Phosphate Crystal Compounds In The Nzp Family Hydrothermal Synthesis

In this paper, by using (NH4)2HPO4 as phosphorus source and ZrO(NO3)2 as zirconium source, the phosphate compound NH4Zr2(PO4)3 which belonging to NZP family had been synthesized by coprecipitation combined with hydrothermal crystallization method. The effects of hydrothermal temperature and time, mineralizer (fluorine ion) dosage,crystal seeds and pH values on phase of the products were studied. The optimum reaction condition was obtained via single factor experiments, and the phase, specific surface area, total pore volume, average pore size and pore size distribution of NH4Zr2(PO4)3 prepared in this condition were characterized. In addition, by using H3PO4 as phosphorus source, the NaZr2(PO4)3 and KZr2(PO4)3 crystal compounds were prepared. The specific surface area, total pore volume, average pore size and pore size distribution of NaZr2(PO4)3 were characterized. On the basis of former research, draw on phosphate molecular sieves and mesoporous materials synthesis methods, the effects of the introduction of template during the hydrothermal reaction on specific surface area, total pore volume and pore size distribution of NH4Zr2(PO4)3 and NaZr2(PO4)3 were preliminary studied, with a view to obtain a new catalytic materials belonging to NZP family which has large specific surface area and uniform pore size distribution. The results indicate that:(1)Well-crystallized NH4Zr2(PO4)3 compounds can be obtained by hydrothermally crystallizing at aboute 250℃with out adding seeds and mineralizer. The hydrothermal treating temperature can be reduced from 250℃to 200℃when adding 15% seeds to get NH4Zr2(PO4)3 crystal. And to maintain the addition quantity of mineralizer F- between n(F-)/n(ZrO2)=0.5～4, the single-phase NH4Zr2(PO4)3 crystals can be obtained when hydrothermally crystallized at 100-200℃for 20-24h.(2) F- is a comparatively ideal structure-directing agent for the formation of the crystal compounds belonging to NZP family; but the alkali metal cation Na+, organic amine EDA and quaternary ammonium salt CTAB have no obvious structure-directing effect in the hydrothermal conditions(150℃,24h) we had selected.(3) Keep the addition quantity of mineralizer F- at n(F-)/n(ZrO2)=1 and add 15% seeds into the hydrothermal system, the single-phase NH4Zr2(PO4)3 crystals can be obtained when hydrothermally crystallizing at 50℃for 24h. Study shows that the reaction system at the acidic environment conducive to NH4Zr2(PO4)3 formation by hydrothermal crystallization. XRD patterns and TEM show that the NH4Zr2(PO4)3 powders possesses pure phase, particles are uniformly distributed without agglomeration. Powders'specific surface area is 3.173m2/g, total pore volume is 0.00493mL/g, average pore diameter is 3.11nm, but the pore size distribution is uneven.(4) Well-crystallized NaZr2(PO4)3 and KZr2(PO4)3 can be obtained by hydrothermal synthesis when using H3PO4 as phosphorus source, but the specific surface area and total pore volume of the NaZr2(PO4)3 are almost to 0.(5) When CTAB,EDA,DDA,HDA and PEG had been separately introduced into the hydrothermal reaction systems of NH4Zr2(PO4)3 and NaZr2(PO4)3,the phase analysis, specific surface area and pore structurs characterization results of the products showed that in the template agents EDA, DDA presence, both NZP crystal compounds'specific surface area and total pore volume had been markedly improved than those without template agents, but had not been able to form the pore structure in an orderly arrangement.