Microwave-assisted synthesis and characterization of AlPO4-5

Effect of organic gel composition and the crystallization conditions on the synthesis of AlPO4-5 by using microwave heating technique were investigated. The AlPO4-5 samples were obtained by hydrothermal synthesis at 150-200°C in a Teflon autoclave in microwave oven. Samples prepared by different molar compositions of the reactants; 85% H3PO4, aluminium isopropoxide, tripropylamine hydroxide, tripropylamine, triethylamine and 40% HF and water. Influence of heating power (120-800 W), heating times (60-180 s) and simultaneous heating modes on the crystallization were investigated. Samples were analysed by SEM, XRD, surface analysis techniques. Usage of microwave heating drastically reduced the crystallization times compared with conventional methods. Morphology and phase purity of the AlPO4-5 molecular sieves strongly depended on the initial gel composition and heating periods. Perfect hexagonal AlPO4-5 products with good crystallinity with rod-like shape, well-defined edges and faces formed, were synthesized. The average crystal sizes in length along the c-axis were obtained ca. 5 mm length from the SEM images. In the XRD patterns recorded for the AlPO4-5 crystals, the (100), (210), (002) and (211) peaks were detected at d values 11.92 , 4.51 , 4.19 and 3.97 respectively, in addition to small features around 15° 2q. Average BET surface area of AlPO4-5's were 107 m2/g and average pore diameter was 1.7 nm.