1,721,010 research outputs found
Ethene dimerization over Ni-beta catalysts prepared by solid-state ion exchange
No full textOwing to the environmental and technological problems of current commercial homogeneous organometallic catalysts, developing efficient heterogeneous catalysts for ethene dimerization is of industrial importance. Nickel-exchanged zeolite beta (Ni-beta) is a promising catalyst for this reaction due to its highly stable 1-butene yield. Here, we report that the Ni-beta catalyst shows a considerably better 1-butene yield when prepared by solid-state ion exchange compared to liquid-phase ion exchange and incipient wetness impregnation. A combination of CO IR, Ni K-edge X-ray absorption and UV-vis spectroscopies, and density functional theory calculations demonstrate that solid-state ion exchange is an efficient method to form the intrazeolitic mono(μ-oxo)dinickel ([Ni-O-Ni]11Nsciescopu
THE PHOTOCATALYTIC EFFECTS OF TIO2 BASED CATALYSTS MODIFIED BY TRANSITION METALS FOR REMOVAL OF POLLUTANTS IN LIQUID PHASE
No full text11scopu
Targeted Synthesis of a Zeolite with Pre-established Framework Topology
No full textGiven their great potential as new industrial catalysts and adsorbents, the search for new zeolite structures is of major importance in nanoporous materials chemistry. However, although innumerable theoretical frameworks have been proposed, none of them have been synthesized by a priori design yet. We generated a library of diazolium-based cations inspired from the organic structure-directing agents (OSDAs) recently reported to give two structurally related zeolites (PST-21 and PST-22) under highly concentrated, excess-fluoride conditions and compared the stabilization energies of each OSDA cation in ten pre-established hypothetical structures. A combination of the ability of the OSDA selected in this way with the excess-fluoride approach has allowed us to crystallize PST-30, the targeted aluminosilicate zeolite structure. We anticipate that our approach, which aims to rationally couple computational predictions of OSDAs with an experimental setup, will advance further development in the synthesis of zeolites with desired properties.11Nsciescopu
Propylene/propane separation on a ferroaluminosilicate levyne zeolite
No full textThe propylene/propane separation properties of levyne zeolites with different framework Si/Al and Fe/Al ratios have been examined and compared with those of the four well-studied zeolite adsorbents (i.e., Na-A, Ca-A, Na-X and ITQ-12) for this separation. Both zeolite framework structure and composition were found to be critical for the propylene uptake, kinetic separation and adsorbent durability. Among the zeolites studied here, the mixed CaNH4 form of a ferroaluminosilcate levyne (Si/Al = 15.5 and Fe/Al= 0.27) showed the highest propylene/propane selectivity (11). Under vacuum-swing adsorption mode at 298 K and reservoir pressure of 1.2 bar, this partially iron-substituted zeolite was characterized by a higher propylene uptake (ca. 1.0 vs 0.7 mmol g(-1)) than its aluminosilicate version, which can be attributed to a combination of the molecular sieve effect of its framework topology and relatively weaker acidity. The results of this study demonstrate that, in contrast to widely held belief, zeolite adsorbents selective for propylene/propane separation do not need to be a pure-silica composition.11Nsciescopu
A Zeolite Family Nonjointly Built from the 1,3-Stellated Cubic Building Unit
No full textFrom a technological point of view, the synthesis of new high-silica zeolites is of prime importance owing to their high potential as industrial catalysts and catalyst supports. Two such materials have been synthesized which are made up of the 1,3-stellated cubic unit (hexahedral ([4254]) bre unit) as a secondary building unit, with the aid of existing imidazolium-based structure-directing agents under “excess fluoride” conditions. One of them, denoted PST-21, is the first aluminosilicate zeolite consisting of 9-ring apertures solely; it displays exceptional activity towards steering the skeletal isomerization of 1-butene to isobutene and bridges the gap between small- and medium-pore structures. A series of hypothetical structures are also described that are nonjointly built from the bre unit; all of these structures are chemically feasible and will thus be helpful in designing the synthesis of novel zeolites containing 9-ring and/or 10-ring channels. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim11Nsciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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