Ethyl benzene oxidative dehydrogenation to styrene on Al-B and Al-B-Sb catalysts

Alumina (Al), alumina-boron (Al-15B), alumina-boron-antimony (Al-B-Sb) and alumina-antimony (Al-15Sb) catalysts were synthesized by sol-gel method using ethanol as a solvent and ammonia gas as a gel forming agent. These catalysts were studied for the dehydrogenation of ethylbenzene (EB) to styrene in the presence of oxygen and steam. The reaction was carried out in the temperature range of 450-500 degrees C with EB contact time 0.54 g(cat).s/cm(3). The synthesized catalysts were characterized by using N-2-physisorption, XRD, XPS, TEM-HRTEM-EDS and NH3-TPD-mass spectral analysis techniques. At 475 degrees C, only 58% of styrene selectivity with 32% of EB conversion was observed on Al. Addition of 15 mol.% of B to Al significantly enhanced the selectivity of styrene to 94% with 46% EB conversion at 475 degrees C. Addition of 15 mol.% Sb to Al reduced the EB conversion (38%) and styrene selectivity (75%) compared to Al-15B catalyst. Interestingly, small amount of Sb (5 mol.%) addition to Al-B improved the EB conversion to 52.5% with 92% of styrene selectivity at 475 degrees C. The acid sites of weak and moderate strength were increased in Al-15B catalyst compared to Al. Boron played a dual role as Al densification suppressing agent and to some extent deposited on the surface of Al which improved the styrene selectivity. However, small amount of Sb addition to Al-15B not only retained weak and moderate strength acid sites of Al-B but also generated acid sites of Sb which led to the formation of N2O and NO during NH3-TPD-mass analysis. Hence, the styrene yield (48.8%) was improved on Al-B-5Sb compared to Al-15B catalyst (43%). It is noteworthy that Al-15B and Al-B-5Sb catalysts were stable for more than 60h of reaction.