Deactivation-free ethanol steam reforming at nickel-tipped carbon filaments

Abstract

Ni based catalysts have been widely studied for H₂ production due to the ability of Ni to break C–C and C–H bonds. In this work, we study inverse catalysts prepared by well-controlled sub-monolayer deposition of CeO₂ nanocubes onto Ni thin films for ethanol steam reforming (ESR). Results show that controlling the coverage of CeO₂ nanocubes on Ni enhances H₂ production by more than an order of magnitude compared to pure Ni. Contrary to the idea that C deposits must be continuously oxidized for sustained H₂ production, the surface of the most active catalysts show significant C deposition, yet no deactivation is observed. HAADF-STEM analysis reveals the formation of carbon filaments (CFILs), which propel Ni particles upward at the filament tips via a catalytic tip growth mechanism, resulting in a Ni@CFIL active phase for ESR. Near-ambient pressure XPS indicates that the Ni@CFIL active phase forms as a result of C gradients at the interface between regions of pure Ni metal and domains of closely packed CeO₂ nanocubes. These results show that the mesoscale morphology of deposited CeO₂ nanocubes is responsible for templating the formation of a Ni@CFIL catalyst, which resists deactivation leading to highly active and stable H₂ production from ethanol.