J. Serb. Chem. Soc. 71 (3) 235–249 (2006) UDC 546–328:549.514 JSCS – 3414 Original scientific paper The influence of the nature and textural properties of different supports on the thermal behavior of Keggin type heteropolyacids ALEXANDRU POPA 1* , VIOREL SASCA 1 , MIRCEA STEFANESCU 2 , ERNE E. KI[ 3# and RADMILA MARINKOVI]-NEDU^IN 3# 1 Institute of Chemistry “Coriolan Dr|gulescu” TimiÕoara, Bl. Mihai Viteazul 24, (e-mail: sandu@acad-icht.tm.edu.ro) 2 ”Politehnica” University, TimiÕoara, P-ta Victoriei 2, Romania and 3 University of Novi Sad, Faculty of Technology, Cara Lazara 1, Novi Sad, Serbia and Montenegro (Received 17 November 2004, revised 3 April 2005) Abstract: In order to obtain highly dispersed heteropolyacids (HPAs) species, H 3 PMo 12 O 40 and H 4 PVMo 11 O 40 were supported on various supports: silica (Aerosil - Degussa and Romsil types) and TiO 2 . The structure and thermal decomposition of sup- ported and unsupported HPAs were followed by different techniques (TGA-DTA, FTIR, XRD, low temperature nitrogen adsorption, scanning electron microscopy). All the supported HPAs were prepared by impregnation using the incipient wetness tech- nique with a 1:1 mixture of water–ethanol. Samples were prepared with different con- centrations to examine the effect of loading on the thermal behavior of the supported acid catalysts. The thermal stability was evaluated with reference to the bulk solid acids and mechanical mixtures. After deposition on silica types supports, an important de- crease in thermal stability was observed on the Romsil types and a small decrease on the Aerosil type. The stability of the heteropolyacids supported on titania increased due to an anion-support interaction, as the thermal decomposition proceeded in two steps. The structure of the HPAs was not totally destroyed at 450 ºC as some IR bands were still preserved. A relatively uniform distribution of HPAs on the support surface was ob- served for all compositions of the active phase. No separate crystallites of solid phase HPAs were found in the SEM images. Keywords: heteropolyacids, Keggin type, silica, titania, non-isothermal decomposition. INTRODUCTION Heteropolyacids with the Keggin structure are known to be highly active cata- lysts for both acid-catalyzed and oxidation reactions. 1–9 Different forms of HPAs are used as catalysts, among them molybdophosphoric acid H 3 [PMo 12 O 40 ] . xH 2 O (HPMo) and 1-vanado-11-molybdophosphoric acid H 4 [PMo 11 VO 40 ] . yH 2 O (HPVMo) as a consequence of their high catalytic activity in the selective oxidation of unsat- urated aldehydes and the oxidation of low alcohols. 10–17 235 doi: 10.2298/JSC0603235P * Corresponding author. # Serbian Chemical Society active member.