| 12-tungstophosphoric acid (PW) containing Platinum (Pt) catalysts supported on modified zeolites such as USY, modernite and Beta zeolite were prepared. The catalysts were tested in n-heptane hydroisomerization reaction with a fixed bed continuous flow microreactor. Their physicochemical properties were characterized by N2 adsorption, temperature programmed desorption of ammonia (NH3-TPD), infrared spectrum (IR), thermogravimetry-differential scanning calorimetry (TG-DSC), and X-ray diffraction (XRD) techniques. Based on these characterizations, the catalytic performances of the catalysts in n-heptane hydroisomerization are discussed in detail.For a series of Pt-PW/USY catalysts, XRD patterns show that the modified USY zeolite retains the perfect crystallinity of Y zeolite upon loading PW with the concentration of 20%, and PW is highly dispersed on the surface of the support. The BET surface area of catalyst shows that PW mainly leads to the drastical decrease of surface area of the mesopores in PW/USY, indicating that PW anions might largely locate in the mesopores of the modified USY. The IR result shows that PW physically interacts with the modified zeolite with its Keggin primary structure unaltered. The TG-DSC measurement of the catalysts reveals that the supported heteropolyacid is thermally stable when heated up to 700℃, in contrast, the pure PW decomposes upon heating at 610℃. NH3-TPD profiles show that not only acid amount but also acid strength are improved by introducing PW into USY.Heteropolyacid catalysts supported on different zeolites were tested in the n-heptane hydroisomerization reaction. By measuring catalytic performances of Pt-PW/USY catalysts, it is found that both hydrothermal treatment temperature and time for the USY support influence the catalytic activity remarkably. It is revealed that 650℃ and 5h are the optimal hydrothermal treatment temperature and time, respectively. Moreover, the pretreatment conditions for the catalyst influence the conversion of n-heptane substantially, and at the same time, the isomerization selectivity comparatively remains stable. The Pt-PW/USY catalyst with a calcinationtemperature of 200℃ without prereduction possesses the maximum activity. On the other hand, the reaction results over the catalysts with different PW and Pt loadings lead to the conclusion that n-heptane hydroisomerization over this kind of catalyst follows the classical bifunctional mechanism. Compared with Pt/USY catalysts, Pt-PW/USY catalysts improve not only the conversion of n-hetane but also the selectivity to isomers. For example, under the same reaction conditions, the catalytic activity and isomerization selectivity of 0.4%Pt/USY catalyst are 49.0% and 77.0%, and they are increased over 0.4%Pt-10%PW/USY by 16.1% and 5.2%, respectively.Very similar results are achieved over Pt-PW/Hβcatalysts to those over Pt-PW/USY. The Pt-PW/Hβcatalyst exhibits the conversion of n-heptane of 39.6% and a high selectivity to isomers of 88.5%, which is much higher than those over Pt/Hβ.For Pt-PW/HM catalysts, the optimal hydrothermal treatment temperature and time for modified HM are found to be 400℃ and 5h, respectively, and the optimal calcination and prereduction temperature are both 200℃. At this moment, the catalyst comes to the highest catalytic activity of 80.2%. However, its isomerization selectivity drops to a very low value of 36.0%, probably due to the diffusion limitation of the reaction intermediates inside the unidimensional channel of mordernite zeolite. On the other hand, lower reaction temperature is needed for Pt-PW/HM catalyst to achieve the comparable catalytic activity compared with Pt/HM catalyst, which results in a higher isomerization selectivity over the PW-containing catalyst. Comparison of Heteropolyacid catalysts supported on the above modified zeolites with those on meso-structured material SBA-15 was also studied. It is found that the acidity and pore structure of the catalysts are important factors affecting the catalytic performance. High...
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