Catalytic effect of metal additives on free radical recombination rates in H2+O2+N2 flames

The metals Mg, Cr, Mn, Sn, U are shown to cause significant catalysis of free radical recombination rates in fuel-rich, premixed H 2 +O 2 +N 2 flames in concentrations of ∼1 part per million (or even less) of additive in the burned gases. The metals are therefore about 2 orders of magnitude more effective than the previously reported catalysts, NO and SO 2 . Although no one general scheme seems capable of accounting for all the observations made, a common factor is the possibility of catalytic cycles involving metal oxide and hydroxide intermediates. Both heterogeneous and homogeneous schemes are discussed.