Catalyst development for dry reforming of methane and low-temperature water-gas shift reaction
thesisposted on 15.01.2017, 23:11 by Kam, Rothman Yu-Fai
Both dry reforming of methane (DRM) and low-temperature water-gas shift (LT-WGS) processes can be integrated into a fuel cell plant and are utilised for the production of hydrogen as an important energy source for fuel cells. Improvement of current catalytic systems, and identification and development of alternative catalysts for DRM and LT-WGS reactions have formed the basis of this study. In the first stage of the work, the influence of WO3 on a Pt/CeO2 catalyst was investigated for the dry reforming of methane. It was found that Pt/CeO2 catalysts loaded with WO3 at 10 mol% to 20 mol% were very stable during 20 hours of dry reforming of methane operation in comparison to a commercial Ni catalyst. However further addition of WO3 (>70%) promoted coking on the Pt/CeO2 sample, ultimately leading to catalyst deactivation. It was also desirable to develop catalysts with higher activity to reduce operating cost, thus the physicochemical properties of different materials were assessed to identify parameters important for LT-WGS activity. Copper catalysts on metal oxide support (CeO2, ZnO, TiO2, SiO2, Al2O3, ZrO2, MgO and SnO2) were screened, while characterisation showed the catalyst adsorbing H2O and CO was crucial in generating LT-WGS activity, with Cu/ZnO attaining the highest LT-WGS activity. Lanthanum (La) was known to have high affinity for H2O, hence the effects of La doping on Cu/ZnO catalysts for use in LT-WGS reaction was investigated. The findings indicated the La promoter improved activity at a loading of 2.3 wt%, above which the activity significantly decreased. A systematic investigation has also been conducted on the effects of oxygen introduction on the Cu-based and Pt-based catalysts during LT-WGS operation with particular attention on the pyrophoricity (i.e. vulnerability to oxidative sintering) of the catalysts, and the impacts on key material characteristics. The objective was to examine whether the catalysts were suitable for fuel cell applications. It was observed that the Cu-based catalysts were pyrophoric and therefore not a suitable catalyst. No pyrophoricity was observed for Pt-based catalysts. Pt/CeO2 was the only catalyst that retained its activity, displaying no loss in specific surface area or metal dispersion throughout the entire process, rendering it a suitable candidate for fuel cell systems.