Chemical and microstructural investigation of Pt/CeO2 catalysts reduced at temperatures ranging from 473 to 973 K

The combined application of chemical techniques and HREM shows that platinum deactivation in Pt/CeO₂ catalysts steadily increases with the reduction temperature (T_r: 473–1173 K). Though no suppression of the H₂ adsorption was observed, the TPD-H₂ traces indicate the occurrence of significant chemical changes with T_r. As revealed by HREM, the metal decoration starts at T_r: 973 K, a temperature well above those at which the chemical effects can be observed.     

Deactivation on Vehicle-Aged Diesel Oxidation Catalysts

This paper studies oxidation catalytic converters that were vehicle-aged in a diesel automobile. The deposition of several atoms (S, P, C, Si, Ca, Zn and Fe) was detected by several chemical analysis techniques. Moreover, AlPO₄ and Al₂(SO₄)₃ were identified by XRD. The catalytic performance of the aged catalysts with different mileages showed a similar degree of deactivation for CO and C₃H₆ oxidation. By contrast, laboratory sintering carried out on fresh catalysts revealed that it may have certain impact in the deactivation of diesel catalysts. Nevertheless, the possibility that the impact of chemical deposition on deactivation has a threshold value cannot be discarded.     

Deactivation on vehicle-aged diesel oxidation catalysts

Topics in Catalysis - This paper studies oxidation catalytic converters that were vehicle-aged in a diesel automobile. The deposition of several atoms (S, P, C, Si, Ca, Zn and Fe) was detected by...     

Deactivation of real three way catalysts by CePO4 formation

The contaminants present in a real three way catalysts (TWC) aged under real working conditions for ca. 30 000 km have been determined. The X-ray fluorescence (TXRF) and energy-dispersive X-ray analysis (EDS) showed that P, Ca, Zn, Pb, Cr, Ni, Fe, Cd and Cu are present in the used catalysts. Distribution within the washcoat was scrutinised by scanning electron microscopy (SEM-EDS) analysis. The more external region (10–15 μm) of the washcoat are very concentrated in Ca and P. CePO₄ was detected by X-ray diffraction (XRD). Other phases that can be formed between contaminants themselves and with the washcoat components were not detected by XRD. Temperature-programmed reduction (TPR) experiments show that an important fraction of the Ce present in the washcoat is unable to participate in Ce³⁺/Ce⁴⁺ redox pair under oxidising–reducing treatments. CePO₄ is proposed to explain the locking of the Ce³⁺/Ce⁴⁺ redox couple. Although other contaminants like Pb can be also poisoning the catalyst, the formation of CePO₄ can be invoked to explain the worse catalytic properties displayed by used sample. The locked Ce pair is unable of participating in the rapid Ce³⁺/Ce⁴⁺ redox couple required for correct oxygen storage capacity (OSC) properties and for the proper functioning of TWC.