Ring-Opening and Oxidation Pathways of Furanic Oxygenates on Oxygen-Precovered Pd(111)

Abstract

The surface reactivity of furan, furfural, and furfuryl alcohol on oxygenprecovered Pd(111) (O/Pd (111)) was studied via temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) to understand the oxidation processes of more complex alcohols and aldehydes. The primary reaction pathway explored was furfuryl alcohol dehydrogenation to furfural, followed by decarbonylation to furan and subsequent ring opening of furan through O−C α scission; however, furfuryl alcohol and furfural also underwent other parallel reactions. At high coverages, deoxygenation of furfuryl alcohol to methylfuran was observed simultaneously with furfural production near 320 K, possibly through a disproportionation reaction of two alcohol adsorbates. Observation of furfural as a reaction product at this temperature was related to an increased prevalence of a weakly bound η 1 (O) aldehyde state near 250 K on O/Pd(111) as compared to clean Pd(111). Furfural also reacted with surface O to produce furoate (C 4 H 3 OCOO−), which primarily underwent decarboxylation to furan and CO 2 . The presence of surface oxygen resulted in a new, higher-temperature desorption channel for furan at 340 K; this channel was accompanied by the desorption of partial oxidation products 2(5H)-furanone and maleic anhydride. TPD experiments on 18 O/Pd(111) showed incorporation of surface oxygen into furfural, H 2 O, CO 2 , CO, 2(5H)-furanone, and maleic anhydride products, with the isotopic distributions suggesting that partial oxidation of furan occurred partly through a ringopened carboxylate.

Ring‐Opening Reaction of Furfural and Tetrahydrofurfuryl Alcohol on Hydrogen‐Predosed Iridium(1 1 1) and Cobalt/Iridium(1 1 1) Surfaces

“…To aid in the assignment of the vibrational modes, HREEL spectra of structurally similar chemicals, furfuryl alcohol (FA) and tetrahydrofuran (THF), were also measured (Figure ). The experimentally measured vibrational frequencies of furfural were compared to those calculated by using DFT and those of previous studies of furanic molecules on Pd(1 1 1) surfaces …”

Metal Catalysts for the Efficient Transformation of Biomass‐derived HMF and Furfural to Value Added Chemicals

“…Biomass‐derived furans such as 2‐furfuraldehyde (furfural) and 5‐hydroxymethyl‐2‐furfural (HMF) can be efficiently produced by the acid‐catalysed dehydration of pentose and hexose, respectively . As furans have highly reactive side chains, ‐CHO and/or ‐CH 2 OH with furan ring, these can be explored for the production of different C5, C6 or higher carbon containing valuable chemicals such as 2,5‐furandicarboxylic acid (FDCA), 2‐furoic acid, levulinic acid (LA), ketones/diketones, 1,6‐hexanediol (1,6‐HDO), 1‐hydroxyhexane‐2,5‐dione (1‐HHD), cyclopentanone (CPO), adipic acid, maleic anhydride (MA), caprolactam, caprolactone, γ‐valerolactone, 2,5‐dimethylfuran (DMF), alkanes and so on, having wide applications in various pharmaceutical and polymer industries as well as in the production of fuel components …”

Insight into the Oxidation Mechanism of Furanic Compounds on Pt(111)

“…The valorization of such compounds often involves separation processes followed by energy intensive thermochemical processing, but aqueous phase thermo-catalytic and electro-catalytic methods have received attention for economically viable oxidation of furanic molecules 6 . Thermochemically, 5-hydroxymethylfurfural oxidation has been shown to be active on Pd/C catalysts to form 2,5-furan dicarboxylic acid 7 and Pd(111) has been shown to oxidize primary alcohols, furanic, and benzylic compounds [8][9][10] . Electrocatalytic systems have shown successful oxidation of HMF to furandicarboxylic acid (FDCA) [11][12][13][14][15][16][17] .…”

“…These thermochemical and electrocatalytic systems, often in aqueous environments, complicate efforts to probe surface-adsorbate interactions, and can introduce surface adsorbed O or OH species to participate in reactions 18,19 . Understanding the role of surface adsorbed oxygen in facilitating or directing furanic species oxidation can aid in selective catalyst design 9 .…”

“…Furfuryl alcohol was found to undergo dehydrogenation to furfural, which reacted with surface oxygen to produce an adsorbed furoate (C 4 H 3 OCOO*) that decarboxylated to produce furan and CO 2 9 . Furan reacted with surface oxygen to produce partial oxidation products 2(5H)-furanone (25HF) and maleic anhydride (MA) 9 . Similar results were seen for benzyl alcohol on oxygen-precovered Pd(111) 10 .…”