Title

Investigation of Palladium-Ceria Catalysts for Selective Hydrogenation of Acetylene in Ethylene

Author

Tengteng Lyu

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Date of Award

Fall 2018

Abstract

Acetylene-selective hydrogenation in excess ethylene is a critical reaction for the purification process in the polyethylene industry to remove traces of acetylene from the feedstock. Palladium (Pd) catalyst is industrially used for this process. However, the catalytic performance of supported Pd catalyst is far from ideal on account of its limited ethylene selectivity and the promotion of undesirable ethane, oligomers, or, in other words, "œgreen oil." Since the production of ethylene has reached billions of pounds, a small improvement of ethylene selectivity will reduce the cost dramatically for the industrial purification process. This investigation aimed to design and modify the ceria-supported Pd catalysts for acetylene selective hydrogenation with various techniques including non-thermal plasma, reduction, and calcination and to make ceria-supported Pd catalysts possess desirable surface properties and excellent catalytic performance. The surface properties were aimed at controlling the formation of small Pd particles, including single atoms, on ceria surfaces with specific interaction with Pd metal. Pd/CeO2 catalysts with 0.05%, 0.1%, and 0.2% Pd loadings were prepared via incipient wetness impregnation method for selective hydrogenation of acetylene in ethylene. Pa loading effect, calcination temperature effect, reduction pretreatment effect, and argon dielectric barrier discharge (DBD) plasma pretreatment effect were studied in this research work. Pd/CeO2 catalyst could be activated in situ by the feed gas during reactions, and the catalyst without reduction showed much better ethylene selectivity in high temperatures than the reduced one due to the formation of oxygen vacancies after reduction. The best yield of 74% was obtained at 200 ℃ for 0.1% Pd/CeO2 800 ℃ catalyst and at 176 ℃ for 0.2% Pd/CeO2 800 ℃ catalyst due to the strong interaction between Pd and ceria. The surface properties of catalysts were characterized with various techniques, such as atomic absorption spectroscopy (AAS), thermogravimetric analysis (TGA), pulse H2 chemisorption, hydrogen temperature programmed reduction (H2TPR), in-situ Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC).

Advisor

Ben W.-L. Jang

Subject Categories

Chemistry | Physical Sciences and Mathematics

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