Preparation of the Nanostructured Ni-Mg-O Oxide System by a Sol–Gel Technique at Varied pH

Abstract

In the present work, a series of two-component Ni-Mg-O oxide systems were prepared using a sol–gel technique at varied pH of hydrolysis procedure. The aqueous solutions of nitric acid or ammonia were added to control the pH values. The xerogel samples obtained after drying were analysed using a thermogravimetric approach. The oxide systems were characterized by a set of physicochemical methods (low-temperature nitrogen adsorption, X-ray diffraction analysis, scanning electron microscopy, UV-vis spectroscopy, and temperature-programmed reduction method). The thermal stability of the samples was examined in a testing reaction of CO oxidation in a prompt thermal aging regime. It was revealed that the pH value during the magnesium methoxide hydrolysis stage significantly affects the properties of the intermediate hydroxide and final oxide nanomaterials. The thermal decomposition of nitric acid or ammonia is accompanied by exothermal effects, which noticeably influence the textural characteristics. Moreover, the pH of the hydrolysing solution defines the strength of the nickel interaction with the MgO matrix. An increase in pH facilitates the formation of the NixMg1−xO solid solution with a higher amount of incorporated nickel, which is characterized by the reproducible broad temperature range of the hydrogen uptake and the enhanced thermal stability.

Ternary Ni-Ce-Mg-O Composites: In-Depth Optical Spectroscopy Study and Catalytic Performance in CO Oxidation

“…The experimental value E g ∼ 4.22 eV corresponded to particles with a nickel content as in Ni 0.62 Mg 0.38 O. This value was close to that obtained earlier for the similar Ni-Mg-O oxide system (15 wt% NiO) synthesized using the sol-gel method at pH = 1 [40]. When comparing UV-vis data with XRD results, it should be taken into account that in the case of a wide distribution of particles for Ni content, the E g value will be determined by a portion of the particles with a concentration of Ni above average, integrally contributing enough to the absorption spectrum to form a band-gap edge.…”

“…Table 3 summarizes the catalytic data for the Ni-containing samples under st Despite the fact that the Ni15Ce5 sample showed the highest values of CO conversion Figure 10d compares the activity of the Ni15Ce5 sample with a sample containing 15 wt% NiO and 85 wt% MgO (labeled as Ni15), which was studied previously [40,90]. At the initial stages of the catalytic test, both samples behaved similarly.…”

“…Compa of T50 values at various aging temperatures for the samples under study (c). Comparison of the stability of the Ni15Ce5 sample with the Ni15 sample reported previously[40] (d).…”

“…In our previous publications, a simplified approach based on sol-gel technology to prepare MgO-containing systems was proposed [40][41][42][43]. The main idea of this approach was to introduce the second and further components in the form of an aqueous solution of suitable precursors at the stage of magnesium methoxide hydrolysis.…”

Synthesis, characterization and humidity sensing applications of calcium oxide nanoparticles synthesized by facile chemical precipitation method

“…UV-Visible absorbance spectra were obtained by applying AE-S90-2D UV-Visible spectrophotometer in the electromagnetic radiations range of 200-800 nm. The spectra were then converted to Kubelka-Munk function [21,22]. The value of energy band gap (Eg) was then estimated by applying the Tauc's plot for the obtained direct allowed transitions.…”