Green Energy&Environment

Heterogeneous catalysis under flow for the 21st century fine chemical industry

Rosaria Ciriminna, Mario Pagliaro, Rafael Luque

2021, 6(2): 161-166. doi: 10.1016/j.gee.2020.09.013

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Due to metal leaching and poor catalyst stability, the chemical industry's fine chemical and pharmaceutical sectors have been historically reluctant to use supported transition metal catalysts to manufacture fine chemicals and active pharmaceutical ingredients. With the advent of new generation supported metal catalysts and flow chemistry, we argue in this study, this situation is poised to quickly change. Alongside heterogenized metal nanoparticles, both single-site molecular and single-atom catalyst will become ubiquitous. This study offers a critical outlook taking into account both technical and economic aspects.

Detecting confined fluid behavior by SFA: Past, present, and future

Yihui Dong, Feng Huo, Aatto Laaksonen

2021, 6(2): 167-168. doi: 10.1016/j.gee.2020.08.002

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Scalable and facile synthesis of V₂O₅ nanoparticles via ball milling for improved aerobic oxidative desulfurization

Yiru Zou, Chao Wang, Hanxiang Chen, Haiyan Ji, Qian Zhu, Wenshu Yang, Linlin Chen, Zhigang Chen, Wenshuai Zhu

2021, 6(2): 169-175. doi: 10.1016/j.gee.2020.10.005

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In recent years, transition-metal oxides (TMOs) have been long employed for aerobic oxidative desulfurization. However, the inherent bottlenecks, such as the low explosion of active sites, limit the application of bulk TMOs catalyst. In this study, V₂O₅ nanoparticles with oxygen vacancies were prepared in large-scale via facile ball milling strategy with adding oxalic acid as a reducing agent. The as-prepared catalysts exhibit remarkable sulfur removal for oils with different initial S-concentrations and different substrates. Sulfur removal could reach up to 99.7% (< 2 ppm) under the optimized reaction conditions. This work provides a feasible desulfurization strategy for fuel oils.

Natural gas purification by asymmetric membranes: An overview

Xi Chen, Gongping Liu, Wanqin Jin

2021, 6(2): 176-192. doi: 10.1016/j.gee.2020.08.010

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Natural gas, as a very important source of energy and chemical feedstock, can be used in place of coal to lower net carbon dioxide emissions. Membrane separation technology is an attractive alternative for natural gas purification where the impurities represented by acid gases (CO₂ and H₂S) as well as inert gases (N₂) must be removed to meet the transportation and usage specifications. From the economic benefits viewpoint, asymmetric membranes are required for industrial manufacture and applications. This paper aims to review the latest development of various kinds of asymmetric membranes for natural gas purification, mainly focusing on CO₂ removal from CH₄, including H₂S and N₂ separation from CH₄ as well. According to material types, polymeric, inorganic, mixed-matrix and carbon molecular sieve membranes are introduced. The associated fabrication approaches and transport properties are discussed for each kinds of asymmetric membranes. Towards the practical implementation, an emphasis is placed on hollow fiber asymmetric structure for these polymeric, mixed-matrix and carbon molecular sieve membranes.

Two-dimensional material separation membranes for renewable energy purification, storage, and conversion

Liheng Dai, Kang Huang, Yongsheng Xia, Zhi Xu

2021, 6(2): 193-211. doi: 10.1016/j.gee.2020.09.015

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The current energy crisis has prompted the development of new energy sources and energy storage/conversion devices. Membranes, as the key component, not only provide enormous separation potential for energy purification but also guarantee stable and high-efficiency operation for rechargeable batteries and fuel cells. Remarkably, two-dimensional (2D) material separation membranes have attracted intense attention on their excellent performance in energy field applications, owing to high mechanical/chemical stability, low mass transport resistance, strict size-exclusion, and abundant modifiable functional groups. In this review, we concentrate on the recent progress of 2D membrane and introduce 2D membranes based on graphene oxide (GO), MXenes, 2D MOFs, 2D COFs, and 2D zeolite nanosheets, which are applied in membrane separation (H₂ collection and biofuel purification) and battery separators (vanadium flow battery, Li–S battery, and fuel cell). The mass transport mechanism, selectivity mechanism, and modification methods of these 2D membranes are stated in brief, mainly focusing on interlayer dominant membranes (GO and MXenes) and pore dominant membranes (MOFs, COFs, and zeolite nanosheets). In conclusion, we highlight the challenges and outlooks of applying 2D membranes in energy fields.

Engineering optimization approach of nonaqueous electrolyte for sodium ion battery with long cycle life and safety

Haiying Che, Xinrong Yang, Yan Yu, Chaoliang Pan, Hong Wang, Yonghong Deng, Linsen Li, Zi-Feng Ma

2021, 6(2): 212-219. doi: 10.1016/j.gee.2020.04.007

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Electrolyte design strategies are closely related to the capacities, cycle life and safety of sodium–ion batteries. In this study, we aimed to optimize electrolyte with the focus on engineering aspects. The basic physicochemical properties including ionic conductivity, viscosity, wettability and thermochemical stability of the electrolytes using NaPF₆ as the solute and the mixed solvent with different components of EMC, DMC or DEC in PC or EC were systematically measured. Ah pouch cell with NaNi_1/3Fe_1/3Mn_1/3O₂/hard carbon electrodes was used to evaluate the performance of the prepared electrolytes. By using the Inductive Coupled Plasma Emission Spectrometer (ICP), X-ray photoelectron spectroscopy (XPS), Thermogravimetric-differential scanning calorimetry (TG-DSC) and Accelerating Rate Calorimeter (ARC), we show that an optimized electrolyte can effectively promote the formation of a protective interfacial layer on two electrodes, which not only retards parasitic reactions between the electrodes and electrolyte but also suppresses dissolution of metal ions from the cathode. With an optimized electrolyte, a NaNi_1/3Fe_1/3Mn_1/3O₂/hard carbon cell can attain 56.16% capacity retention under the low temperature of −40 °C, and can be able to retain 80% capacity retention after more than 2500 cycles while presenting excellent thermal safety.

Nitrogen-doped lignin based carbon microspheres as anode material for high performance sodium ion batteries

Linlin Fan, Zhiqiang Shi, Qingjuan Ren, Lei Yan, Fuming Zhang, Liping Fan

2021, 6(2): 220-228. doi: 10.1016/j.gee.2020.06.005

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Nitrogen-doped lignin-based carbon microspheres are synthesized using 3-aminophenol as a nitrogen source by the hydrothermal method. The structural change and the effect on the electrochemical properties are systematically investigated. Nitrogen-doped lignin-based carbon microspheres represent well-developed spherical morphology with many active sites, ultramicroporous (< 0.7 nm) structure, and large interlayer spacing. Consistent with the obtained physical structures and properties, the nitrogen-doped carbon microspheres exhibit fast sodium ion adsorption/intercalation kinetic process and excellent electrochemical performance. For example, a reversible specific capacity of 374 mAh g⁻¹ at 25 mA g⁻¹ with high initial coulombic efficiency of 85% and high capacitance retention of 90% after 300 cycles at 100 mA g⁻¹ and stable charge/discharge behavior at different current density is obtained. The additional defects and abundant ultramicroporous structure can enhance sloping capacity, and large interlayer spacing is considered to be the reason for improving plateau capacity.

Ionic liquid-derived core–shell gold@palladium nanoparticles with tiny sizes for highly efficient electrooxidation of ethanol

Hong Zhang, Ying Luo, Dong Chen, Hui Liu, Penglei Cui, Jun Yang

2021, 6(2): 229-235. doi: 10.1016/j.gee.2020.03.007

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To maximize the size and structural advantages of nanomaterials in electrooxidation of ethanol, we herein report the synthesis of core–shell gold (Au)@Palladium (Pd) nanoparticles smaller than 3 nm in an ionic liquid, which combines the advantages of ionic liquids in preparing fine metal nanoparticles with the benefits of core–shell nanostructures. This synthetic strategy relies on the use of an ionic liquid (1-(2′-aminoethyl)-3-methyl-imidazolum tetrafluoroborate) as a stabilizer to produce Au particles with an average size of ca. 2.41 nm, which are then served as seeds for the formation of tiny core–shell Au@Pd nanoparticles with different Au/Pd molar ratios. The strong electronic coupling between Au core and Pd shell endows the Pd shell with an electronic structure favorable for the ethanol oxidation reaction. In specific, the ionic liquid-derived core–shell Au@Pd nanoparticles at an Au/Pd molar ratio of 1/1 exhibit the highest mass- and area-based activities, approximately 11 times than those of commercial Pd/C catalyst for ethanol electrooxidation.

Co-CoO_x supported onto TiO₂ coated with carbon as a catalyst for efficient and stable hydrogen generation from ammonia borane

Guang Yang, Shuyan Guan, Sehrish Mehdi, Yanping Fan, Baozhong Liu, Baojun Li

2021, 6(2): 236-243. doi: 10.1016/j.gee.2020.03.012

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Ammonia borane (AB) can be catalytically hydrolyzed to provide hydrogen at room temperature due to its high potentaial for hydrogen storage. Non-precious metal heterogeneous catalysts have broad application in the field of energy catalysis. In this article, catalysts precursor is obtained from Co-Ti-resorcinol-formaldehyde resin by sol–gel method. Co/TiO₂@N-C (CTC) catalyst is prepared by calcining the precursor under high temperature conditions in nitrogen atmosphere. Co-CoO_x/TiO₂@N-C (COTC) is generated by the controllable oxidation reaction of CTC. The catalyst can effectively promote the release of hydrogen during the hydrolytic dehydrogenation of AB. High hydrogen generation at a specific rate of 5905 mL min⁻¹ g_Co⁻¹ is achieved at room temperature. The catalyst retains its 85% initial catalytic activity even for its fifth time use in AB hydrolysis. The synergistic effect among Co, Co₃O₄ and TiO₂ promotes the rate limiting step with dissociation and activation of water molecules by reducing its activation energy. The applied method in this study promotes the development of non-precious metals in catalysis for utilization in clean energy sources.

One-step synthesis of defected Bi₂Al₄O₉/β-Bi₂O₃ heterojunctions for photocatalytic reduction of CO₂ to CO

Ying Liu, Jian-guo Guo, Yue Wang, Ying-juan Hao, Rui-hong Liu, Fa-tang Li

2021, 6(2): 244-252. doi: 10.1016/j.gee.2020.04.014

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Defect and charge transfer efficiency of nano-photocatalysts are important factors which influence their photocatalytic performance. In this work, oxygen vacancies are successfully introduced in the synthesis process of Bi₂Al₄O₉/β-Bi₂O₃ heterojunctions through one-step in situ self-combustion method. High-resolution transmission electron microscopy (HRTEM), UV-Vis diffuse reflectance spectra (UV-Vis DRS), and electron spin resonance (ESR) measurements confirm the existence of oxygen vacancies. In addition, by controlling the ratio of reactants of Bi(NO₃)₃ to Al(NO₃)₃, the ratio of Bi₂Al₄O₉ and β-Bi₂O₃ in the heterojunction can be easily adjusted. Photocurrent responses and surface photovoltage spectroscopy (SPV) indicate that the construction of the Bi₂Al₄O₉/β-Bi₂O₃ heterostructure improves the separation efficiency of the photo-generated electrons and holes. CO₂-TPD results imply that the amounts and stability of heterojunctions are enhanced compared with their counterparts. The Bi₂Al₄O₉/β-Bi₂O₃ heterojunction with 14 mol% Bi₂Al₄O₉ shows the highest photocatalytic ability for reduction of CO₂ into CO. The enhanced photoreduction of CO₂ performance can be ascribed to the synergistic effects of the heterojunction for electron separation and oxygen vacancies for CO₂ activation.

High CO₂ absorption capacity of metal-based ionic liquids: A molecular dynamics study

Biwen Li, Chenlu Wang, Yaqin Zhang, Yanlei Wang

2021, 6(2): 253-260. doi: 10.1016/j.gee.2020.04.009

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The absorption of CO₂ is of importance in carbon capture, utilization, and storage technology for greenhouse gas control. In the present work, we clarified the mechanism of how metal-based ionic liquids (MBILs), Bmim[XCl_n]_m (X is the metal atom), enhance the CO₂ absorption capacity of ILs via performing molecular dynamics simulations. The sparse hydrogen bond interaction network constructed by CO₂ and MBILs was identified through the radial distribution function and interaction energy of CO₂-ion pairs, which increase the absorption capacity of CO₂ in MBILs. Then, the dynamical properties including residence time and self-diffusion coefficient confirmed that MBILs could also promote the diffusion process of CO₂ in ILs. That's to say, the MBILs can enhance the CO₂ absorption capacity and the diffusive ability simultaneously. Based on the analysis of structural, energetic and dynamical properties, the CO₂ absorption capacity of MBILs increases in the order Cl⁻ → [ZnCl₄]²⁻→ [CuCl₄]²⁻→ [CrCl₄]⁻ → [FeCl₄]⁻, revealing the fact that the short metal–Cl bond length and small anion volume could facilitate the performance of CO₂ absorbing process. These findings show that the metal–Cl bond length and effective volume of the anion can be the effective factors to regulate the CO₂ absorption process, which can also shed light on the rational molecular design of MBILs for CO₂ capture and other key chemical engineering processes, such as IL-based gas sensors, nano-electrical devices and so on.

Ternary deep eutectic solvents catalyzed d-glucosamine self-condensation to deoxyfructosazine: NMR study

Pengfei Liu, Christian Marcus Pedersen, Jiaojiao Zhang, Rui Liu, Zhenzhou Zhang, Xianglin Hou, Yingxiong Wang

2021, 6(2): 261-270. doi: 10.1016/j.gee.2020.04.010

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Ternary deep eutectic solvents (TDESs) comprising choline chloride (ChCl), glycerol and l-arginine were synthesized as catalysts and solvents for the conversion of d-glucosamine (GlcNH₂) into deoxyfructosazine (DOF). The interactions between these three components in the prepared TDESs were studied by ¹H-, ³⁵Cl-NMR spectra and ¹H diffusion-ordered spectroscopy (DOSY) measurements. The chemical shift changes of active hydrogen in the ¹H-NMR spectra of TDES system and widening of signals in the ³⁵Cl-NMR spectra confirmed the hydrogen bonding interaction between the components, which was further supported by the decrease of diffusion coefficients (D) of the TDES components according to ¹H DOSY measurements. The influences of reaction temperature and l-arginine content in the TDESs on the yield of DOF were also studied. The experimental results have shown that when the molar ratio of ChCl, glycerol, and l-arginine was 1:2:0.1, DOF was the major product with a yield of 22.6% at 90 °C for 120 min. The chemical shift titration indicated that the carboxyl group of l-arginine in the TDES is the catalytical active site, so the mechanism of the catalytic reaction between GlcNH₂ and the TDES was proposed. Moreover, a reaction intermediate, dihydrofructosazine, was identified in the self-condensation reaction of GlcNH₂ by an in situ ¹H NMR technique.

Novel multi–SO₃H functionalized ionic liquids as highly efficient catalyst for synthesis of biodiesel

Meichen Li, Jie Chen, Ling Li, Changshen Ye, Xiaocheng Lin, Ting Qiu

2021, 6(2): 271-282. doi: 10.1016/j.gee.2020.05.004

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Biodiesel is an attractive alternative to fossil fuels due to the energy and environmental concerns. In this paper, seven different multi –SO₃H functionalized ILs based on the low-cost less-substituted amines, which contained massive sites for functionalization of sulfonic acid groups and further treatment of sulfonate-based anions, were prepared as catalysts with high acidity and desirable catalytic activity for the synthesis of biodiesel from the esterification of oleic acid with methanol. The physicochemical properties of these acidic ILs were characterized by a variety of analytical techniques such as FT-IR, EA, TGA, and the Brønsted acidity was well determined by UV–vis. Among the ILs prepared, [EDA-PS][P-TSA] showed the highest catalytic activity for esterification due to its high acidity and appropriate miscibility with reactants, with an ultrahigh 97.58% conversion of oleic acid under the optimum conditions (i.e. reaction time, 1.8 h; catalyst amount, 3 wt%; alcohol/acid molar ratio, 13:1, temperature 70 °C) acquired from the Box–Behnken response surface methodology. With the novel strategy of multi –SO₃H modification on ILs, our catalyst had an approaching or even superior oleic acid conversion rate compared to other reported catalysts with considerably lower catalyst dosage and shorter reaction time. More importantly, it also exhibited high generality for converting various FFA feedstocks into biodiesel with considerable conversion within 93.59–94.33% under a rather lower catalyst dosage, which showed the valuable potential for converting low-cost oils into biodiesel from an economic and environmental perspective.

Regulating catalyst morphology to boost the stability of Ni–Mo/Al₂O₃ catalyst for ebullated-bed residue hydrotreating

Huihong Zhu, Zhiwei Mao, Bin Liu, Tao Yang, Xiang Feng, Hao Jin, Chong Peng, Chaohe Yang, Jifeng Wang, Xiangchen Fang

2021, 6(2): 283-290. doi: 10.1016/j.gee.2020.05.001

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Hydrotreating of vacuum residue by ebullated-bed shows tremendous significance due to more stringent environmental regulations and growing demand for lighter fuels. However, enhancing the catalyst stability still remains as a challenging task. Herein, two Ni–Mo/Al₂O₃ catalysts with distinct morphologies (i.e., spherical and cylindrical) were first designed, and the morphology effect on deactivation was systematically elucidated employing multi-characterizations, such as HRTEM with EDX mapping, electron microprobe analysis, FT-IR, TGA and Raman. It is found that spherical catalyst exhibits superior hydrotreating stability over 1600 h. The carbonaceous deposits on spherical catalyst with less graphite structure are lighter, and the coke weight is also smaller. In addition, the metal deposits uniformly distribute in the spherical catalyst, which is better than the concentrated distribution near the pore mouth for the cylindrical catalyst. Furthermore, the intrinsic reason for the differences was analyzed by the bed expansion experiment. Higher bed expansion rate together with the better mass transfer ability leads to the enhanced performance. This work sheds new light on the design of more efficient industrial hydrotreating catalyst based on morphology effect.

Efficient fixation of CO₂ into propylene carbonate with [BMIM]Br in a continuous-flow microreaction system

Yuxin Wu, Yuncheng Ding, Jianhong Xu, Yundong Wang, Kathryn Mumford, Geoffrey W. Stevens, Weiyang Fei

2021, 6(2): 291-297. doi: 10.1016/j.gee.2020.04.016

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Utilization of carbon dioxide (CO₂) is of great significance in the development of CO₂ absorption and the solution of greenhouse gas effect. Highly efficient conversion of CO₂ into cyclic carbonate with green catalysts is essential for the more sustainable expansion of CO₂ fixation. Traditional batch reactor is limited by low efficiency, high cost and low security. Meanwhile, continuous flow system showcased a myriad of virtues, including shortening the residence time from hours to seconds, and decreasing reaction temperature, and possessing the nature of easy industrial scale-up. In this paper, a continuous-flow microreaction system was developed to synthesis propylene carbonate (PC) from propylene oxide (PO) and CO₂ using 1-butyl-3-methylimidazolium bromide ([BMIM]Br) as catalyst. By observing the flow patterns inside microreaction system, the effects of reaction temperature, molar fraction of catalyst, operating pressure, residence time, molar ratio of CO₂/PO as well as recycling performance of catalyst on the overall performances were comprehensively evaluated into details. Under different reaction conditions, the flow patterns were set to vary between slug flow and annular flow. The results showed that the yield of propylene carbonate (PC) can reach 99.7% at 140 °C and 3.0 MPa with the residence time of 166 s, while the recycling performance of the designed system greatly conforms the future trend of green chemistry.

Highly efficient energy harvest via external rotating magnetic field for oil based nanofluid direct absorption solar collector

Debing Wang, Wenwen Liang, Zhiheng Zheng, Peiyu Jia, Yunrui Yan, Huaqing Xie, Lingling Wang, Wei Yu

2021, 6(2): 298-307. doi: 10.1016/j.gee.2020.03.014

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Nanofluids based direct absorption solar collectors (DASCs) are considered as the important alternative for further improve the utilization of solar energy. However the low-quality energy and aggregation of nanoparticles obstructs their large-scale application. In this work, a new method of using magnetic nanofluids in DASCs is proposed. By this method, not only high-quality energy is got as well as the problems of blockage and corrosion in heat exchanger are well avoided. The result shows that the maximum temperature can reach 98 °C under 3 solar irradiations and the photothermal conversion efficiency can be further increased by 12.8% when the concentration is 500 ppm after adding an external rotating magnetic field. The highest viscosity of working fluid reduced by 21% when the concentration is 500 ppm at 95 °C after separating the Fe₃O₄@C nanoparticles from the nanofluids via magnetic separation technology. Meanwhile, the obtained pure base liquids with high temperature flow to heat exchanger, which also reduces the flow resistance in pipeline and avoids the problems such as blockage and corrosion in heat exchanger. This research promotes a new way for the efficient utilization of solar energy.

2021 Vol. 6, No. 2

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Special Issue: Molecular Thermodynamics for Green Engineering

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