Cooperative catalysis of Co-promoted Zn/HZSM-5 catalysts for ethane dehydroaromatization

Abstract

Zn/HZSM-5 is a promising catalyst for ethane dehydroaromatization despite rapid deactivation within 13 h. Herein, the effect of introducing a cobalt promoter into the Zn/HZSM-5 catalyst was investigated to improve catalytic performance. Co-promoted Zn/HZSM-5 was superior to unpromoted Zn/HZSM-5 in terms of both catalytic activity and stability. Additionally, the total yield of benzene, toluene, and xylene over 1CoZn/HZSM-5 was 10.2%, even after 25 h of reaction, compared to the total yield over Zn/HZSM-5 catalyst at less than 1% at the time. XRD, UV–vis, TEM, and H2-TPR demonstrated that Co introduction improved ZnO dispersion in the prepared catalysts. Furthermore, the characterization of the spent catalyst via XRD, TEM, Raman, TGA, and N2 adsorption/desorption proposed that the conversion of graphite coke precursor to carbon nanotube and amorphous carbon prevented the micropores in the zeolite from being blocked. Thus, a considerable number of Brønsted acid sites in micropore could be preserved, thereby enhancing their catalytic stability. However, excessive Co clusters favored CC and CH bond dissociation, primarily producing methane and coke rather than aromatics. Therefore, adding an appropriate amount (1 wt%) of Co to Zn/HZSM-5 improves catalytic performance and the resistance to deactivation.