(575ah) Deactivation of a Platinum-Molybdenum-Rhenium Water Gas Shift Catalyst for on-Site Hydrogen Generation

The mechanism of deactivation and methods for regeneration of a PtMoRe water gas shift catalyst supported on a stabilized zirconia were studied. High activity for the water gas shift reaction below 250C makes this catalyst an ideal candidate for hydrogen generation applications. However, under certain conditions, the catalyst activity has been observed to decay as much as 50% during the initial 60 hours of steady state operation. A series of activity tests were performed to study the influence of reaction conditions on catalyst decay. Experimental results revealed the existence of stable and unstable operating regimes that depend on the reaction temperature, CO concentration, H2O/H2 ratio, and GHSV. Lower reaction temperatures, higher CO concentrations, and higher ratios of H2O/H2 were found to result in more rapid catalyst decay. The high activity of this catalyst relies upon a synergetic relationship between the platinum, molybdenum, and rhenium which form an alloy generating the catalytically active phase. Based on our experimental results, we have concluded water contained in the feed gas oxidizes the Mo/Re metals, disrupts this synergy (de-alloys), and deactivates the catalyst. Higher GHSV was also found to result in greater catalyst decay. While the role of GHSV is not completely understood, experimental results suggest GHSV indirectly influences catalyst stability though the concentration gradient that forms along the length of the catalyst bed. In all cases, the catalyst decay was fully reversible when treated in a reductive gas. Heating the catalyst in a hydrogen or reformate gas reduces the oxides back to metals, reforms the PtMoRe alloy, and restores the activity of the catalyst.