Catalytic Hydrogenolysis of Glycerol to Propylene Glycol over Mixed Oxides Derived from a Hydrotalcite-Type Precursor

Abstract

Selective hydrogenolysis of glycerol to propylene glycol was performed using an environmentally friendly hydrotalcite-derived mixed-metal oxide catalyst. The Mg/Al, Zn/Al, Ni/Mg/Al, Ni/Co/Mg/Al, and Cu/Zn/Al mixed-metal oxide catalysts were prepared from their corresponding hydrotalcite precursors having M 2+ /M 3+ compositions over the range of 0.5-3.0. The physicochemical properties of the catalysts were studied by X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), NH 3 and CO 2 temperatureprogrammed desorption (TPD), and nitrogen adsorption studies. The XRD patterns of pure hydrotalcites exhibited characteristics of hydrotalcite phases, while those of calcined hydrotalcites showed the formation of corresponding metal oxides. The ICP-MS analysis showed agreement between the calculated and actual metal compositions. The prepared catalysts were evaluated for the hydrogenolysis of glycerol to propylene glycol in a Parr reactor. The activity studies indicated a maximum glycerol conversion and selectivity toward propylene glycol in the case of Cu/Zn/Al mixed-metal oxide catalysts. Further, the reaction parameters were optimized with the most active Cu/Zn/Al catalyst, and it was found that at a catalyst concentration of 5% (w/w) of aqueous glycerol, a hydrogen pressure of 200 psig, and 80% glycerol dilution, a maximum glycerol conversion of 52% with 93-94% selectivity toward propylene glycol were obtained.

Effect of sulfatation on the physicochemical and catalytic properties of molecular sieves

“…As compared with the result of Meher et al [33], our results showed lower conversions, possibly due to the weak interactions between sulfate ions and the molecular sieves and thus, homogenous catalysis is likely over the solids studied. Also, the dehydration of glycerol suffered from an extensive deactivation phenomena, especially when the reaction was carried out at temperatures as high as 300°C, as shown by the Raman results.…”

“…It is possible that the reaction conditions studied to produce hydroxyacetone could be milder than that of previous findings with other molecular sieves such as ZSM-5 and oxides [17,[31][32][33], because the reaction would reach the equilibrium. As compared with the result of Meher et al [33], our results showed lower conversions, possibly due to the weak interactions between sulfate ions and the molecular sieves and thus, homogenous catalysis is likely over the solids studied.…”

Co-Production of Ethanol and 1,2-Propanediol via Glycerol Hydrogenolysis Using Ni/Ce–Mg Catalysts: Effects of Catalyst Preparation and Reaction Conditions

“…Since water is a by-product in the hydrogenolysis of glycerol, its presence favors the reverse reaction of dehydration, thereby inhibiting hydrogenolysis [45,46]. At a lower water content, 1,2-PDO and ethanol selectivities declined, which may have resulted from the degradation or polymerization of these products [47][48][49]. The decrease in ethanol selectivity may also be caused by an increase in n-propanol production at lower water contents, which competes with the subsequent ethanol production.…”

Glycerol Hydrogenolysis over Co Catalysts Derived from a Layered Double Hydroxide Precursor

“…For instance, Cu-Zn-Al oxides, derived from the corresponding hydrotalcite precursor, proved to be highly active and selective in glycerol hydrogenolysis at 473 K, giving a glycerol conversion of 48.0% and a 1,2-propanediol (1,2-PDO) selectivity of 93.9% [18]. We have recently reported that Co/MgO catalysts provided a glycerol conversion of 44.8% and a 1,2-PDO selectivity of 42.2% in glycerol hydrogenolysis at 473 K, but the hydration of MgO to Mg(OH) 2 , under the reaction conditions, caused severe aggregation of the cobalt particles [11].…”