Dehydrogenation of propane with CO
2over Cr/H[B]MFI catalysts
Qingjun Zhu a, Makoto Takiguchi b, Masashi Yamaguchi b Toshiyuki Yokoi a, Junko N. Kondo a , Takashi Tatsumi a,*
a Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-850, Japan Email: [email protected]
b Mitsubishi Chemical Group, Science and Technology Research Center, 1000 Kamoshida-cho, Aoba-ku, Yokohama 227-8502, Japan.
Abstract
The borosilicate H[B]MFI was found to be an effective support for Cr catalyst in the oxidative dehydrogenation of propane reaction with the oxidant of CO2, providing a potential catalyst for the future application in industry.
Introduction
The endothermic conversion of propane to propylene is an interesting research subject to meet the increasing demand of propylene. Several industrial plants have been in operation during the past decade. Recent major concerns are to develop more efficient catalysts, and there are continuous efforts to correlate the catalytic performance of the catalysts with their physicochemical properties.
Experimental
The support materials of silicalite-1 (MFI topology) and borosilicate H[B]MFI (Si to B ratio of 42) were prepared by hydrothermal synthesis at 443 K. Cr (3.0 wt.%) was loaded on the supports by the impregnation method with Cr(NO3)3•9H2O as the precursor. The catalysts were designated as Cr/Silicalite and Cr/H[B]MFI, respectively.
The catalysts were characterized by various characterization techniques such as UV-vis spectroscopy. The catalytic reaction of oxidative dehydrogenation in the presence of CO2 was carried out in a fixed-bed reactor at 873 K.
Results and discussion
The conversion of propane as a function of time on stream (TOS) over the prepared catalysts at 873 K is shown in Fig.1. The initial propane conversion over Cr/H[B]MFI was more than 50%, but decreased quickly to ca. 20% in 2 h whereas the conversion of propane remained lower than 10% over Cr/Silicalite under the given reaction conditions. The representative selectivities of the reactions are listed in Table 1. The selectivity toward desired propylene product was similar. Clearly, the presence of
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0 1 2 3 0
20 40 60
4
Propane conversion (%)
Time on stream (h)
Cr/H[B]MFI
Cr/Silicalite
200 400 600 800
0 1 2 3 4 5 6
463 604 362
Cr/Silicalite
Cr/H[B]MFI
Intensity (a.u.)
Wavelength (nm) 268
Fig.1. Time on stream of oxidative
dehydrogenation propane over various catalysts. Fig.2. UV-vis spectroscopy of various catalysts.
boron in the support of zeolitic materials was beneficial for the production of propylene.
Table 1
Oxidative propane dehydrogenation over catalysts at 873 K (TOS = 3h) Selectivity (%) Catalyst
CH4 C2H4 C2H6 C3H6
Cr/Silicalite 2 0 6 92
Cr/H[B]MFI 2 5 2 91
The diffuse reflectance UV-vis spectra of prepared catalyst are displayed in Fig.2.
The bands at 268 and 362 nm are attributed to the charge transfer of O-Cr (VI) bonds.
The bands at 463 and 604 nm can be assigned to the Cr(III) in Cr2O3 or CrOx clusters.
It is evident that the Cr(III) species in Cr/H[B]MFI catalyst are minor compared with Cr/Silicalite. Further information of the identification of Cr species and the study of interaction between the active component and support materials will be discussed.
Reference
K. Takehira, Y. Ohishi, T. Shishido, T. Kawabata, K. Takaki, Q. Zhang, Y. Wang, J. Catal. 224 (2004) 404.
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