The Nzp Family Of Mesoporous Phosphate Materials Synthesis Research

In this paper, mesoporous CaZr4(PO4)6 (CZP) which belongs to the NZP family had been successfully synthesized by sol-gel method using cetyltrimethylammonium bromide (CTAB) as template. The influence of liquid phase synthesis conditions, calcining temperature and template dosage on the phase and on the pore structure of CZP materials were studied. On the basis of former research, the effects of composite template on the pore structure of CZP were preliminary studied. In addition, the Zr(HPO4)2 and NH4Zr2(PO4)3 crystal compounds were prepared respectively through hydrothermal crystallization process using CTAB as template. The synthesized samples were characterized by means of X-ray diffraction (XRD), infrared spectroscopy (IR), N2 adsorption method and high resolution transmit electron microscopes (HRTEM). According to the above research results, it is promising to explore the application area of the powder with NZP family structure from traditional low thermal expansion ceramic to the innovation area of molecular sieve catalytic materials. The results indicate that:(1) A new amorphous phosphate mesoporous molecular sieve with a low-ordered pore structure was prepared by sol-gel route using CTAB as template. The crystalline compound CaZr4(PO4)6 with a low-ordered mesoporous structure, which belonging to the NZP family, was obtained when calcining the above amorphous mesoporous materials at 650℃for 2h.(2) Template CTAB's dosage was one of the key to form mesoporous structure. Mesoporous CZP with a low-ordered pore structure was obtained when using proper amount of CTAB as template, and its average pore size is 8.5nm, specific surface area is 67·80m2·g-1,pore volume is 0.17～0.21cm3·g-1 but its pore size distribution is wider.(3) Mesoporous CZP with a narrow pore size distribution was obtained by using composite template PEG/CTAB as template through a sol-gel process, and the synthesized CZP have an average pore size of 3.6nm, a specific surface area of 65m2·g-1 and a pore volume of 0.13cm3·g-1.(4) By using (NH4)2HPO4 as phosphorus source and ZrO(NO3)2 as zirconium source, mesoporous Zr(HPO4)2 with a low-ordered pore structure was obtained under the condition of pH=7.5, hydrothermally crystallized at 120℃for 48h without adding structure-directing agent. The synthesized Zr(HPO4)2 have an average pore size of 3.6nm, a specific surface area of 66.9m2·g-1 and a pore volume of 0.11cm3·g-1.(5) Structure-directing agent F- and Ca2+ directed to form NH4Zr2(PO4)3 crystal compound. Only when both of them exist in the hydrothermal system, the pure-phase 3 crystal compound can be obtained, but the synthesized sample is dense matter and its specific surface area is between 2.35～3.60m2·g-1.(6) Neither BrΦnsted nor Lewis acid sites was shown on the surface of the synthesized mesoporous CZP and mesoporous Zr(HPO4)2.