02-P-23 - The influence of different silica sources on the crystallization kinetics of zeolite beta

This chapter discusses the influence of different silica sources on the crystallization kinetics of zeolite beta. Zeolite beta is synthesized with different silicon sources. The dissolution of the silicon sources and the reaction temperature determines the crystallization rate of the zeolite. Silica sol reacted rapidly at 110, 140, and 170°C while fumed silica and tetraethyl orthosilicate (TEOS) only reacted readily at 170°C. The aluminum content in the reaction gel determines the termination of the crystal growth: after all aluminum is consumed, the crystal growth stopped. The acidic properties of the obtained materials are very similar, but a significant influence of the silicon source on the particle size of the resulting zeolite is observed

Anthraquinones formation on zeolites with BEA structure

Zeolites with BEA structure are in focus mainly in the field of conversion of hydrocarbons. However, their unique physico-chemical properties let to suppose that these systems can be successfully used in reactions of organic synthesis. Such zeolites can be used as catalysts for the synthesis of large organic molecules. The interaction of phthalic anhydride with aromatic hydrocarbons is a subject for investigation, both for science purposes and for industrial applications. The use of zeolites in this reaction is an example of the acylation of aromatics on solid-acid catalysts; on the other hand, such a study creates the possibilities of developing more appropriate technology for the production of anthraquinone compounds. This chapter presents experimental material on the investigation of catalytic properties of zeolites with BEA structure in anthraquinones formation. The chapter presents a study of the interaction of both initial reagents and reaction products with acid sites of zeolite using IR technique. On the base of the obtained data, a mechanism of formation of reaction products was proposed. The catalytic properties of zeolite with BEA structure were examined in the reaction in the range of 225–500°C. Increasing the reaction temperature can cause the decomposition of not only anthraquinone molecules but also of phthalic anhydride and benzoylbenzoic acid, which can lose CO and CO2 giving benzophenone, biphenyl, and 9-fluorenone as reaction products

Propane Transformation on In-Modified Zeolite BEA

In-modified zeolites possess promising catalytic properties for light alkane dehydrogenation and aromatization. However, the role of different indium species, which are present in zeolite pores after activation, remains unknown. Here, the transformation of propane on BEA zeolite containing either In+ or InO+ species in zeolite pores has been monitored with 13C MAS NMR at 298–773 K. It is inferred that In+/H-BEA zeolite with In+ sites is inactive for alkane conversion at T +/H-BEA zeolite occurs by two parallel routes: dehydrogenation of propane followed by the formed alkene aromatization to simple aromatic hydrocarbons and the alkane oxidation resulting in C2–C3 carboxylic acids. Propane activation by either C–H or C–C bond cleavage on InO+ sites and pathways of carboxylic acid formation from the products of the alkane dissociative adsorption are discussed

Different Efficiency of Zn²⁺ and ZnO Species for Methane Activation on Zn-Modified Zeolite

Understanding methane activation pathways on Zn-modified high-silica zeolites (ZSM-5, BEA) is of particular importance because of the possibility of methane involvement in coaromatization with higher alkanes on this type of zeolites. Herein, two samples of Zn-modified zeolite BEA containing exclusively either small zinc oxide clusters or isolated Zn²⁺ cations have been synthesized and thoroughly characterized by a range of spectroscopic methods (¹H MAS NMR, DRIFTS, XPS, EXAFS, HRTEM) to show that only one of the Zn-species, either Zn²⁺ cations or ZnO small clusters, exists in the void of zeolite pores. The ability of zinc sites of different nature to promote the activation of methane C–H bond with the zeolite Brønsted acid sites (BAS) has been examined in the reactions of methane H/D hydrogen exchange with BAS and the alkylation of benzene with methane. It has been found that both ZnO and Zn²⁺ species promote the reaction of H/D exchange of methane with BAS. The rate of H/D exchange is higher by 2 and 3 orders of magnitude for the zeolite loaded with ZnO or Zn²⁺ species, respectively, compared to pure acid-form zeolite H-BEA. So, the promoting effect of Zn²⁺ cations is more profound than that of ZnO species for H/D exchange reaction. This implies that the synergistic effect of Zn-sites and BAS for C–H bond activation in methane is significantly higher for Zn²⁺ cations compared to small ZnO clusters. It has been revealed, however, that only Zn²⁺ cations promote the alkylation of benzene with methane, whereas ZnO species do not. The isolated Zn²⁺ cations provide the formation of zinc-methyl species, which are further transformed to zinc-methoxy species. The latter is the key intermediate for the performance of the alkylation reaction. Hence, while both zinc oxide clusters and Zn²⁺ cationic species are able to provide a synergistic effect for the activation of C–H bonds of methane displayed by the dramatic acceleration of H/D exchange reaction, only the Zn²⁺ cationic species perform methane activation toward the alkylation of benzene with methane. This implies that only the Zn²⁺ cations in Zn-modified zeolite can activate methane for the reaction of methane coaromatization with higher alkanes