The present work examines the interaction of propanoic acid and I-propanol, I-butanol, I-ethanol, and I-hexanol with clean, oxidized, and anodized aluminum to identify the nature of the chemical bond on these surfaces. The investigations were carried out by x-ray photoelectron spectroscopy, at temperatures ranging from -20 to 500 ·C. Initially at room temperature, chemisorbed acid molecules break up on clean AI, leading to attachment of aliphatic chain fragments to the surface via carbon atoms. As adsorption continues, acid molecules react with Al via the functional group to oxidize the surface. In contrast, aliphatic alcohols chemisorb on clean AI via the functional group alone. At elevated temperatures, the acid and alcohols dissociate on the clean surface along similar reaction paths. On oxidized and anodized surfaces, the acid and alcohols chemisorb via the functional group and desorb at elevated temperatures without molecular dissociation.

Oxidative destruction of organic compounds in water streams could significantly reduce environmental effects associated with discharging waste. We report the development of a process to oxidise phenol in aqueous solutions, a model for waste stream contaminants, using Fenton’s reactions combined with in situ synthesised hydrogen peroxide (H2O2). Bifunctional palladium-iron supported catalysts, where Pd is responsible for H2O2 synthesis while Fe ensures the production of reactive oxygen species required for the degradation of phenol to less toxic species is reported. A comparison is made between in situ generated and commercial H2O2 and the effect of phenol degradation products on catalyst stability is explored.

The direct synthesis of hydrogen peroxide (H 2 O 2 ) from molecular H 2 and O 2 offers an attractive, decentralized alternative to production compared to the current means of production, the anthraquinone process. Herein we evaluate the performance of a 0.5%Pd–4.5%Ni/TiO 2 catalyst in batch and flow reactor systems using water as a solvent at ambient temperature. These reaction conditions are considered challenging for the synthesis of high H 2 O 2 concentrations, with the use of sub-ambient temperatures and alcohol co-solvents typical. Catalytic activity was observed to be stable to prolonged use in multiple batch experiments or in a flow system, with selectivities towards H 2 O 2 of 97% and 85%, respectively. This study was carried out in the absence of halide or acid additives that are typically used to inhibit sequential H 2 O 2 degradation reactions showing that this Pd–Ni catalyst has the potential to produce H 2 O 2 selectively. This article is part of a discussion meeting issue ‘Science to enable the circular economy’.

Low temperature oxidation of alcohols over heterogeneous catalysts is exceptionally challenging, particularly under neutral conditions. Herein, we report on an efficient, base-free method to oxidise glycerol over a 0.5%Pd-0.5%Fe/SiO2 catalyst at ambient temperature in the presence of gaseous H2 and O2. The exceptional catalytic performance was attributed to the in situ formation of highly reactive surface-bound oxygenated species, which promote the dehydrogenation on the alcohol. The PdFe bimetallic catalyst was determined to be significantly more active than corresponding monometallic analogues, highlighting the important role both metals have in this oxidative transformation. Fe leaching was confirmed to occur over the course of the reaction but sequestering experiments, involving the addition of bare carbon to the reactions, confirmed that the reaction was predominantly heterogeneous in nature. Investigations with electron paramagnetic resonance spectroscopy suggested that the reactivity in the early stages was mediated by surface-bound reactive oxygen species; no homogeneous radical species were observed in solution. This theory was further evidenced by a direct H2O2 synthesis study, which confirmed that the presence of Fe in the bimetallic catalyst neither improved the synthesis of H2O2 nor promoted its decomposition over the PdFe/SiO2 catalyst.

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