Catalytic pyrolysis performance of alkanes to light olefins over bifunctional ZSM-5 zeolites

Light alkanes in naphtha are difficult to crack into light olefins due to high energy chemical bonds. Here, we proposed a method to improve the conversion of light alkanes by promoting C-H bonds breakage. According to the results of thermodynamic analysis, it was discovered that light olefins yield generated by dehydrogenation cracking of alkanes was about 15% higher than that by protonation cracking, indicating that light olefins yield could be enhanced by promoting C-H bonds cleavage of alkanes. After that, bifunctional ZSM-5 zeolites were modified with phosphorus and transition metals to enhance the dehydrogenation and cracking of alkanes. It showed that Ag-P-ZSM-5 zeolite could improve C5-C7 alkanes conversion by 3.88%−36.09%, and light olefins yield by 1.60%−14.81%, compared with P-ZSM-5 zeolite. The characterization results showed that silver modification could increase Lewis acid sites on zeolite, and promote C-H bonds breakage of alkanes. Furthermore, Ag+ and Agnd+ species were active centers that promote C-H bonds cleavage. This work could provide a good foundation to the preparation of catalysts for naphtha catalytic pyrolysis.