(544fy) Metal-Promoted Dehydroaromatization of Ethylene over ZSM-5 Catalysts

Authors: 
Zhou, Y., University of Houston
Hsieh, M. F., University of Houston
Thirumalai, H., University of Houston
Grabow, L. C., University of Houston
Rimer, J. D., University of Houston

Industrial production of aromatics heavily relies on catalytic reforming in refineries.1-2 Driven by the limited supply of fossil fuels and the recent shale gas revolution, it is highly desirable to develop methane- and/or light olefin-based processes to meet the growing demand for aromatics. Ethylene dehydroaromatization (DHA) over Ag-ZSM-5 is one of the promising technologies given the availability of ethylene feedstock. Ag-ZSM-5 was chosen for the ethylene DHA reaction, in part because Ag-ZSM-5 was reported to promote aromatic selectivity in the isobutane aromatization,3 and to facilitate non-oxidative methane upgrading at moderate reaction temperatures.4 Here, we will report the influence of Ag species in Ag-ZSM-5 on ethylene DHA without and with co-feeding methane. We observe that Ag-ZSM-5 greatly promotes aromatic selectivities by ~3-fold. In contrast, H-ZSM-5 tends to produce light olefins and other aliphatic hydrocarbons under otherwise identical conditions.5 With methane co-feed, Ag- and H-ZSM-5 both exhibit very similar catalytic behavior compared to the conditions without methane. Interestingly, methane is activated over Ag-ZSM-5 (≤ 5% conversion), but H-ZSM-5 is inactive for methane conversion.

Through systematic studies of Ag/H-ZSM-5 by a combination of experiments and density functional theory calculations at different reaction conditions, we have been able to differentiate the role of Ag species in methane/ethylene activation with enhanced product selectivities to value-added aromatics. We have also extended this study to several metals in an attempt to establish more robust structure-performance relationships in DHA catalysis. Collectively, this work provides new insights into the design of metal-containing zeolite catalysts for natural gas upgrading.

1. Franck, H.-G.; Stadelhofer, J. W., Industrial Aromatic Chemistry. Spring: 1988.

2. Arpe, H.-J.; Hawkins, S., Industrial Organic Chemistry. 5 ed.; 2010.

3. Ono, Y., Transformation of Lower Alkanes into Aromatic Hydrocarbons over ZSM-5 Zeolites. Catalysis Reviews 1992, 34 (3), 179-226.

4. Ono, Y.; Baba, T., Unique properties of silver cations in solid-acid catalysis by zeolites and heteropolyacids. Physical chemistry chemical physics : PCCP 2015, 17 (24), 15637-15654.

5. Hsieh, M.-F.; Zhou, Y.; Thirumalai, H.; Grabow, L. C.; Rimer, J. D., Silver-Promoted Dehydroaromatization of Ethylene over ZSM-5 Catalysts. ChemCatChem 2017, 9 (9), 1675-1682.