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    Chinese Journal of Catalysis
    2021, Vol. 42, No. 12
    Online: 18 December 2021

    Cover: This special issue is dedicated to Prof. Qin Xin on the occasion of one year of his passing away. Prof. Xin (1939–2020) had been working in the field of fundamental catalytic research for more than 30 years at Dalian Institute of Chemical Physics, Chinese Academy of Sciences. He made remarkable contributions to the study of molecular adsorption states on catalyst surfaces, spectral characterization of catalysts and the reaction kinetics. He mentored many young scholars.
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    Editorial
    Preface to Special Issue of Chinese Journal of Catalysis in Memory of Professor Qin Xin
    Feng-Shou Xiao, Wenzhen Li
    2021, 42 (12):  2089-2090.  DOI: 10.1016/S1872-2067(21)63906-2
    Abstract ( 111 )   HTML ( 115 )   PDF (666KB) ( 172 )  
    Highlight
    Direct and selective methanation of biomass via oxygen vacancy-mediated catalysis
    Ye Wang
    2021, 42 (12):  2091-2093.  DOI: 10.1016/S1872-2067(21)63914-1
    Abstract ( 93 )   HTML ( 23 )   PDF (1719KB) ( 84 )  
    Reviews
    Electrocatalysts development for hydrogen oxidation reaction in alkaline media: From mechanism understanding to materials design
    Yang Qiu, Xiaohong Xie, Wenzhen Li, Yuyan Shao
    2021, 42 (12):  2094-2104.  DOI: 10.1016/S1872-2067(21)64088-3
    Abstract ( 413 )   HTML ( 27 )   PDF (4283KB) ( 313 )  
    Supporting Information

    Anion exchange membrane (AEM) fuel cells have gained great attention partially due to the advantage of using non-precious metal as catalysts. However, the reaction kinetics of hydrogen oxidation reaction (HOR) is two orders of magnitude slower in alkaline systems than in acid. To understand the slower kinetics of HOR in base, two major theories have been proposed, such as (1) pH dependent hydrogen binding energy as a major descriptor for HOR; and (2) bifunctional theory based on the contributions of both hydrogen and hydroxide adsorption for HOR in alkaline electrolyte. Here, we discuss the possible HOR mechanisms in alkaline electrolytes with the corresponding change in their Tafel behavior. Apart from the traditional Tafel-Volmer and Heyrovsky-Volmer HOR mechanisms, the recently proposed hydroxide adsorption step is also discussed to illustrate the difference in HOR mechanisms in acid and base. We further summarize the representative works of alkaline HOR catalyst design (e.g., precious metals, alloy, intermetallic materials, Ni-based alloys, carbides, nitrides, etc.), and briefly describe their fundamental HOR reaction mechanism to emphasize the difference in elementary reaction steps in alkaline medium. The strategy of strengthening local interaction that facilitates both H2 desorption and Hads + OHads recombination is finally proposed for future HOR catalyst design in alkaline environment.

    Highly selective catalysts for the hydrogenation of alkynols: A review
    Xiao Chen, Chuang Shi, Changhai Liang
    2021, 42 (12):  2105-2121.  DOI: 10.1016/S1872-2067(20)63773-1
    Abstract ( 331 )   HTML ( 12 )   PDF (5879KB) ( 283 )  

    The semi-hydrogenation of alkynols to enols is a crucial process in the production of pharmaceuticals, agrochemicals, fragrances, and flavors that involves a complex set of parallel and consecutive isomerization and hydrogenation reactions and proceeds via several key intermediates. In view of the industrial importance of large-scale enol production through alkynol hydrogenation, various noble and non-noble metal (e.g., Ni and Pd)-based catalysts promoting this transformation have been developed. This paper reviews the design of highly selective catalysts for the semi-hydrogenation of alkynols, focusing on the role of additives, second metals, catalyst supports, and reaction conditions and combining catalytic reaction kinetics with theoretical calculations to establish the reaction mechanism and the decisive factors for boosting selectivity. Finally, a strategy for designing highly efficient and selective catalysts based on the characteristics of aqueous-phase alkynol hydrogenation is proposed.

    In situ spectroscopic insights into the redox and acid-base properties of ceria catalysts
    Xiang Wang, Meijun Li, Zili Wu
    2021, 42 (12):  2122-2140.  DOI: 10.1016/S1872-2067(21)63806-8
    Abstract ( 188 )   HTML ( 14 )   PDF (4017KB) ( 206 )  

    Cerium oxide (ceria) plays an important and fascinating role in heterogeneous catalysis as illustrated by its versatile use as a catalyst, a catalyst support, or a promotor in various oxidation and reduction reactions. Central to these reactions is the rich defect chemistry, facile redox capability, and unusual acid-base properties of ceria. Understanding the unique redox and acid-base properties of ceria is essential to build the structure-catalysis relationship so that improved catalytic functions can be achieved for ceria-based materials. Among the characterization toolbox, spectroscopic approach indisputably stands out for its unparalleled power in offering chemical insights into the surface properties of ceria at atomic and molecular level. In this review, we summarize advances in revealing the redox and acid-base properties of ceria via a variety of spectroscopic methods including optical, X-ray, neutron, electronic and nuclear spectroscopy. Both direct spectroscopy characterization and its coupling with probe molecules are analyzed to illustrate how the nature, strength and density of different surface sites are influenced by the pretreatment, the morphology and size of ceria nanoparticles. Further directions in taking advantage of in situ/operando spectroscopy for better understanding the catalysis of ceria-based materials are proposed in the summary and outlook section.

    Full life cycle characterization strategies for spatiotemporal evolution of heterogeneous catalysts
    Renyang Zheng, Zaiku Xie
    2021, 42 (12):  2141-2148.  DOI: 10.1016/S1872-2067(20)63786-X
    Abstract ( 187 )   HTML ( 8 )   PDF (5329KB) ( 558 )  

    The sustainable development of the chemical industry requires novel and efficient catalysts and catalytic processes, especially eco-friendly and intrinsically safe processes. The idea is to improve the selectivity, activity, and stability of the catalyst in an appropriate reactor. Therefore, it is of great academic and industrial significance to conduct in-situ characterization of a working catalyst while testing its catalytic performance. This is beneficial for a comprehensive study on the dynamic evolution of the catalyst structure under real conditions, deepening the understanding of the structure-performance relationship of catalysts, and providing a scientific basis for the development of future generation catalytic technology. Thus far, it is still a great challenge to realize full life cycle characterization of heterogeneous catalysts from catalyst formation and function to deactivation under real world conditions. In this mini review, we summarize the characterization strategies for heterogeneous catalysts, using zeolite, metal, and metal oxide catalysts as typical examples. The research strategies for the approximation of industrial conditions, multi-scale in-situ characterization devices, and computational modeling of realistic conditions should provide insight for the research and development of industrial catalysis.

    Electrocatalytic H2O2 generation for disinfection
    Yachao Zeng, Gang Wu
    2021, 42 (12):  2149-2163.  DOI: 10.1016/S1872-2067(20)63781-0
    Abstract ( 261 )   HTML ( 17 )   PDF (8405KB) ( 253 )  

    Epidemics are threatening public health and social development. Emerging as a green disinfectant, H2O2 can prevent the breakout of epidemics in migration. Electrochemical H2O2 production powered by renewable electricity provides a clean and decentralized solution for on-site disinfection. This review firstly discussed the efficacy of H2O2 in disinfection. Then necessary fundamental principles are summarized to gain insight into electrochemical H2O2 production. The focus is on exploring pathways to realize a highly efficient H2O2 production. Progress in advanced electrocatalysts, typically single-atom catalysts for the two-electron oxygen reduction reaction (2e- ORR), are highlighted to provide high H2O2 selectivity design strategies. Finally, a rational design of electrode and electrolytic cells is outlined to realize the on-site disinfection. Overall, this critical review contributes to exploiting the potentials and constraints of electrochemical H2O2 generation in disinfection and pinpoints future research directions required for implementation.

    Articles
    Product selectivity controlled by manganese oxide crystals in catalytic ammoxidation
    Hai Wang, Qingsong Luo, Liang Wang, Yu Hui, Yucai Qin, Lijuan Song, Feng-Shou Xiao
    2021, 42 (12):  2164-2172.  DOI: 10.1016/S1872-2067(21)63803-2
    Abstract ( 200 )   HTML ( 9 )   PDF (4578KB) ( 210 )  
    Supporting Information

    The performances of heterogeneous catalysts can be effectively tuned by changing the catalyst structures. Here we report a controllable nitrile synthesis from alcohol ammoxidation, where the nitrile hydration side reaction could be efficiently prevented by changing the manganese oxide catalysts. α-Mn2O3 based catalysts are highly selective for nitrile synthesis, but MnO2-based catalysts including α, β, γ, and δ phases favour the amide production from tandem ammoxidation and hydration steps. Multiple structural, kinetic, and spectroscopic investigations reveal that water decomposition is hindered on α-Mn2O3, thus to switch off the nitrile hydration. In addition, the selectivity-control feature of manganese oxide catalysts is mainly related to their crystalline nature rather than oxide morphology, although the morphological issue is usually regarded as a crucial factor in many reactions.

    High activity and durability of carbon-supported core-shell PtPx@Pt/C catalyst for oxygen reduction reaction
    Wei-Ze Li, Bang-An Lu, Lin Gan, Na Tian, Peng-Yang Zhang, Wei Yan, Wei-Xin Chen, You-Hu Chen, Zhi-You Zhou, Shi-Gang Sun
    2021, 42 (12):  2173-2180.  DOI: 10.1016/S1872-2067(21)63901-3
    Abstract ( 202 )   HTML ( 12 )   PDF (3051KB) ( 124 )  
    Supporting Information

    Alloying Pt with transition metals can significantly improve the catalytic properties for the oxygen reduction reaction (ORR). However, the application of Pt-transition metal alloys in fuel cells is largely limited by poor long-term durability because transition metals can easily leach. In this study, we developed a nonmetallic doping approach and prepared a P-doped Pt catalyst with excellent durability for the ORR. Carbon-supported core-shell nanoparticles with a P-doped Pt core and Pt shell (denoted as PtPx@Pt/C) were synthesized via heat-treatment phosphorization of commercial Pt/C, followed by acid etching. Compositional analysis using electron energy loss spectroscopy and X-ray photoelectron spectroscopy clearly demonstrated that Pt was enriched in the near-surface region (approximately 1 nm) of the carbon-supported core-shell nanoparticles. Owning to P doping, the ORR specific activity and mass activity of the PtP1.4@Pt/C catalyst were as high as 0.62 mA cm-2 and 0.31 mA μgPt-1, respectively, at 0.90 V, and they were enhanced by 2.8 and 2.1 times, respectively, in comparison with the Pt/C catalyst. More importantly, PtP1.4@Pt/C exhibited superior stability with negligible mass activity loss (6% after 30000 potential cycles and 25% after 90000 potential cycles), while Pt/C lost 46% mass activity after 30000 potential cycles. The high ORR activity and durability were mainly attributed to the core-shell nanostructure, the electronic structure effect, and the resistance of Pt nanoparticles against aggregation, which originated from the enhanced ability of the PtP1.4@Pt to anchor to the carbon support. This study provides a new approach for constructing nonmetal-doped Pt-based catalysts with excellent activity and durability for the ORR.

    Identification of the structure of Ni active sites for ethylene oligomerization on an amorphous silica-alumina supported nickel catalyst
    Jinghua Xu, Ruifeng Wang, Yaru Zhang, Lin Li, Wenjun Yan, Junying Wang, Guodong Liu, Xiong Su, Yanqiang Huang, Tao Zhang
    2021, 42 (12):  2181-2188.  DOI: 10.1016/S1872-2067(21)63827-5
    Abstract ( 112 )   HTML ( 5 )   PDF (1168KB) ( 204 )  
    Supporting Information

    Abstract: The structure of Ni active sites supported on amorphous silica-alumina supports with different contents of Al2O3 loadings in relation to their activities in ethylene oligomerization were investigated. Two kinds of Ni sites were detected by in situ FTIR-CO and H2-TPR experiments, that are Ni2+ cations as grafted on weak acidic silanols and Ni2+ cations at ion-exchange positions. The ethylene oligomerization activities of these Ni/ASA catalysts were found an ascending tendency as the Al2O3 loading decreased, which could be attributed to the enriched concentration of Ni2+ species on acidic silanols with a weaker interaction with the amorphous silica-alumina support. These Ni2+ species were more easily to be evolved into Ni+ species, which has been identified to be the active sites of ethylene oligomerization. Thus, it seems reasonable to conclude that Ni2+ species grafted on acidic silanols were the precursors of active sites.

    Amino acid-assisted synthesis of TS-1 zeolites containing highly catalytically active TiO6 species
    Yuyao Wang, Li Li, Risheng Bai, Shiqin Gao, Zhaochi Feng, Qiang Zhang, Jihong Yu
    2021, 42 (12):  2189-2196.  DOI: 10.1016/S1872-2067(21)63882-2
    Abstract ( 175 )   HTML ( 16 )   PDF (2403KB) ( 364 )  
    Supporting Information

    Tailoring the Ti coordination states in titanosilicate zeolites to simultaneously improve feedstock conversion and maximize the target product selectivity remains a challenge in the pursuit of high-performance catalysts for selective oxidation reactions. Herein, we provide a facile strategy to synthesize hierarchical anatase-free TS-1 (MFI-type) zeolites with tetrahedrally coordinated (TiO4) and octahedrally coordinated Ti species (TiO6). The TiO4 species provide high epoxide selectivity, while the TiO6 species afford improved alkene conversion. This strategy is achieved by synergistically using an L-lysine-assisted approach and a two-step crystallization; the two-step crystallization approach prevents the formation of anatase TiO2, while L-lysine stabilizes the TiO6 species and ensures efficient incorporation of TiO6 into the anatase-free TS-1 zeolites. Compared with their conventional counterparts, which only contain TiO4 species, the as-prepared TS-1 zeolites (Si/Ti = 36.9) result in a higher 1-hexene conversion (33%), higher TON value (153), and comparable epoxide selectivity (95%). This synthetic strategy provides avenues to tailor the amount and distribution of Ti species in titanosilicate zeolites to achieve high catalytic performances in various processes.

    Pore-mouth catalysis boosting the formation of iso-paraffins from syngas over bifunctional catalysts
    Mengheng Wang, Yaoyao Han, Suhan Liu, Zhiming Liu, Dongli An, Zhiqiang Zhang, Kang Cheng, Qinghong Zhang, Ye Wang
    2021, 42 (12):  2197-2205.  DOI: 10.1016/S1872-2067(20)63770-6
    Abstract ( 215 )   HTML ( 9 )   PDF (2899KB) ( 175 )  
    Supporting Information

    Recent studies confirm that the emerging bifunctional catalysts consisting of metal oxide and zeolites can directly convert syngas into high-quality gasoline, however, the formation mechanism of iso-paraffins and the difference with the conventional FT/zeolite catalyst have not been investigated. Herein, three one-dimensional SAPO zeolites with diverse micropore sizes were synthesized and assembled with ZnAlOx with spinel structure. It was found that ZnAlOx/SAPO-41 and ZnAlOx/SAPO-11 with medium micropore sizes favored the formation of C5-C11 hydrocarbons with a high content of iso-paraffins. The characterizations pointed out that the formation of iso-paraffins over SAPO-11 followed a pore-mouth catalysis mechanism, which means the isomerization of linear hydrocarbons can only take place near the pore mouth region of zeolites. This mechanism only allows the formation of mono-branched iso-paraffins in the C5-C11 range, which are less prone to be cracked than their di-branched isomers. A careful comparative analysis between ZnAlOx/SAPO-11 and Co/H-meso-ZSM-5 was also made in terms of product distribution, activity, and stability.

    Optimizing the nickel boride layer thickness in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in glycerol oxidation
    Steffen Cychy, Sebastian Lechler, Zijian Huang, Michael Braun, Ann Cathrin Brix, Peter Blümler, Corina Andronescu, Friederike Schmid, Wolfgang Schuhmann, Martin Muhler
    2021, 42 (12):  2206-2215.  DOI: 10.1016/S1872-2067(20)63766-4
    Abstract ( 251 )   HTML ( 9 )   PDF (6543KB) ( 203 )  
    Supporting Information

    The influence of the drop-casted nickel boride catalyst loading on glassy carbon electrodes was investigated in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in alkaline glycerol electrooxidation. The continuously operated radial flow cell consisted of a borehole electrode positioned 50 µm above an internal reflection element enabling operando FTIR spectroscopy. It is identified as a suitable tool for facile and reproducible screening of electrocatalysts under well-defined conditions, additionally providing access to the selectivities in complex reaction networks such as glycerol oxidation. The fast product identification by ATR-IR spectroscopy was validated by the more time-consuming quantitative HPLC analysis of the pumped electrolyte. High degrees of glycerol conversion were achieved under the applied laminar flow conditions using 0.1 M glycerol and 1 M KOH in water and a flow rate of 5 µL min-1. Conversion and selectivity were found to depend on the catalyst loading, which determined the catalyst layer thickness and roughness. The highest loading of 210 µg cm-2 resulted in 73% conversion and a higher formate selectivity of almost 80%, which is ascribed to longer residence times in rougher films favoring readsorption and C-C bond scission. The lowest loading of 13 µg cm-2 was sufficient to reach 63% conversion, a lower formate selectivity of 60%, and, correspondingly, higher selectivities of C2 species such as glycolate amounting to 8%. Thus, only low catalyst loadings resulting in very thin films in the few μm thickness range are suitable for reliable catalyst screening.

    Selective tandem hydrogenation and rearrangement of furfural to cyclopentanone over CuNi bimetallic catalyst in water
    Shujing Zhang, Hong Ma, Yuxia Sun, Xin Liu, Meiyun Zhang, Yang Luo, Jin Gao, Jie Xu
    2021, 42 (12):  2216-2224.  DOI: 10.1016/S1872-2067(21)63842-1
    Abstract ( 241 )   HTML ( 19 )   PDF (3904KB) ( 252 )  
    Supporting Information

    Tandem catalysis for the hydrogenation rearrangement of furfural (FA) provides an attractive solution for manufacturing cyclopentanone (CPO) from renewable biomass resources. The CuNi/Al-MCM-41 catalyst was synthesized and afforded excellent catalytic performance with 99.0% conversion and 97.7% selectivity to CPO in a near-neutral solution under 2.0 MPa H2 at 160 °C for 5 h, much higher than those on other molecular sieve supports including MCM-41, SBA-15, HY, and ZSM-5. A small amount of Al highly dispersed in MCM-41 plays an anchoring role and ensures the formation of highly dispersed CuNi bimetallic nanoparticles (NPs). The remarkably improved catalytic performance may be attributed to the bimetallic synergistic and charge transfer effects. In addition, the initial FA concentration and the aqueous system pH required precise control to minimize polymerization and achieve high selectivity of CPO. Fourier transform infrared spectroscopy and mass spectra results indicated that polymerization was sensitive to pH values. Under acidic conditions, FA and intermediate furfuryl alcohol polymerize, while the intermediate 4-hydroxy-2-cyclopentenone mainly polymerizes under alkaline conditions, blocking the cascade of multiple reactions. Therefore, near-neutral conditions are most suitable for minimizing the impact of polymerization. This study provides a useful solution for the current universal problems of polymerization side reactions and low carbon balance for biomass conversion.

    Promoting propane dehydrogenation with CO2 over Ga2O3/SiO2 by eliminating Ga-hydrides
    Yi Liu, Guanghui Zhang, Jianyang Wang, Jie Zhu, Xinbao Zhang, Jeffrey T. Miller, Chunshan Song, Xinwen Guo
    2021, 42 (12):  2225-2233.  DOI: 10.1016/S1872-2067(21)63900-1
    Abstract ( 116 )   HTML ( 6 )   PDF (3312KB) ( 200 )  

    Due to the shortage supply of propylene and the development of shale gas, there is increased interest in on-purpose propane dehydrogenation (PDH) technology for propylene production. Ga-based catalysts have great potential in PDH, due to the high activity, low carbon deposit and deactivation. Ga-hydrides formed during PDH reduce the rate, selectivity and yield of propylene. In this contribution, CO2 is introduced into PDH as a soft oxidant to eliminate the unfavorable intermediate species Gaδ+-Hx re-generating Ga3+-O pairs, and also minimize coke deposition thereby improving the catalytic performance. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy experiments show that CO2 can effectively eliminate Gaδ+-Hx. At different temperatures, co-feeding CO2 during PDH over Ga2O3/SiO2 catalysts with different loadings significantly improves the stability of the conversion and selectivity, especially the latter, and provide a new dimension for improving the performance of PDH process.

    Shape impact of nanostructured ceria on the dispersion of Pd species
    Chunyan Dong, Yan Zhou, Na Ta, Wenlu Liu, Mingrun Li, Wenjie Shen
    2021, 42 (12):  2234-2241.  DOI: 10.1016/S1872-2067(20)63725-1
    Abstract ( 182 )   HTML ( 13 )   PDF (2100KB) ( 183 )  
    Supporting Information

    The shape impact of nanostructured ceria on the dispersion of Pd species was investigated by analyzing the atomic configuration and the bonding environment of Pd species over spherical and cubic ceria particles, using STEM and XPS. Amorphous Pd particles of about 2.0 nm, with a substantial amount of tiny Pd species, dispersed on spherical ceria, primarily due to the enriched surface oxygen vacancies that bonded the Pd species tightly. While faceted Pd particles of about 2.9 nm located on cubic ceria with distinct interfaces where Pd atoms embedded into the ceria lattice. The crystalline Pd particles on ceria cubes were highly active and stable for methane combustion that occurred on the metal surface via a facile PdO/Pd redox cycle; while the amorphous Pd particles on spherical ceria particles were featured by a significantly higher activity and stability towards CO oxidation, where the Pd-ceria interface served as the active sites.

    Effect of the modification of alumina supports with chloride on the structure and catalytic performance of Ag/Al2O3 catalysts for the selective catalytic reduction of NOx with propene and H2/propene
    Jia Wang, Rui You, Kun Qian, Yang Pan, Jiuzhong Yang, Weixin Huang
    2021, 42 (12):  2242-2253.  DOI: 10.1016/S1872-2067(21)63904-9
    Abstract ( 78 )   HTML ( 4 )   PDF (1690KB) ( 121 )  

    The effect of the modification of an alumina support with chloride on the structure and the catalytic performance of Ag/Al2O3 catalysts (SA) was investigated for the selective catalytic reduction (SCR) of NO using C3H6 or H2/C3H6 as reductants. The Ag/Al2O3 catalyst and Cl--modified Ag/Al2O3 catalysts (SA-Cl) were prepared by a conventional impregnation method and characterized by X-ray diffraction, Brunauer-Emmett-Teller isotherm analysis, electron probe microanalysis, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and hydrogen temperature-programmed reduction. The catalytic activities in the C3H6-SCR and H2/C3H6-SCR reactions were evaluated, and the reaction mechanism was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy and synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV-PIMS). We found that Cl- modification of the alumina-supported Ag/Al2O3 catalysts facilitated the formation of oxidized silver species (Agnᵟ+) that catalyze the moderate-temperature oxidation of hydrocarbons into partial oxidation products (mainly acetate species) capable of participating in the SCR reaction. The low-temperature promoting effect of H2 on the C3H6-SCR ("hydrogen effect") was found to originate from the enhanced decomposition of strongly adsorbed nitrates on the catalyst surface and the conversion of these adsorbed species to -NCO and -CN species. This "H2 effect" occurs in the presence of Agnᵟ+ species rather than the metallic Ag0 species. A gaseous intermediate, acrylonitrile (CH2CHCN), was also identified in the H2/C3H6-SCR reaction using SVUV-PIMS. These findings provide novel insights in the structure-activity relationship and reaction mechanisms of the SA-catalyzed HC-SCR reaction of NO.

    Preparation of MIL-88B(Fex,Co1‒x) catalysts and their application in one-step liquid-phase methanol oxidation to methyl formate using H2O2
    Jianfang Liu, Zhenzhen Ran, Qiyan Cao, Shengfu Ji
    2021, 42 (12):  2254-2264.  DOI: 10.1016/S1872-2067(20)63749-4
    Abstract ( 109 )   HTML ( 5 )   PDF (2475KB) ( 183 )  

    The selective oxidation of methanol to methyl formate is one of the most attractive processes to obtain value-added methanol-downstream products. The development of highly efficient and stable catalysts is critical for this transformation. In this study, a series of MIL-88B(Fex,Co1-x) bimetallic catalysts with different Fe/Co molar ratios were prepared through a one-pot hydrothermal method. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption, and inductively coupled plasma-mass spectrometry characterization were performed to elucidate the structure of the catalysts. The activity of the catalysts were assessed in the one-step oxidation of methanol to methyl formate with H2O2 in a liquid-phase batch reactor. The results show that the MIL-88B(Fex,Co1-x) catalysts exhibit uniform needle-like morphologies with an average length and width of 400-600 nm and 100-150 nm, respectively. Co2+ is incorporated into the framework by partially replacing Fe3+ in MIL-88B. Moreover, the catalyst efficiently promoted the conversion of methanol to methyl formate. When MIL-88B(Fe0.7,Co0.3) catalyst was used with a molar ratio of H2O2 to methanol of 0.5 at 80 °C for 60 min, 34.8% methanol conversion was achieved, and the selectivity toward methyl formate was 67.6%. The catalysts also showed great stability with a steady conversion and selectivity even after four cycles. The preliminary oxidation mechanism was also studied. It was determined that H2O2 is first adsorbed on the Fe3+ sites and subsequently activates these sites. Methanol is adsorbed by the O atoms of the framework through hydrogen bonding and is gradually oxidized to formic acid. Subsequently, formic acid reacts with the residual methanol at the Fe3+ and Co2+ Lewis acid sites to form methyl formate.

    Direct hydrothermal synthesis of Mo-containing MFI zeolites using Mo-EDTA complex and their catalytic application in cyclohexene epoxidation
    Haoyang Zhang, Lifen Xu, Xinyu Chang, Songsong Miao, Yuting Sun, Mingjun Jia
    2021, 42 (12):  2265-2274.  DOI: 10.1016/S1872-2067(21)63826-3
    Abstract ( 152 )   HTML ( 10 )   PDF (3796KB) ( 215 )  
    Supporting Information

    A series of Mo-containing MFI zeolites with different Mo loadings (Mo-MFI-n, n represent the initial Si/Mo molar ratio) was hydrothermally synthesized by using tetrapropylammonium hydroxide as the template and Mo-EDTA complex as the Mo source. Various characterization results demonstrated that the use of the Mo-EDTA complex is beneficial for the incorporation of more Mo species into the MFI-type zeolites. The special complexing capability of EDTA2- plays a critical role in adjusting the release rate of the Mo species to combine with the Si tetrahedron species during the zeolite growth process, thus leading to a uniform distribution of Mo in the MFI framework. In addition, a small portion of extra-framework Mo clusters may be distributed inside the channels or near the pore window of the zeolites. The catalytic properties of these Mo-containing MFI zeolites were evaluated for the epoxidation of cyclohexene with H2O2 as the oxidant. The composition-optimized catalyst, Mo-MFI-50, efficiently converted cyclohexene to the corresponding epoxide with a relatively high conversion (93%) and epoxide selectivity (82%) at 75 °C after 9 h of reaction. Moreover, the resultant Mo-containing MFI catalyst exhibited excellent structural stability and recoverability and was easily recycled by simple filtration without the need for calcination treatment.

    Template-free synthesis of Co3O4 microtubes for enhanced oxygen evolution reaction
    Jiani Hu, Xiaofeng Zhang, Juan Xiao, Ruchun Li, Yi Wang, Shuqin Song
    2021, 42 (12):  2275-2286.  DOI: 10.1016/S1872-2067(21)63902-5
    Abstract ( 99 )   HTML ( 10 )   PDF (12847KB) ( 351 )  
    Supporting Information

    To fully exploit the superiority of tubular structures, in this study, we systematically explore the optimal preparation conditions for Ni/Co3O4, including cation species and content, additive species and content, and anion species. Our results reveal that the formation of an initial cobalt nickel acetate hydroxide prism is the key factor and directly affects the final microtubular structure. Moreover, P is subsequently doped into the Ni/Co3O4 lattice to increase the M3+/M2+ molar ratio (M = Co and Ni), promote reaction kinetics, and optimize electronic structure. Consequently, the oxygen evolution reaction performance of P-doped tubular Ni/Co3O4 is significantly higher than that of undoped Ni/Co3O4 and the state-of-the-art RuO2 electrocatalyst.

    Different roles of MoO3 and Nb2O5 promotion in short-chain alkane combustion over Pt/ZrO2 catalysts
    Bingheng Cen, Cen Tang, Jiqing Lu, Jian Chen, Mengfei Luo
    2021, 42 (12):  2287-2295.  DOI: 10.1016/S1872-2067(20)63771-8
    Abstract ( 165 )   HTML ( 8 )   PDF (2284KB) ( 159 )  
    Supporting Information

    Pt/ZrO2 catalysts promoted with MoO3 and Nb2O5 were tested for the combustion of short-chain alkanes (namely, methane, ethane, propane, and n-hexane). For short-chain alkane combustion, the inhibition of MoO3 (for the methane reaction) dramatically transformed to promotion (for the ethane, propane, and n-hexane reactions) as the carbon chain length increased, whereas the remarkable promotion of Nb2O5 gradually weakened with an increase in the carbon chain length. Based on a detailed study of the oxidation reactions of methane and propane over the catalysts, the different roles of the promoters in the reactions were ascribed to differences in the acidic properties of the surface and the oxidation or reduction states of the Pt species. The MoO3 promoter could decorate the surface of the Pt species for a Pt-Mo/ZrO2 catalyst, whereas the Nb2O5 promoter on the support could be partially covered by Pt particles for a Pt-Nb/ZrO2 catalyst. The formation of accessible Pt-MoO3 interfacial sites, a high concentration of metallic Pt species, and a high surface acidity in Pt-Mo/ZrO2 were responsible for the enhanced activity for catalytic propane combustion. The lack of enough accessible Pt-Nb2O5 interfacial sites but an enhanced surface acid sites in Pt-Nb/ZrO2 explained the slight improvement in activity for catalytic propane combustion. However, the stabilized Ptn+ species in Pt-Nb/ZrO2 were responsible for the much-improved activity for methane combustion, whereas the Ptn+ species in Pt-Mo/ZrO2 could be reduced during the oxidation reaction, and the fewer exposed surface Pt species because of MoO3 decoration accounted for the inhibited activity for methane combustion. In addition, it can be concluded that MoO3 promotion is favorable for the activation of C-C bonds, whereas Nb2O5 promotion is more beneficial for the activation of C-H bonds with high energy.

    Electrocatalytic generation of hydrogen peroxide on cobalt nanoparticles embedded in nitrogen-doped carbon
    Basil Sabri Rawah, Wenzhen Li
    2021, 42 (12):  2296-2305.  DOI: 10.1016/S1872-2067(21)63804-4
    Abstract ( 199 )   HTML ( 8 )   PDF (3993KB) ( 266 )  

    Electrocatalytic reduction of oxygen is a growing synthetic technique for the sustainable production of hydrogen peroxide (H2O2). The current challenges concern seeking low-cost, highly active, and selective electrocatalysts. Cobalt-nitrogen-doped carbon containing catalytically active cobalt-nitrogen (Co-Nx) sites is an emerging class of materials that can promote the electrochemical generation of H2O2. Here, we report a straightforward method for the preparation of cobalt-nitrogen-doped carbon composed of a number of Co-Nx moieties using low-energy dry-state ball milling, followed by controlled pyrolysis. This scalable method uses inexpensive materials containing cobalt acetate, 2-methylimidazole, and Ketjenblack EC-600JD as the metal, nitrogen, and carbon precursors, respectively. Electrochemical measurements in an acidic medium show the present material exhibits a significant increase in the oxygen reduction reaction current density, accompanied by shifting the onset potential into the positive direction. The current catalyst has also demonstrated an approximate 90 % selectivity towards H2O2 across a wide range of potential. The H2O2 production rate, as measured by H2O2 bulk electrolysis, has reached 100 mmol gcat.-1 h-1 with high H2O2 faradaic efficiency close to 85% (for 2 h at 0.3 V vs. RHE). Lastly, the catalyst durability has been tested (for 6 h at 0.3 V vs. RHE). The catalyst has shown relatively consistent performance, while the overall faradic efficiency reaches approximate 85% throughout the test cycle indicating the promising catalyst durability for practical applications. The formed Co-Nx moieties, along with other parameters, including the acidic environment and the applied potential, likely are the primary reasons for such high activity and selectivity to H2O2 production.

    Surface regulated Ni nanoparticles on N-doped mesoporous carbon as an efficient electrocatalyst for CO2 reduction
    Min Wang, Qi Xie, Huimin Chen, Guangbo Liu, Xuejing Cui, Luhua Jiang
    2021, 42 (12):  2306-2312.  DOI: 10.1016/S1872-2067(21)63903-7
    Abstract ( 80 )   HTML ( 5 )   PDF (2920KB) ( 120 )  
    Supporting Information

    Low cost, highly selective and efficient electrocatalysts for CO2 reduction reaction (CO2RR) is crucial for lowering the global carbon footprint and mitigating energy shortages. Here, we first report a highly selective and efficient electrocatalyst for CO2RR to CO using a surface-regulated Ni nanoparticles supported on N-doped CMK-3 (N,O-Ni/CMK3). Compared with most Ni metal catalysts previously reported with severe competitive hydrogen evolution during the CO2RR, the N,O-Ni/CMK3 catalyst presents a superior CO faradaic efficiency of about 97%, a high CO partial current density (13.01 mA cm-1) and turnover frequency (4.25 s-1). The comprehensive characterization provides evidence that the N,O co-regulated Ni acts as the active center. Taking advantage of the N, O co-regulated chemical environment, N,O-Ni/CMK3 also displays a decent stability at negative potentials. Our work paves a novel approach for developing transition metal catalysts for CO2RR with enhanced activity and selectivity via regulating surface chemical environment.

    Synthesis of high-crystallinity MIL-125 with outstanding xylene isomer separation performance
    Liping Yang, Jiacheng Xing, Danhua Yuan, Lin Li, Yunpeng Xu, Zhongmin Liu
    2021, 42 (12):  2313-2321.  DOI: 10.1016/S1872-2067(21)63905-0
    Abstract ( 233 )   HTML ( 6 )   PDF (13322KB) ( 263 )  
    Supporting Information

    MIL-125 is a metal-organic framework with great potential for the adsorption and separation of xylene isomers. However, MIL-125 is usually synthesized under anhydrous and anaerobic conditions. In this study, homogeneously shaped and highly crystalline MIL-125 was synthesized by introducing water-resistant titanium-containing oligomers into the synthesis process. With the assistance of the novel oligomers, MIL-125 can be synthesized in the presence of water, which meets batch-production requirements. The adsorption separation performance of the obtained highly crystalline MIL-125 was also significantly enhanced. The para-xylene/meta-xylene selectivity can reach 13.5 in mesitylene, which is higher than the selectivity values of most previously reported para-selective adsorbents. The MIL-125 xylene separation performance was verified using both batch adsorption and breakthrough experiments in the liquid phase. In addition, the influence of the solvent effect was evaluated through microcalorimetric experiments, liquid-phase adsorption experiments, and theoretical calculations.