Abstract
The numerous parallel reactions in glycerol conversion substantially challenge the effective synthesis of target chemical from oversupplied glycerol. Herein, we intensively studied the control of the complex reaction network in glycerol conversion, and realized the selective production of lactic acid or glycolic acid by integrating the use of different bases with Cu/γ-Al2O3 catalyst. The results indicated that base promoted the oxidation dehydrogenation of glycerol over Cu/γ-Al2O3 catalyst to glyceraldehyde intermediate. Remarkably, base significantly contributed to the control of the competitive reactions in the next glyceraldehyde transformation. DFT calculation revealed that strong base (NaOH) independently promoted the removal of H in C2 of glyceraldehyde, thereby facilitating the dehydration reaction and leading to the selective production of lactic acid. Combing with First-principles calculation, it was revealed that both NaHCO3 and CuO species contributed to increase the electrophilicity of C2 and C3 in glyceraldehyde, thereby directing the conversion of the resultant glyceraldehyde intermediate towards the cleavage of C2-C3 to glycolal. Cu/γ-Al2O3 then separately catalyzed the oxidation of glycolal selectively to glycolic acid. This work might provide a promising approach and give some clues for the valorization of glycerol in widespread applications, thus affording profitable possibilities for the sustainable biodiesel.
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