Effects of Transition‐Metal Substitution on the Catalytic Properties of Barium Hexaaluminogallate

The effects of the substitution of transition-metal ions and/or reductant gases on the catalytic properties of barium hexaaluminogallate were investigated. Transition-metal-substituted hexaaluminogallates (BaM(Al,Ga) 11 O 19 , M = transition metal, Al/Ga = 9/3) were synthesized from aqueous metal nitrates and ammonium carbonate by the coprecipitation followed by crystallization at 1100°C. The direct NO x reduction was observed over BaM(Al,Ga) 11 O 19 to be around 10%. The NO x removal activity of BaM(Al,Ga) 11 O 19 powders was improved by addition of C 3 H 6 as a reductant gas. Co-, Ni- and Cu-substituted BaM(Al,Ga) 11 O 19 catalysts exhibited about 40% NO x reduction with C 3 H 6 in excess oxygen at a high space velocity of 10000 h -1 . The NO x reduction on Mn- and Fe-substituted BaM(Al,Ga) 11 O 19 catalysts was less than 10% even in the presence of C 3 H 6 . The temperature of the effective NO x reduction on BaM(Al,Ga) 11 O 19 catalysts could be adjusted from 350° to 500°C by the selection of the transition-metal substitution in the catalysts. The catalysts hold high activities for NO x reduction even at 500°C in water vapor produced in the combustion system of reductant gases.

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