Μmol Gcat Research Articles

Enhanced photocatalytic hydrogen production via water splitting using cobalt-based organic nanofibers under visible light irradiation.

This study focuses on the development of cobalt-based organic nanofibers as efficient photocatalysts for hydrogen production via water splitting under visible light irradiation. The depletion of fossil fuels necessitates the exploration of alternative energy sources, with hydrogen emerging as a promising candidate due to its clean and renewable nature. While conventional photocatalysts have shown potential, their limited activity under visible light and fast electron-hole recombination hinder their efficiency. In this work, cobalt acetate/poly(vinyl alcohol) (CoAc/PVA) nanofibers were electrospun and treated in a novel reactor design under water gas atmosphere at 160 °C to produce continuous, smooth, and stable nanobelts. The nanofibers displayed a band gap energy of 2.29 eV, indicating strong absorption in the visible light range. Detailed characterization using FTIR, XPS, SEM, and TGA confirmed the formation of organic-inorganic hybrid nanofibers with uniform cobalt distribution. Hydrogen production experiments showed that the proposed nanofibers significantly outperformed Co3O4 nanofibers, with an optimal hydrogen generation rate of 3.266 mmol gcat -1 s-1 at 70 vol% methanol. Furthermore, the treated nanofibers demonstrated good stability over multiple cycles, maintaining a constant hydrogen production rate after the third run. The study highlights the advantages of cobalt-based organic nanofibers in overcoming the limitations of traditional photocatalysts, providing a novel route for sustainable hydrogen production.

Selective and durable H2O2 electrosynthesis catalyst in acid by selenization induced straining and phasing

Developing efficient electrocatalysts for acidic electrosynthesis of hydrogen peroxide (H2O2) holds considerable significance, while the selectivity and stability of most materials are compromised under acidic conditions. Herein, we demonstrate that constructing amorphous platinum–selenium (Pt–Se) shells on crystalline Pt cores can manipulate the oxygen reduction reaction (ORR) pathway to efficiently catalyze the electrosynthesis of H2O2 in acids. The Se2‒Pt nanoparticles, with optimized shell thickness, exhibit over 95% selectivity for H2O2 production, while suppressing its decomposition. In flow cell reactor, Se2‒Pt nanoparticles maintain current density of 250 mA cm−2 for 400 h, yielding a H2O2 concentration of 113.2 g L−1 with productivity of 4160.3 mmol gcat−1 h−1 for effective organic dye degradation. The constructed amorphous Pt–Se shell leads to desirable O2 adsorption mode for increased selectivity and induces strain for optimized OOH* binding, accelerating the reaction kinetics. This selenization approach is generalizable to other noble metals for tuning 2e‒ ORR pathway.

Photocatalytic Synthesis of Glycine from Methanol and Nitrate

AbstractPhotocatalytic utilization of methanol and nitrate as carbon and nitrogen sources for the direct synthesis of amino acids could provide a sustainable way for the valorization of green “liquid sunlight” and nitrate waste. In this study, we develop an efficient photochemical method to synthesize glycine directly from methanol and nitrate, which cascades the C−C coupling to form glycol, nitrate reduction to NH3, and finally C−N coupling to generate glycine. Interestingly, the involved photocatalytic tandem reactions show a synergistic effect, in which the presence of nitrate is the dominant factor to enable the overall reaction and reach high synthetic efficiency. Ba2+−TiO2 nanoparticles are confirmed as a feasible and efficient catalyst system for the photosynthesis of glycine with a remarkable glycine photosynthesis rate of 870 μmol gcat−1 h−1 under optimal conditions. This work establishes a novel catalytic system for amino acid synthesis from methanol and nitrate under mild conditions. These results also allow us to further suppose the formation pathways of amino acids on the primitive earth, as an extension to proposals based on the Miller‐Urey experiments.

A Strongly Coupled Metal/Hydroxide Heterostructure Cascades Carbon Dioxide and Nitrate Reduction Reactions toward Efficient Urea Electrosynthesis.

The direct coupling of nitrate ions and carbon dioxide for urea synthesis presents an appealing alternative to the Bosch-Meiser process in industry. The simultaneous activation of carbon dioxide and nitrate, however, as well as efficient C-N coupling on single active site, poses significant challenges. Here, we propose a novel metal/hydroxide heterostructure strategy based on synthesizing an Ag-CuNi(OH)2 composite to cascade carbon dioxide and nitrate reduction reactions for urea electrosynthesis. The strongly coupled metal/hydroxide heterostructure interface integrates two distinct sites for carbon dioxide and nitrate activation, and facilitates the coupling of *CO (on silver, where * denotes an active site) and *NH2 (on hydroxide) for urea formation. Moreover, the strongly coupled interface optimizes the water splitting process and facilitates the supply of active hydrogen atoms, thereby expediting the deoxyreduction processes essential for urea formation. Consequently, our Ag-CuNi(OH)2 composite delivers a high urea yield rate of 25.6 mmol gcat. -1 h-1 and high urea Faradaic efficiency of 46.1 %, as well as excellent cycling stability. This work provides new insights into the design of dual-site catalysts for C-N coupling, considering their role on the interface.

Reversible Hydrogen Acceptor–Donor Enables Relay Mechanism for Nitrate‐to‐Ammonia Electrocatalysis

Electrocatalytic nitrate reduction is a crucial process for sustainable ammonia production. However, to maximize ammonia yield efficiency, this technology inevitably operates at the potentials more negative than 0 V vs. RHE, leading to high energy consumption and competitive hydrogen evolution. To eradicate this issue, hydrogen tungsten bronze (HxWO3) as reversible hydrogen donor‐acceptor is partnered with copper (Cu) to enable a relay mechanism at potentials positive than 0 V vs. RHE, which involves rapid intercalation of H into HxWO3 lattice, prompt de‐intercalation of the lattice H and transfer onto Cu, and spontaneous H‐mediated nitrate‐to‐ammonia conversion on Cu. The resulting catalysts demonstrated a high ammonia yield rate of 3332.9±34.1 mmol gcat−1 h−1 and a Faraday efficiency of ~100 % at 0.10 V vs. RHE, displaying a record‐low estimated energy consumption of 17.6 kWh kgammonia−1. Using these catalysts, we achieve continuous ammonia production in an enlarged flow cell at a real energy consumption of 17.0 kWh kgammonia−1.

Heterointerface of Monodispersed Ultrathin-MnO2@Amorphous Carbon to Attain Durable Lattice Oxygen Redox Chemistry through Creation of Dual Lattice Oxygens.

Lattice oxygen (OL) redox chemistry is a key to alleviating the energy and environmental crisis, but it faces challenges in activating the OL while ensuring structural stability. We disclosed herein that engineering a heterogeneous interface between ultrathin oxide and amorphous carbon can attain the durable OL redox chemistry without introducing catalytically impure sites. To this end, we proposed a green strategy to grow ∼3.9 nm-thickness wrinkled δ-MnO2 nanosheets that are rich in defects and are vertically aligned on amorphous carbon spheres. Experiments and calculations reveal that the electrons can easily migrate from the amorphous carbon to MnO2 at the δ-MnO2@C heterointerface. The heterogeneous interfaces can not only regulate the Mn-O bond and create oxygen defects in δ-MnO2 but also introduce lattice oxygen with varying reactivities. Specifically, the δ-MnO2@C structure carries more activated lattice oxygen that contributes to the enhanced activity on catalytic oxidation of bioderived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), with a high FDCA formation rate of 1759 μmol gcat-1 h-1 and a high selectivity of 95%. The heterogeneous interface of MnO2@C also brings inert lattice oxygen, so that it manifests high structural stability during the oxidation reactions. This work deepens the fundamental understandings in the engineering of lattice oxygen for durable lattice oxygen redox chemistry and showcases an effective interface technique in creating advanced catalysts for clean sustainable energy.

Active Learning Guided Discovery of High Entropy Oxides Featuring High H2-production.

High entropy oxides (HEOs) represent a class of solid solutions comprising multiple elements, offering significant scientific potential. Due to the enormous combination types of elements, the design of HEOs with desirable properties within high-dimensional composition spaces has traditionally relied heavily on knowledge and intuition. In this study, we present an active learning (AL) strategy tailored to efficiently explore the vast compositional space of HEOs. Our approach operates as a closed-loop system, iteratively cycling through "Training, Prediction, and Experiment" stages. Across multiple AL iterations, we have successfully identified four novel HEOs from a vast array of potential compositions. These newly discovered materials exhibit exceptional stability and demonstrate outstanding performance in H2 evolution rate (251 μmol gcat-1 min-1) during the water-gas shift reaction, surpassing benchmarks set by established catalysts such as Pt/γ-Al2O3 (135 μmol gcat-1 min-1) and Cu/ZnO/Al2O3 (81 μmol gcat-1 min-1). X-ray photoelectron spectroscopy and density functional theory calculations revealed a loss of elemental identity in the selected HEOs. This catalyst discovery process underscores the efficacy of Machine Learning in accelerating the identification of HEOs with unique characteristics by effectively leveraging insights from limited experimental data.

Direct Oxidation of Methane to C1 Oxygenates on Cu/ZSM‐5: Reaction Property and Configuration of Cu Species

AbstractDirect oxidation of methane (DOM) under mild conditions is arguably one of the holy grails in chemistry. Cu‐based zeolite catalysts have attracted much attention for their high yield and selectivity of C1 oxygenates. However, the structure‐activity relationships of DOM remain controversial due to the complex configurations of Cu on zeolites. Herein, we prepared Cu/ZSM‐5 catalysts with various Cu loading and investigated the effects of Cu configurations on the DOM reaction. By combining the characterization techniques and evaluating the catalytic performance, we found that the configurations of Cu species could significantly affect the yield and distribution of C1 oxygenates, which was strongly dependent on Cu loading. The highly dispersed mononuclear CuII in the channels of ZSM‐5 is proved to be highly active. While the multinuclear Cu species inhibit the formation of HCOOH, simultaneously suppressing the overall reaction yield. The agglomerated CuO species on the surface of ZSM‐5 show a relatively low correlation with DOM reaction. Thus, the relationship between the yield of C1 oxygenates and Cu loading exhibits a typical volcanic curve and 2.2 wt.% Cu/ZSM‐5 possess the best performance using H2O2 as oxidant (productivity of 17,000 μmol gcat−1 h−1 with 98.6 % selectivity at 50 °C).

Sulfur-doped Bi2O2CO3 nanosheet for enhanced visible-light-driven photocatalytic CO2 reduction to CO with ultra-high selectivity.

The photocatalytic reduction of carbon dioxide (CO2) has emerged as a compelling strategy for the conversion of renewable energy. However, the expeditious recombination of photogenerated charge carriers and the inadequate light absorption capabilities are currently predominant challenges. Herein, we developed a facile hydrothermal approach to synthesize a sulfur doped Bi2O2CO3 nanosheet with a tunable energy band structure designed to enhance visible light absorption. Our findings indicate that the incorporation of sulfur into the catalytic sites induces an electron sink effect, significantly improving the separation efficiency of photogenerated charge carriers. Consequently, this sulfur-doped Bi2O2CO3 catalyst exhibits a remarkable carbon monoxide (CO) yield of 16.64 μmol gcat-1 h-1 with nearly 100 % selectivity under illumination ranging from 420 to 780 nm. Through in-situ characterization techniques and theoretical calculations, it was revealed that sulfur-coordinated bismuth sites greatly enhance CO2 adsorption and decrease the energy barrier for critical intermediates formation (*COOH), thus selectively driving the reaction towards CO production. This work not only advances our understanding of mechanisms underlying photocatalytic reduction of CO2 on sulfur-doped bismuth-based catalysts but also sets a precedent for developing sophisticated photocatalytic systems for enhanced photoreduction reactions.

Ultrathin Porous Carbon Nitride Anchored with Pt Nanoclusters for Synergistic Enhancement of Hydrogen Production in Alkaline Photocatalytic Polyester Reforming.

Photocatalytic reforming (PR) of polyester waste, fueled by renewable sources like solar energy, offers a sustainable method for producing clean H2 and valuable by-products under mild conditions. The design of high-performance photocatalyst plays a pivotal role in determining the efficacy of an alkaline polyester PR system, influencing H2 generation activity and selectivity. Here, ultrathin porous carbon nitride nanosheets (UP-CN) loaded with Pt nanoclusters (Pt NCs, average diameter of 1.7nm) with uniform Pt NCs distribution are introduced. The resulting Pt NCs/UP-CN catalyst can accelerate charge and mass transfer while providing additional active sites, achieving superior H2 generation rates of 11.69mmol gcat -1 h-1 and 2923mmol gPt -1 h-1 under AM 1.5 light, which nine times higher than that of Pt nanoparticles-bulk graphitic carbon nitride composite (1.29mmol gcat -1 h-1 and 258mmol gPt -1 h-1) as counterpart. This performance also surpasses that of previously reported carbon nitride-based and TiO2-based photocatalysts. Moreover, the density functional theory calculations reveal a significant reduction in the energy barrier for the water dissociation step (H2O + * → *H + OH) at the interface between UP-CN and anchored Pt NCs, showcasing the synergistic effect between Pt NCs and UP-CN. This catalytic system also exhibits universality across various polyester plastics.

A C-modified engineering strategy of porous In2O3 catalysts for point-concentrated solar-driven photothermal CO2 hydrogenation

The solar-driven photothermal CO2 conversion serves as an effective approach for addressing the substantial challenges of energy crises and global environmental issues. In this work, various forms of In2O3 catalysts, including In2O3-c, In2O3-r, In2O3-s, and porous spherical In2O3, along with a C-modified porous spherical In2O3 catalyst (C-In2O3), were successfully synthesized through a hydrothermal method. An in-depth analysis was conducted to evaluate the performance of these catalysts in the point-concentrated solar-driven photothermal CO2 hydrogenation. As a result, the porous C-In2O3 catalyst exhibited a superior CO2 conversion rate of approximately 13.2 % under simulated sunlight irradiation, with a light intensity of 44.6 mW/cm2. Notably, all catalysts demonstrated nearly 100 % selectivity towards CO (CO production rate of around 8.51 mmol gcat−1h−1) during the photothermal catalytic reaction, without any formation of CH4. The outstanding performance of the C-In2O3 catalyst was attributed to the modification of In2O3 band structure by the incorporation of C, which significantly enhanced the intensive solar light absorption of the catalyst. Furthermore, incorporating C into In2O3 substantially augments its basic strength and significantly elevates the quantity of basic sites, thereby endowing it with outstanding CO2 adsorption and conversion capabilities. This work provides a C-modified engineering strategy to design efficient photothermal catalysts for boosting point-concentrated photothermal CO2 hydrogenation.

Regulating N-Cu/MoxC interfacial effect coupling β-Mo2C/γ-MoC phase engineering to achieve efficient hydrolysis dissociation and methanol dehydrogenation for hydrogen production

Methanol steam reforming (MSR) is a promising solution for achieving the integration of hydrogen storage, transportation, and in-situ supply. However, it is limited by the slow rate of hydrogen generation and low selectivity. This study constructed a highly active N-Cu/MoxC catalyst with strong interaction between Cu and MoxC, effectively enhancing methanol activation, hydrolysis, and hydrogen production efficiency. Under optimized condition, the 2.8 N-Cu/MoxC catalyst achieved a remarkable H2 productivity of 147.9 mmol gcat−1 h−1 and H2 selectivity of 65.7 %. N induced a partial transition from β-Mo2C phase to γ-MoC phase, resulting in a doubling of H2 production rate. The interfacial N-Cu-MoxC sites facilitated highly reactive efficient CH bond dissociation to convert CO+4H and OH activation, as well as the highly efficient CO reforming. Additionally, temperature programmed surface reaction and isotope testing futher coroborated its superiority in methanol dehydrogenation and hydrolysis dissociation. These discoveries can provide guidance for the design of advanced MSR catalysts.

Nanoarchitectonics of MIL-101(Fe)/g-C3N4 S-Scheme heterojunction for photocatalytic nitrogen fixation: Mechanisms and performance

Recently, there has been a growing interest in the fundamental understanding of the mechanism of how MIL-101(Fe)/g-C3N4 heterojunctions facilitate the occurrence of photocatalytic nitrogen fixation reactions, especially the electron transfer mechanism has attained increasing attention in photocatalysis. Herein, we implemented a "triple win scenario" strategy to fabricate the S-scheme MIL-101(Fe)/g-C3N4 heterojunction through a straightforward solvothermal process. The MC-6 heterojunction minimizes the recombination of photogenerated carriers, enhances light utilization efficiency, and activates the N≡N bond, thus boosting photocatalytic nitrogen fixation efficiency. The transition metal iron activates the N≡N bond, while S-scheme heterojunctions reduce the photogenerated carrier recombination. In addition, the decrease in band gap (Eg) leads to an increase in visible light utilization efficiency. ISIXPS proved the mechanism of interelectron transfer of MIL-101(Fe)/g-C3N4 heterojunction under illumination. Upon the creation of the heterojunction, electrons migrate from g-C3N4 to MIL-101(Fe), establishing an inherent electric field due to the disparate Fermi levels between the two materials. The electrons (e-) on the g-C3N4 CB with a more negative reduction potential and the holes (h+) on the MIL-101(Fe) VB are retained, which increased the redox capacity to a great extent required for the reduction of N2 to NH3. The ammonia production efficiency of MC-6 photocatalyst was 160 µmol gcat-1 h-1, representing an 8-fold and 2.8-fold improvement over pristine g-C3N4 (20 µmol gcat-1 h-1) and MIL-101(Fe) (57 µmol gcat-1 h-1), respectively.

A Strongly Coupled Metal/Hydroxide Heterostructure Cascades Carbon Dioxide and Nitrate Reduction Reactions toward Efficient Urea Electrosynthesis

The direct coupling of nitrate ions and carbon dioxide for urea synthesis presents an appealing alternative to the Bosch–Meiser process in industry. The simultaneous activation of carbon dioxide and nitrate, however, as well as efficient C–N coupling on single active site, poses significant challenges. Here, we propose a novel metal/hydroxide heterostructure strategy based on synthesizing an Ag‐CuNi(OH)2 composite to cascade carbon dioxide and nitrate reduction reactions for urea electrosynthesis. The strongly coupled metal/hydroxide heterostructure interface integrates two distinct sites for carbon dioxide and nitrate activation, and facilitates the coupling of *CO (on silver, where * denotes an active site) and *NH2 (on hydroxide) for urea formation. Moreover, the strongly coupled interface optimizes the water splitting process and facilitates the supply of active hydrogen atoms, thereby expediting the deoxyreduction processes essential for urea formation. Consequently, our Ag‐CuNi(OH)2 composite delivers a high urea yield rate of 25.6 mmol gcat.–1 h–1 and high urea Faradaic efficiency of 46.1%, as well as excellent cycling stability. This work provides new insights into the design of dual‐site catalysts for C–N coupling, considering their role on the interface.

Ethanol synthesis via catalytic CO2 hydrogenation over multi-elemental KFeCuZn/ZrO2 catalyst.

Technological enablers that use CO2 as a feedstock to create value-added chemicals, including ethanol, have gained widespread appeal. They offer a potential solution to climate change and promote the development of a circular economy. However, the conversion of CO2 to ethanol poses significant challenges, not only because CO2 is a thermodynamically stable and chemically inert molecule but also because of the complexity of the reaction routes and uncontrollability of C-C coupling. In this study, we developed an efficient catalyst, K-Fe-Cu-Zn/ZrO2 (KFeCuZn/ZrO2), which enhances the EtOH space time yield (STYEtOH) to 5.4 mmol gcat -1 h-1, under optimized conditions (360 °C, 4 MPa, and 12 L gcat -1 h-1). Furthermore, we investigated the roles of each constituent element using in situ/operando spectroscopy such as X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). These results demonstrate that all components are necessary for efficient ethanol synthesis.

Photocatalytic Synthesis of Glycine from Methanol and Nitrate.

Photocatalytic utilization of methanol and nitrate as carbon and nitrogen sources for the direct synthesis of amino acids could provide a sustainable way for the valorization of green "liquid sunlight" and nitrate waste. In this study, we developed an efficient photochemical method to synthesize glycine directly from methanol and nitrate, which cascades the C-C coupling to form glycol, nitrate reduction to NH3, and finally C-N coupling to generate glycine. Interestingly, the involved photocatalytic tandem reactions show a synergistic effect, in which the presence of nitrate is the dominant factor to enable the overall reaction and reach high synthetic efficiency. Ba2+-TiO2 nanoparticles are confirmed as a feasible and efficient catalyst system for the photosynthesis of glycine with a remarkable glycine photosynthesis rate of 870 μmol gcat-1 h-1 under optimal conditions. This work establishes a novel catalytic system for amino acid synthesis from methanol and nitrate under mild conditions. These results also allow us to further suppose the formation pathways of amino acids on the primitive earth, as an extension to proposals based on the Miller-Urey experiments.

Atomically Dispersed Iron‐Copper Dual‐Metal Sites Synergistically Boost Carbonylation of Methane

AbstractThe direct liquid‐phase oxidative carbonylation of methane, utilizing abundant natural gas, offers a mild and straightforward alternative. However, most catalysts proposed for this process suffer from low acetic acid yields due to few active sites and rapid C1 oxygenate generation, impeding their industrial feasibility. Herein, we report a highly efficient 0.1Cu/Fe‐HZSM‐5‐TF (TF denotes template‐free synthesis) catalyst featuring exclusively mononuclear Fe and Cu anchored in the ZSM‐5 channels. Under optimized conditions, the catalyst achieved an unprecedented acetic acid yield of 40.5 mmol gcat−1 h−1 at 50 °C, tripling the previous records of 12.0 mmol gcat−1 h−1. Comprehensive characterization, isotope‐labeled experiments and density functional theory (DFT) calculations reveal that the homogeneous mononuclear Fe sites are responsible for the activation and oxidation of methane, while the neighboring Cu sites play a key role in retarding the oxidation process, promoting C−C coupling for effective acetic acid synthesis. Furthermore, the methyl‐group carbon in acetic acid originates solely from methane, while its carbonyl‐group carbon is derived exclusively from CO, rather than the conversion of other C1 oxygenates. The proposed bimetallic catalyst design not only overcomes the limitations of current catalysts but also generalizes the oxidative carbonylation of other alkanes, demonstrating promising advancements in sustainable chemical synthesis.

Regulating Adsorption Behavior of Reactants on NiO/CuO/Co3O4 Surface by Electronic Effect to Promote Electrosynthesis

AbstractDeveloping efficient electrooxidation 5‐hydroxymethylfurfural (HMF) catalysts with high selectivity and fast reaction kinetic is challenging. The HMF oxidation reaction (HMFOR) involves the adsorption of HMF and OH− on the catalyst, thus understanding the adsorption behavior between the catalyst surface and reactants is vital. In this work, by studying the relationship between HMFOR performance and the adsorption behavior of reactants on different transition metal oxides (TMOs), it is discovered that the catalytic performance of TMOs is related to the adsorption capacity of OH− and HMF simultaneously. Subsequently, TMOs with different HMF and OH− adsorption abilities are coupled to further optimize the catalytic performance of HMFOR. Experimental and theoretical calculation results indicate that the electronic interactions between different TMOs can regulate the substrate adsorption behavior and electron transfer ability of the catalysts, which is beneficial for HMFOR. Among them, due to the strong interaction between the three components optimizes the adsorption capacity for HMF and OH−, NiO/CuO/Co3O4 exhibits the best HMFOR performance with FDCA selectivity of 99.6 % and formation rate of 16.45 mmol gcat−1 h−1. This work provides a design principle for HMFOR catalysts by modulating the adsorption behavior of reaction molecules.

Silicate minerals enable the efficient photocatalytic RWGS reaction

Silicate minerals are the most abundant minerals on Earth’s crust and can originate from rock-forming minerals with the low risk to the environment. Herein, the chain pyroxene mineral NaFeSi2O6 nanosheets loaded with highly dispersed Cu nanoparticles have been used as an archetype platform for the efficient photocatalytic reverse water gas shift (RWGS) reaction. The resultant Cu/NaFeSi2O6 catalyst demonstrated high performance metrics in the gas-phase photocatalytic hydrogenation of CO2 to CO, with a yield as high as 13144 μmol gcat–1 h–1. It is shown that the coordinately unsaturated Fe atom in NaFeSi2O6 can serve as a robust Lewis acid site for adsorbing and activating CO2 molecules, while the metal/support interface facilitates the formation of intermediate species and the subsequent production of CO products through hydrogen spillover. The surface plasmon resonance (SPR) effect of Cu further promotes the injection of hot electrons into NaFeSi2O6 and the carrier separation and migration at the Schottky heterojunction. This low-cost and earth-abundant mineral-based catalyst exhibits 100 h of long-term photocatalytic stability, indicating its potential as a promising and feasible candidate for the future development of renewable synthetic fuels.

Impact of copper on activity, selectivity, and deactivation in the photocatalytic reduction of CO2 over TiO2

The photocatalytic reduction of CO2 to hydrocarbons may be a promising mechanistic route to reduce greenhouse gas CO2, convert it into useful products, and limit the direct emission of CO2. The photocatalytic reduction of CO2 is a reaction in which photons activate the photocatalyst by generating reduced and oxidized sites, that are re-oxidized and re-reduced by the reactants. The photocatalytic reduction of CO2 can produce various products, including CO, formic acid, formaldehyde, methanol, methane, etc.Here, the activity/selectivity of produced hydrocarbons in the presence of oxygen on various photocatalysts (TiO2, 5 wt%Cu-TiO2, 5 wt%Cu-C-TiO2) was determined.The reaction rate increased with increasing reaction time up to the first half an hour of the reaction but then started to decrease with photocatalysts, indicating photocatalyst deactivation, a rate-limiting step by hydroxyl radicals and adsorption of intermediates on TiO2. Carbon deposition as the origin of photocatalyst deactivation was confirmed using the TGA of the spent photocatalyst. Additionally, absorption of intermediates on spent catalysts were confirmed by FTIR. On the other hand, the conversion increased with time when copper was used as a promoter on a TiO2 compared with TiO2 due to its larger surface area and having more active sites.The photocatalysts were characterized using BET, ICP-OES, XRD, TGA, XPS, Fourier-Transform Infrared Spectroscopy (FTIR), and UV–Vis. The focus of this study was to determine the activity and efficacy of different photocatalysts (TiO2, 5 wt%Cu-TiO2, 5 wt%Cu-C-TiO2) by gas phase measurement, with a particular emphasis on obtaining reproducible data on conversion and selectivity as a function of irradiation time.The copper on TiO2 was found to be more selective towards sodium formate/formic acid with a maximum selectivity of ∼90 % in 4 h and had higher activity (74.3 µmol gcat-1 h-1). A maximum CO with a selectivity of 86 % was found when TiO2 was used in 4 h.Copper transfer electrons on the TiO2 surface enhance CO2 adsorption on the catalytic surface and is the reason for having higher valuable product on Cu-C-TiO2 and Cu-TiO2 compared with TiO2. Carbon in this experiment did not have a role and its effect was negligible.