Intrinsic kinetics study of LPDME process from syngas over bi-functional catalyst

The intrinsic kinetics of the three-phase dimethyl ether (DME) synthesis from syngas over a bi-functional catalyst has been investigated in a agitated slurry reactor at 20–50 bar, 200–240 °C and H₂/CO feed ratio from 1 to 2. The bi-functional catalyst was prepared by physical mixing of CuO/ZnO/Al₂O₃ as methanol synthesis catalyst and H-ZSM-5 as methanol dehydration catalyst. The three reactions including methanol synthesis from CO and H₂, methanol dehydration and water gas shift reaction were chosen as the independent reactions. A kinetic model for the combined methanol and DME synthesis based on a methanol synthesis model proposed by Graaf et al. [G.H. Graaf, E.J. Stamhuis, A.A.C.M. Beenackers, Kinetics of low pressure methanol synthesis, Chem. Eng. Sci. 43 (12) (1988) 3185; G.H. Graaf, E.J. Stamhuis, A.A.C.M. Beenackers, Kinetics of the three-phase methanol synthesis, Chem. Eng. Sci. 43 (8) (1988) 2161] and a methanol dehydration model by Bercic and Levec [G. Bercic, J. Levec, Intrinsic and global reaction rate of methanol dehydration over γ-Al₂O₃ pellets, Ind. Eng. Chem. Res. 31 (1992) 399–434] has been fitted our experimental data. The obtained coefficients in equations follow the Arrhenius and the Van’t Hoff relations. The calculated apparent activation energy of methanol synthesis reaction and methanol dehydration reaction are 115 kJ/mol and 82 kJ/mol, respectively. Also, the effects of different parameters on the reactor performance have been investigated based on the presented kinetic model.     

新型氨基脲衍生物的合成及其阴离子识别性能

以3-异氰酸丙基三乙氧基硅烷和2, 4-二硝基苯肼为原料,制备了一种氨基脲衍生物阴离子受体R,其结构通过1H/13C NMR等方法表征。在纯DMSO体系下,受体R通过紫外-可见吸收光谱的变化及溶液颜色的显著差别对F-、Ac-和CN-离子表现出良好的识别能力。此外,通过向体系中加入30%的竞争溶剂H2O可以达到对CN-离子的单一识别效应。根据Benesi-Hidebrand方程,受体R单一识别氰根离子的络合常数为8.58 ? 103 L/mol,且检出限为1.47 uM,Job曲线分析证实受体与阴离子的结合比为1 : 1。利用1H NMR滴定实验及理论计算表明受体R与阴离子是以氢键形式相结合的识别机制,未发现脱质子过程。     

Li-substituted P2-Na0.66LixMn0.5Ti0.5O2 as an advanced cathode material and new “bi-functional” electrode for symmetric sodium-ion batteries

In this study, we have introduced the layered materials P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ as cathode materials for sodium ion batteries (SIBs), and then P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ was employed as bi-functional electrode in SIBs. The structural stability and electrochemical properties of P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ were promoted by inserting lithium. The Na_0.66Li_0.2Mn_0.5Ti_0.5O₂ as a cathode material can exhibit a reversible discharge capacity of 128?mA?h?g^?1 at 0.1C after 100 cycles, and even deliver 72?mA?h?g^?1 at 5C. Interestingly, the P2-Na_0.66Li_0.2Mn_0.5Ti_0.5O₂ is studied as a “bi-functional” active material for symmetric sodium-ion batteries. This novel symmetric full cell exhibits 65?mA?h?g^?1 at a current density of 20?mA?g^?1.     

Transition metal carbides coupled with nitrogen-doped carbon as efficient and stable Bi-functional catalysts for oxygen reduction reaction and hydrogen evolution reaction

Developing non-precious metal catalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for proton exchange membrane fuel cell (PEMFC), metal-air batteries and water splitting. Here, we report a in-situ simple approach to synthesize ultra-small sized transition metal carbides (TMCs) nanoparticles coupled with nitrogen-doped carbon hybrids (TMCs/NC, including WC/NC, V₈C₇/NC and Mo₂C/NC). The TMCs/NC exhibit excellent ORR and HER performances in acidic electrolyte as bi-functional catalysts. The potential of WC/NC at the current density of 3.0 mA cm^?2 for ORR is 0.814 V (vs. reversible hydrogen electrode (RHE)), which is very close to Pt/C (0.827 V), making it one of the best TMCs based ORR catalysts in acidic electrolyte. Besides, the TMCs/NC exhibit excellent performances toward HER, the Mo₂C/NC only need an overpotential of 80 mV to drive the current density of 10 mA cm^?2, which is very close to Pt/C (37 mV), making it the competitive alternative candidate among the reported non-precious metal HER catalysts.     

A DFT Study of Pyrrole-Isoxazole Derivatives as Chemosensors for Fluoride Anion

The interactions between chemosensors, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (AIC) derivatives, and different anions (F⁻ Cl⁻, Br⁻, AcO⁻, and H₂PO₄⁻) have been theoretically investigated using DFT approaches. It turned out that the unique selectivity of AIC derivatives for F⁻ is ascribed to their ability of deprotonating the host sensors. Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT). The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only.     

Highly efficient methanol oxidation on durable PtxIr/MWCNT catalysts for direct methanol fuel cell applications

Development of highly active and durable Pt based anode materials with higher utilization of Pt is quite crucial towards the commercial viability of direct methanol fuel cells (DMFCs). Herein, multi-walled carbon nanotube supported Pt_xIr nanostructures (Pt_xIr/MWCNT) are successfully prepared by one-pot wet chemical reduction without any surfactants. The role of Ir content and its bi-functional mechanism on kinetics of methanol oxidation reaction (MOR) was studied. The MOR on Pt_xIr/MWCNT follows Langmuir-Hinshelwood mechanism by successive oxidative removal of CO. The co-existence of IrO₂ plays a vital role as catalytic promotor. Amongst, Pt₂Ir/MWCNT shows enhanced electrocatalytic activity (mass activity (MA), 933.3 mA/mg_Pt) and durability (13.8% loss of MA after 5000 potential cycles) thru the well-balanced electronic and bi-functional effects. This study implies that the optimized composition of Pt₂Ir/MWCNT exhibits efficient methanol oxidation and could be a potential catalyst for direct methanol fuel cells.     

基于杯[4]芳烃的选择性识别二酸的化学传感器

设计、合成了以杯[4]芳烃为平台,以氨基吡啶基团为双识别位点的新型化学传感器,并用红外光谱、质谱、核磁共振和元素分析方法对其进行了表征。紫外和荧光光谱研究结果表明,该受体分子在二氯甲烷溶液中能选择性识别脂肪二酸,络合常数可达103~104L/mol,络合能力大小顺序为:丙二酸>草酸>丁二酸>戊二酸>已二酸。     

Detection and Discrimination of Mixed Odor Strands in Overlapping Plumes Using an Insect-Antenna-Based Chemosensor System

Olfactory signals, a major means of communication in insects, travel in the form of turbulent odor plumes. In terrestrial environments, an odor blend emitted from a single point source exists in every strand of the plume, whereas, in confluent plumes from two different odor sources, the strands have some chance of being coincident and comprising a new third odor in those strands. Insects have the ability to detect and interpret necessary olfactory information from individual filamentous odor strands in complex multifilament odor plumes. However, behaviorists have had no way to measure the stimulus situations they are presenting to their temporally acute insect subjects when performing Y-tube olfactometer or confluent pheromone plume wind tunnel assays. We have successfully measured the degree of plume-strand mixing in confluent plumes in a wind tunnel by using a multichannel insect-antenna-based chemosensor. A PC-based computer algorithm to analyze antennal signals from the probe portion of the system performed real-time signal processing and, following a short training session, classified individual odorant/mixture strands at sub-second temporal resolution and a few tens of millimeters of spatial resolution. In our studies, the chemosensor classified a higher frequency of strands of two different odorants emitted from two closely spaced filter papers as being “mixed” when the sources were located only 1 or 2 cm apart than when the sources were 5 or 10 cm apart. These experiments demonstrate the chemosensor’s potential to be used for measuring odor stimulus situations in more complex multiple-plume environments.     

2D MXenes and their heterostructures for HER,OER and overall water splitting: A review

MXenes are a family of 2D transition metal carbides, nitrides, and carbonitrides that have surface termination groups such as –OH, –O, and –F. The presence of transition metal imparts conductivity, surface termination groups induce hydrophilicity and layered structure offers large surface area which makes MXenes a potential candidate to be utilized as an electro-catalyst with enhanced efficiency. The Water Electrolysis (WE) efficiency of an electro-catalysts is dependent on the performance of half-cell reactions i.e. Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER). The OER kinetics of most of the bi-functional electrocatalysts are considered sluggish due to which they are tested in alkaline media. However, due to the metallic nature and surface properties of MXenes, they as substrate not only improve HER performance of grown electro-catalyst but also facilitate OER kinetics which is considered sluggish for most bi-functional electrocatalysts. This review presents the significance of MXenes as HER, OER, and bi-functional electrocatalysts by discussing the electrocatalytic properties of a wide range of MXenes and how their hetero-structures affect HER, OER, and bi-functional electrocatalytic performance. In the end, the current challenges, and future perspectives of MXenes and their nanocomposites for water electrolysis have been discussed.     

Colorimetric detection of Hg2+ using a mixture of an anionic azo dye and a cationic polyelectrolyte in aqueous solution

We investigated a colorimetric chemosensor for Hg²⁺ based on a mixture of xylidyl blue I as an anionic organic dye and poly(diallyldimethylammonium chloride) as a cationic polyelectrolyte in an aqueous solution at pH 7.5. The addition of Hg²⁺ to the mixture induced a bathochromic shift in the absorption spectra with a distinct color change from red to green which was readily identifiable by the naked eye, whereas the other metal ions gave rise to insignificant color changes. By contrast, upon adding Hg²⁺ to xylidyl blue I alone, the solution underwent no significant change in color. Moreover, a stoichiometric ratio for the complex between xylidyl blue I and Hg²⁺ in the presence of poly(diallyldimethylammonium chloride) was determined to be 1:1 by the absorption titration curve and Job's plot. Thus, the mixture can be used as a selective naked‐eye colorimetric chemosensor for Hg²⁺ over other common metal ions. This study raises the possibility that the combination of an organic dye and an oppositely charged polyelectrolyte is a potential candidate for the easy construction of a new chemosensor system. © 2018 Society of Chemical Industry