Suppressing on-stream deactivation of CuSiO2 catalysts in the dehydrogenation of bioethanol to acetaldehyde†

Abstract

Bioethanol upgrading to valuable platform molecules is a cornerstone of the emerging “integrated biorefinery” concept. Although active catalysts have already been developed for the non-oxidative dehydrogenation of ethanol to acetaldehyde, their rapid deactivation – through coking and sintering – is still an unsolved challenge. Herein, we study a 7.4 wt% Cu–SiO₂ catalyst at 573 K for 8 or 24 hours under stable ethanol feed, we report in-depth characterization of the spent catalysts to univocally describe deactivation phenomena, and we propose reaction engineering procedures based on gas co-feed (O₂ or H₂) to decisively enhance the catalyst stability. Under the standard conditions, the pristine catalyst undergoes fast deactivation, as conversion drops from ∼95% to ∼25% in about 8 hours. While sintering is shown to occur during the reaction, we demonstrate that the main cause of deactivation is actually the accumulation of carbonaceous deposits. Even if such deactivation is shown to be reversible (regeneration by oxidative treatment), it is more attractive to prevent it from happening. Studying the effect of gas doping, we show that introducing a small fraction of oxygen (0.44 vol%) leads to a marked decrease of the extent of coking and stabilization of catalytic activity at a much higher conversion level (75% after 24 h). A slightly higher O₂ concentration (1.77 vol%) leads to complete stabilization of the ethanol conversion (90% after 24 h), but concomitantly provokes a slight drop in acetaldehyde selectivity. With the findings of this study, with optimized reaction conditions and an ameliorated catalyst formulation, an outstanding acetaldehyde productivity (2.9 g_aca g_cat⁻¹ h⁻¹) was maintained fully stable for 24 h.