Insights into Improved Coking Resistance of Pd/Al ₂ O ₃ Modified by Atomic Layer Deposition of Fe ₂ O ₃ for Dry Reforming of Methane

High Resolution Image Download MS PowerPoint Slide Atomic layer deposition (ALD) of an ∼0.4 nm iron oxide overlayer on a Pd/Al 2 O 3 catalyst was investigated. TEM/EDS mapping, XRD, and XPS analyses confirmed the formation of an Fe 2 O 3 layer over the Pd particles, forming a protective ‘core-shell’ structure. The deposited film remained thermally stable and XRD-amorphous, with crystallinity related to α-Fe 2 O 3 emerging above 900 °C. All catalytic assessments and characterizations were conducted under conditions where the Fe 2 O 3 phase was defined. After high temperature treatment, the Fe 2 O 3 layer maintained good interfacial contact with Pd, and this interaction inhibited coking from deactivating Pd despite exposure to CH 4 -rich streams at 900 °C for 100 h of operation. In contrast, conventional catalysts, prepared by incipient wetness infiltration (IWI), deactivated over this duration. When these catalysts were tested for dry reforming of methane (DRM), the ALD catalyst maintained its activity under differential conditions while the IWI-prepared catalysts exhibited decreased reaction rates after they were pretreated under CH 4 -rich conditions at 900 °C. Rich CH 4 conditions were selected to stress the catalysts at shorter timescales. Additionally, the morphology of the coke formed on the ALD catalyst differed from that formed on IWI catalysts. Based on TGA and XPS, the carbon formed on the ALD catalyst was more disordered and could be oxidized in air at lower temperatures (500 °C), whereas the carbon formed on uncoated Pd exhibited ordered whisker-like structures and was more resistant to oxidation (700 °C). Finally, mechanistic insights into the role of Fe 2 O 3 in stabilizing Pd for DRM and inhibiting coke formation were supported by XPS analysis.