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 H-2-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.

Automated summary

Careful NH3 or urea treatment can improve the catalytic activity of Pd catalysts, while the newly designed CO-TPR method is closely related to catalyst reducibility and total oxygen storage capacity. When using the most effective Urea-PP technology during monolith converter preparation, an outer layer is needed to protect the inner layer.