Enhancement of activity and selectivity to nitrogen in catalytic nitrate reduction by use of conductive carbon catalytic supports and control of hydrogen mass transfer regime

Abstract Carbon materials with different structural properties (activated carbon, carbon nanofibers, reduced graphene oxide, graphite, and carbon black) were used as supports of Pd-Cu (5 wt%) catalysts for the catalytic reduction of NO3- in batch reactors. In general, those catalyst with smaller metal nanoparticles and carbon supports with higher specific surface area were more active, although remarkable activity was also observed for catalysts with relatively large nanoparticles and conductive supports. Conductivity of carbon supports also contributed to a lower selectivity to NH4+, which can be ascribed to higher charge transfer between metal and support reducing activation of intermediate species. The decrease of H2 feed into the reaction system resulted in external (gas-liquid) mass transfer constrains, as evidenced by the parameters describing control regime, and led to diminished NH4+ selectivity, particularly in the case of catalysts with conductive supports. Approaches combining control of mass transfer regime and conductive carbon catalytic supports can be useful to enhance selectivity to N2, which is a major challenge in catalytic NO3- reduction.