CATALYTIC DEHYDROGENATION OF 10,11-DIHYDRO-5H-DIBENZ[B.F]AZEPINE (IMINODIBENZYL) TO 5H-DIBENZ[B.F]AZEPINE (IMINOSTILBENE) OVER POTASSIUM-PROMOTED IRON-OXIDES

The catalytic dehydrogenation of 10,11-dihydro-5H-dibenz[b.f]azepine(i minodibenzyl) to 5H-dibenz[b.f]azepine (iminostilbene) has been invest igated over potassium-promoted iron oxide catalysts in the presence of steam. The reaction was performed at 550-600-degrees-C and steam/imin odibenzyl ratios of 50-300 mol/mol. Under the conditions used selectiv iies to iminostilbene up to 80% at nearly 100% iminodibenzyl conversio n were achieved. The observed overall reaction behaviour was influence d by contributions from heterogeneous (catalytic) and homogeneous (non -catalytic) reactions. The homogeneous reaction pathway became promine nt at high space time factors (W(cat)/F(IDB) > 2 g(cat) h/g(IDB) and/o r high temperatures above 600-degrees-C. Potassium-promoted catalysts (7 wt.-% K) prepared from different iron oxide phases, hematite, maghe mite and magnetite, showed all similar selectivities to iminostilbene, indicating that the choice of the iron oxide precursor had no signifi cant influence on the selectivity of the final potassium-promoted iron oxide catalyst. The activity of the catalysts increased with higher B ET surface area. The behaviour of all catalysts was strongly influence d by the steam/iminodibenzyl ratio in the feed. Both selectivity to im inostilbene and conversion of iminodibenzyl increased with higher stea m/iminodibenzyl ratios. The different roles of steam in the catalytic reaction are discussed.