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Methane decomposition and partial oxidation in a cyclic mode over supported Co and Ni catalysts Li, Jerry Kai Hsu

Abstract

CH₄ decomposition to produce C and H₂, followed by partial oxidation of the C has been investigated in a cyclic process over supported Co and Ni catalysts. The catalysts are characterized by TPR, BET surface area, XRD and TEM. A tapered element oscillating microbalance (TEOM), used in the present study to monitor the reactions, operates as fixed bed micro-reactor that can measure the real time mass change of the catalyst during reaction. Product gases from the TEOM reactor were analyzed continuously by a quadrupole mass spectrometer. Ni catalysts showed a better activity and stability compared to Co catalysts. At 773 K, the initial CH₄ decomposition rate at 773 K of Ni catalysts (1.23 x 10⁻⁵ mol/(g·s)) was faster than Co catalysts (9.44 x10⁻⁶ mol/(g·s)). Steady H₂ production and initial CH₄ decomposition rate were achieved for 6 cycles over Ni catalysts, but complete deactivation was observed after the 2nd cycle over Co catalysts. A time delay of up to 2500 seconds occurred between the introduction of CH₄ and the production of H₂ on Co catalysts but no such induction period occurred for Ni catalysts. Catalysts can also be regenerated by carbon removal using CO₂. The CO to H₂ ratio during CH₄ decomposition decreased compared to carbon removal with O₂ since formation of NiO was reduced. However, the rate of carbon removal by CO₂ was too slow for any practical application of the cyclic reaction. The H₂ production profile obtained during the first cycle of CH₄decomposition on a freshly loaded Ni catalyst was in qualitative agreement with that predicted by the deactivation model proposed by Zhang and Smith (2005). The H₂ production rate reached a maximum initially, decreased rapidly and then increased slowly before decreasing again. The statistical analysis of a fractional factorial design of experiments for the CH₄ decomposition, partial oxidation cyclic reaction indicated that higher H₂ production rate can be obtained by conducting the CH₄ decomposition at a higher temperature with a shorter duration. No significant effects were identified for selectivity to CO during oxidation and the overall quantity of CO produced during CH₄ decomposition.

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