The effect of ceria and
zirconia grafting onto
alumina (α and θ-δ phases) as supports for
silicotungstic acid for the
dehydration of
glycerol to
acrolein was studied. 30 %
Silicotungstic acid (STA) supported on 5 %
zirconia/δ,θ-
alumina was the best catalyst, producing 85 % selectivity to
acrolein at 100 %
glycerol conversion, and it showed stable activity without using
oxygen as a co-feed. The catalyst produced a STA of 90 g(
acrolein) kg(cat)(-1) h(-1), which was greater than the STA simply supported on δ,θ-
alumina, which only demonstrated 75 % selectivity towards
acrolein. The effect of grafting on the support material was investigated by means of
nitrogen adsorption,
ammonia temperature-programmed desorption, thermogravimetric analysis, Raman spectroscopy, and
powder X-ray diffraction. A pulsed-field gradient (PFG) NMR technique was also used to study diffusion processes associated with the catalysts. Diffusion studies of the grafted catalysts showed that
zirconia contributes to the formation of more tortuous pathways within the pore structure, leading to the diminution of
acid strength and making the catalyst less susceptible to
coke formation.