CO2 Catalysis Research Articles

Oxygen vacancies–elusive but common catalytic key defects for thermal upgrading of CO2 to CH4, CO and CH3OH

Single carbon products (C1 compounds) are simple but important chemicals in the road towards energy transition. Catalytic conversion of CO2 with H2 (desirably renewable) can be performed over reducible oxides supporting transition metals to obtain products such as CH4, CO and MeOH. Oxygen vacancies (O-vacancies), which are inherent defects of reducible metal oxides, play an enormous role in driving the catalytic performance (activity, selectivity, stability) for the desired reactions. Yet, the assessment of O-defects at realistic conditions is often complex. Only few techniques can provide direct evidence for their existence and influence in CO2 activation. Among them, electron paramagnetic spectroscopy (EPR), Raman spectroscopy, scanning probe microscopies (SPM) and environmental transmission electron microscopy (ETEM) are nowadays the most informative. In most cases, however, the measurements require reaction conditions far away from CO2 valorization applications. Although great efforts have been fruitful in explaining and demonstrating the huge importance of O-vacancies in CO2 catalysis, still ambiguous or erroneous interpretations about structure-function correlations involving O-vacancies are found in literature, especially, when information is not properly gathered, e.g., by O 1s ex-situ X-ray photon spectroscopy (XPS). Moreover, despite the recognized importance of O-vacancies for CO2 valorization, critical literature compilations about their effects in thermal processes are scarce. Herein, we attempt to contribute in closing this gap by integrally encompassing representative investigations on the thermo-catalytic production of CH4, CO and MeOH. Particularly, we emphasize in the proper selection of assessment tools (direct/indirect) to unambiguously establish structure-function relationships to design optimized O-defective catalysts for the targeted compounds.

Carbonic anhydrase-embedded ZIF-8 membrane reactor with improved the recycling and stability for efficient CO2 capture

Carbonic anhydrase (CA) enzyme-based absorption technology for CO2 capture has been intensively investigated. However, low solubility of CO2 and poor stability of CA severely limits its industrial utilization. Here, hydrolyzed polyacrylonitrile (PAN) membrane (HPAN) was first modified by polyethyleneimine (PEI) with a large number of amino groups, which has a strong affinity for CO2. Then, ZIF-8 was grown in situ on the surface of HPAN/PEI membrane by using the metal chelation of PEI and Zn2+. In this process, CA was embedded inside ZIF-8 by co-precipitation (CA@HPAN/PEI/ZIF-8). The resultant CA@HPAN/PEI/ZIF-8 exhibited high catalytic activity for CO2 capture compared with free CA, which was due to the synergistic enhancement of CO2 capture by PEI and ZIF-8 with high affinity to CO2 and enzymatic catalysis. The yield of CaCO3 by CA@HPAN/PEI/ZIF-8 in the process of one-time conversion of CO2 was 13.6-fold higher than free CA. Furthermore, the CA@HPAN/PEI/ZIF-8 showed better thermal stability, storage and reusability than free CA. Free CA retained only 18.3 % of its original activity after 18 days of storage, whereas CA@HPAN/PEI/ZIF-8 remained 48.7 % of its original activity. The total CaCO3 yield by CA@HPAN/PEI/ZIF-8 was 74.9-fold that of free CA after 8 consecutive rounds of CO2 conversion.

Rapid CO2 catalytic activation of binary cementing system of CSA and Portland cement

This study presents a novel approach to activating a binary cementing system composed of calcium sulfoaluminate (CSA) cement and ordinary Portland cement (OPC) using an instant CO2 catalysis. The activation led to significant and rapid strength enhancement, with the binary cement achieving a strength of 15.42 MPa immediately after activation, all within 1 min. The rapid CO2 activation catalyzed a notable heat release, accelerating the hydration of ye'elimite to form ettringite, which is a crucial component capable of bridging gaps and imparting high initial strength. Simultaneously, the CO2 activation catalyzed the increase in sulfur concentration, which in turn, also facilitated the formation of ettringite at an early age. Subsequent strength development was attributed to belite hydration. Apart from the rapid strength gain, employing CO2 activation facilitated control over the pH value of the pore solution, thus enabling the manipulation of ettringite's crystal morphology to strategically enhance the microstructure. Samples with lower pH values exhibited needle-like ettringite formations, whereas samples with higher pH values yielded rod-like and column-like ettringite crystal structures. Comprehensive analytical investigations were analyzed using XRD, FTIR, TGA, 27Al NMR, MIP, SEM, and ICP-OES. The present study provides a new perspective on the potential application of CSA-based cement, such as precast concrete element, instant concrete product delivery, and urgent reconstruction.

Structure and Defect Identification at Self-Assembled Islands of CO2 Using Scanning Probe Microscopy.

Understanding how carbon dioxide (CO2) behaves and interacts with surfaces is paramount for the development of sensors and materials to attempt CO2 mitigation and catalysis. Here, we combine simultaneous atomic force microscopy (AFM) and scanning tunneling microscopy (STM) using CO-functionalized probes with density functional theory (DFT)-based simulations to gain fundamental insight into the behavior of physisorbed CO2 molecules on a gold(111) surface that also contains one-dimensional metal-organic chains formed by 1,4-phenylene diisocyanide (PDI) bridged by gold (Au) adatoms. We resolve the structure of self-assembled CO2 islands, both confined between the PDI-Au chains as well as free-standing on the surface and reveal a chiral arrangement of CO2 molecules in a windmill-like structure that encloses a standing-up CO2 molecule and other foreign species existing at the surface. We identify these species by the comparison of height-dependent AFM and STM imaging with DFT-calculated images and clarify the origin of the kagome tiling exhibited by this surface system. Our results show the complementarity of AFM and STM using functionalized probes and their potential, when combined with DFT, to explore greenhouse gas molecules at surface-supported model systems.

Surface ligand-promoted heterogeneous CO2 catalysis

Surface ligand-promoted heterogeneous CO2 catalysis

A Data-Driven Approach for Enhanced CO2 Capture with Ruthenium Complexes.

To attain carbon neutrality, significant efforts have been made to capture and utilize CO2. The homogeneous hydrogenation of CO2 catalyzed by transition metal complexes, particularly the ruthenium complexes, has demonstrated significant advantages and is regarded as a viable approach for practical application. Insertion of CO2 into the Ru-H bond, producing the Ru-formate product, is the key step in the hydrogenation of CO2. In order to parameterize the catalytic activities in the CO2 insertion into the Ru-H bond, the concept of simplified mechanism-based approach with data-driven practice (SMADP) has been introduced in this paper. The results showed that the hydricity of the Ru-H complex (ΔGH-) might serve as a single active descriptor in the process of CO2 insertion, and that a novel ruthenium complex in CO2 catalysis may not be easily obtained by mere modification of the auxiliary ligand at the ruthenium metal site.

Carbon-based materials for low concentration CO2 capture and electrocatalytic reduction

The gradual increase in carbon dioxide (CO2) concentration in the atmosphere has been recognized as a significant problem for humankind. CO2 flue gas is one of the most apparent contributing sources of emissions. CO2 capture and conversion are environmental-friendly and efficient ways to reduce atmospheric carbon dioxide emissions from flue gases. Considering the traditional expensive gas purification process of low-concentration CO2, the low-cost capturing and electrocatalytic CO2 reduction (ECR) at low concentration by newly-developed carbon-based materials provide an attractive approach to convert low-concentration CO2 in flue gas into high-value fuels and chemicals. Developing and integrating carbon-based capturing and catalytic materials with an understanding of the mechanism has a promising future and will promote this technology toward practical application. This review describes recent progress in the design, preparation, and structural characterization of existing carbon-based materials for the capture and catalysis of low-concentration CO2. The crucial factors of capturing and catalysis performance of all the carbon-based materials are also summarized. Furthermore, the review identifies existing research problems and challenges, and outlines future research directions. We also discuss the prospects for the industrialization of low-concentration CO2 capture and ECR. The remaining technological challenges and future directions for enhancing and applying of carbon-based materials for CO2 capture and electrocatalytic reduction are highlighted.

Bifunctionality of amine-modified metal-organic frameworks for CO2 capture and selective utilization in cycloaddition

In this study, copper- and chromium-based (HKUST-1 and MIL-101(Cr), respectively) metal-organic frameworks (MOF) functionalized with amine groups (HKUST-1‒NH2 and MIL-101(Cr)‒NH2, respectively) were directly synthesized using 2-aminoterephthalic acid as an organic linker via hydrothermal method without adding hydrofluoric acid. They were then investigated for their potential applications in dynamic carbon dioxide (CO2) adsorption and conversion of epoxides with CO2. The functionalized MOF (HKUST-1‒NH2 and MIL-101(Cr)‒NH2) retained their desired textural properties, while gaining a significantly enhanced Lewis basic character for CO2 capture and catalysis application. Both HKUST-1‒NH2 and MIL-101(Cr)‒NH2 not only showed an improved CO2 uptake capability, but also an excellent and stable regenerability over multiple adsorption-desorption cycles. MIL-101(Cr)‒NH2 exhibited a higher performance than the parent MOF and HKUST-1‒NH2 in the transformation of styrene oxide (SO) with CO2 to styrene carbonate (SC) and carbonate oligomers (COL) due to combined effect of its textural properties and basicity. Under solvent-free system, COL from monomeric SC was directly obtained, up to 72.4 % yield, via in situ oligomerization. Optimization of the solvent-free reaction conditions was carried out to control the selective pathway of CO2 utilization between cycloaddition and oligomerization. In the presence of acetonitrile, a > 97 % yield of SC was achieved over MIL-101(Cr)‒NH2 under a mild reaction condition (120 °C and 20 bar of CO2). Reaction mechanisms for the cycloaddition and oligomerization of SO with CO2 are also proposed to comprehend the role of MOF, amine group, and co-catalyst. The combined efficient CO2 adsorption and capability to produce CC and COL makes the synthesized MOF promising materials for CO2 capture and selective utilization.

Hierarchical Carbon Nanocages as Superior Supports for Photothermal CO2 Catalysis.

The exploitation of hierarchical carbon nanocages with superior light-to-heat conversion efficiency, together with their distinct structural, morphological, and electronic properties, in photothermal applications could provide effective solutions to long-standing challenges in diverse areas. Here, we demonstrate the discovery of pristine and nitrogen-doped hierarchical carbon nanocages as superior supports for highly loaded, small-sized Ru particles toward enhanced photothermal CO2 catalysis. A record CO production rate of 3.1 mol·gRu-1·h-1 with above 90% selectivity in flow reactors was reached for hierarchical nitrogen-doped carbon-nanocage-supported Ru clusters under 2.4 W·cm-2 illumination without external heating. Detailed studies reveal that the enhanced performance originates from the strong broadband sunlight absorption and efficient light-to-heat conversion of nanocage supports as well as the excellent intrinsic catalytic reactivity of sub-2 nm Ru particles. Our study reveals the great potential of hierarchical carbon nanocages in photothermal catalysis to reduce the fossil fuel consumption of various industrial chemical processes and stimulates interest in their exploitation for other demanding photothermal applications.

Defects orchestrate concerted CO2 catalysis

Defects orchestrate concerted CO2 catalysis

Coordination-tuned Ru single-atom catalyst for efficient catalysis of CO2 to CH4 on RuBxN4-x@TiN (x=0–4)

Creating useful chemicals or fuels from CO2 is one of the most promising ways to reach carbon neutral. In this work, through the formation of Lewis acid sites, a string of boron-atom-coordinated Ru single-atom catalysts (SACs), namely RuBxN4-x@TiN (x=0–4), were constructed, and their CO2 reduction reaction (CO2RR) was systematically studied. The results show that o-RuB2N2@TiN, p-RuB2N2@TiN, and RuB3N1@TiN are able to efficiently inhibit the competitive hydrogen evolution reaction (HER) and activate CO2, with a potential-determining step lower than 0.7 eV and high selectivity for CH4 generation. This work shows that the synergistic effect of B and Ru atoms are able to effectively improve the catalytic activity, which is expected to offer a possible tactic for the sensible creation of effective CO2RR catalysts.

Photothermal CO2 Catalysis toward the Synthesis of Solar Fuel: From Material and Reactor Engineering to Techno-Economic Analysis.

Carbon dioxide (CO2), a member of greenhouse gases, contributes significantly to maintaining a tolerable environment for all living species. However, with the development of modern society and the utilization of fossil fuels, the concentration of atmospheric CO2 has increased to 400ppm, resulting in a serious greenhouse effect. Thus, converting CO2 into valuable chemicals is highly desired, especially with renewable solar energy, which shows great potential with the manner of photothermal catalysis. In this review, recent advancements in photothermal CO2 conversion are discussed, including the design of catalysts, analysis of mechanisms, engineering of reactors, and the corresponding techno-economic analysis. A guideline for future investigation and the anthropogenic carbon cycle are provided.

Engineering Photothermal Catalytic CO2 Nanoreactor for Osteomyelitis Treatment by In Situ CO Generation.

Photocatalytic carbon dioxide (CO2) reduction is an effective method for in vivo carbon monoxide (CO) generation for antibacterial use. However, the available strategies mainly focus on utilizing visible-light-responsive photocatalysts to achieve CO generation. The limited penetration capability of visible light hinders CO generation in deep-seated tissues. Herein, a photothermal CO2 catalyst (abbreviated as NNBCs) to achieve an efficient hyperthermic effect and in situ CO generation is rationally developed, to simultaneously suppress bacterial proliferation and relieve inflammatory responses. The NNBCs are modified with a special polyethylene glycol and further embellished by bicarbonate (BC) decoration via ferric ion-mediated coordination. Upon exposure to 1064nm laser irradiation, the NNBCs facilitated efficient photothermal conversion and in situ CO generation through photothermal CO2 catalysis. Specifically, the photothermal effect accelerated the decomposition of BC to produce CO2 for photothermal catalytic CO production. Benefiting from the hyperthermic effect and in situ CO production, in vivo assessments using an osteomyelitis model confirmed that NNBCs can simultaneously inhibit bacterial proliferation and attenuate the photothermal effect-associated pro-inflammatory response. This study represents the first attempt to develop high-performance photothermal CO2 nanocatalysts to achieve in situ CO generation for the concurrent inhibition of bacterial growth and attenuation of inflammatory responses.

Exploring and Leveraging the basic principle for molecular reduction catalysis of biorenewables, CO2, and plastics using light, electric and heat energy

Biorenewable energy and chemicals hold great promise for a greener, more sustainable future. Biomass is organic materials that can be used to generate electricity and gas in the form of bioenergy. Catalysis is required to convert the biomass into a useful form. At the Saito Research Group in the Noyori Laboratory at the Graduate School of Science, Nagoya University, Japan, Professor Susumu Saito and the team are engaged in the design and development of catalysts for exactly this. In one line of research, the team is developing upcycling catalysts for highly oxidised chemical compounds (HOCs). The idea is that these catalysts can be used to quickly and efficiently synthesise high-value-added organic molecules from carbon resources. In another project, the researchers are exploring organic synthesis based on one electron transfer from H2 or H2O using molecular and semiconductor photocatalysis. One electron (radical) species (OES) such as hydrogen atom (H•) can be produced from the homolytic cleavage of chemical bonds of H2 or H2O, occurring by visible/near-UV light energy inducing photo-excited states of tailored homogeneous and heterogeneous (semiconductor) catalysts. These OESs can be used in addition reactions and H-abstraction reactions to generate carbon-centred radical species and achieve artificial photosynthesis directed toward selective organic synthesis (APOS). A key focus for the team is on molecular metal catalysis. They designed novel (PNNP)M catalysts, with the PNNP representing two-phosphine and two-nitrogen coordinative atoms and the M representing metals, from which they derived robust reduction/dehydration catalysts with catalytic activity that can be sustained for a long period of time under visible light, electric and heat energy.

Modulation of the Structure-function Relationship of the "nano-greenhouse effect" towards Optimized Supra-photothermal Catalysis.

Photothermal catalytic CO2 hydrogenation holds great promise for relieving the global environment and energy crises. The "nano-greenhouse effect" has been recognized as a crucial strategy for improving the heat management capabilities of a photothermal catalyst by ameliorating the convective and radiative heat losses. Yet it remains unclear to what degree the respective heat transfer and mass transport efficiencies depend on the specific structures. Herein, the structure-function relationship of the "nano-greenhouse effect" was investigated and optimized in a prototypical Ni@SiO2 core-shell catalyst towards photothermal CO2 catalysis. Experimental and theoretical results indicate that modulation of the thickness and porosity of the SiO2 nanoshell leads to variations in both heat preservation and mass transport properties. This work deepens the understandings on the contributing factor of the "nano-greenhouse effect" towards enhanced photothermal conversion. It also provides insights on the design principles of an ideal photothermal catalyst in balancing heat management and mass transport processes.

In Situ Anchoring of Small-Sized Silver Nanoparticles on Porphyrinic Triazine-Based Frameworks for the Conversion of CO2 into α-Alkylidene Cyclic Carbonates with Outstanding Catalytic Activities under Ambient Conditions.

The preparation of catalytic hybrid materials by introducing highly dispersed metallic nanoparticles into porous organic polymers (POPs) may be an ideal and promising strategy for integrated CO2 capture and conversion. In terms of the carboxylative cyclization of propargyl alcohols with CO2, the anchoring of silver nanoparticles (AgNPs) on functional POPs to fabricate efficient heterogeneous catalysts is considered to be quite intriguing but remains challenging. In the contribution, well-dispersed AgNPs were successfully anchored onto the porphyrinic triazine-based frameworks by a simple "liquid impregnation and in situ reduction" strategy. The presence of N-rich dual active sites, porphyrin and triazine, which acted as the electron donor and acceptor, respectively, offered a huge opportunity for the nucleation and growth of metal nanoparticles. Significantly, the as-prepared catalyst Ag/TPP-CTF shows excellent catalytic activity (up to 99%) toward the carboxylative cyclization of propargyl alcohols with CO2 at room temperature, achieving record-breaking activities (TOF up to 615 h-1 at 1 bar and 3077 h-1 at 10 bar). Moreover, the catalyst can be easily recovered and reused at least 10 times with retention of high catalytic activity. The possible mechanism involves small-sized AgNP-mediated alkyne activation, which may promote highly efficient and green conversion of CO2. This work paves the way for immobilizing metal nanoparticles onto functional POPs by surface structure changes for enhanced CO2 catalysis.

Substituent Engineering in Pore-Space-Partitioned Metal-Organic Frameworks for CO2 Selective Adsorption and Fixation.

Comprehensive understanding of substituent groups located on the pore surface of metal-organic frameworks (which we call substituent engineering herein) can help to promote gas adsorption and catalytic performance through ligand functionalization. In this work, pore-space-partitioned metal-organic frameworks (PSP MOFs) were selected as a platform to evaluate the effect of organic functional groups on CO2 adsorption, separation, and catalytic conversion. Twelve partitioned acs metal-organic frameworks (pacs-MOFs, named SNNU-25-Rn here) containing different functional groups were synthesized, which can be classified into electron-donor groups (-OH, -NH2, -CH3, and -OCH3) and electron-acceptor groups (-NO2, -F, -Cl, and -Br). The experimental results showed that SNNU-25-Rn with electron donors usually perform better than those with electron acceptors for the comprehensive utilization of CO2. The CO2 uptake of the 12 SNNU-25-Rn MOFs ranged from 30.9 to 183.6 cm3 g-1 at 273 K and 1 bar, depending on the organic functional groups. In particular, SNNU-25-OH showed the highest CO2 adsorption, SNNU-25-CH3 had the highest IAST of CO2/CH4 (36.1), and SNNU-25-(OH)2 showed the best catalytic activity for the CO2 cycloaddition reaction. The -OH functionalized MOFs with excellent performance may be attributed to the Lewis acid-base and hydrogen-bonding interactions between -OH groups and the CO2 molecules. This work modulated the effect of the microenvironment of MOFs on CO2 adsorption, separation, and catalysis in terms of substituents, providing valuable information for the precise design of porous MOFs with a comprehensive utilization of CO2.

Co3InC0.75-In2O3 composite construction and its synergetic hydrogenation catalysis of CO2 to methanol

The efficient catalytic hydrogenation of CO2 to methanol is a promising route for CO2 emission mitigation and utilization. Recently, the Co-In based materials as one of the excellent alternative catalysts for CO2 hydrogenation to methanol have received intense attention. Herein, we developed new and efficient Co-In based catalysts (the composite of Co3InC0.75 and In2O3) by Prussian Blue analogues (PBA) pyrolysis. And a series of Co3InC0.75-In2O3 composites with tunable proportion of Co3InC0.75 and In2O3 has been prepared. The experimental results demonstrate the Co3InC0.75-In2O3 catalysts have high catalytic CO2 hydrogenation performance into methanol, reaching a methanol yield up to 0.62 gMeOHgcat−1h−1 at 300 °C, 5 MPa, 24000 cm3STPgcat−1h−1, and H2/CO2 = 3:1, the high reaction stability and air resistance. The synergetic effects between Co3InC0.75 and In2O3 for the enhanced methanol production were confirmed by a series of characterizations, and a positive correlation between methanol production activity and the fraction of Co3InC0.75/In2O3 was well established.

Synthesis of 3D Porous Cu Nanostructures on Ag Thin Film Using Dynamic Hydrogen Bubble Template for Electrochemical Conversion of CO2 to Ethanol.

Cu-based nanomaterials have been widely considered to be promising electrocatalysts for the direct conversion of CO2 to high-value hydrocarbons. However, poor selectivity and slow kinetics have hindered the use of Cu-based catalysts for large-scale industrial applications. In this work, we report on a tunable Cu-based synthesis strategy using a dynamic hydrogen bubble template (DHBT) coupled with a sputtered Ag thin film for the electrochemical reduction of CO2 to ethanol. Remarkably, the introduction of Ag into the base of the three-dimensional (3D) Cu nanostructure induced changes in the CO2 reduction reaction (CO2RR) pathway, which resulted in the generation of ethanol with high Faradaic Efficiency (FE). This observation was further investigated through Tafel and electrochemical impedance spectroscopic analyses. The rational design of the electrocatalyst was shown to promote the spillover of formed CO intermediates from the Ag sites to the 3D porous Cu nanostructure for further reduction to C2 products. Finally, challenges toward the development of multi-metallic electrocatalysts for the direct catalysis of CO2 to hydrocarbons were elucidated, and future perspectives were highlighted.

Modeling Adsorption of CO2 in Rutile Metallic Oxide Surfaces: Implications in CO2 Catalysis

CO2 is the most abundant greenhouse gas, and for this reason, it is the main target for finding solutions to climatic change. A strategy of environmental remediation is the transformation of CO2 to an aggregated value product to generate a carbon-neutral cycle. CO2 reduction is a great challenge because of the large C=O dissociation energy, ~179 kcal/mol. Heterogeneous photocatalysis is a strategy to address this issue, where the adsorption process is the fundamental step. The focus of this work is the role of adsorption in CO2 reduction by means of modeling the CO2 adsorption in rutile metallic oxides (TiO2, GeO2, SnO2, IrO2 and PbO2) using Density Functional Theory (DFT) and periodic DFT methods. The comparison of adsorption on different metal oxides forming the same type of crystal structure allowed us to observe the influence of the metal in the adsorption process. In the same way, we performed a comparison of the adsorption capability between two different surface planes, (001) and (110). Two CO2 configurations were observed, linear and folded: the folded conformations were observed in TiO2, GeO2 and SnO2, while the linear conformations were present in IrO2 and PbO2. The largest adsorption efficiency was displayed by the (001) surface planes. The CO2 linear and folded configurations were related to the interaction of the oxygen on the metallic surface with the adsorbate carbon, and the linear conformations were associated with the physisorption and folded configurations with chemisorption. TiO2 was the material with the best performance for CO2 interactions during the adsorption.