查看更多>>摘要：An economically viable approach for the synthesis of different a, p-unsaturated aldehydes through modified cross-aldol condensation reaction has been developed. In this synthetic process, acetaldehyde is generated in situ through the catalytic dehydrogenation of the ethanol. The dehydrogenation reaction is found to occur over copper oxide nanoparticles supported on magnesium exchanged zeolite-Y. The formation of acetaldehyde through dehydrogenation of ethanol is confirmed by the modified Hantzsch reaction. Different kinetic studies have been performed to predict the rate of acetaldehyde as well as cinnamaldehyde formation. The formation of α, β-unsaturated aldehydes through the dehydrogenative cross-aldol reaction of ethanol with various aldehydes are found to be dependent on different reaction parameters viz temperature, catalyst amount, time, and the nature of bases. The catalytic dehydrogenation process is found to occur within 80-100 °C. TDDFT calculations are used to correlate the electronic spectra of Hantzsch reaction product with the experimental one.
查看更多>>摘要：Transition metal dichalcogenides have shown promising electromagnetic wave absorption performance but the low conductivity of their stable phases, such as 2H, has restricted further development in their applications. In this work, a stable 1T' MoTe2/m-SiO2 composite was successfully synthesized by a phase-tailoring chemical vapor deposition method. Highly ordered mesoporous SiO2 was selected as template due to its capability to reducing the permittivity and increasing the interfacial polarization loss through its porous structure. Different configurations of the composites were analyzed, it was found that the microwave absorption activity is determined by the content of 1T' MoTe2. The composite prepared with a 56.78 wt% content of 1T' MoTe2 presented an optimized reflection loss of 63.17 dB at the Ku band with 1.8 mm of thickness. Its effective absorption bandwidth was as large as 4.7 GHz at 1.8 mm in the Ku band. These findings indicate that 1T' MoTe2/m-SiO2 composite can be applied as microwave absorbers with efficient performance.
查看更多>>摘要：High aspect ratio zeolite crystals and their seeding on support are of high desire for the fabrication of oriented zeolite membranes. Here, platelike MFI crystals, as zeolite seeds, are successfully seeded on a α-Al2O3 disk support through a transfer printing method. Firstly, platelike MFI crystals are spread on a flat substrate pre-coated with films of polyvinyl alcohol (PVA) and a fluoropolymer (4200UR) followed by coating a polymethyl methacrylate (PMMA) film. After dissolving the PVA film, the free-standing sandwich-like 4200UR-MFI-PMMA film is transferred onto the support. Then, platelike MFI crystals are successfully seeded after removing the organic species by calcination. Finally, highly (h0h)-oriented, dense and continuous silicalite-1 membranes are fabricated after a secondary growth in a zeolitic synthesis system, confirmed by XRD and SEM techniques. Binary separation of butane isomer has been performed on the silicalite-1 membranes prepared with different synthesis time, achieving a n-butane permeance and a separation factor of 2.27 x 10~(-7) mol m~(-2) s~(-1)·Pa~(-1)) and 28.8 for an equimolar n-butane/i-butane mixture at 343 K, respectively.
查看更多>>摘要：A simple preparation of sulfonated-silica/carbon (SiO2/C-SO3H) composites from rice husk at different carbonization temperatures have been demonstrated. These composites have been employed as heterogeneous Br0nsted acid catalysts in converting fructose into methyl levulinate (ML) in a one-pot reaction that involves dehydration, etherification, and rehydration processes. As the carbonization temperature increased, the results from N2 adsorption-desorption isotherm showed porosity and the surface area of the composites were increased. The acid strength was also increased, as confirmed by the Temperature-Programmed Desorption of Ammonia (NH3-TPD) profile. Energy-Dispersive X-ray (EDX) analysis revealed the SiO2/C weight ratios of the composite were increased, but S/C weight ratios were decreased. 90% yield of ML was synthesized at 165 °C for 7 h in methanol solvent. Pearson's correlation test showed that hydrophilicity is the main factor in obtaining high turnover number (TON). The yield was dropped in recycling experiments due to carbonaceous deposition, which caused deactivation, as corroborated by the Thermogravimetric Analysis (TGA) and N2 sorption analysis. These composites were also able to convert fructose into 56-74% yield of 5-hydroxymethylfurfural (HMF) in dimethylsulfoxide (DMSO) solvent at 130 °C for 5 h.
查看更多>>摘要：Silver-functionalized silica aerogel (Ag~0-Aerogel) is considered a promising porous adsorbent for the capture of iodine from nuclear fuel reprocessing off-gas. The Ag~0-Aerogel, nevertheless, experiences a steady loss of capacity when exposed to NO2 in the off-gas. This phenomenon is known as aging and its governing processes remain unclear. We exposed Ag~0-Aerogel samples to 2% NO2 in dry air at 150 °C for up to 1 month, followed by I2 loading. Samples were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Our results elucidated the precise Ag species in Ag~0-Aerogel that adsorb I2: (i) Ag~0 nanoparticles, (ii) Ag thiolates (Ag-S-r) covering the nanoparticles and the aerogel backbone, and (iii) Ag-S complexes including amorphous Ag2S. We unraveled the two predominant underlying processes of aging in NO2: (i) Ag-S-r is oxidized by NO2 forming silver sulfonate (Ag-SO3-r) which is oxidized further to silver sulfate (Ag2SO4) molecules, (ii) Ag2SO4 molecules then migrate from the pores to the aerogel surface and aggregate yielding Ag2SO4 particles that do not adsorb I2. Plausible reaction pathways and aggregation mechanisms are explored. These findings may be used to guide the discovery of more advanced materials for iodine capture and the development of accurate predictive models.
查看更多>>摘要：To develop an efficient hydrogen purification adsorbent, M-MOF-74 (M = Mg, Co, Ni, Zn and Cu) was synthesized by hydrothermal method, and super activated carbon (AX-21) was incorporated to form a new type of porous material for H2 purification from COG. Prepared samples were characterized by physical and structural properties and then compared by adsorption equilibrium. The dynamic adsorption performance of the materials during H2 purification was comprehensively evaluated by binary, multi-component measurements and multi-component breakthrough profiles. Adsorption isotherms were used to estimate selectivity values for CO2/H2, CH4/H2, N2/H2 and (CO2 + CH4 + N2)/H2. The results show that Mg-MOF-74 has the largest selectivity value among M-MOF-74. AX-Mg-MOF-74 incorporated with AX-21 at a mass ratio of 0.15 exhibited an average 30.88% increase in CO2, CH4, N2 and H2 adsorption capacity compared to pure Mg-MOF-74. In addition, the mean selectivity values for CO2/H2, CH4/H2, N2/H2 and (CO2 + CH4 + N2)/H2 are increased by 8.3%, 6.8%, 47.7% and 11.0% respectively.
查看更多>>摘要：Defects in silicalite-1 membrane is readily healed by an alkaline-treatment in aqueous solutions of NaOH and organic additives such as cetyltrimethylammonium bromide (CTAB) and tetramethylammonium bromide (TMABr). In this study, we investigated the role of organic additive in the course of alkaline-treatment. From the evaluation of weight and micropore volume of silicalite-1, it was shown that 3.6 and 3.1 molecules per unit cell of CTA~+ and TMA~+ entered the micropore of silicalite-1 during the treatment. CTA~+ or TMA~+ locating in the micropore inhibited the diffusion of NaOH into the micropore of zeolite and suppressed the dissolution from the inside of crystal. In contrast, the defect in silicalite-1 membrane was not healed by using an aqueous solution of NaOH and tetrabutylammonium bromide (TMABr), which was not able to enter the micropore of silicalite-1. We concluded that the use of organic additives, which can enter the micropore, was important for the defect-healing of siliclaite-1 membrane by the alkaline-treatment.
查看更多>>摘要：Two liquid-loaded covalent organic framework composites (IL-COFs) with exceptional periodic molecular ordering, porosities and well-defined pores were constructed by loading ionic liquid (IL, [Emim]ESe) into TFPB-TAPT COF and BTA-TAPT COF. The as prepared IL-COFs present excellent electrochemical properties, especial for [Emim]ESe-TFPB-TAPT COF. It shows an initial specific capacitance of 521 F/g at the current density of 1 A/g and remains 372 F/g at a high current density of 4 A/g with prominent rate performance. In addition, it could retain 76% of the initial capacitance after 5000 charge-discharge cycles (396 F/g), which was better than those of the most of analogous materials reported previously. This work may shed light on designing and fabricating the COF-based electrode materials for supercapacitors.
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