Mechanistic aspects of ethylbenzene dehydrogenation with CO_2 over K_2O/B_2O_3 -TiO_2-ZrO_2 bi-functional catalysts

摘要

TiO_2-ZrO_2 bi-functional catalysts were prepared by co-precipitation method using aqueous NH_3 solution as a hydrolyzing agent. Either K_2O promoter or B_2 O_3 promoter has been deposited 60% HO_2 -ZrO_2 by wet-impregnation techniques. The catalytic activity of both K_2O promoted and B_2 O_3 promoted TiO_2 -ZrO_2 acid base bi-functional catalysts has been studied for the oxidative dehydrogenation of ethylbenzene in the presence of CO_2. The higher conversion of ethylbenzene and higher selectivity of styrene has been obtained on the K_2O promoted TiO_2-ZrO_2 catalysts. On the other hand, B_2O_3 promoted TiO_2 -ZrO_2 catalysts exhibited lower catalytic activity than those of K_2O promoted TiO_2 -ZrO_2 catalysts. In the mechanistic point of view both K_2O promoted TiO_2 -ZrO_2 catalysts and B_2O_3 promoted TiO_2 -ZrO_2 catalysts following the different pathways. This synergistic promotional effects of K_2O and CO_2 enhanced the selectivity of styrene (98 - 99%) by sustaining the higher conversions of ethylbenzene (60 -65%).