Water Is Not Universally Promotional: Size-Dependent Inversion of Water Effects in Methanol Steam Reforming

Area of Science:

• Catalysis
• Surface Chemistry
• Materials Science

Background:

• Methanol steam reforming is crucial for hydrogen production.
• Water's role in reforming catalysis is often assumed to be universally beneficial.
• The influence of catalyst structure and support properties is not fully understood.

Purpose of the Study:

• To investigate the effect of metal nuclearity (single-atom vs. nanoparticle) and support hydroxyl chemistry on water's role in methanol steam reforming.
• To uncover the underlying mechanisms of water's influence on catalyst activity and selectivity.
• To establish a predictive framework for optimizing reforming catalysts.

Main Methods:

• Utilized well-defined platinum (Pt) single-atom and nanoparticle catalysts.
• Employed hydroxyl-rich ceria (CeO₂) and hydroxyl-poor alumina (Al₂O₃) supports.
• Analyzed catalyst performance in methanol steam reforming under varying water conditions.

Main Results:

• Observed a size-dependent inversion of water effects, contrary to universal promotion assumptions.
• On Pt nanoparticles supported by CeO₂, water-derived hydroxyls enhanced activity by mitigating CO poisoning.
• On single-atom Pt catalysts, these hydroxyls inhibited conversion by competing for sites and stabilizing intermediates.

Conclusions:

• Water's effect in methanol reforming is not universally promotional and depends critically on metal nuclearity and support properties.
• A predictive framework for understanding and controlling water effects in catalysis has been established.
• Findings are generalizable to other single-atom catalysts and reducible supports.