Selective hydrogenation of eggshell/clamshell to methane with the assistance of the alkaline earth and transition metals at room temperature

•Mechanochemical hydrogenation of shell wastes was studied at room temperature.•Alkaline metals can selectively assist the hydrogenation of shell wastes to CH4.•The calcium metal has a better effect and the methane yield can reach 45.04%.•By doping Ru the methane yield of shell wastes can be improved to 54.76%.•This study provides a method to eliminate shell wastes and produce CH4 fuel.