The time-on-stream stability of some selected bifunctional nanoporous-based catalysts in n -heptane hydroisomerisation

In this work, some commercial nanoporous-based catalysts, such as USY, beta and mordenite zeolites loaded with Platinum metal acting as bifunctional catalysts, were used for hydroisomerisation experiments in a fixed-bed reactor at the atmospheric pressure and at feed space time 5.12 h −1 to hydroisomerise n -heptane over a temperature range of 210–270 °C. The study aimed to evaluate the changes with time-on-stream in the catalytic activity, product selectivity and manner of deactivation of metal-loaded zeolite catalysts, at constant contact time of 5.13 h −1 and a hydrogen-to- n -heptane molar ratio fixed at 9. Various analytical techniques were used to characterise fresh and aged catalysts. Results show that pore architecture is the most important factor affecting coke formation and deactivation in zeolite catalysts, and those catalysts with three-dimensional pore structures lacking cavities or cages were best able to resist deactivation. In addition, it was found that those catalysts with high Si/Al ratios and those which had been acid-leached or steamed showed better activity, higher selectivity towards isomeric products and better time stability. Moreover, the balance between the number of metal sites and the number of acid sites played an important role in determining the activity, selectivity and stability of the bifunctional catalysts.