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Developing a New Array of Sustainable Hydrotalcites as Catalysts for the Selective Reductive Disassembly of Lignin Model Compounds


Nearly completely reliant on petroleum for organic platform chemicals, we are in desperate need of a more sustainable source. Lignin, a renewable, abundant, oxygen and aromatic rich biopolymer, is an exceptional potential source of chemical feedstocks. Previous studies in our laboratory have shown that copper doped porous metal oxides (CuPMOs) in supercritical methanol (s.c.-MeOH) catalyze the conversion of lignins and lignocellulose composites such as sawdust to organic liquids without the formation of char. Due to the high complexity of lignin, maintaining aromatic content while achieving full conversion continues to be a challenge. Here we present the ongoing efforts towards understanding the reactivity and selectivity of lignin model compounds through catalyst modification.

First we examine the effects of doping the CuPMOs with a series of lanthanides (Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) with Phenyl β-D glucopyranoside (PDG), a model compound with a variety of linkages more reminiscent of cellulose. Then we discuss the effects of introducing samarium(III), homogenously and heterogeneously, and formic acid, into the catalytic system. The models studied are benzyl phenyl ether, 2-phenylethyl phenyl ether, diphenyl ether, biphenyl, and 2,3-dihydrobenzofuran, which are respective mimetics of the α-O-4, β-O-4, 4-O-5, 5-5, and β-5 linkages characteristic of lignin. Also, briefly investigated as a substrate is poplar organosolv lignin. Next, we examine a niobium doped catalyst with α-O-4 benzyl phenyl ether, phenol, o-cresol, m-cresol, dimethylphenol and dimethylanisole towards selective methylation. Finally we investigate a molybdenum doped catalyst with α-O-4 linkage benzyl phenyl ether, β-5 linkage 2,3 dihydrobenzofuran, methyl p-toluene sulfonate and benzyl mercaptan to monitor the stability of the catalyst in the presence of sulfur. We discuss the aromaticity of the reaction products can be preserved through selective catalytic modifications.

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