Gas-phase CO Research Articles

MPS@BWO with High Adsorption Capacity for Efficient Photocatalytic Reduction of CO2

Photocatalysis can reduce CO2 to available energy by means of light energy, which is considered to be an effective solution to alleviate energy and environmental problems. In this paper, an MPS@Bi2WO6 composite photocatalyst was prepared by in situ hydrothermal method. BWO grew on the surface of MPS, which increased the CO2 absorption capacity of the photocatalyst and improved the microstructure. Under the synergistic effect of the two aspects, BWS achieves the enhancement of light energy absorption capacity and can effectively excite electron-hole pairs. The transition electrons with high reduction ability migrate to the surface and contact with high concentrations of CO2, achieving efficient CO2 reduction under visible light. Among the photocatalysts in this paper, BWS-1 (BWO: MPS = 1:1) has efficient CO2 gas phase reduction ability under visible light, and the CO yield reaches 29.51 μmol/g. The MPS@BWO photocatalyst is a low-cost and efficient CO2 photoreduction catalyst with broad application prospects.

Addition of CuO to form CuO/TiO2 and CuO/ZnO heterojunctions for photocatalytic CO2 conversion to methanol

Photocatalytic conversion of carbon dioxide (CO2) to value-added products is a promising route towards sustainability. In this work, gas phase CO2 in presence of water vapor and UV irradiation source was converted to methanol using TiO2, ZnO, CuO/TiO2 and CuO/ZnO photocatalysts. Characterization by physico-chemical, optical and First-principle based techniques revealed that CuO/TiO2 possessed increased oxygen vacancy, highest average electron lifetime, transfer rate, injection efficiency and highest separation efficiency. The maximum methanol (∼28 %) yield of CuO/TiO2 is ascribed due to combined effect of heterojunction formation and increment in surface oxygen vacancies by doping with CuO, acted as electron-trapping cocatalyst.

Comparison and analysis on comprehensive performance of CO2 multiphase refrigeration systems using liquefied natural gas cold energy

In order to fully apply liquefied natural gas (LNG) cold energy to the refrigeration system, four different types of CO2 multiphase refrigeration systems using LNG cold energy are designed. In this paper, (1) CO2 single-stage compressed solid and gas phase refrigeration cycle (SSCC1), (2) CO2 single-stage compressed solid and solid phase refrigeration cycle (SSCC2), (3) CO2 double-stage compressed solid and gas phase refrigeration cycle (DSCC1), and (4) CO2 double-stage compressed solid and solid phase refrigeration cycle (DSCC2) are combined with CO2 liquid phase secondary refrigerant cycle (RC), respectively, to effectively use LNG cold energy. The performance analysis, exergy analysis, economic analysis, and CO2 emission analysis of the proposed systems are carried out by establishing the mathematical models. The results show that the intermediate pressure of DSCC1-RC and DSCC2-RC reaches the best performance at 0.3 MPa, and the system performance decreases with the increase in intermediate temperature. The refrigerating capacity of the CO2 liquid phase secondary refrigerant cycle, the COP, and the exergy efficiency of four kinds of CO2 multiphase refrigeration systems decrease with the increase in the refrigerating capacity of the CO2 refrigeration cycle, while the power consumption of SSCC2-RC and DSCC2-RC decreases, SSCC1-RC and DSCC1-RC increased. The system with the shortest exergy loss is DSCC2-RC at 654.01 kW, while the system with the shortest payback period is SSCC2-RC at 0.88 years, and DSCC2-RC has the smallest CO2 emission. Four CO2 multiphase refrigeration systems and the ammonia combined refrigeration system with the same total refrigerating capacity are compared and analyzed, respectively; the results show that the performance, economy, and CO2 emission of CO2 multiphase refrigeration system are better than those of ammonia combined refrigeration system; and the exergy loss of CO2 multiphase refrigeration system is generally larger than that of ammonia combined refrigeration system because of the large temperature difference in heat transfer.

Photocatalytic Synergy Between α-Bi2O3 Nanosphere and Spindle MIL-88A for Gas-Phase CO2 Reduction.

Visible light-active photocatalysts play a crucial role in gas-phase photocatalytic CO2 reduction, offering significant potential for sustainable energy conversion. Herein, we present the synthesis of spindle-shaped Iron (Fe)-based metal-organic framework (MOF) MIL-88 A, coupled with distinct α-Bi2O3 nanospheres. The α-Bi2O3/MIL88A heterostructure is formed by interacting opposite surface charges, enhancing visible-light absorption and efficient interfacial charge-carrier separation. Such low-cost photocatalysts have a 1.75 eV band gap and demonstrate enhanced efficacy in converting CO2 to CO, CH4, and H2 in water without using any sacrificial agents or noble metals compared to pristine MIL88A. In addition, in-situ Electron Spin Resonance (ESR) analyses revealed that these unique catalysts combination promoted enhanced interfacial charge dynamics, creating efficient trapping sites for photogenerated carriers. Further, in-situ Diffuse Reflectance Infrared Fourier Transfer Spectroscopy (DRIFTS) investigation elucidates the plausible reaction mechanism and provides an effective methodology for catalyst screening for CO2 photoreduction. This study offers an effective approach for synthesizing the earth-abundant heterostructure from metal oxide and low-cost MOFs, enhancing photocatalytic activity for sustainable carbon dioxide conversion into invaluable chemicals.

(Invited) Perspectives from in Situ spectroscopy on the Molecular-Level Interactions of Carbon Dioxide in Nanomaterials for Capture and Conversion

Understanding the molecular level foundations of CO2 capture and conversion might unveil design strategies for efficient materials for these key decarbonization technologies. The control over the reaction channel in the complex network of reactions to produce selectively and on-demand chemicals from CO2 via electrocatalysis is appealing to scientists worldwide on a fundamental and technological level. Operando techniques have become very popular to help achieve this goal as demonstrated by a flourishing number of dedicated studies [1-3] and other initiatives for discussion [4-6]. In this contribution, I will present recent work on the spectroscopic characterisation of the CO2 interaction with several prototypical nanostructural systems of relevance, [7-11] emphasising characteristic spectroscopic fingerprints and their critical assessment. This contribution aims to discuss opportunities and current limitations encountered in situ X-ray methods to extract mechanistic insights.[1] Y. Han, H. Zhang, Y. Yu, Z. Liu, In Situ Characterization of Catalysis and Electrocatalysis Using APXPS, ACS Catalysis, 11 (2021), 1464-1484.[2] V. Pfeifer, M. Hävecker, J. J. Velasco Vélez, A. Knop-Gericke, R. Schlögl, R. Arrigo, An in situ electrochemical cell for studying OER materials, Topics in Catalysis, 61 (2019), 2064-2084.[3] G. Held, F. Venturini, D. C. Grinter, P. Ferrer, R. Arrigo, L. Deacon, W. Quevedo Garzon, K. Roy, A. Large, C. Stephens, A. Watts, P. Larkin, M. Hand, H. Wang, L. Pratt, J. J. Mudd, T. Richardson, S. Patel, M. Hillman and S. Scott, Ambient-pressure end station of the Versatile Soft X-ray (VerSoX) beamline at Diamond Light Source, J. Synchrotron Rad., 27 (2020), 1153-1166.[4] R. Arrigo, A. Logsdail, L. Torrente-Murciano, Highlights from Faraday Discussion on Designing Nanoparticle Systems for Catalysis, London, UK, May 2018, (Conference Report) Chem. Commun., 2018, 54, 9385-9393DOI: 10.1039/C8CC90324G;[5] R. Arrigo et al., The challenges of characterising nanoparticulate catalysts: general discussion Faraday Discussion, 208 (2018), 339-394.[6] C. R. A. Catlow, P. wells, D. Gianolio Synchrotron radiation techniques in catalytic science, Phys. Chem. Chem. Phys., 22 (2020), 18745-18746.[7] R. Arrigo, R. Blume, V. Streibel, C. Genovese, A. Roldan, M. E. Schuster, C. Ampelli, S. Perathoner, J.-J. Velasco-Vélez, M. Hävecker, A. Knop-Gericke, R. Schlögl, G. Centi, Dynamics at Polarized, Carbon Dioxide/Iron Oxyhydroxide Interfaces Unveil the Origin of Multicarbon Product Formation, ACS Catalysis, 12 (2021) 411-430.[8] J.-J. Velasco-Vélez, T. Jones, D. Gao, E. Carbonio, R. Arrigo, C.-J. Hsu, Y.-C. Huang, C.-L. Dong, J.-M. Chen, J.-F. Lee, P. Strasser, B. Roldan Cuenya, R. Schlögl, A. Knop-Gericke, C.-H. Chuang, The Role ofthe Copper Oxidation State in the Electrocatalytic Reduction of CO2 into Valuable Hydrocarbons, ACS Sustainable Chem. Eng., 7 (2019), 1485–1492.[9] J.-J. Velasco-Vélez, C.-H. Chuang, D. Gao, Q. Zhu, D. Ivanov, H. S. Jeon, R. Arrigo, R. V. Mom, E. Stotz, H.-L. Wu, T. E. Jones, B. Roldan Cuenya, A. Knop-Gericke, R. Schlögl, On the activity/selectivity and phase stability of thermally grown copper oxides during the electrocatalytic reduction of CO2, ACS Catalysis, 10 (2020) 11510-11518.[10] J-J. Velasco-Velez, R.V. Mom, L.-E. Sandoval-Diaz, L. J. Falling, C.-H. Chuang, D. Gao, T. E. Jones, Q. Zhu, R. Arrigo, B. Roldan Cuenya, A. Knop-Gericke, T. Lunkenbein, R. Schlögl, Revealing the ActivePhase of Copper during the Electroreduction of CO2 in Aqueous Electrolyte by Correlating In Situ X-ray Spectroscopy and In Situ Electron Microscopy, ACS Energy Lett., 5 (2020), 2106–2111.[11] R. Arrigo, R. Blume, A. Large, J.-J. Velesco-Velez, M., Haevecker, A. Knop-Gericke, G. Held, Dynamics over a Cu-graphite electrode during the gas-phase CO2 reduction investigated by APXPS, Faraday Discuss., 236 (2022) 126-140.

Inhibiting salt precipitation on the gas diffusion electrode surface in gas-phase CO2 electroreduction to formate by using an acidic anolyte

The gas-phase CO2 electroreduction to formate represents one of the most promising CO2 conversion processes due to its scalability, as the product concentration surpasses 30 % wt. However, the use of alkaline media anolytes, intended to improve the efficiency and selectivity of formate production, causes the carbonate and bicarbonate salts to precipitate over the Gas Diffusion Electrode (GDE). This precipitation clogs the porous structure, leading to a rapid loss of electrode stability. In this work, we address this issue by proposing the use of acid anolytes, based on K2SO4, to mitigate the precipitation of insoluble salt on the GDE structure, thereby achieving longer and more stable GDE operation times. Various anolyte concentrations and pHs are evaluated, with 0.3 M K2SO4 at pH 1, adjusted using H2SO4, providing the best compromise. This condition inhibited potassium carbonate and bicarbonate precipitation, as observed through XRD, SEM, and EDS analysis, while maintaining high CO2 electroreduction to formate performance, with a concentration of 69 g L−1, and a Faradaic Efficiency of 33 %. Furthermore, the anolyte flowrate per geometric area is optimized to maximize the system performance. At a flowrate of 0.85 mL min−1 cm−2, enhanced concentration of 88 g L−1 and a Faradaic Efficiency of 42 % are reached. Besides, long-term experiments demonstrated that GDEs used with alkaline conditions exhibit a larger deactivation constant (0.7652) compared to the GDEs used with acid anolytes (0.3891). This indicates that salt precipitation more rapidly reduces GDE performance under alkaline conditions. These results represent a promising advance in obtaining longer-lasting GDEs, which are crucial to successfully scaling up the CO2 electroreduction to formate.

Exploring the roles of atomic radius on methane oxidation in different M(Y, Sm, and Ni)-doped CeO2 catalysts using operando DRIFTS-MS and DFT computation

Ce-based oxides doped with different metal ions can greatly improve CH4 catalytic activity, but the relationship between the surface microstructure and its activity is not clear. In this article, M(Y, Sm, and Ni)-CeO2 catalyst prepared by aerosol method is used as the research object. CH4 is used as a molecular probe for the study. Operando DRIFTS-MS and DFT computation are used to verify the structure-activity relationship between the surface structure and activity of M-CeO2. Ni-CeO2 with the smallest atomic radius ratio has the best CH4 oxidation performance (550 °C) and excellent redox characteristics. Operando DRIFTS-MS results show that the NiO is more likely to adsorb CH4 and form the intermediates CH3*, gas-phase CO2, CO, and H2O at low temperatures. At high temperatures, Ni-OH, Ni-O-Ce, and CeO further react with CH4. Among them, the formation of M-Ov-Ce has a positive role in promoting the decomposition of O₂. Importantly, carbonate is the rate-determining step that affects the activation of M-Ov-Ce. Monodentate carbonates decompose more easily at low temperatures. These findings reveal a novel doping effect and provide a new idea for the design and development of Ce based catalysts with high CH4 removal ability

Carbon Dioxide Capture and Storage (CCS) in Saline Aquifers versus Depleted Gas Fields

Saline aquifers have been used for CO2 storage as a dedicated greenhouse gas mitigation strategy since 1996. Depleted gas fields are now being planned for large-scale CCS projects. Although basalt host reservoirs are also going to be used, saline aquifers and depleted gas fields will make up most of the global geological repositories for CO2. At present, depleted gas fields and saline aquifers seem to be treated as if they are a single entity, but they have distinct differences that are examined here. Depleted gas fields have far more pre-existing information about the reservoir, top-seal caprock, internal architecture of the site, and about fluid flow properties than saline aquifers due to the long history of hydrocarbon project development and fluid production. The fluid pressure evolution paths for saline aquifers and depleted gas fields are distinctly different because, unlike saline aquifers, depleted gas fields are likely to be below hydrostatic pressure before CO2 injection commences. Depressurised depleted gas fields may require an initial injection of gas-phase CO2 instead of dense-phase CO2 typical of saline aquifers, but the greater pressure difference may allow higher initial injection rates in depleted gas fields than saline aquifers. Depressurised depleted gas fields may lead to CO2-injection-related stress paths that are distinct from saline aquifers depending on the geomechanical properties of the reservoir. CO2 trapping in saline aquifers will be dominated by buoyancy processes with residual CO2 and dissolved CO2 developing over time whereas depleted gas fields will be dominated by a sinking body of CO2 that forms a cushion below the remaining methane. Saline aquifers tend to have a relatively limited ability to fill pores with CO2 (i.e., low storage efficiency factors between 2 and 20%) as the injected CO2 is controlled by buoyancy and viscosity differences with the saline brine. In contrast, depleted gas fields may have storage efficiency factors up to 80% as the reservoir will contain sub-hydrostatic pressure methane that is easy to displace. Saline aquifers have a greater risk of halite-scale and minor dissolution of reservoir minerals than depleted gas fields as the former contain vastly more of the aqueous medium needed for such processes compared to the latter. Depleted gas fields have some different leakage risks than saline aquifers mostly related to the different fluid pressure histories, depressurisation-related alteration of geomechanical properties, and the greater number of wells typical of depleted gas fields than saline aquifers. Depleted gas fields and saline aquifers also have some different monitoring opportunities. The high-density, electrically conductive brine replaced by CO2 in saline aquifers permits seismic and resistivity imaging, but these forms of imaging are less feasible in depleted gas fields. Monitoring boreholes are less likely to be used in saline aquifers than depleted gas fields as the latter typically have numerous pre-existing exploration and production well penetrations. The significance of this analysis is that saline aquifers and depleted gas fields must be treated differently although the ultimate objective is the same: to permanently store CO2 to mitigate greenhouse gas emissions and minimise global heating.

Mapping gas–phase CO<sub>2</sub> in the headspace of two champagne glasses through infrared laser absorption spectroscopy: ŒnoXpert glass versus INAO glass

Mapping gas–phase CO<sub>2</sub> in the headspace of two champagne glasses through infrared laser absorption spectroscopy: ŒnoXpert glass versus INAO glass

Theoretical Insights into Enhancing Catalytic Performance of Al-Cu Alloy for CO2 Electroreduction toward Ethene Production.

The understanding of the reaction mechanism of CO2 electroreduction (CO2RR) is essential for the precise design of catalysts for specific products with high selectivity. In this work, combined with the computational hydrogen electrode model and kinetic energy barrier calculations, CO2RR pathways on Cu(100) and Al1Cu3(100) are intensively investigated. The free energy barrier of the rate-determining step of ethylene formation is reduced from 1.08 eV for *CCOH formation on Cu(100) to 0.51 eV for *CH2OCHOH formation on Al1Cu3(100) and enhances the catalytic activity. The reaction free energy of *CO-*CO coupling is remarkably reduced from 0.86 eV on Cu(100) to -0.43 eV on Al1Cu3(100) and the coupling barrier is reduced from 0.97 to 0.37 eV, suppressing the production of gas phase CO and enhancing the production of C2 products. Furthermore, the selectivity toward C-O breaking of *CH2CHOH on Cu(100) and *CH2CH2OH on Al1Cu3(100) ensures high selectivity toward ethene rather than ethanol.

Unveiling the Mechanism of Plasma-Catalyzed Oxidation of Methane to C2+ Oxygenates over Cu/UiO-66-NH2.

Nonthermal plasma (NTP) offers the potential for converting CH4 with CO2 into liquid products under mild conditions, but controlling liquid selectivity and manipulating intermediate species remain significant challenges. Here, we demonstrate the effectiveness of the Cu/UiO-66-NH2 catalyst in promising the conversion of CH4 and CO2 into oxygenates within a dielectric barrier discharge NTP reactor under ambient conditions. The 10% Cu/UiO-66-NH2 catalyst achieved an impressive 53.4% overall liquid selectivity, with C2+ oxygenates accounting for ∼60.8% of the total liquid products. In situ plasma-coupled Fourier-transform infrared spectroscopy (FTIR) suggests that Cu facilitates the cleavage of surface adsorbed COOH species (*COOH), generating *CO and enabling its migration to the surface of Cu particles. This surface-bound *CO then undergoes C-C coupling and hydrogenation, leading to ethanol production. Further analysis using CO diffuse reflection FTIR and 1H nuclear magnetic resonance spectroscopy indicates that in situ generated surface *CO is more effective than gas-phase CO (g) in promoting C-C coupling and C2+ liquid formation. This work provides valuable mechanistic insights into C-C coupling and C2+ liquid production during plasma-catalytic CO2 oxidation of CH4 under ambient conditions. These findings hold broader implications for the rational design of more efficient catalysts for this reaction, paving the way for advancements in sustainable fuel and chemical production.

Astrochemical effect of the fundamental grain surface processes

Context. Thermal diffusion is one of the basic processes for the mobility and formation of species on cosmic dust grains. The rate of thermal diffusion is determined by the grain surface temperature, a pre-exponential factor, and an activation energy barrier for diffusion. Due to the lack of laboratory measurements on diffusion, prior astrochemical models usually assume that the diffusion pre-exponential factor is the same as that for desorption. This oversimplification may lead to an uncertainty in the model predictions. Recent laboratory measurements have found that the diffusion pre-exponential factor can differ from that for desorption by several orders of magnitude. However, the newly determined pre-exponential factor has not been tested in astrochemical models so far. Aims. We aim to evaluate the effect of the newly experimentally measured diffusion pre-exponential factor on the chemistry under cold molecular cloud conditions. Methods. We ran a set of parameters with different grain temperatures and diffusion barrier energies using the NAUTILUS astro-chemical code and compared the molecular abundance between the models with the abundance obtained using the experimentally determined pre-exponential factor for diffusion and with the abundance obtained using the values commonly adopted in prior models. Results. We found that statistically, more than half of the total gas-phase and grain surface species are not affected by the new pre-exponential factor after a chemical evolution of 105 yr. The most abundant gas-phase CO and grain surface water ice are not affected by the new pre-exponential factor. For the grain surface species that are affected, compared to the commonly adopted value of the pre-exponential factor for diffusion used in the chemical models, they could be either overproduced or underproduced with the lower diffusion pre-factor used in this work. The former case applies to radicals and the species that serve as reactants, while the latter case applies to complex organic molecules (COMs) on the grain and the species that rarely react with other species. Gas-phase species could also be affected due to the desorption of the grain surface species. The abundance of some gas-phase COMs could be varied by over one order of magnitude depending on the adopted grain surface temperature and/or the ratio of diffusion to desorption energy in the model. Key species whose diffusion pre-exponential factor significantly affects the model predictions were also evaluated, and these species include CH3OH, H2CO, and NO. Conclusions. The results presented in this study show that the pre-exponential factor is one of the basic and important parameters in astrochemical models. It strongly affects the chemistry and should be determined carefully. More experiments to determine the diffusion of grain surface species are helpful for constraining their properties.

GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114

The enormous increase in mid-IR sensitivity and spatial and spectral resolution provided by the JWST spectrographs enables, for the first time, detailed extragalactic studies of molecular vibrational bands. This opens an entirely new window for the study of the molecular interstellar medium in luminous infrared galaxies (LIRGs). We present a detailed analysis of rovibrational bands of gas-phase CO, H2O, C2H2, and HCN toward the heavily obscured eastern nucleus of the LIRG VV 114, as observed by NIRSpec and the medium resolution spectrograph on the Mid-InfraRed Instrument (MIRI MRS). Spectra extracted from apertures of 130 pc in radius show a clear dichotomy between the obscured active galactic nucleus (AGN) and two intense starburst regions. We detect the 2.3 μm CO bandheads, characteristic of cool stellar atmospheres, in the star-forming regions, but not toward the AGN. Surprisingly, at 4.7 μm, we find highly excited CO (T ex ≈ 700–800 K out to at least rotational level J = 27) toward the star-forming regions, but only cooler gas (T ex ≈ 200 K) toward the AGN. We conclude that only mid-infrared pumping through the rovibrational lines can account for the equilibrium conditions found for CO and H2O in the deeply embedded starbursts. Here, the CO bands probe regions with an intense local radiation field inside dusty young massive star clusters or near the most massive young stars. The lack of high-excitation molecular gas toward the AGN is attributed to geometric dilution of the intense radiation from the bright point source. An overview of the relevant excitation and radiative transfer physics is provided in an appendix.

Unlocking the Potential of Cu/Ti3C2Tx MXene Catalyst in Plasma Catalytic CO2 Hydrogenation

Plasma catalytic CO2 hydrogenation has emerged as a promising approach for converting CO2 into valuable chemicals such as CO, offering a potential solution to mitigate greenhouse gas emissions. In this study, we investigate the synergistic effect between plasma and a Cu/Ti3C2Tx MXene catalyst for CO2 hydrogenation via the reverse water gas shift (RWGS) reaction in a dielectric barrier discharge (DBD) reactor. Our findings reveal a significant enhancement in CO2 conversion (33.1%) and CO yield (31.9%) when using the Cu/Ti3C2Tx catalyst compared to plasma alone or with a Ti3C2Tx foam. Plasma treatment creates unsaturated Ti sites on the Ti3C2Tx surface, dramatically improving CO2 adsorption and activation, while Cu nanoparticles significantly enhances the activation and dissociation of H2 molecules on the catalyst surface. These surface adsorbed hydrogen species readily hydrogenate adsorbed CO2 molecules through the Langmuir-Hinshelwood mechanism. Furthermore, these surface hydrogen species can also participate in the conversion of gas-phase CO2 molecules through the Eley-Rideal pathway. This work sheds light on the synergistic plasma catalytic mechanism and provide insights for optimizing CO2 hydrogenation processes using MXene catalysts.

Solar Gas-Phase CO2 Hydrogenation by Multifunctional UiO-66 Photocatalysts.

Solar-assisted CO2 conversion into fuels and chemical products involves a range of technologies aimed at driving industrial decarbonization methods. In this work, we report on the development of a series of multifunctional metal-organic frameworks (MOFs) based on nitro- or amino-functionalized UiO-66(M) (M: Zr or Zr/Ti) supported RuOx NPs as photocatalysts, having different energy band level diagrams, for CO2 hydrogenation under simulated concentrated sunlight irradiation. RuOx(1 wt %; 2.2 ± 0.9 nm)@UiO-66(Zr/Ti)-NO2 was found to be a reusable photocatalyst, to be selective for CO2 methanation (5.03 mmol g-1 after 22 h;, apparent quantum yield at 350, 400, and 600 nm of 1.67, 0.25, and 0.01%, respectively), and to show about 3-6 times activity compared with previous investigations. The photocatalysts were characterized by advanced spectroscopic techniques like femto- and nanosecond transient absorption, spin electron resonance, and photoluminescence spectroscopies together with (photo)electrochemical measurements. The photocatalytic CO2 methanation mechanism was assessed by operando FTIR spectroscopy. The results indicate that the most active photocatalyst operates under a dual photochemical and photothermal mechanism. This investigation shows the potential of multifunctional MOFs as photocatalysts for solar-driven CO2 recycling.

G-C3N4 as ballistic electron transport “Tunnel” in CsPbBr3-based ternary photocatalyst for gas phase CO2 reduction

Perovskite CsPbBr3 quantum dot shows great potential in artificial photosynthesis, attributed to its outstanding optoelectronic properties. Nevertheless, its photocatalytic activity is hindered by insufficient catalytic active sites and severe charge recombination. In this work, a CsPbBr3@Ag-C3N4 ternary heterojunction photocatalyst is designed and synthesized for high-efficiency CO2 reduction. The CsPbBr3 quantum dots and Ag nanoparticles are chemically anchored on the surface of g-C3N4 sheets, forming an electron transfer tunnel from CsPbBr3 quantum dots to Ag nanoparticles via g-C3N4 sheets. The resulting CsPbBr3@Ag-C3N4 ternary photocatalyst, with spatial separation of photogenerated carriers, achieves a remarkable conversion rate of 19.49 μmol·g−1·h−1 with almost 100 % CO selectivity, a 3.13-fold enhancement in photocatalytic activity as compared to CsPbBr3 quantum dots. Density functional theory calculations reveal the rapid CO2 adsorption/activation and the decreased free energy (0.66 eV) of *COOH formation at the interface of Ag nanoparticles and g-C3N4 in contrast to the g-C3N4, leading to the excellent photocatalytic activity, while the thermodynamically favored CO desorption contributes to the high CO selectivity. This work presents an innovative strategy of constructing perovskite-based photocatalyst by modulating catalyst structure and offers profound insights for efficient CO2 conversion.

Molecular Mechanism for Converting Carbon Dioxide Surrounding Water Microdroplets Containing 1,2,3-Triazole to Formic Acid.

Spraying water microdroplets containing 1,2,3-triazole (Tz) has been found to effectively convert gas-phase carbon dioxide (CO2), but not predissolved CO2, into formic acid (FA). Herein, we elucidate the reaction mechanism at the molecular level through quantum chemistry calculations and ab initio molecular dynamics (AIMD) simulations. Computations suggest a multistep reaction mechanism that initiates from the adsorption of CO2 by Tz to form a CO2-Tz complex (named reactant complex (RC)). Then, the RC either is reduced by electrons that were generated at the air-liquid interface of the water microdroplet and then undergoes intramolecular proton transfer (PT) or switches the reduction and PT steps to form a [HCO2-(Tz-H)]- complex (named PC-). Subsequently, PC- undergoes reduction and the C-N bond dissociates to generate COOH- and [Tz-H]- (m/z = 69). COOH- easily converts to HCOOH and is captured at m/z = 45 in mass spectroscopy. Notably, the intramolecular PT step can be significantly lowered by the oriented electric field at the interface and a water-bridge mechanism. The mechanism is further confirmed by testing multiple azoles. The AIMD simulations reveal a novel proton transfer mechanism where water serves as a transporter and is shown to play an important role dynamically. Moreover, the transient •COOH captured by the experiment is proposed to be partly formed by the reaction with H•, pointing again to the importance of the air-water interface. This work provides valuable insight into the important mechanistic, kinetic, and dynamic features of converting gas-phase CO2 to valuable products by azoles or amines dissolved in water microdroplets.

Dehydration and reduction reactions favored under medium pressure and temperature assisted by photocatalysis

The impact of UV irradiation on the catalytic transformation of dihydroxyacetone molecule (DHA) has been investigated under inert atmosphere, medium pressure (5 Bars) and temperature (<=120°C) in presence of commercial anatase TiO2 samples (UV100 and A100), rutile TiO2 (R100) and mixture of anatase and rutile phase (P90). In absence of light, the main products formed are pyruvaldehyde and lactic acid whatever the temperature playing only a role on kinetic. Under UV irradiation, we highlighted their decomposition and the formation of new compounds, hydroxyacetone (HydA) in high concentration and acrylic acid (AcrAc) together with H2, CO2 and acetaldehyde in gas phase and new condensation products. The higher the number of photons emitted, the greater the HydA and AcrAc formation highlighting the importance of light and especially of the (e-, h+) pairs generated by photocatalysis. Actually, whereas the formation of HydA and AcrAc is similar in presence of all TiO2 samples containing anatase phase, these compounds are formed in low concentration in presence of TiO2 rutile. Mechanisms of the formation of hydA and AcrAc under photocatalysis assisted by pressure and temperature were discussed considering the formation of H+ and reducing agent made possible thanks to simultaneous oxidation reaction occurring via h+ and or OH°

CO Oxidation Promoted by NO Adsorption on RhMn2O3- Cluster Anions.

CO oxidation represents an important model reaction in the gas phase to provide a clear structure-reactivity relationship in related heterogeneous catalysis. Herein, in combination with mass spectrometry experiments and quantum-chemical calculations, we identified that the RhMn2O3- cluster cannot oxidize CO into gas-phase CO2 at room temperature, while the NO preadsorbed products RhMn2O3-[(NO)1,2] are highly reactive in CO oxidation. This discovery is helpful to get a fundamental understanding on the reaction behavior in real-world three-way catalytic conditions where different kinds of reactants coexist. Theoretical calculations were performed to rationalize the crucial roles of preadsorbed NO where the strongly attached NO on the Rh atom can greatly stabilize the products RhMn2O2-[(NO)1,2] during CO oxidation and at the same time works together with the Rh atom to store electrons that stay originally in the attached CO2- unit. The leading result is that the desorption of CO2, which is the rate-determining step of CO oxidation by RhMn2O3-, can be greatly facilitated on the reactions of RhMn2O3-[(NO)1,2] with CO.

Gas-phase CO2 electrolysis using carbon-derived bismuth nanospheres on porous nickel foam gas diffusion electrode

The successful electrochemical reduction of CO2 (eCO2R) into valuable fuels and chemicals relies on the development of low-cost, effective carbon-bonded metal catalysts. Carbon-bonded metal catalysts are crucial for efficient eCO2R due to their dual functionality—high electrical conductivity from carbon and catalytic activity from the metal. In this study, a facile hydrothermal method was used to synthesize carbon-derived bismuth oxide nanospheres (C-BiOx) on porous nickel foam (NF) electrodes as electrocatalysts for eCO2R. The eCO2R activity of this catalyst was evaluated in H-type cells and compared with commercially available Pd/C and Ag-nanoparticle catalysts. Our finding revealed that C-BiOx/NF exhibited a higher eCO2R activity (corresponding to the CO Faradaic efficiency (FE) of 16.2 % at −1 V vs. reversible hydrogen electrode (RHE) and HCOOH FE of 85.4 % at −0.7 V vs. RHE) than those of the Ag nanoparticle-based and Pd/C catalysts. Mechanistic insights from DFT-based studies further supported the enhanced catalytic activity of C-BiOx for HCOOH production over Ag catalysts. The fabricated catalyst was further utilized in a zero-gap CO2 electrolyzer for gas-phase CO2 reduction containing a self-supporting C-BiOx/NF gas diffusion layer (GDL). An anion exchange membrane-based CO2 electrolyzer demonstrated a higher FE for CO formation (47.1%) with an energy efficiency (EE) of 29.5% as compared to those of a polymer electrolyte membrane-based CO2 electrolyzer (FE: 25.2%, EE: 18.4%). Notably, the C-BiOx/NF catalyst exhibited remarkable stability (8 h) in the gas-phase GDL compared to that observed during the liquid-phase eCO2R. Our work provides new insights into utilizing improved catalyst designs in conjunction with flow cells for successful commercial implementation of this promising technology.