Improvement of Silica–alumina Supports for Diesel Oxidation Catalysts through Control of Both Composition and Pore Structure

Abstract

The aim of this study was to improve the performance of alumina-based diesel oxidation catalysts by optimization of both the composition and pore structure of the support material. For this purpose, we prepared a series of alumina-based supports via sol-gel methodology and loaded these materials with the active catalytic components Pt and/or Pd. In terms of the composition, SiO₂ showed promise as a secondary component at an optimum concentration of approximately 4 wt%. With regard to the pore structure, the catalytic activity for the oxidation of hydrocarbons and NO improved as the support mesopore size was increased up to approximately 10 nm. In addition, in the case of diesel fuel mist oxidation, it was shown that the presence of macropores above 1 μm was beneficial. On the basis of these results, we developed hybrid supports with both mesopores and macropores by the addition of a pore forming agent during the SiO₂–Al₂O₃ preparation process, and confirmed a subsequent improvement in catalytic activity.