Kinetic Study of Pd-Promoting Effect on Cu/ZnO/Al2O3 Catalyst for Glycerol Hydrogenolysis to Produce 1,2-Propanediol at Low Hydrogen Pressure

Abstract

The promoting effect of Pd on a Cu/ZnO/Al2O3 catalyst for the aqueous glycerol hydrogenolysis process to produce 1,2-propanediol was studied. At a lower hydrogen pressure (2.07 MPa), using the Cu/ZnO/Al2O3 catalyst with 2 wt% Pd doped, could significantly improve the glycerol conversion (97.2%) and 1,2-propanediol selectivity (93.3%) compared with the unpromoted catalyst (69.4% and 89.7%, respectively). A power-law kinetic model, which took into account all the elementary reactions including glycerol dehydration and its reverse reaction, acetol hydrogenation, side reactions and ethylene glycol formation, was developed to comprehensively investigate the effect of Pd. Though the rate of glycerol dehydration using the Pd-promoted catalyst was found to be slightly lower, mainly due to the reduced number of acidic sites after adding Pd, the glycerol conversion rate was notably higher compared with using the unpromoted catalyst, mainly attributed to the enhanced activity of acetol hydrogenation by Pd. The rapid hydrogenation of acetol can inhibit the reverse reaction of glycerol dehydration, resulting in a higher glycerol conversion rate, so that glycerol dehydration is considered as the rate-determining step. In contrast, when the unpromoted catalyst was used, the rate of reverse glycerol dehydration was drastically increased due to the elevated acetol concentration, especially at a lower hydrogen pressure, resulting in a slower glycerol conversion rate; thus, acetol hydrogenation became the rate determining step. In addition, Pd can improve the reducibility of the catalyst, allowing the CuO to be reduced in situ during the reaction. Therefore, catalyst deactivation due to any potential oxidation of metallic copper during the reaction can be prevented.

Hollow Au1Cu1(111) Bimetallic Catalyst Promotes the Selective Electrochemical Conversion of Glycerol into Glycolic Acid

“…The utilization of biomass as a feedstock for producing high-value chemicals has garnered significant interest in recent years, driven by the growing global energy demand and related environmental issues. − Polyols, such as glycerol, 1,2-propanediol, and ethylene glycol, are particularly noteworthy as potential feedstocks. Their highly functionalized nature and oversupply means that they possess several economic benefits, compared with other low carbon building blocks. , However, the C–C bond cleavage is relatively facile in polyols due to the adjacent hydroxyl groups, which can hinder selective transformations and result in the formation of lower-value compounds, such as formic acid. Thus, the production of desirable high-value products from polyols, with stable selectivity and high conversion, remains a significant challenge.…”