The chromium terephthalate MIL‐101 has been prepared rapidly and efficiently by using microwave‐assisted hydrothermal synthesis. The resulting material exhibits giant pores and very large surface ...areas and demonstrates a huge, rapid adsorption of benzene in both vapor (see figure) and liquid phases.
As a size‐selective molecular sieve, the coordination polymer formed from cobalt and pyridine‐2,4‐dicarboxylic acid (CUK‐1, see figure) shows unprecedented selectivity for O2 and preferential ...selectivity for CO2 over CH4. The present sorption results encourage the development of new adsorbent materials that may find use in the production of high‐purity gas products. This work demonstrates that CUK‐1 can be utilized, for the first time, in the separation of light gases via gas chromatography.
Zeolitic imidazolate frameworks (ZIFs) possess unique structural, textural, and physico-chemical properties and, therefore, they are promising materials for the synthesis of catalysts. The presence ...of acidic and basic sites in the structure of ZIFs and the possibility of controlling their number and accessibility offer various ways of using ZIFs in acid-base catalysis. Domestic and foreign works devoted to the study of the catalytic properties of ZIFs in reactions of the acid-base type and published within the recent 15 years are reviewed. Special attention is given to the effect of the crystal size of ZIFs on their catalytic properties in such reactions as condensation, cyclization, and esterification. The advantages and drawbacks of ZIFs as catalysts and the main questions that arise during practical use are considered.
Bifunctional heterogeneous catalysts with pore structure have been synthesized by the coupling between nickel oxide and titanium oxide. The resulting porous nanocomposites show promising bifunctional ...catalytic activity against the selective epoxidation of olefin molecules as well as visible light driven photolysis.
Cerium-containing mesoporous materials have been synthesized by hydrothermal method and characterized by IR, DR-UV–vis and DRIFT spectroscopy, XRD and N
2 adsorption methods. Important factors ...affecting the catalytic activity of Ce-SBA-15, namely the effect of cerium content, the state of cerium ions, the state of silanol groups on the surface of Ce-SBA-15 and stability of the catalyst have been studied in the cyclohexanol and cyclohexene oxidation with hydrogen peroxide. The reaction mechanism was discussed.
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Cerium-containing mesoporous materials have been synthesized by hydrothermal method and characterized by IR, DR-UV–vis and DRIFT spectroscopy, XRD and N
2 adsorption methods. It was established that the
d
100 and unit-cell (
a
0) parameter increase with the increase of cerium content up to 2% in SBA-15 and then tend to remain the same. According to DR-UV–vis spectroscopic data, an agglomeration of cerium atoms was observed in the form of fine CeO
2 crystallites. Important factors affecting the catalytic activity of Ce-SBA-15, namely the effect of cerium content, the state of cerium ions, the state of silanol groups on the surface of Ce-SBA-15, and stability of the catalyst have been studied in the cyclohexanol and cyclohexene oxidation with hydrogen peroxide.
Oligomerization of isobutene has been investigated using several zeolite catalysts to produce triisobutenes that are useful as chemical feedstocks. Stable isobutene conversion and high selectivity ...for trimers are attained over a beta zeolite with high concentration of Lewis acid sites. Isobutene is quantitatively oligomerized over a beta zeolite with selectivity for trimers
>
50
%
up to 100 h at a high isobutene WHSV of 10 h
−1. Moreover, a deactivated catalyst can be easily regenerated by calcining in flowing air. Zeolite beta's high stability, quantitative conversion, high selectivity, and facile regeneration make it an attractive potential catalyst for isobutene trimerization.
Catalytic properties of transition-metal-containing silicate materials with hexagonally packed mesopore-channels, Ti-MMM-2 and Ce-SBA-15, have been studied in oxidative cleavage of cyclohexene (CyH) ...to adipic acid using aqueous H2O2 as oxidant. In a solvent-free system, the yield of adipic acid reached 10-15% at H2O2/CyH 3.6 mol mol-1 and 80 deg C after 72 h. The stepwise addition of the oxidant to the reaction mixture allowed increasing the yield of the target product up to 33 and 18% for Ti-MMM-2 and Ce-SBA-15, respectively. For both catalysts, the yield of adipic acid decreased significantly in the second run despite CyH conversion attained 100%. The catalyst stability and the reasons of the deactivation have been explored. For both catalytic materials, partial decrease of the mesopore surface area and mesopore volume was observed after the CyH oxidation run. DRS-UV-vis study revealed irreversible formation of oligomerized TiO2-like species on the Ti-MMM-2 surface due to interaction of Ti centres with the oxidant and the reaction products. The elemental analysis data showed that adipic acid causes leaching of titanium from Ti-MMM-2 into solution. Ce-SBA-15 was found to be more stable with respect to the active metal leaching but prone to deactivation due to agglomeration of cerium ions to form cerium oxide nanocrystallites; partial reduction of Ce(IV) to Ce(III) also occurred.
Pure and Ru-doped nanostructured SnO
2 sensing materials were synthesized using a modified Pechini route. Incorporation of Ru in SnO
2 results in the reduction of particle size (8.3
nm) compared with ...that of the pure SnO
2 (28.2
nm). Moreover, the sensor exhibited a reasonably good sensitivity towards both H
2 and liquified petroleum gas (LPG). The effect of Ru incorporation, operating temperature, and gas concentration on the structure, morphology, and sensitivity is discussed using the results of X-ray diffraction (XRD), and scanning electron microscopy (SEM) along with sensing performance.
To evaluate the role of chronic cerebral lactic acidosis in mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS).
The authors studied 91 individuals from 34 families ...with MELAS and the A3243G point mutation and 15 individuals from two families with myoclonus epilepsy and ragged red fibers (MERRF) and the A8344G mutation. Subjects were divided into four groups. Paternal relatives were studied as controls (Group 1). The maternally related subjects were divided clinically into three groups: asymptomatic (no clinical evidence of neurologic disease) (Group 2), oligosymptomatic (neurologic symptoms but without the full clinical picture of MELAS or MERRF) (Group 3), and symptomatic (fulfilling MELAS or MERRF criteria) (Group 4). The authors performed a standardized neurologic examination, neuropsychological testing, MRS, and leukocyte DNA analysis in all subjects.
The symptomatic and oligosymptomatic MELAS subjects had significantly higher ventricular lactate than the other groups. There was a significant correlation between degree of neuropsychological and neurologic impairment and cerebral lactic acidosis as estimated by ventricular MRS lactate levels.
High levels of ventricular lactate, the brain spectroscopic signature of MELAS, are associated with more severe neurologic impairment.
Nickel in the form of porous nickel phosphate VSB-5 has been used as a shape-selective catalyst for epoxidation of cyclic olefins such as cyclohexene and cyclooctene using hydrogen peroxide. The ...VSB-5 showed high selectivity to cyclohexene oxide and cyclohexane diol, much higher productivity per catalyst weight in the epoxidation of cyclohexene, and high selectivity to cyclooctene oxide in the epoxidation of cyclooctene. The VSB-5 behaved as a heterogeneous catalyst in the epoxidation and can be used many times without structure degradation, leaching of active nickel species, or significant activity loss. It has been concluded that the epoxidation reaction with VSB-5 proceeds via a free-radical mechanism by taking into consideration a sharp activity loss in the presence of a radical scavenger, hydroquinone. The effect of radical scavengers with different molecular dimension on the catalytic activity also indicates the shape selectivity in the pores of VSB-5.
