Catalytic fast pyrolysis of rice straw to aromatic compounds over hierarchical HZSM-5 produced by alkali treatment and metal-modification

The synthesis of highly selective catalysts for the catalytic fast pyrolysis (CFP) of biomass into valuable aromatics remains a challenge. This report describes the synthesis of hierarchical ZSM-5 catalysts by the NaOH desilication of conventional HZSM-5 for the CFP of rice straw to aromatics in a Tandem μ-reactor system coupled directly to a GC/MS equipped with FID and TCD. Catalysts were treated with a mild HCl wash and metal loading to increase the catalytic activity and reduce the deactivation. The effects of acidity, mesoporosity and incorporation of metals on the production of aromatics were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption and desorption (N₂-BET) and temperature-programmed desorption of NH₃ (NH₃-TPD). The highest total acidity, especially the strong acidity, of the hierarchical ZSM-5 treated by 0.2 and 0.4 NaOH followed by HCl washing (AHZ-0.2 and AHZ-0.4) gave the highest yields of aromatics. Suitable mesopores introduced by alkali treatment enhanced mass transfer of reactants, increasing the yield of aromatics. Finally, the loading of a suitable amount of Ni and Cu produced more aromatics than standard HZSM-5 due to the improved decarboxylation/decarbonylation reactions leading to higher yields of olefins.