Hybrid Organic−Inorganic Solids That Show Shape Selectivity

Hybrid organic−inorganic solids featuring millimolar/gram concentrations of intracrystalline organic moieties and shape-selectivity are synthesized. Pure-silica zeolite beta crystals are coated with zirconia and treated in aqueous sodium hydroxide to create defects and mesoporosity within the crystalline structure. Aminopropyl organic groups are subsequently grafted onto the generated intracrystalline silanol groups. After grafting, characterization data indicate a high organic concentration localized primarily within the intracrystalline voids. Specifically, thermogravimetric analysis shows an organic loading of 0.7 mmol of NH_2/g, ^(29)Si solid-state nuclear magnetic resonance (NMR) spectra display a quantitative decrease in Q^3 silicon atoms with a corresponding resharpening of the Q^4 resonances, and N_2 adsorption data show a decrease in micropore volume to 0.10 cm^3/g. Knoevenagel condensation reactions are catalyzed by the aminopropyl-functionalized materials using differently sized aldehydes and the results show that the zirconia-protected functionalized solid have shape selective properties

Deviations of Fischer-Tropsch products from an Anderson-Schulz-Flory distribution

Negative deviations from an Anderson-Schulz-Flory distribution have been observed for the product of the Fischer-Tropsch synthesis. The catalyst was a complex-derived iron-calcium catalyst promoted with cesium sulphate, therefore, neither carrier acidity nor shape selectivity can explain the deviations. This is the first time that chemical modifications of the catalyst are observed to result in negative ASF deviations

Characteristic and Catalytic for Mordenite and Zsm-5 Reaction in Produce Hydrocarbons

Conversion of methanol to the use of the treated mordenite and ZSM-5 studied in this description. Mordenite catalyst activity which showed a decrease in activity without modified quickly. After hydrothermally dealuminated mordenite done and acidification with HCl, it turns out that longer life of the catalyst thus obtained. Furthermore treated mordenite showed high selectivity to olefin formation. Acidity is measured with predictably by Spectrophotometer Infra Red observations of pyridine adsorbed, also signal of the adsorbed NO. Number of sites was reduced in the presence of acid dealumination treatment. There is no longer detectable acidity found in mordenite which has dealuminated well. Pore volume measured by the adsorption of toluene. The better stability and selectivity of the catalyst in forming various olefins in the use of the treated mordenite discussed here in terms of acidity and shape selectivity

Neural delays shape selectivity to interaural intensity differences in the lateral superior olive

Neurons in the lateral superior olive (LSO) respond selectively to interaural intensity differences (IIDs), one of the chief cues used to localize sounds in space. LSO cells are innervated in a characteristic pattern: they receive an excitatory input from the ipsilateral ear and an inhibitory input from the contralateral ear. Consistent with this pattern, LSO cells generally are excited by sounds that are more intense at the ipsilateral ear and inhibited by sounds that are more intense at the contralateral ear. Despite their relatively homogeneous pattern of innervation, IID selectivity varies substantially from cell to cell, such that selectivities are distributed over the range of IIDs that would be encountered in nature. For some time, researchers have speculated that the relative timing of the excitatory and inhibitory inputs to an LSO cell might shape IID selectivity. To test this hypothesis, we recorded from 50 LSO cells in the free-tailed bat while presenting stimuli that varied in interaural intensity and in interaural time of arrival. The results suggest that, for more than half of the cells, the latency of inhibition was several hundred microseconds longer than the latency of excitation. Increasing the intensity to the inhibitory ear shortened the latency of inhibition and brought the timing of the inputs from the two ears into register. Thus, a neural delay of the inhibition helped to define the IID selectivity of these cells, accounting for a significant part of the variation in selectivity among LSO cells

Shape Selectivity by Guest- Driven Restructuring of a Porous Material

A flexible metal-organic framework selectively sorbs para- (pX) over meta-xylene (mX) by synergic restructuring around pX coupled with generation of unused void space upon mX loading. The nature of the structural change suggests more generally that flexible structures which are initially mismatched in terms of fit and capacity to the preferred guest are strong candidates for effective molecular separations

Charge-Transfer Probes for Molecular Recognition \u3cem\u3evia\u3c/em\u3e Steric Hindrance in Donor-Acceptor Pairs

Molecular association of various aromatic hydrocarbons (D, including sterically hindered donors) with a representative group of diverse acceptors (A = quinone, trinitrobenzene, tetracyanoethylene, tropylium, tetranitromethane, and nitrosonium) is visually apparent in solution by the spontaneous appearance of distinctive colors. Spectral (UV−vis) analyses of the colored solutions reveal their charge-transfer origin (λCT), and they provide quantitative information of the intermolecular association in the form of the KDA and εCT values for the formation and visualization, respectively, of different [D,A] complexes. Importantly, such measurements establish charge-transfer absorption to be a sensitive analytical tool for evaluating the steric inhibition of donor−acceptor association. For example, the steric differences among various hindered aromatic donors in their association with quinone are readily dramatized in their distinctive charge-transfer (color) absorptions and verified by X-ray crystallography of the charge-transfer crystals and/or QUANTA molecular modeling calculations of optimum intermolecular separations allowed by van der Waals contacts

Xylene isomerization over zeolite catalysts

Paraxylene is used as a raw material for the production of the synthetic fibers. The production of paraxylene can be obtained by isomerization of xylene using zeolites as catalyst. At equilibrium, the mixture of xylene contains 24% para, 24% ortho and 52% of metaxylene. The objective of this experiment is to access the effectiveness of several zeolite catalysts for the isomerization of xylene. The study was carried out using micro reactor packed with zeolite (0.5g). In this work, the activity and selectivity of the catalyst in the isomerization of xylene depend on the type of zeolite used. HZSM-5 catalyst gives higher activity and selectivity over other type of zeolite