Synthesis of phenol from degraded lignin using synergistic effect of iron-oxide based catalysts: Oxidative cracking ability and acid-base properties

The effects of ZrO2 and TiO2 incorporated into Fe2O3 matrix on oxidative cracking of degraded lignin and on the acid-base properties were investigated. After lignin degradation, cracking into lower-molecular-weight products was greatest using ZrO2-FeOX. Reactivity of the lattice oxygen was evaluated using H2-TPR, which revealed that the reactivity was improved. Thus, ZrO2-FeOX promoted oxidative decomposition of lignin to oligomers. In the cracking of 2-methoxyphenol, TiO2-FeOX and ZrO2-FeOX resulted in a 5-to 6-fold greater yield of phenol than the yield over Fe2O3. According to Mulliken population analysis, the charge density difference between Fe-O increased by ca. 12% in TiO2-FeOX and ZrO2-FeOX as compared with Fe2O3. This result suggests that addition of TiO2 and ZrO2 improved the acid-base properties of the catalyst, which promoted demethoxylation of 2-methoxyphenol. Thus, ZrO2-FeOX enhanced oxidative decomposition using its lattice oxygen that converted degraded lignin into lower molecule oligomers, followed by demethoxylation to produce phenol.

Automated summary

The effects of ZrO2 and TiO2 on the oxidative cracking of degraded lignin and on the acid-base properties were investigated in Fe2O3 matrix. ZrO2-FeOX showed the greatest cracking into lower-molecular-weight products and improved reactivity of lattice oxygen. TiO2-FeOX and ZrO2-FeOX resulted in significantly higher phenol yield in the cracking of 2-methoxyphenol compared to Fe2O3.