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Abstract  

β-MCM41 composite molecular sieves were hydrothermally synthesized using NaOH treated β zeolite as precursors, and Pt/β-MCM41 bifunctional catalysts were prepared by impregnation. Hβ, desilicated Hβ by NaOH treatment (Dβ), and the physical mixture of Hβ and MCM41 (β+MCM41) were also used as control supports for bifunctional catalysts. All the catalysts were characterized by ICP, XRD, BET, nitrogen adsorption–desorption isotherm and NH3-TPD, and evaluated in the hydroisomerization of n-heptane using an atmospheric fixed bed flow reactor. Dβ, β+MCM41, or β-MCM41 supported Pt catalysts showed higher selectivity to isoheptanes than the counterpart Pt/Hβ did due to the presence of mesopores in addition to the zeolite micropores. Moreover, Pt/β-MCM41 was demonstrated to be a much more selective catalyst among them because the connection between mesopores and micropores accelerated the diffusion of larger molecules of isoheptanes. Under optimal conditions, Pt/β-MCM41 provided a very high selectivity to isomerization of 96.5%, coupled with a considerable high conversion of n-heptane of 56.0%.

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) Takemoto, Y. Org. Biomol. Chem. 2005 , 3 , 4299–4306; for other reviews on bifunctional catalysts, see: (b) Doyle, A. G.; Jacobsen, E. N. Chem. Rev. 2007 , 107 , 5713–5743 and (c) Lu, L.-Q.; An, X.-L.; Chen, J.-R.; Xiao, W.-J. Synlett 2012 , 23 , 490

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Abstract  

Pt/WOx–ZrO2 bifunctional catalysts were synthesized using impregnation and polymeric precursor methods. After the synthesis process the samples were calcined at 600, 700 and 800C and characterized by X-ray diffraction, nitrogen adsorption and temperature programmed reduction study by thermogravimetry. DTG-TPR profiles showed between three and five reduction events at different temperatures attributed to platinum reduction and to different stages of tungsten species reduction. A comparative study of the synthesis method influence on the DTG-TPR curves was accomplished.

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(C 7 –C 9 ) is also very important because of the much higher octane number of the corresponding isoparaffins, wherein n -heptane is usually used as a model reactant for fundamental research [ 1 , 2 ]. Since the commercial bifunctional catalyst Pt

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Introduction Hydroisomerization and hydrocracking of n -paraffins are important reactions in refinery processes for the production of high quality fuels employing bifunctional catalysts. These catalysts comprised of a metal

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branching of the carbon chain. The reaction is carried out over bifunctional catalysts, containing small metal particles such as Pt or Pd dispersed on an acid support. According to the bifunctional mechanism, n-alkenes resulting from the dehydrogenation of

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Abstract  

Alkaline earth metal (Mg, Ca, Sr and Ba) ions were exchanged into Hβ zeolite, which were used as the supports to load the noble metal Pt to prepare bifunctional catalysts for hydroisomerization of n-heptane. The catalysts were characterized by ICP, XRD, BET, NH3-TPD, H2-TPR and H2-chemisorption techniques, and evaluated in an atmospheric fixed bed reactor. The catalysts promoted by the alkaline earth metals are revealed to present much higher selectivity to isomerization than the counterpart Pt/Hβ. Moreover, the Ba-bearing catalyst loaded with 0.4 wt% Pt and 5:1 molar ratio of Ba to Pt gives a very high selectivity to iso-heptanes 95.4% with a considerable high conversion of n-heptane 61.7%. The promotion effect of alkaline earth metals is briefly discussed in relation to characterization data.

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the rather low Pt/ZSM-22 activity. In contrast, all the acid sites of bifunctional catalysts containing large pore zeolites are accessible and their hydroisomerization activity is very high, but often at the expense of the selectivity to isomers [ 17

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-range alkanes with bifunctional catalysts ” Peng , B. , Yao , Y. , Zhao , C. , Lercher , J. A. Angewandte Chemie International Edition 2012 , 51 , 2072 – 2075 . “ Triphase microfluidic-directed self-assembly: Anisotropic

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. Garrido Pedrosa , AM , Souza , MJB , Lima , SH , Dulce , MAMelo , Souza , AG , Araujo , AS . 2007 . Influence of the synthesis methods of the DTG-TPR profiles of Pt/WOx-ZrO 2 bifunctional catalysts . J Therm Anal Calorim . 87 : 703 – 707 10

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