Calcined hydrotalcites for the catalytic decomposition of N2O in simulated process streams

Abstract

Various hydrotalcite based catalysts were prepared for testing for the catalytic decomposition of N2O. Co---Al, Ni---Al, Co/Pd---Al, Co/Rh---Al, and Co/Mg---AL substituted hydrotalcites and Co---La---Al hydroxides offer very good activity at modest temperatures. Precalcination of these materials at ca. 450–500°C, which destroys the hydrotalcite phase, is necessary for optimum activity and life. For Co substituted hydrotalcites, the optimal ratio of Co/Al is 3.0. The temperature for 50% conversion of N2O of these calcined cobalt hydrotalcites is ca. 75°C lower than for the previous highly active Co-ZSM-5. These calcined cobalt hydrotalcite materials display sustained life at temperatures in excess of 670°C in an O2 rich, wet stream with high levels of N2O [10%]. Excess O2 does not seriously impact N2O decomposition, but the combination of both water vapor and O2 does reduce activity by ca. 50%.