Alkali metals as promoters in Co-Mn-Al mixed oxide for N2O decomposition

Abstract

Alkali promoted Co4MnAlOx mixed oxide (molar ratio of alkali metal/Co = 0.037) were prepared by impregnation of calcined Co–Mn–Al hydrotalcite (molar ratio Co:Mn:Al = 4:1:1) with an aqueous solution of Li, Na, K, Rb or Cs nitrate. The catalysts were characterized by AAS, SEM/EDX, N2 physisorption, XRPD, XPS, H2-TPR, TPD of CO2 and NH3 and tested for N2O decomposition in inert gas and simulated waste gas from HNO3 production. N2O conversion over alkali promoted Co4MnAlOx mixed oxide decreased in order Cs > Rb > K > Na = Co4MnAlOx > Li in inert gas and was shifted to the lower values in the presence of typical components (NOx, O2 and H2O) of flue gas. The addition of alkali promoters to the Co4MnAlOx mixed oxide resulted in a modification of both electronic properties of active metals and acid–base function of the catalyst surface. The promotional effect of alkali metals is connected with their ionization potential, the charge transfer to the catalyst and a decrease in binding energies of all catalyst components (Co, Mn, Al and O). Pilot plant verification of N2O decomposition over K-promoted Co4MnAlOx is shown.