High Value-added Chemicals Research Articles

Replacing oxygen evolution reaction in water splitting process by electrochemical energy-efficient production of high-added value chemicals with co-generation of green hydrogen

The utilization of biomass represents a promising alternative to the use of fossil fuels in facing both the energy problem and environmental pollution. Using the electrochemical oxidation of organic pollutants instead of the oxygen evolution reaction at the anode and the hydrogen evolution reaction at the cathode of an electrolyzer, it is possible to make high-value chemicals, break down pollutants, and produce hydrogen efficiently at the same time. In this study, the scale-up of the electrochemical treatment was investigated by treating technical cashew nutshell liquid effluent using a photovoltaic-driven electrochemical reactor with two compartments and equipped with a boron-doped diamond electrode as the anode and a Ni stainless-steel mesh as the cathode. Tests were carried out varying the anode current densities (40, 70, and 100 mA cm-2), the nature of the electrolyte solution (NaOH and Na2SO4), and the concentration of technical cashew nutshell liquid (0.01, 0.05, or 0.10 %). The results clearly shown that it is possible to successfully scale up a divided electrochemical reactor (passing from the batch approach of previous works to the flow approach of this study), favoring a selective accumulation of acetate (600 mg L-1) in the anodic compartment. In addition, the simultaneous production of green hydrogen (0.182 L h-1) was achieved when electrolyzing a biomass effluent containing 0.10 % technical cashew nutshell liquid in 1 mol L-1 NaOH and applying a current density of 40 mA cm-2. In conclusion, the sustainable electrochemical transformation of the waste (from technical cashew nutshell liquid into valuable products and energy carriers) was successfully achieved. We believe that the results will help the energy transition towards zero carbon emission and a cost-effective production of hydrogen through an integrated-hybrid process.

Direct oxidation of alcohols to carboxylic acids using simple and economical Pd@Glu-HTC catalyst: Practical and scalable approach towards biomass based value added chemicals

Sustainable catalytic transformation of bio-based alcohols to high value-added fine chemicals is an important topic of research. This work described preparation of simple and economical Pd@Glu-HTC catalyst from biomass derived low cost d-glucose. Hydrothermal carbonization of glucose was carried out in first step to synthesize Glu-HTC support in a simpler, greener, economical and efficient manner followed by incorporation of palladium metal on surface of the catalyst in second step. The catalyst was characterized using techniques such as Fourier Transform Infrared Spectroscopy (FT-IR), Solid-state Cross-Polarization Magic Angle Spinning Carbon-13 (13C CPMAS), Energy-dispersive X-ray spectroscopy (EDAX), Powder X-ray diffraction (P-XRD), X-ray photoelectron spectroscopy (XPS), Thermogravimetric/Differential Thermal Analyzer (TG-DTA), Field emission scanning electron microscopy (FE-SEM) and High-resolution transmission electron microscopy (HR-TEM). The catalyst was evaluated for direct oxidation of alcohols to yield carboxylic acids and exhibited very good catalytic activity for wider substrate scope. Oxidation of alcohols was carried out using milder base, molecular oxygen and water as a solvent to achieve 92–99 % excellent yields. The practical utility of current strategy was also studied for gram scale synthesis of bio-based value added industrially important chemicals such as furoic acid (flavouring agent and preservative in industry), 2, 5-furan-dicarboxylic acid (monomer to 100 % fossil-free, recyclable polymer polyethylene furanoate (PEF), tetrahydro-2-furoic acid (production of many drugs) and vanillin (important product of flavor and fragrance industry). Pd@Glu-HTC catalyst was found to be reusable for four recycles and the catalytic performance was retained without any loss in its activity after four cycles.

Revisit coupling of CO2 to ethylene carbonate with an integrated imidazolium and zinc halides catalyst by a study on its decomposition: Active center and mechanism

Coupling of carbon dioxide (CO2) to cyclic carbonates with an epoxide and further into linear carbonates as the indispensable solvents for the lithium-ion batteries has been being one of the hottest topics in transforming CO2 into high value-added chemicals. Nevertheless, the extremely ultrahigh purity requirement for them causes a low efficiency and a modest yield due to the undesired reactions and byproducts occurring in the separation and purification sections. In this work, a novel imidazolium based ionic liquid catalyst system with different anions and cations was studied by a thorough insight into the decomposition reaction of ethylene carbonate (EC), which reveals the synergistic mechanism of the composite catalysts both in section of cyclic carbonate separation from the catalyst for recirculated utilization and purification from the byproducts, and in section of synthesis with high efficiency. Effects of imidazolium cations and halogen anions in the ionic liquid molecule on EC decomposition were investigated by the elaborately designed experiments, thermodynamic estimations, molecular dynamics simulation and DFT assessment. It was found that combining imidazole salts and zinc halides can greatly boost the activity of EC synthesis and decomposition with the effective structure of catalytic center being [EMIm]ZnX4. Furthermore, it was indicated that Br- has a higher activity for EC synthesis and its reversed pyrolysis, while Cl- will promote a side reaction of ring-opening polymerization of EC. Finally, a most favorable catalyst composition with ZnBr2 and [EMIm]Br for EC synthesis was achieved with a high efficiency in synthesis and a low tendency to initiate the side reactions in separation section.

Boosting Interfacial Electron Transfer and CO2 Enrichment on ZIF-8/ZnTe for Selective Photoelectrochemical Reduction of CO2 to CO.

Artificial photosynthesis is an effective way of converting CO2 into fuel and high value-added chemicals. However, the sluggish interfacial electron transfer and adsorption of CO2 at the catalyst surface strongly hamper the activity and selectivity of CO2 reduction. Here, we report a photocathode attaching zeolitic imidazolate framework-8 (ZIF-8) onto a ZnTe surface to mimic an aquatic leaf featuring stoma and chlorophyll for efficient photoelectrochemical conversion of CO2 into CO. ZIF-8 possessing high CO2 adsorption capacity and diffusivity has been selected to enrich CO2 into nanocages and provide a large number of catalytic active sites. ZnTe with high light-absorption capacity serves as a light-absorbing layer. CO2 molecules are collected in large nanocages of ZIF-8 and delivered to the ZnTe surface. As evidenced by scanning electrochemical microscopy, the interface can effectively boost interfacial electron transfer kinetics. The ZIF-8/ZnTe photocathode with unsaturated Zn-Nx sites exhibits a high Faradaic efficiency for CO production of 92.9% and a large photocurrent of 6.67 mA·cm-2 at -2.48 V (vs Fc/Fc+) in a nonaqueous electrolyte at AM 1.5G solar irradiation (100 mW·cm-2).

Solar Energy-Driven Reverse Water Gas Shift Reaction: Photothermal Effect, Photoelectric Activation and Selectivity Regulation.

Excessive carbon dioxide (CO2) emissions are one of the main causes of the greenhouse effect. Thermal catalytic reverse water gas shift (RWGS) reaction, which is a pre reaction for Fischer-Tropsch synthesis, is considered an effective way to convert CO2 and synthesize high value-added chemicals in industry. However, traditional thermal catalysis requires a large amount of fossil fuels to drive reactions, which cannot achieve the true goal of carbon neutrality. Photothermal catalysis, as a novel conversion pathway, can achieve efficient CO2 conversion while significantly improving solar energy utilization. This review provides a detailed introduction of CO2 and H2 adsorption/activation and reaction pathways in thermal catalysis, as well as the catalytic mechanisms of thermal and chemical effects in photothermal catalytic RWGS to supply readers valuable insights on the mechanism of photothermal catalytic RWGS reaction and provide a reference for better catalyst design.

Fabrication of Keggin heteropolyacid modified macroporous covalent triazine frameworks with cyano group-rich defects for high-value utilization of carbohydrates

Designing an efficient, stable and recyclable solid acid for catalytic conversion of biomass and its derived compounds to synthesize high value-added organic chemicals could effectively alleviate the environmental problems caused by the energy crisis and carbon dioxide emissions. We prepared a Keggin heteropolyacid modified macroporous covalent triazine frameworks (PW12-MCTF) catalyst using a simple template method and post-impregnation technology for efficient conversion of carbohydrates to produce 5-hydroxymethylfurfural (HMF). Abundant structural defects of MCTF can be constructed in situ through incomplete polymerization, which can firmly bind H3PW12O40 through physical confinement effect and bonding interactions. Under optimized conditions, PW12-MCTF exhibited high HMF yield (79.4 % or 44.4 %) and the highest turnover frequency (4.39 min−1 or 1.86 min−1) in microwave-assisted catalytic conversion of fructose or inulin, respectively. Its catalytic activity surpassed that of bulk PW12-CTF and commercial acid zeolite and resin catalysts, due to its appropriate acid properties, well-dispersed nature in DMSO, inter-connected pore structure and outstanding nucleophilic effect of N-rich units. Density Functional Theory (DFT) study provides a plausible mechanism in PW12-CTF-catalyzed fructose dehydration. The catalytic performance of PW12-MCTF remained unchanged after three cycles due to strong bonding interaction between the Keggin units and framework of MCTF. This study will provide a new strategy for the fabrication of heteropolyacid modified covalent organic frameworks with structural defects to achieve the high-value utilization of carbohydrates.

Recent Progress in the Conversion of Methylfuran into Value-Added Chemicals and Fuels.

2-methylfuran is a significant organic chemical raw material which can be produced by hydrolysis, dehydration, and selective hydrogenation of biomass hemicellulose. 2-methylfuran can be converted into value-added chemicals and liquid fuels. This article reviews the latest progress in the synthesis of liquid fuel precursors through hydroxyalkylation/alkylation reactions of 2-methylfuran and biomass-derived carbonyl compounds in recent years. 2-methylfuran reacts with olefins through Diels-Alder reactions to produce chemicals, and 2-methylfuran reacts with anhydrides (or carboxylic acids) to produce acylated products. In the future application of 2-methylfuran, developing high value-added chemicals and high-density liquid fuels are two good research directions.

Atomically dispersed Zn-NxCy sites on N-doped carbon for catalytic transfer hydrogenation of ethyl levulinate into γ-valerolactone

Catalytic transfer hydrogenation (CTH) of biomass-derived carbonyl compounds provides a viable strategy to synthesize high value-added chemicals and biofuels, for which the development of efficient catalysts still remains a formidable challenge. Here, we report a Zn-based single-atom catalyst (Zn/NC-950), prepared by pyrolysis of ZIF-8 at 950 °C, for the CTH of ethyl levulinate to γ-valerolactone (GVL). This catalyst exhibited excellent performance, affording a GVL selectivity of 95.3 % at an ethyl levulinate conversion of 100 %, using isopropanol as the hydrogen source at 200 °C and autogenous pressure. The structural characterization and theoretical calculation demonstrate that such extraordinary efficacy of the Zn/NC-950 catalyst is attributed to the dual Zn-N3C1 and Zn-N2C2 sites of low Zn oxidation states, which work synergistically to generate the active hydrogen species and activate the carbonyl bonds, respectively. This work provides a rationale for the precise design of the non-noble metal single-atom catalysts efficient for the biomass valorization.

Photochemical Aerobic Upcycling of Polystyrene Plastics.

Although the introduction of plastics has improved humanity's everyday life, the fast accumulation of plastic waste, including microplastics and nanoplastics, have created numerous problems with recent studies highlighting their involvement in various aspects of our lives. Upcycling of plastics, the conversion of plastic waste to high-added value chemicals, is a way to combat plastic waste that is receiving increased attention. Herein, we describe a novel aerobic photochemical process for the upcycling of real-life polystyrene-based plastics into benzoic acid. A new process employing a thioxanthone-derivative, in combination with N-bromosuccinimide, under ambient air and 390 nm irradiation is capable of upcycling real-life polystyrene-derived products in benzoic acid in yields varying from 24-54%.

Heterostructured In2O3/In2S3 hollow fibers enable efficient visible-light driven photocatalytic hydrogen production and 5-hydroxymethylfurfural oxidation

Solar light driven hydrogen production from water splitting and oxidation of biomass-derivatives is attractive for the conversion of solar energy to high value-added chemicals. The fabrication of heterostructure photocatalysts with matched band structure between two semiconductors is a promising approach for efficient photocatalysis. In this work, a novel In2O3/In2S3 heterostructured hollow fiber photocatalyst was successfully fabricated through two-step ion exchange and chemical bath deposition methods, where the In2S3 nanoparticles (NPs) anchored on the surface of In2O3 hollow fibers via strong interfacial interaction between the In2O3 (222) and In2S3 (220) facets. The photocatalyst was used for efficient visible-light-driven photocatalytic hydrogen production integrated with selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF). Compared with pristine In2O3 and In2S3, the optimal In2O3/In2S3 heterostructure exhibits an enhanced photocatalytic hydrogen production rate (111.2 μmol h−1 g−1), HMF conversion efficiency (56%) and DFF selectivity (68%) under visible light irradiation. The experimental and theoretical investigations illustrate the phase interface between well matched In2O3 (222) and In2S3 (220) facets gives rise to facilitated photogenerated charge separation and transfer. This study presents the development of high-performance heterostructured photocatalysts for high efficient hydrogen production coupled with biomass oxidation.

Advances in electrocatalytic carbon dioxide reduction reactors, electrolytes and catalysts

With the advance of The Times, people's demand for fossil energy has greatly increased, and it is the main energy for people to develop economy and science and technology. However, the large-scale exploitation of fossil energy has led to environmental pollution and energy crisis, and the concentration of CO2 in the air continues to rise, and the greenhouse effect is becoming more and more serious. Therefore, the conversion of CO2 into the high value-added fuels and chemicals we need will be a major measure to solve environmental problems. So, converting CO2 into fuels or high value-added chemicals using CO2 electrocatalytic reduction (CO2RR) technology is an effective way to alleviate the current problems of energy and environment. In this paper, we summarize the research progress in reaction systems, electrolyte effects, and catalyst development in CO2RR experiments, focusing on the electrocatalytic aspects of CO2. Finally, we provide an outlook on the CO2 electrocatalysis industry.

ReaxFF reactive molecular dynamic and density functional theory study on the co-pyrolysis mechanism of waste 1,1,1,2-tetrafluoroethane and waste plastics to produce high value-added chemicals and fuels

Pyrolysis is one of the potential way for the degradation of hydrofluorocarbons, but it is difficult to make effective use of the complex pyrolysis products. The addition of plastics can provide sufficient hydrogen source for the degradation of hydrofluorocarbons to generate the high value-added chemicals and fuels. Density functional theory calculation and reactive molecular dynamic simulation are employed to investigate the co-pyrolysis mechanism of 1,1,1,2-tetrafluoroethane and low-density polyethylene in this work. The results show that the H atoms provided by low-density polyethylene promote the defluorination reactions of 1,1,1,2-tetrafluoroethane to generate HF and short chain hydrocarbons, and the number of F atoms in HF molecules accounted for nearly 80 % of the whole reaction system, achieving a better defluorination effect. The defluorination rate of 1,1,1,2-tetrafluoroethane and plastics co-pyrolysis is more than 5 times that of pure 1,1,1,2-tetrafluoroethane pyrolysis. The main co-pyrolysis products of 1,1,1,2-tetrafluoroethane and low-density polyethylene are H2, HF and short chain hydrocarbons, the purpose of hydrofluorocarbons degradation into high value-added chemicals and fuels is realized in this study. This work provides a green, effective way for the conversion waste hydrofluorocarbons and waste plastics into high value-added chemicals and fuels, and achieves the conversion of waste hydrofluorocarbon refrigerants to more economical products.

Doping Efects on Ethane/Ethylene Dehydrogenation Catalyzed by Pt2X Nanoclusters.

The catalytic dehydrogenation of light alkanes is key to transform low-cost hydrocarbons to high value-added chemicals. Although Pt is extremely efficient at catalyzing this reaction, it suffers from coke formation that deactivates the catalyst. Dopants such as Sn are widely used to increase the stability and lifetime of Pt. In this work, the dehydrogenation reaction of ethane catalyzed by Pt3 and Pt2X (X=Si, Ge, Sn, P and Al) nanocatalysts has been studied computationally by means of density functional calculations. Our results show how the presence of dopants in the nanocluster structure affects its electronic properties and catalytic activity. Exploration of the potential energy surfaces show that non-doped catalyst Pt3 present low selectivity towards ethylene formation, where acetylene resulting from double dehydrogenation reaction will be obtained as a side product (in agreement with the experimental evidence). On the contrary, the inclusion of Si, Ge, Sn, P or Al as dopant agents implies a selectivity enhancement, where acetylene formation is not energetically favoured. These results demonstrate the effectiveness of such dopant elements for the design of Pt-based catalysts on ethane dehydrogenation.

Photoelectrochemically converting CO2 over Z-scheme heterojunction CoPc/K7HNb6O19 with high Faraday efficiency

Photoelectrochemically converting CO2 into the high value-added chemicals and fuels is a hopeful sustainable energy conversion and storage road to alleviate the energy crisis and global warming. In this study, CoN-x Z-scheme heterojunctions were prepared by coupling CoPc with K7HNb6O19 rich in oxygen vacancy with a low-temperature calcination, and used for photoelectrocatalytic (PEC) reduction of CO2 to CO. The prepared heterojunctions demonstrate Faraday efficiency of >90 % and TOF values over a wide voltage range (−0.65 ∼ −1 V vs. RHE). The superior PEC CO2 reduction performance is mainly attributed to the designed Z-scheme heterojunction, which endows a built-in electric field to the interface of the two semiconductors, benefiting the separation of electrons and holes greatly. Additionally, the oxygen vacancy from K7HNb6O19 provides an alternative pathway for CO2 adsorption and activation, and simultaneously the incorporated K7HNb6O19 inhibits the aggregation of cobalt phthalocyanine molecules, which is beneficial for the stability of PEC catalysts. Density-functional-theory (DFT) calculation also elucidates a favorable CO2 activation energy over CoPc coupling oxygen-vacancy-rich K7HNb6O19 heterojunctions. This work may provide a viable pathway for the rational designing of efficient PEC systems to reduce CO2 to valuable fuels.

ReaxFF reactive molecular dynamic and density functional theory study on supercritical water gasification of waste hydrofluorocarbons to fuels

Hydrofluorocarbon (HFC) working fluid with high global warming potential are step out of the stage of history due to the intensifying global greenhouse effect. Supercritical water gasification (SCWG), an effective and clean waste disposal method, may have better potential for the conversion of waste HFCs working fluid. ReaxFF reactive molecular dynamic and density functional theory method are used in this work to investigate the SCWG mechanism of HFC-245fa. The results indicate that the main products of HFC-245fa SCWG are high value-added chemicals and fuels such as CO, CO2, H2, and HF. During the gasification process, almost 100 % of the F atoms in HFC-245fa have the potential to become HF, which means that the SCWG method has a strong defluorination effect. The generation of H2 molecules is promoted and the formation of CO molecule is inhibited in the presence of H2O molecules. More importantly, hydrogen bonds are formed between HFC-245fa and H2O molecules, which results in the dissociation of HFC-245fa is improved by the SCWG environment. This work provides an available and environmentally friendly route for the efficient conversion of waste HFCs to fuels.

Enzymatic Mesoporous Metal Nanocavities for Concurrent Electrocatalysis of Nitrate to Ammonia Coupled with Polyethylene Terephthalate Upcycling.

Electrochemical upcycling of waste pollutants into high value-added fuels and/or chemicals is recognized as a green and sustainable solution that can address the resource utilization on earth. Despite great efforts, their progress has seriously been hindered by the lack of high-performance electrocatalysts. In this work, bimetallic PdCu mesoporous nanocavities (MCs) are reported as a new bifunctional enzymatic electrocatalyst that realizes concurrent electrocatalytic upcycling of nitrate wastewater and polyethylene terephthalate (PET) plastic waste. Abundant metal mesopores and open nanocavities of PdCu MCs provide the enzymatic confinement of key intermediates for the deeper electroreduction of nitrate and accelerate the transport of reactants/products within/out of electrocatalyst, thus affording high ammonia Faradic efficiency (FENH3) of 96.6% and yield rate of 5.6mgh-1mg-1 at the cathode. Meanwhile, PdCu MC nanozymes trigger the selective electrooxidation of PET-derived ethylene glycol (EG) into glycolic acid (GA) and formic acid with high FEs of >90% by a facile regulation of potentials at the anode. Moreover, concurrent electrosynthesis of value-added NH3 and GA is disclosed in the two-electrode coupling system, further confirming the high efficiency of bifunctional PdCu MC nanozymes in producing value-added fuels and chemicals from waste pollutants in a sustainable manner.

Synthesis and characterization of catalytic active oxazolidine/Schiff complexes using 2-quinoline formaldehyde and tris-base for carbon dioxide chemical fixation

Catalytic chemical fixation of carbon dioxide to high value-added chemicals has attracted extensive attention and the discovery of new catalytic system has always been a research hotspot in carbon dioxide chemistry. Three complexes were synthesized by using 2-quinoline formaldehyde and tris-base precursor through Schiff base reaction and characterized. Compound Co[L1]2Cl2·2H2O (1) and compound Ni[L1]2Cl2·2H2O (2) are two mononuclear complex with derived schiff base ligand (L1 = 2-(hydroxymethyl)-2-((quinolin-2-ylmethylene)amino)propane-1,3-diol), while compound Cu2[L2]2Cl2∙2CH3OH (3) is a dinuclear complex containing derived deprontonated ligand (L2 = (2-(quinolin-2-yl)oxazolidine-4,4-diyl)dimethanol) The self-assembly process of these complexes were monitored by ESI-MS. The catalytic explore for the cycloaddition of CO2 and different reaction substrates and preliminary kinetic studies shows that all complexes are active and the reaction is an intramolecular Lewis acid-base catalytic mechanism. This is the first report of oxazolidine complex/ tetrabutylammonium halide catalyst in for cycloaddition of epoxides and CO2 reaction and the complex 3 is more active than the other two complexes, which provides new notions for the design and solicitation of Schiff base/oxazolidine catalysts.

Regulation of the d-band center of metal–organic frameworks for energy-saving hydrogen generation coupled with selective glycerol oxidation

The hybrid electrolyzer coupled glycerol oxidation (GOR) with hydrogen evolution reaction (HER) is fascinating to simultaneously generate H2 and high value-added chemicals with low energy input, yet facing a challenge. Herein, Cu-based metal-organic frameworks (Cu-MOFs) are reported as model catalysts for both HER and GOR through doping of atomically dispersed precious and nonprecious metals. Remarkably, the HER activity of Ru-doped Cu-MOF outperformed a Pt/C catalyst, with its Faradaic efficiency for formate formation at 90% at a low potential of 1.40 V. Furthermore, the hybrid electrolyzer only needed 1.36 V to achieve 10 mA cm-2, 340 mV lower than that for splitting pure water. Theoretical calculations demonstrated that electronic interactions between the host and guest (doped) metals shifted downward the d-band centers (εd) of MOFs. This consequently lowered water adsorption and dissociation energy barriers and optimized hydrogen adsorption energy, leading to significantly enhanced HER activities. Meanwhile, the downshift of εd centers reduced energy barriers for rate-limiting step and the formation energy of OH*, synergistically enhancing the activity of MOFs for GOR. These findings offered an effective means for simultaneous productions of hydrogen fuel and high value-added chemicals using one hybrid electrolyzer with low energy input.

Targeted electron transfer effect of enzyme-like Co-NX catalysts for enhanced C = O hydrogenation

In response to increasing energy and environmental concerns, enzyme-like catalysts (ELC) have been widely and artificially created for the conversion of biomass into alternative chemicals. However, the precise construction of desired ELC and the clarification of their conformational relationships still face great challenges. Here, we report a metal nitrogen-doped carbon-based catalyst with enzyme-like properties for targeted adsorption-selective hydrogenation of biomass molecules containing conjugated double bonds. Density-functional theory (DFT) calculations show that nitrogen doping excites electron-directed transfer effects, which promote the polarization and rearrangement of surface charges. This promotes the target adsorption of C = O bonds and reducing the energy barrier for the hydrogenation of RC(CH3) = CHCHO* to RC(CH3) = CHCHOH*. Kinetic calculations indicate that the decrease in the reaction activation energy 67.1 kJ/mol to Ea = 30.86 kJ/mol was due to the doping of the N. This work lays a theoretical foundation for further clarification of the structure–activity relationship of ELC and provides an important paradigm for realizing the conversion of biomass platform molecules into high value-added chemicals.

A covalent organic framework integrating photocatalytic center and electron reservoir for photocatalytic CO2 reduction to HCOOH

Direct and efficient photocatalytic conversion of CO2 into fuels and high value-added chemicals under sunlight is of great significance in alleviating the energy crisis and environmental issues. Covalent organic frameworks (COFs) have attracted much attention in the photocatalytic field as materials that can be pre-designed on demand. Taking advantage of the pre-designable properties of COFs materials, the integration of organic building blocks with photocatalytic activity and photoelectron-resident properties into frameworks can improve the electron-hole separation efficiency and photocatalytic performance. Here, we report a newly designed COF (COF-TVBT-N) with triazine and alkenyl groups that can be used as a photocatalyst to accomplish the photoreduction of CO2 to HCOOH under simulated sunlight without the assistance of metal sites and photosensitizers. Furthermore, we unambiguously reveal that the photocatalytic active center in COF-TVBT-N is TVBT through the combination of experiments and theoretical calculations. DFT calculations suggest that the adsorption of H near the active center is beneficial for the adsorption and photoreduction of CO2 in this photocatalytic system. The photoexcitation process and photocatalytic CO2 reduction mechanism of COF-TVBT-N are also reasonably deduced based on DFT calculations. This work provides ideas for the design of COFs as photocatalysts for CO2 reduction and gives insights into the mechanism of CO2 conversion to HCOOH.