Özet:
The aim of this work is to design and develop Au-based catalysts that suppress secondary methanation activity and show high WGS activity and stability. In this context trimetallic Au-Re-V/CeO2 catalysts were prepared, characterized, and tested for their WGS performance. Au- and Re-loadings were kept fixed at 1 and 0.5 wt%, respectively, while V-loading levels were chosen as 0.5, 1, and 3 wt%. Performance tests were conducted under flow of ideal and realistic feed compositions, with high and low H2O/CO ratios, at the temperature range of 250-400 °C with GHSV fixed at 120,000 ml gcat-1 h-1. Freshly reduced and spent catalysts were characterized by SEM-EDX, XPS, XRD, and Raman spectroscopy analyses. The performance test results showed that increasing V-loading in Au-Re-V system gradually decreased WGS activity and stability. Among three catalysts, 1Au-0.5Re-0.5V/CeO2 prevailed with the highest WGS activity and stability. Higher H2O/CO feed ratio in ideal feed increased WGS activity at high temperature. Catalysts with 0.5 and 1 wt% V-loading produced additional H2 under realistic feed compositions. SEM-EDX analysis showed that low V-loadings yielded high Au and Re dispersions; whereas, 3 wt% V-loading resulted in formation of large size Au clusters, which were responsible for the low activity of the catalyst. XPS analysis indicated that Ce3+ content increased during reaction as a consequence of high WGS activity. Significant increase in Ce3+ content at high temperature and under flow of high H2O/CO ratio feed suggested involvement of Ce3+ ions in H2O activation. Lower V-loading resulted in higher Ce3+ content. XRD results suggested possible interation between V and CeO2 that changed CeO2 crystalline size. Combined evaluation of XPS and Raman spectroscopy results showed that V2O5 and CeVO4 formations were present on the catalyst. Raman spectroscopy also spotted coke formation on some spent catalysts implying that deactivation via depletion of surface oxygen might be of concern.
