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|Title:||Acetylation of anisole on TPA/ZrO₂|
BrØnsted acid sites
|Abstract:||Zirconia loaded with 5-20 wt% of tungstophosphoric acid (TPA) were prepared by suspending solid hydrous zirconia in methanolic TPA solution followed by evaporation of methanol and calcination at 400ºC for 4 h. The product were characterized by X-ray diffraction, photoacoustic FTIR spectroscopy, and NH₃₋TPD. XRD results show the formation of single tetragonal phase of ZrO₂ only for the sample loaded with 5wt% of TPA (5-TPA/ZrO₂), whereas the samples loaded with 10, 15 and 20wt% of TPA show two separate phases; cubic phase of hydrogen tungsten phosphate hydrate and tetragonal phase of ZrO₂. The photoacoustic FTIR- spectra of pyridine chemisorbed catalysts show the existence of both BrØnsted (BC) and Lewis (LC) acid sites. The intensity of BrØnsted acid sites band (at 1535 cm⁻¹) and the intensity ratios of BrØnsted to Lewis acid site bands increase with increased loading of TPA from 5 to 15 wt% and decrease with 20 wt% loading of TPA. This is correlating with catalytic yields (4- and 2-methoxy acetophenone) obtained for catalysts loaded with 5-20 wt% of TPA for the acetylation of anisole reaction with acetic anhydride. The results suggest that only the BrØnsted acid sites of catalyst take part in the acetylation of anisole reaction. The NH₃₋TPD curves of above catalysts show that the ‘strong’ acid sites which are in the >450ºC region participate in the reaction.|
|Appears in Collections:||IJCT Vol.15(1) [January 2008]|
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|IJCT 15(1) (2008) 36-40.pdf||133.78 kB||Adobe PDF||View/Open|
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