Thermogravimetric analysis of the spent catalysts in air determines a total mass loss of 20 wt% for HY-5 of which strongly bound, bulky carbonaceous deposits represent more than 17 wt% (Figure ). Siralox 30, on the other hand, shows a minimal weight loss of 3.3 wt% from 200-600 °C which could be due to weakly bound deposits. Thus, the stronger and greater number of acid sites on HY-5 are not only more active, but also lead to increased carbon deposition. Those block the catalyst pores and thus decrease the accessibility of active sites, as highlighted by the strongly diminished microporous surface area of spent HY-5 (Table ). The observed slight increase in the mesoporous surface area of HY is due to carbon deposition as confirmed by TGA. In comparison, the surface area of spent Siralox 30 is almost completely retained due to its mesoporous structure.