Kinetic Modeling of Erythritol Deoxydehydration and Consecutive Hydrogenation over the ReO _x -Pd/CeO₂ Catalyst

The reaction kinetics of deoxydehydration + hydrogenation (DODH + HG; didehydroxylation) of erythritol to butanediols and n-butane over the ReOx-Pd/CeO2 catalyst was investigated. Competitive adsorption of polyols and catalyst deactivation during the DODH + HG reaction were necessary to be considered in the kinetics. The order of the adsorption strength on the catalyst surface was erythritol >1,2-butanediol > water >1,4-butanediol and monoalcohols. The deactivation during the reaction was investigated with two models: time-dependent and conversion-dependent ones. The conversion-dependent model better fitted both the activities of reused catalysts and the time-course data. The deactivated catalysts were characterized with TG-DTA and Raman spectroscopy. The weight loss and the temperature for the combustion of deposited organic species in TG-DTA did not correlate with the deactivation degree. On the other hand, a growing signal at around 910 cm(-1) was observed in Raman spectroscopy in line with deactivation, which can be explained by the formation of aggregated ReOx species. The low activity of aggregated ReOx species was supported by DFT calculations showing that the activation energy of dimeric Re2OxHy/CeO2 catalyst species for the cleavage of two C-O bonds is higher than that of monomeric ReOxHy/CeO2 species.