Preparation of polyoxometalate compound (NH4)6(β-P2W18O62)/SiO2 by sol-gel method and its characterization

Abstract

Preparation of polyoxometalate compound of (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O supported with silica derived from the hydrolysis of tetraethyl orthosilicate by sol-gel method has been conducted. The compound was synthesized and characterized using FT-IR spectrophotometer, crystallinity using XRD analysis and the determination of acidity via quantitatively and qualitatively. Qualitative analysis was performed using ammonia and pyridine adsorption and quantitative analysis using potentiometric titration. FT-IR spectrum of (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O appeared in wavenumber 786.96 cm -1 (W-O C -W), 918.12 cm -1 (W-O e -W), 964.41 cm -1 (W=O), 1087.85 cm -1 (P-O), 3572.17 cm -1 (O-H), 1404.18 cm -1 (N-H) reinforced with wavenumber 1612.49 cm -1 with show vibration NH dari NH + , and to (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O/SiO 2 appears in wavenumbers 794.67 cm -1 (W-O c -W), 918.12 cm -1 (W-O e -W), 1049.28 cm -1 (W=O), 1087.85 cm -1 (P-O), 3564.15 cm -1 (O-H), 470.63 cm -1 (Si-O). Diffraction pattern of (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O and (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O/SiO 2 compound show high crystanillity. The acidic properties showed (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O/SiO 2 more acidic than (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O. Analysis of the effect of temperature on the stability of the compounds polyoxometalate (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O/SiO 2 show that the temperature of 600ºC the shift in wavenumbers of the compounds caused by vibration W=O, W-O C -W, W-O e -W has been lost. This shows that at a temperatures of 600ºC on heating can cause changes in the structure of polyoxometalate (NH 4 ) 6 (β-P 2 W 18 O 62 )nH 2 O/SiO 2. Keywords : (NH 4 ) 6 (β-P 2 W 18 O 62 ).nH 2 O, Polyoxometalate, SiO 2