Catalytic oxidative coupling of methane in supercritical water: Investigations on a catalytically active species

• Main Authors: Hassan, M.A., Miyao, T., Komiyama, M.
• Format: Article
• Published: 2019
• Online Access: https://www.scopus.com/inward/record.uri?eid=2-s2.0-85054344899&doi=10.1016%2fj.supflu.2018.07.001&partnerID=40&md5=6a85d655fa2aba2573d2986444ba3681; http://eprints.utp.edu.my/22159/

Catalyst survey for oxidative coupling of methane (OCM) under supercritical water (SCW) environment at 658 K and 26 MPa using an 8.8-mL batch reactor and H2O2 as a molecular oxygen source was performed at a feed concentration molar ratios of 0.10 CH4/H2O and 0.15 O2/CH4. First and second transition metal oxides (V, Cr, Co, Cu, Zr and Mo) and some lanthanide oxides (La and Ce) showed relatively high OCM activities of ca. 0.5�1 C yield at a very low catalyst loading of 0.05 g. Exploration of catalyst formulations found that oxides of transition metals combined with ZrO2 were effective, with MnO2�ZrO2 showing a high synergy effect giving almost twice as much methane coupling yield. The OCM activity was correlated with the surface amount of a low 1s binding energy (O1s, 526�527 eV) oxygen species on the catalyst, as well as its energy separation from the lattice oxygen. In terms of this oxygen species, SCW-OCM activity of Mn/Na2WO4/SiO2, known as a good gas phase OCM catalyst and also showed a high turnover efficiency for SCW-OCM was further improved by supporting Mn/Na2WO4 on ZrO2 instead of SiO2. © 2018 Elsevier B.V.