Supported nickel catalysts are widely used in hydrocarbon reforming for hydrogen production. However, coke formation often leads to the rapid deactivation of Ni-based catalysts. In this work, we applied Mo dopants into Ni catalysts for gasoline partial oxidation. The Ni-Mo catalyst showed high activity and stability with isooctane conversion of 97% and H2 yield of 73%. Whereas rapid deactivation was observed for monometallic Ni catalyst. XRD, TGA and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. XRD data also showed a bigger average Ni crystallite size for Ni catalyst compared to that of Ni-Mo catalyst following the partial oxidation reaction, which indicates that the higher degree of sintering took place for the sample without Mo. To examine the effects of the addition of Mo in Ni/YSZ on preventing coking during the partial oxidation of isooctane reaction, CH cleavage and CC coupling reactions over Ni and Ni-Mo catalysts were studied using DFT calculations. The results showed that Ni-Mo catalysts enhanced carbon-tolerance by increasing activation barriers of CH cleavage and CC coupling in the presence of Mo as compared with pure Ni/YSZ system. The DFT calculations further showed that in the presence of Mo, the d-band center of Ni-Mo/YSZ shifts towards Fermi level. Consequently, the adsorbed C atoms have more electronic interaction with the Ni atoms located nearby Mo. Hence, the diffusion of C atoms is harder over the Ni atoms in the presence of Mo. This leads to more carbon-tolerant Ni-Mo/YSZ catalyst than Ni/YSZ. Based on this finding, Ni-Mo catalyst was used as an internal micro-reforming layer on top of conventional Ni-YSZ anode supported single cells. The single cell without the catalyst layer showed an unstable voltage and the overall cell performance exhibited a rapid degradation rate of 49 mV/h after 6 h of operation. By applying the catalytic reforming layer, the single cell displayed significantly improved stability with a low degradation rate during the 15 h test. The improved performance stability denoted the positive function of the catalytic layer for efficiently reforming complex hydrocarbon fuels in the anode and suppressing carbon deposition.

Enhancing the performance of partial oxidation of gasoline over Ni catalysts with Mo addition for SOFCs application: An experimental and DFT study

2019 Spring National Meeting

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