Abstract:
The aim of this study is to design and develop Pt-based catalysts having high WGS performance with suppressed methanation activity in HTS-LTS transition temperature region. In this context, a series of trimetallic Pt-Re-V/CeO2 catalysts and a reference bimetallic Pt-Re/CeO2 were prepared, characterized, and tested for their WGS performance. Pt- and Re-loadings of the catalysts were kept fixed as 1 wt.%, while V-loading levels were chosen as 0, 0.5, 1, and 3 wt.%. Performance tests were conducted at 300, 350 and 400 °C for two ideal and two real feed compositions with fixed GHSV as 120,000 ml gcat-1 h-1. In the tests, effects of V loading and reaction conditions (H2O/CO ratio and temperature) on the WGS activity, selectivity and stability of the Pt-Re-V/CeO2 cataysts were investigated. Results indicated that all catalysts used in this study showed plausible WGS performance, ie. high CO conversion levels and positive net H2 production values with no methanation activity, and between those 1Pt-1Re-0.5V/CeO2 and 1Pt-1Re-1V/CeO2 catalysts have superior performance, ie. high activity and selectivity with performance stability, indicating their quite high potential to be used in a practical fuel processor. The freshly reduced and spent forms of the catalyst samples were characterized by SEM-EDX, XPS, XRD and Raman spectroscopy. SEM-EDX results showed that large Pt particle size may have a positive effect on high catalytic activity of the V-promoted catalysts compared to that of V-free sample. XPS analysis revealed that Ce3+ content, thus the extent of the electron transfer between the support and the metal sites, decreased during reaction as a consequence of high WGS activity. XRD results indicated there might be an interaction between V and CeO2 leading to changes in CeO2 crystallite size. Combined evaluation of XPS and Raman spectroscopy results revealed that VO2 and CeVO4 formations and polyvanadate surface species were present in the catalyst. No bulk V2O5 crystals were observed in any samples, inferring that the vanadium was highly dispersed at the surface. Coke formation was not observed on any spent samples.
