Study on the Dispersion of Nickel Ions in the NiO−MgO System by X-ray Absorption Fine Structure

Abstract

NiO−MgO samples (Ni x Mg1-x O:x = moles of Ni/(moles of Ni + moles of Mg)) were prepared by impregnation of MgO powder with an aqueous solution of Ni(NO3)2, followed by calcination at 773 K. The dispersion of Ni ions in these samples has been studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). XPS of the depth profile of the samples shows that the atomic concentration of Ni and Mg against the depth is almost constant and close to those of bulk concentrations. The analyses by EXAFS and XANES reveal the absence of the preferential segregation of nickel oxide phase or magnesium oxide phase in all samples, suggesting the substitution of Ni ions for Mg ions. A detailed analysis by the curve-fitting method indicates that Ni ions dissolving into MgO are dispersed at random, regardless of the compositions of the samples. These results suggest that these samples form solid solutions over the entire composition range, even by calcination at 773 K.

Valence of Highly Dispersed Cerium Oxide Species on Silica Quantitatively Estimated by Ce L<SUB>III</SUB>-edge XANES

“…The energy was defined by assigning the first characteristic peak of the Cu foil spectrum to 8978.9 eV. 26) The spectrum of the Ce/SiO 2 sample of high Ce loading (>1 mol%) was recorded in a transmission mode. For determination of incident x-ray intensity, an ionization chamber (17 cm) filled with N 2 (30%)-He(70%) was used, and for transmission x-ray an ionization chamber (31 cm) filled with N 2 (85%)-Ar(15%) was used.…”

Structural Analysis of CoO-MgO System by XAFS

“…In addition, the k3-weighted CO Kedge EXAFS of the sample of X = 0.02 (Fig. 2.4 was almost identical to the k3-weighted Ni K-edge EXAFS of Ni0.02Mg0.980 solid solution, [3] supporting the formation of Co0.02Mg0.980 solid solution. As shown in Fig.…”

“…Previously, we reported that Ni ions form a solid solution with MgO when the samples were prepared by impregnation of MgO powder with an aqueous solution of Ni(NO3h, followed by calcination at 773 K [3]. In the present work, we prepared Coo-MgO samples (CoxMgl-,O : X = m01 of CO / (m01 of CO + m01 of Mg )) with the same method, and investigated the atomic concentration range of CO for formation of a solid solution and the state of CO ions dissolving in the samples mainly by XAFS.…”

Phase Composition of Ni/Mg1−xNixO as a Catalyst Prepared for Selective Methanation of CO in H2‐Rich Gas

“…Calcination at 650 ∘ C or higher is beneficial for formation of the solid solution [2,3]. It is also reported that at calcination temperature of 500 ∘ C the solid solution was formed without or with formation of a minor amount of NiO [4,5]. It appears that a uniform dispersion of the two kinds of metallic ions in precursor allows the solid solution formed at a lower calcination temperature [6].…”