Co,Ba,K/ZrO2 coated onto metallic foam (AISI 314) as a structured catalyst for soot combustion: Coating preparation and characterization

Abstract

Co,Ba,K/ZrO2 coating onto the wall surface of an AISI 314 (American Iron and Steel Institute) foam was obtained using a sequential process: (1) original foam calcination, (2) ZrO2 layer formation and (3) active metal incorporation. After the different processes, the samples were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Laser Raman Spectroscopy (LRS), Energy Dispersive X-ray Analysis (EDX) and Scanning Electron Microscope (SEM) and the coating adherence was confirmed by means of an ultrasound test. Their catalytic behavior was evaluated using the soot combustion (Temperature-programmed Oxidation (TPO) and isothermal reactions). The soot particles were added via immersion in a 600-ppm soot suspension in n-hexane. The sequential process used to produce catalytic coatings proved to be efficient. After calcination at 900 ◦C, the wall surface of the original foam was covered with a uniform rich Cr oxide layer. This layer presented an interesting roughness, which favored the anchorage of the ZrO2 layer, obtained via washcoating. The latter layer was characterized by its mosaic-type morphology, an important fraction of the surface being rich in Zr (ZrO2 flakes). In this fraction, ZrO2 prevented the reaction between the active elements (Co, Ba, and K) and Cr2O3. The major components in the catalytic coating were Co3O4, BaCO3, KNO3 and ZrO2. Each one of these components and the synergy between them generated a good combination for catalysts to be used in the abatement of soot and NOx in diesel exhausts. The whole catalytic system has an interesting mechanical and thermal stability and the apparent activation energies for soot conversions lower than 0.5 (92 kJ mol−1) are comparable to the global activation energy reported for the powder Co,Ba,K/ZrO2 catalyst (82 kJ mol−1).