Microwave-assisted synthesis of highly active nanosized ceria-zirconia solid solutions for CO oxidation

Abstract

Superior ceria-zirconia (CexZr1−xO2; 1 : 1 mole ratio) solid solution was synthesised by employing a poly-block copolymer surfactant combined with microwave treatment. For comparison purpose an identical composition ceria-zirconia solid solution was also prepared by a conventional coprecipitation method. The structural and textural characteristics of the synthesised samples were investigated using X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area, and BJH pore size distribution (PSD) methods. The catalytic activity was evaluated for CO oxidation at normal atmospheric pressure. The XRD measurements revealed the presence of cubic Ce0.75Zr0.25O2 and Ce0.6Zr0.4O2 phases in the conventional coprecipitation and surfactant-controlled microwave treated samples, respectively. The CexZr1−xO2 solid solution prepared by surfactant-controlled microwave-assisted method exhibited a high specific surface area and mesoporosity. The SEM images suggested that all samples consist of typical spherical agglomerates with almost uniform size within the nanometer range. The TEM measurements revealed that the nanosized crystallites are in the narrow range between 4 nm and 8 nm and densely packed. Raman measurements revealed existence of more oxygen vacancies in the surfactant-controlled microwave treated sample. Interestingly, the CexZr1−xO2 solid solution obtained by surfactant-controlled microwave treatment exhibited better CO oxidation activity than the conventional coprecipitated sample. Enhanced activity of the surfactant-controlled microwave treated sample is correlated with smaller crystallite size, mesoporosity, and more number of defects.