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Free keywords:
iron oxide, epitaxy, in-situ, catalysis, styrene
19: Iron oxide model catalysts: Adsorption and catalysis
Abstract:
I will review a fairly successful attempt to bridge the gaps between surface science studies and real catalysis for the case of ethylbenzene (EB) dehydrogenation to styrene (St) over unpromoted and K-promoted iron oxide catalysts. Epitaxial films of Fe3O4(111), a-Fe2O3(0001), KxFe22O34 and KFeO2 were prepared and characterized using surface science methods. Their catalytic behavior was studied after vacuum-transfer in a micro flow reactor, followed by post-reaction surface analysis. The results are : (i) Defects are necessary for the dehydrogenation step; (ii) most active is Fe3+ in Fe2O3 or KFexOy; (iii) unpromoted catalysts deactivate by reduction to Fe3O4 and by coking; (iv) both can be prevented by some oxygen in the feed; (v) K is catalytically inactive but suppresses reduction and catalyses carbon removal; (vi) K2Fe22O34 and KFeO2 are K-reservoir phases; (vii) “steaming” (reaction in steam without EB) exhausts the K-reservoir phases; (viii) coke has non-zero catalytic activity and contributes to conversion in real catalysis. In cooperation with the ICVT in Stuttgart, microkinetic modelling was performed aiming at a prediction of the behaviour of technical catalysts. Using physically meaningful parameters, mostly determined in surface science experiments, an excellent fit was achieved which could even be extented to porous samples.
