Roles of morphology and foreign metals of ceria-based catalysts in improving oxidations of Diesel vehicle pollutants

The present work highlights well-defined nanostructured ceria; a morphology that bestows exceptional catalytic activity on ceria towards soot oxidation. The work includes also introduction of promoting foreign metals, such as praseodymium and zirconium, to well-defined nanostructured ceria as a means of improving reducibility, thermal stability and oxygen storage capacity of the catalyst. Temperature-programmed oxidation (TPO) has been used for analyzing catalytic activity. At the first stage of the research, nanostructured equimolar ceria-praseodymia (denoted as Ce50Pr50-NP) was found to have the highest amount of surface oxygen, the highest reducibility and the highest catalytic activity towards soot oxidation. The nanostructured morphology has been proven to raise the functionality of praseodymia as the foreign metal in ceria. The work also introduces small, silane-stabilized Pt nanoparticles. Upon calcination, silyl ligands are transformed into siliceous patches that prevent the particle from migrating/coalescing. Cu nanoparticles have been prepared the same way as Pt nanoparticles; however, they sinter even under milder thermal treatment. The small Pt-NPs are proven active towards all pollutant oxidations, including NOx-assisted soot oxidation, and they function better with nanostructured ceria as the support. Unexpectedly, Ce50Pr50-NP gives higher activity towards NOx-assisted soot oxidation than Pt catalysts. Intense NO conversion and NO2 adsorption on the surface of Ce50Pr50-NP are the reason behind its high activity.