Effect of ethylene glycol on structure, thermal stability, oxygen storage capacity, and catalytic CO and CH₄ oxidation activities of binary CeO₂–Al₂O₃ and ternary CeO₂–ZrO₂–Al₂O₃ cryogels

Porous and homogeneous cryogels of binary ceria-alumina (CA) and ternary ceria-zirconia-alumina (CZA) were prepared from cerium nitrate, zirconium (IV) dinitrate oxide hydrate, and aluminium sec-butoxide by a one-pot sol–gel technique in an aqueous system and subsequent freeze drying, and effect of ethylene glycol (EG) used for chelation of cerium ions on structure, thermal stability, reducibility, oxygen storage capacity, and catalytic carbon monoxide and methane oxidation activities of the catalysts was investigated. EG did not significantly affect surface area, pore volume, mean pore size, and surface morphology of the catalysts after calcination and subsequent oxidative/reductive atmosphere heating at 900 °C. Whereas use of EG resulted in much finer particles of cerium oxides and ceria-zirconia solid solution for CA and CZA, respectively, distributed throughout alumina with high dispersion. X-ray diffraction (XRD) and Raman spectra suggested that while a cubic CeO₂ phase was observed for CA after the oxidative heating regardless of whether or not EG was employed, finely-divided cerium oxides or crystalline CeAlO₃ were respectively obtained after the reductive heating depending on whether EG was respectively used or not used. As for CZA, while a pseudo-cubic t″ phase was seen after the reductive heating regardless of whether EG was used or not, mixed phases of pseudo-cubic t″ and cubic or a cubic one were respectively observed after the oxidative heating depending on whether EG was respectively employed or not employed. The solid solubility of zirconia in ceria was improved by EG for CZA. The oxygen storage capacity and catalytic CH₄ and CO oxidation activities were also enhanced by employing EG for both catalysts, which was ascribed fundamentally to the finer particles of cerium oxides and ceria-zirconia solid solution for CA and CZA, respectively, although CO oxidation on CA was unimproved by EG after the reductive heating.