To valorize lignin as a renewable source of aromatics, it is necessary to develop selective heterogeneous catalysts for the hydrodeoxygenation reaction of aromatic oxygenates such as anisole. Most of the metal supported catalysts tested so far exhibit a high conversion but a low selectivity towards valuable aromatic hydrocarbons, yielding mainly phenolic compounds. To gain insights into that catalytic system, we performed surface science experiments (X-ray Photoelectron Spectroscopy and Temperature Programmed Desorption)under Ultra-High Vacuum conditions (UHV). Dosing anisole on Pt(111) surprisingly gave benzene, carbon monoxide and hydrogen as the main desorbing products of decomposition.With the help of Density Functional Theory (DFT) we successfully explain the unexpected selectivity. In the present work we show in particular that phenoxy PhO stands as a key intermediate. Although the UHV conditions do not allow the hydrogenation of phenoxy into phenol, i.e. the catalytic product, they reveal the key role of both hydrogen and carbonaceous species. Under UHV conditions, anisole gets extensively dehydrogenated: it results in the formation of carbonaceous fragments, which can actually perform the deoxygenation of phenoxy into benzene, but also, more importantly, coke. This detailed study opens the door to a rational design of hydrodeoxygenation catalysts based on supported metals.

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Formic acid can undergo dehydration or dehydrogenation with variable selectivity over a range of metal catalysts. The selectivity among these reactions depends on the reaction mechanism and reaction conditions pertinent on each surface. This work provides mechanistic insight on the decomposition of formic acid on cobalt at high and low temperature regimes. The adsorption and decomposition of formic acid on a Co(0001) single crystal was studied in ultra-high vacuum by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Insight is provided using DFT calculations. In the low temperature regime, formic acid adsorbs molecularly on the surface at 130 K. Partial decomposition produces CO at 140 K, and at 160 K the decomposition of formic acid into formate, which is a thermodynamic sink, is dominant. Water can be formed at low temperature via bimolecular processes. At high temperature (>400 K) the similar barriers for decomposition of the formate species lead to the concomitant production of CO, CO2 and H2. The correlation between experiment and theory provides a framework for the interpretation of surface species and reaction path operating in different regimes.

The decomposition of phenol, anisole, and 2-phenoxyethanol on Pt(111) in ultrahigh vacuum is studied as a model to understand the reactivity of the β-O-4 linkage in lignin. Desorption of the multilayer and monolayer is observed as well as the generation of decomposition products. Using RAIRS to monitor the vibrational signatures of all the species, we observed the appearance of the characteristic 1480 cm–1 vibration for the phenoxy group. This, in conjunction with changes in other bands, is used to identify the phenoxy species (as opposed to the oxocyclohexadienyl moiety) as the common key intermediate in the decomposition of the three molecules. The nature of the phenoxy species is discussed in comparison with previous literature and may lead to insight into the reaction–product selectivity of the decomposition.