(769g) Designed Synthesis of Co3O4 Total Oxidation Catalysts

In recent years, nanocrystalline cobalt oxides have received increased attention due to their unprecedented activity as low temperature CO oxidation catalysts and their potential for use in various hydrocarbon oxidation reactions. [1] However, despite high levels of interest in these materials and a growing body of work devoted to synthesizing size and shape controlled cobalt oxide nanostructures, observations of catalytic performance and reported structure-activity relationships are often varied. This is likely due to the multitude of Co₃O₄ catalytic properties, including lattice oxygen mobility, Co³⁺ reducibility and Co³⁺ surface enrichment related to the size, morphology, and faceting of the nanostructures. Additionally, the existence of mesoporous, polycrystalline, and defected Co₃O₄ nanostructures and the very diverse set of synthesis methodologies employed further confuses the elucidation of important structural properties and synthesis conditions. [2]â??[4] Because the intricate relationships between synthesis, structural properties, and performance in various systems are not exhaustively understood, our ability to utilize Co₃O₄ oxidation catalysts under various reaction schemes and operating conditions is limited by how quickly and precisely we can explore the relevant parameter space.

In our work, a statistical design and analysis platform was used to develop cobalt oxide based oxidation catalysts prepared via one pot metal salt reduction, a widely used and versatile synthesis technique. An emphasis was placed upon understanding the effects of synthesis conditions, such as heating regimen and Co²⁺ concentration on the metal salt reduction mechanism as well as the resultant nanomaterial properties, such as size, crystal structure, and crystal faceting. This was accomplished by carrying out XRD, TEM, and FTIR studies on synthesis intermediates and products. Additionally, high-throughput experimentation was employed to study and optimize the performance of Co₃O₄ oxidation catalysts over a wide range of synthesis and reaction conditions using a 16-channel fixed bed reactor equipped with a parallel infrared imaging system. Specifically, Co₃O₄ nanomaterials of varying properties were evaluated for their performance as CO oxidation and hydrocarbon oxidation catalysts. Figure-of-merits including light-off temperature, activation energy, and stability, which were measured and mapped back to the aforementioned catalyst properties and synthesis conditions. Statistical analysis methods were used to elucidate significant property-activity relationships as well as the design rules relevant in the synthesis of active catalysts.

References

[1] X. Xie, W. Shen, Nanoscale, vol. 1, no. 1 (2009) pp. 50.

[2] L. Hu, Q. Peng, L. Yadong, J. Am. Chem. Soc. 130 (2008) pp 16136â??16137.

[3] C. Liu, Q. Liu, L. Bai, A. Dong, G. Liu, S. Wen, J. Mol. Catal. A Chem. 370 (2013) pp 1â??6.

[4] X. Xie, Y. Li, Z.-Q. Liu, M. Haruta, W. Shen, Nature, vol. 458, no. 7239 (2009) pp 746-749.