Structural insight into an atomic layer deposition (ALD) grown Al2O3 layer on Ni/SiO2: impact on catalytic activity and stability in dry reforming of methane

Abstract

The development of stable Ni-based dry reforming of methane (DRM) catalysts is a key challenge owing to the high operating temperatures of the process and the propensity of Ni for promoting carbon deposition. In this work, Al₂O₃-coated Ni/SiO₂ catalysts have been developed by employing atomic layer deposition (ALD). The structure of the catalyst at each individual preparation step was characterized in detail through a combination of in situ XAS–XRD, ex situ²⁷Al NMR and Raman spectroscopy. Specifically, in the calcination step, the ALD-grown Al₂O₃ layer reacts with the SiO₂ support and Ni, forming aluminosilicate and NiAl₂O₄. The Al₂O₃-coated Ni/SiO₂ catalyst exhibits an improved stability for DRM when compared to the benchmark Ni/SiO₂ and Ni/Al₂O₃ catalysts. In situ XAS–XRD during DRM together with ex situ Raman spectroscopy and TEM of the spent catalysts confirm that the ALD-grown Al₂O₃ layer suppresses the sintering of Ni, in turn reducing also coke formation significantly. In addition, the formation of an amorphous aluminosilicate phase by the reaction of the ALD-grown Al₂O₃ layer with the SiO₂ support inhibited catalysts deactivation via NiAl₂O₄ formation, in contrast to the reference Ni/Al₂O₃ system. The in-depth structural characterization of the catalysts provided an insight into the structural dynamics of the ALD-grown Al₂O₃ layer, which reacts both with the support and the active metal, allowing to rationalize the high stability of the catalyst under the harsh DRM conditions.