H2O.

Reactor design for solar-driven photothermal catalytic CO2 reduction into fuels

Proper reactor design is of vital importance for highly-efficient photothermal catalytic CO2 reduction into solar fuels. With respect to the whole chain from capturing solar energy through energy and mass transfer to the final reduction of CO2 into fuels, this work proposes a systematic model of elaborately designing solar-driven photothermal catalytic reactors based on comprehensively studying the broadband light harvesting, energy and mass transport, and chemical conversion processes in the entire reduction of CO2 by harnessing solar energy. The established numerical model including the optical and electrical simulations of the catalyst nanoparticle as well as the flow, thermal, and chemical reaction field in the reactor is developed to integrate the overall process of the photocatalytic CO2 reduction, so as to analyze the effectiveness of the reactor and further obtain the optimal design strategy. Based on the analysis of the calculated results, methods are put forward to promote the chemical reaction by changing various parameters to regulate the light capture, radiation transfer, temperature field, and reactant supply in the catalyst layer. Most importantly, the designed reactor shows solar energy harnessing-conversion capability with remarkable light absorptivity, energy confinement, and reactants enrichment characteristics, thus realizing outstanding catalytic performance. This innovative reactor design strategy could greatly facilitate the solar-driven photothermal catalytic CO2 reduction process.

One-Pot Synthesis of Dihydropyrans via CO2 Reduction and Domino Knoevenagel/oxa-Diels-Alder Reactions.

Catalytic CO2 reduction with phenylsilane under solvent-free conditions was linked with the one-pot synthesis of 3,4-dihydropyrans from β-dicarbonyl compounds and styrenes. The synthesis includes three processes: (1) bis(silyl)acetal formation from CO2 and phenylsilane and a domino reaction of (2) Knoevenagel condensation and (3) inverse-electron-demand oxa-Diels-Alder reaction. The first process was catalyzed by a pentanuclear ZnII complex (0.07 mol %) to generate bis(silyl)acetals, which were hydrolyzed into formaldehyde to be used in the second step.

Constructing Defective Heterojunctions of BiOBr Nanosheets and Hollow NH2 -functionalized MOFs for Visible-light-driven CO2 Reduction with Nearly 100% CO Selectivity by Pure H2 O.

To rationally design photocatalysts with high generation rate and selectivity of target product remains an ongoing challenge for CO2 conversion in pure H2 O. Herein, from the viewpoint of enhancing the separation efficiency of photoinduced electron-hole pairs and the adsorption ability of CO2 molecule, we have constructed a series of Z-scheme defective heterojunctions of BiOBr nanosheets and hollow NH2 -functionalized metal-organic framework (MOF) MIL-125 with Ti ions as metal centers (noted as NH2 -MIL-125(Ti)). Systematic characterization demonstrates that the BiOBr nanosheets are anchored on the surface of hollow NH2 -MIL-125(Ti), which facilitates the efficient visible-light-driven catalytic reduction of CO2 to CO with nearly 100% selectivity by pure H2 O. Especially, the CO generation rate of optimized catalyst with oxygen vacancies reaches 459.7 μmol g-1 h-1 , which is higher than those of all the previously reported photocatalysts without sacrificial reagents. This approach provides a new insight for using inorganic semiconductors to fabricate semiconducting MOFs for high-efficiency photocatalytic reduction CO2 into value-added chemicals by pure H2 O.

Constructing Bi2MoO6/Pomelo-Peel-Derived Carbon 0D/3D Heterojunctions To Enhance Photothermal Catalytic CO2 Reduction in Full Solar Spectrum

The carrier migration limitation has been a key factor restricting the photothermal catalytic CO2 reduction. To further enhance carrier transport, Bi2MoO6 quantum dots (BM QDs) are deposited on the surface of alkali-activated pomelo-peel-derived carbon (CPP-A) to construct CPP-A/BM QDs 0D/3D heterojunctions in this paper. BM QDs have extremely short carrier transport distances and achieve photothermal synergy through the graded utilization of the full solar spectrum. The carbon framework of CPP promotes the high dispersion of BM QDs (3 nm) and allows the local surface temperature of the catalyst to increase rapidly up to 100 °C. The critical role of heat enhances the diffusion, adsorption, and carrier migration processes of CO2 and provides the energy to cross the CO2 activation energy barrier. More importantly, the oxygen-containing groups of CPP and BM QDs form a C–O–Bi interfacial electron bridge, which provides a high-speed channel for carrier transport across the interface, allowing many electrons generated by BM QDs to migrate rapidly to the CPP surface, inducing CPP as a new electron-rich surface for rapid CO2 activation, which results in an ultrahigh CO yield of 61.44 μmol/(g·h) for CPP-A/BM QDs, and the catalytic activity is increased by 9.12 times.

Dual‐Atom‐Site Sn‐Cu/C3N4 Photocatalyst Selectively Produces Formaldehyde from CO2 Reduction

AbstractThe solar‐driven catalytic reduction of CO2 to value‐added chemicals is under intensive investigation. The reaction pathway via *OCHO intermediate (involving CO2 adsorbed through O‐binding) usually leads to the two‐electron transfer product of HCOOH. Herein, a single‐atom catalyst with dual‐atom‐sites featuring neighboring Sn(II) and Cu(I) centers embedded in C3N4 framework is developed and characterized, which markedly promotes the production of HCHO via four‐electron transfer through the *OCHO pathway. The optimized catalyst achieves a high HCHO productivity of 259.1 µmol g−1 and a selectivity of 61% after 24 h irradiation, which is ascribed to the synergic role of the neighboring Sn(II)–Cu(I) dual‐atom sites that stabilize the target intermediates for HCHO production. Moreover, adsorbed *HCHO intermediate is detected by in situ Fourier transform infrared spectroscopy (CO stretches at 1637 cm−1). This study provides a unique example that controls the selectivity of the multi‐electron transfer mechanisms of CO2 photoconversion using heteronuclear dual‐atom‐site catalyst to generate an uncommon product (HCHO) of CO2 reduction.

Ternary Ni–Co–Fe oxides based on Prussian blue analog for efficient photothermal catalytic CO2 reduction to CO and CH4

Photothermal catalytic CO2 reduction is an attractive way to alleviate the current energy crisis, but it is important to prepare catalysts with efficient catalytic capacity. In this work, Prussian blue analogs were firstly prepared, and then calcined to obtain porous transition metal (Ni, Co, Fe) oxides (TMOs). The metal composition of catalysts has great influences on their structures and catalytic properties. Among them, NCF-TMO catalyst shows excellent photothermal catalytic performance, and can produce 2.9 mmol g-1 h-1 CO and 1.6 mmol g-1 h-1 mmol CH4 at low CO2 and H2 concentrations. For the NCF-TMO, its superior catalytic performance mainly benefitted from two reasons: (1) The construction of heterojunction between NiO, Co3O4 and Fe2O3, which promotes the efficient dynamic processes of charge carriers; (2) The formation of abundant surface reactive active sites facilitates the efficient conversion of CO2 molecules. This study offers a bright direction for the resource utilization of CO2.

Design and selective photocatalytic activity of highly concentrated C, N, O co-doped Zn, S co-defective ZnS particles mediated by ethylenediamine derivatives

ZnS particles are synthesized by adding ethylenediamine (en) and its derivatives, triethylenetetramine (trien) and ethylenediaminetetraacetate (EDTA), as capping agents. In the capped ZnS particles, Zn and S defects due to O, N-doping and loading of carbon dots (CDs) are confirmed. The degree of defects is suggested from photoluminescence (PL) spectra and density of states calculations. The intensities of PL are lowered in the order of ZnS-none> ZnS-EDTA> ZnS-en> ZnS-trien, while the photocurrent densities are increased in the opposite order. Time resolved PL shows extremely slow recombination of photo-excited charges in ZnS-trien. ZnS-trien is the most suitable for catalyzing CO2 reduction, and ZnS-en is the best for water-splitting. The excellent photocatalytic activity of ZnS-trien encapsulated with N-CDs shell maintains without photo-corrosion over more than five recycling experiments. Eventually, this study reveals that well-ordered ZnS with C, N, O co-doping-induced Zn, S co-defects is self-assembled using en-derivatives as capping agents, exhibits good photocatalytic activity without grafting with other particles.