Superiority of ZrO2 surface enrichment on ZSM-5 zeolites in n-pentane catalytic cracking to produce light olefins

In order to reveal the influences of ZrO2 distribution on the catalytic performance of ZSM-5 zeolites, the Zrincorporation has been carried out via the impregnation and chemical liquid deposition (CLD) methods to realize the random distribution and surface enrichment. Catalyst characterizations, including TEM, EDX point scan, XRF, XPS, XRD, H-2-TPR, N-2 adsorption-desorption isotherms, NH3 -TPD, Py-IR, TMPy-IR, ect., confirmed that the Zr-incorporation via the impregnation and CLD methods mostly preserved the characteristic crystal of ZSM-5 zeolites, while made a difference on the acid distribution. Compared with the Zr-impregnation, the Zr-CLD forced the introduced ZrO2 concentrating on the external surface and generated a porous overlayer. The surface enrichment of ZrO2 on ZSM-5 achieved a relatively stable activity as well as light olefins production, and decreased the coke deposit in n-pentane catalytic cracking in comparison to the parent HZSM-5. Also, it was found that ZrO2 surface enrichment was more efficient to inhibit coke formation in comparison to ZrO2 random distribution, and exhibited a coke deposit of 8.8 mg that was ca. 38% lower than the latter (14.3 mg) in the catalytic stability tests (i.e. n-pentane catalytic cracking at 550 degrees C for 12 h on stream with a WHSV of 3.7 h(-1)). Furthermore, SO42-/ZrO2/ZSM-5 was prepared by the sequential Zr-CLD and sulfation of ZSM-5 zeolites. As expected, it achieved the highest light olefins production of 3.87 gin the catalytic stability tests, which was 9.6% and 25.6% higher than that of the Zr-CLD modified and parent HZSM-5.