title: Bifunctional Molybdenum Polyoxometalates for the Combined Hydrodeoxygenation and Alkylation of Lignin-Derived Model Phenolics.
abstract: Reductive catalytic fractionation of biomass has recently emerged as a powerful lignin extraction and depolymerization method to produce monomeric aromatic oxygenates in high yields. Here, bifunctional molybdenum-based polyoxometalates supported on titania (POM/TiO2) are shown to promote tandem hydrodeoxygenation (HDO) and alkylation reactions, converting lignin-derived oxygenated aromatics into alkylated benzenes and alkylated phenols in high yields. In particular, anisole and 4-propylguaiacol were used as model compounds for this gas-phase study using a packed-bed flow reactor. For anisole, 30 % selectivity for alkylated aromatic compounds (54 % C-alkylation of the methoxy groups by methyl balance) with an overall 72 % selectivity for HDO at 82 % anisole conversion was observed over H3PMo12O40/TiO2at 7 h on stream. Under similar conditions, 4-propylguaiacol was mainly converted into 4-propylphenol and alkylated 4-propylphenols with a selectivity to alkylated 4-propylphenols of 42 % (77 % C-alkylation) with a total HDO selectivity to 4-propylbenzene and alkylated 4-propylbenzenes of 4 % at 92 % conversion (7 h on stream). Higher catalyst loadings pushed the 4-propylguaiacol conversion to 100 % and resulted in a higher selectivity to propylbenzene of 41 %, alkylated aromatics of 21 % and alkylated phenols of 17 % (51 % C-alkylation). The reactivity studies coupled with catalyst characterization revealed that Lewis acid sites act synergistically with neighboring Brønsted acid sites to simultaneously promote alkylation and hydrodeoxygenation activity. A reaction mechanism is proposed involving activation of the ether bond on a Lewis acid site, followed by methyl transfer and C-alkylation. Mo-based POMs represent a versatile catalytic platform to simultaneously upgrade lignin-derived oxygenated aromatics into alkylated arenes.
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Anderson
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Anthony
authors.initials: A
authors.lastname: Crisci
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Karthick
authors.initials: K
authors.lastname: Murugappan
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Yuriy
authors.identifier: 0000-0002-0025-4233
authors.initials: Y
authors.lastname: Román-Leshkov
mesh_terms: D000478:Alkylation; D006859:Hydrogen / Q000737:chemistry*; D008031:Lignin / Q000737:chemistry*; D008956:Models, Chemical; D008982:Molybdenum / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D017973:Tungsten Compounds / Q000737:chemistry*; D000099294:Polyoxometalates
chemical_list: D006859:Hydrogen; D008031:Lignin; D008982:Molybdenum; D010636:Phenols; D017973:Tungsten Compounds; C102296:polyoxometalate I; D000099294:Polyoxometalates
keywords: alkylation; biomass; hydrodeoxygenation; molybdenum; polyoxometalates