Direct partial oxidation of low-concentration methane to methanol with copper-based clay catalysts

Abstract

Partial oxidation of methane to methanol (POMM) is an economic and environmental technology, especially for utilizing low-concentration methane resources in the explosive range. In this paper, mineral clays like sepiolite (SEP), attapulgite (ATP), montmorillonite (MMT), bentonite (BEN), kaolin (KAO) and diatomite (DIA) were used as supports to prepare copper-based clay catalysts by impregnation method and their performance in continuous direct POMM with O2 as oxygen source were tested. The methanol yields of these catalysts at 320 °C with feed ratio of CH4: O2: H2O = 2: 1: 8 exhibited the following order: Cu/KAO (145.26 μmol/gCu/h) > Cu/ATP (74.18 μmol/gCu/h) > Cu/SEP (63.99 μmol/gCu/h) > Cu/MMT (51.59 μmol/gCu/h) > Cu/DIA (42.29 μmol/gCu/h) > Cu/BEN (39.64 μmol/gCu/h). This demonstrated that copper-based clay catalysts were promising for use in POMM considering their economy and environmental acceptability. Additionally, these copper-based clay catalysts were characterized and it was found that different clays could tailor the interaction of Cu species with supports, alter the reducibility and surface acidity, thereby changing the methanol yield. What's more, it was confirmed that the superior methanol yield of Cu/KAO was attributed to its relatively more [Cu2O)]2+ sites with Cu–O, Cu–Si/Al and Cu–Cu coordination structures similar to that of copper-based zeolite catalysts.