Hydrodeoxygenation of Lignin-Derived Aromatic Oxygenates Over Pd-Fe Bimetallic Catalyst: A Mechanistic Study of Direct C
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Hydrodeoxygenation of Lignin‑Derived Aromatic Oxygenates Over Pd‑Fe Bimetallic Catalyst: A Mechanistic Study of Direct C–O Bond Cleavage and Direct Ring Hydrogenation Jianghao Zhang1 · Berlin Sudduth1 · Junming Sun1 · Yong Wang1,2 Received: 8 June 2020 / Accepted: 4 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Hydrodeoxygenation of lignin-derived phenols could be achieved generally with three reaction pathways: tautomerization, direct ring hydrogenation and direct C–O bond cleavage. The former pathway has been extensively studied over Pd/Fe catalyst in liquid-phase reaction, however, the contribution of the latter two is yet subject to further investigations. In this report, a comparative study of direct C–O bond cleavage and direct ring hydrogenation reaction pathways is presented on Pd/Fe, Fe and Pd/C catalysts using diphenyl ether as modelling compound. Despite its much higher activation energy than direct ring hydrogenation, direct C–O bond cleavage is dominant over Pd/Fe with much higher rates than the monometallic analogues due to the synergic catalysis of Pd–Fe. Based on this study and our previous results, the detailed reaction network for HDO of diphenyl ether is proposed. Graphic Abstract
Keywords C–O bond cleavage · Direct ring hydrogenation · Pd–fe catalyst · Mechanistic study · Aromatic oxygenate
1 Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-020-03352-3) contains supplementary material, which is available to authorized users. * Junming Sun [email protected] * Yong Wang [email protected] 1
The Gene & Linda Voiland, School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352, USA
2
Hydrotreating is one of the key process in oil refining to remove heteroatoms such as sulfur, nitrogen, and oxygen [1, 2]. Similar to hydrodesulfurization and hydrodenitrogenation, which have been comprehensively studied in petroleum industry due to the consideration of environment and engine protection [3], hydrodeoxygenation (HDO) is an important research topic since the large oxygen content in bio-oil needs to be reduced to increase its energy density, stability and volatility [4]. The HDO of lignin-derived phenols is highly challenging in bio-oil upgrading and generally proceeds through three reaction pathways: tautomerization, direct ring hydrogenation and direct C–O bond cleavage [5–7]. The
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tautomerization pathway involves a fast and reversible isomerization of phenols to form unstable ketone intermediates over the surface of the catalyst [8]. Accordingly, the recalcitrant Caromatic–O is transformed to a weaker C=O bond, and the oxygen can be readily removed with a lower reaction barrier. Although this pathway is able to produce arenes, as reported in vapor-phase reactions at low pressures [8, 9], we have proven that tautom
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