Filamentous carbons as a support for heteropoly acid

Abstract For an heterogenization, different kinds of catalytic filamentous carbons (CFC) were used as a support for some heteropoly acids (HPAs): H 6 P 2 W 21 O 71 (H 2 O) 3 (P 2 W 21 ), H 6 As 2 W 21 O 69 (H 2 O) (As 2 W 21 ), Dawson type α-H 6 P 2 W 18 O 62 (P 2 W 18 ) and Keggin type H 3 PW 12 O 40 (PW). The support properties, which affect the interaction between HPAs and supports were studied. Concentration of Bronsted acidic sites in PW and PW/support was determined from the ESR studies of the stable nitroxyl radical (4-hydroxy-2,2′,6,6′-tetramethylpyperidin- N -oxyl (TEMPOL)) adsorbed from hexane. The reaction of 2,6-di- tert -butyl-4-methylphenol (DMBP) with toluene as tert -butyl acceptors was studied using bulk and supported PW and P 2 W 18 . It was found that P 2 W 18 was more active than PW. It was shown that catalytic activities of HPAs supported on SiO 2 and CFC were approximately equal. The activity of the surface protons in HPA/support increased monotonically as the total HPA loading increased, reaching a maximum for the bulk HPA.