PNNL

Abstract

The mechanistic steps that underlie the formation of higher hydrocarbons in catalytic carbon monoxide (CO) hydrogenation at atmospheric pressure over cobalt-based catalysts (Fischer-Tropsch synthesis) have remained poorly understood. We reveal nonisothermal rate-and-selectivity oscillations that are self-sustained over extended periods of time (>24 hours) for a cobalt/cerium oxide catalyst with an atomic ratio of cobalt to cerium of 2:1 (Co2Ce1) at 220 degrees C and equal partial pressures of the reactants. A microkinetic mechanism was used to generate rate-and-selectivity oscillations through forced temperature oscillations. Experimental and theoretical oscillations were in good agreement over an extended range of reactant pressure ratios. Additionally, phase portraits for hydrocarbon production were constructed that support the thermokinetic origin of our rate-and-selectivity oscillations. Funding: R.Z. acknowledges financial support from Chambroad Chemical Industry Research Institute Co., Ltd. R.Z. and Y.W. acknowledge financial support from the US Department of Energy Basic Energy Sciences Catalysis Science program, grant DE-FG02-05ER15712. N.K. thanks the National Science Foundation for financial support under contract no. CBET-1438227. Author contributions: R.Z. performed the experiments and contributed to the drafting of the manuscript. Y.W. provided advice and contributed to the final drafting of the manuscript. P.G. performed the theoretical calculations and contributed to the drafting of the manuscript. N.K. initiated and supervised the project and also took the lead in drafting the manuscript.