Eco-friendly CaO-based catalysts derived from waste oyster shells for the oxidative coupling of methane

In this study, we developed an economical and eco-friendly high-performance catalyst for the oxidative coupling of methane from waste oyster shells, which cause environmental pollution. The oyster shells were successfully transformed into CaO-based catalysts by the calcining at different temperatures. During calcination process, foreign elements (Na, Mg, and Al) naturally present in waste oyster shells caused the generation of oxygen vacancies and changes in the surface chemical properties (base sites and surface oxygen species) of the catalysts. When the catalysts were used in oxidative methane coupling, the oxygen vacancies on the catalyst surface played a crucial role in the conversion of methane to methyl radicals, which are expected to dimerize to ethane. However, the moderately basic sites and electrophilic lattice oxygen species facilitated the production of ethylene through the dehydrogenation of ethane. Therefore, the sample calcined at 800 °C not only exhibited an outstanding catalytic activity in the oxidative coupling of methane but also high long-term stability because of its abundant active sites: oxygen vacancies, moderately basic sites, and electrophilic lattice oxygen species. The study demonstrates that waste oyster shells can be successfully recycled into a high value-added product, such as a catalyst applicable in the oxidative coupling of methane.

Graphical abstract