III International Conference

Yield, %PP-II-122Dynamics of variations of C 2 H 6 concentrations and reaction products formation weremonitored by on-line FTIR gas analyzer.Variations of ethane and reaction products (ethylene, methane, CO, CO 2 ) yields overPt/ZnO/Al 2 O 3 at 500 o C are displayed in Fig. 1.Reaction stagePurgingDuring the first seconds of ethaneAir impulsestageimpulse a maximum formation of CO, CO 210Pt/ZnO/Al 2 O 3 and methane was observed. Carbon oxides9500 o C8are presumably formed due to a reaction of7EthaneEthylene ethane and ethylene with weakly bounded6СО2СОoxygen. Ethylene is dominant product of5Methaneethane oxidation and ethylene yield passes4through the maximum after 2-3 minutes of3the reaction. Presumably during this period2“easily accessible” oxygen is consumed, and10further ethylene formation proceeds via a00:00 02:53 05:46 08:38 11:31 14:24Time, mm:sscombination of a non-oxidative dehydrogenationand oxidative dehydrogenation byFig. 1 Transient responses upon supplying of thePt/ZnO/Al 2 O 3 catalyst with 600 s impulse of ethanefollowed by purging with nitrogen and supplying of air oxygen diffused from the catalyst bulk. Theimpulsefollowing air impulse resulted in an intensive(up to 25 %) CO 2 evolution due to oxidation of carbon containing deposits accumulated onthe catalyst surface during C 2 H 6 ODH.Analysis of the reaction products indicates that one of the main factors limiting theprocess selectivity is a formation of CH 4 during the first stage of ODH, and carbon depositionof the catalyst surface (probably coke formation). It was found that modification ofPt/ZnO/Al 2 O 3 with Sn allow us to suppress undesirable side-reactions and increase ethyleneselectivity significantly (Fig. 2, 3).Ethylene yield, %12108642500 o CPt-Sn/ZnO/Al2O3Pt/ZnO/Al2O3Pt/Al2O3Ethylene selectivity, %8070605040302010500 o CPt-Sn/ZnO/Al2O3Pt/ZnO/Al2O3Pt/Al2O3000:00 01:26 02:53 04:19 05:46Time, mm:ssFig.2 Variations of ethylene yield over Pt/Al 2 O 3 ,Pt/ZnO/Al 2 O 3 and Pt-Sn/ZnO/Al 2 O 3000:00 01:26 02:53 04:19 05:46Time, mm:ssFig.3 Variations of ethylene selectivity over Pt/Al 2 O 3 ,Pt/ZnO/Al 2 O 3 and Pt-Sn/ZnO/Al 2 O 3389