Deactivation of copper, nickel, and cobalt catalysts by interaction with aliphatic amines

Abstract

The deactivation of alumina-supported and unsupported copper, nickel, and cobalt catalysts resulting from interaction with aliphatic amines was studied using the catalyzed disproportionation of methylamine and dimethylamine as test reactions. Temperature-programmed desorption (TPD) and surface reaction (TPSR) studies performed with the deactivated catalyst samples indicate that three different deactivation processes have to be considered, namely the formation of metal nitride, and the formation of metal carbide and carbonaceous deposits. With copper only nitride formation is observed. With nickel and cobalt all three deactivation processes can occur at temperatures used for catalytic disproportionation or animation. Hydrogen prevents metal nitride formation and inhibits the formation of metal carbide and carbonaceous deposits. TPSR studies carried out with a mixture of hydrogen in nitrogen showed for both the deactivated Ni Al 2O 3 and Co Al 2O 3 two maxima in the methane evolution curve, indicating the coexistence of carbon species with different reactivity towards hydrogen. The more reactive carbon species, probably consisting of chemisorbed carbon atoms and metal carbide, were unstable at high temperature (770 K), and slowly converted into a less reducible form.