Novel Hierarchical Cerium-Incorporated MFI Zeolite Catalysts for the Catalytic Fast Pyrolysis of Lignocellulosic Biomass

Abstract

We report the synthesis of a new multifunctional mesoporous zeolite catalyst with cerium incorporated within the framework. This catalyst shows a shift in selectivity from typical HZSM-5 products (benzene, toluene, and xylenes) to valuable oxygenated chemicals (furans, ketones, aldehydes) during the catalytic fast pyrolysis of lignocellulosic biomass. The cerium-incorporated hierarchical zeolite was synthesized using a dry-gel method followed by steam-assisted crystallization. The catalyst was characterized by X-ray diffraction (XRD), N 2 physisorption, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), NH 3 temperature-programmed desorption (NH 3 -TPD), diffuse reflectance FT-IR, and diffuse reflectance UV−Visible (UV−Vis) spectroscopy. The multifunctional catalyst was then studied in the catalytic fast pyrolysis of glucose (a carbohydrate model compound) at 600 °C. The new catalyst was compared with a mesoporous HZSM-5 catalyst with incipient wetness incorporated cerium and an ion exchanged commercial HZSM-5 catalyst. These catalysts behaved similarly to the parent materials, but the new catalyst with cerium incorporated into the zeolite framework exhibited selectivities greatly shifted from aromatics to oxygenated chemicals. Furthermore, this catalyst produced less coke (40 wt % or 11 mol % carbon) and increased CO production through decarbonylation reactions. These properties persisted after catalyst regeneration and recycle.

Catalytic Stepwise Pyrolysis of Technical Lignin

“…The volume in the pores can prevent repolymerization and coke formation. The acid sites can promote the cleavage of C-O and C-C bonds and catalytic transformation of intermediates through reactions like dealkylation, dehydroxylation, demethoxylation, aromatization, dehydration, cracking, isomerization, and oligomerization (Mullen and Boateng 2010;Neumann and Hicks 2012;Yu et al 2012). Therefore, the relative content of aromatic hydrocarbons increased while the relative content of total phenolic compounds decreased in the catalytic stepwise pyrolysis process.…”

“…Different kinds of catalysts have been adopted in the pyrolysis reactor, such as metal chlorides, metal oxide catalyst, and zeolites (Mullen and Boateng 2010;Neumann and Hicks 2012;Asadieraghi et al 2015;Chen et al 2015b). Zeolites are the most commonly used catalysts in the literature for catalytic pyrolysis of lignin because of their special pore structure and acid sites that can induce oligomerization, dehydration, deoxygenation, demethoxylation, and aromatization reactions .…”

A survey of catalysts for aromatics from fast pyrolysis of biomass

“…Additionally, a large fraction (>90%) of total coke is classified as "soluble" coke, which is continuously thermally disintegrated, especially at reaction temperatures of 500-550 • C [42,43]. The remaining is "insoluble" coke that deposits on the external surface and inside the pores, where strong acidic sites with small apertures or cages exists [35,44]. Thus, in a scaled-up continuous process, much of the soluble coke will be continuously removed from the catalyst surface, ensuring longer catalyst active time before regeneration is required.…”

The Efficient and Sustainable Pyrolysis and Gasification of Biomass by Catalytic Processes

“…Jeon et al [107] reported that large pore mesoporous material (such as SBA-15, Pt/SBA-15, AlSBA-15, and Pt/AlSBA-15) could promote the pyrolysis of cellulose, hemicellulose, and lignin. It was found that AlSBA-15 had a considerable amount of acid sites that are advantageous for dehydration, cracking, and decarbonylation reactions [107,108].…”