Improving Catalysts for Biogas Dry Reforming: Coupling of Mechanochemical Treatment with Enhanced Microwave Chemistry

Abstract

In the present study, enhanced microwave (EMW) synthesis, where microwave radiation is coupled with reflux conditions, was used to prepare different metal oxide catalyst systems (CeM-10Cu-O; M: La, Sm). It is well known that ceria-based oxides feature high redox properties including high population of oxygen vacancies [Ovac]. These properties are crucial for hydrocarbon catalytic reactions such as CO2 reforming of methane (dry reforming of biogas), in the sense that they contribute to coke reduction. Post synthetically, the doped catalysts with 10% Cu were ball milled under both, wet and dry conditions, at different milling times. The ball milling technique is expected to further improve the oxygen vacancies and give higher efficiency for uniform multi-component mixed oxides in consideration of time and energy usage. The EMW synthesis conditions affected the crystallinity of the catalysts (XRD), and crystal growth, generating particles with crystallite size in the ranges of ~4.5-7.8 nm for La-doped ceria, and 7.0-7.8 nm for Sm-doped ceria. The ball-milled catalysts of both systems exhibited bigger crystallite size (XRD) compared to the pristine, and larger surface area of Ce-La-10CuO was observed (8.1 m2 /g). This, in fact, enhanced the oxygen mobility in ceria support lattice (H2-TPR) and led to the formation of more O vacancies (Raman). The surface/bulk diffusion of lattice oxygen ( 16O) was recorded at ideally low temperature (350°C), compared to similar catalysts of interest from literature, using 16O/18O isotopic exchange experiments. Ball milling also affected the acid/basic sites on the surfaces under study and this was evaluated employing NH3/CO2 Temperature programmed desorption (TPD).

Date of Award	Oct 2019
Original language	American English