A review on the catalytic pyrolysis of lipids to produce alternative aromatic hydrocarbons: Synthesis of hierarchically porous zeolites and aromatization mechanism

Catalytic pyrolysis of non-edible lipids to produce alternative aromatic hydrocarbons is an important strategy to reduce CO₂ emission in the petrochemical industry, which is hindered by coking and quick deactivation of zeolites. Hierarchically porous zeolites can mitigate this problem. In this review, the catalytic pyrolysis of non-edible lipids for aromatic hydrocarbons and the mechanism of aromatization are comprehensively summarized. First, the synthesis of hierarchically porous zeolite catalysts, including hard template methods, soft template methods, and postprocessing methods, which are necessary for further discussion of catalyst applications and aromatization mechanisms, is discussed. Hierarchically porous zeolite catalysts, which retain the excellent catalytic activity and selectivity of microporous zeolites, can essentially and substantially improve mass transfer and diffusion efficiency in zeolites to avoid fast deactivation of catalysts due to coking. Second, the application of hierarchically porous zeolites in aromatic hydrocarbon production is summarized. The loading of metal oxides in hierarchically porous zeolites can largely improve the deoxygenation performance of oxygen-containing lipid feedstocks. This review also discusses the aromatization mechanism used during catalytic pyrolysis to produce renewable liquid products. The formation of olefins or unsaturated groups and dehydrogenation are the critical steps for aromatization. Future research can prioritize the synergistic interaction between micropores and mesopores in hierarchically porous zeolite catalysts. Efforts can also be directed towards rational modification of the acidity of catalysts through methods such as surface modification and support optimization. This review provides necessary information about technologies for the sustainable transformation from fossil fuel-based aromatic hydrocarbons to bio-based aromatic hydrocarbons.