Preparation of palladium-based catalysts and use for depolymerization of larch bark tannins

In this study, we synthesized eight palladium-based catalysts using two carriers, ZrO₂ and MCM-41. These catalysts were used for the degradation of condensed tannins extracted from larch bark. The average polymerization degree and degradation rate of the products were used as indicators to evaluate the efficiency of degradation. The effects of different Pd:Cu loading ratios under the same carrier conditions and the effects of different carriers under the same Pd:Cu loading ratio were investigated. The results revealed that when the carrier was kept constant, the Pd:Cu ratio of 1:1 exhibited the highest efficiency in degrading condensed tannins. Moreover, when the Pd:Cu loading ratio was the same, the degradation efficiency was higher when ZrO₂ was used as the carrier. Based on these findings, the catalyst (Pd₁-Cu₁)₅/ZrO₂ (where “1” are the molar ratios of Pd to Cu added during the preparation of the catalyst and where ‘5’ is the mass percentage of Pd/Cu metal to total catalyst, i.e., 5 wt%), with ZrO₂ as the carrier and a Pd:Cu ratio of 1:1, demonstrated the highest degradation efficiency, with a degradation rate of 73.89%. This catalyst successfully reduced the average polymerization degree of condensed tannins from 9.5 to 2.48.