Search Results
Abstract
The catalytic properties of a novel MFI-type zeolite with different SiO2/Al2O3 ratio in the dehydration of glucose to levulinic acid (LA) were investigated in this work. The results demonstrate the strength of acidic sites and the mesoporosity of the zeolites have significant effects on LA formation.
Abstract
Water adsorption at temperatures of 286 and 296 K on silicalite-I, ZSM-5 (Si/Al=16), ZSM-48 (Si/Al=50) and AlPO4-5 is followed by gravimetry with a quasi-equilibrium continuous adsorptive introduction. The results show that all of these samples are characterized by a continuous distribution of strongly energetic water adsorption sites (from 60 to 120 kJ·mol−1) for which the adsorption is irreversible at the experimental temperature. This probably justifies the presence of hysteresis on desorption at very low relative pressure values. Adsorption of water in these systems firstly occurs by site. This is then followed by cluster formation and it is suggested that it is the ability of the adsorbent to build up these clusters within the microporous structure which determines intracrystalline uptake. It is put forward that the zeolites, silicalite-I and ZSM-5, do not accommodate cluster formation within its microporous network. However, an external flexible microporous structure, containing Lewis sites, may be present for large crystals. This flexible secondary structure may then be able to opened (swelled) at high relative pressures. On the other hand, for the aluminophosphate AlPO4-5, it is believed that a change in the aluminium coordination on the formation of a crystal hydrate together with capillary condensation results in a large step in the adsorption isotherm, which is itself preceded by a smaller step, revealing a brutal densification of the adsorbed phase.
alkali-metal exchanged MFI zeolites with various Si/Al ratios. Adsorption is common industrial separation process, but its application to CO 2 capture is relatively new and very attractive topic at present time because the importance of the carbon
Abstract
Ferrisilicates of MFI structure (HZSM-5) with Si/Fe ratios of 27.5, 35 and 67 have been studied by in situ Mössbauer spectroscopy, and the results are correlated with studies on catalytic conversions of toluene. Various species of iron ions are identified from 300 K spectra recorded after combinations of evacuation and reduction at 570 and 670 K, respectively. The roles of identified species are suggested in catalytic processes.
cytometer and analyzed using CXP software (Beckman Coulter). Relative measurement of CD16 expression was obtained by determining the mean fluorescence intensity (MFI) of neutrophils. Initially neutrophils were labeled as a distinct population based on side
The adsorption of argon and nitrogen on a series of MFI-type zeolites (silicalite-I (Si/Al>1000) and HZSM-5 (16<Si/Al<120)) was studied by isothermal microcalorimetry, volumetry and neutron diffraction.
By means of simultaneous DTA-, TG- and DTG-technique, the silicate gels and the MFI crystals obtained from these gels have been investigated. The gels have been prepared in presence and in absence of tetrapropylammonium cation (TPA+) and with Li+, Na+, NH4 + and K+ fluorides. In absence of TPA+ no thermal effects have been observed in Li+- and Na+-gels. The effects observed in the NH4 + -gel stem from a decomposition and release of inorganic phases: SiF4, NH4F, NH3. The DTA/DTG effects in the TPA+ containing gels and in the MFI crystals of monodisperse size are attributed to the decomposition of TPA+ cation. It can be concluded from these effects that the interaction between the gels and the TPA+ cation is rather weak. The interaction between TPA+ and MFI crystals obtained in fluoride medium is stronger than the interaction with crystals obtained from alkaline media. Similar thermal effects are obtained after grinding the long crystals to those having a large distribution of crystal sizes.
Abstract
Then-alkanes of different lengths were preadsorbed to selectively block part of the micropores of a MFI-type zeolite, Silicalite-I. The porosity available to argon and nitrogen was then studied by quasi-equilibrium adsorption microcalorimetry and volumetry at 77K and compared to what was found for the bare zeolite. Indeed, although partial adsorption ofn-alkanes does not alter the value of the differential enthalpies of adsorption for both argon and nitrogen, then-butane preadsorption diminishes the adsorption capacity by inducing inaccessible volumes in the micropore network. Moreover, the microcalorimetric experiments clearly show thatn-butane is not evenly distributed in the zeolite channel network while the longern-alkanes used are.
Abstract
We have investigated the interaction of water with Na+-ion exchanged zeolites of different structures (LTA, FAU, ERI, MOR and MFI) by means of temperature-programmed desorption (TPD). The non-isothermal desorption of water shows, depending on the zeolite type, differently structured desorption profiles. In every case the profiles have, however, two main ranges. Using a regularization method, desorption energy distribution functions have been calculated. The desorption energy distributions between 42–60 kJ mol−1, which can be attributed to a non-specific interaction of water, show two clearly distinguished energy ranges. The water desorption behaviour of this range correlates with the electronegativity of the zeolites and the average charge of the lattice oxygen atoms calculated by means of the electronegativity equalization method (EEM). The part of the desorption energy distributions in the range of 60–90 kJ mol−1, reflecting interactions of water with Na+ cations, shows two more or less pronounced maxima. In agreement with vibrational spectroscopic studies in the far infrared region, it may be concluded that all samples under study possess at least two different cation sites.
Absztrakt:
A veseátültetés utáni hosszú távú túlélést befolyásoló tényezők egyike az antitestmediált rejekció (ABMR). A szerzők áttekintést nyújtanak az ABMR jelenleg ismert diagnosztikai és kezelési hátteréről. A Debreceni és a Pécsi Egyetem transzplantációs központjainak együttműködése alapján áttekintik a 2013 és 2017 közötti időszakban végzett veseátültetések után kialakult korai ABMR-eseteket és a releváns közleményeket. A két központban összesen 454 veseátültetés történt. ABMR-diagnózist összesen 18 esetben állítottunk fel (4%). Minden esetben perkután biopszia történt. A betegek közül 22% volt primer, 78% retranszplantált eset. Az átlagéletkor 51,2 ± 6 év volt. A veseátültetés után az ABMR diagnózisáig eltelt idő 15,4 ± 22,1 hónap volt. A C4d-pozitivitást 7 esetben sikerült igazolni, ami az összes ABMR-eset 39%-a. Összesen 16 betegnél történt szteroidbolus + intravénás immunglobulin (IVIG) + plazmaferézis (PF) kezelés, a 6 debreceni beteg közül 5 kapott ezenfelül rituximabot és 1 alemtuzumabot. 9 (47,4%) beteg él működő beültetett vesével, 4 beteg meghalt (21%), és 5 került vissza művesekezelésre graftvesztés miatt (31%). Az ABMR veszélyes szövődmény a veseátültetés után. A diagnosztikus kritériumok sokáig változtak. A gold standard a szövettan. A C4d-esetekben is lehet akcelerált ABMR. A retranszplantáción átesett fiatalabb, preformált donorspecifikus antitesttel (DSA) jelentkező betegek és azok, akik EC-donorból kapnak vesét, kockázati csoportot jelentenek. A de novo DSA megjelenése, az átlagos fluoreszcenciaintenzitás (MFI) kinetikája lehet az a pont, amely felhívja a figyelmet az akut ABMR veszélyére. A rituximab hatékonyságát megkérdőjelezik, az új gyógyszerekkel (belatacept, bortezomib vagy ekulizumab) még nincs elég tapasztalat, vagy rendkívül drágák. Saját anyagunkban a 40% feletti gyógyulási arány kiemelkedően jó eredmény. Orv Hetil. 2018; 159(46): 1913–1929.
