Methodology development for laboratory-scale exhaust gas catalyst studies on phosphorus poisoning

Deactivation of powdery automotive exhaust gas catalyst components (Rh or Pt loaded cerium–zirconium mixed oxides) was studied in laboratory-scale by developing two different chemical ageing procedures: incipient wetness impregnation with an aqueous salt solution of (NH4)2HPO4 and the adding of the (NH4)2HPO4 salt solution into the samples from a gaseous phase. Vehicle-aged commercial exhaust gas catalysts were used as a reference material for phosphorus poisoning. Phosphorus contamination in the poisoned samples was detected with X-ray fluorescence spectroscopy (XRF). Scanning electron microscope equipped with energy dispersive spectrometer (SEM–EDS) as well as XRF were used to analyze contaminants in the reference catalysts. Poison compounds formed on the catalytic surface of both laboratory-scale aged samples and vehicle-aged reference catalysts were identified with X-ray diffraction spectroscopy (XRD). The poisoning induced changes in the catalytic activities and characteristic surface areas of the samples were studied with activity tests and BET measurements, respectively. By both ageing methods, phosphorus could be added to the samples repeatably, time-savingly, affordably, and safely, and the same phosphorus compounds formed under real driving conditions were detected. These methods are therefore considered to be potential ageing procedures when studying accelerated chemical poisoning of powdery automotive exhaust catalyst components in laboratory-scale.