An X-ray diffraction computed tomography study determining failure mechanisms in industrial Cu/ZnO/Al2O3(−Cs2O) water–gas shift catalysts

The water–gas shift (WGS) reaction is a key process for industrial hydrogen production used in ammonia synthesis, where Cu–Zn–Al (CZA) catalysts are typically employed. Since similar formulations are also used for methanol synthesis, 1 wt% Cs 2 O is often added to mitigate its formation as an unwanted side product. However, this addition has recently been suggested to decrease the mechanical strength of the catalyst, particularly during initial reduction, leading to premature failure. In this study, we investigate how gas composition (particularly water content) and pressure affect the structural and chemical evolution of recovered CZA pellets after a typical reduction protocol, using pseudo- in situ X-ray Diffraction Computed Tomography (XRD-CT). We find that high water content (∼20 vol%) combined with increasing Cs 2 O loading markedly promotes Cu 0 crystallite growth, favours formation of Cu 2 O, and enhances ZnO sintering. These effects are most severe at the pellet periphery and ultimately compromise mechanical integrity. The results highlight the critical interplay between steam, pressure, and Cs promotion in governing catalyst stability during activation