Catalytic oxidation and conversion of kraft lignin into phenolic products using zeolite‐encapsulated Cu(II) [H₄]salen and [H₂]salen complexes

The encapsulated copper (II) tetrahydro‐salen and salen complexes were prepared in NaY for oxidation of kraft lignin to obtain phenolic monomer. Structural information obtained by spectroscopies suggested that geometry was correlated to the enhanced chemical behavior of the complexes. Characterization using gas chromatography–mass spectrometry demonstrated that catalyzed reactions of kraft lignin in the presence of CH 3 COOOH produced major products including 2‐methoxy phenol, 4‐hydroxy benzaldehyde, 4‐hydroxy‐3,5‐dimethoxyphenyl ethanone. The encapsulation and hydrogenation of complexes could improve reactivity. There was a greater improvement in reactivity for complexes on the immobilization by ship‐in‐a‐bottle method (SB) as compared with by impregnation method, and additionally a methanol fraction in the solvent proved beneficial effect for the product generation over these complexes in the oxidation of kraft lignin. Cu([H 4 ]salen)/SB was proved to be most active as giving the highest kraft lignin converted per mole metal ion and selectivity.