(579d) Role of O in Ru Catalyst in Hydrodeoxygenation of Furfural

Weiqing Zheng,¹ Konstantinos A. Goulas, ¹ Ayman Karim,² Prashant Kumar,³ Andre Mkhoyan,³ Michael Tsapatsis,³ Dionisios G. Vlachos¹

1. Catalysis Center for Energy Innovation, University of Delaware, 221 Academy St. Newark, DE 19716

2. Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA

3. Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN

Recent theoretical investigations in our group has shown the importance of surface oxygen vacancies in the furfuryl alcohol hydrodeoxygenation (HDO) reaction over ruthenium oxide structures.^[1] We have also demonstrated the critical roles of metallic Ru and RuO₂ (physical mixture) in HDO of hydroxymethylfurfural (HMF) and furfural.^[2,3] On a single metallic surface, the surface and subsurface oxygen species play a significant role in HDO. In this work, we present evidence of the coexistence of metal and oxide (nonstoichiometric Ru_xO_y) on Ru catalyst surface by atomic resolution high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) at lower electron beam potential. This structure is further confirmed by X-ray absorption spectroscopic analyses of fresh, used and in situ reduced Ru/C catalyst. The results show that the fresh catalyst is predominately RuO₂ with small quantities of metallic Ru.

In order to directly correlate the nonstoichiometric Ru_xO_y structure to the reaction of furfural HDO we performed in operando X-ray absorption spectroscopy at beamline X18B, NSLS, BNL. All the experiments were performed with a custom-made XAS cell, which was charged with 1wt% furfural-isopropanol and pressurized with 400 psi He, heated up to defined temperatures (140 °C, 160 °C and 180 °C). Based on both near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses of the data, we conclude that the confirmed nonstoichiometric Ru_xO_y structure can be directly correlated to the 2-methylfuran (MF) production from furfural via catalytic transfer hydrogenation. However, once the surface is dominated by metallic Ru, MF formation is suppressed.

Reference

1. A. Mironenko and D. Vlachos. J. Am. Chem. Soc. 2016, 138, 8104
2. J. Jae, W. Zheng, R. Lobo, D. Vlachos, ChemSusChem, 2013, 7, 1158
3. J. Jae, W. Zheng, A. Karim, W. Guo, R. Lobo, D. Vlachos, ChemCatChem, 2014, 6, 848