Structured glass catalysts for diesel particulate filters

Abstract

Efforts to create a structured glass catalyst coating for use in diesel particulate filters (DPF) are described. Several methods for producing porous ceramics were investigated as possible routes to increase the active surface area of a K–Ca–Si–O (KCS) glass catalyst coating applied via a sol-gel route. A carbon pitch template yielded a desirable fibrous glass catalyst structure, but the fibers lay predominantly parallel to the substrate surface, minimizing their effectiveness in capturing soot particles and blocking the cordierite pore structure. A mesophase carbon microbead template yielded a structure that was too fragile for practical use. A chemical blowing agent (CBA) based on ethylene cellulose encapsulated KHCO3 was developed that offered a means to orient glass catalyst fibers away from the surface. However the viscosity of the CBA/fiber loaded sol makes it unsuited for applying into DPF channels. Finally, phase separation by addition of polypropylene glycol (PPG) was successful for creating a microporous K–Ca–Si–O glass catalyst coating on a cordierite filter. A PPG/KCS coated cordierite filter provides 2.8 times higher active surface area than a non-porous KCS coated cordierite filter, and a T50 (the temperature when half of the carbon is oxidized) that is 30°C lower than a non-porous KCS-coated cordierite filter. The excellent performance of the PPG/KCS coated cordierite filter is attributed to its higher catalyzed surface area and more intensive soot-catalyst interaction.