Turning poison into medicine: NH3 or urea treatment leads to improved Pd-based three-way catalysts

Contrary to the stereotype that exposure to NH3 or urea should be strictly avoided when preparing three-way catalysts using Pd due to Pd2+-NH3 coordination, remarkable catalytic activity improvement was realized with careful NH3 or urea treatment towards the oxides support or Pd precursor. And with the help of a newly designed facile CO temperature-programmed reduction (TPR) method, developed to replace traditional H2-TPR, it was found that the catalytic activity is closely related with the catalyst reducibility and total oxygen storage capacity (OSC, represented by the integrated area of a CO-TPR curve), thus showing the potential of this CO-TPR method for screening candidate catalysts. When applying the most effective “Urea-PP” technology during monolith converter preparation, this method could no longer show its advantage, unless an outer layer was coated to protect the highly active but also highly sensitive inner layer.