Selective conversion of guaiacol to alkylphenols in supercritical ethanol over acid-modified and re-doped Mo/HBEA

Phenolic derivatives rich in hydroxyl and methoxy groups, obtained from lignin depolymerization, possess significant potential for conversion into alkylphenols. A critical challenge in the alkylation process lies in maintaining the phenolic hydroxyl structure while selectively cleaving the C-O bond. This study demonstrates a method for the selective conversion of guaiacol into substituted alkylphenols in supercritical ethanol, utilizing Mo/HBEA catalysts modified through acid treatment and Re doping. This approach facilitates precise demethoxylation by breaking the C-O bond while simultaneously introducing alkyl groups to form substituted alkylphenols. The effects of acid treatment on the catalyst's surface acidic sites and the influence of Re doping on Mo properties were systematically investigated. The 2HCA-Mo/HBEA catalyst achieved an alkylphenol selectivity of 85.4%, while the Mo5Re2/HBEA catalyst reached 85.6%. Compared to 5Mo/HBEA, these catalysts exhibited an improvement in alkylphenol selectivity by 3.5% and 3.7%, respectively, along with a more focused product distribution. Acid treatment induced significant dealumination and realumination effects via citric acid, leading to notable changes in the acidic sites of the catalyst. Specifically, the Lewis acidity of 2HCA-Mo/HBEA increased by 6.4% relative to 5Mo/HBEA. Analysis of alkylation products, intermediates, and the evolution of functional groups revealed the conversion pathway of guaiacol, offering a theoretical reference for the high-value utilization of lignin.