Experimental and DFT investigations of the performance of ZrO2 catalysts modified with Ce, La, Y, Mg, and Ba oxides during methyl stearate ketonization

Abstract

This work highlights the promotional effects of a CeO2 promoter and other transition and alkaline metal oxide promoters on a tetragonal ZrO2 catalyst during the gas-phase methyl stearate ketonization of 18-pentatriacontanone. The CeO2 promoter was found to enhance the selectivity of the ZrO2 catalyst towards the main product owing to an increase in the surface acidity and total Lewis acid sites. Moreover, the theoretical aspect of such an increase in acidity was confirmed by performing density functional theory (DFT) calculations, which revealed a strong interaction between the NH3 probe molecule and the Ce4O4/ZrO2 catalyst surface model, where all catalyst surface models were constructed based on their X-ray diffraction and X-ray photoelectron spectroscopy profiles. Various promoters were tested; for instance, although the conversion was high in the case of the Ba4O4/ZrO2 catalyst, the selectivity was suppressed. This was due to the two parameters that were found from the DFT calculations to be low for the BaO-promoted catalysts, which confirmed the weak interaction of the NH3 probe molecule in such a system. Thus, when ZrO2–based catalysts are prepared, their (i) surface acidity and (ii) total Lewis acid sites should be considered, and a promoter that improves these parameters would be beneficial.