Room temperature and atmospheric pressure aqueous partial oxidation of ethane to oxygenates over AuPd catalysts

Abstract

New modes of chemical manufacturing based on small-scale, distributed facilities have been proposed to supplement many existing production operations in the chemical industry, including the synthesis of value-added products from light alkanes. Motivated by this prospect, herein the aqueous partial oxidation of ethane over unsupported AuPd nanoparticle catalysts is investigated, with emphasis on outcomes for reactions occurring at 21 °C and 1 bar ethane. When H₂O₂ is used as an oxidant, the system generates numerous C₂ oxygenates, including ethyl hydroperoxide/ethanol, acetaldehyde, and acetic acid. Ethyl hydroperoxide is found to be the primary product resulting from the direct oxidation of ethane: it is produced with 100% selectivity in batch reactions with short durations and with low initial H₂O₂ concentrations. At longer times or in more oxidizing conditions, deeper product oxidations expectedly occur. In batch experiments, the maximum observed yield of oxygenates is 7707 μmol g_AuPd⁻¹ h⁻¹. Product distributions differ when H₂O₂ is replaced by H₂ and O₂ in the headspace. Additionally, to simulate a scenario wherein H₂O₂ is produced on-site and to study ethane oxidation in steady, low H₂O₂ concentrations over 50 h, a semi-batch configuration facilitating continuous injection of dilute H₂O₂ was implemented. These efforts showed that H₂O₂ can serve as an oxygenate-selective oxidant of ethane when its concentration is kept low during reaction. These and other experimental results, as well as initial computational results using density functional theory, suggest that paths forward for aqueous ethane conversion exist, and systems should be engineered to emphasize product stabilization.