Effect of Preparation Conditions on Formation and Features of Micro/Mesoporous Composite Materials on Base of Zeolites MCM-22, ZSM-5, and Beta

Abstract

UDC 544.723.21 V. L. Struzhko, P. S. Yaremov, E. V. Senchylo, V. M. Solomakha, and V. G. Ilyin XRD, TPDA, and IR spectroscopy of pyridine were used to study the effect of the synthesis conditions on the formation, adsorption characteristics, and acid properties of composite micro/mesoporous materials. Spatially well-ordered phases such as Beta, were found to exist in our samples. Variation of the preparation conditions permitted us to regulate the porosity and adsorption characteristics of the composite materials and the type, concentration, and strength distribution of the acid sites in the samples. The strength of the acid sites of the composite micro/mesoporous materials and their concentration are much higher than for mesoporous AlSi-MCM-41 but somewhat less than in the initial zeolites. Analysis of the results suggested that the samples obtained under similar conditions are not ordinary mechanical mixtures of two phases (zeolite and AlSi-MCM-41), but rather unique composites with tightly bound nanoparticles due to formation in a single reaction medium.Zeolites are commonly used as catalysts in the petrochemical and petroleum refining industry due largely to their crystal structure, porosity, and acid properties. However, small pore diameter (<0.75 nm) limits their use in the catalytic conversion of bulky molecules, in particular, in extensive catalytic cracking reactions and fine organic synthesis [1]. It was assumed that mesoporous molecular sieves (MMS), in particular, MCM-41-type materials with pore diameter £3-5 nm, possessing high specific surface (up to 1000 m 2 /g) could be used in such and similar processes. However, further investigation showed that the amorphous nature of the framework-forming substance and relatively low condensation lead to weak acidity and relatively low hydrolytic stability. Hence, the development of new materials with hybrid micro/mesoporous structure, combining the advantages of zeolites and MMS, holds considerable interest in regard to their possible application in adsorption and catalytic processes.There are presently several approaches being explored for the preparation of meso/microporous materials. One of them involves the creation of mesopores in zeolite crystals by dealumination and/or disilication upon acid, hydrothermal, or alkaline treatment [2]. Other approaches involve, somewhat generalizing, the preparation of micro/mesoporous composites from precursor zeolite crystal seeds formed in the first stages of the synthesis, the use of delaminated (fragmentized) zeolite particles as construction units, partial zeolitization of the MMS framework upon hydrothermal treatment in the presence of suitable

Bulk and composite catalysts combining BEA topology and mesoporosity for the valorisation of furfural

“…[37][38][39][40][41][42][43] This approach is interesting for preparing catalyst formulations in which the mesoporous phase acts as an inorganic binder of nanocrystallites, provides a somewhat regular network of mesoporous channels for facilitated mass transport of reagents/products and active sites accessibility. This approach has been used to prepare composites of several zeolites (Beta, 38,40,42,[44][45][46][47][48][49][50][51][52][53] Y, [54][55][56] L, [57][58][59] A, 60,61 , ZSM-5 34,35,39,48,[62][63][64][65][66][67][68] , MCM-22 69 ) or zeotypes (SAPO-5, 70,71 silicalite-1 72 ) embedded in mesoporous siliceous phases. The structure of the mesoporous component depends partly on the type and concentration of the templating agent used: e.g.…”