Structural and chemical state of doped and impregnated mesoporous Ni/CeO2 catalysts for the water-gas shift

Vovchok, Dimitriy; Guild, Curtis J.; Llorca, Jordi; Palomino, Robert M.; Waluyo, Iradwikanari; Rodriguez, José A.; Suib, Steven L.; Senanayake, Sanjaya D.

doi:10.1016/j.apcata.2018.08.026

Title: Structural and chemical state of doped and impregnated mesoporous Ni/CeO₂ catalysts for the water-gas shift

Journal Article · Wed Aug 29 00:00:00 EDT 2018 · Applied Catalysis. A, General

DOI:https://doi.org/10.1016/j.apcata.2018.08.026· OSTI ID:1482568

^[1]; Guild, Curtis J. ^[2];

^[3]; Palomino, Robert M. ^[4]; Waluyo, Iradwikanari ^[4];

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Stony Brook Univ., Stony Brook, NY (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
Univ. of Connecticut, Storrs, CT (United States)
Technical Univ. of Catalonia, Barcelona (Spain)
Brookhaven National Lab. (BNL), Upton, NY (United States)

Mesoporous Ni/CeO₂ catalysts of variable loadings were prepared using in-situ doping and impregnation synthesis techniques. The catalysts were found to exhibit activity for the water-gas shift (WGS) reaction, particularly at temperatures above 250 °C. Structural, electronic, and surface chemical characterizations of the materials were carried out using in-situ X-ray diffraction (XRD), in-situ X-ray absorption (XANES), and in-situ infrared (DRIFTS) techniques. The effects of metal loading and preparation method on these properties were studied in order to develop a more complete understanding of the design and application of Ni-loaded mesoporous CeO₂ catalysts. For WGS reaction activity, the in-situ doping method was observed to be superior, and overall activity was observed to increase with increasing metal loadings. Simple normalization of activity data to nominal nickel content revealed a trend favoring lower loadings, indicating higher activity per unit nickel. The reduction of the catalyst is observed with increasing reaction temperature (Ni²⁺ → Ni°, Ce⁴⁺ → Ce³⁺) while the active states of all catalysts were identified as a stable, partially reduced ceria fluorite lattice (Ce⁴⁺/Ce³⁺) with Ni²⁺ and Ni°. In Situ DRIFTS showed nearly identical surface chemistry for both doped and impregnated samples, likely involving an associative pathway at lower temperatures and a redox pathway at higher temperatures. Structural properties and surface chemistry were observed to depend both on metal loading and preparation method. As a result, nickel loadings as low as 1 wt% prepared by in-situ doping were found to display the most favorable metal-support interactions for the WGS reaction.