Construction of a tandem HZSM-5 with CuZnAl catalyst for alkylation of benzene with syngas

Aiming at the problem of over-production of benzene and the demand for aromatics in industry, a CuO/ZnO/Al2O3 catalyst was prepared by a coprecipitation method, and mixed with ZSM-5 to form a bifunctional composite catalyst. The prepared catalyst is used in an alkylation reaction of benzene with synthesis gas in a liquid phase in a slurry bed reactor. A series of analytical methods such as ammonia gas temperature programmed desorption (NH3-TPD), X-ray diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscopy (SEM) and inductively coupled plasma emission spectrometry (ICP) were conducted to characterize the catalyst. The results show that the structure and acidity of the modified ZSM-5 have changed during the modification process, and ZSM-5 produces a more mesoporous structure after desiliconization. Therefore, the specific surface area of the modified ZSM-5 zeolite increases and the number of acid sites become smaller than those of the unmodified zeolite. The results show that the acid-modified ZSM-5 improves the conversion of CO, while the selectivity of CO to aromatics decreases. In contrast, only alkali modification and acid-alkali co-modification on ZSM-5 contributed to increasing the selectivity to aromatics, especially acid-alkali co-modified ZSM-5. The reason for this can be attributed to the fact that the modified zeolite produces a mesoporous structure, enhancing the mass transfer ability further. Moreover, the amount of strong acid sites on the modified ZSM-5 is reduced, which reduces the side reaction of methanol and olefin, thereby improving the selectivity of CO to aromatics.