An experimental study on optimization of Pt-based trimetallic WGS catalysts

Abstract

The overall purpose of this study is to design and develop Pt-based, CeO2 supported trimetallic Pt-Re-V/CeO2 catalysts(s) having high WGS activity, selectivity and stability with suppressed methanation under realistic feed (i.e. feeds simulating typical reformer outlet) flow in HTS-LTS transition temperature region, allowing the use of a single WGS reactor in fuel processors. In this context trimetallic Pt-Re-V/CeO2 catalysts prepared by incipient to wetness impregnation were characterized and tested for their WGS reaction performance. In the performance tests, metal loading levels, feed composition and temperature were used as the experimental parameters. Both freshly reduced and spent catalysts were characterized by XPS and Raman spectroscopy analyses. The results revealed that 1Pt-0.5Re-1V/CeO2 and 1Pt-0.5Re-0.5V/CeO2 have great potentials to be used in a fuel processor as the WGS catalyst owing to their high activity, stability and selectivity. Another important point is that those catalysts can make the use of a single stage WGS unit in an FP instead of conventional two stage (HTS and LTS) WGS unit. XPS analysis reported Ce3+ content is slightly higher in the case of the catalysts with higher WGS activity since Ce3+ plays a crucial role in increasing electron transfer ability from support to metallic sites and Ce3+ ions are highly active towards reactants due to excess electrons that are left behind when an oxygen atom is removed. Raman spectroscopy results showed no detectable bands for bulk V2O5 crystals in any of the samples. This result indicates that vanadium is highly dispersed at the surface without bulk V2O5 formation. XPS and Raman spectroscopy results showed the formation of CeVO4 species and VO2 compound, which has been reported to have promotion effect in the WGS activity, were present on the catalyst. Raman results also revealed the existence of polyvanadate surface species in the catalyst. Moreover, no coke formation was observed on any spent samples.