(656f) Advancing the Selective Oxidation of Ethylene Glycol Via Combining Novel Catalyst Design and Density Functional Theory (DFT) Calculations

Ethylene glycol (EG) is the simplest diol that can be produced from hydration of ethylene oxide or hydrogenolysis of biomass (cellulose) ¹. In recent work, significant research work is focused on EG electroxidation for fuel cells ². This status is attributed to the fact that EG has higher boiling point (198 ^oC) making it a safer liquid fuel and has higher energy density compared to ethanol and methanol. However, in order to harvest the total amount of energy during this process, EG is fully converted into CO₂ that aggravates global warming. In this context, conversion of EG into value-added products chemically could be more attractive. A number of papers are available on EG oxidation in aqueous alkali medium using a non-hazardous oxidizing agent – oxygen gas ^3-6. However, the data reported on this reaction system are mainly on EG conversion and little is known on the reaction mechanism or the viability of applying different catalysts. Moreover, glycolic acid is usually the main product, while formic acid and CO₂ are believed as the side products of over oxidation rather than desirable oxalic acid (dicarboxylic acid) ⁶. At the same time, current oxalic acid production suffers from the problems of using corrosive and stoichiometric reagents (nitric acid and sulfuric acid), with low yield and selectivity ^7,8. Suitable catalysts for a single-step conversion of EG to oxalic acid are highly desirable, that would be important to both industrial application and fundamental understanding of alcoholic group oxidation in polyols.

In this study, a series of monometallic catalysts (including Ag, Pd, Ru, Rd, Fe, Pt) supported on CeO₂ were synthesized by using a novel solvothermal method. The oxidation tests were conducted at a mild condition (70 ^oC, ambient pressure O₂) in aqueous alkali solution. The catalysts were characterized by H₂ chemisorption, inductively coupled plasma (ICP), transmission electron microscopy (TEM) for the metal content, dispersion and morphology information. Volcano plots of normalized TOF values vs. density functional theory (DFT) calculated Gibbs Free energy was established for EG oxidation. Furthermore, a bimetallic Pt-Fe catalyst showed a significant rate enhancement and selectivity in one-step conversion of EG-to-oxalic acid. The reaction mechanism for EG catalytic oxidation by O₂ on (100) and (111) surfaces was studied using DFT calculations which rationalizes the experimental observations that the bimetallic Pt-Fe catalyst has a significantly higher activity (TOF) compared to the monometallic catalysts (Pt and Fe). Fundamental concepts in the computational chemistry and its relation to experimentally observed performance of bimetallic catalysts will be presented in this work.

References

1. Yue, H., Zhao, Y., Ma, X., & Gong, J. (2012). Ethylene glycol: properties, synthesis, and applications. Chemical Society Reviews, 41(11), 4218-4244.

2. Serov, A., & Kwak, C. (2009). Review of non-platinum anode catalysts for DMFC and PEMFC application. Applied Catalysis B: Environmental, 90(3), 313-320.

3. Sakharov, A. M., Sakharov, P. A., & Zaikov, G. E. (2012). Catalytic Oxidation of Ethylene Glycol by Dioxygen in Alkaline Medium. The New Example of One-Stage Oxidative Cleavage of С‒С Bond. Molecular Crystals and Liquid Crystals, 555(1), 168-176.

4. Berndt, H., Pitsch, I., Evert, S., Struve, K., Pohl, M. M., Radnik, J., & Martin, A. (2003). Oxygen adsorption on Au/Al 2 O 3 catalysts and relation to the catalytic oxidation of ethylene glycol to glycolic acid. Applied Catalysis A: General, 244(1), 169-179.

5. Case, J. M. (2009). Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study (Doctoral dissertation, University of Cape Town).

6. Kopeykina, L. Y., Vodyankina, O. V., Kurina, L. N., & Golovko, A. K. Selective ethylene glycol oxidation on the oxide catalysts. In Science and Technology, 2001. KORUS'01. Proceedings. The Fifth Russian-Korean International Symposium on (Vol. 2, pp. 177-179). IEEE.

7. Isshiki, T., Suzuki, T., Yashima, Y., & Yonemitsu, E. (1972). U.S. Patent No. 3,678,107. Washington, DC: U.S. Patent and Trademark Office.

8. Knepper, W., & Rohl, H. (1975). U.S. Patent No. 3,864,393. Washington, DC: U.S. Patent and Trademark Office.