A co-coordination strategy to realize janus-type bimetallic phosphide as highly efficient and durable bifunctional catalyst for water splitting

In this work,a Janus-type dual-ligand metal-organic frameworks derived bimetallic (Fe,Co)P nanoparticles embedded carbon nanotube (CNT) skeleton (DLD-FeCoP@CNT) is presented and synthesized via a facile co-coordination synthesis strategy.The DLD-FeCoP@CNT hybrid shows much better performances for OER and HER with much lower Tafel slope of 39.6 (57.1) mV dec-1,an overpotential of 286 (166) mV@10 mA cm-2 and better stability for OER (HER) in 1 M KOH.Being both cathode and anode for water splitting,it requires only a low voltage of 1.67 V to obtain 10 mAcm-2 with nearly 100％ faradaic efficiency,which is close to Pt/C//RuO2 cell.Density functional theory calculations based on the bimetallic phosphide (Fe0.3Co0.7P) model reveal that,compared with the monometallic FeP or CoP,the enhanced catalytic activities of Fe0.3Co0.7P is mainly manifested in its free energy of H adsorption (△GH*) closer to zero,larger binding strength for H2O and higher electrical conductivity.     

Boron bridged NiN4B2Cx single-atom catalyst for superior electrochemical CO2 reduction

Single-atom nickel catalysts hold great promise in the application of electrocatalytic carbon dioxide reduction reaction (CO₂RR), but suffer from the sluggish kinetics and serious competitive hydrogen evolution reaction (HER), which restrict their overall catalytic performance. Herein, we report a boron-bridging strategy to manipulate the atomic coordination structure and construct a single-atom nickel catalyst with an active center of NiN₄B₂ to realize excellent CO₂RR performance. Density functional theory analysis suggests that the unique NiN₄B₂ sites with tuned electronic structure facilitate the adsorption of CO₂ molecules and effectively suppress the HER pathway by increasing corresponding energy barrier. As-obtained Ni-SAs@BNC catalyst with a NiN₄B₂ structure exhibits significantly enhanced catalytic activity and selectivity than commonly used single-atom nickel catalysts with a NiN₄ structure, especially at high applied potentials. A high current density of up to (214 ± 21) mA cm⁻² at a potential of −1.2 V with a high CO Faraday efficiency (FE_CO) of ∼97% was achieved in a flow cell. This work inspires new insights into the rational design of atomic coordination structure of single-atom catalysts with tunable electronic structure for superior electrocatalytic activities.     

含氮多孔炭的制备及其在二氧化碳吸附中的应用

以甲醛(F)和间苯二酚(R)为炭源,赖氨酸为催化剂,采用快速溶胶凝胶法所制含氮多孔炭(RFL)对CO2具有较高的吸附能力;为增加RFL的氮含量,引入适量的三聚氰胺(M),制得的多孔炭(RFLM)含N量增加,比表面积和孔体积也有所增加;在合成体系中进一步引入谷氨酸(G),可使聚合反应速率得到控制,且多孔炭(RFLMG)的织构性质也得到进一步优化。RFLM和RFLMG对CO2的吸附能力较RFL弱,说明多孔炭的含N量与其对CO2的吸附能力没有明确的线性关系,而含氮官能团的存在形式会影响多孔炭对CO2的吸附能力。     

二氧化碳腐蚀机理及影响因素

综述了钢材发生二氧化碳腐蚀的机理，较系统地介绍了影响二氧化碳腐蚀的因素诸如材质因素和环境因素等。     

二氧化碳气瓶瓶阀爆破片爆破浅析

20 0 1年 2月天津某医院一只二氧化碳气瓶瓶阀爆破片爆破 ,经分析 ,计算确认为低温时充装过量 ,常温时超压引起的并总结了应注意的问题     

Enhancing both selectivity and coking-resistance of a single-atom Pd<Subscript>1</Subscript>/C<Subscript>3</Subscript>N<Subscript>4</Subscript> catalyst for acetylene hydrogenation

Selective hydrogenation is an important industrial catalytic process in chemical upgrading,where Pd-based catalysts are widely used because of their high hydrogenation activities.However,poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns.In this work,atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C3N4) using atomic layer deposition.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation.During selective hydrogenation of acetylene in excess ethylene,the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/A12O3 and Pd/SiO2 catalysts.In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement.More impressively,the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance.Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.     

Effect of palladium precursor and preparation method on the catalytic performance of Pd/SiO2 catalysts for benzene hydrogenation

Supported Pd catalysts on silica were prepared by different synthesis methods using Pd(Ac)₂ and PdCl₂ as salts precursors. The obtained materials were characterized by X-Ray Diffraction (XRD), H₂ chemisorption, and temperature programmed desorption of hydrogen (H₂-TPD). The catalytic performances of these catalysts have been evaluated in the hydrogenation of benzene. The obtained results show that metal dispersion and catalytic activity are strongly dependent on the salts precursor and the method of preparation of the catalyst. The catalysts prepared by hydrazine reduction exhibit higher activity in benzene hydrogenation than that by the polyol reduction method. Moreover, the catalyst prepared with palladium acetate showed higher catalytic activity than those prepared with palladium chloride. The superior catalytic performance of this catalyst in the hydrogenation of benzene was ascribed to a significantly better dispersion of Pd particles on the silica support.     

Experimental investigation on the effect of mixing length on the performance of two-phase ejector for CO2 refrigeration cycle with and without heat exchanger

In ejector system using the promising natural refrigerant CO₂, the mixing of high-speed two-phase primary flow and suction vapor is crucial in designing an efficient ejector. In this study, the effect of mixing length on ejector system performance was analyzed experimentally. The mixing lengths used were 5 mm, 15 mm, and 25 mm, with constant rectangular cross-section. The experiments were performed for both ejector and conventional expansion systems with and without internal heat exchanger (IHX) at different operating conditions. Based on the experimental results, mixing length had significant effect on entrainment ratio and on magnitude and profile of pressure recovery. The 5 mm and 15 mm types yielded the lowest and highest ejector efficiency and COP in all of the conditions used in this research, respectively. The use of IHX had net positive effect on system performance which verified the results of our previous study. A COP improvement of up to 26% over conventional system was obtained but improper sizing of mixing length lowered the COP by as much as 10%.     

Theoretical and experimental analysis of a CO2 heat pump for domestic hot water

This paper describes the development of a CO₂ air/water heat pump for the production of tap hot water in a residential building. The basic design consists of a single-stage piston compressor, a coaxial type gas cooler, an electronic expansion valve, a finned tube evaporator and a low pressure receiver. The heat pump is combined with a storage tank designed to maintain internal water stratification.The gas cooler pressure optimisation in the case of fixed water delivery temperature was theoretically analysed.A new control method for the upper cycle pressure was developed to maximise the COP of the heat pump, while the water mass flow was adjusted to maintain the set water temperature at the gas cooler exit.Before commissioning, the heat pump was factory tested to verify its energy performance and to validate the high pressure control logic.     

一种基于QCM的液相混合微芯片的制作与应用

生物定量检测中,生物样品是否均匀混合的研究意义重要。石英晶体微质量天平(QCM)因其振幅谐振机理,而具备优异的超声混合性能。本文结合微电子机械系统(MEMS)工艺,利用双面曝光、QCM预支撑和120℃长时间烘胶等改进方法,制备了尺寸可控、表面平整、结合紧密的SU-8芯片主体结构,利用聚二甲基硅氧烷(PDMS)封装获得完整的液相混合微芯片,最后利用罗丹明B荧光染料和SiO2纳米球对芯片的混合性能进行了表征。同时,本文提供了一种小体积、便捷、通用性好的液相混合微芯片的制备方法。     

Thermodynamic analysis and experimental investigation of a CO2 household heat pump dryer

Carbon dioxide is regarded as an optimal working fluid for heat pump dryers. The transcritical cycle well fits the closed-loop drying process which requires dehumidification and re-heating according to high temperature lift of the air stream.In this paper, the transcritical CO₂ cycle is compared with a sub-critical R134a cycle. The theoretical analysis is based on fixed temperature approach values at the heat exchangers. The study considers optimal high pressure for the transcritical cycle and optimal refrigerant subcooling for the sub-critical cycle. The theoretical analysis investigates the energy performance of the thermodynamic cycle as a function of the temperature and mass flow rate of the drying air. The optimisation of the operating conditions for CO₂ involves lower air temperature than in the case of R134a; this conditions can be satisfied by a suitable design of the appliance, whose thermal balance is achieved when the dissipated heat corresponds to the work spent by the compressor and the fan; the air temperature is a floating variable that adjusts its value to comply with the thermal balance. Experimental results, conducted on a prototype, give a positive assessment for CO₂ as working fluid for heat pump dryers: a negligible decrease in the electric power consumption, with a limited (+9%) increase in the cycle time, is shown in comparison with the reference R134a heat pump dryer.     

Experimental evaluation of a cascade refrigeration system prototype with CO2 and NH3 for freezing process applications

A prototype of a cascade refrigeration system using NH₃ and CO₂ as refrigerants has been designed and built. The prototype is used to supply a 9 kW refrigeration capacity horizontal plate freezer at an evaporating temperature of −50 °C as design conditions. The prototype includes a specific control system and a data acq*uisition system. The experimental evaluation started with the real conditions within the design operating parameters. Subsequently, several tests were performed fixing four CO₂ evaporating temperatures (−50, −45, −40 and −35 °C). At each one of the evaporating temperatures evaluated, the CO₂ condensing temperature was varied from −17.5 to −7.5 °C and an experimental optimum value of CO₂ condensing temperature was determined. The discussions on the experimental results include the influence of the operating parameters on the cascade system’s performance. In addition, the experimental results are compared with two common double stage refrigeration systems using NH₃ as refrigerant.     

Simple method for synthesis of carbon nanotubes over Ni-Mo/Al2O3 catalyst via pyrolysis of polyethylene waste using a two-stage process

Synthesis of valuable multi-walled carbon nanotubes (MWCNTs) by thermal pyrolysis of low-density polyethylene (LDPE) waste was investigated via a two-stage process. The first stage was the thermal pyrolysis of LDPE to gaseous hydrocarbons, and the second stage was the catalytic decomposition of the pyrolysis gases over Ni-Mo/Al₂O₃ catalysts. Two catalysts with the compositions of 5.2%Ni-10.96%Mo/Al₂O₃ and 10%Ni-9.5%Mo/Al₂O₃ were tested for carbon nanotubes (CNTs) formation. The catalyst containing 10%Ni showed better activity in terms of CNTs production. Accordingly, the impact of either pyrolysis or decomposition temperatures was investigated using the 10%Ni-9.5%Mo/Al₂O₃ catalyst. TEM, XRD, Raman spectroscopy, TGA, TPR, and BET analysis tools were used to characterize the fresh catalysts as well as the obtained carbon nanomaterials. TEM images proved that MWCNTs with various morphological structures were obtained at all pyrolysis and decomposition temperatures. Moreover, cup-stacked carbon nanotubes (CS-CNTs) were observed at the decomposition temperature of 600°C. MWCNTs with the best quality were produced at decomposition temperature of 750°C. The optimum pyrolysis and decomposition temperatures in terms of CNTs production were at 700 and 650°C, respectively.     

Development of a Coulometric Method for Assessing the Concentration of Ambient Levels of CO2/Air in Compressed Gas Mixtures

The coulometric method presented here is a reliable method for the direct analysis of CO₂/air cylinder gas mixtures. It is based on Faraday’s laws of electrolysis and therefore no external standardization is required. A series of CO₂/air cylinder gas mixtures ranging in concentration from 300 to 375 µmol/mol (ppm) were analyzed and the results compared to those results obtained by non-dispersive infrared (NDIR) analysis with traceability to gravimetric standards. The coulometric method is rapid, sensitive, precise, and with the proper experimental controls, will yield accurate results.     

Solvothermal synthesis of hybrid nanoarchitectonics nickel-metal organic framework modified nickel foam as a bifunctional electrocatalyst for direct urea and nitrate fuel cell

Urea and nitrate-based fuel cells have emerged as promising electricity generation devices. However, most of these catalysts are expensive and limited in supply, which limits their practical applications. Hence, metal-organic frameworks (MOF) have been explored as catalysts due to their low cost, easy preparation, and high redox activity. Here, we synthesize nickel-based MOF (Ni-MOF) via one-pot solvothermal technique as bifunctional electrocatalyst for the direct urea and nitrate fuel cell. The as-synthesized Ni-MOF is deposited on nickel foam (NF) and used as working electrode (Ni-MOF/NF) which demonstrates a peak current density of 188 mA/cm² for urea oxidation reaction (UOR) and −14 mA/cm² for nitrate reduction reaction (NRR) at an onset potential of ∼ 1.58 V (vs RHE), and ∼ 1.12 V (vs RHE), respectively The enhanced functionality of the Ni-MOF/NF electrode can be attributed to the high catalytic efficacy of the Ni-MOF. This is mainly due to the presence of multiple oxidation states of N (i.e., Ni^2+/3+) and excellent electronic conductivity of the organic ligands in MOF structure. Moreover, Ni-MOF/NF electrodes retain ∼ 71.2% and ∼ 83.9% capacity after 20000 s of UOR and NRR, respectively. This efficacy of the as-fabricated electrocatalyst proves MOF as a promising platform for direct fuel cell applications.     

Performance of an Array of Tin Dioxide-Based Ceramic Sensors for CO and SO2 Selective Detecting

Changes in electrical resistance of tin dioxide based ceramic pellets have been studied (as received and doped with Tl, Zn, Rh, Cu, Pt, Ir, Cd and Co) in air and at various concentrations of nitrogen mixed with CO and SO₂. In response to changes in the amount of adsorbed oxygen, the electric conductivity in direct current of the materials tested modifies accordingly. This behaviour is influenced by physical (diffusion in nitrogen) and chemical (CO and SO₂ oxidation) phenomena. It was showed that the electric answers of the sensors doped with Zn, Cu, Pt and Ir could be combined for the simultaneous determination of CO and SO₂.     

首钢35000m~3/h空分设备分子筛纯化系统故障分析及处理

简介了首钢35000m3/h空分设备分子筛纯化系统,针对空分设备运行中分子筛纯化系统出口空气中二氧化碳含量不符合要求的问题,通过对分子筛纯化系统的局部改造及合理操作,实现了分子筛纯化系统出口空气中二氧化碳含量的正常和稳定,对整套空分设备的长期稳定运行起到了重要作用。     

Infinite-Dilution Binary Diffusion Coefficients of 2-Propanone, 2-Butanone, 2-Pentanone, and 3-Pentanone in CO2 by the Taylor Dispersion Technique from 308.15 to 328.15 K in the Pressure Range from 8 to 35 MPa

Infinite-dilution binary diffusion coefficients of 2-propanone, 2-butanone, 2-pentanone, and 3-pentanone in carbon dioxide were measured by the Taylor dispersion method at temperatures from 308.15 to 328.15 K and pressures from 7.60 to 34.57 MPa. The D ₁₂ values were obtained from the response curves by the method of fitting in the time domain. The accuracy in the fitting error was examined for each measurement. The measured D ₁₂ data were found to be well correlated by the Schmidt number correlation, with AAD%=3.74% for all solutes.