Characterization of phosphorus-poisoned automotive exhaust catalysts

Oil-derived contaminants on light-off catalysts from high mileage taxis wer e characterized by a variety of physical and chemical methods. The contamin ants (mostly phosphates) deposit in a strong axial gradient from the front to the back of the monolithic catalyst channels. Two major forms of phospho rus contamination were observed: (1) an overlayer of Zn, Ca, and Mg phospha tes, and (2) aluminum phosphate within the washcoat. The data also suggest the formation of cerium(IR) phosphate. Laboratory catalytic reaction measur ements on core samples from the taxi catalysts confirm a strong deactivatin g effect due to the phosphorus contamination. The activity improves dramati cally after removing phosphorus via an oxalic acid wash. (C) 2001 Elsevier Science B.V. All rights reserved.