CATALYTIC DEHYDROGENATION OF 10,11-DIHYDRO-5H-DIBENZ[B.F]AZEPINE (IMINODIBENZYL) TO 5H-DIBENZ [B,F]AZEPINE (IMINOSTILBENE) OVER POTASSIUM-PROMOTED IRON-OXIDES - EFFECT OF STEAM, POTASSIUM PROMOTION AND CARBON-DIOXIDE TREATMENT

The dehydrogenation of 10,11-dihydro-5H-dibenz[b.f]azepine (iminodiben zyl) to 5H-dibenz[b.f] azepine (iminostilbene) was investigated over p otassium-promoted iron oxide catalysts. The catalytic behaviour of the catalysts was found to be strongly influenced by the oxidation state of iron and by the amount of carbon deposits on the catalyst surface. Dilution of the iminodibenzyl feed by steam prevents reduction of the active iron oxide phase and reduces drastically the deposition of carb on, leading to high steady-state activities of potassium-promoted cata lysts. Promotion of the iron oxides with 0.5 wt.-% potassium increases significantly the activity of the catalysts. Potassium improves the r educibility of iron oxides probably by enhancing the electron exchange between Fe3+ and Fe2+ ions, and results in an apparent increase of th e number of sites active for the dehydrogenation of iminodibenzyl. Pot assium carbonate and magnetite represent the main phases under reactio n conditions in the presence of steam and are proposed as the active p hases in the dehydrogenation of iminodibenzyl. Gasification of carbona ceous deposits by steam leads to the formation of carbon dioxide and p otassium carbonate under normal reaction conditions. Therefore, the ac tive centres are not sensitive to further carbon dioxide treatment.