Lignin-Mediated Preparation of Hierarchical ZSM-5 Catalysts and Their Effects in the Catalytic Co-pyrolysis of Softwood Biomass and Low-Density Polyethylene Mixtures

Biomass-mediated modification in zeolite synthesis has outstanding potential in directing new porous structures and improved catalyst properties. This study reports the preparation of hierarchical ZSM-5 catalysts by a successive treatment of desilication and lignin-mediated reassembly. The changes in physicochemical properties of the hierarchical ZSM-5 including crystallinity, porosity, acidity, and morphology were characterized by foreseeing the application of lignin as a green template. The hierarchical pore system containing moderately strengthened acidity was directed with 1 wt % lignin addition, which attained more desirable products and less solid residue than the microporous ZSM-5. The catalytic conversion of biomass and plastic feedstocks was performed using analytical and bench-scale reactor systems to evaluate desired mixtures and product distribution. It was found that the surface and intracrystalline mesopores in hierarchical ZSM-5 were beneficial for the conversion of macromolecules, such as aromatic oxygenates and long-chain hydrocarbons. While the plastic-derived olefins synergistically interacted with the biomass derivatives within the pyrolytic vapor, the hierarchical structure extended reactant accessibility from the catalyst surface into the microporous channels and internal acid sites.