Catalytic hydropyrolysis of lignocellulosic biomass to BTX and biofuels over zeolite beta based catalysts

Catalytic hydropyrolysis of eucalyptus leaves was investigated in a batch reactor over four catalysts (H-BEA, Ni/BEA, Ni/Fe-BEA and Fe/BEA). HBEA catalyst exhibited a higher monoaromatic hydrocarbons (MAHs) selectivity compared to non-catalytic pyrolysis. However, the selectivity to polyaromatic hydrocarbons (PAHs) was not significantly reduced by the addition of a protonic zeolite. The highest cycloalkanes selectivity (78.5%) was observed over Ni/BEA, owing to its high concentration of Ni sites as well as acid sites, facilitating the hydrogenation and ring-opening of polyaromatic hydrocarbons together with the hydrodeoxygenation of phenols. In contrast, the Ni/Fe-BEA exhibits the highest selectivity of MAHs, suggesting the Ni-Fe species facilitate the partial hydrogenation of PAHs and hydrogenolysis of phenols but restrict the further hydrogenation of aromatic monomers. Moreover, the reduction of CO to CH4 was restricted over Ni-Fe/BEA compared to Ni/BEA. A high selectivity of phenols and PAHs was detected over Fe/BEA due to the high oxophilicity but low hydrogenation activity of Fe species, hindering the hydrogenation of PAHs and HDO of phenols. The spent Ni/BEA and spent Ni/Fe-BEA catalysts exhibited a higher surface area and pore volume as well as lower mass of deposited carbon compared to spent HBEA and spent Fe/BEA catalysts, suggesting the catalyst deactivation was restricted by hydrogenation metal (Ni, Ni-Fe) and dissociated H species. Besides, high H2 pressure promoted the hydrogenation and ring-opening of polyaromatic hydrocarbons, and high reaction temperature hindered the hydrogenation of MAHs to cycloalkanes. The highest selectivity to MAHs (85.1%) with a 62% selectivity of BTEX was observed over Ni/Fe-BEA catalyst at 400 °C and an initial H2 pressure of 3.0 MPa.