Deactivation Mechanism of Cu/SiO₂ Catalysts in the Synthesis of Ethylene Glycol via Methyl Glycolate Hydrogenation

Abstract

Cu/SiO 2 catalysts are prone to deactivation in the dimethyl oxalate (DMO) hydrogenation when high content of methyl glycolate (MG) is produced at a high weight hourly space velocity (WHSV). However, few research studies have focused on the deactivation mechanism, which has become the bottleneck for improving the efficiency of the syngas-to-ethylene glycol (EG) technology. Herein, the deactivation mechanism of copper-based catalysts in the synthesis of EG was studied with MG hydrogenation as the model reaction. The stability test results proved that carrier loss in the form of tetramethoxysilane (TMOS) during the reaction could destroy the structure of the catalysts to some extent. The aggregation of copper nanoparticles (NPs) was also one of the reasons for the deactivation. However, the major factor for the deactivation of the Cu/SiO 2 catalyst was deduced to be carbon deposition. The weak acid−base sites of the catalyst led to some side reactions such as alcohol dehydration, condensation, and aromatization via the intermediate of glycolic aldehyde. Larger molecules were formed and accumulated in the pores of the catalyst, leading to the carbon deposition, which caused a rapid deactivation of the catalysts. This deactivation mechanism provides an important guide to develop a highly stable copper-based catalyst for the DMO hydrogenation to EG.

Ambient-pressure synthesis of ethylene glycol catalyzed by C 60 -buffered Cu/SiO 2

“…1D). The introduction of C 60 apparently allows the Cu catalyst to activate substrates more efficiently (table S3) (14)(15)(16)(17)(18)(19), and by contrast to those working in high pressures (>20 bar) of H 2 previously reported for the DMO-to-EG process, even in homogeneous pathways (26)(27)(28).…”

“…In addition, high H 2 pressure (30 bar) was required (14). Alternatively, a copper-silica (Cu/SiO 2 ) catalyst that selectively hydrogen-ates the DMO-to-EG reaction may be used (15)(16)(17)(18); however, Cu/SiO 2 suffers from insufficient activity at low pressure as well as poor stability (7,9,14,17). Efforts have been primarily directed toward promoting the Cu/SiO 2 catalyst by adding promoters such as B, Zn, and Au to tailor the electronic density of Cu species or enhance metal-support interactions (16,(19)(20)(21)(22).…”

Density Functional Theory Study on the Morphology Evolution of Hydroxylated β-Cristobalite Silica and Desilication in the Presence of Methanol

“…Previous experiments had suggested that the hydroxylated silica surfaces could be etched in the presence of methanol via the formation of tetramethyl orthosilicate. ,, In the present work, DFT calculations were used to study the methanol etching processes over three fully hydroxylated β-cristobalite silica surfaces. Upon methanol adsorption, the Si–O s surface bond is broken via methanol dissociation, forming a surface Si-bonded methoxy (Si–O m CH 3 ) and hydroxyl (O s H) groups.…”

Engineered Chemical Utilization of CO2 to Methanol via Direct and Indirect Hydrogenation Pathways: A Review

“…The leading cause of the deactivation of copper-based catalysts is thermal sintering and agglomeration due to their low Hütting temperature (134 °C), which leads to unstable and agglomerated Cu nanoparticles above 174.6 °C . Since the reaction temperature for EC hydrogenation (∼180 °C) is lower than the Tamman temperature of copper (407 °C), the growth of Cu particles could not be caused by thermal migration of Cu but through Ostwald ripening, occurring by reactive adsorbates on the support (like hydroxyl). ,− Besides, copper active sites can easily get agglomerated and imbalanced as a result of poor thermal stability of the Cu-based catalyst and from the strong reduction of H 2 and oxidation of C–O groups, which may make the Cu 0 and Cu + unstable during the hydrogenation process. , The Cu particle distribution, interparticle spacing, support structure, and metal–support interaction influence the deactivation rate of Cu-based catalysts …”