Boosting the Long-Term Stability of Hydrotalcite-Derived Catalysts in Hydrogenolysis of Glycerol by Incorporation of Ca(II)

Abstract

Selective hydrogenolysis of biomass-derived glycerol into 1,2-propanediol (1,2-PDO) is of practical importance to upgrade the huge amounts of surplus glycerol derived from renewable biomass. Herewith, we report that hydrotalcite-derived catalysts have been employed for selective hydrogenolysis of glycerol into 1,2-PDO under aqueous phase and base-free conditions. In particular, the catalyst of Co 2 -Ca 4 -Al 3 was recorded as a good catalyst with an optimum glycerol conversion of 100% and 1,2-PDO selectivity of 90.5% in glycerol hydrogenolysis. Meanwhile, it exhibited high stability in consecutive catalytic recycles under batch-wise operation conditions. Furthermore, the catalyst also demonstrated high glycerol conversion (ca. 95.0%) and selectivity to 1,2-PDO (ca. 90.0%) with a long-term catalytic stability (280 h) by a continuous-flow fixed-bed reactor. Additionally, the catalyst can be further extended to selective hydrogenolysis of some other sugar polyols to 1,2-PDO (selectivity up to 50.5%−68.5%). The activity tests and characterizations demonstrated that Co 0 existing in the catalysts acted as active sites in glycerol hydrogenolysis. Also, the further characterization by XRD, HRTEM, and EDS element maps revealed that the distribution of Co was basically consistent with that of Al, while Ca species were adjacent to Co and Al species. The mixed metal oxides CaO-CoAl 2 O 4 were generated arising from a strong interaction between Co(II) and Ca(II) oxides species, which endowed more electron-deficient Co(II) sites and also led to large amounts of moderate basic sites, being favorable for enhancing catalytic activity and selectivity. Notably, the forming CaCO 3 phase played a crucial role in preventing the leaching of moderate basic sites and metal species by covering CaO-CoAl 2 O 4 mixed metal oxides, which was the crucial reason that the present Co 2 -Ca 4 -Al 3 catalyst showed the remarkable catalytic stability under aqueous phase reaction conditions. On the basis of the results above, the reaction pathway has been discussed as well.

Transition Metal Catalysts for the Glycerol Reduction: Recent Advances

“…[150] The presence of Co 0 nanoparticles is very important: a hydrotalcite-derived Co 2 -Ca 4 -Al 3 catalyzed several steps for the formation of 1,2-PD. [151] XRD characterization revealed the formation of a CaCO 3 layer on the surface of the catalyst that reduced the number of strong basic sites, enhanced the number of moderate basic sites, and helped to avoid the metals leaching during the reaction, carried out at 483 K and 40 bar H 2 in a continuous-flow fixed-bed reactor. So, the product was obtained with excellent selectivity (91 %) at complete GL conversion.…”

“…So, the product was obtained with excellent selectivity (91 %) at complete GL conversion. [151] Cobalt aluminate nanoparticles were also used as catalyst in the gas phase GL transformation. They were prepared by flame spray pyrolysis and employed for the catalytic reaction at 573 K and 1 bar H 2 .…”

Recovery and utilization of crude glycerol, a biodiesel byproduct

“…In general, the hydrogenolysis of glycerol utilizes a homogeneous base (i.e., Ca(OH) 2 , NaOH, and Ba(OH) 2 ) and a supported transition metal catalyst (i.e., Pd, Pt, Ru, Ni, or Cu) to catalyze this process, which can selectively break the C-C and/or C-O bonds. [52][53][54] Gong et al 55 employed hydrotalcite-derived catalysts to selectively hydrolyze glycerol to 1,2-propanediol in aqueous phase and under alkali-free conditions. Their results showed that the Co 2 -Ca 4 -Al 3 catalyst reached 100% optimal glycerol conversion and 90.5% 1,2-propanediol selectivity in glycerol hydrogenolysis.…”

Selective Hydrogenative Rearrangement of Furfural to Cyclopentanol over Alloyed Cu–Co Supported on Sulfur-Doped Coffee Biochar

“…into them, which could lead to high catalytic activity and selectivity. 40 However, the LDH-derived catalysts usually appear as aggregated lumps, which have a negative impact on the mass transfer processes and the exposure of active sites in the catalytic reactions. 41,42 Therefore, grafting LDH precursors onto other supports with abundant space through in situ growth strategies could be beneficial for improving their catalytic performance.…”