<p>The deactivation of the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) on a commercial Cu/SiO₂ catalyst was studied in the present work. The results showed that the primary cause of catalyst deactivation is carbon deposition stemming from the incomplete hydrogenation of methyl glycolate (MG) instead of an increase in the copper nanoparticle size and loss of silica. Furthermore, the acid–base sites on the catalyst surface facilitated side reactions such as alcohol dehydration, condensation, and aromatization, proceeding through the glycolic aldehyde as an intermediate, leading to the accumulation of larger molecules within the catalyst pores, which in turn covered the active sites and blocked the catalyst pores, thereby accelerating catalyst deactivation. This insight into deactivation provides crucial guidance for the development of highly stable copper-based catalysts for the hydrogenation of DMO to EG.</p> Graphical Abstract <p></p>