Studying the surface reaction between NiO and Al₂O₃viatotal reflection EXAFS (ReflEXAFS)

Abstract

The reaction between NiO and (0001)- and (1102)-oriented Al2O3 single crystals has been investigated on model experimental systems by using the ReflEXAFS technique. Depth-sensitive information is obtained by collecting data above and below the critical angle for total reflection. A systematic protocol for data analysis, based on the recently developed CARD code, was implemented, and a detailed description of the reactive systems was obtained. In particular, for (1102)-oriented Al2O3, the reaction with NiO is almost complete after heating for 6 h at 1273 K, and an almost uniform layer of spinel is found below a mixed (NiO + spinel) layer at the very upmost part of the sample. In the case of the (0001)-oriented Al2O3, for the same temperature and heating time, the reaction shows a lower advancement degree and a residual fraction of at least 30% NiO is detected in the ReflEXAFS spectra.

Digitization in Catalysis Research: Towards a Holistic Description of a Ni/Al2O3 Reference Catalyst for CO2 Methanation

“…The inactive form (NiO/Al 2 O 3 ) of the catalyst was measured ex situ as a pellet in transmission mode. 6 Ni−O pairs at 2.05 Å fit to literature values of NiO [32] and NiO/Al 2 O 3 in literature (2.06 Å), [33] especially if these results are compared with smaller NiO particles, since the Ni−O distance decreases with smaller particle size [34] . Also, the Ni−Ni distance of 2.96 Å in the 2 nd shell fits the literature distance of 3.0 Å [33] .…”

“…[34] Also, the NiÀ Ni distance of 2.96 Å in the 2 nd shell fits the literature distance of 3.0 Å. [33] However, the NiÀ Al pair around 4.0 Å shows a different distance than the literature (4.13 Å). [35] Noticeable is the intense peak for NiÀ O distance around 2 Å and less intense peak around 3 Å is reversed for NiO without support, meaning that NiÀ Ni peak is more intense than the NiÀ O signal.…”

“…6 Ni−O pairs at 2.05 Å fit to literature values of NiO [32] and NiO/Al 2 O 3 in literature (2.06 Å), [33] especially if these results are compared with smaller NiO particles, since the Ni−O distance decreases with smaller particle size [34] . Also, the Ni−Ni distance of 2.96 Å in the 2 nd shell fits the literature distance of 3.0 Å [33] . However, the Ni−Al pair around 4.0 Å shows a different distance than the literature (4.13 Å) [35] .…”

The role of the local chemical environment of Ag on the resistive switching mechanism of conductive bridging random access memories

“…Note that in all cases the beam footprint was shorter than the samples in order to obtain absolute values for reflectivity. 23 Clusters from metallic Ag and Ag 2 S were used as starting structures and the structural model used for the data fit consisted of a balanced mix of these two phases. 21 ReflEXAFS data were analyzed by using the CARD code.…”

“…21 ReflEXAFS data were analyzed by using the CARD code. 22,23 The ReflEXAFS data are guaranteed to be relative to the surface of the sample (the fluorescence data could in principle be contaminated by bulk contributions in the case of high roughness) and are presented to validate the fluorescence data under total reflection conditions. In all cases the theoretical EXAFS paths were generated using the Feff8 code.…”