Mechanistic study of the hydrodeoxygenation of lignin-derived oxygenates on a CoPt bimetallic catalyst: reaction of anisole on Co-modified Pt(111)

Abstract

Temperature programmed desorption and high-resolution electron energy loss spectroscopy were used to characterize the adsorption and reaction of anisole (C 6 H 5 -OCH 3 ) on Pt(111) and Codecorated Pt(111) surfaces. On both surfaces anisole was found to undergo O-CH 3 bond cleavage to form an oxocyclohexadienyl-structured intermediate (C 6 H 6 O) which bonds to the surface in a η 5 -π configuration. Interaction of the O atom in this intermediate with Co adatoms was found to facilitate selective cleavage of the C-O bond to produce adsorbed benzene or phenyl groups. In parallel with this pathway, unselective decomposition of adsorbed anisole was also found to occur. The results obtained in this study along with those previously reported for the reaction of anisole on Zn-decorated Pt(111) surfaces provide further insight into how the addition of a second more oxyphilic metal to Pt affects surface reaction pathways and the hydrodeoxygenation selectivity of lignin-derived aromatic oxygenates.

Metal–Acid Synergy: Hydrodeoxygenation of Anisole over Pt/Al‐SBA‐15

“…Such promotion may either reflect a new (facile) reaction pathway for anisole, such as transalkylation, demethylation or hydrolysis, or the suppression of the poisoning of Pt active sites by reaction intermediates formed over Pt/SBA‐15. As the same products are observed for Pt/Al‐SBA‐15 and Pt/SBA‐15 (methoxycyclohexane, cyclohexane and benzene), we can infer that the former scenario is improbable, whereas experimental and theoretical studies on model Pt catalysts suggest that anisole is indeed prone to decomposition to strongly chemisorbed species (consistent with the latter scenario) . The strong synergy between Pt and Brønsted acid sites confers a several‐hundredfold increase in the average cyclohexane productivity over 6 h (from 15 to 6500 mmol g Pt −1 h −1 ) for a common low Pt loading, associated with a dramatic rate enhancement coupled with a sharp rise in cyclohexane selectivity (from 15 to 92 %).…”

Mechanisms and Trends of Guaiacol Hydrodeoxygenation on Transition Metal Catalysts

“…The interaction between the O atoms in guaiacol and the metal weakens the C−O bonds, indicating the bond activation (Gao et al, 2015;Liu et al, 2018a;Shi and Vohs, 2018). Many publications have considered the C−O bond elongation upon the guaiacol adsorption as a descriptor for the deoxygenation activity (Zhou et al, 2019;Liu et al, 2018b).…”

Metal–Acid Synergy: Hydrodeoxygenation of Anisole over Pt/Al‐SBA‐15

“…The TOF for 0. and Pt/SBA-15 (methoxycyclohexane, cyclohexane and benzene), we can infer that the former scenario is improbable, whereas experimental and theoretical studies over model Pt catalysts suggest that anisole is indeed prone to decomposition to strongly chemisorbed species (consistent with the latter scenario). 69,[79][80][81] The strong synergy between Pt and Brønsted acid sites confers a several hundredfold increase in average cyclohexane productivity over 6 h (from 15 mmol.gPt -1 .h -1 to 6500 mmol.gPt -1 h -1 ) for a common, low Pt loading, associated with a dramatic rate enhancement coupled with a sharp rise in cyclohexane selectivity (from 15 % to 92 %). Note that this synergy is significantly weaker for high metal loadings typically adopted in the literature, resulting in a smaller 6 h productivity enhancement (8 mmol.gPt -1 .h -1 versus 161 mmol.gPt -1 .h -1 , see To establish whether support acidity influences the deoxygenation of reactively-formed methoxycyclohexane, its reactivity was compared over the SBA-15 and Al-SBA-15, and Pt functionalized analogues (Figure S10).…”