We report the effects of alloying Cu into silica supported Pd nanoparticles on the catalytic activity, surface composition, and particle structure during CO oxidation where CO and O2 composition match those of Low Temperature Combustion (LTC) diesel exhaust. Pd is highly active for CO oxidation under LTC exhaust concentrations but suffers from poisoning and inhibition from relevant competitive reagents (e.g. NO) at low temperatures (< 150 °C). By alloying Cu into Pd nanoparticles low temperature activity is achieved for CO oxidation in the presence of NO. Diffuse reflectance infrared Fourier transform spectroscopy studies illustrate that by alloying Pd with Cu, the formation of surface nitrosyl (NO-Pd) is eliminated. X-ray absorption spectroscopy studies illustrate the Pd in the alloy nanoparticle remains metallic during simulated diesel oxidation catalysis, independent of temperature. The nanoparticles in the catalyst only containing Pd material undergo a structural transformation to form a surface oxide at high temperature. Cu K-edge XAS data for the alloy indicates Cu oxidizes when the alloy catalyst becomes active. DRIFTS studies show that the Cu segregates to the surface as the alloy catalyst becomes active for diesel oxidation. These experiments demonstrate alloying Cu into Pd requires the Pd in the catalyst to remain metallic after light-off. The monometallic Pd catalyst forms a surface Pd-O layer when active. This combined with the oxidation of Cu during activation suggest the Cu plays the role of oxygen adsorber in the alloy during oxidation.
Stephen is a fifth year PhD student in the Goulas Research Group. The work Stephen is presenting on was completed as part of an SCGSR fellowship performed at the SLAC National Accelerator Laboratory.