CO selectivity CO2 decomposition CeO2 DBD plasma Ga–In alloys H2 generation H2S oxidation Manganese NH3 decomposition NOx conversion VOC abatement adsorption-plasma catalysis air pollution ammonia synthesis bimetal calcium carbonate decomposition catalyst catalyst preparation dielectric barrier discharge dielectric barrier discharge (DBD) dry reforming of methane gallium gas composition gas temperature in plasma-catalysis indium isotope labelling methane reforming mineralization mode transition