Faujasite

Abstract: Zeolite beta, first described in 19671, is an active catalyst and a useful sorbent1 Sorption1,2 and catalytic data3,4 suggest that the zeolite could possess a three-dimensional 12-ring pore system Such a pore system suggests technological potential similar to that of faujasite framework materials, but until now the structure of this zeolite has eluded determination Powder X-ray diffraction patterns comprise both sharp and broad features, indicative of an extensively faulted structure Here we determine the structure of zeolite beta by high-resolution electron microscopy, electron diffraction and computer-assisted modelling The zeolite is an intergrown hybrid of two distinct but closely related structures Both are constructed from the same centrosymmetrlcal tertiary building unit arranged in layers, and both possess three-dimensional 12-ring pore systems One end member, polymorph A, forms an enantiomorphic pair, with symmetries P4122 and P4322, with a = 124 A and c = 265 A Polymorpb B, in which the stacking of layers alternates in handedness, is achiral with space group P1 ¯, and a ≃ b = 124 A, c = 145 A, α ≃ β = 73°, γ ≃ 90° The high density of stacking faults in zeolite beta materials arises because successive layers must interconnect in either a left- or a right-handed fashion, and both modes of linkage occur with almost equal probability

Abstract: Nanosized faujasite (FAU) crystals have great potential as catalysts or adsorbents to more efficiently process present and forthcoming synthetic and renewable feedstocks in oil refining, petrochemistry and fine chemistry. Here, we report the rational design of template-free nanosized FAU zeolites with exceptional properties, including extremely small crystallites (10-15 nm) with a narrow particle size distribution, high crystalline yields (above 80%), micropore volumes (0.30 cm(3) g(-1)) comparable to their conventional counterparts (micrometre-sized crystals), Si/Al ratios adjustable between 1.1 and 2.1 (zeolites X or Y) and excellent thermal stability leading to superior catalytic performance in the dealkylation of a bulky molecule, 1,3,5-triisopropylbenzene, probing sites mostly located on the external surface of the nanosized crystals. Another important feature is their excellent colloidal stability, which facilitates a uniform dispersion on supports for applications in catalysis, sorption and thin-to-thick coatings.

Abstract: The development of green, selective, and efficient catalysts, which can aerobically oxidize a variety of alcohols to their corresponding aldehydes and ketones, is of both economic and environmental significance. We report here the synthesis of a novel aerobic oxidation catalyst, a zeolite-confined nanometer-sized RuO(2) (RuO(2)-FAU), by a one-step hydrothermal method. Using the spatial constraints of the rigid zeolitic framework, we sucessfully incorporated RuO(2) nanoparticles (1.3 +/- 0.2 nm) into the supercages of faujasite zeolite. Ru K-edge X-ray absorption fine structure results indicate that the RuO(2) nanoclusters anchored in the zeolite are structurally similar to highly hydrous RuO(2); that is, there is a two-dimensional structure of independent chains, in which RuO(6) octahedra are connected together by two shared oxygen atoms. In our preliminary catalytic studies, we find that the RuO(2) nanoclusters exhibit extraordinarily high activity and selectivity in the aerobic oxidation of alcohols under mild conditions, for example, air and ambient pressure. The physically trapped RuO(2) nanoclusters cannot diffuse out of the relatively narrow channels/pores of the zeolite during the catalytic process, making the catalyst both stable and reusable.