Lanthanum modified Fe-ZSM-5 zeolites for selective methane oxidation with H2O2

Abstract

Selective partial oxidation of methane to methanol under ambient conditions is a great challenge in chemistry. Iron modified ZSM-5 catalysts are shown to be effective for this reaction using H₂O₂ as the oxidant. However, the high consumption of H₂O₂ over this catalyst presents a major disadvantage. Here we report a lanthanum modified Fe-ZSM-5 (LaFe-ZSM-5) catalyst for enhanced selective methane oxidation with suppressed H₂O₂ consumption. Using 0.5 wt% LaFe-ZSM-5 pretreated with H₂ the productivity of primary oxygenated products (CH₃OH, CH₃OOH, HCOOH) is 3200 mol kg_LaFe⁻¹ h⁻¹ in 0.1 M H₂O₂, with a selectivity of 98.9% to primary oxygenated products. The productivity is increased to 11 460 mol kg_LaFe⁻¹ h⁻¹ in 0.5 M H₂O₂. Compared with Fe-ZSM-5, LaFe-ZSM-5 uses 31% less H₂O₂ for obtaining per mol of product under the same conditions. In situ DRIFT spectroscopy and solid state MAS NMR revealed the high H₂O₂ consumption in ZSM-5 based catalyst maybe closely related to the acidity of strong Brønsted acid sites (Si(OH)Al). The La modified ZSM-5 catalyst can decrease the acidity of the strong Brønsted acid sites and this suppresses the decomposition of H₂O₂.