Na-Y with defined numbers of extraframework aluminum cations were prepared by exchange in an aqueous solution of aluminum nitrate. A maximum concentration of Brønsted acidic bridging OH groups in supercages (SiOH sup Al) was reached upon dehydration of zeolites Al,Na-X and Al,Na-Y at 423 K. Further raising of the dehydration temperature led to a dehydroxylation of zeolites due to the recombination of aluminum hydroxyl groups with hydroxyl protons of bridging OH groups. High-field 27 Al multiple-quantum magic-angle spinning (MQMAS) NMR spectroscopy was utilized to study zeolites Al,Na-X/61 and Al,Na-Y/63 dehydrated at 423 K. Second-order quadrupolar effect parameters of 10.1-11.0 MHz for tetrahedrally coordinated framework aluminum atoms, compensated in their negative charge by hydroxyl protons (Al IV /H + ) and aluminum cations (Al IV /Al x+ ), 3.6-4.4 MHz for tetrahedrally coordinated framework aluminum atoms compensated by sodium cations (Al IV /Na + ), and 5.6-7.6 MHz for pentacoordinated extraframework aluminum cations (Al x+ cat.) were obtained. Comparison of the number of AlOH groups with the number of pentacoordinated extraframework aluminum cations determined by one-dimensional highfield 27 Al MAS NMR spectroscopy gave a ratio near 1:1. This finding and the five-fold coordination of the cationic extraframework aluminum species hint to the presence of HO-Al + -O-Al + -OH compounds, but also a minor number of Al(OH) 2 + and AlO + species could exist. The enhanced acid strength of bridging OH groups in zeolites Al,Na-X and Al,Na-Y in comparison with zeolites H,Na-X and H,Na-Y, as found by adsorption of acetonitrile, may be due to a polarizing effect of cationic extraframework aluminum species in the vicinity of Brønsted acid sites.

Bioactive glass nanoparticles (BGN) are promising materials for a number of biomedical applications. Many parameters related to the synthesis of BGN using sol-gel methods can affect their characteristics. In this study, the influence of timing of calcium nitrate (calcium precursor) addition during processing on BGN characteristics was investigated. The results showed that the addition timing could affect the morphology, dispersity and composition of BGN. With delayed addition of calcium nitrate, larger, more regular and better dispersed BGN could be synthesized while the gap between nominal and actual compositions of BGN was widened. However, the addition timing had no significant influence on structural characteristics, as BGN with different addition-timing of calcium nitrate exhibited similar infrared spectra and amorphous nature. The results also suggested that monodispersed BGN could be synthesized by carefully controlling the addition of calcium nitrate. The synthesized monodispersed BGN could release Si and Ca ions continuously for up to at least 14 days. They also showed in vitro bioactivity and non-cytotoxicity towards rat bone marrow-derived mesenchymal stem cells (rBMSCs). In conclusion, the timing of calcium precursor addition is an essential parameter to be considered when producing BGN which should exhibit monodisperse characteristics for biomedical applications.

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The direct experimental evidence shows that ethylbenzene disproportionation is a transition state shape selective reaction on zeolites: a bimolecular reaction mechanism via diphenylethane-mediated pathway on large-pore zeolites X and Y (ca. 0.74 nm) and a monomolecular reaction mechanism on medium-pore zeolites ZSM-5 (ca. 0.56 nm) via the ethoxy-mediated intermolecular ethyl group transfer. The lifetime of bulky diphenylethane species was prolonged by a fine-tune of FAU-zeolites, which makes this transition state detectable by 13C MAS NMR spectroscopy. Due to tunable catalytic properties and pore shapes, zeolites are promising catalysts toward emulating the efficiency and selectivity in desired reactions.

By means of solid-state 15N NMR spectroscopy, evidence for the formation of nitrilium ions as intermediates of the Beckmann rearrangement of 15N-cyclohexanone oxime to epsilon-caprolactam on silicalite-1, H-ZSM-5, and H-[B]ZSM-5 is reported. The zeolites under study are characterized by different acid strengths (silicalite-1 < H-[B]ZSM-5 < H-ZSM-5). Depending on the nature of catalytically active surface OH groups, reactant and product molecules exist in the nonprotonated or protonated state. In addition, formation of byproducts such as 5-cyano-1-pentene and epsilon-aminocapric acid as a result of dehydration and hydrolysis of the reactant and product molecules, respectively, were observed.

Abstract:In the present work we show, how a high pressure hydrogenation of commercial anatase or anatase/rutile powder can create a photocatalyst for hydrogen evolution that is highly effective and stable without the need of any additional co-catalyst. This activation effect can not be observed for rutile. For anatase/rutile mixtures, however, a strong synergistic effect is found (similar to findings commonly observed for noble metal decorated TiO 2 ). ESR measurements indicate the intrinsic co-catalytic activation of anatase TiO 2 to be due to specific defect centers formed during hydrogenation. 2Ever since the groundbreaking work of Fujishima and Honda in 1972 [1], TiO 2 is considered as a promising photocatalyst for the splitting of water into H 2 and O 2 . In the original experiment, Fujishima et al. used a TiO 2 photoanode, connected via an external circuit to a platinum counter electrode -the latter was needed to successfully evolve H 2 from water. Due to the simplicity of the concept, illumination of a cheap and abundant semiconductor to create photoexcited charge carriers that can be transferred directly to water to form a high density energy fuel (H 2 ), the report found a tremendous scientific resonance. Meanwhile, more than 10000 papers have been published on using TiO 2 in a large palette of morphologies and modifications, to trigger a wide range of photocatalytic ractions (for overviews see e.g. refs.[2-8]). While numerous photoelectrochemical studies (i.e., using an illuminated TiO 2 electrode in an electrochemical circuit) where performed, still the most direct and economic approach is the use of TiO 2 in the form of particle suspensions -thus using the photocatalytic system without an external applied voltage. However, under these so called open-circuit conditions (OCP), TiO 2 alone is not efficient for the photoproduction of hydrogen without the use of a co-catalyst -mostly this is a noble metal (M), such as Pt, Pd or Au -for overviews see e.g. refs. [9][10][11]. These combined photocatalytic M@TiO 2 systems have therefore been widely investigated in view of optimizing their efficiency towards H 2 generation from water (with or without using sacrificial agents such as ethanol) [9,12].In general, the function of the noble metal co-catalyst has been described in terms of i) providing an electron acceptor that mediates electron transfer to the electrolyte, ii) forming solid state junctions (metal/semiconductor), or iii) acting as a hydrogen recombination center that strongly promotes H 2 formation [9][10][11]. In M@TiO 2 catalysts it has been generally observed that the crystalline phase of TiO 2 is a very important factor for the performance of such photocatalytic H 2 -generation systems [6-9, 13, 14]. Anatase and rutile are the most commonly used polymorphs in photoactivated TiO 2 applications. In photocatalytic water splitting, generally M@anatase combinations are found to be more efficient than M@rutile. 3This difference in photocatalytic activity is commonly attributed to a higher charge recom...