Catalytic depolymerization of calcium lignosulfonate by NiMgFeO derived from sub-micron sized NiMgFe hydrotalcite prepared by introducing hydroxyl compounds

A new method for regulating the synthesis of NiMgFe hydrotalcites (NMF LDHs) with the addition of hydroxyl compounds was proposed. A series of NMF LDHs were prepared by the above method, and then were calcined to obtain the NiMgFeOx (NMFOx) samples. The NMFOx samples were characterized by XRD, SEM, TG-DTG, XPS and CO2-TPD, respectively. The catalytic performance of NMFOx for depolymerizing calcium lignosulfonate (CLS) was evaluated by hydrothermal reaction. The results showed that the addition of hydroxyl compounds favored reducing the particle sizes of NMF LDHs. For the depolymerization of CSL, the yield of liquid product increased from 45% to 75.8% with the addition of NMFOx-ethanol (NMFOx-ET). The liquid products were mainly phenolics, aromatics, ketones and esters. The total selectivity of oxy-containing compounds was over 90.6%, among them, the phenolics were approximately 35.2%. The valence of Ni and Fe, crystalline phase and basicity almost remained unchanged. The NMFOx-ET samples were recycled for the depolymerization of CLS, moreover, the NMFOx-ET samples had high activity and stability after 4 cycles.