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    Chinese Journal of Catalysis
    2019, Vol. 40, No. 2
    Online: 28 February 2019

    Cover:

    Electrocatalytic ammonia synthesis under mild conditions offers an attractive and challenging process, but requires efficient and stable catalysts to reduce overpotential. Prof. Wang and co-authors have investigated a series of MXene-supported transition metal monoatomic catalysts in the electrocatalytic synthesis of ammonia by density functional theory. By comparing the Gibbs free energy of the possible potential-determining steps, the overpotential needed for the reaction can be easily obtained.

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    Contents
    Table of Contents for VOL.40 No.2
    2019, 40 (2):  0-0. 
    Abstract ( 130 )   PDF (862KB) ( 291 )  
    Communications
    The origin of the extraordinary stability of mercury catalysts on the carbon support: the synergy effects between oxygen groups and defects revealed from a combined experimental and DFT study
    Jian Li, Jiangtao Fan, Sajjad Ali, Guojun Lan, Haodong Tang, Wenfeng Han, Huazhang Liu, Bo Li, Ying Li
    2019, 40 (2):  141-146.  DOI: 10.1016/S1872-2067(19)63271-7
    Abstract ( 412 )   [Full Text(HTML)] () PDF (580KB) ( 690 )  
    Supporting Information

    Thermal stability of HgCl2 has a pivotal importance for the hydrochlorination reaction as the loss of mercuric compounds is toxic and detrimental to environment. Here we report a low-mercury catalyst which has durability over 10000 h for acetylene hydrochlorination under the industrial condition. The stability of the catalyst is carefully analyzed from a combined experimental and density functional theory study. The analysis shows that the extraordinary stability of mercury catalyst is resulted from the synergy effects between surface oxygen groups and defective edge sites. The binding energy of HgCl2 is increased to be higher than 130 kJ/mol when adsorption is at the edge site with a nearby oxygen group. Therefore, the present study revealed that the thermal stability problem of mercury-based catalyst can be solved by simply adjusting the surface chemistry of activated carbon. Furthermore, the reported catalyst has already been successfully applied in the commercialized production of vinyl chloride.

    Highly active and stable porous polymer heterogenous catalysts for decomposition of formic acid to produce H2
    Yan Zhang, Yuan Lyu, Yuqing Wang, Cunyao Li, Miao Jiang, Yunjie Ding
    2019, 40 (2):  147-151.  DOI: 10.1016/S1872-2067(19)63275-4
    Abstract ( 195 )   [Full Text(HTML)] () PDF (588KB) ( 432 )  
    Supporting Information

    Formic acid (FA) has attracted extensive attention as a hydrogen storage material. Here, we develop two heterogeneous catalysts based on porous organic polymers (POPs). After loading the Ru species, the catalyst bearing the triphenylphosphine ligand showed excellent performance in terms of activity and stability for the decomposition of FA to produce hydrogen.

    Articles
    A theoretical study of electrocatalytic ammonia synthesis on single metal atom/Mxene
    Yijing Gao, Han Zhuo, Yongyong Cao, Xiang Sun, Guilin Zhuang, Shengwei Deng, Xing Zhong, Zhongzhe Wei, Jianguo Wang
    2019, 40 (2):  152-159.  DOI: 10.1016/S1872-2067(18)63197-3
    Abstract ( 461 )   [Full Text(HTML)] () PDF (3042KB) ( 1399 )  
    Supporting Information

    Electrocatalytic ammonia synthesis under mild conditions is an attractive and challenging process in the earth's nitrogen cycle, which requires efficient and stable catalysts to reduce the overpotential. The N2 activation and reduction overpotential of different Ti3C2O2-supported transition metal (TM) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Ag, Cd, and Au) single-atom catalysts have been analyzed in terms of the Gibbs free energies calculated using the density functional theory (DFT). The end-on N2 adsorption was more energetically favorable, and the negative free energies represented good N2 activation performance, especially in the presence Fe/Ti3C2O2 (-0.75 eV). The overpotentials of Fe/Ti3C2O2, Co/Ti3C2O2, Ru/Ti3C2O2, and Rh/Ti3C2O2 were 0.92, 0.89, 1.16, and 0.84 eV, respectively. The potential required for ammonia synthesis was different for different TMs and ranged from 0.68 to 2.33 eV. Two possible potential-limiting steps may be involved in the process:(i) hydrogenation of N2 to *NNH and (ii) hydrogenation of *NH2 to ammonia. These catalysts can change the reaction pathway and avoid the traditional N-N bond-breaking barrier. It also simplifies the understanding of the relationship between the Gibbs free energy and overpotential, which is a significant factor in the rational designing and large-scale screening of catalysts for the electrocatalytic ammonia synthesis.

    Integrating non-precious-metal cocatalyst Ni3N with g-C3N4 for enhanced photocatalytic H2 production in water under visible-light irradiation
    Jianhua Ge, Yujie Liu, Daochuan Jiang, Lei Zhang, Pingwu Du
    2019, 40 (2):  160-167.  DOI: 10.1016/S1872-2067(19)63283-3
    Abstract ( 131 )   [Full Text(HTML)] () PDF (1404KB) ( 486 )  

    Photocatalytic H2 production via water splitting in a noble-metal-free photocatalytic system has attracted much attention in recent years. In this study, noble-metal-free Ni3N was used as an active cocatalyst to enhance the activity of g-C3N4 for photocatalytic H2 production under visible-light irradiation (λ > 420 nm). The characterization results indicated that Ni3N nanoparticles were successfully loaded onto the g-C3N4, which accelerated the separation and transfer of photogenerated electrons and resulted in enhanced photocatalytic H2 evolution under visible-light irradiation. The hydrogen evolution rate reached~305.4 μmol h-1 g-1, which is about three times higher than that of pristine g-C3N4, and the apparent quantum yield (AQY) was~0.45% at λ=420. Furthermore, the Ni3N/g-C3N4 photocatalyst showed no obvious decrease in the hydrogen production rate, even after five cycles under visible-light irradiation. Finally, a possible photocatalytic hydrogen evolution mechanism for the Ni3N/g-C3N4 system is proposed.

    Highly enhanced visible-light photocatalytic hydrogen evolution on g-C3N4 decorated with vopc through π-π interaction
    Yanan Liu, Liubo Ma, Congcong Shen, Xin Wang, Xiao Zhou, Zhiwei Zhao, Anwu Xu
    2019, 40 (2):  168-176.  DOI: 10.1016/S1872-2067(18)63191-2
    Abstract ( 229 )   [Full Text(HTML)] () PDF (571KB) ( 721 )  
    Supporting Information

    Photocatalytic H2 evolution reactions on pristine graphitic carbon nitrides (g-C3N4), as a promising approach for converting solar energy to fuel, are attractive for tackling global energy concerns but still suffer from low efficiencies. In this article, we report a tractable approach to modifying g-C3N4 with vanadyl phthalocyanine (VOPc/CN) for efficient visible-light-driven hydrogen production. A non-covalent VOPc/CN hybrid photocatalyst formed via π-π stacking interactions between the two components, as confirmed by analysis of UV-vis absorption spectra. The VOPc/CN hybrid photocatalyst shows excellent visible-light-driven photocatalytic performance and good stability. Under optimal conditions, the corresponding H2 evolution rate is nearly 6 times higher than that of pure g-C3N4. The role of VOPc in promoting hydrogen evolution activity was to extend the visible light absorption range and prevent the recombination of photoexcited electron-hole pairs effectively. It is expected that this facile modification method could be a new inspiration for the rational design and exploration of g-C3N4-based hybrid systems with strong light absorption and high-efficiency carrier separation.

    Synthesis of spiropyrrolidine oxindoles through Rh(II)-catalyzed olefination/cyclization of diazooxindoles and vinyl azides
    Ruxia Yi, Leilei Qian, Boshun Wan
    2019, 40 (2):  177-183.  DOI: 10.1016/S1872-2067(18)63200-0
    Abstract ( 162 )   [Full Text(HTML)] () PDF (452KB) ( 552 )  

    A simple and efficient process involving the Rh(Ⅱ)-catalyzed[1+1+3] annulation of diazooxindoles and vinyl azides has been developed for the synthesis of spiropyrrolidine oxindoles with potential biological activity and significant synthetic applications. This process involves a novel rhodium-catalyzed olefination of diazo compounds, followed by annulation with vinyl azides. This method is compatible with a broad range of substrates and affords moderate to good yields under mild reaction conditions.

    Rod-shaped porous alumina-supported Cr2O3 catalyst with low acidity for propane dehydrogenation
    Xin-Qian Gao, Wen-Duo Lu, Shou-Zhao Hu, Wen-Cui Li, An-Hui Lu
    2019, 40 (2):  184-191.  DOI: 10.1016/S1872-2067(18)63202-4
    Abstract ( 222 )   [Full Text(HTML)] () PDF (983KB) ( 872 )  
    Supporting Information

    Direct catalytic propane dehydrogenation (PDH) to obtain propylene is a more economical and environmentally friendly route for propylene production. In particular, alumina-supported Cr2O3 catalysts can have better potential applications if the acidic properties could be tuned. Herein, a series of rod-shaped porous alumina were prepared through a hydrothermal route, followed by calcination. It was found that the acidity of the synthesized alumina was generally lower than that of the commercial alumina and could be adjusted well by varying the calcination temperature. Such alumina materials were used as supports for active Cr2O3, and the obtained catalysts could enhance the resistance to coke formation associated with similar activity in PDH reaction compared to the commercial alumina. The amount of coke deposited on a self-made catalyst (Cr-Al-800) was 3.6%, which was much lower than that deposited on the reference catalyst (15.7%). The lower acidity of the catalyst inhibited the side reactions and coke formation during the PDH process, which was beneficial for its high activity and superior anti-coking properties.

    Effective production of γ-valerolactone from biomass-derived methyl levulinate over CuOx-CaCO3 catalyst
    Xuejuan Cao, Huai Liu, Junnan Wei, Xing Tang, Xianhai Zeng, Yong Sun, Tingzhou Lei, Geng Zhao, Lu Lin
    2019, 40 (2):  192-203.  DOI: 10.1016/S1872-2067(19)63270-5
    Abstract ( 271 )   [Full Text(HTML)] () PDF (1262KB) ( 469 )  
    Supporting Information

    The production of γ-valerolactone (GVL) from lignocellulosic biomass has become a focus of research owing to its potential applications in fuels and chemicals. In this study, (n)CuOx-CaCO3 (where n is the molar ratio of Cu to Ca) compounds were prepared for the first time and shown to function as efficient bifunctional catalysts for the conversion of biomass-derived methyl levulinate (ML) into GVL, using methanol as the in-situ hydrogen source. Among the catalysts with varied Cu/Ca molar ratios, (3/2)CuOx-CaCO3 provided the highest GVL yield of 95.6% from ML. The incorporation of CaCO3 with CuO resulted in the formation of Cu+ species in a CuOx-CaCO3 catalyst, which greatly facilitated the hydrogenation of ML. Notably, CuOx-CaCO3 also displayed excellent catalytic performance in the methanolysis products of cellulose, even in the presence of humins. Therefore, a facile two-step strategy for the production of GVL from cellulose could be developed over this robust and inexpensive catalyst, through the integration of cellulose methanolysis catalyzed by sulfuric acid, methanol reforming, and ML hydrogenation in methanol medium.

    Interface-controlled synthesis of CeO2(111) and CeO2(100) and their structural transition on Pt(111)
    Yi Zhang, Wei Feng, Fan Yang, Xinhe Bao
    2019, 40 (2):  204-213.  DOI: 10.1016/S1872-2067(18)63171-7
    Abstract ( 196 )   [Full Text(HTML)] () PDF (1358KB) ( 811 )  

    Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties. To obtain a molecular-level understanding of their surface chemistry, controlled synthesis of ceria with well-defined surface structures is required. We have thus studied the growth of CeOx nanostructures (NSs) and thin films on Pt(111). The strong metal-oxide interaction has often been invoked to explain catalytic processes over the Pt/CeOx catalysts. However, the Pt-CeOx interaction has not been understood at the atomic level. We show here that the interfacial interaction between Pt and ceria could indeed affect the surface structures of ceria, which could subsequently determine their catalytic chemistry. While ceria on Pt(111) typically exposes the CeO2(111) surface, we found that the structures of ceria layers with a thickness of three layers or less are highly dynamic and dependent on the annealing temperatures, owing to the electronic interaction between Pt and CeOx. A two-step kinetically limited growth procedure was used to prepare the ceria film that fully covers the Pt(111) substrate. For a ceria film of~3-4 monolayer (ML) thickness on Pt(111), annealing in ultrahigh vacuum (UHV) at 1000 K results in a surface of CeO2 (100), stabilized by a c-Ce2O3(100) buffer layer. Further oxidation at 900 K transforms the surface of the CeO2(100) thin film into a hexagonal CeO2(111) surface.

    Synergism of Pt nanoparticles and iron oxide support for chemoselective hydrogenation of nitroarenes under mild conditions
    Pei Jing, Tao Gan, Hui Qi, Bin Zheng, Xuefeng Chu, Guiyang Yu, Wenfu Yan, Yongcun Zou, Wenxiang Zhang, Gang Liu
    2019, 40 (2):  214-222.  DOI: 10.1016/S1872-2067(19)63276-6
    Abstract ( 189 )   [Full Text(HTML)] () PDF (642KB) ( 569 )  
    Supporting Information

    An efficient and low-cost supported Pt catalyst for hydrogenation of niroarenes was prepared with colloid Pt precursors and α-Fe2O3 as a support. The catalyst with Pt content as low as 0.2 wt% exhibits high activities, chemoselectivities and stability in the hydrogenation of nitrobenzene and a variety of niroarenes. The conversion of nitrobenzene can reach 3170 molconv h-1 molPt-1 under mild conditions (30℃, 5 bar), which is much higher than that of commercial Pt/C catalyst and many reported catalysts under similar reaction conditions. The spatial separation of the active sites for H2 dissociation and hydrogenation should be responsible for the high chemoselectivity, which decreases the contact possibility between the reducible groups of nitroarenes and Pt nanoparticles. The unique surface properties of α-Fe2O3 play an important role in the reaction process. It provides active sites for hydrogen spillover and reactant adsorption, and ultimately completes the hydrogenation of the nitro group on the catalyst surface.