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

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 degrees 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 degrees 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 degrees C in an O-2 rich, wet stream with high levels of N2O [10%]. Excess O-2 does not seriously impact N2O decomposition, bur the combination of both water vapor and O-2 does reduce activity by ca. 50%.