Effects of Nd on the properties of CeO2–ZrO2 and catalytic activities of three-way catalysts with low Pt and Rh

Abstract

A series of Ce0.35Zr0.65−xNdxO2−x/2 (x=0.05, 0.10, 0.15, 0.20 and 0.25) were prepared, and the combinational effects of Nd and noble metals on the catalytic activities of monolithic cordierite honeycomb catalysts were elucidated. The results showed that the BET surface area and pore volume of CZN3F reach a maximum, 97m2/g and 0.19ml/g, but all aged samples undergo a sharp decline. The CZN2 has more oxygen vacancy and higher oxygen storage capacity (OSC) before and after ageing, but OSC of the samples with high Nd content decreases. All fresh samples have cubic Ce0.40Zr0.60O2 phase with nano-size, but the aged samples with low Nd content still exhibit cubic Ce0.40Zr0.60O2 phase. When Nd content (CZN4A) is 20mol% after ageing at 1000°C, small Ce0.60Nd0.40O1.80 is segregated from CeO2–ZrO2 cubic phase; when the doped Nd increases to 25mol% (CZN5A), the CeO2–ZrO2 cubic phase completely converts into Nd050Zr0.50O1.75 cubic phase with 12.4nm, accompanying a sharp decline of OSC; and O2 pretreatment can change the reductive behavior and H2 consumption of samples because of oxygen absorbed. Noble metals can influence the reduction of Ce0.35Zr0.65−xNdxO2−x/2. Ce0.35Zr0.65−xNdxO2−x/2 shows important differences in the TPR and H2 consumption and can change the dispersion and sintering of noble metals, resulting in different catalytic activities. The light-off temperature (T50%) of catalysts containing CZN2F (C2F) can be as low as 160°C for CO, 211°C for NO and 259°C for C3H8, indicating that appropriate Nd doping is helpful for the improving catalytic activity.