A novel, simple and efficient integrated catalyst exhibits an extremely high selectivity of 98% to ethanol in gas-phase hydrogenation of dimethyl oxalate.
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.
In
the utilization of renewable resources derived from biomass,
hydrodeoxygenation (HDO) is one of the most critical steps in the
bio-oil upgrading process. Herein, a series of copper phyllosilicate
nanotube (CuPSNT) catalysts were successfully prepared and applied
in the chemosynthesis of cyclohexane via the phenol HDO reaction.
Against the presumption that mono-metal copper was not active for
the complete hydrogenation of aromatic compounds, a cyclohexane yield
of 97.8% at the total conversion of phenol was achieved at 230 °C
on the CuPSNT catalysts with a Cu/Si ratio of 1:1. The kinetic analysis
suggested that further conversion of cyclohexanol to cyclohexane is
the rate-determining step in the phenol HDO. Cu0 accounts
for the hydrogenation, while Cu+ is responsible for the
adsorption of phenol and cyclohexanol and in charge of further cyclohexanol
dehydration. This conclusion is further confirmed by density functional
theory calculations. This work demonstrates that the synergy between
Cu0 and Cu+ species of CuPSNT catalysts plays
a critical role in the HDO process of phenol, and mono-metal Cu can
accomplish both the saturation of aromatic rings and the removal of
oxygen groups.
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