Preparation of Pt/Al2O3 and PtPd/Al2O3 Catalysts by Supercritical Deposition and Their Performance for Oxidation of Nitric Oxide and Propene

Abstract Pt/Al2O3 and bimetallic PtPd/Al2O3 catalysts were prepared via supercritical deposition method using supercritical carbon dioxide. The effects of Pt loading of Pt/Al2O3 and Pd addition to Pt/Al2O3 on particle size, particle size distribution (PSD) and activity for NO and C3H6 oxidation and C3H6-selective catalytic reduction (C3H6-SCR) were investigated. Pt/Al2O3 catalysts were prepared with Pt loadings of 0.6, 1.2 and 2.1 wt% and a bimetallic PtPd/Al2O3 catalyst was prepared with total metal loading of 1.4 wt% and Pt:Pd molar ratio of 1.3:1. A small fraction of the particles agglomerated after calcination at 550 °C. Around 98% of the particles had an average particle size of ∼1 nm. The rest of the particles were larger and average size of these larger particles was ∼10 nm for monometallic catalysts and ∼6.5 nm for PtPd/Al2O3. All catalysts were found to be active for NO and C3H6 oxidation and C3H6-SCR reactions. NO oxidation performance of 1.2 wt% Pt/Al2O3 catalyst was the highest. C3H6 oxidation activity increased with increasing metal content. Light-off temperature for C3H6 oxidation shifted to higher temperature in the presence of NO, suggesting competitive oxidation of C3H6 and NO. Concentration profiles indicated that C3H6-SCR started when C3H6 conversion by oxidation reached 50%; C3H6 was consumed both by oxidation and C3H6-SCR at higher conversions.