Catalytic oxidation of methane for methanol production over copper sepiolite: Effect of noble metals

Abstract

The direct oxidation of methane to methanol (DOMM) has been recognized as a significant technology for efficiently utilizing low-concentration coalbed methane (LCMM) and supplying liquid fuel. Herein, the noble metals (Pt, Pd and Ru) modified Cu/alkalized sepiolite (CuX/SEPA) catalysts were prepared and used for the DOMM in a gas-phase system at low temperatures. The CuRu/SEPA exhibited the highest methanol production of 53 μmol·g⁻¹·h⁻¹ and methanol selectivity of 90% under the optimal reaction conditions. Various characterizations demonstrated that the addition of Ru promoted the formation of Cu²⁺ and the contraction of Cu—Si/Al bonds to reduce the distance between framework Al atoms of SEPA to further generate more Al pairs, which facilitated the formation of reactive dicopper species ([Cu₂O]²⁺ or [Cu₂O₂]²⁺). Investigation of the reaction mechanism revealed that [Cu₂O]²⁺ or [Cu₂O₂]²⁺ species could adsorb and activate methane to form CH₃O∗ species and ultimately generated methanol with the assistance of water.