(617do) Cobalt-Copper Alloy Nanoparticle Catalysts for Higher Alcohol Synthesis from Syngas

Authors: 
Snider, J., SLAC National Accelerator Laboratory
Mendes, L., Stanford University
Fleischman, S. D., SLAC National Accelerator Laboratory
Kibsgaard, J., Stanford University
Aranda, D., Federal University of Rio de Janeiro
Jaramillo, T. F., Stanford University
Higher alcohols, those with two or more carbons, are of great interest for their applications as both liquid fuels and synthetic feedstocks. While synthesis gas (a mixture of CO and H2) has long been used to synthesize long-chain hydrocarbon fuels via the Fischer-Tropsch process, an analogous process for the direct production of higher alcohols from syngas still faces many challenges. Theoretical studies and prior work in the field have shown that cobalt-cobalt alloys are among the most selective catalysts for the higher alcohol synthesis reaction [1-3], but further improvements are necessary. In this work, the authors synthesize cobalt-copper nanoparticles via a controlled liquid-phase synthesis to give greater control of particle size and composition and evaluate higher alcohol synthesis performance of the catalysts.

Co2.5Cu alloy nanoparticles were synthesized by a polyol synthesis in which metal acetates are reduced in refluxing diethylene glycol with a polyvinylpyrrolidone capping agent to control particle size. The nanoparticle catalysts were then supported on a variety of metal oxides and tested in a packed bed reactor under Fischer-Tropsch conditions (250° C, 40 bar, 2:1 H2:CO) to evaluate their activity and selectivity. The best performing sample, supported on alumina, had a 11.3% carbon selectivity towards higher alcohols, primarily ethanol. Nanoparticle composition and structure, both before and after reaction, were confirmed ex situ using a combination of transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). A consistent alloy phase and composition was observed prior to reaction, suggesting the synthesis successfully reduced the metal precursors to the cobalt-copper alloy phase. After reaction, new phases were observed to have formed via metal segregation and cobalt carbide formation. The alumina-supported sample, which had the highest performance, also showed minimal formation of these new phases, indicating a possible correlation between the observed performance and the extent of alloy degradation. Future investigations are focused on improving the stability of the desired alloy phase under reaction conditions.

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