?MODIFIED ZIRCONIA-SUPPORTED HEMATITE CATALYSTS FOR ETHYLBENZENE DEHYDROGENATION WITH CARBON DIOXIDE?

M. C. RANGEL; C. SOUZA DE MIRANDA; A. P. DE MELO MONTEIRO; S.G. MARCHETTI; S. BARBOSA LIMA; S. BARBOSA LIMA

La Rochelle

Simposio; ?2nd International Symposium on Green Chemistry Renewable Carbon and Eco-Efficient Processes?; 2013

Styrene, an important chemical used for the production of plastics and resins, is currently produced by ethylbenzene dehydrogenation with steam. However, due to reaction endothermicity and thermodynamic limitation, as well as to catalyst deactivation, new processes are required. A promising alternative is the ethylbenzene dehydrogenation with carbon dioxide, which is exothermic and has no thermodynamic limitation. However, this reaction still has some drawbacks such as the lack of efficient catalysts [1].  In the present work, zirconia-supported hematite modified with cerium, chromium, aluminum and lanthanum were studied aiming to find active and selective catalysts. The supports (modified zirconia) were prepared by precipitation followed by impregnation of iron nitrate and calcination. Samples were characterized by thermogravimetry, differential thermal analysis, infrared spectroscopy, X-ray diffraction, thermoprogrammed reduction and Mössbauer spectroscopy and evaluated in ethylbenzene dehydrogenation with carbon dioxide at several temperatures. Hematite and zirconia (monoclinic and tetragonal phases) were found for all catalysts. The specific surface areas of the catalysts increased due to the dopants, especially for chromium, followed by lanthanum. The reducibility of the solids changed depending on kind of the dopant, lanthanum led to the least reducible solid while chromium produced the most reducible one. All samples were more active than the dopant-free catalyst (zirconia-supported hematite) and than a commercial catalyst. For all solids, both activity and selectivity changed with temperature depending on the dopant (Fig. 1).  In a general tendency, the chromium-doped catalyst was the most active and the least selective one while the cerium-doped one showed and opposite behavior for all temperature range. The most promising catalyst for ethylbenzene dehydrogenation with carbon dioxide  is the cerium-doped one which led to the highest values of styrene yield at low temperatures (530-570 oC). The different behaviors of the catalysts were related to the different interactions between hematite and the modified supports.       [1] E. A.  Mamedov, Appl. Catal. A: Gen. 116 (1994) 49-70.