Noble metal modified copper-exchanged mordenite zeolite (Cu-ex-MOR) catalysts for catalyzing the methane efficient gas-phase synthesis methanol

Abstract

Copper mordenite catalysts are key for methane oxidation to methanol, yet lack sufficient activity. In this paper, noble metal (Au, Ru, Pt and Pd) modified copper ion-exchanged mordenite catalysts were prepared by the ion-exchange method for further improving the methanol yield in the gas-phase continuous catalytic direct partial oxidation of methane to methanol reaction, and the role of noble metal doping on Cu-ex-MOR catalysts was investigated. Experimental results showed that the doping of Ru resulted in a significant increase in the methanol yield of Ru/Cu-ex-MOR catalyst to 157.36 μmol/gcat/h compared to that of Cu-ex-MOR catalyst (12.89 μmol/gcat/h). SEM, XRD, FT-IR, N2 adsorption-desorption, XPS, NH3-TPD and H2-TPR results showed that Ru/Cu-ex-MOR had uniformly dispersed Ru elements and the largest number of surface acidic and oxidation sites, which facilitated the adsorption and activation of methane. Additionally, it was found by TEM, in situ FT-IR and DFT characterization that Ru played a role in stabilizing the Cu active sites, the adsorptive activation of water on the Ru site and the H-transfer process reduced the energy required for breaking C–H bond of CH4 at the Cu active site, which significantly improved the methane activation capacity of the Ru/Cu-ex-MOR catalysts, resulting in higher methanol yields.