Stability improvement to a ruthenium catalyst for partial oxidation of methane

Abstract: Catalytic partial oxidation of methane (CPOM) is an energy-efficient alternative to steam reforming, the currently prevailing method for energy production from natural gas. Hulteberg Chemistry & Engineering AB has developed a catalyst for the partial oxidation of methane into syngas, for use in solid oxide fuel cells. In its current form, the catalyst rapidly deactivates, causing increased material cost and a need for frequent stopping of the process to regenerate the catalyst. This thesis focuses on improvements to the stability of the catalyst to increase its lifetime and thus commercial viability. Several new granular catalyst formulations were prepared and tested for activity, selectivity and stability in a lab-scale reactor. All catalysts were supported on magnesia-alumina and used low loadings of ruthenium as the main component of the active phase. Modifications were made to the support by adding magnesium, and to the active phase by doping with platinum or palladium. The activity tests showed that all tested catalysts were active for CPOM, with methane conversion and selectivity towards syngas close to the thermodynamic equilibrium. The activity was virtually unaffected by varying the space velocity from 10,000 to 160,000 h-1. Long-term stability tests found that the addition of 10 wt% magnesium to the catalyst support significantly increased stability, although deactivation continued at a reduced rate even after 100 hours. Through kinetic modelling, a catalyst half-life of 123 hours was determined for the modified catalyst compared to 69 hours for the standard catalyst. Characterization of the long-term tested catalysts by pulse chemisorption found that the modified catalyst had a surface area of 0.21 m2/gsample, compared to 0.14 m2/gsample for the standard catalyst, indicating that addition of magnesium increases stability during the calcination and reduction. Overall, the increased stability by the addition of magnesium gives a good starting point for further research. Several prepared formulations are yet to be long-term tested and characterized; doing this could result in further improvements to catalyst stability.