Methane to methanol over copper mordenite: yield improvement through multiple cycles and different synthesis techniques

Abstract

Copper mordenite was used for the conversion of methane to methanol in a cyclic operation. Repeated cycling was possible using catalysts having different loadings prepared via aqueous ion exchange using copper(II) acetate (Cu-MOR_A) and solid state ion exchange using copper(I) chloride (Cu-MOR_S). For Cu-MOR_A, the yield increased by at least 30% on the second cycle and remained constant afterwards. Linear combination fitting of the XANES identified a similar increase in the fraction of Cu^I formed upon reacting with methane on the second cycle. For Cu-MOR_S residual chlorine initially hindered the production of methanol. Successive cycles removed chlorine and yielded significantly more methanol per copper than Cu-MOR_A. Over successive cycles of Cu-MOR_S, the fraction of the Cu^II species that was reduced to Cu^I upon reacting with methane correlated well with the amount of methanol produced. Although commonly done, analyzing only one reaction cycle is not representative of the long-term performance of methane to methanol over copper mordenite. Copper species equilibrate with cycling.