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Stepwise methane to methanol conversion: Effect of copper loading on the formation of active species in copper-exchanged mordenite
Catalysis Today ( IF 5.3 ) Pub Date : 2021-01-12 , DOI: 10.1016/j.cattod.2020.11.027
Stefanie C.M. Mizuno , Siriwan Dulnee , Tássia C.P. Pereira , Ricardo J. Passini , Ernesto A. Urquieta-Gonzalez , Jean Marcel R. Gallo , João B.O. Santos , José M.C. Bueno

This work investigates the influences of Cu content, Si/Al ratio, and sample preparation method on the active Cu species in mordenite (MOR). The Cu/MOR prepared by multiple Cu-exchange procedures showed an optimum Cu/Al ratio for the formation of the most active species for methanol formation. XANES spectra indicated that isolated Cu+ species were formed after CH4 interaction and were re-oxidized under a flow of water steam. The Cu-MOR samples obtained by ion-exchange method presented well-dispersed CuO in the zeolite pores, while samples obtained by impregnation method presented segregated CuO and were inactive for CH4 activation. The methodology used for in situ UV–vis spectra analyses indicated that different Cu species were active for CH4 oxidation. Isolated Cu2+ species were not involved in CH4 activation at temperatures lower than 300 °C. The isolated Cu2+ species were partially hydrolyzed by O2 treatment and species like [CuOH]+ and [CuOx]n or polynuclear Cu2+-oxyhydroxide were formed. The formation of polynuclear species in substitution of di-copper would impact the specific activity with the Cu content and decrease the activity for methanol production.



中文翻译:

甲烷到甲醇的逐步转化:铜负载量对铜交换丝光沸石中活性物种形成的影响

这项工作研究了 Cu 含量、Si/Al 比和样品制备方法对丝光沸石 (MOR) 中活性 Cu 物种的影响。通过多个 Cu 交换程序制备的 Cu/MOR 显示出最佳的 Cu/Al 比率,以形成最活跃的甲醇形成物质。XANES 光谱表明分离的Cu +物质在CH 4相互作用后形成并在水蒸汽流下被重新氧化。通过离子交换法获得的Cu-MOR样品在沸石孔隙中呈现出良好分散的CuO,而通过浸渍法获得的样品呈现出偏析的CuO并且对CH 4活化没有活性。原位使用的方法UV-vis 光谱分析表明不同的Cu 物种对CH 4氧化具有活性。在低于 300 °C 的温度下,分离的 Cu 2+物种不参与 CH 4活化。分离出的Cu 2+物质通过O 2处理部分水解,形成[CuOH] +和[CuO x ] n或多核Cu 2+ -羟基氧化物等物质。多核物种取代二铜的形成会影响铜含量的比活性并降低甲醇生产的活性。

更新日期:2021-01-12
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