Deactivation, Regeneration, and Stable Performance of a PtMoRe Water Gas Shift Catalyst for On-Site Hydrogen Generation: Part 2

Abstract

This paper analyzes the mechanism of deactivation and methods of regeneration of a PtMoRe water gas shift catalyst supported on a stabilized zirconia. Although this catalyst initially possesses high activity below 250 °C, a decrease in CO conversion ranging from 10 to 50% was observed over a period of 60 h. To determine the mechanism responsible for the decay, a series of activity tests and high resolution transmission electron microscopy analyses were done. Experimental results revealed the existence of stable and unstable operating regimes that depend on the reaction temperature, CO concentration, and H2O/H2. The high initial 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. While not completely understood, CO is required for this oxidation mechanism to occur and possible explanations are discussed. 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. Conditions for stable performance are consistent with use as a mid-temperature range water gas shift catalyst for on-site hydrogen generation.