Chinese Journal of Catalysis

Table of Contents for VOL.38 No.4

2017, 38 (4): 0-0.

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Engineering vacancies for solar photocatalytic applications

Mingce Long, Longhui Zheng

2017, 38 (4): 617-624. DOI: 10.1016/S1872-2067(17)62821-3

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In contrast to the exploration of novel photocatalytic materials, vacancy engineering of traditional photocatalysts comprising earth-abundant elements represents an effective method for enhancing photocatalytic performance without introducing alien elements. This minireview analyzes the latest progress in engineering vacancies in photocatalysts, remarks on state-of-the-art characterization techniques for vacancies, and reviews the formation chemistry and fundamental benefits of anion and cation vacancies in typical photocatalysts. Although knowledge of these vacancies is increasing, challenges remain in this field, and possible further research is therefore also discussed.

Selective aerobic oxidation promoted by highly efficient multi-nitroxy organocatalysts

Kexian Chen, Haiying Xie

2017, 38 (4): 625-635. DOI: 10.1016/S1872-2067(17)62777-3

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Selective oxidation with molecular oxygen as the sole oxidant under mild conditions is of crucial importance for the long-term sustainable exploitation of available feedstocks and the formation of required intermediates for organic synthesis and industrial processes. Among the developed oxidation protocols, innovative strategies using hydroxyimide organocatalysts in combination with metallic or metal-free cocatalysts have attracted much attention because of the good activities and selectivities of such catalysts in the oxo functionalization of hydrocarbons. This method is based on the reaction using N-hydroxyphthalimide, which was first reported by Ishii's group in the 1990s. Although the important and wide-ranging applications of such catalysts have been summarized recently, there are no reviews that focus solely on oxidation strategies using multi-nitroxy organocatalysts, which have interesting properties and high reactivities. This review covers the concise synthetic methods and mechanistic profiles of known multi-nitroxy organocatalysts and summarizes significant advances in their use in efficient aerobic oxidation. Based on a combination of experimental and theoretical results, guidelines for the future rational design of multi-nitroxy organocatalysts are proposed, and the properties of various model multi-nitroxy organocatalysts are predicted. The present overview of the advantages, limitations, and potential applications of multi-nitroxy organocatalysts can provide useful tools for researchers in the field of selective oxidation.

Supercritical synthesis of platinum-modified titanium dioxide for solar fuel production from carbon dioxide

Susana Tostón, Rafael Camarillo, Fabiola Martínez, Carlos Jiménez, Jesusa Rincón

2017, 38 (4): 636-650. DOI: 10.1016/S1872-2067(17)62766-9

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This paper investigates the properties of TiO₂-based photocatalysts synthesised under supercritical conditions. Specifically, the characteristics of Pt dispersed on TiO₂ catalysts obtained in supercritical CO₂ are discussed and compared with those of commercial TiO₂. The photocatalytic activity of the synthesised catalysts in the CO₂ photoreduction reaction to produce solar fuel is tested. The main conclusion of the study is that photocatalysts with better or similar features, including high surface area, crystallisation degree, hydroxyl surface concentration, pore volume, absorbance in the visible range and methane production rate, to those of commercial TiO₂ may be produced for the reduction of CO₂ to fuel by synthesis in supercritical media.

Simple synthesis of sub-nanometer Pd clusters: High catalytic activity of Pd/PEG-PNIPAM in Suzuki reaction

Zhe Chen, Yu Liang, Da-Shuang Jia, Zhi-Min Cui, Wei-Guo Song

2017, 38 (4): 651-657. DOI: 10.1016/S1872-2067(17)62797-9

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Ultra-small metal nanoclusters have high surface energy and abundant active sites, and therefore their catalytic activities are usually significantly higher than those of larger nanoparticles. A temperature-responsive copolymer, namely poly(ethylene glycol)-co-poly(N-isopropylacrylamide) (PEG-PNIPAM) was synthesized as the first step, and then ultra-small Pd clusters stabilized within PEG-PNIPAM copolymer micelles were formed by direct reduction. Pd nanoclusters of size less than 2 nm showed outstanding catalytic activity in the Suzuki coupling reaction. The reaction between iodobenzene and phenylboronic acid was completed in as little as 10 s (turnover frequency=4.3×10⁴ h^-1). A yield of 64% was achieved in 5 min in the reaction between chlorobenzene and phenylboronic acid. The catalyst showed significant deactivation during three consecutive runs. However, this composite catalyst consisting of Pd/PEG-PNIPAM can be easily recycled based on the reversible phase transition of temperature-responsive PEG-PNIPAM. This catalyst therefore has good potential for practical applications.

Cu₂O/SiC as efficient catalyst for Ullmann coupling of phenols with aryl halides

Yibing Wang, Xiaoning Guo, Manqian Lü, Zhaoyang Zhai, Yingyong Wang, Xiangyun Guo

2017, 38 (4): 658-664. DOI: 10.1016/S1872-2067(17)62785-2

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ACu₂O/SiC heterogeneous catalyst was prepared via a two-step liquid-phase method using diethylene glycol as both the solvent and the reducing agent. The catalyst was characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and H₂ temperature-programmed reduction. All the results indicate that Cu is present on the SiC support primarily as Cu₂O. The SEM and TEM results show that cubic Cu₂O nanoparticles are uniformly dispersed on the β-SiC surface. The reaction conditions, namely the temperature, reaction time, and amounts of base and catalyst used, for the Ullmann-type C-O cross-coupling reaction were optimized. A model reaction was performed using iodobenzene (14.0 mmol) and phenol (14.0 mmol) with Cu₂O/SiC (5 wt% Cu) as the catalyst, Cs₂CO₃ (1.0 equiv.) as the base, and tetrahydrofuran as the solvent at 150℃ for 3 h; a yield of 97% was obtained and the turnover frequency (TOF) was 1136 h^-1. The Cu₂O/SiC catalyst has a broad substrate scope and can be used in Ullmann-type C-O cross-coupling reactions of aryl halides and phenols bearing a variety of different substituents. The catalyst also showed high activity in the Ullmann-type C-S cross-coupling of thiophenol with iodobenzene and substituted iodobenzenes; a TOF of 1186 h^-1 was achieved. The recyclability of the Cu₂O/SiC catalyst in the O-arylation of phenol with iodobenzene was investigated under the optimum conditions. The yield decreased from 97% to 64% after five cycles. The main reason for the decrease in the catalyst activity is loss of the active component, i.e., Cu₂O.

Purification and characterization of alkaline chitinase from Paenibacillus pasadenensis CS0611

Xiaoxiao Guo, Pei Xu, Minhua Zong, Wenyong Lou

2017, 38 (4): 665-672. DOI: 10.1016/S1872-2067(17)62787-6

Abstract ( 355 ) [Full Text(HTML)] ()

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An extracellular chitinase produced by Paenibacillus pasadenensis CS0611 was purified by ammonium sulfate precipitation, HiTrap DEAE FF and HiLoad 26/600 Superdex 200pg column chromatography. The apparent molecular mass determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis was 69 kDa. The optimum pH and optimum temperature of the chitinase were 5.0 and 50℃, respectively. The enzyme showed high stability at alkaline pH values and temperatures below 40℃. Additionally, the metal ions Mn²⁺, Mg²⁺, and Co²⁺ inhibited activity of the chitinase. The chitinase was active on colloidal chitin with an apparent K_m of 4.41 mg/mL and V_max of 1.08 mg/min. Substrate spectrum analysis indicated that the chitinase reacted preferentially with the glucosidic bond between GlcNAc-GlcNAc. The enzymatic hydrolysate was analyzed by high-performance liquid chromatography and thin layer chromatography, and clearly showed that a subunit of (GlcNAc)₂ was the main hydrolysis product.

Fe, N, S-doped porous carbon as oxygen reduction reaction catalyst in acidic medium with high activity and durability synthesized using CaCl₂ as template

Chi Chen, Zhiyou Zhou, Yucheng Wang, Xue Zhang, Xiaodong Yang, Xinsheng Zhang, Shigang Sun

2017, 38 (4): 673-682. DOI: 10.1016/S1872-2067(17)62807-9

Abstract ( 354 ) [Full Text(HTML)] ()

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Proton exchange membrane fuel cells suffer from the sluggish kinetics of the oxygen reduction reaction (ORR) and the high cost of Pt catalysts. In the present work, a high-performance ORR catalyst based on Fe, N, S-doped porous carbon (FeNS-PC) was synthesized using melamine formaldehyde resin as C and N precursors, Fe(SCN)₃ as Fe and S precursors, and CaCl₂ as a template via a two-step heat treatment without a harsh template removal step. The results show that the catalyst treated at 900℃ (FeNS-PC-900) had a high surface area of 775 m²/g, a high mass activity of 10.2 A/g in an acidic medium, and excellent durability; the half-wave potential decreased by only 20 mV after 10000 potential cycles. The FeNS-PC-900 catalyst was used as the cathode in a proton exchange membrane fuel cell and delivered a peak power density of 0.49 W/cm². FeNS-PC-900 therefore has good potential for use in practical applications.

Correlation between H-ZSM-5 crystal size and catalytic performance in the methanol-to-aromatics reaction

Lingzhi Yang, Zhiyuan Liu, Zhi Liu, Wenyong Peng, Yunqi Liu, Chenguang Liu

2017, 38 (4): 683-690. DOI: 10.1016/S1872-2067(17)62791-8

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The porosity of H-ZSM-5 zeolite is known to facilitate the diffusion of molecules in the methanol-to-aromatics (MTA) reaction. The activity and selectivity of the H-ZSM-5 catalyst in the MTA reaction has been studied as a function of crystal size. ZSM-5 zeolites with different crystal sizes were successfully synthesized by conventional hydrothermal methods. Tailoring ZSM-5 particle size was easily controlled by changes to the sol-gel composition, and in particular, the deionized water to tetrapropylammonium hydroxide ratio, and crystallization time. The structure of the H-ZSM-5 zeolites were characterized by X-ray diffraction and the morphology of the zeolite particles was determined by scanning electron microscopy. N₂ adsorption-desorption measurements established changes to the textural properties, and compositional properties were characterized by X-ray fluorescence spectroscopy. Acidity measurements of the catalysts were measured by pyridine-adsorbed Fourier transform infrared spectroscopy and the temperature-programmed desorption of ammonia. After subjecting the catalysts to the MTA reaction, the total amount of coke formed on the spent deactivated catalysts was determined by thermal gravimetric analysis. The results show that the SiO₂/Al₂O₃ molar ratios and acidic properties of the H-ZSM-5 samples are similar, however, the nano-sized hierarchical ZSM-5 zeolite with an additional level of auxiliary pores possesses a higher surface area, larger mesopore volume and larger macropore volume, resulting in more effective mass transportation properties. The H-ZSM-5 zeolite catalysts were evaluated for their activity towards the MTA reaction as a function of crystal size. The nano-sized H-ZSM-5 catalyst having shorter diffusion path lengths, substantial mesoporosity and a high external surface area showed excellent selectivity toward aromatics (average > 42%) and benzene, toluene and xylenes (37% at 180 min). Furthermore, lower coking levels were observed on the nano-sized H-ZSM-5 catalyst when compared with the H-ZSM-5 catalysts possessing larger particle sizes and is attributed to a reduction in polyaromatic hydrocarbons being deposited within the internal surface area.

Porous Rh/BINAP polymers as efficient heterogeneous catalysts for asymmetric hydroformylation of styrene: Enhanced enantioselectivity realized by flexible chiral nanopockets

Tao Wang, Wenlong Wang, Yuan Lü, Kai Xiong, Cunyao Li, Hao Zhang, Zhuangping Zhan, Zheng Jiang, Yunjie Ding

2017, 38 (4): 691-698. DOI: 10.1016/S1872-2067(17)62790-6

Abstract ( 365 ) [Full Text(HTML)] ()

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A new chiral monomer, (S)-5,5'-divinyl-BINAP, was successfully synthesized and embedded into two different porous organic polymers (Poly-1 and Poly-2). After loading a Rh species, the catalysts were applied for the heterogeneous asymmetric hydroformylation of styrene. Compared with the homogeneous BINAP analogue, the enantioselectivity of Rh/Poly-1 catalyst was drastically increased by approximately 70%. The improved enantioselectivity of the porous Rh/BINAP polymers was attributed to the presence of flexible chiral nanopockets resulting from the increased bulk of the R groups near the catalytic center.

Influence of supports for selective production of 2,5-dimethylfuran via bimetallic copper-cobalt catalyzed 5-hydroxymethylfurfural hydrogenolysis

Sanjay Srivastava, G.C.Jadeja, Jigisha Parikh

2017, 38 (4): 699-709. DOI: 10.1016/S1872-2067(17)62789-X

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The hydrogenolysis of carbon-oxygen bonds is an important model reaction in upgrading biomass-derived furanic compounds to transportation fuels. One of these model reactions, namely conversion of 5-hydroxymethylfurfural (HMF) to the gasoline additive 2,5-dimethylfuran (DMF), is especially attractive. In this study, bimetallic Cu-Co catalysts supported on CeO₂, ZrO₂, and Al₂O₃were used for the selective hydrogenolysis of HMF to DMF. The structures of the fresh and used catalysts were studied using X-ray diffraction, the Brunauer-Emmett-Teller method, transmission electron microscopy, temperature-programmed reduction by H₂, temperature-programmed desorption of NH₃, and CHNS analysis. The structures were correlated with the catalytic activities. The Cu-Co/CeO₂ catalyst produced mainly 2,5-bis(hydroxymethyl)furan via reduction of C=O bonds on large Cu particles. The Cu-Co/Al₂O₃ catalyst gave the best selectivity for DMF, as a result of a combination of highly dispersed Cu, mixed copper-cobalt oxides, and suitable weak acidic sites. Cu-Co/ZrO₂ had low selectivity for DMF and produced a combination of various over-hydrogenolysis products, including 2,5-dimethyltetrahydrofuran and 5,5-oxybis(methylene)-bis(2-methylfuran), because of the presence of strong acidic sites. The reaction pathways and effects of various operating parameters, namely temperature, H₂ pressure, and time, were studied to enable optimization of the selective conversion of HMF to DMF over the Cu-Co/Al₂O₃ catalyst.

Synthesis, characterization and application of BiVO₄ photoanode for photoelectrochemical oxidation of chlorate

Seyed Ghorban Hosseini, Saeid Safshekan

2017, 38 (4): 710-716. DOI: 10.1016/S1872-2067(17)62788-8

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A high-quality polycrystalline bismuth vanadate (BiVO₄) film was prepared on a fluorine-doped tin oxide substrate via a facile two-step strategy involving electrodeposition and annealing processes. The morphology and structural characterization of the resulting film were investigated by different methods including scanning electronmicroscopy, transmission electron microscopy,X-ray diffraction (XRD), and Fourier transform infrared, ultraviolet-visible (UV-vis) absorption, and Raman spectroscopies. XRD patterns as well as optical measurements revealed that BiVO₄ film crystallized with a pure monoclinic scheelite structure. The prepared BiVO₄ film was used for heterogeneous oxidation of chlorate ions in aqueous solution via electrochemical (EC), photochemical (PC), and photoelectrochemical (PEC) processes. The decrease in concentration of chlorate was monitored using UV-vis absorption spectroscopy. The results revealed that BiVO₄ could effectively perform chlorate oxidation under light irradiation through a PEC method. The kinetics of chlorate oxidation was consistent with a first-order reaction, and the rate constant for the PEC process was found to be much higher than those of EC and PC. Furthermore, a possible photocatalytic oxidation mechanism for chlorate mainly based on the formation of perchlorate ions is proposed.

CO₂ hydrogenation to methanol over Cu/Zn/Al/Zr catalysts prepared by liquid reduction

Xiaosu Dong, Feng Li, Ning Zhao, Yisheng Tan, Junwei Wang, Fukui Xiao

2017, 38 (4): 717-725. DOI: 10.1016/S1872-2067(17)62793-1

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Cu/Zn/Al/Zr catalysts containing Cu in three valence states (Cu²⁺, Cu⁺ and Cu⁰) were prepared using a liquid reduction method and subsequently calcined at different temperatures. The effects of the calcination temperature on the catalyst structure, interactions among components, reducibility and dispersion of Cu species, surface properties and exposed Cu surface area were systematically investigated. These materials were also applied to the synthesis of methanol via the hydrogenation of CO₂. The results show that a large exposed Cu surface area promotes catalytic CO₂ conversion and that there is a close correlation between the Cu⁺/Cu⁰ ratio and the selectivity for methanol. A calcination temperature of 573 K was found to produce a Cu/Zn/Al/Zr catalyst exhibiting the maximum activity during the synthesis of methanol.

Ordered mesoporous Sn-SBA-15 as support for Pt catalyst with enhanced performance in propane dehydrogenation

Bing Li, Zhenxin Xu, Wei Chu, Shizhong Luo, Fangli Jing

2017, 38 (4): 726-735. DOI: 10.1016/S1872-2067(17)62805-5

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A series of Sn-incorporated SBA-15 materials with high specific surface areas and highly ordered mesoporous structures were synthesized by a facile one-pot method and used as catalyst supports. A reference sample was also prepared using a conventional impregnation method. The catalysts were characterized using various methods, and their activities in propane dehydrogenation were investigated. The incorporation of Sn into the SBA-15 matrix led to strong interactions between Sn species and the support, and these helped to maintain the oxidation states of Sn species during the reaction. Substitution with Sn changed the interfacial properties of the Pt species and improved the function and effect of the Sn promoter. The catalytic activities and stabilities of the Pt catalysts supported on Sn-incorporated SBA-15 were better than those of the impregnated sample. However, the catalytic performance deteriorated when an excessive amount of Sn was introduced and the interactions among Pt, Sn species, and the support became weaker. The Pt/0.5Sn-SBA-15 catalyst gave the best propene selectivity, i.e., 98.5%, with a corresponding propane conversion of about 43.8%.

Transformation of carbon dioxide into valuable chemicals over bifunctional metallosalen catalysts bearing quaternary phosphonium salts

Wuying Zhang, Rongchang Luo, Qihang Xu, Yaju Chen, Xiaowei Lin, Xiantai Zhou, Hongbing Ji

2017, 38 (4): 736-744. DOI: 10.1016/S1872-2067(17)62802-X

Abstract ( 441 ) [Full Text(HTML)] ()

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The chemical transformation of CO₂ under mild conditions remains a great challenge because of its exceptional kinetic and thermodynamic stability. Two important reactions in the transformation of CO₂ are the N-formylation reaction of amines using hydrosilanes and CO₂, and the cycloaddition of CO₂ to epoxides. Here, we report the high efficiency of bifunctional metallosalen complexes bearing quaternary phosphonium salts in catalyzing both of these reactions under solvent-free, mild conditions without the need for co-catalysts. The catalysts' bifunctionality is attributed to an intramolecular cooperative process between the metal center and the halogen anion. Depending on the reaction, this activates CO₂ by permitting either the synergistic activation of Si-H bond via metal-hydrogen coordinative bond (M-H) or the dual activation of epoxide via metal-oxygen coordinative bond (M-O). The one-component catalysts are also shown to be easily recovered and reused five times without significant loss of activity or selectivity. The current results are combined with previous work in the area to propose the relevant reaction mechanisms.

Nanoscale graphene oxide sheets as highly efficient carbocatalysts in green oxidation of benzylic alcohols and aromatic aldehydes

Alireza Sedrpoushan, Masoud Heidari, Omid Akhavan

2017, 38 (4): 745-757. DOI: 10.1016/S1872-2067(17)62776-1

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Nanoscale graphene oxide (NGO) sheets were synthesized and used as carbocatalysts for effective oxidation of benzylic alcohols and aromatic aldehydes. For oxidation of alcohols in the presence of H₂O₂ at 80℃, the NGOs (20% mass fraction) as carbocatalysts showed selectivity toward aldehyde. The rate and yield of this reaction strongly depended on the nature of substituents on the alcohol. For 4-nitrobenzyl alcohol, <10% of it was converted into the corresponding carboxylic acid after 24 h. By contrast, 4-methoxybenzyl alcohol and diphenylmethanol were completely converted into the corresponding carboxylic acid and ketone after only 9 and 3 h, respectively. The conversion rates for oxidation of aromatic aldehydes by NGO carbocatalysts were higher than those for alcohol oxidation. For all the aldehydes, complete conversion to the corresponding carboxylic acids was achieved using 7% (mass fraction) of NGO at 70℃ within 2-3 h. Possible mechanisms for NGO carbocatalyst structure-dependent oxidation of benzyl alcohols and structure-independent oxidation of aromatic aldehydes are discussed.

Zirconium triflate grafted on SBA-15 as a highly efficient solid acid catalyst for ring opening of epoxides by amines and alcohols

Kamlesh N.Tayade, Lianyue Wang, Sensen Shang, Wen Dai, Manish Mishra, Shuang Gao

2017, 38 (4): 758-766. DOI: 10.1016/S1872-2067(17)62794-3

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Metal (Al, Ti, Zr) triflate grafted mesoporous SBA-15 (AlTf/S, TiTf/S, ZrTf/S) samples were synthesized as inexpensive solid acid materials by a simple one-pot-two-step synthesis methodology. These materials were characterized by X-ray diffraction, N₂-sorption, thermogravimetric analysis, Fourier transform infrared spectroscopy (FT-IR), in-situ pyridine FT-IR spectroscopy, and elemental analysis. ZrTf/S was found to be a highly efficient and reusable solid acid catalyst for ring opening of epoxides with amines and alcohols and produced β-amino alcohols and β-alkoxy alcohols respectively under ambient reaction conditions. The ZrTf/S catalyst showed the highest activity, which was attributed to its high acidity compared with that of the Ti and Al containing samples.

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