Synthesis of mesoporous complex framework zirconium phosphates via organicinorganic nanocomposites: genesis of structure
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Synthesis of mesoporous complex framework zirconium phosphates via organicinorganic nanocomposites: genesis of structure, adsorption and catalytic properties Yulia V. Frolova 1, 2, Vladislav A. Sadykov1, 2, S. N. Pavlova2, S. A. Veniaminov2, R. V. Bunina2, E. B. Burgina2, V. N. Kolomiichuk2, T. V. Larina2, N. V. Mezentseva1, 2, M. A. Fedotov2, A. M. Volodin2, E.A. Paukshtis2, V.B. Fenelonov2, R. Roy 3, D. Agrawal3. 1
Novosibirsk State University, Pirogova st, 2, Novosibirsk, 630090, Russia,
2
Boreskov Institute of Catalysis, pr. Lavrentieva 5, Novosibirsk, 630090, Russia.
3
Materials Research Laboratory, Penn State University.
ABSTRACT This work presents the first results of synthesis of framework binary phosphates of zirconium and transition metal cations (Co, Cu, Ce) via nanocomposites of starting inorganic salts with citric acid and studies of their structure genesis. Nanoparticles of layered Zr phosphates with typical sizes in the range of 18-24 Ǻ are formed at the mixing stage. Less basic Cu and Co cations are mainly octa-coordinated with both phosphate groups of those nanoparticles and citric acid molecules. At subsequent thermal treatment, Cu and Co cations are incorporated within Zr phosphate nanoparticles acquiring a low coordination approaching a tetrahedral one while rearranging the nuclei structure into that of a framework type. Removal of citric acid by heating under air at 200—300oC preserves the size of nanoparticles while their ordered stacking forms mesoporous structure with a narrow pore size distribution ~ 50 Å and specific surface area up to 200 m2/g after calcination at 600oC. The binary phosphates promoted by a small amount of Pt were found to be effective catalysts of NOx selective reduction by decane in the oxygen excess not subjected to coking with a high and stable performance at high space velocities in the presence of steam. INTRODUCTION Framework zirconium phosphates of the NZP type have a stable flexible structure enabling to conduct homovalent and heterovalent cation substitution without destruction of the lattice [1]. Materials based upon those systems possess a high cationic conductivity, a high radiation and corrosion stability [1, 2]. For heterogeneous catalysis, especially for the low-temperature processes, a high surface area of catalysts and mesoporosity are very important [3]. The known way of preparation of mesoporous materials with controlled pore sizes is based on application of organic supramolecular templates (surfactant micelles) [3, 4]. However, the materials prepared by this method are often microporous with a small pore volume due to shrinkage during calcination. Recently, citric acid not forming micelles has been found to possess the ability to provide mesoporous amorphous silica with a high specific surface area [5]. This work presents the first results of binary framework phosphates synthesis using this new method (via nanocomposites of starting inorganic salts with citric acid), their structure genesis being considered as well.
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