O.A. Ponomareva, F. Testa, V.V. Yuschenko, F.Fajula, I.I. Ivanova
"Catalysis by unique metal ion structures in solid matrices. From science to application" Pruhonice-Prague, p.34 (2000)
ABSTRACT. While Ga- and Fe-containing zeolite materials have proven to be very active and selective catalysts for aromatization, cracking, oligomerization, alkylation and many other processes, rather poor information can be found in the literature concerning the catalytic properties of Ga- and Fe-substituted mesoporous materials. In this contribution, we present the results on ethylbenzene dehydrogenation over Ga- and Fe- micelle-templated silicas (MTS). Al- and Si-MTS materials have also been studied for comparison.
MTS materials were synthesized using the procedure described in [1] and activated by calcination in a flow of dry air at 823 K for 20-24 h. The structure of MTS samples was characterised by XRD and IR spectroscopy. All the samples obtained featured high surface areas of ~ 500-600 m2/g and pore sizes of ~ 30 A. The Si/T molar ratio was ~20 for Ga- and Fe-MTS and ~100 for Al-MTS. The strength of the acidic sites and centers of ethylbenzene adsorption probed by TPD of NH3 and ethylbenzene, respectively, increased in the following order of catalysts: Si-MTS < Fe-MTS < Ga-MTS < Al-MTS. The redox properties probed by H2 TPR were in the following oder: Si-MTS, Al-MTS << Ga-MTS < Fe-MTS.
Ethylbenzene (EB) dehydrogenation was studied at atmospheric pressure in the temperature range of 773-873 K , weight hourly space velocity (WHSV) of 0.2- 1.2 h-1, Ar:EB molar ratio 2.5:1. All the catalysts showed stable catalytic activity during 3-4 h of experiment. The catalysts were also resistant to oxidative regeneration. The main reaction pathways observed on Al-MTS include cracking and disproportionation of EB. On the contrary, on Ga-, Fe- and Si-MTS dehydrogenation was the major reaction; the conversion into styrene increased in the following range of catalysts: Si-MTS<<Ga-MTS<Fe-MTS. Fe-MTS showed the best catalytic performance in the whole range of experimental conditions studied. Under the optimal conditions found for this catalyst (803-853 K and WHSV= 0.2-1.2 h-1 ), ethylbenzene conversion was 12-19%, while selectivity to styrene was 88-93 wt%.