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Thermal Decomposition and Oxidative Decomposition Mechanism of HFC-134a by Experimental and DFT Method

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Journal of Thermal Science 2024年第5期33卷 1990-2003页

作者： xu Yunting ZHANG Kai dai Xiaoye SHI Lin Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power EngineeringTsinghua UniversityBeijing 100084China

In response to the Kigali Amendment to the Montreal Protocol and global low-carbon emission environmental requirements,the phase-out and decomposition of numerous HFC refrigerants have become urgent,necessitating efficient and mild decomposition *** study investigates the thermal decomposition and oxidative thermal decomposition pathways of the typical hydrofluorocarbon refrigerant HFC-134a,employing a combination of experimental and quantum chemical DFT simulation *** chemical simulations reveal that the initial reaction bond cleavage serves as the rate-determining step during the thermal decomposition process,with the most easily detectable closed-shell products including CF_(2)=CHF,HF,CH_(3)F,CHF_(3),CH_(2)F_(2),and CF_(4).Reactive oxygen species can significantly reduce the Gibbs free energy barrier for HFC-134a *** achieve efficient degradation of HFC-134a,appropriate catalysts should be developed and selected to increase the level of reactive oxygen species in the reaction *** studies further corroborate that HFC-134a may undergo degradation through distinct reaction pathways under varying temperature(240℃to360℃)and pressure(0.1 MPa to 4.5 MPa)conditions,in agreement with simulation predictions.

关键词： HFC-134a pyrolysis oxidative thermal decomposition DFT refrigerant

Hydrogen generation from methanolysis of sodium borohydride over Co/Al_2O_3 catalyst

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Journal of Natural Gas Chemistry 2012年第5期21卷 488-494页

作者： Dongyan xu Lin Zhao Ping dai Shengfu Ji College of Chemical Engineering Qingdao University of Science and TechnologyQingdao 266042ShandongChina College of Electromechanical Engineering Qingdao University of Science and TechnologyQingdao 266061ShandongChina State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical TechnologyBeijing 100029China

Co/Al2O3 catalyst is prepared with an impregnation-chemical reduction method and used to catalyze the methanolysis of sodium borohydride （NaBH 4） for hydrogen *** solution temperature of 0 C,the methanolysis reaction can be effectively accelerated using Co/Al2O3 catalyst and provide a desirable hydrogen generation rate,which makes it suitable for applications under the circumstance of low environmental *** byproduct of methanolysis reaction is analyzed by X-ray diffraction （XRD） and Fourier transform infrared spectroscopy （FTIR）.The characterization results indicate that methanol can be easily recovered after methanolysis reaction by hydrolysis of the methanolysis byproduct,NaB（OCH 3） *** catalytic activity of Co/Al2O3 towards NaBH 4 methanolysis can be further improved by appropriate calcination *** catalytic methanolysis kinetics and catalyst reusability are also studied over the Co/Al2O3 catalyst calcined at the optimized temperature.

关键词： hydrogen generation sodium borohydride methanolysis cobalt

General trends in surface stability and oxygen adsorption behavior of transition metal diborides(TMB_2)

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Journal of Materials Science & Technology 2019年第4期35卷 584-590页

作者： Wei Sun Fuzhi dai Huimin xiang Jiachen Liu Yanchun Zhou Aerospace Research Institute of Materials & Processing Technology School of Materials Science and Engineering Tianjin University

The potential applications of transition metal diborides(TMB_2) in extreme environments are particularly attractive but still blocked by some intrinsic properties such as poor resistances to thermal shock and oxidation. Since surface plays a key role during grain growth and oxygen adsorption, an insight into the surface properties of TMB_2 is essential for understanding the materials performance and accelerating the development of ultra-high temperature ceramics. By employing two-region modeling method, the stability and oxygen adsorption behavior of TMB_2 surfaces were investigated by first-principles calculations based on density functional theory. The effects of valance electron concentration on the surface stability and oxygen adsorption were studied and the general trends were summarized. After analyzing the anisotropy in surface stability and oxygen adsorption, the observed grain morphology of TMB_2 were well explained, and it was also predicted that YB_2, HfB_2 and TaB_2 may have better initial oxidation resistance than ZrB_2.

关键词： Transition metal diborides First-principles calculation Surface energy Grain morphology Oxidation resistance

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

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Green Energy & Environment 2021年第2期6卷 193-211页

作者： Liheng dai Kang Huang Yongsheng Xia Zhi xu State Key Laborutory of Chemical Engineering Schood of Chemical Engineering East China University of Science and Technology 130 Meilong RoadShanghai200237China State Key Laboratory of Materials-Oriented Chemical Engineering College of Chemical EngineeringNanjing Tech Universiy30 Puzhu Road(S)Nanjing211816China

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 sizeexclusion, 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.

关键词： Two-dimensional materials Membranes Separation New energy

Process Parameter Optimizing and Studies on Microstructure and Properties of AZ31 Alloy Prepared by Semisolid Rolling Process

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Acta Metallurgica Sinica(English Letters) 2013年第3期26卷 293-298页

作者： Renguo GUAN Zhanyong ZHAO xiang WANG Chunguang dai Chunming LIU School of Materials and Metallurgy Northeastern University

A novel continuous semisolid rolling process for producing AZ31 alloy strip was developed. The process parameters were optimized, and microstructure and properties of AZ31 alloy prepared by the process were studied. The results reveal that primary grains of the strip become coarse, and the grain structure transforms from round shape to dendrite with the increment of casting temperature gradually. Eutectic phase fraction and primary grain size increase with the increment of roll speed. The primary grain size decreases firstly and then increases with the increment of the vibration frequency correspondingly. When the casting temperature is from 650℃to 690℃, the roll speed is 0.069 m·s- 1, and the vibration frequency is about 80 Hz, AZ31 alloy strip with a cross section size of 4 mm×160 mm was prepared by the proposed process. The ultimate tensile strength and elongation are improved 1% and 57 %, respectively.

关键词： Semisolid Sloping plate Rolling AZ31 alloy Microstructure Property

A linear supramolecular polymer based on host-guest recognition and metal-ligand coordination

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Chinese Chemical Letters 2018年第6期29卷 970-972页

作者： Chao xu Lei xu xiang Ma Key Laboratory for Advanced Materials and Institute of Fine Chemicals School of Chemistry and Molecular Engineering East China University of Science and Technology

linear main-chain supramolecular polymer was constructed in aqueous solution via g-CD host recognition with coumarin unit as well as metal-ligand coordination between terpyridine unit and Zn2＋.Therein, the multiple non-covalent interactions produce the ternary system as the primary ***, the self-assembly behavior and morphological properties of this supramolecular polymer system were characterized by DLS and TEM experiments

关键词： Supramolecular polymer Host-guest recognition Metal-ligand coordination y-Cyclodextrin

Dynamic output feedback control of systems with event-driven control inputs

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Science China(Information Sciences) 2020年第5期63卷 24-37页

作者： Jinhui ZHANG Hao xu Li dai Yuanqing XIA School of Automation Beijing Institute of Technology

In this paper, a dynamic output feedback control problem is investigated for systems with eventdriven control inputs. With both continuous and sampled output measurements in the systems, two types of dynamic output feedback controllers are designed based on a predefined event-driven scheduler for the control signals, respectively. With the proposed event-driven control scheme, the Zeno behavior can be avoided, and the states of closed-loop systems are also guaranteed to be globally uniformly ultimately bounded. Detailed parameters of the event-driven controllers are constructed under the stabilizable conditions of the closedloop systems. Finally, both the effectiveness and merits of the proposed design techniques are verified by the numerical examples.

关键词： networked control systems NCSs event-driven control dynamic output feedback control

Source characteristics of the mainshock and aftershocks of the 2019 Changning earthquake sequence:Implications for fluid effects

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Science China Earth Sciences 2023年第6期66卷 1321-1333页

作者： Kun dai Yong ZHENG Rumeng GUO Jianqiao xu School of Physics Huazhong University of Science and TechnologyWuhan 430074China Innovation Academy for Precision Measurement Science and Technology Chinese Academy of SciencesWuhan 430071China State Key Laboratory of Geological Processes and Mineral Resources School of Geophysics and GeomaticsChina University of GeosciencesWuhan 430074China

The 2019 M_(S)6.0 Changning earthquake occurred in the tectonically stable Sichuan Basin,where the epicenter and its adjacent areas are important shale gas and salt mine production fields,resulting in hot debates on whether the seismogenic mechanism of the 2019 Changning earthquake is related to human *** source characteristics and fluid pressure can provide important constraints on whether an earthquake is induced,weinvestigate the seismogenic mechanisms of the mainshock and 9 MW≥4.0 *** overall,the mainshock and the majority of the aftershocks are characterized by relatively shallow focal depths(1‒4 km)and significant non-double-couple(non-DC)***,the mainshock and the aftershocks differ in two aspects:(1)the compensated-linear-vector-dipole components dominate the non-DC components of the mainshock,whereas the isotropic components dominate the most aftershocks;(2)the fluid overpressure of the mainshock is over 30 MPa,whereas the fluid overpressure of the most aftershocks is less than 10 ***,we propose that the mainshock is triggered by weakened fault strength with long-term fluid injection,and that its large non-DC components are associated withcomplex rupture ***,the aftershocks may be triggered by postseismic stress transfer by combining the Coulomb failure stress changes in the poroelastic *** results highlight the possible role of fluid in the occurrence of the Changning earthquake sequence.

关键词： The 2019 Channing earthquake Induced earthquakes Non-double-couple components Focal depths Poroelasticity

Potential Effects of the COVID-19 Pandemic on the Developing Brain

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Neuroscience Bulletin 2023年第2期39卷 343-347页

作者： xiang Yu Xiu xu State Key Laboratory of Membrane Biology School of Life SciencesPeking-Tsinghua Center for Life Sciencesand Peking University McGovern InstitutePeking UniversityBeijing 100871China Autism Research Center of Peking University Health Science Center Beijing 100191China Chinese Institute for Brain Research Beijing 102206China Department of Child Healthcare Children’s Hospital of Fudan UniversityShanghai 201102China

By now,the COVID-19 pandemic has affected all corners of the world for over two *** years constitutes 4%of the life experience of a 50-year-old,or 50%of the life experience of a ***,in terms of the sheer proportion of... 详细信息

关键词： has she ID