Aromatization of alkanes over Pt promoted conventional and mesoporous gallosilicates of MEL zeolite

0375912 - ÚFCH JH 2013 RIV NL eng J - Journal Article
Akhtar, M. N. - Al-Yassir, N. - Al-Khattaf, S. - Čejka, Jiří
Aromatization of alkanes over Pt promoted conventional and mesoporous gallosilicates of MEL zeolite.
Catalysis Today. Roč. 179, č. 1 (2012), s. 61-72. ISSN 0920-5861. E-ISSN 1873-4308
Institutional research plan: CEZ:AV0Z40400503
Keywords : alkane aromatization * ZSM-11 * GaHZSM-11
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 2.980, year: 2012

Aromatization of hexane and propane was investigated over Pt promoted mesoporous gallium-containing HZSM-11 with controlled mesoporosity generated by desilication. Prepared catalysts were characterized by nitrogen adsorption, X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared of chemisorbed pyridine, and NH3 temperature programmed desorption confirming the development of intracrystalline mesoporosity of Ga-containing HZSM-11. The catalytic activities, which were compared in the aromatization of n-hexane and propane, increased upon desilication. The aromatization of n-hexane decreased in the following order, Pt/mesoporous GaZSM-11 > Pt/conventional GaZSM-11 > mesoporous GaZSM-11 > conventional GaZSM-11. Hexane conversion reached 70.1% over mesoporous Pt/GaZSM-11 with Si/Ga of 61, as compared with 29.6 and 24.9% for corresponding mesoporous and conventional GaZSM-11 (Si/Ga = 94), respectively, for experiments at liquid hour space velocity of 3.6 h(-1), and 540 degrees C. Comparison of BTX (benzene-toluene-xylene) selectivity at the conversion level of similar to 21.0% revealed that Pt/mesoporous GaZSM-11 is more selective than corresponding mesoporous and conventional GaZSM-11. The BTX selectivity over Pt/mesoporous GaZSM-11 (Si/Ga = 94), which showed strong dependence on the conversion, reached 28.2%, whereas over corresponding mesoporous and conventional GaZSM-11catalysts reached 19.1% and 5.5%, respectively. A higher conversion and better selectivity can be attributed to the improved accessibility to the active extra-framework Ga species owing to the generation of mesopores inside the zeolite particles and shortening the contact time. It is worth mentioning that the prepared catalysts exhibited quite low activity in propane aromatization but exhibiting similar trends as for hexane aromatization.
Permanent Link: http://hdl.handle.net/11104/0208451