High-entropy oxide catalysts for the reductive depolymerization of organosolv lignin

Reductive catalytic depolymerization of lignin yields phenylalkane monomers that can be used as building blocks for the polymer industry. In literature, widely employed precious monometallic catalysts suffer from selectivity loss due to excessive ring saturation (with loss of desirable phenolic -OH groups) and substantial deactivation by poisoning and coking. In this work, high-entropy oxide catalysts (noble and completely non-noble formulation each) were synthesized and tested for the first time on the reductive depolymerization of organosolv lignin in batch. Their activity was measured by GPC-RID as a function of reducing molecular weight (Mw) of lignin, and compared to a benchmark Pd/Al2O3. The benchmark catalyst led to a catalytic activity (Mw reduction) of 40.16 ± 1.41%, whereas noble catalyst (PdCuNiCoCr)Ox outperformed with 57.63 ± 4.41%. HSQC NMR and GC-MS analyses were undertaken to analyze the resultant product pool. Furthermore, H2-TPR, XRD, XPS, SEM-EDX characterizations revealed structural and electronic information about the catalysts.