Improved Hydrothermal Stability in Glass Diesel Soot Oxidation Catalysts

Abstract

The hydrothermal stability of K-Ca-Si-O glass soot oxidation catalysts has been improved by substitution of Ce and Zr for Ca. This work demonstrates that glasses can be tailored to withstand the challenging diesel exhaust hydrothermal environment by considering the field strengths and partial molar free energies of the hydration reactions (ΔGi) of the cation species in the glass. The result is a glass that shows less formation of precipitates after 2 h hydrothermal exposure in air with 7% H2O at temperatures ranging from 300–700 °C. A K-Ca-Si-O glass with a soot T50 (the temperature when 50% of the soot is oxidized) of 394 °C was found to degrade to 468 °C after a 2 h, 700 °C hydrothermal exposure, whereas the improved K-Ce-Zr-Si-O glass only changed from 407 °C to 427 °C after the same treatment.

Catalytic Soot Combustion─General Concepts and Alkali Promotion

“…For some catalysts (i.e., perovskites), a decrease in activity due to potassium loss was observed, ,, while for some active phases (i.e., potassium–TM mixed oxides, glasses), it remains nearly intact. ,,, It has been reported that the alkali precursors in particular counteranions play an important role in terms of activity and stability (KNO 3 > K 2 CO 3 ) . A promising method of alkali metal stabilization is their immobilization within an oxide matrix, by forming nanostructured phases or glasses, ,, which can be further optimized by adding other dopants …”

“…150 A promising method of alkali metal stabilization is their immobilization within an oxide matrix, by forming nanostructured phases 218 or glasses, 226,228,229 which can be further optimized by adding other dopants. 145 The stability of the soot combustion catalysts containing alkali promoters has been also investigated in the presence of contaminants such as SO 2 74,81,252,254 or water vapor. 252,254 Alkali-modified perovskites exhibit good resistance to both sulfur and water, 252 while potassium-promoted ceria shows low resistance to sulfur and water at high temperatures.…”

Most Recent Advances in Diesel Engine Catalytic Soot Abatement: Structured Catalysts and Alternative Approaches

“…The use of alcohol−water solutions for the impregnation of cobalt had positive effects, since smaller particles with a high dispersion on the ceramic fibers were obtained, differently than when pure water was utilized. Temperature-programmed oxidation (TPO) results have shown that the catalysts prepared by using alcohol solvents had the best catalytic performance in terms of soot conversion as well as of maximum rate for soot combustion (at about Zokoe et al investigated the possibility of improving K-Ca-Si-O glass soot oxidation catalysts with higher hydrothermal stability in a diesel exhaust environment [53]. The authors used Zr and Ce for substituting Ca in a K-Ca-Si-O glass, obtaining a more hydrothermal resistant catalyst.…”

“…In particular, the authors used different Ce/Zr ratios in the range of 1/9-1/1 and studied morphology, phase structure, and physicochemical properties of the obtained fibers. The results have shown that the sample CZ-2-700 Zokoe et al investigated the possibility of improving K-Ca-Si-O glass soot oxidation catalysts with higher hydrothermal stability in a diesel exhaust environment [53]. The authors used Zr and Ce for substituting Ca in a K-Ca-Si-O glass, obtaining a more hydrothermal resistant catalyst.…”

“…(b) Temperature-programmed oxidation (TPO) profiles (normalized with carbon content). From [52].Zokoe et al investigated the possibility of improving K-Ca-Si-O glass soot oxidation catalysts with higher hydrothermal stability in a diesel exhaust environment[53]. The authors used Zr and Ce for substituting Ca in a K-Ca-Si-O glass, obtaining a more hydrothermal resistant catalyst.…”