Mechanochemically Engineered Bimetallic PtNi/CeO$_2$ Catalysts for Enhanced Methane Steam Reforming

Bimetallic PtNi/CeO2 catalysts were successfully synthesized via a mechanochemical approach, specifically ball milling, and evaluated for methane steam reforming (MSR). A fractional factorial design of experiments was employed to systematically explore the effects of key milling parameters─milling frequency, milling time, and ball-to-powder ratio─on the catalysts’ structural properties and catalytic performance. The catalysts were characterized by X-ray diffraction, H$_2$ temperature-programmed reduction, transmission electron microscopy, and Raman spectroscopy. Catalytic activity tests were performed in a plug flow reactor under a high gas hourly space velocity (200,000 mL g$_{cat}$$^{–1}$ h$^{–1}$) at a steam-to-carbon ratio of 2 between 700 and 950 °C. The mechanochemically synthesized catalysts were benchmarked against those prepared via incipient wetness impregnation. The most active milled catalysts achieved a methane conversion rate of ca. 22 mol CH$_4$ g$_{Ni}$$^{–1}$ h$^{–1}$ at 700 °C (83.5% methane conversion for a PtNi/CeO$_2$ mechanochemically synthesized), outperforming the impregnated counterpart (64% methane conversion under the same reaction conditions). ... mehrNotably, increasing the milling intensity resulted in enhanced catalytic activity, with milling frequency emerging as the most influential factor─correlating with the formation of smaller NiO particles. To elucidate the role of Pt addition, in situ X-ray absorption near-edge structure (XANES) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) measurements were conducted on the most active milled catalysts under MSR conditions. NAP-XPS revealed surface segregation of Pt during MSR, alongside an inhibitory effect on solid carbon deposition, suggesting the potential for a coke-resistant catalyst. These findings highlight the power of mechanochemical synthesis in tuning catalyst properties, offering a scalable and efficient route to high-performance catalysts for methane reforming and hydrogen production.