Mild modification of lignin pyrolysis vapors by metal oxide catalysts: A comparative study with molecular sieve catalysts

Compared with strongly acidic molecular sieve catalysts, metal oxide catalysts are less prone to deactivation by coking due to their mild acid-base properties. Several metal oxides (Al2O3, MgO, CaO, CuO, Fe2O3, NiO, ZnO, ZrO2, TiO2 and CeO2) were selected for mild catalytic pyrolysis of lignin and compared with molecular sieve catalysts (MCM-41, HZSM-5, ZSM-5). Among the metal oxide catalysts studied, CuO, Fe2O3 and TiO2 inhibited the formation of acids/alcohols (1–2%) and promoted the production of hydrocarbons (15.31%, 20.17% and 28.83%, respectively). Especially when TiO2 catalyst was added, the proportion of hydrocarbons reached the highest (28.83%), but it inhibited the production of phenols (3.3%). The presence of CuO promoted the production of phenols (9.70%), showing a good deoxidation performance. Compared with the oxide catalysts, the addition of molecular sieve catalysts only resulted in 2 ~ 3% phenols. Compared with strongly acidic molecular sieve catalysts, metal oxide catalysts showed certain catalytic activity in deoxidation and cracking, and showed some advantages in the formation of phenols.