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Chinese Journal of Catalysis
2023, Vol. 53
Online: 18 October 2023

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Cover: Professor Shengwei Liu and coworkers developed freeze-drying assisted method to assembly 1D crystalline g-C₃N₄ (CCN) nanorods onto 2D Ti₃C₂T_x MXene nanosheets in a special 1D/2D configuration, with matching crystal orientation and strengthening interfacial interactions. Superior to conventional 2D/2D configuration, this novel 1D-CCN/2D-Ti₃C₂T_x Schottky-junction photocatalyst significantly suppressed interfacial charge transfer barrier and promoted interfacial photoelectron transfer efficiency, greatly enhancing photocatalytic CO₂RR activity and selectivity. Read more about the article behind the cover on page 109–122.

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Electrocatalytic CO2 conversion toward large-scale deployment Li Lin, Xiaoyang He, Shunji Xie, Ye Wang 2023, 53:  1-7.  DOI: 10.1016/S1872-2067(23)64524-3 Abstract ( 808 )   HTML ( 72 )   PDF (2061KB) ( 360 )   The electrocatalytic conversion of CO2 into chemicals and liquid fuels, powered by renewable energy sources, is expected to reach commercial applications. This comment outlines the research directions that focus on advancing practical deployment of CO2 electrolysis. Furthermore, the bottlenecks that limit the high-efficiency conversion of CO2 and promising approaches to overcome them are discussed.

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Some thoughts about the electrochemical nitrate reduction reaction Xianbiao Fu 2023, 53:  8-12.  DOI: 10.1016/S1872-2067(23)64521-8 Abstract ( 963 )   HTML ( 42 )   PDF (1540KB) ( 560 )   The past five years have witnessed significant development of efficient electrocatalysts for nitrate reduction. Most of the reports focused on the Faraday efficiency of ammonia, current density, and ammonia production rates. However, some scientific and practical challenges are rarely discussed. This perspective summarized some bottlenecks and limitations, such as the sustainable nitrate supply, species balance of overall reaction, mass transfer limitation of nitrate, and stability of catalysts. The proposed challenges are opportunities for moving this field forward in the future.

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Progress in wastewater treatment via organic supramolecular photocatalysts under sunlight irradiation Weixu Liu, Chang He, Bowen Zhu, Enwei Zhu, Yaning Zhang, Yunning Chen, Junshan Li, Yongfa Zhu 2023, 53:  13-30.  DOI: 10.1016/S1872-2067(23)64530-9 Abstract ( 563 )   HTML ( 40 )   PDF (8236KB) ( 280 )   Semiconductor photocatalysis offers a promising and sustainable avenue for wastewater treatment due to its ease of separation and recyclability. However, their practical application is currently hampered by limited energy utilization, insufficient mineralization, and low treatment capacity under sunlight. This account summarizes our progress in developing broad-spectrum responsive (extended to 950 nm) supramolecular organic photocatalysts capable of sunlight-driven over 95% pollutant mineralization. Through modulation of molecular dipole and crystallinity, we enhance the built-in electric field, thereby improving charge separation and photodegradation rates. Furthermore, to overcome the low-flux constraints of traditional photocatalysis, we integrated the Fenton catalyst to construct photo-self-Fenton systems, realizing a 29.63 L m-2 h-1 high-flux mineralization under sunlight. Finally, a brief conclusion and outlook on organic photocatalysts have also been presented.

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Electrocatalytic water vapor splitting via lattice-matched hetero-structure catalyst Shaoqing Song 2023, 53:  31-33.  DOI: 10.1016/S1872-2067(23)64529-2 Abstract ( 186 )   HTML ( 7 )   PDF (1789KB) ( 52 )

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Selective electrochemical oxidation of alkene: Recent progress and perspectives Jin Wang, Justin Zhu Yeow Seow, Zhichuan J. Xu, Xiao Ren 2023, 53:  34-51.  DOI: 10.1016/S1872-2067(23)64522-X Abstract ( 834 )   HTML ( 41 )   PDF (8945KB) ( 414 )   Alkene oxidation is an important industrial process that produces considerable quantities of commodity chemicals, notably ethylene oxide and propylene oxide. However, typical thermal oxidation processes are characterized by harsh reaction conditions and limited selectivity. Thus, electrochemical alternatives with enhanced product selectivity emerge as promising solutions with the possibility of using renewable input energy sources. Herein, we discuss strategies to improve the selectivity of alkene electrooxidation, specifically focusing on the regulation of the geometric and electronic structures of electrocatalysts, as well as the application of mediated indirect oxidation. Furthermore, we also provide an overview of the current challenges and problems requiring further investigation in improving industrial feasibility of electrochemical alkene oxidation.

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The dynamic behaviors of heterogeneous interfaces in electrocatalytic CO2 reduction Shenyu Shen, Qingfeng Guo, Tiantian Wu, Yaqiong Su 2023, 53:  52-71.  DOI: 10.1016/S1872-2067(23)64543-7 Abstract ( 172 )   HTML ( 10 )   PDF (7711KB) ( 70 )   The electrocatalytic CO2 reduction reaction (CO2RR) is a highly promising renewable energy technology that can convert greenhouse gases into valuable fuels and chemicals. However, under ordinary operating conditions, significant dynamic evolution behavior occurs on the catalyst surface, which is mainly manifested as surface morphology evolution and property changes, eventually leading to changes in the active sites of the reaction, affecting selectivity and efficiency. To develop efficient electrocatalytic systems with excellent performance, an essential prerequisite is to understand the underlying mechanism of surface dynamic evolution. Studying the influence of the external environment on dynamic evolution is as important as studying the intrinsic structural properties of catalysts. In this review, we first introduce the concept of dynamic evolution and then emphasize the influence of the external environment (applied potential, temperature, electrolyte, and impurities) on CO2RR dynamic evolution. We also address the use of operando characterization techniques and pulsed CO2 electrolysis methods for monitoring and controlling dynamic evolution behaviors under working conditions, along with theoretical methods, including ab initio calculations and machine learning that can simulate dynamic behavior. Finally, we present several current challenges and prospects for the development of techniques for controlling the CO2RR dynamic evolution.

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Recent advances in the built-in electric-field-assisted photocatalytic dry reforming of methane Yiming Lei, Jinhua Ye, Jordi García-Antón, Huimin Liu 2023, 53:  72-101.  DOI: 10.1016/S1872-2067(23)64520-6 Abstract ( 413 )   HTML ( 16 )   PDF (18578KB) ( 164 )   Methane (CH4) and carbon dioxide (CO2) are two major greenhouse gases that contribute to global warming. The dry reforming of methane (DRM) is an ideal method for dealing with the greenhouse effect because it simultaneously consumes CH4 and CO2 to produce syngas. However, conventional technologies require high temperatures to trigger the DRM process owing to the high energy barriers associated with activating CH4 and CO2. While the development of photocatalysts provides opportunities for initiating the DRM under mild conditions, photocatalytic efficiency nonetheless remains unsatisfactory, which is largely attributable to rapid photoexcited charge-carrier recombination. A promising strategy for overcoming this deficiency involves constructing a built-in electric field that enhances the separation and transfer dynamics of charge carriers. This review introduces reaction mechanisms and thermal catalysts for DRM applications. The advantages of photocatalytic DRM (PDRM) and potential photocatalysts are also summarized. Recent advances have enhanced PDRM by introducing electric fields through the fabrication of photocatalysts that exhibit ferroelectric effects (ferroelectric-based photocatalysts), have heterojunction structures, or undergo localized surface plasmon resonance (LSPR). In addition, significant advanced in-situ-characterization studies and theoretical calculations are introduced along with their potential impact to provide young researchers engaged in the PDRM field with simple guidance. Finally, current challenges facing the built-in electric-field-assisted PDRM field are discussed and possible strategies proposed to encourage more in-depth research in this area.

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Tailoring ligand fields of metal-azolate frameworks for highly selective electroreduction of CO2 to hydrocarbons at industrial current density Huan Xue, Jia-Run Huang, Zhi-Shuo Wang, Zhen-Hua Zhao, Wen Shi, Pei-Qin Liao, Xiao-Ming Chen 2023, 53:  102-108.  DOI: 10.1016/S1872-2067(23)64519-X Abstract ( 200 )   HTML ( 10 )   PDF (6483KB) ( 79 )   Supporting Information The catalytic activity of a metal complex is often contingent upon factors such as its valence state, coordination configuration of the metal ion, and coordination ability of the ligand. Hence, revealing the influence of the ligand field of the active metal center on the selectivity of the product for electrochemical CO2 reduction is crucial. Herein, three isostructural metal-azolate frameworks (MAFs) (Cu-BTP, Cu-BTTri, and Cu-BTT) with the same cyclic tetracopper(II) cluster units, namely [Cu3(BTP)2] (Cu-BTP, H3BTP = 1,3,5-tris(1H-pyrazol-4-yl)benzene), [Cu3(BTTri)2] (Cu-BTTri, H3BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), and [Cu3(BTT)2] (Cu-BTT, H3BTT = 1,3,5-tris(2H-tetrazol-5-yl)benzene) were synthesized using pyrazolate-, triazolate-, and tetrazolate-based ligands, respectively. The synthesized MAFs were subjected to analysis to evaluate their electrochemical capabilities for reducing CO2 under identical reaction conditions. Among them, the pyrazolate MAF, Cu-BTP, delivers a current density of 1.25 A cm−2 in a flow cell device with the highest Faradiac efficiency for hydrocarbons (CH4, 60%; C2H4, 22%). Furthermore, the system shows no obvious degradation over 60 h of continuous operation. The order of selectivity of the three MAFs for hydrocarbon production is consistent with the corresponding pKa values of the azolate ligands. Theoretical calculations show that a stronger Lewis basicity of the organic ligand, resulting in a stronger ligand field strength, is conducive to strengthening the binding of metal centers with key intermediates, such as *CO and *CHO. This ultimately leads to the deep reduction of CO2 to hydrocarbons.

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Regulating interfacial coupling of 1D crystalline g-C3N4 nanorods with 2D Ti3C2Tx MXene for boosting photocatalytic CO2 reduction Ruiyu Zhong, Yujie Liang, Fei Huang, Shinuo Liang, Shengwei Liu 2023, 53:  109-122.  DOI: 10.1016/S1872-2067(23)64513-9 Abstract ( 258 )   HTML ( 18 )   PDF (3162KB) ( 108 )   Supporting Information Two-dimensional (2D) layered photocatalysts coupled with 2D Ti3C2Tx (T = OH, O, or F) MXene cocatalysts in 2D/2D configuration have been extensively studied for use in artificial photosynthesis. Unfortunately, the overall photoreaction efficiency of these cocatalysts is often limited by weak 2D/2D interfacial van der Waals interactions, high interfacial electrostatic barriers, and slow interfacial charge transfer. In this study, 1D crystalline g-C3N4 (CCN) nanorods are grown along the c-axis using the molten-salt method and assembled onto a 2D Ti3C2Tx substrate by freeze-drying-assisted interfacial coupling, forming a unique Schottky junction photocatalyst in a 1D/2D configuration with interfacial hydrogen bonds. Transfer of photoelectrons in the CCN nanorods could along the radial π-conjugated plane to the hydrogen-bonded 2D Ti3C2Tx in the 1D/2D configuration is more efficient than the slow interlayer charge transfer in catalysts with a conventional 2D/2D configuration. Consequently, the optimized 1D-CCN/2D-Ti3C2Tx hybrid photocatalyst assembled by freeze-drying (TC/CCN-FD) exhibited an outstanding photocatalytic CO2 reduction activity at a rate of 2.13 μmol g-1 h-1, being 5.6 and 8.9 times more efficient than the pristine 1D CCN and 2D bulk g-C3N4 counterparts, respectively. Moreover, the selectivity towards the multielectron reduction product (CH4) was significantly enhanced over TC/CCN-FD owing to the faster interfacial charge transfer across the CCN/Ti3C2Tx interface and the higher density of photoelectrons on the Ti3C2Tx cocatalysts. This work will inspire further studies on suppressing the interfacial charge transfer barrier by matching the interfacial crystal orientation and strengthening the interfacial interactions.

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1D/0D heterostructured ZnIn2S4@ZnO S-scheme photocatalysts for improved H2O2 preparation You Wu, Yi Yang, Miaoli Gu, Chuanbiao Bie, Haiyan Tan, Bei Cheng, Jingsan Xu 2023, 53:  123-133.  DOI: 10.1016/S1872-2067(23)64514-0 Abstract ( 388 )   HTML ( 25 )   PDF (4787KB) ( 303 )   Supporting Information Solar photocatalysis is a promising, green, and sustainable technique for the synthesis of H2O2. In this study, low-dimensional ZnO/ZnIn2S4 S-scheme heterojunction photocatalysts are fabricated using electrostatic spinning and chemical bath deposition methods for the efficient photocatalytic production of H2O2. ZnO nanofibers loaded with 20 wt% ZnIn2S4 exhibit a superior H2O2 production rate of 928 μmol g-1 h-1, which is more than four times higher than that seen in pristine hexagonal phase ZnO and ZnIn2S4. First-principles calculations and in-situ X-ray photoelectron spectroscopy reveal the charge separation and transfer mechanisms in the S-scheme heterojunction. The construction of the S-scheme heterojunction facilitates the spatial separation of charge carriers, and electrons and holes with higher redox abilities are retained. Photoelectrochemical and photoluminescence tests further show that the formation of an S-scheme heterojunction is beneficial for the separation of photoinduced charge carriers. Electrochemical tests and electron paramagnetic resonance measurements indicate that H2O2 production is primarily via a two-step single-electron O2 reduction path. This study provides a new approach for the construction of S-scheme heterojunction materials that can efficiently produce H2O2 under solar irradiation.

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High-valence metal-doped amorphous IrOx as active and stable electrocatalyst for acidic oxygen evolution reaction Ning Zhang, Jiayi Du, Na Zhou, Depeng Wang, Di Bao, Haixia Zhong, Xinbo Zhang 2023, 53:  134-142.  DOI: 10.1016/S1872-2067(23)64517-6 Abstract ( 698 )   HTML ( 28 )   PDF (3676KB) ( 233 )   Supporting Information Proton-exchange membrane water electrolysis, particularly driven by renewable electricity, is a sustainable strategy for green hydrogen production. However, developing highly active and stable electrocatalysts to accelerate the oxygen evolution reaction (OER) remains challenging. Herein, we introduce an effective strategy for constructing high-valence metal-doped IrOx with abundant oxygen vacancies, while simultaneously enhancing the catalytic activity and stability of the acidic OER. The synthesized Ta-doped IrOx (350-Ta@IrOx) exhibits ultramicroscopic nanoparticle morphology and abundant surface oxygen vacancies, enabling a rapid OER process with a low overpotential of 223 mV at 10 mA cm-2 and 147.7 times higher mass activity (1207.4 A gIr-1) than that of commercial IrO2 at 1.55 V versus the reversible hydrogen electrode. More importantly, 350-Ta@IrOx affords excellent stability with insignificant potential degradation after 500 h of electrolysis at 10 mA cm-2, originating from the low operating potential and suppressed dissolution and oxidation of oxygen vacancy active sites via Ta doping. Density functional theory calculations suggest that Ta doping and oxygen defect engineering are effective in facilitating the nucleophilic attack of water molecules, thereby accelerating the rate-determining step toward high catalytic OER activity on Ta-doped IrOx. We anticipate that this study will provide an effective method to obtain active and stable electrocatalysts via high-valence metal doping.

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Enhanced electrocatalytic glycerol oxidation on CuCoN0.6/CP at significantly reduced potentials Kai Shi, Di Si, Xue Teng, Lisong Chen, Jianlin Shi 2023, 53:  143-152.  DOI: 10.1016/S1872-2067(23)64515-2 Abstract ( 330 )   HTML ( 7 )   PDF (2020KB) ( 140 )   Supporting Information Electrocatalytic alcohol oxidation coupled with the hydrogen evolution reaction, wherein a thermodynamically favorable oxidation reaction replaces the sluggish kinetics of the oxygen evolution reaction, has recently attracted considerable attention. However, the development of nonprecious-metal electrocatalysts capable of delivering much lower oxidation potentials holds great significance. In this study, we proposed and developed CuCoN0.6 nanowires loaded on conductive carbon paper (denoted as CuCoN0.6/CP) as an efficient catalyst for selective glycerol oxidation to formate. Our catalyst achieved a remarkably high faradic efficiency of 90.0% towards formate production. More notably, it required an anode potential as low as 1.07 V to achieve a current density of 10 mA cm−2, a significantly lower potential than that reported in the literature. Experimental characterizations reveal that the oxidations of Cu+ and Co2+ ions promoted the formation of reactive hydroxyl species, which are responsible for the substantially reduced oxidation potential and enhanced glycerol oxidation performance. Furthermore, we investigated the reaction pathway of glycerol oxidation and structural changes in the catalysts. The catalyst reconstruction led to the formation of CoOOH, which is considered as the active site for glycerol oxidation. Finally, we successfully separated high-purity and value-added potassium diformate product. This work not only advances the electrocatalytic conversion of biomass-derived alcohols but also provides insights into the design of electrocatalysts with broad applications.

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Engineering a localized electrostatic environment to enhance hydroxyl activating for electrocatalytic biomass conversion Yuxuan Lu, Liu Yang, Yimin Jiang, Zhenran Yuan, Shuangyin Wang, Yuqin Zou 2023, 53:  153-160.  DOI: 10.1016/S1872-2067(23)64516-4 Abstract ( 301 )   HTML ( 12 )   PDF (3278KB) ( 104 )   Supporting Information The 5-hydroxymethylfurfural electrocatalytic oxidation reaction (HMFOR) is a sustainable and efficient route for converting biomass platform molecules into high-value chemicals. The HMFOR process involves the simultaneous oxidation of hydroxyl and aldehyde groups. Optimizing the reaction pathways by modulating the adsorption behavior of 5-Hydroxymethylfurfural molecules toward a higher conversion rate is vital for achieving an efficient HMFOR. In this study, the HMFOR electrocatalytic performance of NiO was enhanced by regulating the surface microenvironment through the decoration of NiO nanosheets with polypyrrole (PPy). Operando Fourier transform infrared spectroscopy, density functional theory calculation, and electrochemical behavior characterizations demonstrated that electropositive PPy can optimize the adsorption behavior of electronegative hydroxyl groups and modulate the reaction pathway toward the formation of 2,5-diformylfuran intermediates. By modulating the local microenvironment, the designed NiO-PPy catalyst showed excellent HMFOR performance with a threefold increase in current density. This study emphasizes the significance of the surface microenvironment in modulating reaction pathways to achieve selective biomass electrocatalytic conversion.

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Relay catalysis for conversion of secondary amine to formamide Dongxia Jiao, Jinghua An, Huixiang Li, Zhipeng Huang, Yehong Wang, Feng Wang 2023, 53:  161-170.  DOI: 10.1016/S1872-2067(23)64518-8 Abstract ( 186 )   HTML ( 8 )   PDF (1053KB) ( 49 )   Supporting Information The direct formylation of amines with CO is an ideal way to produce formamides with 100% atom economy. However, the conversion of secondary amines via this process remains a great challenge owing to their low reactivity. In this study, a relay catalysis strategy was developed to lower the activation energy of dimethylamine to N,N′-dimethyl formaldehyde (DMF) over a Ru-hydroxyapatite (Ru-HAP) catalyst, with methylamine as a promoter. Through the relay catalysis of RuOx and HAP, the formylation of dimethylamine consists of two steps: (1) efficient direct formylation of methylamine with CO to produce the active intermediate methylformamide (MF) over RuOx species owing to its low activation energy, and (2) transformylation reaction of dimethylamine with the generated MF to produce DMF under the acid-base catalysis of HAP. Up to 82% yield of DMF was achieved, which is much higher than that with direct formylation of dimethylamine (32%). In addition, the lower environmental impact factor suggested that the relay catalysis strategy not only decreased the waste of DMF production, but also lowered the energy consumption for separation. This study presents a new path for the conversion of secondary amines to formamides.

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In situ monitoring multi-carbon alcohol oxidation by combined electrochemistry with spatially selective NMR spectroscopy Haolin Zhan, Lifei Ji, Shuohui Cao, Ye Feng, Yanxia Jiang, Yuqing Huang, Shigang Sun, Zhong Chen 2023, 53:  171-179.  DOI: 10.1016/S1872-2067(23)64526-7 Abstract ( 245 )   HTML ( 5 )   PDF (2599KB) ( 72 )   Supporting Information In situ electrochemical nuclear magnetic resonance (EC-NMR) plays a pivotal role in electrochemical observation on liquid fuel cells, but its applications are generally trapped by insufficient spectral resolution caused by spatiotemporal variations of magnetic fields. Herein, we develop a general spectroelectrochemistry protocol to address this problem and facilitate real-time electrooxidation analyses. This protocol enables the direct extraction of well-resolved and undistorted NMR signals from standard NMR instruments, thus it is commonly applicable to in situ electrochemical studies. The effectiveness for electrooxidation mechanism investigations on multi-carbon alcohols is validated by 1-butanol electrooxidation. It is verified that the direct oxidation of 1-butanol to butyric acid becomes more significant along with higher potentials on Pt/C at 60 °C, while 1-butanol oxidation is more likely to yield gaseous products (mainly CO2) at lower potentials. Additionally, this protocol reveals that Pt/C rather than PtRu/C is inclined to accomplish the β-C-H bond breaking process for CO2 generation at a high potential of 1.2 V (vs. SCE). Therefore, this study provides a promising paradigm for electrooxidation investigations on fuel cells, and it may take a meaningful step toward wider electrochemical studies and NMR applications.