2020 Vol. 5, No. 4

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Editorial
Green Catalysis and Kinetics
Xuezhi Duan, Hao Jiang, Jia Yang
2020, 5(4) doi: 10.1016/j.gee.2020.12.003
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Research highlight
Production of lithium metal with ion-selective solid electrolytes
Yongan Yang
2020, 5(4): 382-384. doi: 10.1016/j.gee.2020.04.011
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Short Review
Catalyst design strategies towards highly shape-selective HZSM-5 for para-xylene through toluene alkylation
Xin Huang, Ruizhuang Wang, Xu Pan, Chuanfu Wang, Maohong Fan, Yufei Zhu, Yonggang Wang, Jin Peng
2020, 5(4): 385-393. doi: 10.1016/j.gee.2019.12.001
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With the shape selective zeolite catalyst, toluene alkylation with methanol to para-xylene (MTPX) technology could produce highly pure para-xylene (PX) in one step. The lower feedstock cost and less energy consumption in products separation make it more competitive compared to the current toluene disproportionation route. Thus, MTPX is regarded as the most reasonable production route for PX production. This article reviews the strategies that applied to the preparation of high-performance catalysts for MTPX, with special focus on the precise control of pore dimension and acid sites distribution in zeolite to achieve the highest selectivity to PX. The outlook of the MTPX catalyst is also proposed to guide the catalyst development in the field.
Review article
Environmentally benign synthesis of crystalline nanosized molecular sieves
Xiaoxin Chen, Guoju Yang, Valentin Valtchev
2020, 5(4): 394-404. doi: 10.1016/j.gee.2020.10.014
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Zeolites and zeo-type materials with nanosized dimensions are of great practical interest owing to their favorable transport properties, faster adsorption kinetics, and large external surface area. This mini-review presents recent developments in the organic template-free synthesis of nanosized zeolites and related materials. The advantages and challenges of these methods are addressed with particular attention to the green synthesis of nanozeolites.
Research paper
Efficient transesterification over two-dimensional zeolites for sustainable biodiesel production
Hao Pang, Guoju Yang, Lin Li, Jihong Yu
2020, 5(4): 405-413. doi: 10.1016/j.gee.2020.10.024
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Basic zeolites have shown great potential as efficient catalysts for biodiesel production in the transesterification reactions. However, conventional three-dimensional (3D) basic zeolites generally suffer from limited base sites and severe mass-transfer restriction, thereby suppressing their catalytic activity. Herein, 2D basic zeolites with large external surface areas, hierarchical characteristics, and abundant accessible and stable base sites are prepared by expansion, delamination and subsequent solid-state ion-exchange (SSIE) approach. The facile SSIE method provides more advantages in stabilizing and dispersing high concentration of strong basic sites than the conventional liquid-phase ion-exchange (LIE) approach. Due to the excellent mass transportation and stable basic sites, the 2D Na/ITQ-2 prepared by the SSIE approach shows remarkably enhanced activity and recyclability in the transesterification of triglycerides to produce biodiesel, compared to 3D zeolites and other reported basic zeolites. This work will open the boulevard to the rational design of 2D basic catalysts and expand the potential application of 2D zeolites to biodiesel production and other industrial reactions involving bulky molecules.
Boron carbide boosted Fenton-like oxidation: A novel Fe(III)/Fe(II) circulation
Peng Zhou, Feng Cheng, Gang Nie, Yangyang Yang, Kunsheng Hu, Xiaoguang Duan, Yongli Zhang, Shaobin Wang
2020, 5(4): 414-422. doi: 10.1016/j.gee.2020.09.007
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The sluggish kinetics of Fe(Ⅱ) recovery in Fenton/Fenton-like reactions significantly limits the oxidation efficiency. In this study, we for the first time use boron carbide (BC) as a green and stable promotor to enhance the reaction of Fe(Ⅲ)/H2O2 for degradation of diverse organic pollutants. Electron paramagnetic resonance analysis and chemical quenching/capturing experiments demonstrate that hydroxyl radicals (•OH) are the primary reactive species in the BC/Fe(Ⅲ)/H2O2 system. In situ electrochemical analysis indicates that BC remarkably boosts the Fe(Ⅲ)/Fe(Ⅱ) redox cycles, where the adsorbed Fe(Ⅲ) cations were transformed to more active Fe(Ⅲ) species with a higher oxidative potential to react with H2O2 to produce Fe(Ⅱ). Thus, the recovery of Fe(Ⅱ) from Fe(Ⅲ) is facilitated over BC surface, which enhances •OH generation via Fenton reactions. Moreover, BC exhibits outstanding reusability and stability in successive cycles and avoids the secondary pollution caused by conventional organic and metalliferous promotors. Therefore, metal-free BC boosting Fe(Ⅲ)/H2O2 oxidation of organics provides a green and advanced strategy for water decontamination.
Structured NiFe catalysts derived from in-situ grown layered double hydroxides on ceramic monolith for CO2 methanation
Huong Lan Huynh, Wakshum Mekonnen Tucho, Zhixin Yu
2020, 5(4): 423-432. doi: 10.1016/j.gee.2020.09.004
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Monolithic catalysts for CO2 methanation have become an active research area for the industrial development of Power-to-Gas technology. In this study, we developed a facile and reproducible synthesis strategy for the preparation of structured NiFe catalysts on washcoated cordierite monoliths for CO2 methanation. The NiFe catalysts were derived from in-situ grown layered double hydroxides (LDHs) via urea hydrolysis. The influence of different washcoat materials, i.e., alumina and silica colloidal suspensions on the formation of LDHs layer was investigated, together with the impact of total metal concentration. NiFe LDHs were precipitated on the exterior surface of cordierite washcoated with alumina, while it was found to deposit further inside the channel wall of monolith washcoated with silica due to different intrinsic properties of the colloidal solutions. On the other hand, the thickness of in-situ grown LDHs layers and the catalyst loading could be increased by high metal concentration. The best monolithic catalyst (COR-AluCC-0.5M) was robust, having a thin and well-adhered catalytic layer on the cordierite substrate. As a result, high methane yield was obtained from CO2 methanation at high flow rate on this structured NiFe catalysts. The monolithic catalysts appeared as promising structured catalysts for the development of industrial methanation reactor.
Enhancing the dynamic electron transfer of Au species on wormhole-like TS-1 for boosting propene epoxidation performance with H2 and O2
Dong Lin, Xiuhui Zheng, Xiang Feng, Nan Sheng, Zhaoning Song, Yibin Liu, Xiaobo Chen, Zhenping Cai, De Chen, Chaohe Yang
2020, 5(4): 433-443. doi: 10.1016/j.gee.2020.10.021
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Engineering unique electronic structure of catalyst to boost catalytic performance is of prime scientific and industrial importance. Herein, the identification of intrinsic electronic sensitivity for direct propene epoxidation was first achieved over highly stable Au/wormhole-like TS-1 catalyst. Results show that the electron transfer of Au species can be regulated by manipulating the dynamic evolutions and contents of Au valence states, thus resulting in different catalytic performance in 100 h time-on-stream. By DFT calculations, kinetic analysis and multi-characterizations, it is found that the Au0 species with higher electronic population can easily transfer more electrons to activate surface O2 compared with Au1+ and Au3+ species. Moreover, there is a positive correlation between Au0 content and activity. Based on this correlation, a facile strategy is further proposed to boost Au0 percentage, resulting in the reported highest PO formation rate without adding promoters. This work harbors tremendous guiding significance to the design of highly efficient Au/Ti-containing catalyst for propene epoxidation with H2 and O2.
Active sites and reaction mechanism for N-doped carbocatalysis of phenol removal
Mingjie Zhang, Chen Han, Wenyao Chen, Wei Luo, Yueqiang Cao, Gang Qian, Xinggui Zhou, Xiaoguang Duan, Shaobin Wang, Xuezhi Duan
2020, 5(4): 444-452. doi: 10.1016/j.gee.2020.05.006
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Heteroatom-doping of carbocatalysts has been a powerful strategy to remarkably enhance the catalytic performance. Herein, the underlying nature of N promotional effects on peroxymonosulfate (PMS) activation for phenol removal is understood by combining kinetics analysis with multiple techniques. A strategy using mixed acid oxidation of carbon nanotube (CNT) followed by NH3 treatment is employed to yield a series of catalysts with different N-doping contents but similar fraction of sp2-hybridized carbon and defective degree, endowing with a chance to discriminate the dominant N-containing active sites. The multi-sites kinetics analysis suggests the graphitic N-containing sites as the dominant active sites. The mechanism of the surface-bound reactive species is also discriminated as the dominant reaction mechanism. The insights reported here could provide the methodology to fundamentally understand the heteroatom-doping effects of carbocatalysis.
Primary amine coupling on nanocarbon catalysts: Reaction mechanism and kinetics via fluorescence probe analysis
Fan Li, Xueya Dai, Wei Qi
2020, 5(4): 453-460. doi: 10.1016/j.gee.2020.09.008
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Non-metallic nanocarbon materials catalyzed coupling reactions of primary amines to produce imine is an efficient, green and sustainable synthetic route, which has a wide application prospect in fine chemicals or pharmaceutical molecules. In the present study, we show firstly the relatively high catalytic activity of graphene oxide in the reaction of oxidative coupling of benzylamine (OCB), which is even comparable with typical metal-based catalysts, indicating the great potential of nanocarbon materials in this reaction system. More importantly, a novel two-photon fluorescence probe molecule (N-propyl-4-hydrazinyl-1, 8-naphthalimide, NA) with special chemical structure of hydrazine functionality was synthesized. The probe NA could selectively react with aldehyde or ketone compounds, leading to the photoluminescence enhancement via inhibition of photo induced electron transfer (PET) process. The synthesized NA was applied as probe in carbon catalyzed OCB system to predict the existence of reaction intermediate benzaldehyde (BA), indicating the reaction pathway of oxidation-deamination-condensation in nanocarbon catalyzed OCB process. The proposed luminescence-probe strategy for revealing the kinetics and mechanism may also shed light in other reaction systems concerning the intermediates or products of ketones or aldehydes.
Core-shell particles of C-doped CdS and graphene: A noble metal-free approach for efficient photocatalytic H2 generation
Muhammad Zubair, Estelle Marie M. Vanhaecke, Ingeborg-Helene Svenum, Magnus Rønning, Jia Yang
2020, 5(4): 461-472. doi: 10.1016/j.gee.2020.10.017
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To achieve efficient photocatalytic H2 generation from water using earth-abundant and cost-effective materials, a simple synthesis method for carbon-doped CdS particles wrapped with graphene (C-doped CdS@G) is reported. The doping effect and the application of graphene as co-catalyst for CdS is studied for photocatalytic H2 generation. The most active sample consists of CdS and graphene (CdS-0.15G) exhibits promising photocatalytic activity, producing 3.12 mmol g−1 h−1 of H2 under simulated solar light which is ~4.6 times superior than pure CdS nanoparticles giving an apparent quantum efficiency (AQY) of 11.7%. The enhanced photocatalytic activity for H2 generation is associated to the narrowing of the bandgap, enhanced light absorption, fast interfacial charge transfer, and higher carrier density (ND) in C-doped CdS@G samples. This is achieved by C doping in CdS nanoparticles and the formation of a graphene shell over the C-doped CdS nanoparticles. After stability test, the spent catalysts sample was also characterized to investigate the nanostructure.
Engineering three-layer core–shell S-1/TS-1@dendritic-SiO2 supported Au catalysts towards improved performance for propene epoxidation with H2 and O2
Zhaoning Song, Juncong Yuan, Zhenping Cai, Dong Lin, Xiang Feng, Nan Sheng, Yibin Liu, Xiaobo Chen, Xin Jin, De Chen, Chaohe Yang
2020, 5(4): 473-483. doi: 10.1016/j.gee.2020.11.017
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The advocacy of green chemical industry has led to the development of highly efficient catalysts for direct gas-phase propene epoxidation with green, sustainable and simple essence. The S-1/TS-1@dendritic-SiO2 material with three-layer core–shell structure was developed and used as the support for Au catalysts, which showed simultaneously fantastic PO formation rate, PO selectivity and stability (over 100 h) for propene epoxidation with H2 and O2. It is found that silicalite-1 (S-1) core and the middle thin layer of TS-1 offer great mass transfer ability, which could be responsible for the excellent stability. The designed dendritic SiO2 shell covers part of the acid sites on the external surface of TS-1, inhibiting the side reactions and improving the PO selectivity. Furthermore, three kinds of SiO2 shell morphologies (i.e., dendritic, net, mesoporous shell) were designed, and relationship between shell morphology and catalytic performance was elucidated. The results in this paper harbour tremendous guiding significance for the design of highly efficient epoxidation catalysts.
Nitrogen-rich isoindoline-based porous polymer: Promoting knoevenagel reaction at room temperature
Shengtai Hou, Yunhao Sun, Xueguang Jiang, Pengfei Zhang
2020, 5(4): 484-491. doi: 10.1016/j.gee.2020.06.021
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Nitrogen-rich porous organic polymers (POPs) with basic features have already shown promising performance in various organic reactions. But the harsh conditions, tedious synthetic methods and the requirement of specific monomers impede their further application. Herein, we introduce isoindoline chemistry into POP community. An isoindoline formation process between aniline and bromomethylbenzene—coupling nucleophilic substitution, HBr elimination, and intramolecular cyclization in one pot, is utilized for POPs synthesis. Nitrogen-rich isoindoline-based porous polymers (IPPs) were obtained with specific surface areas up to 408 m2 g−1. Unexpectedly, mechanochemistry could enable the rapid (3 h) and solid-state synthesis of IPP catalysts. Moreover, this nitrogen-rich catalyst presents excellent activity (isolated yield: 99%), scalable ability (up to 14 g per run) and recyclability (five runs) towards the Knoevenagel condensation reaction under mild reaction conditions (water as solvent at room temperature).
Highly surface electron-deficient Co9S8 nanoarrays for enhanced oxygen evolution
Haoxuan Zhang, Jingyu Wang, Qilin Cheng, Petr Saha, Hao Jiang
2020, 5(4): 492-498. doi: 10.1016/j.gee.2020.07.010
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Tailoring valence electron delocalization of transition metal center is of importance to achieve highly-active electrocatalysts for oxygen evolution reaction (OER). Herein, we demonstrate a “poor sulfur” route to synthesize surface electron-deficient Co9S8 nanoarrays, where the binding energy (BE) of Co metal center is considerably higher than all reported Co9S8-based electrocatalysts. The resulting Co9S8 electrocatalysts only require the overpotentials (η) of 265 and 326 mV at 10 and 100 mA cm−2 with a low Tafel slope of 56 mV dec−1 and a 60 h-lasting stability in alkaline media. The OER kinetics are greatly expedited with a low reaction activation energy of 27.9 kJ mol−1 as well as abundant OOH∗ key intermediates (24%), thus exhibiting excellent catalytic performances. The surface electron-deficient engineering gives an available strategy to improve the catalytic activity of other advanced non-noble electrocatalysts.
Cobalt-doped Mn3O4 nanocrystals embedded in graphene nanosheets as a high-performance bifunctional oxygen electrocatalyst for rechargeable Zn–Air batteries
Mengyang Dong, Xu Liu, Lixue Jiang, Zhengju Zhu, Yajie Shu, Shan Chen, Yuhai Dou, Porun Liu, Huajie Yin, Huijun Zhao
2020, 5(4): 499-505. doi: 10.1016/j.gee.2020.06.022
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A non-noble-metal bifunctional catalyst with efficient and durable activity towards both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is crucial to the development of rechargeable Zn-air batteries. Herein, a facile one-step hydrothermal method is reported for the synthesis of a high-performance bifunctional oxygen electrocatalyst, cobalt-doped Mn3O4 nanocrystals supported on graphene nanosheets (Co–Mn3O4/G). Compare to pristine Mn3O4, this Co–Mn3O4/G exhibits greatly enhanced electrocatalytic activity, delivering a half-wave potential of 0.866 V for the ORR and a low overpotential of 275 mV at 10 mA cm−2 for the OER. The zinc-air battery built with Co–Mn3O4/G shows a reduced charge–discharge voltage of 0.91 V at 10 mA cm−2, an power density of 115.24 mW cm−2 and excellent stability without any degradation after 945 cycles (315 h), outperforming the state-of-the-art Pt/C–Ir/C catalyst-based device.
Realizing optimal hydrogen evolution reaction properties via tuning phosphorous and transition metal interactions
Haishun Jiang, Siyu Zhao, Wenyao Li, Tobias P. Neville, Isil Akpinar, Paul R. Shearing, Dan J.L. Brett, Guanjie He
2020, 5(4): 506-512. doi: 10.1016/j.gee.2020.07.009
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Hydrogen is one of the most attractive renewables for future energy application, therefore it is vital to develop cost-effective and highly-efficient electrocatalysts for the hydrogen evolution reaction (HER) to promote the generation of hydrogen from mild methods. In this work, Co–Mo phosphide nanosheets with the adjustable ratio of Co and Mo were fabricated on carbon cloth by a facile hydrothermal-annealing method. Owing to the unique nanostructures, abundant active surfaces and small resistance were achieved. Excellent electrocatalytic performances are obtained, such as the small overpotential of ∼67.3 mV to realize a current density of 10 mA cm−2 and a Tafel slope of 69.9 mV dec−1. Rapid recovery of the current response under multistep chronoamperometry is realized and excellent stability retained after the CV test for 2000 cycles. The change of electronic states of different elements was carefully studied which suggested the optimal electrochemical performance can be realized by tuning phosphorous and metal interactions.

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