On the consistency of results arising from different techniques concerning the nature of supported metal oxide (nano)particles. The case of NiO/Al2O3

•The formation of NiO particles on NiO/Al2O3 was studied by different techniques.•XRD, FESEM and vis reveal NiO in NiO/Al2O3 at 20% wtNiO/wSUPP loading and above.•TPR shows the NiO reduction peak at 50% wtNiO/wSUPP loading and above.•UV spectroscopy shows the absorption of NiO at 159% wtNiO/wSUPP and above.•Different techniques give different results because they reveal different properties.

It is shown that different techniques (XRD, TPR, FE-SEM, IR, visible and UV spectroscopies) reveal the presence of bulk NiO particles in NiO/Al2O3 catalyst precursors at different loadings. This is explained considering both the different properties revealed by the different techniques and the likely different effect of particle size, shape and interaction with the support on these properties. Oxide-like supported particles revealed by XRD and FE-SEM in these and maybe similar catalyst systems may have well different electronic and chemical properties with respect to unsupported bulk particles. Different Ni oxide surface species may give rise to different catalytic behaviors in CO2 methanation and steam reforming of ethanol–phenol mixture.

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