THF-FER沸石的系列研究IV.固体酸性及C5烯烃骨架异构化催化性能

在四氢呋喃(THF)-Na2O-SiO2-Al2O3-H2O体系中水热合成的THF-FER沸石,经酸交换／焙烧或焙烧／酸交换处理可制得H-FER-1和H-FER-2两种H型沸石．红外光谱及NH3-TPD等实验结果表明,两者的强酸位主要是对烯烃骨架异构化反应有贡献的Bronsted酸位．1073K／10h的高温水蒸汽处理会导致沸石骨架脱铝,但并未产生过多的末端硅羟基．两者比较,H-FER-1沸石的结构缺陷较少,Bronsted酸位较多,骨架更完美．由THF-FER沸石制备的H-FER催化剂,对C5正构烯烃骨架异构化反应显示了优良的催化活性、选择性及稳定性．     

Synthesis and crystal structure of langbeinite related mixed‐metal phosphates K1.822Nd0.822Zr1.178(PO4)3 and K2LuZr(PO4)3

Two potassium lanthanide zirconium orthophosphates with general composition K_1.822Nd_0.822Zr_1.178(PO₄)₃ (KNdZrP) and K₂LuZr(PO₄)₃ (KLuZrP) were prepared using the flux technique. Original synthetic procedure has been examined for the flux growth of the complex phosphates containing zirconium and lanthanide. Both compounds have been synthesized in the complex melts containing at the same time potassium phosphates and transition metal fluorides. The structures were solved from the single crystal (KNdZrP) and powder (KLuZrP) X‐ray diffraction data. Both compounds are isotypic to langbeinite mineral and crystallize in cubic system (sp. gr. P2₁3) with the cell parameters a = 10.3228(2) and a = 10.29668(5) Å respectively. The rigid framework is built up from the isolated [MO₆] octahedra and [PO₄] tetrahedra interlinked via vertices. The potassium cations are located in the large closed cavities of the framework. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Absorption of dilaton partial waves by D3-branes

We calculate the leading term in the low-energy absorption cross section for an arbitrary partial wave of the dilaton field by a stack of many coincident D3-branes. We find that it precisely reproduces the semiclassical absorption cross section of a 3-brane geometry, including all numerical factors. The crucial ingredient in making the correspondence is the identification of the precise operators on the D3-brane world-volume which couple to the dilaton field and all its derivatives. The needed operators are related through T-duality and the IIA/M-theory correspondence to the recently determined M(atrix) theory expressions for multiple moments of the 11D supercurrent. These operators have a characteristic symmetrized trace structure which plays a key combinatorial role in the analysis for the higher partial waves. The results presented here give new evidence for an infinite family of non-renormalization theorems which are believed to exist for two-point functions in N=4 gauge theory in four dimensions.     

Absolute binding free energies for octa-acids and guests in SAMPL5

As part of the SAMPL5 blind prediction challenge, we calculate the absolute binding free energies of six guest molecules to an octa-acid (OAH) and to a methylated octa-acid (OAMe). We use the double decoupling method via thermodynamic integration (TI) or Hamiltonian replica exchange in connection with the Bennett acceptance ratio (HREM-BAR). We produce the binding poses either through manual docking or by using GalaxyDock-HG, a docking software developed specifically for this study. The root mean square deviations for our most accurate predictions are 1.4 kcal mol^?1 for OAH with TI and 1.9 kcal mol^?1 for OAMe with HREM-BAR. Our best results for OAMe were obtained for systems with ionic concentrations corresponding to the ionic strength of the experimental solution. The most problematic system contains a halogenated guest. Our attempt to model the σ-hole of the bromine using a constrained off-site point charge, does not improve results. We use results from molecular dynamics simulations to argue that the distinct binding affinities of this guest to OAH and OAMe are due to a difference in the flexibility of the host. We believe that the results of this extensive analysis of host-guest complexes will help improve the protocol used in predicting binding affinities for larger systems, such as protein-substrate compounds.     

Determination of Internal Energy Distributions of Laser Electrospray Mass Spectrometry using Thermometer Ions and Other Biomolecules

The internal energy distributions for dried and liquid samples that were vaporized with femtosecond duration laser pulses centered at 800 nm and postionized by electrospray ionization-mass spectrometry (LEMS) were measured and compared with conventional electrospray ionization mass spectrometry (ESI-MS). The internal energies of the mass spectral techniques were determined by plotting the ratio of the intact parent molecular features to all integrated ion intensities of the fragments as a function of collisional energy using benzylpyridinium salts and peptides. Measurements of dried p-substituted benzylpyridinium salts using LEMS resulted in a greater extent of fragmentation in addition to the benzyl cation. The mean relative internal energies, int> were determined to be 1.62?±?0.06, 2.0?±?0.5, and 1.6?±?0.3 eV for ESI-MS, dried LEMS, and liquid LEMS studies, respectively. Two-photon resonances with the laser pulses likely caused lower survival yields in LEMS analyses of dried samples but not liquid samples. In studies with larger biomolecules, LEMS analyses of dried samples from glass showed a decrease in survival yield compared with conventional ESI-MS for leucine enkephalin and bradykinin of ~15% and 11%, respectively. The survival yields for liquid LEMS analyses were comparable to or better than ESI-MS for benzylpyridinium salts and large biomolecules. Figure

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The double phosphates MIMIIPO4 (MI – Na,K; MII – Mg,Mn, Co,Ni, Zn) – synthesis from chloride melts and characterization

The particularities of the chemical interaction in systems M^IPO₃‐M^IIO(or Mn₂O₃)‐M^ICl (M^I – Na, K; M^II – Mg, Co, Ni, Zn) have been investigated at the temperature 1073 K and molar ratios P/M^x = 1 or 2 and M^ICl/(M^IPO₃ + M^IIO(or Mn₂O₃)) = 30. The conditions of formation of complex phosphates M^ІM^IIPO₄ and Na₄Ni₃(PO₄)₂P₂O₇ have been found. Influences of the nature of alkali and bivalent metals on the products composition were discussed. The advantages of chloride melts using (synthesis time reduction and temperature reducing) for preparing of complex phosphates were shown. The synthesized compounds have been characterized using the powder X‐ray diffraction, Fourier transform infrared and diffuse reflectance spectroscopies.     

Interaction between Co2P4O12 and alkali metal nitrate (chloride) melts

Reactions between Co₂P₄O₁₂ and alkali metal nitrate (chloride) melts was studied in the temperature range 350–400°C (800–850°C) at different phosphate/melt ratios. The effect of the nature of an alkali metal and the ratio between the components in the Co₂P₄O₁₂-M^INO₃ (M^ICl) system on composition of the reaction products was established. The resulting crystalline phases (NaCoPO₄, Na₄Co₃(PO₄)₂P₂O₇, Na₉Co₃(PO₄)₅ and KCoPO₄) were studied by X-ray powder diffraction, IR and electron spectroscopy, and scanning electron microscopy. The features of transformation of the Co₂P₄O₁₂ framework into KCoPO₄ under the effect of excessive alkali metal ions in the melt are discussed.     

Direct Air Capture of CO2 by Physisorbent Materials

Sequestration of CO₂, either from gas mixtures or directly from air (direct air capture, DAC), could mitigate carbon emissions. Here five materials are investigated for their ability to adsorb CO₂ directly from air and other gas mixtures. The sorbents studied are benchmark materials that encompass four types of porous material, one chemisorbent, TEPA‐SBA‐15 (amine‐modified mesoporous silica) and four physisorbents: Zeolite 13X (inorganic); HKUST‐1 and Mg‐MOF‐74/Mg‐dobdc (metal–organic frameworks, MOFs); SIFSIX‐3‐Ni , (hybrid ultramicroporous material). Temperature‐programmed desorption (TPD) experiments afforded information about the contents of each sorbent under equilibrium conditions and their ease of recycling. Accelerated stability tests addressed projected shelf‐life of the five sorbents. The four physisorbents were found to be capable of carbon capture from CO₂‐rich gas mixtures, but competition and reaction with atmospheric moisture significantly reduced their DAC performance.