Unexpected contraction of a zeolite framework upon isomorphous substitution of Si by Al

Isomorphous substitution of Si by Al in the framework of sodalites synthesized in ethylene glycol causes an unexpected contraction of the zeolite framework

Synthesis and catalytic activity of Ti-ITQ-7: a new oxidation catalyst with a three dimensional system of large pore channels

Isomorphous substitution of Si by Ti in the framework of ITQ-7, the crystalline silica polymorph of lowest density, has been achieved by direct synthesis, affording its three dimensional system of large pore channels to be used in selective oxidation reactions.CICYT (project MAT97-0723)Peer reviewe

Sandwich-type zeolite intergrowths with MFI and the novel extralarge pore IDM-1 as ordered end-members

Stacking faults are two-dimensional planar defects frequently arising in zeolites, modifying their properties and potentially affecting their performance in catalysis and separation applications. In classical zeolite intergrowths, a topologically unique zeolite layer may often pile up after some spatial transformation (lateral translation, rotation, and/or reflection) that may occur in different amounts or directions with about similar probabilities, leading to a difficult to control disorder. Here, we present a new kind of zeolite intergrowth that requires an additional topologically distinct layer rather than a spatial transformation of a unique one. Stacking of the so-called pentasil layers produces the well-known medium pore zeolite MFI. Intercalation in strict alternation of a topologically distinct second layer sandwiched between pentasil layers expands the structure to produce the new extra-large pore IDM-1. Stacking disorder modulates the structural expansion along the stacking direction. The disordered materials have been studied by simulation of the X-ray diffraction patterns using the program DIFFaX and by Cs-corrected high-resolution electron microscopy. We show that disorder does not occur at random but in extended domains and can be controlled all the way from MFI to IDM-1 by just varying the concentration of the synthesis mixture

Structural characterization of HPM-7, a more ordered than expected germanosilicate zeolite

HPM-7, a germanosilicate synthesized using long imidazolium-based dications with two different linkers, is shown to possess the POS topology, although disorder may exist but it is very difficult to discern. First, three simple ordered polymorphs (POS-A to POS-C) with very similar energies and structural motifs could give rise to intergrowths that would be very difficult to recognize by powder X-ray diffraction, according to DIFFaX simulations. Another four structures (POS-D to POS-G) can be derived from POS by changing the orientation of two single four rings within the structure, possibly providing an additional source of disorder. While 3D EDT strongly suggests that HPM-7 basically possesses the POS-A (i.e. POS) topology, a detailed HR-STEM study demonstrates the rare existence of some disorder compatible with the polymorph POS-D. The general avoidance of polymorphs with very similar structural motifs and comparable energies points to a rather specific structure-direction by the organic dications used

The Si-Ge substitutional series in the chiral STW Zeolite Structure Type

The whole compositional range (Ge$_f$ = Ge/(Ge+Si)= 0 to 1) of zeolite STW has been synthesized and studied by a comprehensive combined experimental--theoretical approach. The yield of zeolite goes through a maximum and then drops at the GeO$_2$ side of the series, following the inverse of the calculated free energy curve. The unit cell generally expands, roughly linearly, as the Ge$_f$ increases, but a notable resilience to expansion is observed at the high silica side. This can be attributed to the more rigid character of SiO$_2$ and the ability of Ge units to deform. Density functional theory calculations provide a new assignment of the previously controversial $^{19}$F MAS NMR resonances for occluded fluoride, which is based not only in the number of Ge atoms in the double-4-ring units but also on the way they are associated (namely, no Ge, isolated Ge, Ge pairs or closed Ge clusters). While we found an overall good agreement between the experimental and theoretical trends in preferential occupation by Ge of different crystallographic sites, the theoretical models show more sharp and abrupt tendencies, likely due both to limitations of the approach and to kinetic factors that allow metastable configurations to actually exist.Comment: 26 page

Hybridization and invasive species in a threatened freshwater fish community under environmental pressures: Morphometric and molecular evidence

Mediterranean freshwater systems are under threat owing to increased drought driven by climate change, intensive human land uses and non-native species. This is causing increased fish hybridization in isolated watercourses. The genetic and morphological characteristics of hybrids of sympatric native and non-native fish species were studied in four streams of the Mediterranean Guadalquivir basin (south-west Spain). Fish morphology was analysed using geometric morphometrics, and molecular determination of parenthood was inferred through one mitochondrial gene (cytb) and one nuclear gene (Beta-actin) for all hybrids and a subset of pure parental specimens. Molecular analyses confirmed hybrids between the native Squalius alburnoides and non-native Alburnus alburnus in a stream with continuous flow. Haplotype analyses suggested that they originated from backcrossing of hybrid offspring. Intergeneric crosses between native species S. alburnoides and Pseudochondrostoma willkommii, and S. alburnoides and Iberochondrostoma lemmingii were detected in streams under reduced connectivity scenarios. Morphometrics revealed that hybrid phenotypes were similar to S. alburnoides. In some cases, molecular markers uncovered hybridization events that were neither detected in the field nor by morphometric analyses, potentially supporting a backcrossing/introgression scenario. Hybridization is likely to be increasing in Mediterranean rivers where S. alburnoides are present owing to increased fragmentation caused by summer drought exacerbated by climate change and human land uses and pressures. This can become a problem for these endemic vulnerable species if genetic diversity is lost, morphological homogenization occurs and hybrids cannot be easily detected in the field. The potential risks could be addressed by monitoring and eradication of non-native species and segregation from natives. To avoid native–native crosses, habitat quality and desiccation risk could be tackled by improved water quality and riparian reforestation to provide shade and reduce evapotranspiration. This would need increased coordination and intervention between the institutions that share conservation responsibilities in the area

Lung-Function Trajectories Leading to Chronic Obstructive Pulmonary Disease

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is thought to result from an accelerated decline in forced expiratory volume in 1 second (FEV1) over time. Yet it is possible that a normal decline in FEV1 could also lead to COPD in persons whose maximally attained FEV1 is less than population norms. METHODS: We stratified participants in three independent cohorts (the Framingham Offspring Cohort, the Copenhagen City Heart Study, and the Lovelace Smokers Cohort) according to lung function (FEV1 ≥80% or <80% of the predicted value) at cohort inception (mean age of patients, approximately 40 years) and the presence or absence of COPD at the last study visit. We then determined the rate of decline in FEV1 over time among the participants according to their FEV1 at cohort inception and COPD status at study end. RESULTS: Among 657 persons who had an FEV1 of less than 80% of the predicted value before 40 years of age, 174 (26%) had COPD after 22 years of observation, whereas among 2207 persons who had a baseline FEV1 of at least 80% of the predicted value before 40 years of age, 158 (7%) had COPD after 22 years of observation (P<0.001). Approximately half the 332 persons with COPD at the end of the observation period had had a normal FEV1 before 40 years of age and had a rapid decline in FEV1 thereafter, with a mean (±SD) decline of 53±21 ml per year. The remaining half had had a low FEV1 in early adulthood and a subsequent mean decline in FEV1 of 27±18 ml per year (P<0.001), despite similar smoking exposure. CONCLUSIONS: Our study suggests that low FEV1 in early adulthood is important in the genesis of COPD and that accelerated decline in FEV1 is not an obligate feature of COPD. (Funded by an unrestricted grant from GlaxoSmithKline and others.)

Zeolita ITQ-7

Traducción de Patente Europea E99959428 (fecha de solicitud, 22/12/1999).-- Prioridad: ES199812229802697 .-- Titulares: Universidad Politécnica de Valencia (UPV), Consejo Superior de Investigaciones Científicas (CSIC).La presente invención se refiere a un material cristalino microporoso de naturaleza zeolítica denominado ITQ-7, al procedimiento de su preparación y a la utilización de ITQ-7 en procesos de separación y transformación de compuestos orgánicos. En estado calcinado y anhidro, la composición química del material ITQ-7 corresponde a la fórmula empírica:X(M{1/n}XO{sub,2}):y YO{sub,2}:SiO{sub,2}donde x posee un valor inferior a 0,06, pudiendo ser igual a cero; y tiene un valor inferior a 0,1, pudiendo ser igual a cero; M es H{sup,+} o un catión inorgánico de carga +n; X es un elemento químico de estado de oxidación +3(Al, Ga, B, Cr) e Y es un elemento químico con estado de oxidación +4(Ti, Ge, V). Cuando x=0 e y=0 el material ITQ-7 puede describirse como una nueva forma polimórfica de la sílice de carácter microporoso. El material zeolítico de esta invención se caracteriza también por su patrón de difracción de rayos X característico y sus propiedades microporosas. El proceso de preparación se caracteriza por el uso de uno o varios aditivos orgánicos en una mezcla de reacción que se hace cristalizar mediante calentamientoPeer reviewe

Zeolita ITQ-3

Traducción de Patente Europea E98921501 (fecha de solicitud, 29/05/1998).-- Prioridad: ES199705319701229.-- Titulares: Consejo Superior de Investigaciones Científicas (CSIC), Universidad Politécnica de Valencia (UPV).La presente invención se refiere a un material cristalino microporoso de naturaleza zeolítica designado como ITQ-3, a su método de obtención y a sus aplicaciones. El material se caracteriza por su composición química y por su modelo de difracción de rayos X. En su forma anhidra y calcinada, la composición química de ITQ-3 se puede representar por la fórmula empírica: x(M_1/n XO2):yYO2:SiO2 en la que x tiene un valor inferior a 0,15, y puede ser igual a cero; e y tiene un valor inferior a 0,1, y puede ser igual a cero; M es H+ o un catión inorgánico de carga +n, X es un elemento químico con estado de oxidación +3 (Al,Ge,B,Cr) e Y es un elemento químico de estado de oxidación +4 (Ti, Ge, V); cuando x = 0 e y = 0, el material puede ser descrito como un nuevo polimorfo de sílice de naturaleza microporosa. En el modo de realización preferido de la presente invención ITQ-3 tiene, en estado calcinado y anhidro, la composición: x(HXO2):SiO2 donde X es un elemento trivalente y x tiene un valor inferior a 0,1 y puede ser igual a cero, en cuyo caso el material se puede describir por la fórmula SiO2.Peer reviewe