Selective Crystallization of AlPO 4 -41 Molecular Sieve in the Presence of Diethylamine
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lective Crystallization of AlPO4-41 Molecular Sieve in the Presence of Diethylamine M. R. Agliullina, * and B. I. Kutepova aInstitute
of Petrochemistry and Catalysis, Ufa Federal Research Center, Russian Academy of Sciences, Ufa, Republic of Bashkortostan, 450075 Russia *e-mail: [email protected] Received February 10, 2020; revised March 12, 2020; accepted April 10, 2020
Abstract—A promising method providing the practical implementation of synthesis of AlPO4-41 alumophosphate molecular sieve with high phase purity using boehmite, phosphoric acid, and diethylamine as the template has been proposed. It has been shown that the mixing of the precursors at room temperature leads to the formation of a gel consisting of diethylamine phosphate, an amorphous aluminophosphate, and undissolved boehmite. It has been found that the introduction of the stage of gel aging at 90°C leads to the dominant formation of an amorphous aluminophosphate, the subsequent crystallization of which ensures the formation of high phase purity AlPO4-41 having cubic morphology of crystals with a size of 0.5–1 μm, a BET specific surface area S of 210 m2/g, and a micropore volume of 0.08 cm3/g. DOI: 10.1134/S0965544120080022
Currently, zeolite-containing materials are commonly used in industry as catalysts and adsorbents [1, 2]. In general, zeolites used in actual practice have a chemical composition of aluminosilicates. In 1982, Wilson et al. (Union Carbide researchers) reported the discovery of a new class of molecular sieves based on aluminophosphates AlPO4-n (n indicates the structure type) [3]. The AlPO4-n structure is composed of strictly alternating AlO4 and PO4 tetrahedra linked through common oxygen atoms. Aluminophosphates AlPO4-n are characterized by a wide variety of structures that differ in both pore size (AlPO4-34, 3.8 × 3.8Å; AlPO4-36, 6.5 × 7.5Å; VPI-5, 12.7 × 12.7Å) and channel dimension (1D-AlPO4-11, 2D-AlPO4-40, 3D-AlPO4-50) [4]. Currently, more than 50 AlPO4-n structures are known. A unique feature of aluminophosphates is the ability of their framework to isomorphously incorporate various elements [5]. Thus, the replacement of P atoms by Si atoms leads to the formation of SAPO-n molecular sieves exhibiting acidic properties. The replacement of Al atoms by transition metal atoms, such as Co or Mn, leads to the formation of MeAPO-n molecular sieves exhibiting redox properties [6]. Among the wide variety of AlPO4-n aluminophosphates, mesoporous molecular sieves AlPO4-11, AlPO4-31, and AlPO4-41 are of particular interest due to the presence of a one-dimensional channel system with pores having an average size of ~5 Å. Thus, Co-, Mn-, and Fe-containing molecular sieves are promising catalyst systems for the liquid-phase oxidation of
cyclohexane to cyclohexanone and cyclohexanol, the liquid-phase oxidation of p-cresol to p-hydroxybenzaldehyde, and phenol hydroxylation with hydrogen peroxide [7–12]. Silicon-containing (SAPO-11,31,41) and magnesium-containing molecular sieves (MAPO-11,31,41) are promising catalyst systems for hyd
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