Abstract:
A novel strategy to synthesize micro-structured cobaltite (ACo sub(2)O sub(4); A = Fe, Mn, Cu) catalysts with tunable catalytic properties exhibiting highly selective production of glycerol carbonate via urea glycerolysis reaction is demonstrated. FeCo sub(2)O sub(4) microcubes, MnCo sub(2)O sub(4) microspheres, and CuCo sub(2)O sub(4) micro-octahedrons were produced via an ultrasonication-assisted hydrothermal approach. The impact of urea (U), semicarbazide (S) as structure directing agents (SDAs), and metal ion substitution (A = Fe sup(3+), Mn sup(3+), Cu sup(2+)) on catalyst morphology and acid-base active sites in cobaltite is confirmed using various material characterization techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, NH sub(3) and CO sub(2) temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). The enhanced catalytic properties resulted in a significant improvement in their catalytic performance, particularly in terms of activity and selectivity. The order of yield (Y) and selectivity (S) for GC production is FeCo sub(2)O sub(4)-U microcubes (Y95 plus-minus 3 percent, S99 percent) greater than MnCo sub(2)O sub(4)-S microspheres (Y91.5 plus-minus 3 percent, S98.5 percent) greater than CuCo sub(2)O sub(4)-S micro-octahedrons (Y83.4 plus-minus 3 percent, S92.4 percent) greater than Co sub(3)O sub(4) (Y35 plus-minus 3 percent, 99 percent), as determined using the GC-MS analysis. This performance is attributed to the effective catalytic activation of urea, leading to enhanced GC production via the isocyanic acid pathway. Therefore, the strategies presented in this work could be further extended to other spinel compounds to achieve desired catalytic properties for chemical transformations of industrial interest.
