Understanding the Role of SnO₂ Support in Water‐Tolerant Methane Combustion: In situ Observation of Pd(OH)₂ and Comparison with Pd/Al₂O₃

Abstract

Quantitative analysis of poisonous Pd hydroxide phase formation during methane combustion in the presence of water is performed via in situ X‐ray absorption spectroscopy from 200 to 500 deg C for palladium catalysts supported on tin and aluminum oxides. Water presence inhibits oxidation of the metallic Pd; for the Pd/Al2O3 catalyst the major oxidation product is Pd(OH)2, with PdO being the dominant phase on the Pd/SnO2 system. Tin dioxide is reduced during methane oxidation in the presence of water, regardless of the excess oxygen in the feed. Temperature‐programmed surface reactions at anaerobic and low‐oxygen conditions revealed that the Pd/SnO2 catalyst has an inability to catalyze methane steam reforming, as opposed to Pd/Al2O3. We suggest that tin oxide extracts hydroxyls from the PdO surface, which makes the latter more active in methane combustion in the presence of water but inactive in methane steam reforming.

Microkinetic Modeling of the Oxidation of Methane Over PdO Catalysts—Towards a Better Understanding of the Water Inhibition Effect

“…For this model adaptation, thermodynamic consistency is still guaranteed, because the microkinetic mechanism remains uniform, which is the main advantage of the chosen method. Whether the active particles react to the gaseous environment with a different active facet or shape, i.e., as observed for Zn-O-Cu catalysts for methanol synthesis [30][31][32], or in combination with hydroxyl formation [33], solely a change in F cat,geo accounts for a different catalytic activity.…”

Role of Water on the Structure of Palladium for Complete Oxidation of Methane

“…So far, there have been different interpretations of the inhibitory effects of water on methane oxidation, and a clear explanation of it is still missing 6,10,[24][25][26] . It was initially reported that the formation of stable and inactive surface hydroxide, Pd(OH) 2 , inhibited and deactivated supported palladium catalysts 8,12 27 . They also showed that water inhibits the oxidation of metallic palladium, which is supported by temperature programmed oxidation (TPO) experiments 28 and electron microscopy 29 .…”

Spatially-resolved investigation of the water inhibition of methane oxidation over palladium

“…In this work, the known inhibitory effect of water on the steady-state, lean methane oxidation activity 46,52,95 of a commercial 3%Pd/Al2O3 monolith catalyst, has been axially profiled using the SpaciMS technique. The resulting reaction profiles have been utilised in screening a number of hypothesised global kinetic models via a built in parameter estimation routine developed using Athena Visual Studios, coupled with a 1D heterogeneous single channel model.…”