(618b) Controlled Doping of CeO2-ZrO2 Nanoparticles to Modify Catalytic Activity

Authors: 
Dorman, J. A., Louisiana State University
Wang, Y., Louisiana State University
Larriviere, J., Louisiana State University
Safavinia, B., Louisiana State University
Dooley, K. M., Louisiana State University
According to Environmental Protection Agency, over 55% of NOx production in the US is caused by automobile exhaust, also resulting in the formation of CO and hydrocarbon residues. Recently, three-way catalysts, which include CeO2-ZrO2 (CZO) nanoparticles (NPs), have been fundamental to the mediation of these byproducts into environmentally friendly products such as H2O, CO2, N2, etc. However, the stability of these structures under reaction conditions has been shown to reduce the oxygen storage capacity and catalytic activity over time. To address this, the current work aims to engineer the structural and atomic properties of CZO NPs via co-doping of transition metal (TM) and rare earth (RE) elements to engineer improved stability and homogeneity, and increased lattice strain. The increased strain is expected to increase the oxygen storage capacity and limit sintering due to the lower reaction temperatures made possible here.
In this work, a new, two-step process, co-precipitation/molten salt synthesis (MSS), has been explored for a CZO:Ni/RE catalyst, comparing its homogeneity and vacancy concentration to a standard prepared by a sol-gel technique. XRD and TEM confirm that the NPs synthesized via co-precipitation/MSS are monodisperse at 15 nm diameter with the expected fluorite structure. Additionally, XRD characterization indicates a homogeneous crystal structure without any secondary phases. Raman Spectroscopy measurements show strong scattering peaks up to 800 cm-1 which dampen and red-shift with Ni incorporation. The endothermic energy associated with the dry reforming of methane was extracted via DSC, resulting in comparable values for this synthesis (8.31 mW mg-1) compared to the sol-gel method (8.46 mW mg-1) despite their reduced initial surface area at 33 m2 g-1 compared to 60-70 m2 g-1 for the sol-gel synthesis. Furthermore, by incorporating RE dopants, it is possible to slightly modify the Zr-O bond distances which can be observed via changes in the energy input. Additionally, the bond lengths and oxygen vacancy concentrations were probed via steady-state/time-resolved photoluminescence and x-ray adsorption spectroscopy.