Study of Pt–Rh/CeO2–ZrO2–MxOy (M = Y, La)/Al2O3 three-way catalysts

Abstract

CeO2–ZrO2–MxOy (M=Y; La) mixed oxides, prepared by co-precipitation method and characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Raman spectra (RM) and oxygen pulse reaction, were comparatively investigated to elucidate the combinational effects of Y and/or La oxide promoters on the catalytic activity and anti-aging performance of monolithic cordierite honeycomb catalysts with low Pt and Rh content. The catalytic activities, water-gas shift (WGS) and steam reforming reaction (SR) were studied under a simulated gas mixture. The catalysts were also characterized by H2-temperature-programmed reduction (H2-TPR) and O2-temperature-programmed desorption (O2-TPD). The results showed that the prepared CeO2–ZrO2–MxOy oxides have a face-centered cubic fluorite structure and are nanosize. La3+ ions can significantly improve thermal stability and efficiently retard CeO2–ZrO2 crystal sintering and growth. Doped CeO2–ZrO2 with Y3+ and La3+ has 105 and 60m2/g surface area and 460 and 390μmol/g OSC before and after aging. The T50 of fresh Pt–Rh/CZYL/LA is 170°C for CO, 222°C for C3H8 and 189°C for NO, and shift to 205, 262 and 228°C after hydrothermal aging, which are better than those of Pt–Rh/CZY/LA or Pt–Rh/CZL/LA. WGS and SR are relate to the OSC of oxygen storage materials and absorbed oxygen species on the catalyst surface and affect the three-way catalytic activities of catalysts. The reductive property of noble metals and the dissociatively adsorbed O2 on the surface of catalysts are closely related to the catalytic activities.