Stability of Supported Metal Oxide Catalysts for the Non-Oxidative Dehydrogenation of Propane: An in Situ/Operando Raman Study

Stability of supported metal oxide catalysts for the non-oxidative dehydrogenation of propane: An in situ/operando Raman Study

Jorge Moncada, Lindsey Parsons, Carlos A. Carrero*

Department of Chemical Engineering, Auburn University, Auburn, Alabama 36849, United States

* cac0134@auburn.edu

In this study, we investigate the activity, selectivity, and stability of VO_x/Al₂O₃ and (VO_x)_m-(M₂O_y)_n/Al₂O₃ (M₂ = Mn, Mo, Zr, Ta) catalysts in the non-oxidative dehydrogenation of propane. We will highlight the promoting effect of M₂O_y for tuning the type and amount of carbon produced during the catalyst’s deactivation process. Among the current on-purpose processes to produce light olefins, either platinum or chromium supported catalyst are the most used primarily because of their significant activity and selectivity [1]. However, both the high price and environmental restrictions demand the discovery of alternative catalytic materials to produce light olefins [2]. Both vanadium and molybdenum oxide supported catalysts have already shown promising results in the dehydrogenation of light olefins, [1, 3, 4] although improvements are still needed. The main challenge to overcome in the non-oxidative dehydrogenation of light hydrocarbons is the catalyst’s stability during both the reaction and the regeneration process. The chemical nature of the carbon formed during the catalyst’s deactivation is directly related to the thermal stability of such carbonaceous species and, therefore, to the regeneration process [5]. In situ/operando Raman spectroscopy is a suitable technique to identify and monitor changes of the type of carbon produced during catalytic processes [5]. Our preliminary results indicate that basic metals oxides, such as manganese, promotes the formation of principally amorphous carbon while acidic promoters lead to more graphitic carbon. By monitoring the combustion products (CO and CO₂) using operando Raman spectroscopy and Raman-spectrokinetics [6], we aim to gain further insights both in the thermal stability and the chemical nature of the carbonaceous species either deposited on the catalyst surface or reacting with the catalytic component(s) forming, for instance, metal carbides.

References

[1] Liu G, Zhao Z-J, Wu T, Zeng L, Gong J. Nature of the Active Sites of VOx/Al2O3 Catalysts for Propane Dehydrogenation. ACS Catalysis 2016; 6 (8):5207-14.

[2] Sattler JJ, Ruiz-Martinez J, Santillan-Jimenez E, Weckhuysen BM. Catalytic dehydrogenation of light alkanes on metals and metal oxides. Chem Rev 2014; 114 (20):10613-53.

[3] Gong J, Zhao Z, Wu T, Xiong C, Sun G, Mu R, et al. Hydroxyl-mediated Non-oxidative Propane Dehydrogenation over VO_x/Al₂O₃ Catalysts with Promoted Stability. Angew Chem Int Ed Engl 2018;Advance online publication.

[4] Zhao H, Song H, Chou L, Zhao J, Yang J, Yan L. Insight into the structure and molybdenum species in mesoporous molybdena–alumina catalysts for isobutane dehydrogenation. Catalysis Science & Technology 2017; 7 (15):3258-67.

[5] An H, Zhang F, Guan Z, Liu X, Fan F, Li C. Investigating the Coke Formation Mechanism of H-ZSM-5 during Methanol Dehydration Using Operando UV–Raman Spectroscopy. ACS Catalysis 2018; 8 (10):9207-15.

[6] Moncada J, Adams W, Thakur R, Julin M, Carrero C. A, Developing a Raman-spectrokinetic approach to gain insights on the structure-reactivity relationship of supported metal oxide catalysts, ACS Catalysis; 2018; 8, 8976