Propylphenol to Phenol and Propylene over Acidic Zeolites: Role of Shape Selectivity and Presence of Steam

This contribution studies the steam-assisted dealkylation of 4-<i>n</i>-propylphenol (4-<i>n</i>-PP), one of the major products derived from lignin, into phenol and propylene over several micro- and mesoporous acidic aluminosilicates in gas phase. A series of acidic zeolites with different topology (<i>e.g</i>., FER, TON, MFI, BEA, and FAU) are studied, of which ZSM-5 outperforms the others. The catalytic results, including zeolite topology and water stability effects, are rationalized in terms of thermodynamics and kinetics. A reaction mechanism is proposed by (<i>i</i>) analyzing products distribution under varying temperature and contact time conditions, (<i>ii</i>) investigating the dealkylation of different regio- and geometric isomers of propylphenol, and (<i>iii</i>) studying the reverse alkylation of phenol and propylene. The mechanism accords to the classic carbenium chemistry including isomerization, disproportionation, transalkylation, and dealkylation, as the most important reactions. The exceptional selectivity of ZSM-5 is attributed to a pore confinement, avoiding disproportionation/transalkylation as a result of a transition state shape selectivity. The presence of water maintains a surprisingly stable catalysis, especially for ZSM-5 with low acid density. The working hypothesis of this stabilization is that water precludes diphenyl ether(s) formation in the pores by reducing the lifetime of the phenolics at the active site due to the high heat of adsorption of water on H-ZSM-5, besides counteracting the equilibrium of the phenolics condensation reaction. The water effect is unique for the combination of (alkyl)­phenols and ZSM-5

Production of C₅/C₆ Sugar Alcohols by Hydrolytic Hydrogenation of Raw Lignocellulosic Biomass over Zr Based Solid Acids Combined with Ru/C

Producing chemicals from lignocellulosic biomass is important in view of the huge availability of biomass and positive environmental significance by reducing carbon emission due to fast carbon cycle during biomass growth and applications. Here, we prepared zirconium based solid acids for hydrolytic hydrogenation of raw lignocelluloses to coproduce C₅/C₆ sugar alcohols (the important platform for downstream chemicals and fuel production) as combined with commercial Ru/C. Among these solid acids, the amorphous zirconium phosphate (ZrP) presented the largest acidic sites, with medium and strong acidity as the majority, showing the highest goal sugar alcohols yield of 70% at optimal reaction conditions. During pennisetum transformation, this combined catalyst was reusable despite the activity of the second run being lower than the initial one, and the activity could be recovered by recalcination of spent ZrP. The primary structure of surviving lignin remained after cellulose and hemicellulose were converted, showing the significance for fractional biomass applications if considering the further transformation of lignin