Shandong Yuan

Effect of surface tension on the properties of a doped CeO2–ZrO2 composite and its application in a Pd-only three-way catalyst

La and Pr modified ceria–zirconia solid solution materials CeO2–ZrO2–La2O3–Pr6O11 (CZLP) were synthesized through a co-precipitation method, in which the influence of surface tension during the drying process on the textural/structural properties, reduction behavior and oxygen storage capacity of the materials was investigated. The difference in catalytic performance of the supported Pd-only thee-way catalysts was further studied. The results revealed that CZLP3 obtained through a supercritical ethanol drying method which eliminated the surface tension in the drying process exhibited a texture with a larger pore size and wider pore size distribution. Such texture is crucial to improve the thermal stability and anti-aging ability of materials. After calcining at 1000 °C, the specific surface area, cumulative pore volume and average pore radius of CZLP3-a were 52 m2 g−1, 0.52 cm3 g−1 and 20.3 nm, respectively. The XRD and Raman results revealed that a more homogeneous solid solution of Ce, Zr, La and Pr was formed, and the aging-treatment-induced segregation of phases was inhibited for CZLP3. Besides, the slightest grain growth after the aging treatment shown in TEM images indicated the superior anti-aging ability of CZLP3. The Raman and XPS analysis demonstrated the highest concentration of oxygen vacancies and surface Ce3+ species for CZLP3 both before and after the aging treatment, which contributed to the enhancement of its reduction properties and oxygen storage capacity. Consequently, Pd/CZLP3 exhibited outstanding three-way catalytic activity compared with the others both before and after the thermal aging treatment, indicating its tremendous potential possibilities.

Designed synthesis of Zr-based ceria–zirconia–neodymia composite with high thermal stability and its enhanced catalytic performance for Rh-only three-way catalyst

Developing advanced oxygen storage materials that deliver high thermal stability is crucial to meeting increasingly stringent environmental regulations for three-way catalysts (TWCs). The surfactant, trialkylamine (N235, N (CnH2n+1), n = 8–10), was used to prepare the zirconium (Zr)-based ceria–zirconia–neodymia composites with loose morphology for the first time, and the effect of N235 on the properties of the ceria–zirconia–neodymia solid solution composites was investigated systematically. After thermal treatment at 1000 °C for 5 h in air, the obtained material (CZ/N235-1000) presented a high surface area of 31 m2 g−1 and had superior redox properties. As a support material in rhodium (Rh)-only TWCs, the prepared Rh/CZ/N235-f and Rh/CZ/N235-a demonstrated excellent catalytic performances. Particularly, after aging at 1000 °C for 5 h in air, the light off temperature (T50%) of nitrogen oxide and carbon monoxide for Rh/CZ/N235-a were 229 °C and 235 °C, respectively, and were much lower than those (278 °C and 280 °C) of Rh/CZ-a in which the support material was synthesized without N235. Therefore, this work provides a simple and scalable synthesis route for advanced oxygen storage materials.

Catalytic performance of a Pt-Rh/CeO 2 -ZrO 2 -La 2 O 3 -Nd 2 O 3 three-way compress nature gas catalyst prepared by a modified double-solvent method

Abstract A Pt-Rh three-way catalyst (M-DS) supported on CeO2-ZrO2-La2O3-Nd2O3 and its analogous supported catalyst (DS) were developed via a modified double-solvent method and conventional double-solvent method, respectively. The as-prepared catalysts were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), CO-chemisorption, X-ray photoelectron spectroscopy (XPS) and hydrogen temperature-programmed reduction (H2-TPR). The preformed Pt nanoparticles generated using ethanol as a reducing agent on M-DS presented enhanced Pt dispersion regardless of aging treatment as confirmed by XRD and CO-chemisorption measurements. The textural properties and reduction ability of M-DS were maintained to a large extent after aging treatment. This result was consistent with those of the N2 adsorption-desorption and H2-TPR, respectively. Meanwhile, the XPS analysis demonstrated that higher Pt0 species and larger Ce3+ concentration could be obtained for M-DS. In the conversion of a simulated compressed natural gas (CNG) vehicle exhaust, both fresh and aged M-DS showed a significant enhancement in the activity and N2-selectivity. Particularly, the complete conversion temperature (T90) of CH4 over the aged M-DS catalyst was 65 °C lower than that over the aged catalyst by conventional double-solvent method.