CO induced surface segregation as a means of improving surface composition and enhancing performance of CuPd bimetallic catalysts

A series of copper rich CuPd/Al2O3 catalysts were prepared and characterised by FTIR spectroscopy using CO as a probe molecule. After reduction, the surface composition was largely composed of Cu with evidence of a small concentration of isolated Pd atoms. It was found that CO induced surface segregation could be used to increase the surface Pd concentration and depending on the Cu:Pd ratio, the formation of Pd–Pd dimers was possible. Changes in surface composition were quantified and correlated with catalyst activity and selectivity for selective acetylene hydrogenation. For the catalyst with optimum Cu:Pd ratio (50:1), it was possible to use CO induced segregation to increase activity considerably (20 K temperature reduction to achieve 100% conversion) whilst only marginally affecting ethylene selectivity (≈5% decrease in ethylene selectivity). An estimate of the detection limit by FTIR of the minimum surface coverage of isolated Pd and Pd–Pd dimers is given.