New trends in the synthesis of crystalline microporous materials

Abstract

Zeolites and related microporous materials form the most important class of microporous solids due to their practical importance in different technological areas. In spite of the extensive research carried out in previous decades, it is surprising to realize that there is still space for innovation in this area, making microporous crystalline solids special among all classes of materials known today. We illustrate here the most recent advances in the field, focusing on the research topics that, in our opinion, are most likely to provide results of practical interest. Three main topics are discussed: (1) the synthesis of new framework topologies, with particular attention to those having extra-large and/or multidimensional pore systems;(2) the modification of the morphological and textural properties of known zeolites, including the discussion on two-dimensional structures and on the synthesis of nanocrystals and of the hierarchical porous structures; (3) the still poorly explored field of silica-based hybrid organic-inorganic porous crystalline materials (hybrid zeolites). For each of these topics, a selection of the most relevant results reported in the literature is provided together with some considerations on the potentialities and future perspectives.

Cu and Fe modified derivatives of 2D MWW-type zeolites (MCM-22, ITQ-2 and MCM-36) as new catalysts for DeNO x process

“…The great interest in zeolites is caused by their wide applications in industry as catalysts, molecular sieves and ionexchangers [1]. Despite many studies on zeolites, it is still a very interesting and developing group of materials.…”

“…A single layer, showing the MWW-type structure has thickness of one unit cell and a system of two independent pore channels (10 and 12 MR) [5,6]. Upon calcination of MCM-22 precursor the interlayer surfactant is removed with simultaneous 3D framework formation (through the condensation between surface silanol groups), giving a rise to MCM-22 zeolite [1].…”

Synthesis of mesoporous zeolite catalysts by in situ formation of carbon template over nickel nanoparticles

“…Therefore, large efforts have been made in order to improve the catalyst performance. This has been realized by reduction of the intracrystalline diffusion path length in the following possible approaches: synthesis of zeolites with extra-large pores [15][16][17][18][19][20], direct synthesis of zeolite nanocrystals [21][22][23][24][25][26][27], by exfoliating layered zeolites [28,29], and by introducing mesopores in the microporous materials through templating strategies [14,30,31] or demetallation processes [4,[32][33][34][35][36].…”

Progress in zeolite synthesis promotes advanced applications

“…3b). Another approach involves the replacements of the primary SDAs with commercially available low cost organic templates in order to prepare highly desirable zeolites [3].…”

“…Besides the different pore size and shape, the hydrophilic/hydrophobic nature of zeolites renders them as useful selective sorbents and hosts for guest molecules (organic or inorganic) that are stable in gas and liquid phase. In order to control the synthesis process and to obtain zeolites with predetermined properties, significant efforts have been dedicated to the fundamental understanding of the zeolite crystallization process and the influence of numerous variables and their impact on the physicochemical properties of the final product [3,4]. Amongst the number of factors controlling the synthesis of zeolites, the most important to be considered are divided in two groups-chemical and physical parameters (Fig.…”