Highly stable Ni–Al2O3 catalyst prepared from a Ni–Al layered double hydroxide for ethanol decomposition toward hydrogen

• A Ni–Al layered double hydroxide is an efficient precursor to produce a 80% Ni–Al2O3 catalysts with highly dispersed and embedded Ni nanoparticles on an Al2O3 matrix.
• LDH Ni–Al2O3 catalyst exhibits excellent stability towards deactivation during ethanol decomposition to produce H2 as compared to catalysts prepared by impregnation.
• We hypothesize that carbon formation occurs mainly on top Ni whereas on partially embedded Ni particles is slow and none occurs in encapsulated Ni particles.
• Encapsulated Ni particles, when exposed by spalling, can provide fresh surface area to sustain the reaction for longer TOS at high conversion.

The preparation, characterization, activity, and stability of a Ni–Al2O3 catalyst derived from reduction of a Ni–Al layered double hydroxide precursor (LDH, Ni6Al2(OH)16(CO3)0.75(OH)0.25·4H2O) are reported in this paper. In-situ X-ray adsorption spectroscopy shows that reduction of Ni from the LDH precursor to form a highly loaded 80% Ni–Al2O3 catalyst (Ni–Al2O3–LDH) is faster than reduction of a 10% impregnated Ni–Al2O3 alumina (Ni–Al2O3–I) catalyst. The reduced Ni–Al2O3–LDH catalyst exhibits highly dispersed Ni nanoparticles (3–5 nm) distributed on top, partially embedded nanoparticles, and some encapsulated in the Al2O3 matrix. The nanoparticles impregnated on alumina (Ni–Al2O3–I) are larger (∼7–15 nm) and appear on top of the alumina support. Conversion vs time on stream (TOS) results during ethanol decomposition at 250 °C on Ni–Al2O3–LDH exhibits only a slight deactivation during 100 h TOS, while the Ni–Al2O3–I catalyst shows rapid deactivation with no conversion after 2 h TOS. X-ray photoelectron spectroscopy shows that the carbon content increases up to 48% after 100 h TOS on the Ni–Al2O3–LDH catalyst, while a similar increase occurs after 2 h TOS on the Ni–Al2O3–I catalyst. TEM shows that after 100 h TOS either a thin layer of amorphous carbon or carbon nanotubes forms on Ni on top of the alumina matrix and on partially embedded Ni nanoparticles on the Ni–Al2O3–LDH catalyst. Total surface area of the Ni–Al2O3–LDH catalyst increased during TOS, which may be suplying fresh surface Ni from the encapsulated Ni nanoparticles that sustain the high activity.

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