Catalysis Today 179 (2012) 61–72 Contents lists available at ScienceDirect Catalysis Today jou rn al h om epage: www.elsevier.com/locate/cattod Aromatization of alkanes over Pt promoted conventional and mesoporous gallosilicates of MEL zeolite M.N. Akhtar a , N. Al-Yassir a , S. Al-Khattaf a,∗ , Jiˇ rí ˇ Cejka b,∗∗,1 a KAUST Center in Development, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia b J. Heyrovsk´ y Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejˇ skova 3, 182 23 Prague 8, Czech Republic a r t i c l e i n f o Article history: Received 28 April 2011 Received in revised form 31 May 2011 Accepted 1 June 2011 Available online 28 July 2011 Keywords: Alkane aromatization ZSM-11 GaHZSM-11 Desilication Intracrystalline mesoporosity Platinum a b s t r a c t Aromatization of hexane and propane was investigated over Pt promoted mesoporous gallium-containing HZSM-11 with controlled mesoporosity generated by desilication. Prepared catalysts were character- ized by nitrogen adsorption, X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared of chemisorbed pyridine, and NH 3 temperature programmed desorption confirming the devel- opment 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 arom- atization 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 meso- porous and conventional GaZSM-11 (Si/Ga = 94), respectively, for experiments at liquid hour space velocity of 3.6 h -1 , and 540 ◦ C. Comparison of BTX (benzene–toluene–xylene) selectivity at the con- version level of ∼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 meso- porous 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. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Transformation of alkanes into higher value products, in partic- ular aromatization of linear alkanes into BTX aromatics (benzene, toluene, and xylene) has been the subject of interest for last decades [1]. This stems from the wide applications of BTX. They are used as blending mixture to enhance the octane number of gasoline, and are essential raw chemicals for the petrochemical industry (i.e. aro- matics represent about 30% of the some 8 million known organic compounds [2]). Benzene is widely used in downstream chemi- cal processes such as production of styrene and phenol, whereas xylenes are essential for production of purified terephthalic acid ∗ Corresponding author. Fax: +966 3 860 4234. ∗∗ Corresponding author. Fax: +420 28658 2307. E-mail addresses: skhattaf@kfupm.edu.sa, skhattaf@hotmail.com (S. Al-Khattaf), jiri.cejka@jh-inst.cas.cz (J. ˇ Cejka). 1 Joint Professor of the Center of Research Excellence in Petroleum Refining and Petrochemicals, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia. and isophthalic acid [3]. Indeed, the presence of commercial pro- cesses for alkane aromatization (i.e. M-2 Forming (Mobil), Cyclar (BP-UOP), Z-forming (Mitsubishi), and Alpha process (SandyAsahi)) bears testimony to the economic importance of the aromatization process [4–6]. Particular research effort has been directed to gallium- containing medium pore zeolites owing to the unique properties of ZSM-5 including uniform dimensions of pore channel, intrinsic acidity, and ability to confine active metals [7–22]. Zeolites MCM- 22 [23], Beta [24], mesoporous silicate [25] and structured zeolites [26] were also investigated, while metals such as Pt [4,6,18,27,28], Zn [4,6,19,29,30] and to a lower extent Cu [31], Re [32], Co [33] and Ge [34] have received some attention. The main drawback of Ga-containing HZSM-5 is a low dispersion degree of extra frame- work Ga species, which have been demonstrated in many studies, to adversely affect the BTX selectivity. It is generally accepted that it is quite difficult to incorporate Ga 3+ ions into HZSM-5 via methods such as impregnation or physical admixture, as com- pared with other metal cations. This is largely due to highly positive electrostatic charge and the size of gallium aquacomplexes coupled with the hydrophobicity and weak anion field of ZSM-5 0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2011.06.036