Bimetallic Iron Molybdenum Phosphide Catalysts for Selective C-O Bond Cleavage of Lignocellulosic Biomass Model Compounds

Sustainable sources of hydrocarbon materials are important as global economies expand and existing supplies of fossil fuel hydrocarbon sources dwindle. A natural material to help meet this growing need is lignin, a biomass waste-product containing an abundance of aromatic compounds. Converting lignin into useable aromatic hydrocarbons is difficult due to the high bond energy of the C_AROMATIC-O bond in the polymer. A catalyst capable of selectively removing the oxygen atoms without hydrogenating the aromatic components would have value for removing a waste stream while providing an alternative hydrocarbon feedstock. Bimetallic catalysts are stable and capable of selectively cleaving C_AROMATIC-O bonds.

This dissertation details the synthesis, characterization and application of FeMoP for C_AROMATIC-O bond cleavage in lignin model compounds. Batch reactor studies were used to investigate the capability of FeMoP to selectively cleave the C_AROMATIC-O bond without hydrogenation. Flow reactor studies were conducted using FeMoP materials synthesized at varying temperatures to separate the effect of surface acidity from the influence of metal sites. Acidic catalysts were found to be more selective to aromatic products. Variation of the Fe:Mo ratio in Fe_XMo_2-XP catalysts (0.88 ≤ X ≥ 1.55) supported study of the effect of catalyst acidity and hydrogenation capability, the most acidic material was most selective. Once the most selective FeMoP-based catalysts were identified, combinations of transition metals (Cr, Mn, Fe, Co, Ni, and Ru) were added to the bimetallic system to evaluate the deoxygenation rate with the aromatic selectivity. FeMoP was the most selective, but slowest, catalyst. Co, Ni, and Ru catalysts produced significantly higher rates but catalyzed both a direct C_AROMATIC-O bond cleavage pathway and a ring hydrogenation followed by dehydration pathway. Using a range of synthesis parameters and metal combinations indicated that the resulting bimetallic phosphide catalysts materials can be tuned to control rate, selectivity, and reaction pathway.