Transition-metal carbides multifunctionality and durability has led to increased research into these materials as substitutions for traditional noble metal catalysts for reactions such as CO2 reduction or hydrodeoxygenation of lignocellulosic biomass. Current carbonization techniques require high temperatures (600 – 900 oC) with flowing H2 and carbon sources such as methane or light alkanes are commonly used to synthesize transition metal carbides, presenting high cost, safety, and environmental challenges which will impact the commercial viability of these materials for biomass catalytic conversion processes. Here we present a carburization-free amine-gel based strategy to produce molybdenum carbide (MoCx) with control over catalytically relevant physical properties. Utilizing polyethyleneimine or oleylamine, MoCx catalysts were synthesized with tunable crystalline phases and physico-chemical properties. Through manipulation of the molar ratios of amine to MoCl5 precursor, pure β-Mo2C and α-MoC1-x were obtained. Significant increases in total surface area were observed compared to traditionally carburized MoCx materials with an order of magnitude higher micropore volume observed when higher concentrations of the dendritic polyethyleneimine polymer were used. Additionally, the concentration and identity of amine used to form the carbide affected the total acid site and metallic-like hydrogen activation site counts (H*), as determined by NH3 TPD and H2 chemisorption respectively. Testing with the probe reaction of ethylene dehydrogenation allowed for the assessment of these carburization-free MoCx for applications such as the thermochemical conversion biomass to fuels and chemicals. Ethane site time yields for MoCx made with polyethyleneimine were higher than traditionally carburized MoCx materials, indicating more isolated Mo atoms in these materials utilize Mo sites more effectively. These findings demonstrate the tunability of these transition metal carbide materials through milder condition synthesis techniques, allowing for further diversification of their applications for biomass-based conversion processes.

Carburization free synthesis of MoCx with tunable structural and active site properties for catalytic applications

ACS Spring Meeting 2021

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