(517h) Using Inelastic Neutron Scattering to Probe the Active Site for Cobalt-Copper Catalyst for the Conversion of Syngas to Higher Oxygenates

Cobalt-copper catalysts have been proposed for the synthesis of ethanol and higher oxygenates as a substitute of Rh and other high-cost noble metal catalysts^1,2. Two types of sites with atomic proximity are needed to form higher oxygenates: one to dissociate CO and a second to insert CO to the intermediates to form the CH_xCO intermediate ³. Metallic cobalt is responsible for CO dissociation, while the nature of the site for CO insertion is still under study. We have utilized inelastic neutron scattering (INS) at the VISION beamline at SNS to probe intermediate surface species of this cobalt-copper catalyst. This unique technique allows for elucidation of mechanistic details of the CO insertion and subsequent CH_xCO intermediate formation on the metal surfaces (Co⁰, Co₂C and/or Cu⁰). XPS results show that the amount of surface carbon increases significantly after CO hydrogenation reaction. However, in-situ XRD profiles do not show any crystallinity changes of the catalyst in the presence of syngas at 250°C. For CuCoLa₂O₃, freshly reduced sample and post-reaction sample showed distinct XANES profiles. EXAFS results on used CuCoLa₂O₃ shows a peak at lower distance for the first Co-C coordination shells. Our INS spectra show several features at the low energy region (0-150 meV), which can be assigned as the vibration of the oxygenate intermediates on the surface, including methanol, ethanol and acetaldehyde. For instance, the peak at 40 meV is identical with the bending of C-C-O in the calculated spectrum for acetaldehyde. The experimental spectra are compared with the theoretical spectra of CH_xCO on different surfaces: Co⁰, Cu⁰, Co₂C and dual sites of Co⁰-Cu⁰ and Co⁰-Co₂C.

This work was sponsored through the Louisiana Consortium for Neutron Scattering supported by the U.S. Department of Energy under EPSCoR Grant No. DE-SC0012432 with additional support from the LA BOR. This research benefited from the use of the VISION beamline at ORNLâ??s Spallation Neutron Source, which is supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy under Contract No. DE-AC0500OR22725.