Chinese Journal of Catalysis
2022, Vol. 43, No. 8
Online: 18 August 2022

Cover: Shi and coworkers in their review on pages 1964–1990 highlight the utmost importance of hydrogen-bonding interactions and interfacial ionic species as the main factors underlying acid-base catalysis and the associated solvation effects at the solid-aqueous interfaces.
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Special column on surface & interface chemistry connecting thermo-,photo- and electro-catalysis
Preface to special column on surface & interface chemistry connecting thermo-, photo- and electro-catalysis
Weixin Huang, Fan Yang
2022, 43 (8):  1963-1963.  DOI: 10.1016/S1872-2067(22)64135-4
Abstract ( 6 )   HTML ( 1 )   PDF (473KB) ( 2 )  
A critical assessment of the roles of water molecules and solvated ions in acid-base-catalyzed reactions at solid-water interfaces
Xugang Yang, Zonghui Liu, Guoliang Wei, Yu Gu, Hui Shi
2022, 43 (8):  1964-1990.  DOI: 10.1016/S1872-2067(21)64032-9
Abstract ( 37 )   HTML ( 1 )   PDF (5824KB) ( 18 )  

Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems. When it comes to heterogeneous catalysis, however, our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive. This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts, and critically assesses the general and special roles of water molecules, structural moieties derived from water, and ionic species that are dissolved in it, with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase. For alcohol dehydration catalyzed by solid Brønsted acids, rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized. Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption, but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water. For aldol condensation on catalysts exposing Lewis acid-base pairs, the addition of water is generally observed to enhance the rate when C-C coupling is rate-limiting, but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting. Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions. For metallozeolite-catalyzed sugar isomerization in aqueous media, the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states. The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water. A perspective is also provided for future research in this vibrant field.

Special column on surface & interface chemistry connecting thermo-,photo- and electro-catalysis
Selectivity control in alkyne semihydrogenation: Recent experimental and theoretical progress
Xiao-Tian Li, Lin Chen, Cheng Shang, Zhi-Pan Liu
2022, 43 (8):  1991-2000.  DOI: 10.1016/S1872-2067(21)64036-6
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Researchers have been attempting to characterize heterogeneous catalysts in situ in addition to correlating their structures with their activity and selectivity in spite of many challenges. Here, we review recent experimental and theoretical advances regarding alkyne selective hydrogenation by Pd-based catalysts, which are an important petrochemical reaction. The catalytic selectivity for the reaction of alkynes to alkenes is influenced by the composition and structure of the catalysts. Recent progress achieved through experimental studies and atomic simulations has provided useful insights into the origins of the selectivity. The important role of the subsurface species (H and C) was revealed by monitoring the catalyst surface and the related catalytic performance. The atomic structures of the Pd catalytic centers and their relationship with selectivity were established through atomic simulations. The combined knowledge gained from experimental and theoretical studies provides a fundamental understanding of catalytic mechanisms and reveals a path toward improved catalyst design.

Applications of in-situ wide spectral range infrared absorption spectroscopy for CO oxidation over Pd/SiO2 and Cu/SiO2 catalysts
Xuefei Weng, Shuangli Yang, Ding Ding, Mingshu Chen, Huilin Wan
2022, 43 (8):  2001-2009.  DOI: 10.1016/S1872-2067(21)64054-8
Abstract ( 15 )   HTML ( 1 )   PDF (1172KB) ( 4 )  
Supporting Information

Infrared (IR) absorption spectroscopy has been widely used for dynamic characterization of catalysts and mechanism of catalytic reactions. However, due to the strong infrared absorption of heterogeneous catalysts (mainly oxides, or supported metal and metal oxides, etc.) below 1200 cm-1, and the intensity of regular infrared light source rapidly decays at low-wavenumber range, most in-situ infrared spectroscopy studies are limited to the detection of surface adsorbates in the range of 4000-900 cm-1. The change of catalytically active component itself (M-O, M-M bond, etc., 1200-50 cm-1) during the reaction is hard to be tracked under reaction conditions by in-situ IR. In this work, a home-made in-situ IR reactor was designed and a sample preparing method was developed. With such progresses, the changes of reactants, products, surface adsorbates, and catalysts themselves can be measured under the same reaction conditions with a spectral range of 4000-400 cm-1, providing a new opportunity for in-situ characterization of heterogeneous catalysis. CO oxidation on Pd/SiO2 and Cu/SiO2 catalysts were taken as examples, since both the two catalytic systems were extensively used commercially, and moreover reduction and oxidation of palladium and copper occur during the examined reaction conditions. The characteristic bands of Pd2+-O (670, 608 cm-1), Cu+-O (635 cm-1) and Cu2+-O (595, 535 cm-1) were observed by IR, and the changes during CO oxidation reaction were successfully monitored by IR. The oxidation/reduction of palladium and copper were also confirmed by ex-situ XPS. Moreover, Pd0 in Pd/SiO2 and Cu+ in Cu/SiO2 were found as the thermal dynamically stable phases under the examined conditions for CO oxidation.

Direct identification of the carbonate intermediate during water-gas shift reaction at Pt-NiO interfaces using surface-enhanced Raman spectroscopy
Si-Na Qin, Di-Ye Wei, Jie Wei, Jia-Sheng Lin, Qing-Qi Chen, Yuan-Fei Wu, Huai-Zhou Jin, Hua Zhang, Jian-Feng Li
2022, 43 (8):  2010-2016.  DOI: 10.1016/S1872-2067(21)63964-5
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Supporting Information

Noble metal-reducible oxide interfaces have been regarded as one of the most active sites for water-gas shift reaction. However, the molecular reaction mechanism of water-gas shift reaction at these interfaces still remains unclear. Herein, water-gas shift reaction at Pt-NiO interfaces has been in-situ explored using surface-enhanced Raman spectroscopy by construction of Au@Pt@NiO nanostructures. Direct Raman spectroscopic evidence demonstrates that water-gas shift reaction at Pt-NiO interfaces proceeds via an associative mechanism with the carbonate species as a key intermediate. The carbonate species is generated through the reaction of adsorbed CO with gaseous water, and its decomposition is a slow step in water-gas shift reaction. Moreover, the Pt-NiO interfaces would promote the formation of this carbonate intermediate, thus leading to a higher activity compared with pure Pt. This spectral information deepens the fundamental understanding of the reaction mechanism of water-gas shift reaction, which would promote the design of more efficient catalysts.

Probing active species for CO hydrogenation over ZnCr2O4 catalysts
Yunjian Ling, Yihua Ran, Weipeng Shao, Na Li, Feng Jiao, Xiulian Pan, Qiang Fu, Zhi Liu, Fan Yang, Xinhe Bao
2022, 43 (8):  2017-2025.  DOI: 10.1016/S1872-2067(21)64008-1
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Supporting Information

Oxide catalysts are increasingly employed for hydrogenation reactions, among which ZnCrOx is a major catalyst for the oxide-zeolite (OXZEO) process and for the hydrogenation of C1 molecules in general. Owing to the complex nature of ternary oxides, the surface and catalytic properties of ZnCr2O4 spinel have remained controversial for CO hydrogenation. Combining in-situ Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy, we examined the adsorption and reaction of CO/H2 on the ZnCr2O4 catalysts, which were pre-treated under oxidative or reductive conditions. The reduced ZnCr2O4 catalyst was found to expose more surface sites for CO adsorption/reaction than the oxidized ZnCr2O4 catalyst. Exposing the reduced ZnCr2O4 to H2 at room temperature led to the formation of surface hydride species, which would transform into hydroxyl species at elevated temperatures. The reduced ZnCr2O4 surface exhibited much stronger interaction with CO and H2 than ZnO and Cr2O3. Exposing the reduced ZnCr2O4 to the CO and H2 (1:1) mixture gas led to the hydrogenation of CO. However, CO was oxidized by the hydroxyl species via the water-gas-shift reaction, whereas the hydrogenation of CO could only be achieved by surface hydride species on the reduced ZnCr2O4 to formyl or formate species at 373-473 K. Our study has thus shed light on the active species that control elementary reaction process of CO hydrogenation on complex oxide surfaces.

Reversible transformation between terrace and step sites of Pt nanoparticles on titanium under CO and O2 environments
Yang Ou, Songda Li, Fei Wang, Xinyi Duan, Wentao Yuan, Hangsheng Yang, Ze Zhang, Yong Wang
2022, 43 (8):  2026-2033.  DOI: 10.1016/S1872-2067(21)63958-X
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Supporting Information

Understanding the dynamic evolution of active sites of supported metal catalysts during catalysis is fundamentally important for improving its performance, which attracts tremendous research interests in the past decades. There are two main surficial structures for metal catalysts: terrace sites and step sites, which exhibit catalytic activity discrepancy during catalysis. Herein, by using in situ transmission electron microscopy and in situ Fourier transform infrared spectroscopy (FTIR), the transformation between surface terrace and step sites of Pt-TiO2 catalysts was studied under CO and O2 environments. We found that the {111} step sites tend to form at {111} terrace under O2 environment, while these step sites prefer to transform into terrace under CO environment at elevated temperature. Meanwhile, quantitative ratios of terrace/step sites were obtained by in situ FTIR. It was found that this transformation between terrace sites and step sites was reversible during gas treatment cycling of CO and O2. The selective adsorption of O2 and CO species at different sites, which stabilized the step/terrace sites, was found to serve as the driving force for active sites transition by density functional theory calculations. Inspired by the in situ results, an enhanced catalytic activity of Pt-TiO2 catalysts was successfully achieved through tuning surface-active sites by gas treatments.

Boosting chiral carboxylic acid hydrogenation by tuning metal-MOx-support interaction in Pt-ReOx/TiO2 catalysts
Guang Gao, Zelun Zhao, Jia Wang, Yongjie Xi, Peng Sun, Fuwei Li
2022, 43 (8):  2034-2044.  DOI: 10.1016/S1872-2067(21)64021-4
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Supporting Information

Engineering the surface microenvironment by tuning the binary interactions between a supported metal with a secondary metal oxide (MOx) or support has been a common method for improving the catalytic performance of supported metal catalysts. However, few studies have investigated the ternary interactions among the metal, MOx, and support. Here, we report for the first time the formation of metal-MOx-support interaction (MMSI) in reducible TiO2-supported PtReOx catalysts, affording 87% yield and 100% ee in the tandem hydrogenation of an aqueous chiral cyclohexane-1,2-dicarboxylic acid into the corresponding diol; the catalytic activity is eight times higher than that obtained with non-reducible support counterparts in the same reaction via traditional batch synthesis with multiple steps and unfriendly reagents. Detailed experimental and computational studies suggest that the TiO2 crystalline phase-dependent density of the oxygen vacancies induces different Pt-ReOx-TiO2 interactions, which dominate the electron transfer therein and tune the adsorption strength of the carbonyl moiety of the substrate/intermediate, thus promoting the hydrogenation activity and selectivity. In addition, the strong MMSI endows the optimal rutile TiO2 supported PtReOx catalyst with an outstanding lifetime of 400 h in a fixed-bed reactor under acidic aqueous conditions and ensures efficient applications in the selective hydrogenation of aliphatic dicarboxylic acids and functional carboxylic acids. This work provides a promising strategy for the development of efficient and stable supported catalysts for the selective hydrogenation of diverse C-O and C=O bonds.

Direct carbon dioxide hydrogenation to produce bulk chemicals and liquid fuels via heterogeneous catalysis
Zixuan Zhou, Peng Gao
2022, 43 (8):  2045-2056.  DOI: 10.1016/S1872-2067(22)64107-X
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The hydrogenation of carbon dioxide (CO2) to produce chemicals and transportation liquid fuels in huge demand via heterogeneous thermochemical catalysis achieved using renewable energy has received increasing attention, and substantial advances have been made in this research field in recent years. In this study, we summarize our progress in the rational design and construction of highly efficient catalysts for CO2 hydrogenation to methanol, lower olefins, aromatics, and gasoline- and jet fuel-range hydrocarbons. The structure-performance relationship, nature of the active sites, and mechanism of the reactions occurring over these catalysts are explored by combining computational and experimental evidence. The results of this study will promote further fundamental studies and industrial applications of heterogeneous catalysts for CO2 hydrogenation to produce bulk chemicals and liquid fuels.

MXenes for electrocatalysis applications: Modification and hybridization
Xue Bai, Jingqi Guan
2022, 43 (8):  2057-2090.  DOI: 10.1016/S1872-2067(21)64030-5
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Two-dimensional carbides, nitrides, and carbonitrides (MXenes) play important roles in promoting the development of sustainable energy because they have abundant reactive sites on their surfaces. An increasing number of MXenes with diverse elements and composites have been predicted and synthesized for electrocatalysis applications since the first report of a Ti-Mo-based MXene for the hydrogen evolution reaction (HER). Herein, we summarize the progress of MXene-based electrocatalysts for the HER, the oxygen evolution reaction, and the oxygen reduction reaction, including regulated pristine MXenes and modified hybrid MXenes, from both theoretical and experimental perspectives. A brief overview on MXene synthesis is presented first, accompanied by a discussion on the relationship between electrocatalytic properties and M, X, T, vacancies, and morphologies. After reviewing strategies in terms of atom substitution, functional modification, defect engineering, and morphology control, we emphasize the construction of heterojunctions between MXenes and other nanostructures, such as metal nanoparticles, oxides, hydroxides, sulfides, and phosphides. We finally discuss prospects for the future development of MXene-based electrocatalysts.

Roles of heteroatoms in electrocatalysts for alkaline water splitting: A review focusing on the reaction mechanism
Chuqiang Huang, Jianqing Zhou, Dingshuo Duan, Qiancheng Zhou, Jieming Wang, Bowen Peng, Luo Yu, Ying Yu
2022, 43 (8):  2091-2110.  DOI: 10.1016/S1872-2067(21)64052-4
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Alkaline water splitting is a promising technology for “green hydrogen” generation. To improve its efficiency, highly robust catalysts are required to reduce the overpotential for low electrical power consumption. Heteroatom modification is one of the most effective strategies for boosting catalytic performance, as it can regulate the physicochemical properties of host catalysts to improve their intrinsic activity. Herein, aiming to provide an overview of the impact of heteroatoms on catalytic activity at the atomic level, we present a review of the key role of heteroatoms in enhancing reaction kinetics based on the reaction pathways of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. In particular, the introduction of heteroatoms can directly and indirectly optimize the interactions between the active sites and intermediates, thus improving the intrinsic activity. To clearly illustrate this influence in detail, we have summarized a series of representative heteroatom-modified electrocatalysts and discussed the important roles of heteroatoms in the OER and HER reaction pathways. Finally, some challenges and perspectives for heteroatom-modified electrodes are discussed. We hope that this review will be helpful for the development of efficient and low-cost electrocatalysts for water electrolysis and other energy conversion applications.

Inorganic-organic hybrid photocatalysts: Syntheses, mechanisms, and applications
Hui Yang, Kai Dai, Jinfeng Zhang, Graham Dawson
2022, 43 (8):  2111-2140.  DOI: 10.1016/S1872-2067(22)64096-8
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Inorganic-organic hybrid materials are promising for application in the field of photocatalysis because of their excellent properties. Therefore, their syntheses, mechanisms, and applications are reviewed in this paper. First, we introduce the role of inorganic-organic photocatalysts, their advantages and disadvantages, and their design principles. Second, we present the top-down and bottom-up synthesis methods of the hybrid materials. The interaction between inorganic and organic components in hybrid materials is discussed, followed by how to improve inorganic-organic photocatalysts. Third, the applications of hybrid materials in the field of photocatalysis, such as realizing hydrogen evolution, organic pollutant degradation, heavy metals and CO2 reduction, sterilization, and nitrogen fixation, are examined. Finally, the application prospects and development directions of inorganic-organic hybrid materials are explored and the unsolved problems are described.

Bio-inspired nanostructured g-C3N4-based photocatalysts: A comprehensive review
Bo Lin, Mengyang Xia, Baorong Xu, Ben Chong, Zihao Chen, Guidong Yang
2022, 43 (8):  2141-2172.  DOI: 10.1016/S1872-2067(22)64110-X
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As a new organic conjugated semiconductor, graphitic carbon nitride (g-C3N4) is emerging as a fascinating material for various photocatalytic applications due to its adjustable electronic structure, outstanding thermal endurance, appealing chemical stability, low cost, and environmental friendliness. Nevertheless, unmodified bulk g-C3N4 possesses some intrinsic limitations related to poor crystallinity, marginal visible-light harvesting, easy recombination of charge pairs, small surface area, and slow charge migration, which give rise to the low quantum efficiency of photocatalytic reactions. One efficient strategy to overcome these shortcomings is the manipulation of the microstructures of g-C3N4. Other than the traditional structure control, mimicking the structures of creatures in nature to design and construct bio-inspired structures is a promising approach to improve the photocatalytic performance of g-C3N4 and even g-C3N4-based systems. This review summarizes the recent advances of the traditional structure-control of g-C3N4-based systems, and bio-inspired synthesis of g-C3N4-based systems from two aspects of structural bionics and functional bionics. Furthermore, the fundamentals of bio-inspired design and fabrication of g-C3N4-based systems are introduced in detail. Additionally, the different theoretical calculations, diverse photocatalytic applications and various modification strategies of bio-inspired structured g-C3N4-based systems are recapped. We believe that this work will be a guiding star for future research in the new field of biomimetic photocatalysis.

Oxidative co-dehydrogenation of ethane and propane over h-BN as an effective means for C-H bond activation and mechanistic investigations
Hao Tian, Bingjun Xu
2022, 43 (8):  2173-2182.  DOI: 10.1016/S1872-2067(21)64042-1
Abstract ( 56 )   HTML ( 1 )   PDF (1140KB) ( 18 )  
Supporting Information

Hexagonal boron nitride (h-BN) is a highly selective catalyst for oxidative dehydrogenation of light alkanes to produce the corresponding alkenes. Despite intense recent research effort, many aspects of the reaction mechanism, such as the observed supra-linear reaction order of alkanes, remain unresolved. In this work, we show that the introduction of a low concentration of propane in the feed of ethane oxidative dehydrogenation is able to enhance the C2H6 conversion by 47%, indicating a shared reaction intermediate in the activation of ethane and propane. The higher activity of propane makes it the dominant radical generator in the oxidative co-dehydrogenation of ethane and propane (ODEP). This unique feature of the ODEP renders propane an effective probe molecule to deconvolute the two roles of alkanes in the dehydrogenation chemistry, i.e., radical generator and substrate. Kinetic studies indicate that both the radical generation and the dehydrogenation pathways exhibit a first order kinetics toward the alkane partial pressure, leading to the observed second order kinetics of the overall oxidative dehydrogenation rate. With the steady-state approximation, a radical chain reaction mechanism capable of rationalizing observed reaction behaviors is proposed based on these insights. This work demonstrates the potential of ODEP as a strategy of both activating light alkanes in oxidative dehydrogenation on BN and mechanistic investigations.

Breaking the scaling relations for efficient N2-to-NH3 conversion by a bowl active site design: Insight from LaRuSi and isostructural electrides
Ya-Fei Jiang, Jin-Cheng Liu, Cong-Qiao Xu, Jun Li, Hai Xiao
2022, 43 (8):  2183-2192.  DOI: 10.1016/S1872-2067(22)64129-9
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Supporting Information

The design of optimal heterogeneous catalysts for N2-to-NH3 conversion is often dictated by the scaling relations, which result in a volcano curve that poses a limit on the catalytic performance. Herein, we reveal a bowl active site that can break the scaling relations, through investigating the catalytic mechanisms of N2-to-NH3 conversion on the lanthanide intermetallic electride catalyst LaRuSi by first-principles modeling. This bowl active site, composed of four surface La cations and one subsurface Si atom rich in electrons, plays the key role in enabling efficient catalysis. With adaptive electrostatic and orbital interactions, the bowl active site promotes the adsorption and activation of N2 that delivers facile cleavage of N‒N bond, while destabilizes the adsorptions of *NHx (x = 1, 2, 3) species, which facilitates the release of the final NH3 product. By comparison with other electride catalysts isostructural to LaRuSi, we confirm the breaking of scaling relations between the adsorptions of *NHx species and that of *N on the bowl active site. Thus, this bowl active site presents a design concept that breaks the scaling relations for highly efficient heterogeneous catalysis of N2-to-NH3 conversion.

Modulating the microenvironment structure of single Zn atom: ZnN4P/C active site for boosted oxygen reduction reaction
Syed Shoaib Ahmad Shah, Tayyaba Najam, Jiao Yang, Muhammad Sufyan Javed, Lishan Peng, Zidong Wei
2022, 43 (8):  2193-2201.  DOI: 10.1016/S1872-2067(22)64089-0
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Supporting Information

The electronic structure of catalytic active sites can be influenced by modulating the coordination bonding of the central single metal atom, but it is difficult to achieve. Herein, we reported the single Zn-atom incorporated dual doped P, N carbon framework (Zn-N4P/C) for ORR via engineering the surrounding coordination environment of active centers. The Zn-N4P/C catalyst exhibited comparable ORR activity (E1/2 = 0.86 V) and significantly better ORR stability than that of Pt/C catalyst. It also shows respectable performance in terms of maximum peak power density (249.6 mW cm-2), specific capacitance (779 mAh g-1), and charge-discharge cycling stability for 150 hours in Zn-air battery. The high catalytic activity is attributed to the uniform active sites, tunable electronic/geometric configuration, optimized intrinsic activity, and faster mass transfer during ORR-pathway. Further, theoretical results exposed that the Zn-N4P configuration is more electrochemically active as compared to Zn-N4 structure for the oxygen reduction reaction.

Controllable synthesis of a self-assembled ultralow Ru, Ni-doped Fe2O3 lily as a bifunctional electrocatalyst for large-current-density alkaline seawater electrolysis
Tong Cui, Xuejun Zhai, Lili Guo, Jing-Qi Chi, Yu Zhang, Jiawei Zhu, Xuemei Sun, Lei Wang
2022, 43 (8):  2202-2211.  DOI: 10.1016/S1872-2067(22)64093-2
Abstract ( 20 )   HTML ( 1 )   PDF (9414KB) ( 7 )  
Supporting Information

Highly efficient and stable bifunctional electrocatalysts that can be used for large-current-density electrolysis of alkaline seawater are highly desirable for carbon-neutral economies, but their facile and controllable synthesis remains a challenge. Here, self-assembled ultralow Ru, Ni-doped Fe2O3 with a lily shaped morphology was synthesized on iron foam (RuNi-Fe2O3/IF) via a facile one-step hydrothermal process, in which the intact lily shaped RuNi-Fe2O3/IF was obtained by adjusting the ratio of Ru/Ni. Benefitting from the Ru/Ni chemical substitution, the as-synthesized RuNi-Fe2O3/IF can act as free-standing dual-function electrodes that are applied to electrocatalysis for the hydrogen evolution (HER) and oxygen evolution reactions (OER) in 1.0 mol L‒1 KOH, requiring an overpotential of 75.0 mV to drive 100 mA cm-2 for HER and 329.0 mV for OER. Moreover, the overall water splitting catalyzed by RuNi-Fe2O3/IF only demands ultralow cell voltages of 1.66 and 1.73 V to drive 100 mA cm-2 in 1.0 mol L‒1 KOH and 1.0 mol L‒1 KOH seawater electrolytes, respectively. The electrodes show remarkable long-term durability, maintaining current densities exceeding 100 mA cm-2 for more than 100 h and thus outperforming the two-electrode system composed of noble catalysts. This work provides an efficient, economical method to synthesize self-standing bifunctional electrodes for large-current-density alkaline seawater electrolysis, which is of significant importance for ecological protection and energy exploitation.

N-doped carbon layer-coated Au nanocatalyst for H2-free conversion of 5-hydroxymethylfurfural to 5-methylfurfural
Jiang Zhang, Zijian Wang, Mugeng Chen, Yifeng Zhu, Yongmei Liu, Heyong He, Yong Cao, Xinhe Bao
2022, 43 (8):  2212-2222.  DOI: 10.1016/S1872-2067(21)64049-4
Abstract ( 53 )   HTML ( 0 )   PDF (3652KB) ( 14 )  
Supporting Information

Deoxygenative upgrading of 5-hydromethylfurfural (HMF) into valuable chemicals has attracted intensive research interest in recent years, with product selectivity control remaining an important topic. Herein, TiO2 supported gold catalysts coated with a thin N-doped porous carbon (NPC) layer were developed via a polydopamine-coating-carbonization strategy and utilized for pathway-specific conversion of HMF into 5-methylfurfural (5-MF) with the use of renewable formic acid (FA) as the deoxygenation reagent. The as-fabricated Au/TiO2@NPC exhibited excellent catalytic performance with a high yield of 5-MF (>95%). The catalytic behavior of Au@NPC-based catalysts was shown to be correlated with the suitable combination of highly dispersed Au nanoparticles and favorable interfacial interactions in the Au@NPC core-shell hetero-nanoarchitectures, thereby facilitating the preferential esterification of HMF with FA and suppressing unproductive FA dehydrogenation, which promoted the selective formylation/decarboxylation of hydroxy-methyl group in HMF in a pathway-specific manner. The present NPC/metal interfacial engineering strategy may provide a potential guide for the rational design of advanced catalysts for a wide variety of heterogeneous catalysis processes in terms of the conversion of biomass source.

Water oxidation sites located at the interface of Pt/SrTiO3 for photocatalytic overall water splitting
Xianwen Zhang, Zheng Li, Taifeng Liu, Mingrun Li, Chaobin Zeng, Hiroaki Matsumoto, Hongxian Han
2022, 43 (8):  2223-2230.  DOI: 10.1016/S1872-2067(21)64048-2
Abstract ( 23 )   HTML ( 0 )   PDF (6341KB) ( 10 )  
Supporting Information

When a proton reduction cocatalyst is loaded on an n-type semiconductor for photocatalytic overall water splitting (POWS), the location of water oxidation sites is generally considered at the surface of the semiconductor due to upward band-bending of n-type semiconductor which may ease the transfer of the photogenerated holes to the surface. However, this is not the case for Pt/SrTiO3, a model semiconductor based photocatalyst for POWS. It was found that the photogenerated holes are more readily accumulated at the interface between Pt cocatalyst and SrTiO3 photocatalyst as probed by photo-oxidative deposition of PbO2, indicating that the water oxidation sites are located at the interface between Pt and SrTiO3. Electron paramagnetic resonance and scanning transmission electron microscope studies suggest that the interfacial oxygen atoms between Pt and SrTiO3 in Pt/SrTiO3 after POWS are more readily lost to form oxygen vacancies upon vacuum heat treatment, regardless of Pt loading by photodeposition or impregnation methods, which may serve as additional support for the location of the active sites for water oxidation at the interface. Density functional theory calculations also suggest that the oxygen evolution reaction more readily occurs at the interfacial sites with the lowest overpotential. These experimental and theoretical studies reveal that the more active sites for water oxidation are located at the interface between Pt and SrTiO3, rather than on the surface of SrTiO3. Hence, the tailor design and control of the interfacial properties are extremely important for the achievement or improvement of the POWS on cocatalyst loaded semiconductor photocatalyst.

Interfacial-interaction-induced fabrication of biomass-derived porous carbon with enhanced intrinsic active sites
Wenjuan Zhang, Pei Jing, Juan Du, Shujie Wu, Wenfu Yan, Gang Liu
2022, 43 (8):  2231-2239.  DOI: 10.1016/S1872-2067(21)64031-7
Abstract ( 32 )   HTML ( 0 )   PDF (4197KB) ( 6 )  
Supporting Information

Carbon catalysis is an attractive metal-free catalytic transformation, and its performance is significantly dependent on the number of accessible active sites. However, owing to the inherent stability of the C-C linkage, only limited active sites at the edge defects of the basal plane can be obtained even after a harsh oxidation treatment. In this study, the concept of interfacial interactions was adopted to propose an efficient strategy to develop highly active carbon catalysts. The alumina/carbon interface formed in situ acted as a cradle for the generation of oxygen-containing functional groups. In the absence of oxidation treatment, the concentration of oxygen-containing functional groups and the specific surface area can reach 1.27 mmol·g-1 and 2340 m2·g-1, respectively, which are significantly higher than those of carbon prepared by traditional hard template methods. This active carbon shows a significant enhancement in catalytic performance in the oxidative coupling of amine to imine, about 22-fold higher than that of a well-known graphite oxide catalyst. Such interfacial interaction strategies are based on sustainable carbon sources and can effectively tune the porous structure of carbon in the micro- and meso-ranges. This conceptual finding offers new opportunities for the development of high-performance carbon-based metal-free catalysts.

Unveiling the active sites of ultrathin Co-Fe layered double hydroxides for the oxygen evolution reaction
Xue Bai, Zhiyao Duan, Bing Nan, Liming Wang, Tianmi Tang, Jingqi Guan
2022, 43 (8):  2240-2248.  DOI: 10.1016/S1872-2067(21)64033-0
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Supporting Information

Two-dimensional layered double hydroxides (LDHs) have been identified as promising electrocatalysts for the oxygen evolution reaction (OER); however, the simple and effective synthesis of high-quality LDHs remains extremely challenging and the active sites have not been clarified. Herein, we report a facile solution-reaction method for preparing an ultrathin (thickness < 2 nm) nonprecious CoFe-based LDH. Co1Fe0.2 LDH delivers a current density of 10 mA cm-2 and a high turnover frequency of 0.082 s-1 per total 3d metal atoms at a low overpotential of 256 mV. Its mass activity is 277.9 A g-1 at an overpotential of 300 mV for the OER. Kinetic studies reveal the Co site as the main active center for the OER. The doped Fe lowers the reaction barrier by accelerating the charge-transfer process. Theoretical calculations reveal that the surface Co sites adjacent to Fe atoms are the active centers for the OER and the subsurface Fe dopants excessively weaken the OH* adsorption, thus increasing the energy barrier of the rate-determining step. This study can guide the rational design of high-performance CoFe-based LDHs for water splitting.

Direct Z-scheme photochemical hybrid systems: Loading porphyrin-based metal-organic cages on graphitic-C3N4 to dramatically enhance photocatalytic hydrogen evolution
Yang Lei, Jian-Feng Huang, Xin-Ao Li, Chu-Ying Lv, Chao-Ping Hou, Jun-Min Liu
2022, 43 (8):  2249-2258.  DOI: 10.1016/S1872-2067(22)64109-3
Abstract ( 24 )   HTML ( 1 )   PDF (2340KB) ( 21 )  
Supporting Information

The rational design of photochemical molecular device (PMD) and its hybrid system has great potential in improving the activity of photocatalytic hydrogen production. A series of Pd6L3 type metal-organic cages, denoted as MOC-Py-M (M = H, Cu, and Zn), are designed for PMDs by combining metalloporphyrin-based ligands with catalytically active Pd2+ centers. These metal-organic cages (MOCs) are first successfully hybridized with graphitic carbon nitride (g-C3N4) to form direct Z-scheme heterogeneous MOC-Py-M/g-C3N4 (M = H, Cu, and Zn) photocatalysts via π-π interactions. Benefiting from its better light absorption ability, the MOC-Py-Zn/g-C3N4 catalyst exhibits high H2 production activity under visible light (10348 μmol g-1 h-1), far superior to MOC-Py-H/g-C3N4 and MOC-Py-Cu/g-C3N4. Moreover, the MOC-Py-Zn/g-C3N4 system obtains an enhanced turn over number (TON) value of 32616 within 100 h, outperforming the homogenous MOC-Py-Zn (TON of 507 within 100 h), which is one of the highest photochemical hybrid systems based on MOC for visible-light-driven hydrogen generation. This confirms the direct Z-scheme heterostructure can promote effective charge transfer, expand the visible light absorption region, and protect the cages from decomposition in MOC-Py-Zn/g-C3N4. This work presents a creative example that direct Z-scheme PMD-based systems for effective and persistent hydrogen generation from water under visible light are obtained by heterogenization approach using homogeneous porphyrin-based MOCs and g-C3N4 semiconductors.

Conversion of methanol to propylene over SAPO-14: Reaction mechanism and deactivation
Ye Wang, Jingfeng Han, Nan Wang, Bing Li, Miao Yang, Yimo Wu, Zixiao Jiang, Yingxu Wei, Peng Tian, Zhongmin Liu
2022, 43 (8):  2259-2269.  DOI: 10.1016/S1872-2067(22)64123-8
Abstract ( 16 )   HTML ( 1 )   PDF (7429KB) ( 7 )  
Supporting Information

Methanol to olefins (MTO) reaction as an important non-oil route to produce light olefins has been industrialized, and received over 80% ethylene plus propylene selectivity. However, to achieve high single ethylene or propylene selectivity towards the fluctuated market demand is still full of challenge. Small-pore SAPO-14 molecular sieve is a rare MTO catalyst exhibiting extra-high propylene selectivity. It provides us a valuable clue for further understanding of the relationship between molecular sieve structure and MTO catalytic performance. In this work, a seconds-level sampling fixed-bed reactor was used to capture real-time product distributions, which help to achieve more selectivity data in response to very short catalytic life of SAPO-14. Changes in product distribution, especially during the low activity stage, reflect valuable information on the reaction pathway. Combined with in situ diffuse reflectance infrared Fourier-transform spectroscopy, in situ ultraviolet Raman measurements and 12C/13C isotopic switch experiments, a reaction pathway evolution from dual cycle to olefins-based cycle dominant was revealed. In addition, the deactivation behaviors of SAPO-14 were also investigated, which revealed that polymethylbenzenes have been the deactivated species in such a situation. This work provides helpful hints on the development of characteristic methanol to propylene (MTP) catalysts.