(724f) Mechanistic Study of Structured Gallium and Platinum Promoted ZSM-5 in Ethane Dehydroaromatization Including Characterization By Pyridine Drifts

Ethane is the second-largest component of shale gas, its existence in the shale gas pipeline causes condensation, and this separated ethane is often known as stranded gas. Therefore, the utilization of stranded ethane has drawn significant interest from researchers due to its economic value. Previously in our group, it was theorized that the presence of Pt more readily promotes the dehydrogenation of ethane to ethylene, which is considered to be the primary step of dehydroaromatization reaction of ethane. The secondary step is when ethylene oligomerizes to the moderate acid sites (Bronsted acid sites). Additionally, according to the ammonia-temperature-programmed desorption (NH₃-TPD) preformed, the presence of the Pt has increased the strength and number of the moderate acid sites on the bimetallic catalyst, as compared to just the Ga/HZSM-5. The combination of Pt promoted Ga catalyst had bimetallic metal interactions that resulted in a favorable performance in ethane DHA.

In the current study three catalysts: GaPt/ HZSM-5, Pt/ HZSM-5, and Ga/ HZSM-5 were investigated for ethane dehydroaromatization (DHA) in a conventional fixed bed reactor at 615°C for 2 hours. Although, the Pt/HZSM-5 catalyst had a higher conversion, GaPt/HZSM-5 showed the best performance out of the three catalysts tested, having better aromatic selectivity. This follows the theorized roles of the promoters in the previous study. Pt/HZSM-5 had a higher selectivity towards ethylene compared to the GaPt/HZSM-5, proving it has an important role in the first step of ethane DHA.

The three catalysts in the current study were synthesized using the dry impregnation method with specific metal loading. In order to prove the roles of Ga and Pt promoters in each of these catalysts, an acid site characterization was done using pyridine DRIFTS at multiple temperatures of fresh and spent catalyst. The spent catalysts coke was removed in a muffle furnace set to 550°C for 6-hrs, TGA analysis confirmed the complete removal of coke deposits from the spent catalyst. The effects of the metal promoters on the concentrations of the weak and strong acid sites were expressed by ammonia-TPD techniques. Surface area analysis, XRD, and TEM were used to further discuss the catalyst structure before and after reaction.