Catalytic properties of Cu–Mg–Al hydrotalcites, their oxides and reduced phases for ethanol dehydrogenation

Abstract

Different phases of Cu–Mg–Al compounds, hydrotalcites, their oxides, and reduced phases were prepared by co-precipitation and evaluated using the ethanol reactions. The solids were characterized by surface area measurements, X-ray diffraction (XRD), thermogravimetry coupled with differential thermal analysis, H2-temperature-programmed reduction, CO2 temperature-programmed desorption and temperature-programmed oxidation. The catalytic runs were performed at temperatures ranging from 250 to 350 °C. Activation with H2 was previously carried out in situ at 300 °C for the reduced samples. The samples with higher amount of Cu presented high ethanol conversion independent of the phase evaluated. The characterization by XRD after the reaction revealed that all samples exhibited only the metallic phase of Cu, independent of the phase before the reaction. The high selectivity for dehydrogenation was responsible for the transformation of hydrotalcites and mixed oxides into metallic phase during the ethanol reaction. Samples with lower amounts of Cu were deactivated by carbon deposition whereas samples with higher amount of Cu were deactivated mainly by sintering.