Aqueous-phase hydrodeoxygenation of lignin monomer eugenol: Influence of Si/Al ratio of HZSM-5 on catalytic performances

Abstract

Aqueous phase catalytic upgrading of phenolic monomers to hydrocarbons have been explored using Pd/C combined with HZSM-5 zeolite catalysts in the presence of H2. 2-Methoxyl-4-allylphenol (eugenol), which consists of methyl ether bond, hydroxyl group, aromatic ring and propyl olefin bond, was chosen as a classic lignin model compound. This research focuses on the relationship between the acidity of zeolites and the deoxygenation activities basis on the hydrodeoxygenation (HDO) of eugenol. The results indicated that the decrease of Si/Al ratio resulted in the increase of the acidity of the zeolites, which significantly influenced their catalytic performance for product distributions. Over the HZSM-5 (Si/Al=12.5) catalyst, the 2-methoxyl-4-propylphenol conversion of 86.5% and the hydrocarbon selectivity of 73.4% were obtained with the HDO of eugenol under 513K and 5MPa hydrogen pressure. Owing to the lower selectivity of hydrocarbon with HZSM-5 (Si/Al=50) as acidic catalyst, the pore treatment was used to enlarge the outer surface of zeolite. After modified by alkali-treatment, much more acid active sites were provided for feasible accessibility of oxygenated reactants. The selectivity of hydrocarbons was improved by the alkaline treatment of HZSM-5 zeolite with 0.3molL−1 sodium hydroxide solution.