Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-III-40ratio, an increase in the propane conversion and almost no change in the selectivity towardsbutene are observed. In addition, a slightly decrease in the selectivity towards propene withincrease of Si/Al ratio is observed (not shown here).These are likely to be related to thechange of zeolites acidity with varying Si/Al and therefore the number of iron cationsintroduced into zeolites. In the low Si/Al ratios (Si/Al < 40), the percent of products such asCH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , C 3 H 6 formed via the hydrocraking of butane are enhanced. But, thehigher Si/Al ratios lead to an increase in oxidative dehydrogenation of butane to butene andbutadiene.X C4H10,%7060504030201000 100 200 300 400Time,minSM27Fe1.0Z23Fe1.0Z30Fe1.0Z50Fe1.0Z80Fe1.0Z280Fe1.0SC4H8,%70605040302010SM27Fe1.0Z30Fe1.0Z50Fe1.0Z80Fe1.0Z280Fe1.000 100 200 300 400Time, minFig.1. Butane conversion and butane selectivity as a function of time in the presence of N 2 O in the feed(W cat = 0.5 g, T= 723 K, C 4 H 10 :N 2 O=1:1, F total =200ml/min). ZxFey: x= SiO 2 /Al 2 O 3 and y= wt. % Fe.The presence of O 2 as well as N 2 O in the feed over Z280Fe1.0 not only prevents theformation of butane and butadiene, but also leads to a significantly decrease in the conversionof butane, from 50 % to 3.0 %. The butane mainly converts to CO x via total oxidationThe nature of the iron species responsible for the N 2 O decomposition (not shown here)and dehydrogenation of butane appears clearly different as could be observed with of H 2 -TPR, UV/vis, XPS, DRIFT, and NH 3 -TPD. It can be concluded that although N 2 Odecomposition and the total oxidation of butane are favoured over isolated iron-oxo/hydroxocationsformed over Fe-ZSM-5 with low Si/Al, the uncharged nonosized multinuclear ironoxoclusters formed in 80 and 140 of Si/Al can mostly catalyze the dehydrogenation of butane.Additionally, in this work the kinetics of global and elementary steps for oxidativedehydrogenation of butane can be obtained under the unsteady-state and steady-stateexperiments.References:1. A. Ates and A. Reitzmann, J. Catal., 2005, 235, 164-174.2. E. Ananieva and A. Reitzmann, Chem. Eng. Sci., 2004, 59, 5509-5517.381