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In order to obtain highly dispersed heteropolyacids (HPAs) species, H3PMo12O40 and H4PVMo11O40 were supported on various supports: silica (Aerosil - Degussa and Romsil types) and TiO2. 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.

The influence of the nature and textural properties of different supports on the thermal behavior of Keggin type heteropolyacids