Efficient Cu-based catalysts for the selective demethoxylation of guaiacols

Lignin is an attractive feedstock for low molecular weight biobased phenols using depolymerization strategies such as reductive catalytic fractionation or fast pyrolysis. Such strategies often yield a product mixture enriched in lignin-derived monomers with methoxy substituents. Selective catalytic hydrodeoxygenation (HDO) is an effective methodology to demethoxylate these monomers into valuable alkylated phenols. Here, we report the use of non-precious Cu based catalysts supported on SiO_2, ZrO₂, TiO₂ (various forms), MoO₃-ZrO₂, and MoO₃-TiO₂ in a continuous fixed-bed reactor at elevated temperature and pressure (300–360 °C, 10 bar) for the selective demethoxylation of guaiacol. Among the various catalysts, Cu/TiO₂-P25 was found to be an effective and highly stable catalyst (100 h on stream) with a selectivity of 87% to demethoxylated compounds like phenol and cresols at a guaiacol conversion of 98%. A correlation was found between the oxygen storage capacity of the support (TiO₂-P25, TiO₂-A HSA, TiO₂-R, and MoO₃-TiO₂) and guaiacol conversion, indicating that this property plays a role in the catalytic cycle. Besides, the demethoxylation of 4-n-propylguaiacol and a realistic guaiacol-rich feed isolated from a representative pyrolysis oil was successfully demonstrated. 87% of the guaiacols present in the feed were converted to demethoxylated phenols with a selectivity of 81%.