Dehydration of 4-methylpentan-2-ol over CexZr1−xO2/SiO2 nano-composite catalyst

Abstract

Surface stabilized nano-sized ceria–zirconia solid solution on silica support was synthesized through a soft chemical route using colloidal silica dispersion and nitrate precursors of cerium and zirconium. The dispersion and structural stability of the CexZr1−xO2 solid solution after thermal treatments at 773 and 1073K was investigated by means of X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS) and BET surface area techniques. Catalytic performance of the synthesized CexZr1−xO2/SiO2 sample was tested for the conversion of 4-methylpentan-2-ol to 4-methylpent-1-ene in the vapour phase under normal atmospheric pressure. From XRD measurements, the presence of cubic phases of the composition Ce0.75Zr0.25O2, Ce0.6Zr0.4O2 and Ce0.5Zr0.5O2 were identified. The former phase was noted at 773K and the later phases at 1073K indicating enrichment of zirconium in the cubic fluorite type ceria lattice at higher calcination temperature. HREM results revealed existence of very small Ce–Zr mixed oxide crystallites of ∼5 nm size over amorphous silica at 773 K. No appreciable increase in the size of the crystallites was noticed even after calcination at 1073 K. XPS measurements indicated significant amount of Ce3+ present in the samples. All the characterization techniques revealed that silica does not form any unwanted inert compounds with the dispersed Ce–Zr-oxides. The activity studies reveal that the CexZr1−xO2/SiO2 catalyst exhibits a high and stable activity in the time-on-stream experiments with good product selectivity to 4-methylpent-1-ene. Also a significant decrease in the reaction temperature corresponding to 50% conversion is noted over this catalyst.