CuOx-RHO aplicados para conversão de metano em metanol

Abstract

The direct oxidation of methane (CH4) into higher value-added products, such as methanol, has recently gained tremendous interest. The challenge is an over-oxidation of methanol to CO2 and water due to the difficulty in activating methane through C-H bond breaking. Thus, this research attempted to develop an active Cu-exchange RHO catalyst for a selective methane oxidation-to-methanol reaction. In this study, the RHO zeolite was synthesized by hydrothermal treatment using two different methods with and without an organic template (18-crown-6) compound for zeolite. By using the organic template, it is found that the crystalline Na,Cs-RHO were obtained after 2-day synthesis. The crystallinity of Na,CsRHO increases with synthesis time. In contrast, without an organic template, the crystalline Na,Cs-RHO was formed only after 8-d synthesis. The as-prepared samples were characterized by X-ray diffraction, X-ray fluorescence, and nitrogen physisorption, and were catalytically activity tested at several conditions. Among all Na,Cs-RHO samples prepared in this work, our preliminary results showed that a high crystallinity of Na.Cs-RHO synthesized for 8 days is suitable for preparing Cu-exchanged RHO. However, the highest methanol yield obtained from Cu,Na,Cs-RHO-8d is only about 16 μmol of CH3OH/g of catalyst. This could be possibly due to the presence of strong-interacted Cs ions in RHO’s pore leading to a limitation of active Cu species formed. This work further attempted to eliminate Cs and Na by ion exchanging with NH4+ ions prior to Cu ion exchanging, while the phase transformation of zeolite was observed. Still, more investigations must be carried out to develop the highly active Cu-exchanged RHO.