Catalytic reduction of nitrate and nitrite with mono- and bimetallic catalysts supported on pillared clays

Catalytic reduction of nitrate and nitrite has been carried out under ambient-like conditions (25 °C, 1 atm) with H2 and CO2 as reducing and acidifying agents, respectively, using noble metals supported on Al-pillared clays as catalysts. Monometallic catalysts with Ir, Pd, Pt and Rh were tested showing the Pd one the highest activity and the lowest selectivity to ammonium. Bimetallic catalysts with Pd and a second metal (Cu, In and Sn) were prepared and tested for nitrate reduction, all of them yielding higher reaction rates than the monometallic Pd catalyst with very low selectivity to intermediate nitrite. The Pd–In catalyst yielded the lowest selectivity to ammonium (12%). The raw bentonite was acid-treated to prevent the interaction of iron and other cations of the clay structure with the active-phase metals. That treatment improved the activity of the catalysts for nitrate reduction.

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