Hydrogen spillover effect on cumene cracking and n-pentane hydroisomerization over Pt/SiO2 + H-Beta

Abstract

The effects of catalytic component, hydrogen partial pressure, metal amount and dose amount on cumene cracking and n-pentane hydroisomerization over Pt/SiO2+H-Beta physically mixed catalyst were studied with a pulse reactor system to examine the function of spilt-over hydrogen species. In cumene cracking, high catalytic activity was observed on H-Beta containing catalysts. On the contrary, platinum, hydrogen and H-Beta were indispensable for high catalytic activity in n-pentane hydroisomerization. Hydrogen spillover phenomenon inhibited the deactivation in both reactions. Cumene cracking activity decreased with higher hydrogen pressure on the catalyst with larger amount of Pt/SiO2. It was found that the negative reaction order with respect to hydrogen was always negative in cumene cracking. In contrast, in n-pentane hydroisomerization, the positive reaction order with respect to hydrogen was observed under rather low hydrogen pressure, though the order was negative under high hydrogen pressure. This positive tendency became more significant over the catalyst with larger amount of Pt/SiO2.The negative reaction order with respect to hydrogen is suggested to be due to the supply of spilt-over hydride to carbenium ion reaction intermediate before the cracking and isomerization reaction. At the same time, there seems to be another effect of spilt-over hydride. This inhibits the desorption of the carbenium ion as alkene, which is related to the catalyst deactivation. On the other hand, the positive reaction order with respect to hydrogen in n-pentane hydroisomerization is thought to be due to the enhancement of the acid strength by spilt-over hydrogen.On Pt/SO42−-ZrO2 catalyst, the promoting effect of hydrogen on the activity was significant in cumene cracking, however, not in n-pentane hydroisomerization. The effect of hydrogen spillover on the reaction was different. This can be due to the higher concentration of spilt-over hydrogen over on Pt/SiO2+SO42−-ZrO2 than that over Pt/SiO2+H-Beta.