Abstract
Solid acid catalysts prepared by supporting 15 wt%H3PW12O40 heteropoly acid (HPA) on TiO2 ZrO2 and Nb2O5 with a sub-monolayer HPA coverage were characterised at a gas-solid interface regarding their acid properties and chemical structure of HPA on the catalyst surface and compared to standard HPA catalysts such as bulk and silica-supported H3PW12O40 and Cs-2 H-5(0) 5PW12O40. In contrast to the parent acid H3PW12O40 possessing strong Bronsted acid sites the catalysts supported on TiO2 ZrO2 and Nb2O5 have both Bronsted and Lewis acid sites with the latter mainly originating from the oxide support The strength of acid sites in these catalysts is weaker than that in H3PW12O40 and Cs-2 H-5(0) 5PW12O40 The catalytic activity (turnover frequency) in gas-phase isopropanol dehydration decreases in the order H3PW12O40 > Cs-2 H-5(0) 5PW12O40 > 15%H3PW12O40/SiO2 > 15%H3PW12O40/TiO2 > 15%H3PW12O40/Nb2O5 > 15%H3PW12O40/ZrO2 which is in line with the acid strength as determined by NH3 adsorption calorimetry Ammonia adsorption calorimetry P-31{H-1} MAS NMR and FTIR indicate increasing interaction between support and HPA in the following order of supports SiO2 < TiO2 < Nb2O5 < ZrO2 (C) 2010 Elsevier Inc All rights reserved