Guaiacol Hydrodeoxygenation and Hydrogenation over Bimetallic Pt-M (Nb, W, Zr)/KIT-6 Catalysts with Tunable Acidity

Abstract

Owing to a high oxygen content, bio-oils from the fast pyrolysis of biomass require upgrading to meet fuel specification standards. Catalytic hydrodeoxygenation (HDO) of bio-oils faces several challenges such as low hydrocarbon yields, the requirement of high H 2 partial pressure for complete deoxygenation, and catalyst deactivation caused by coking/carbon deposition. In the present work, Pt supported on Nb, W, and Zr-incorporated KIT-6 materials were prepared, characterized, and tested for the gas-phase HDO of guaiacol, a widely used model compound of bio-oil. Facile HDO of guaiacol was observed over a 1 wt % Pt/Nb-KIT-6 catalyst, with ∼90% conversion and ∼75% hydrocarbon selectivity under relatively mild hydrogen partial pressure (0.5 MPa) at 400 °C and 33 h −1 weight hourly space velocity (WHSV). No significant catalyst deactivation was observed during a 24-h continuous run indicating that the mesoporous support provides enhanced coking resistance. Mechanistic investigations indicate that the tunable acidity of the supports promotes transalkylation reactions, which favor increased aromatic hydrocarbon yields. A plausible reaction mechanism is postulated based on correlating the number of metal and acid sites with the measured rates for the individual reaction steps.

Advancements and Perspectives toward Lignin Valorization via O‐Demethylation

“…Reaction network of guaiacol hydrodeoxygenation under H 2 (Gas-phase) over nonacidic (Up) and acidic catalysts (Bottom). [122] excellent protocatechuic acid yield (75 %) from vanillic acid via an oxidative ODM. [125] Additionally, the voltage-biasassisted electrochemical ODM (with intermediate oxidation and reduction) of guaiacol into catechol over a multiwalled carbon nanotube (MWCNT) surface in neutral phosphate buffer solution has been reported.…”

“…[114,121] Non-acidic catalyst 1 % Pt/C displayed a high selectivity (> 80 % catechol at almost complete conversion) in the gas phase hydrogenolysis of guaiacol under atmospheric pressure (0.1 MPa; 1 : 1 N 2 and H 2 ) with a weight hourly space velocity (WHSV) of 33.3 h À 1 at 300 °C (Scheme 8; Entry 17, Table 1). [122] Other non-acidic catalysts (Scheme 8, up) such as 1 % Pt/C-SBA-15, 1 % Pt/Si-KIT-6, and 1 % Pt/Si-ZSM-5 also exhibited high catechol selectivity at the high (65 h À 1 ) WHSV under atmospheric H 2 pressure (0.1 MPa), albeit at low (< 20 %) guaiacol conversion. High contact times (11 h À 1 ) increased conversion at the expense of selectivity.…”

Rebalancing Hydrogenation and Dehydration Performances for Efficient Hydrodeoxygenation of Biomass Derivatives to Match Reaction Temperature-Induced Rate-Determining Step Switch

“…Thus, much research works have been committed to improving the deoxygenation ability by developing bifunctional catalysts. ,,− Metal–acid bifunctional catalysts are one of the promising upgrading catalysts since acid sites accelerate the dehydration process. ,− The early reports on the catalytic HDO system are mostly metal–inorganic acids (H 2 SO 4 and H 3 PO 4 ). , However, the shortcomings of inorganic acids, such as difficult recovery, equipment corrosion, or carbon deposition caused by strong acidity, have forced researchers to turn to solid acid catalysts with moderate acid strength. Therefore, metal–acid bifunctional catalysts supported on solid acids (phosphates, acid resin, acid oxides, and zeolites) have attracted extensive research. − For example, the Ru/HZSM-5 bifunctional catalyst is found to have excellent HDO activity on lignin-derived phenolic compounds .…”

Selective Clipping of a Lignin-Derived Monomer by Plasma for Bio-Oil Upgrading

“…Model compounds are commonly selected to analyze the HDO reaction mechanisms and kinetics due to the complexity of bio-oils. 16 Guaiacol is a typical model compound of the lignin-derived monomer because it contains an aromatic ring and two typical oxygenated functional groups (OH • and OCH 3…”

“…Bio-oil is produced by the decomposition of polymeric biomass into small molecular oxygenates, such as aldehydes, ketones, carboxylic acids, and phenols. Model compounds are commonly selected to analyze the HDO reaction mechanisms and kinetics due to the complexity of bio-oils . Guaiacol is a typical model compound of the lignin-derived monomer because it contains an aromatic ring and two typical oxygenated functional groups (OH · and OCH 3 · ); it is often a preferred prototype for bio-oils .…”