(560ej) Impact of Ni and Mg Loadings on Dry Reforming Performance of Pt/Ceria-Zirconia Catalysts

This work investigates the impact of metal loadings on a series of low temperature Pt/Ce_0.6Zr_0.4O₂ dry reforming catalysts. These catalysts containing either Ni and/or Mg were synthesized using the coprecipitation and incipient wetness method. Characterization techniques such as powdered X-ray diffraction, N_2-pysisorption analysis, H₂-temperature programmed reduction (H₂-TPR) and CO₂-temperature programmed desorption (CO₂-TPD) were used to identify the catalyst properties. The H₂-TPR profiles showed that increasing Ni content enhanced the reducibility of the metal oxide support while the opposite effect was observed with increasing Mg. The CO₂-TPD indicated that the presence of Mg improved the catalyst basicity. The catalyst activity for dry reforming was tested using temperature programmed experiment and the results obtained indicated that Ni enhances CH₄ conversion at lower temperatures while Mg decreases CH₄ conversion and improves the product selectivity (H₂: CO). Among the catalysts investigated, the optimal loading of Ni and Mg were found to be 2.7 wt% and 0.50 wt%, respectively, when tested without the other. The coking rate of the 2.7Ni-CZO after a 10 h time on stream (TOS) study was 5.5E-4 g/gcat.hr whereas no coke was observed for the Mg-based catalyst. These results led to the synthesis of a combined catalyst (2.7Ni-0.50Mg-CZO). Coke formation was not detected on the combined catalyst due to the presence of Mg which improved the catalyst basicity, favored CO₂ dissociation and provided reactive oxygen species for carbon oxidation. The results obtained with the 2.7Ni-0.50Mg-CZO catalyst sample showed that the presence of both Ni and Mg in the catalyst composition is essential to obtain a balance between reactant conversions, H₂:CO ratio, and catalyst stability. The temperature required for 10% CH₄ conversion of the combined and isolated metal catalysts followed the trend; 2.7Ni-CZO < 2.7Ni-0.50Mg-CZO < 0.50Mg-CZO. The activation energy of the samples followed the trend; 2.7Ni-0.50Mg-CZO < 2.7Ni-CZO < 0.50Mg-CZO and were lower or comparable to those in literature. These samples gave low temperature activity with 10 % CH₄ conversions at temperature < 500 ℃ and this indicates their potential application in an intensified process involving both reforming and Fischer Tropsch synthesis.