Theses and Dissertations

ORCID

https://orcid.org/0000-0001-5902-1437

Issuing Body

Mississippi State University

Advisor

Xiang, Yizhi

Committee Member

Toghiani, Hossein

Committee Member

Rai, Neeraj

Committee Member

Meng, Dong

Date of Degree

8-8-2023

Document Type

Dissertation - Campus Access Only

Major

Chemical Engineering

Degree Name

Doctor of Philosophy (Ph.D)

College

James Worth Bagley College of Engineering

Department

Dave C. Swalm School of Chemical Engineering

Abstract

The increasing production of natural gas liquids attracts both academia and industry to develop on-purpose techniques converting those light alkanes to value-added chemicals. Dehydroaromatization is an alternative path for light alkane conversion to produce aromatics but still lacks active and stable catalysts. This work aims at the development of efficient dehydroaromatization catalysts by tuning the metal/acid bifunctionality of the Pt/HZSM-5 catalyst. Additionally, through co-processing light alkane with ammonia during the dehydroaromatization process, this study also proposes a new reaction system that could directly link the C-N bond for nitrile synthesis.

The results suggested that the activity, selectivity, and stability of the monometallic Pt/HZSM-5 catalyst are highly dependent upon the Pt loading, the limit loading of 100 ppm is required to maintain sufficient metal functionality. To further minimize the Pt loading, the chemical properties of the Pt species were tuned by a second metal such as Zn or Cu. Consequently, the activity and stability of the catalyst are enhanced by orders of magnitude and the maximized metal functionality was achieved at Pt loading of 10 ppm. Characterizations show that Pt can be atomically dispersed as a hybrid [Pt1-Zn6] cluster in the Pt-Zn@HZSM-5 or forming single atom alloy type [Pt1-Cu4] ensembles in the Pt-Cu@HZSM-5. Specifically, the initial turnover frequencies of propane and ethane to BTX are up to 178.8 and 128.7 s-1 over the Pt-Cu@HZSM-5, up to 3-4 orders of magnitude higher than the state-of-the-art Pt-based catalyst. Furthermore, the deactivated catalyst can be continuously regenerated, demonstrating excellent stability of such a catalyst under hash oxidation conditions for coke burn-off.

A new catalytic system named ammodehydrogenation (ADeH) for ethane selective conversion to acetonitrile, ethylene, and hydrogen over a bifunctional catalyst is proposed. Ethane ADeH over the Pt/HZSM-5 catalyst is active at low temperatures and atmospheric pressure for CH3CN production. The Pt/HZSM-5 shows high coke-resistibility during the ethane ADeH due to the strong interaction of NH3 with the acid sites of the catalyst. The catalyst can be further optimized by adding Co, the Pt-Co/HZSM-5 catalyst on ethane ADeH indicating that an appropriate balance between the metal and acid functionalities is critical for ethane ADeH.

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