One pot synthesis of aluminum pillared intercalated layered clay supported silicotungstic acid (STA/Al-PILC) catalysts

Abstract One pot synthesis of silicotungstic acid (STA) containing aluminum pillared intercalated layered clay (STA/Al-PILC) catalysts is carried out by addition of STA to aluminum pillared clay synthesis media. STA-Al Keggin type pillar agents which are formed by charge interaction among them are inserted between clay layers. Effect of parameters on catalyst structure such as pH of clay suspension, STA quantity, addition step and its isolation in buffer solution are investigated. STA addition step has a crucial role on properties of catalysts. Conservation of the layered structure of Al-PILC support in the presence of STA is seen from X-ray powder diffraction (XRD) patterns and transmission electron microscopy (TEM) images. Basal spacing values do not show much difference with respect to that of Al-PILC support which is measured as 1.85 nm. The catalyst which owes the best structural properties has 217 m2/g surface area, 0.20 cm3/g pore volume, 0.44 nm average micropore size and 3.90 nm average mesopore size with high STA loading success. Lewis acidity is dominant acid character in all catalysts. Preservation of Keggin structure of STA in PILC structures is seen by X-ray photo electron spectroscopy (XPS) with a clear W4f7/2 and W4f5/2 spin orbital doublet. The increase in STA amount leads no additional increase in STA loading. Agglomeration, which is seen clearly in TEM images, occurs when STA is added either as its powder form to Al-pillar agent media or after isolating it within the buffer solution to Al-pillar agent-clay suspension. The proposed model which assumes the placement of pillar agents between clay layers, either after coupling with each other or alone, explains effects of STA addition steps on structural properties.