(283f) Effects of CeO2 in CuO-ZnO Catalyst for the Deep Purification of CO Derived from Olefins at the Ambient Temperature

Effects of CeO2 in CuO-ZnO catalyst for the deep purification of CO derived from olefins at the ambient temperature

HUANG Jin-hua1,2，YE Li-ping*1,2，YANG Bingxing1,2，Kong Meng 1,2 (1. Shanghai Research Institute of Chemical Industry Co., Ltd, Shanghai 200062, China; 2. State Key Laboratory of Polyolefin and Catalysts，Shanghai 200062，China)

Key words: carbon monoxide; purification; liquid propylene; ceriu moxide; Cu+; DFT

The trace amount of CO in olefins is required to be purified to 3010-9 in order to help the polymerization catalyst (such as metallocene catalyst) obtain a high sensitivity. Catalyst with a high performance plays an important role for the purification process of olefins. Among these catalysts, CuO-ZnO[1] is reported to be an efficient material, and used in industry widely. However, CuO-ZnO catalyst can only decrease the concentration of CO in olefins to 0.110-6 at the temperature more than 70oC. For further improving the efficiency and stability of catalyst, Zr and rare earth (La、Ce、Pr) species are added into CuO-ZnO based catalyst as the promoter in this work.

The purification activity test is carried out at 25oC and 3.0MPa, and the liquid propylene employed as a model compound of olefins. A tri-component catalyst consisting of CuO-ZnO-CeO2 is found to exhibit an excellent catalytic performance especially at a low temperature. It is evaluated that the concentration of CO can be further purified from 1010-6 to less than 1010-9 in the following 150 hours(Fig.1). Such results satisfy the requirement of the deep removal of CO for the polymerization reaction of olefins, providing a probable industrial application.

Furthermore, a series of characterization of BET, H2-TPR, CO-TPR, XRD, TEM, XPS and DFT calculation are employed to elucidate the role of CeO2 in the process of CO purification. The results show that the incorporation of Ce into the CuO-ZnO

increases the specific surface area and pore volume of the catalyst obviously in the BET analysis. From H2-TPR and CO-TPR results, it can be concluded that Ce significantly increases the reducibility and CO adsorption capacity of catalyst, both of which are very critical to catalytic activity. X-ray photoelectron spectroscopy(Fig.2) demonstrate that more active Cu+ and oxygen vacancies are produced when the CuOx are introduced into the CeO2 lattices[2]. Then, the surface structures, O2 adsorption behavior and CO oxidation process over CuO-ZnO-CeO2 catalyst have been investigated using a (DFT + U) method. Results show that the Cu nano-particles gain electrons from the Ce, as a result, the Cu2+ can be reduced to Cu+ in the catalytic system. The combination with CO and Cu+(0.43 eV) is stronger than that with CO and Cu2+ (0.15 eV)[3,4]. In addition, the oxygen atoms at the interface are largely activated by Ce, resulting that a lower formation energy of O vacancies. In the CO oxidation reaction, two possible pathways are investigated, CO reacts with the O2 molecules which are adsorbed on Ce, and the lattice O at the interface respectively. It has been found that CO reacting with the lattice O atom gives a lower reaction barrier than that of adsorbed O2 on Ce. These results are important for understanding of the role of Ce on the CuO-ZnO surface structure.

References

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[2] Liu W, Sarofim A F, Flytzani-stephanopoulos M.Chem. Eng.Sci,1994,49:4871-4888.

[3] Gamarra D, Belver C, Femandez-Garcia M, et al. J Am Chem Soc, 2007, 129(40): 12064-12065.

[4] Hocevar S, Batista J, Lebec J. J Catal, 1999, 184:39-48.