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

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 situ 27Al 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.