Oxidative Dehydrogenation of Cyclohexane on Cobalt Oxide (Co 3 O 4 ) Nanoparticles: The Effect of Particle Size on Activity and Selectivity Eric C. Tyo 1 , Chunrong Yin 2 , Marcel Di Vece 1 , Gihan Kwon 2 , Sungsik Lee 3 , Sönke Seifert 3 , Randall E. Winans 3 Stefan Vajda 1,2,4 1. Yale University, Department of Chemical and Environmental Engineering, New Haven, CT. 2. Materials Science Division, 3. X-ray Sciences Division, and 4. Center for Nanoscale Materials, Argonne National Laboratory, IL. The catalytic dehydrogenation of cyclohexane is a critical step in the reforming of naphtha, and in addition, important in the commercial production of benzene where significant quantities of cyclohexane that remain in the product stream must be removed at a considerable expense 1 . The proper application of nanoparticles in catalytic systems has provided a unique ability to tailor catalytic materials in ways previously unforeseen; and as such, interest has developed in the application of cobalt and cobalt oxides as an alternative catalyst for noble metals. For example, investigations of cobalt nanoparticles determined a strong metal-support effect for oxidized Co 27 in the oxidative dehydrogenation of cyclohexene 2 . In this work we investigate the catalytic properties of 3-7nm vs. 8-15nm Co 3 O 4 nanoparticles deposited on ALD formed Al 2 O 3 supports with respect to cyclohexane oxidative dehydrogenation to benzene. The Co 3 O 4 3-7nm and 8-15nm particles were formed through a surfactant free preparation utilizing Co(CH 3 COO) 2 x4H 2 O and ammonia as the starting material (by the Flytzani- Stephanopoulos group at Tufts University). Temperature programmed reaction (TPRx) was performed in combination with in-situ grazing incidence small angle x-ray scattering (GISAXS) and grazing incidence x-ray absorption spectroscopy (GIXAS) investigations at the Sector 12- ID-C Beam Line of the Advanced Photon Source at ANL to study catalytic activity while observing changes in morphology and chemical state 3 . The GISAXS analysis found reorganization to occur in groups of particles yet no further agglomeration to larger sizes or sintering while GIXAS showed the 8-15nm particles began with a mixed CoO and Co 3 O 4 phase that aged to become entirely Co 3 O 4 in nature after heating in an oxygen rich environment. TPR x analysis determined the 3-7nm particles were more active for the creation of benzene as the turnover rate was 5 times greater than the 8-15nm particles with the greatest activity occurring at 300°C. Acknowledgments: This work was supported by the US Department of Energy, BES Materials Sciences, under Contract DE-AC-02-06CH11357, with UChicago Argonne, LLC, operator of Argonne National Laboratory. The use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE- AC02-06CH11357. References: 1. Dummer, N. F.; Bawaked, S.; Hayward, J.; Jenkins, R.; Hutchings, G. J., Catal. Today 2010, 154, 2-6. 2. Lee, S.; DiVece, M.; Lee, B.; Seifert, S.; Winans, R.; Vajda, S., Physical Chemistry Chemical Physics 2012, 14 (26), 9336-9342. 3. Lee, S.; Lee, B.; Seifert, S.; Vajda, S.; Winans, R. E., Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment 2011, 649 (1), 200-203.