Site requirements for inhibition-free CO oxidation over silica-supported bimetallic PdCu alloys

Abstract

Pd catalysts are highly active for CO oxidation but suffer from inhibition by NO at low temperatures (<150 °C). We posit that incorporation of Cu into the Pd catalyst will improve low-temperature CO oxidation activity and reduce inhibition from competitive adsorbers. To probe this hypothesis, a series of PdCu alloys with different Pd : Cu ratios were synthesized and tested in the temperature-programmed oxidation of CO in the presence and absence of NO. Incorporation of small amounts of Cu into Pd improves the reactivity, as well as the resistance to NO inhibition. Beyond this, Cu incorporation into the Pd has a detrimental effect on the activity for CO oxidation. Based on combined infrared and X-ray absorption spectroscopy studies, we show that high activity and resistance to inhibition requires alloying of Pd and Cu and the formation of a diverse surface, while surface segregation of Cu results in poor activity and inhibition.