Phosphorus poisoning during wet oxidation of methane over Pd@CeO2/graphite model catalysts

•Model Pd@CeO2 based catalysts are poisoned by phosphorus during wet methane combustion.•CePO4 are formed at 450 °C under air, accumulating on the surface/subsurface region of ceria nanoparticles.•Water and phosphorus strongly co-operates to severely poison the catalyst at 600 °C.•The presence of water (5–15%) and P at 600 °C leads to aggregation of ceria nanoparticles, incorporation of Pd active phase and exposure of CePO4 on the catalyst surface.

The influence of phosphorus and water on methane catalytic combustion was studied over Pd@CeO2 model catalysts supported on graphite, designed to be suitable for X-ray Photoelectron Spectroscopy/Synchrotron Radiation Photoelectron Spectroscopy (XPS/SRPES) analysis. In the absence of P, the catalyst was active for the methane oxidation reaction, although introduction of 15% H2O to the reaction mixture did cause reversible deactivation. In the presence of P, both thermal and chemical aging treatments resulted in partial loss of activity due to morphological transformation of the catalyst, as revealed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analysis. At 600 °C the combined presence of PO43− and water vapor caused a rapid, irreversible deactivation of the catalyst. XPS/SRPES analysis, combined with operando X-ray Absorption Near Edge Structure (XANES) and AFM measurements, indicated that water induces severe aggregation of CeO2 nanoparticles, exposure of CePO4 on the outer layer of the aggregates and incorporation of the catalytic-active Pd nanoparticles into the bulk. This demonstrates a temperature-activated process for P-poisoning of oxidation catalysts in which water vapor plays a crucial role.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide