Decomposition of nitrous oxide over the catalysts derived from hydrotalcite-like compounds

Catalytic decomposition of nitrous oxide into nitrogen and oxygen has been carried out on `in situʹ thermally calcined hydrotalcites of general formula M(II)–M(III)-CHT where M(II)=Mg, Co, Ni, Cu or Zn and M(III)=Al, Fe or Cr having different M(II)/M(III) atomic ratios. The reaction was performed in a recirculatory static reactor at 50 Torr (133.3 Pa) initial pressure of N2O in the temperature range 423–773 K. Among the catalysts screened, Ni and Co containing catalysts with Al as the trivalent cation showed good activity (even at 423 K) wherein 50% and 100% conversion was achieved at 463 K and 523 K, respectively. Results on effect of composition for Co–Al system indicated that the activity increased with increase in the active metal ion concentration (Co2+), with closer dependence on the surface concentration (as determined by XPS). The observed activity pattern is explained on the basis of redox property and electronic effects. These materials were further evaluated under flow conditions (at Air Products and Chemicals, USA) simulating the industrial process streams (10% N2O, 2% H2O, 2% O2 and balance N2 and GHSV=18,500). Among the non-precious metal ions investigated, cobalt-based catalysts offered comparable activity similar to metal-exchanged zeolites for removing N2O from combustion and Nylon-6,6 processes.