Applied Catalysis B: Environmental, Vol.236, 13-24, 2018
Catalytic co-aromatization of methane and heptane as an alkane model compound over Zn-Ga/ZSM-5: A mechanistic study
The joint conversion of methane and heptane, a model compound of paraffin-rich raffinate oil, over a Zn-Ga modified zeolite catalyst has been investigated at various reaction times. In comparison with the performance from a N-2 environment, the introduction of methane highly promotes the formation of light aromatic compounds with a single phenyl ring, and increased carbon number and substitution index of chemical constituents formed are indicative of methane incorporation into the liquid product. In addition, with prolonged time, the interaction between catalyst and methane molecules is enhanced. Through cleavage of methane molecules, the formed moieties likely participate in the aromatization reaction, which results in the growth of larger aromatic components through further condensation. According to the NMR spectra, witnessing methane engagement into the phenyl carbon and alkyl carbon sites of the formed liquid aromatics along with increasing reaction time is evidenced C-13-methane incorporation into aromatics. The excellent catalytic performance of Zn-Ga/ZSM-5 might be ascribed to the greatly dispersed metal species on the catalyst surface as well as a certain amount of medium and weak acid sites. With regards to the spent catalyst, the presence of methane could inhibit the aggregation of loaded active metals and coke formation during the co-aromatization process. The elucidation on the co-conversion of methane and high alkane provides great potential for the utilization of natural gas resources and intermediates formed from petrochemical industries.