Promotion of the catalytic activity of a Ag/Al2O3 catalyst for the N2O + CO reaction by the addition of Rh a comparative activity tests and kinetic study

Abstract

Preliminary activity tests show a synergic effect on the yield of the N2O+CO reaction by the addition of small quantities of rhodium in a Ag/Al2O3 catalyst. An analytical comparative kinetic study over Rh/Al2O3, Ag/Al2O3 and Rh-Ag/Al2O3 was performed in order to explain this effect. The reaction kinetics seems to follow a L–H mechanism with competitive adsorption of N2O and CO over the rhodium catalyst, where a strong CO inhibition effect was obvious. On the two other catalysts (silver and mixed) a L–H mechanism with the reactants adsorbed in different active sites seems to be followed. The kinetic, adsorption and thermodynamic constants were calculated and compared. From the results it seems that the synergic effect is connected with an increase of the activity of rhodium since silver offers more active sites for CO adsorption and removes the inhibition effect, while rhodium offers more active sites for both reactants to be adsorbed. The above findings show that there are no strong interactions (e.g. alloying) between silver and rhodium for the catalyst prepared by the method and active constituents concentrations of this study.