CO2 Valorization Research Articles

Zwitterionic bifunctional stable zinc complexes as single catalysts for the valorization of CO2 into cyclic carbonates

Bifunctional pyrrole containing nitrogen Schiff base zinc complexes were developed as single catalysts for the solvent free CO2 cycloaddition into epoxides. Four zwitterionic complexes (Zn-N-SB+/X−) were prepared by quaternarization of their neutral zinc precursor (Zn-N-SB) with different alkyl halides. The experimental compound characterization (NMR, IR, HRMS) was completed using the density functional theory (DFT) to obtain optimized structures. All the bifunctional zinc complexes efficiently promoted the solvent free cycloaddition of CO2 into styrene oxide, acting as both, Lewis acid and Lewis base catalyst, to form styrene cyclic carbonate in very good yields (up to 90 %) reaching TOF values up to 257 h−1. Best catalytic activity was noted for the iodine containing zwitterionic species (Zn-N-SB+/I−) that was used in very small loading (0.2 mol%) to enlarge the reaction scope to other epoxides in solvent free conditions, allowing high cyclic carbonate yields in the case of terminal epoxides. The comparison of the catalytic system formed by the neutral zinc complex (Zn-N-SB) combined to an iodine ammonium salt and its derived zwitterionic iodine containing complex (Zn-N-SB+/I−), showed that the bifunctional catalyst is more active. In order to get mechanistic insights, for both catalytic systems, the reaction order was calculated by VTNA (variable time normalization analysis) and the epoxide opening regioselectivity was determined using aniline as nucleophile.

Housing of electrosynthetic biofilms using a roll-up carbon veil electrode increases CO2 conversion and faradaic efficiency in microbial electrosynthesis cells

Electrode-driven microbial electron transfer enables the conversion of CO2 into multi-carbon compounds. The electrosynthetic biofilms grow slowly on the surface and are highly susceptible to operational influences, such as hydrodynamic shear stress. In this study, a cylindrical roll-up carbon felt electrode was developed as a novel strategy to protect biofilms from shear stress within the reactor. The fabricated electrode allowed hydrogen bubble formation inside the structure, which enabled microbes to uptake hydrogen and convert CO2 to multi-carbon organic compounds. The roll-up electrode exhibited faster start-up and biofilm formation than the conventional linear shape carbon felt. The acetate yield and cathodic faradaic efficiency increased by 80% and 34%, respectively, and the bioelectrochemical stability was improved significantly. The roll-up structure increased biofilm development per unit electrode surface by three to five-fold. The roll-up configuration improved biofilm formation on the electrode, which enhanced the performance of microbial electrosynthesis-based CO2 valorization.

Syngas production through combined steam-dry reforming of raw bio-oil over a NiAl2O4 spinel derived catalyst

The combined steam-dry reforming (CSDR) of raw bio-oil with NiAl2O4 spinel derived catalyst was studied to establish suitable conditions to combine the objectives of CO2 valorization and sustainable production of syngas with suitable H2/CO ratio for the synthesis of chemicals and fuels. The reactions were carried out in an equipment with two units, for controlled pyrolytic lignin deposition and reforming of the remaining oxygenates in an in-line fluidized bed reactor. The CSDR conditions were: 600–800 ºC; CO2/C molar ratio, 0–1.1; steam/carbon (S/C) molar ratio, 0.5–1.7; space time, 0.125 and 0.250 gcatalyst·h/goxygenates, and time on stream, 6 h. The CO2 conversion is positive in a wide range of operating conditions, and there is always a reduction of CO2 emissions compared to the SR process, even under conditions of CO2 formation. 800 ºC, CO2/C ratio of 1.1, S/C of 1.7 and space-time of 0.250 gcatalyst·h/goxygenates allow attaining near 80% oxygenate conversion, 7% CO2 conversion and 90% syngas yield with H2/CO ratio of 1.6. Lowering the S/C ratio to 0.5 noticeably increases the CO2 conversion (> 23%), but reduces the H2/CO ratio of the syngas produced (< 1). The amount, nature and location of coke were characterized with different techniques (XRD, TPO, N2 adsorption-desorption and SEM), being the amorphous coke derived from oxygenates cracking the main responsible of deactivation. Catalyst stability improves along with temperature and space time, slightly with the CO2/C ratio, but with low effect of S/C ratio.

Design of bifunctional 1D nanostructures for the catalytic conversion of carbon dioxide into cyclic carbonates

One dimensional silica-based nanotubes represent an innovative and promising morphology in the context of heterogeneous catalysis. Here these nanostructures were prepared for the first time as bifunctional materials, with hafnium or tin atoms inserted as single sites in the silica structure and imidazolium moieties anchored at the surface. The low dimensional solids thus present both acid sites owing to the presence of metal cations in tetrahedral coordination (co-catalyst) and nucleophilic species coming from the counterion of the imidazolium moieties (catalyst). The design of the catalysts consisted of two main steps. The Hf- or Sn-doped silica solids were initially prepared using a straightforward sol-gel method including a pH adjustment step allowing a quantitative insertion of the metal cations in the silica framework. These materials were post-functionalized with imidazolium moieties. The solids were extensively characterized thus confirming the presence of well-defined and open tubular structure, high specific surface area, successful insertion of Hf and Sn in the silica framework, and a correct functionalization with imidazolium salts. The different catalysts were tested in the valorization of CO2 with styrene oxide to give the corresponding cyclic carbonate. The bifunctional solids were stable and recyclable. The versatility of the best catalyst, represented by the Hf-based material, was confirmed using different epoxides. Finally, by tuning the reaction conditions or changing the imidazolium salt, a further boost of the catalytic performances was achieved.

Niedrige Temperatur Hydrierung von CO2 zu Methanol in Wasser auf ZnO‐geträgerten CuAu‐Nanolegierungen

AbstractDie Optimierung von Prozessen und Materialien für die Valorisierung von CO2 zu Wasserstoffträgern oder Plattformchemikalien ist ein wichtiger Schritt zur Eindämmung der globalen Erwärmung und zur nachhaltigen Verwendung von erneuerbaren Energien. Wir berichten hier über die Hydrierung von CO2 in Wasser an ZnO‐geträgerten CuAu‐Nanolegierungen, basierend auf ≤7 mol % Au. Die CuxAuy/ZnO‐Katalysatoren wurden mit Hilfe von 197Au‐Mössbauer, In situ‐Röntgenabsorption (Au LIII‐ und Cu K‐Kanten) und Umgebungsdruck‐Röntgenphotoelektronen (APXPS) spektroskopische Methoden zusammen mit Röntgenbeugung und hochauflösender Elektronenmikroskopie charakterisiert. Bei 200 °C stieg der CO2‐Umsatz bei einer Erhöhung der Cu93Au7‐Beladung von 1 auf 10 Gew.‐% signifikant um das 34‐fache (von 0.1 auf 3.4 %), wobei die Methanolselektivität bei 100 % blieb. Eine begrenzte CO‐Selektivität (4–6 %) wurde bei einer Temperaturerhöhung bis auf 240 °C beobachtet, die jedoch mit einem ≈3‐fachen Anstieg der CO2‐Umwandlung einherging. Auf der Grundlage von APXPS, während der CO2‐Hydrierung in einem H2O‐reichen Gemisch segregiert Cu bevorzugt an der Oberfläche in einem hauptsächlich metallischen Zustand, während leicht negative‐geladenes Au tiefer in den unterirdischen Bereich eintaucht. Diese Ergebnisse und detaillierte Strukturanalysen sind Gegenstand des vorliegenden Beitrags.

Low-Temperature Hydrogenation of CO2 to Methanol in Water on ZnO-Supported CuAu Nanoalloys.

Optimizing processes and materials for the valorization of CO2 to hydrogen carriers or platform chemicals is a key step for mitigating global warming and for the sustainable use of renewables. We report here on the hydrogenation of CO2 in water on ZnO-supported CuAu nanoalloys, based on ≤ 7 mol% Au. CuxAuy/ZnO catalysts were characterized using 197Au Mössbauer, in-situ X-ray absorption (Au LIII- and Cu K-edges), and ambient pressure X-ray photoelectron spectroscopy (APXP), together with X-ray diffraction and high-resolution electron microscopy. At 200 °C, the conversion of CO2 showed a significant increase by 34 times (from 0.1 to 3.4 %) upon increasing Cu93Au7 loading from 1 to 10 wt.%, while maintaining methanol selectivity at 100%. Limited CO selectivity (4-6%) was observed upon increasing temperature up to 240 °C but associated with a ~3-fold increase in CO2 conversion. Based on APXPS during CO2 hydrogenation in an H2O-rich mixture, Cu segregates preferentially to the surface in mainly metallic state, while slightly charged Au submerges deeper into the subsurface region. These results and detailed structural analyses are topics of present contribution.

Sustainability assessment of CO2 valorisation routes for Latvia: LCA, S-LCA and LCCA

To initiate and maintain the European Green Deal transformative policies, an evident-based multi-sectoral forecasting model needs to be timely and effectively deployed. The overall decarbonisation solutions proposed in this research can be defined as regional CO2 “value spots”– areas in regions where CO2 can be directly (CO2-based new products) or virtually (change in planning and implementation) utilised for the development of high-added value products, ensuring decarbonisation of rural areas, as well as promoting economic growth of the regions.Within the framework of this work, three scenarios for using carbon dioxide are analysed – its use in methanol production, cement production and open-air algae ponds. The analysis aims to assess the potential environmental impacts of CO2 utilisation and consider the impact on the environment, human health, labour rights, working conditions, social equity, and other social factors, as well as costs and economic sustainability.LCA provides a decision-making platform to understand the mid-term and long-term environmental effects of CO2 valorisation scenarios according to the ISO Standard 14044 standard requirements. Sensitivity analysis is performed to exclude high input data uncertainties (if any) and identify model behaviour factors. Effects of CO2 valorisation scenarios on social endpoints (well-being of stakeholders) are identified via S-LCA based on multi-regional input/output methods of qualitative and quantitative generic data. The S-LCA include health and safety, cultural heritage, and governance impact categories covering the interests of such stakeholder groups as workers, the local community, society, and consumers.Cost-effectiveness of CO2 valorisation scenarios is performed. Regional valorisation scenarios are assessed and benchmarked via regional development sustainability indicators. A comparative assessment of core indicators is performed.

Room temperature bio-engineered multifunctional carbonates for CO2 sequestration and valorization

This contribution reports, for the first time, on an entirely green bio-engineering approach for the biosynthesis of single phase crystalline 1-D nano-scaled calcite CaCO3. This was validated using H2O as the universal solvent and natural extract of Hyphaene thebaica fruit as an effective chelating agent. In this room temperature green process, CaCl2 and CO2 are used as the unique source of Ca and CO3 respectively in view of forming nano-scaled CaCO3 with a significant shape anisotropy and an elevated surface to volume ratio. In terms of novelty, and relatively to the reported scientific and patented literature in relation to the fabrication of CaCO3 by green nano-chemistry, the current cost effective room temperature green process can be singled out as per the following specificities: only water as universal solvent is used, No additional base or acid chemicals for pH control, No additional catalyst, No critical or supercritical CO2 usage conditions, Only natural extract of thebaica as a green effective chelating agent through its phytochemicals and proper enzematic compounds, room Temperature processing, atmospheric pressure processing, Nanoscaled size particles, and Nanoparticles with a significant shape anisotropy (1-D like nanoparticles). Beyond and in addition to the validation of the 1-D synthesis aspect, the bio-engineered CaCO3 exhibited a wide-ranging functionalities in terms of highly reflecting pigment, an effective nanofertilizer as well as a potential binder in cement industry.

Exothermic barrier-free carboxylation of alkali methylates. The highest-yield synthesis of dialkyl carbonates out of alcohols and carbon dioxide rationalized and reformulated through quantum-chemical simulations

While the Earth’s atmosphere represents an abundant source of CO2, its valorization by humanity remains at a nascent stage. Synthesizing added-value products out of CO2 and suitable co-reactants is an urgent and appealing chemical challenge to pursue in our busy times. Herein, we perform a rationalization, extension, and ultimate reformulation of the recently proposed highest-yield synthesis of dimethyl carbonate (DMC) and generally dialkyl carbonates out of alcohols and CO2 employing quantum-chemical reaction modeling. The carboxylation of pure methanol (CH3OH) by CO2 is thermochemically prohibited (+33 kJ/mol) and hindered by a heavy activation energy barrier (160 kJ/mol). The existing catalysts decrease the above barrier twice. The catalyzed carboxylation exhibits yields of 5–15 % of DMC depending on a specific catalyst, dehydration agents, and pressure elevation. In turn, the usage of alkali metal methylates – such as CH3OLi, CH3ONa, CH3OK, and CH3ORb – as reactants, instead of CH3OH, fully eliminates the activation barrier. Furthermore, alcoholates make carboxylation exothermic. We stepwise rationalize the origin of such a desirable behavior in terms of thermochemistry, molecular geometries, atomic nucleophilicities, potential energy landscapes, and computed vibrational spectra. All methylates perform decently and exhibit reasonable similarities as reactants. The most favorable reaction was recorded in the case of sodium alcoholate (according to Gibbs free energy) and lithium alcoholate (according to enthalpy). Since the carboxylation smoothly proceeds with the methylates, the synthesis can be carried out under normal conditions. This is contrary to the elevated temperatures and pressures, which have to be routinely supplied to implement the presently known catalytic schemes. Apart from an organic carbonate, the novel reactions produce LiI, NaI, KI, and RbI as major products. The consumed alkali metals need to be restored, for instance, by utilizing electrolysis, for their repetitive usages. The theoretical results are discussed tightly in the context of the recent experiments. The reactions can take place in liquid CH3OH. Exemplified computationally for the methyl radical, the invented scheme must generally work for larger hydrocarbon moieties. This report will interest synthetic chemists, whose work is devoted to the valorization of CO2.

Ni-Based SBA-15 Catalysts Modified with CeMnOx for CO2 Valorization via Dry Reforming of Methane: Effect of Composition on Modulating Activity and H2/CO Ratio.

Dry reforming of methane with ratio CH4/CO2 = 1 is studied using supported Ni catalysts on SBA-15 modified by CeMnOx mixed oxides with different Ce/Mn ratios (0.25, 1 and 9). The obtained samples are characterized by wide-angle XRD, SAXS, N2 sorption, TPR-H2, TEM, UV-vis and Raman spectroscopies. The SBA-15 modification with CeMnOx decreases the sizes of NiO nanoparticles and enhances the NiO-support interaction. When Ce/Mn = 9, the NiO forms small particles on the surface of large CeO2 particles and/or interacts with CeO2, forming mixed phases. The best catalytic performance (at 650 °C, CH4 and CO2 conversions are 51 and 69%, respectively) is achieved over the Ni/CeMnOx/SBA-15 (9:1) catalyst. The peculiar CeMnOx composition (Ce/Mn = 9) also improves the catalyst stability: In a 24 h stability test, the CH4 conversion decreases by 18 rel.% as compared to a 30 rel.% decrease for unmodified catalyst. The enhanced catalytic stability of Ni/CeMnOx/SBA-15 (9:1) is attributed to the high concentration of reactive peroxo (O-) and superoxo (O2-) species that significantly lower the amount of coke in comparison with Ni-SBA-15 unmodified catalyst (weight loss of 2.7% vs. 42.2%). Ni-SBA-15 modified with equimolar Ce/Mn ratio or Mn excess is less performing. Ni/CeMnOx/SBA-15 (1:4) with the highest content of manganese shows the minimum conversions of reagents in the entire temperature range (X(CO2) = 4-36%, X(CH4) = 8-58%). This finding is possibly attributed to the presence of manganese oxide, which decorates the Ni particles due to its redistribution at the preparation stage.

Metal-Oxide-Based Materials for the Sustainable and Tunable Electrochemical CO2 Conversion to Chemicals and Fuels at Industrial Scale

Anthropogenic activities have impacted the planet’s carbon cycle through the emissions of large amounts of greenhouse gases (GHGs), shifting the equilibrium of human history since the industrial revolution. CO2 is the key contributor to global climate change in the atmosphere. For this reason, the synthesis of high-added-value products CO2 conversion is a promising approach to mitigate climate change.1 Among the different alternatives, exploiting CO2 via electrochemical reduction under mild conditions (ambient pressure and temperature) represents an opportunity to support a low-carbon economy.2 The electrocatalytic (EC) CO2 reduction (CO2R) driven by renewable energy can be exploited for the future energy transition, for the carbon storage into valuable products like syngas (H2/CO mixtures), organic acids (formic acid) and chemicals/fuels (C1+ alcohols).3 A big challenge for the industrialisation of this technology is to find low-cost electrocatalysts, efficient reactors and process conditions. In the efforts to develop efficient, selective and stable materials, we have exploited the current knowledge of thermocatalytic CO2 hydrogenation to develop noble-metal-free CO2R electrocatalysts.4 For instance, Cu/Zn/Al synthesised catalyst producing methanol and CO from the CO2 thermocatalytic (TC) hydrogenation (at H2 pressure (P) of 30 bar and temperature (T) > 200 oC) promotes the formation of methanol (⁓32% of FE) during the EC CO2R in a gas-diffusion-electrode system; while operating in the liquid phase, the same catalyst produces syngas with a tunable composition (95% of FE at the most positive applied potential) and other liquid C2+ products (in both cases at ambient T, P).4 On the other hand, Cu/ZnO electrocatalyst also has been tested at industrially relevant current densities in liquid phase configuration.5 We demonstrated through ex-situ characterisations that the presence of ZnO nanoparticles in the mixed Cu/ZnO catalyst plays an important role in forming and stabilising mixed oxidation states of copper and Cu1+/Cu0 interfaces in the electrocatalyst (in bulk and surface). These interfaces seem to promote CO dimerisation to ethanol. Indeed, ethanol was produced with the Cu/ZnO catalyst, reaching ethanol productivity of about 5.3 mmol∙gcat -1∙h-1 in a liquid-phase configuration at ambient conditions. A Cu/ZnO electrocatalyst also has been tested in a catholyte-free configuration with an increased selectivity to ethylene, reaching approximately 70% of FE, demonstrating that the reaction pathways for EC CO2R are largely determined by transport limitations rather than only by the intrinsic properties of the electrocatalysts. Our results open a promising path for the prospective implementation of metal-oxide nanostructures for CO2 conversion to the chemicals and fuels of the future. Acknowledgements This work has received financial support by the EU H2020 Project SunCOChem (grant agreement: 862192). References Guzmán, H., Russo, N. & Hernández, S. CO2 valorisation towards alcohols by Cu-based electrocatalysts: challenges and perspectives. Green Chem. 23, 1896–1920 (2021).Romero Cuellar, N. S., Wiesner-Fleischer, K., Fleischer, M., Rucki, A. & Hinrichsen, O. Advantages of CO over CO2 as reactant for electrochemical reduction to ethylene, ethanol and n-propanol on gas diffusion electrodes at high current densities. Electrochim. Acta 307, 164–175 (2019).Guzmán, H., Farkhondehfal, M. A., Rodulfo Tolod, K., Russo, N. & Hernández, S. Photo/electrocatalytic hydrogen exploitation for CO2 reduction toward solar fuels production. in Solar Hydrogen Production Processes, Systems and Technologies 560 (Elsevier Inc., 2019). doi:10.1016/C2017-0-02289-9.Guzmán, H. et al. How to make sustainable CO2 conversion to Methanol: Thermocatalytic versus electrocatalytic technology. Chem. Eng. J. 417, 127973 (2021).Guzmán, H. et al. CO2 Conversion to Alcohols over Cu/ZnO Catalysts: Prospective Synergies between Electrocatalytic and Thermocatalytic Routes. ACS Appl. Mater. Interfaces 14, 517−530 (2022).

Incorporating Catalytic Units into Nanomaterials: Rational Design of Multipurpose Catalysts for CO2 Valorization.

ConspectusCO2 conversion to valuable chemicals is effective at reducing CO2 emissions. We previously proposed valorization strategies and developed efficient catalysts to address thermodynamic stability and kinetic inertness issues related to CO2 conversion. Earlier, we developed molecular capture reagents and catalysts to integrate CO2 capture and conversion, i.e., in situ transformation. Based on the mechanistic understanding of CO2 capture, activation, and transformation at a molecular level, we set out to develop heterogeneous catalysts by incorporating catalytic units into nanomaterials via the immobilization of active molecular catalysts onto nanomaterials and designing nanomaterials with intrinsic catalytic sites.In thermocatalytic CO2 conversion, carbonaceous and metal-organic framework (MOF)-based catalysts were developed for nonreductive and reductive CO2 conversion. Novel Cu- and Zn-based MOFs and carbon-supported Cu catalysts were prepared and successfully applied to the cycloaddition, carboxylation, and carboxylative cyclization reactions with CO2, generating cyclic carbonates, carboxyl acids, and oxazolidinones as respective target products. Reductive conversion of CO2, especially reductive functionalization with CO2, is a promising transformation strategy to produce valuable chemicals, alleviating chemical production that relies on petrochemistry. We explored the hierarchical reductive functionalization of CO2 using organocatalysts and proposed strategies to regulate the CO2 reduction level, triggering heterogeneous catalyst investigation. Introducing multiple active sites into nanomaterials opens possibilities to develop novel CO2 transformation strategies. CO2 capture and in situ conversion were realized with an N-doped carbon-supported Zn complex and MOF materials as CO2 adsorbents and catalysts. These nanomaterial-based catalysts feature high stability and excellent efficiency and act as shape-selective catalysts in some cases due to their unique pore structure.Nanomaterial-based catalysts are also appealing candidates for photocatalytic CO2 reduction (PCO2RR) and electrocatalytic CO2 reduction (ECO2RR), so we developed a series of hybrid photo-/electrocatalysts by incorporating active metal complexes into different matrixes such as porous organic polymers (POPs), metal-organic layers (MOLs), micelles, and conducting polymers. By introducing Re-bipyridine and Fe-porphyrin complexes into POPs and regulating the structure of the polymer chain, catalyst stability and efficiency increased in PCO2RR. PCO2RR in aqueous solution was realized by designing the Re-bipyridine-containing amphiphilic polymer to form micelles in aqueous solution and act as nanoreactors. We prepared MOLs with two different metallic centers, i.e., the Ni-bipyridine site and Ni-O node, to improve the efficiency for PCO2RR due to the synergistic effect of these metal centers. Sulfylphenoxy-decorated cobalt phthalocyanine (CoPc) cross-linked polypyrrole was prepared and used as a cathode, achieving the electrocatalytic transformation of diluted CO2 benefiting from the CO2 adsorption capability of polypyrrole. We fabricated immobilized 4-(t-butyl)-phenoxy cobalt phthalocyanine and Bi-MOF as cathodes to promote the paired electrolysis of CO2 and 5-hydroxymethylfurfural (HMF) and obtained CO2 reductive products and 2,5-furandicarboxylic acid (FDCA) efficiently.

Process design and utilisation strategy for CO2 capture in flue gases. Technical assessment and preliminary economic approach for steel mills

The steel industry is the most relevant sector in emerging economies due to its application in numerous fields. However, steel manufacturing involves large energy investment and produces significant greenhouse gas emissions. The current world economic and environmental scenario therefore necessitates that improvements in the footprint of the steel industry be made without affecting its viability. Considering the present challenge, we report two possible processes for Carbon Capture and Utilization (CCU). The first process is the competitive capture of CO2–SO2, followed by CO2 valorisation to methane. However, the CO2 capture capacity and lifetime for the adsorbent after multiple cycles could be improved through preliminary desulphurization of the gas current. The improved system demonstrates net profitability in a typical stainless steel plant. Therefore, it can be implemented in an industrial setting without profitability loss to steelmaking operations, fulfilling bot the goal of reducing CO2 emissions while protecting the mainstay of the plant.

Perovskite-Derived Bismuth with I- and Cs+ Dual Modification for High-Efficiency CO2 -to-Formate Electrosynthesis and Al-CO2 Batteries.

Bi-based materials are one of the most promising candidates for electrochemical CO2 reduction reaction (CO2 RR) to formate; however, the majority of them still suffer from low current density and stability that essentially constrain their potential applications at the industrial scale. Surface modification represents an effective approach to modulate the electrode microenvironment and the relative binding strength of key intermediates. Herein, it isdemonstrated that the surface comodification with halides and alkali metal ions from the conversion of Bi-based halide perovskite nanocrystals is a viable strategy to boost the CO2 RR performance of Bi for formate electrosynthesis. Cs3 Bi2 I9 nanocrystals are prepared by a hot-injection method. The as-prepared products feature well-defined hexagonal shape and uniform size distribution. When used as the precatalyst, Cs3 Bi2 I9 nanocrystals are converted to Cs+ and I- comodified Bi. The resultant catalyst exhibits high formate Faradaic efficiency close to 100%, and remarkable partial current density up to 44mA cm-2 in an H-cell and up to 276 mA cm-2 in a flow cell. Moreover, Cs3 Bi2 I9 is used as the cathode catalyst and paired with an Al anode in an Al-CO2 battery for simultaneous CO2 valorization and power generation.

The d band center dependent catalytic activity of n-doped carbon nanospheres with wrinkled cages supported PdPt alloy catalysts in transfer hydrogenation of bicarbonate with glycerol

Catalytic transfer hydrogenation of bicarbonate, a typical product of CO2 captured in an alkaline solution, with glycerol (GLY) as a hydrogen donor to formate (FA) and lactate (LA) is a sustainable and green approach for simultaneous valorization of CO2 and the major byproduct from biodiesel production. Conventional monometallic noble metal catalysts can catalyze this transfer hydrogenation reaction, but generally required a high reaction temperature, leading to a low yield of FA. In this work, N-doped carbon spheres with wrinkled cages (NCSWCs) supported PdPt alloy catalysts were prepared and their electronic structures were determined by Valence Band Spectra (VBS) and Density Functional Theory (DFT). It was found that the relationship between the d band center and catalytic activity exhibits volcano-shaped behaviors, where Pd2Pt1/NCSWCs is on the top of the curve, 85.4% of GLY conversion with 67.3% yield of LA and 56.5% yield of FA can be achieved at 200 °C. DFT calculations also revealed that Pd2Pt1/NCSWCs possessed an intermediate d band center, which tunes the adsorption and dissociation energy of H species on its surface, allowing maximum H transfer during the transfer hydrogenation of bicarbonate, leading to high catalytic activity. Such a d band center catalyst tuning could be efficient way to design new catalysts.

Efforts toward Synthetic Photosynthesis: Visible Light-Driven CO2 Valorization.

Current methods of urethane preparation from amines invariably involve high-energy and often toxic or cumbersome molecules to make the process exergonic. CO2 aminoalkylation using olefins and amines represents an attractive albeit endergonic alternative. We report a moisture-tolerant method that uses visible light energy to drive this endergonic process (+25 kcal/mol at STP) using sensitized arylcyclohexenes. They convert much of the photon's energy to strain upon olefin isomerization. This strain energy greatly enhances alkene basicity, allowing for sequential protonation by and interception of ammonium carbamates. Following optimization steps and amine scope evaluation, an example product arylcyclohexyl urethane underwent transcarbamoylation with some demonstrative alcohols to form more general urethanes with concomitant regeneration of the arylcyclohexene. This represents a closure of the energetic cycle, producing H2O as the stoichiometric byproduct.

Metal-Supported TiO2/SiO2 Core-Shell Nanosphere Photocatalyst for Efficient Sunlight-Driven Methanol Degradation

The development of novel and active photocatalysts to industrialize photocatalysis technology is still a challenging task. In this work, a novel method is presented to prepare TiO2/SiO2 NSs by covering SiO2 nanospheres (NSs) with titanate-nanodiscs (TNDs) followed by calcination. In this regard, SiO2 NSs are first synthesized and then TNDs are deposited on the SiO2 NSs using a layer-by-layer deposition technique. The morphology of the prepared samples is analyzed via SEM and TEM analyses before and after the deposition. The analysis of metal (Cu, Pt, and Ni) loading on calcined TNDs/SiO2 NSs reveals the highest specific surface area (109 m2/g), absorption wavelength extension (up to 420 nm), and photocatalytic activity for the Cu-loaded sample. In addition, studying the effect of metal content shows that loading 3% Cu leads to the highest photocatalytic activity. Finally, it is demonstrated that H2S treatment can improve the photocatalytic activity by around 15%. These findings suggest the calcined TNDs/SiO2 NSs are a versatile photocatalyst with potential applications in other processes such as hydrogen production and CO2 valorization.

Isolated Single-Atom Cobalt in the ZnIn2S4 Monolayer with Exposed Zn Sites for CO2 Photofixation

Constructing highly active photocatalysts with rich reactive sites for photofixation of CO2 with organic compounds implements an environmentally friendly route for CO2 valorization and carbon neutralization. Herein, we report the isolated cobalt (Co) single-atom (SA)-decorated two-dimensional (2D) single-layer ZnIn2S4 (ZIS) nanosheet composites (Co-sZIS) with dual active centers of Co and Zn for CO2 fixation with epoxides under visible light. The unique ensemble of Co-sZIS optimizes light harvesting, promotes charge carrier separation, and enriches the bifunctional active sites for the efficient adsorption and activation of the reactants of epoxides and CO2. Consequently, the Co-sZIS exhibits significantly improved CO2-epoxide cycloaddition performance compared to bulk ZIS. In addition, the synergetic photoredox manner of simultaneously exploiting photogenerated electrons and holes efficiently facilitates the activation of CO2 and epoxides, thereby further reducing the energy barrier of CO2 fixation. This work not only provides a paradigm of rationally interfacial engineered SA-onto-2D semiconductors for CO2 valorization but also highlights the structure–activity relationship by the well-defined active sites in this SA-based hybrid platform.

CO2 electroreduction to multicarbon products from carbonate capture liquid

CO2 electroreduction to multicarbon products from carbonate capture liquid

Enhanced process control of trickle-bed reactors for biomethanation by vertical profiling directed by hydrogen microsensor monitoring

Biomethanation is an emerging Power-to-X technology enabling CO2 valorisation to produce biomethane using renewable H2. A promising reactor for facilitating biomethanation is the trickle bed reactor (TBR), however, these bioreactors are conventionally operated with a black-box approach, where the system is solely described by the input and output characteristics. This study employed a novel approach for process surveillance of internal dynamics in TBRs by installing multiple H2 microsensors along its vertical axis. The H2 microsensor monitoring was demonstrated for 135 days in a TBR integrated into a full-scale biogas plant. Despite achieving an overall CH4 productivity of 12.6 L L-1 d-1, the vertical positioning of microsensors revealed a clear zonation with CH4 productivity zones reaching 54.8 L L-1 d-1 and enabled early warning detection of deteriorating process performance days before detecting it in the product gas. Thus, vertically positioned microsensors present a promising solution for securing process stability.