%0 Journal Article
%T Layered Materials with Catalytic Applications: Pillared and Delaminated Zeolites from MWW Precursors
%A Urbano D¨ªaz
%J ISRN Chemical Engineering
%D 2012
%R 10.5402/2012/537164
%X Delaminated and pillared zeolites are an innovative family of molecular sieves which introduced a different concept inside the synthesis of active catalysts or inorganic supports. These types of materials exhibit an elevated accessibility due to their open structure, characterized by the high external surface area without imposed restrictions controlled by the pore sizes. These open zeolites are conformed by crystalline ordered (pillared zeolites) or disordered (delaminated zeolites) individual layers, exhibiting textural properties which are favorable to carry out catalytic processes in which it is necessary to employ catalysts with completely accessible active sites. The elevated external surface area of these zeolites is profitable to generate more specific organic-inorganic materials, acting in this case as stable inorganic matrixes. The preparation of this open type-zeolites family is based on the modification of, previously synthesized, zeolitic precursors which are preexpanded to obtain the final delaminated or pillared zeolites which exhibit very different physicochemical properties compared with the starting precursors. Along this paper, the most relevant MWW-type high accessible zeolitic materials will be considered. Their nature, characteristics, and reactivity will be shown in the function of the employed synthesis method for their preparation and the postsynthesis treatments carried out, tuning their properties. 1. Introduction: Delamination and Pillarization Concept Layered inorganic precursors are structurally conformed by a consecutive repetition of individual sheets located in parallel spatial planes, being electrostatically bonded by Van der Waals interactions or hydrogen bonds along the perpendicular plane in which the layers are disposed. This structural conformation is present in a great number of inorganic materials, from the simplest such as clays or silicates to another more complex such as layered double hydroxides, metallic layered materials, or zeolitic precursors [1¨C4]. These layered materials exhibit the capacity to modify their structural characteristics through consecutive steps using the free space present between the contiguous inorganic layers. In this way, it is possible to obtain novel mesoporous materials due to the intercalation in the interlayered space of organic or inorganic compounds which act as pillars, avoiding the covalent connection between the inorganic layers after the removing of the ionic molecules which are compensating the surface charges present in the sheets. This type of layered solids is
%U http://www.hindawi.com/journals/isrn.chemical.engineering/2012/537164/