MgO Solid Solution Research Articles

SYNTHESIS OF MULTICOMPONENT ZRO<SUB>2</SUB>:WO<SUB>3</SUB>:AL<SUB>2</SUB>O<SUB>3</SUB>:MGO

In this work, the phase composition and microstructure of multicomponent ZrO2:WO3:Al2O3:MgO ceramics were studied depending on the concentration of the components. The dependences between the concentration of elements in the initial charge and the phase composition, volume shrinkage, density and microstructure of synthesized samples are determined. It was found by Raman spectroscopy that the addition of an Al2O3:MgO mixture to the initial ZrO2:WO3 matrix does not lead to the formation of a ZrO2:WO3:Al2O3:MgO solid solution. With an increase in the content of Al2O3:MgO, there is an increase in volumetric shrinkage and density, which may be associated with the formation of the liquid phase of the WO3:Al2O3 system at a temperature of 1450 °C and, as a result, more efficient migration of pores and defects to the surface. The analysis of the SEM images of the cross sections of the obtained samples showed that all samples have a developed morphology with different grain shapes.

Enhancing sintered magnesia: Role of ZnO in densification, thermal conductivity, and corrosion resistance

This study introduces a method to reduce the thermal conductivity and boost cement clinker corrosion resistance in sintered magnesia using ZnO-modified additives. Solid-solution modified sintered magnesia was prepared at 1700 °C, and the impact of ZnO on the sintering properties, room-temperature strength, thermophysical properties, and corrosion resistance was assessed. ZnO addition enhanced the densification, grain size, and strength of sintered magnesia due to activated sintering from the ZnO and MgO solid-solution reaction at high temperatures. Additionally, ZnO addition improved the thermal stability and thermal shock resistance of sintered magnesia in a high-temperature environment. However, excessive ZnO led to incomplete diffusion, impeding grain growth and degrading the properties of magnesia. The thermal conductivity significantly decreased compared to the unmodified sample, particularly at 1000 °C with 4 mol% ZnO addition. Moreover, ZnO improved the corrosion resistance due to increased grain size and densification, with 4 mol% ZnO yielding the best results.

Cobalt–Magnesium Oxide Catalysts for Deep Oxidation of Hydrocarbons

Co–Mg catalysts for methane combustion were synthesized and studied, revealing the transformation of MgCo2O4 spinel into a CoO–MgO solid solution with oxygen release from the spinel lattice as the calcination temperature increased. Repeated heat treatment of the calcined solid solution at lower temperatures led to spinel regeneration with segregation of the solid solution phase. A TPR of the samples showed the presence of two characteristic peaks, the first of which relates to the transition of Co3+Oh spinel to the Co2+Oh structure of CoO, and the second to the reduction of CoO to Co°. The second peak was observed at 540–620 °C for samples calcined at temperatures below spinel decomposition, and for high-temperature samples at 900–1100 °C. Taking into account the identity of the structure of phases obtained in both cases, the formation of not a true CoO–MgO solid solution, but rather a mixture of ordered oxides (“pseudo-solid solution”) in the low-temperature region, was postulated. A study of the activity of the samples showed the high activity of the spinel systems and a linear relationship between the activation energy of methane oxidation and the heat treatment temperature.

Formation and Segregation of a Pd-MgO Solid Solution Studied by X-ray Absorption Spectroscopy.

Thermal treatment of Pd nanoparticles or Pd(NH3)4(NO3)2 supported on MgO resulted in the formation of a solid solution of Pd-MgO, as evidenced by Pd K-edge X-ray absorption fine structure (XAFS). The valence of Pd in the Pd-MgO solid solution was determined to be 4+ from the comparison of X-ray absorption near edge structure (XANES) with reference compounds. A characteristic shrinkage of the Pd-O bond distance was observed in comparison with that of the nearest-neighboring Mg-O bond in MgO, which agreed with the density functional theory (DFT) calculations. The two-spike pattern was observed in the dispersion of Pd-MgO owing to the formation and successive segregation of solid solutions above 1073 K.

Corrosion behaviour of MgO-based refractories by different existence states of manganese-containing volatile phases

Medium/high manganese steel is great interest because of its excellent energy absorption and strength. Further, it has emerged as a potential advanced high-strength steel in automobiles. In this study, the corrosion behaviour of MgO-based refractories by different existence states of manganese-containing volatile phases was systematically investigated via laboratory experiments of the vacuum treatment of medium/high manganese steel. The dissection of a magnesia crucible indicated that the manganese-containing volatile phases exist in three states: manganese vapour, liquid manganese and manganese oxides. The corrosion mechanism models of the MgO-based refractories were established as follows: (1) For the manganese vapour, the periclase was dissociated into the fine blocks when the magnesia-carbon brick was continuously exposed to the manganese vapour. (2) For the liquid manganese, a MnO layer was detected near the manganese metal, which was resulted from the MgO oxidation, and a further reaction took place to form a MnO·MgO solid solution layer at elevated temperatures, which led to the poor binding ability of the MgO crucibles. (3) For the manganese oxides, the Al2O3 crucibles were preferentially corroded by the molten manganese oxides, which are attributed to the superior thermodynamic driving force for the formation of MnAlO4. Moreover, a reaction layer composed of a MnO·MgO solid solution and a low-melting-point silicic acid phase was formed at the interface between the manganese oxides and the magnesia-carbon brick along the decarburized infiltrated zone. In addition, the molten manganese oxides infiltrated along the periclase grain boundaries into the magnesia-carbon brick and to form a reactive metamorphic layer. Consequently, under the attack of physical and chemical corrosion, the refractory particles were loosened and dropped into the corrosive manganese oxides, causing the irreversible damage of the refractory. This work provides a strong theoretical basis for the qualitative evaluating damage of MgO-based refractories by manganese-containing volatile phases.

Formation of Ir–MgO Solid Solutions Analyzed with X-ray Absorption Spectroscopy

Thermal treatment of MgO-loaded Ir nanoparticles or Ir(OAc)3 formed Ir–MgO solid solutions. The valence of Ir in the Ir–MgO solid solution was 3 +, as evidenced by Ir L3-edge XANES combined with XPS analysis. A slight contraction of the Ir–O bond distance was observed compared to that of the nearest neighboring Mg–O bond in MgO. Ir–MgO dispersion exhibited a two-spike pattern depending on the treatment temperature owing to the formation and successive segregation of the solid solutions.

Revealing a correlation between microstructure, stoichiometry, coherency strains and mechanical behavior of bulk polycrystalline oxide-based age hardened/toughened ceramic alloys

The processing challenges and microstructural inhomogeneity associated with ceramic (nano)composites render it important to develop hardened/toughened oxide-oxide ceramic alloys, possessing good mechanical properties, via a facile solid-state precipitation-based approach. However, detailed understanding of processing-microstructure-property correlations in age-hardened/toughened polycrystalline ceramics is still lacking. The present research, therefore, focuses on understanding the possible effects of variation of dimension/stoichiometry of coherent second-phase precipitate particles in such ceramic alloys on the coherency strains, associated residual stresses and mechanical properties. Polycrystalline MgO-based ceramic alloys have been developed via controlled aging treatments of partially supersaturated Fe(oxide)-containing MgO solid solution. Air-quenching post sintering-cum-solution treatment results in the formation of ultra-fine (∼5–20 nm) coherent intragranular Mg-ferrite precipitates; with subsequent aging treatments causing increases in their size and amount. The intragranular precipitate particles remain coherent with the MgO matrix even upon aging at 1000 °C for 20 h, despite coarsening to ∼130 nm. Detailed compositional analysis using EDS (with HAADF-STEM) and 3D APT reveal progressive increment in Fe-content of the precipitates with aging duration, such that the ultra-fine particles obtained right after solution treatment correspond to non-stoichiometric Fe-deficient Mg-ferrite (with ∼6 at.% Fe), whereas the relatively coarser particles obtained after 20 h of aging correspond to near-stoichiometric MgFe2O4 (with ∼27 at.% Fe). Such increment in Fe-content results in increase in lattice misfit/coherency strains, which dominates the hardening response and improves the hardness despite loss of solution hardening. Furthermore, increase in compressive residual stress in the matrix due to increment in misfit/coherency strains results in improved resistance to crack propagation.

Formation of a Pt-MgO Solid Solution: Analysis by X-ray Absorption Fine Structure Spectroscopy.

Thermal treatment of Pt nanoparticles or Pt(acac)2 supported on MgO resulted in the formation of a solid solution of Pt–MgO, as evidenced by Pt L3-edge X-ray absorption fine structure spectroscopy. The valence of Pt in the Pt–MgO solid solution was determined to be 4+. A characteristic shrinkage of the Pt–O bond distance was observed in comparison with that of the nearest-neighboring Mg–O bond in MgO, which agreed with the density functional theory (DFT) calculations. The segregation of Pt and MgO proceeded with a further increase in the thermal treatment temperature up to 1273 K. The dispersion of Pt on MgO measured through CO adsorption was much higher than that on Al2O3 or SiO2 owing to the formation of the Pt–MgO solid solution.

Propane dry reforming over highly active NiO-MgO solid solution catalyst for synthesis gas production

In the present study, the textural characteristics and catalytic efficiency of the NiO(x)-MgO solid-solution catalysts (x = 10,15,20, and 25 wt.%) were determined in CO2 reforming of propane. All samples were fabricated by the simple mechanochemical preparation route. The chemicophysical characteristics of the synthesized catalysts were determined using XRD, BET, H2-TPR, TPO, and SEM exams. The obtained results demonstrated that the physicochemical properties and catalytic activity of the samples were affected with the increment in NiO content, which is assigned to the change in the concentration of active sites and improvement of the reduction features. The NiO(25)-MgO catalyst was selected as the sample with the highest activity, and the effect of the operating factors and calcination temperature were studied over this catalyst. Also, the TPO analysis showed that the whisker carbon was formed on the spent catalyst and the sample with 25 wt.% Ni possessed the highest amount of deposited carbon. Moreover, the initial catalytic activity of all catalysts was not changed during 300 min time on stream.

Support composition effect on the structures, metallic sites formation, and performance of Ni-Co-Mg-Al-O composite for CO2 reforming of CH4

The relationship among the bulk structure, Ni/Co reduction, site formation, and the catalytic performance of Ni-Co-Al-Mg-O composite synthesized by co-precipitation method was studied for CO2 reforming of CH4 (DRM). Three catalysts were prepared by changing the Mg/Al ratio of the composite from 0.3 to 2. The catalysts were denoted as CopCat-Mg/Al-0.3, CopCat-Mg/Al-1, and CopCat-Mg/Al-2. ICP-MS, XRD, Al-NMR, XPS, TEM, and XANES (Mg, Al, Ni/Co K-edge) were utilized to characterize the crystalline structure, the coordination number, degree of spinel inversion, and the Ni /Co reduction of the catalysts. Results showed that the bulk structure of the calcined precipitates changed from spinel-dominating to the co-existence of spinel and MgO solid solution phases as the Mg/Al ratio changed from 0.3 to 2. In the spinel-dominating structures, Ni and Co reduction was found to be difficult, and a small number of metallic sites with larger nanoparticles were generated after reduction. As the MgO solid-phase became significant, the reduction of Ni and Co was enhanced, and more metallic sites of smaller sizes were formed. These metallic sites performed differently for the activation of CH4 and CO2, as the catalyst with the lowest Mg/Al ratio (<0.5) experienced carbon deposition and produced synthetic gas of low H2/CO ratio, which led to lower catalytic activity and quicker catalyst deactivation during DRM. In contrast, the catalyst with the highest ratio of Mg/Al suppressed carbon formation, maintained a higher catalytic activity and stability due to the improved basicity that promoted the quick conversion of carbon to CO.

Promotional effect of magnesium oxide for a stable nickel-based catalyst in dry reforming of methane

The generation of synthesis gas (hydrogen and carbon monoxide mixture) from two global warming gases of carbon dioxide and methane via dry reforming is environmentally crucial and for the chemical industry as well. Herein, magnesium-promoted NiO supported on mesoporous zirconia, 5Ni/xMg–ZrO2 (x = 0, 3, 5, 7 wt%) were prepared by wet impregnation method and then were tested for syngas production via dry reforming of methane. The reaction temperature at 800 °C was found more catalytically active than that at 700 °C due to the endothermic feature of reaction which promotes efficient CH4 catalytic decomposition over Ni and Ni–Zr interface as confirmed by CH4–TSPR experiment. NiO–MgO solid solution interacted with ZrO2 support was found crucial and the reason for high CH4 and CO2 conversions. The highest catalyst stability of the 5Ni/3Mg–ZrO2 catalyst was explained by the ability of CO2 to partially oxidize the carbon deposit over the surface of the catalyst. A mole ratio of hydrogen to carbon monoxide near unity (H2/CO ~ 1) was obtained over 5Ni/ZrO2 and 5Ni/5Mg–ZrO2, implying the important role of basic sites. Our approach opens doors for designing cheap and stable dry reforming catalysts from two potent greenhouse gases which could be of great interest for many industrial applications, including syngas production and other value-added chemicals.

Propane steam reforming on mesoporous NiO–MgO–SiO2 catalysts for syngas production: Effect of the MgO/SiO2 molar ratio

In this research, a series of NiO-xMgO-SiO2 catalysts with various MgO/SiO2 molar ratios were prepared via precipitation method followed by a hydrothermal treatment in the presence of PVP as surfactant. The synergic effect between MgO and SiO2 leading to the various characteristic and catalytic performance during propane steam reforming was investigated in detail. The results showed that 15 wt% NiO-0.5MgO–SiO2 catalyst possessed the highest catalytic activity (68.9% conversion for C3H8 at 550 °C) with a negligible amount of carbon formation after 20 h of reaction duration. This superior catalytic performance can be attributed to the enhanced basicity strength along with strong metal-support interaction due to the formation of NiO–MgO solid solution, as confirmed by CO2-TPD and TPR analyses, respectively. In addition, the maximum hydrogen yield was obtained through the NiO–MgO sample because of higher progress in other hydrogen production routes as opposed to that of the propane steam reforming. It also can be suggested that relatively weak interaction between active sites and support was probably the main reason for unstable catalytic behavior of NiO–SiO2 sample with the lowest activity. This study confirms that the appropriate MgO/SiO2 ratio led to the sufficient metal-support interaction and delicate balance between acidic/basic sites, which was followed by the great activity, and coke resistance during PSR.

Syngas production via chemical looping reforming biomass pyrolysis oil using NiO/dolomite as oxygen carrier, catalyst or sorbent

Chemical looping reforming (CLR) with biomass pyrolysis oil (BPO) for syngas production was investigated using NiO/dolomite as the bed material which was prepared by the wet impregnation method. The NiO/dolomite was used as catalyst and oxygen carrier in the whole temperature range, while it was also acted as in-situ CO2 sorbent at 600 °C and 700 °C. The syngas production was dominated by the sorption enhanced and catalytic reforming of BPO, due to the formation of NiO–MgO solid solution, which had a lower reducibility at low temperatures. Although, the low level CGE at low temperature could be improved by elevating the oxygen coefficient at the certain extent, poor cyclic performance of NiO/dolomite at 700 °C was observed, owning to the sintering and agglomeration during the repeated carbonation/calcination reactions. High temperatures inhibited the carbonation reaction and facilitated the reduction of NiO–MgO solid solution to provide more lattice oxygen and catalytic active sites. The syngas production was governed by the synergistic effect of lattice oxygen and catalysis at high temperatures. The optimum operating condition for syngas production in CLR was obtained by the analysis showed as follows: the temperature at 900 °C with ϕ = 0.4 in fuel reactor. The corresponding values of cold gas efficiency (CGE), syngas yield (Ysyn) and syngas purity (Psyn) were 80.76%, 1.318 Nm3/kg and 92.06%, respectively. Besides that, the NiO/dolomite exhibited a good cycle performance under this condition. The CGE and Ysyn decreased slightly to 76.26% and 1.265 Nm3/kg after 10 cycles, respectively. Overall, NiO/dolomite is a promising multifunctional material in the CLR process with BPO for syngas production. More attention should be paid to improve the mechanical strength of NiO/dolomite in the future.

Ni–Mg Supported Catalysts on Low-Temperature Electrocatalytic Tri-reforming of Methane with Suppressed Oxidation

10wt%Ni–10wt%Mg–La0.1Zr0.9O2–x (LZO) catalyst shows high reforming activity of methane while suppressing methane combustion on tri-reforming of methane at low temperatures of 473 K in an electric field. On the basis of results of light-on and light-off tests for methane oxidation and temperature dependencies for catalytic methane steam reforming activity with or without the electric field, we found that Mg addition to 10wt%Ni–LZO catalyst suppresses methane combustion, while the methane steam reforming proceeds well by virtue of surface protonics in the electric field. Ni2+ on 10wt%Ni–10wt%Mg–LZO catalyst was more cationic than that on 10wt%Ni–LZO catalyst, and NiO–MgO solid solution formed on LZO support played an important role in combustion suppression.

Simultaneous Removal of SO2 and NOx from Coal-Fired Flue Gas Using Steel Slag Slurry

A method for simultaneously removing sulfur dioxide (SO2) and nitrogen oxides (NOx) from coke oven flue gas using steel slag slurry was proposed. Due to the high removal efficiency of SO2, the effects of operation conditions on the removal of NOx were investigated emphatically. The results showed that the removal efficiency of NOx increased with an increase in steel slag slurry concentration, NOx oxidation ratio, steel slag slurry pH, and NOx and SO2 inlet concentrations and a decrease in reaction temperature. The removal efficiencies of SO2 and NOx could reach 100 and 83.4%, respectively, by optimizing the operation conditions. The mechanism of NOx removal using steel slag slurry was investigated. The results showed that (MgO)0.841·(MnO)0.159 (RO phase, a CaO–FeO–MnO–MgO solid solution) in steel slag was decomposed by H+ and produced Mg2+ and Mn2+. Furthermore, Mn2+ in steel slag slurry could promote the absorption of NO2 via redox reactions with the generation of solid Mn3O4 and MnO(OH).

Magnesium as Promoter of CO2 Methanation on Ni-Based USY Zeolites

CO2 methanation was studied over Ni–Mg–USY zeolite catalysts. Mg was added by incipient wetness impregnation and ion exchange. Whatever the Mg incorporation method used, Mg is able to improve the performance of the Ni-zeolite catalysts. Magnesium impregnation at lower contents (below 2.5%) over a 5%Ni/zeolite leads to an enhancement of the CO2 conversion into methane of 15% at 350–450 °C, probably due to the induced increase of the Ni particle dispersion, as well as to the possible activation of CO2 on the defects present on the MgO surface. At higher Mg contents, the stronger interaction between Ni and Mg oxides, leading to the formation of NiO–MgO solid solutions, seems to reduce the reducibility of the Ni species, decreasing the amount of nickel active sites available and thus the catalytic performance. Furthermore, important improvements of the catalytic performance (CO2 conversion and CH4 selectivity increased around 20% at 350–450 °C) were also found for the Mg-exchanged 5%Ni/zeolite. The results ar...

The effects of MgO and Al2O3 behaviours on softening–melting properties of high basicity sinter

ABSTRACTBecause the behaviours of MgO and Al2O3 during slag formation of high basicity sinter are not clearly understood, the effects of MgO and Al2O3 on softening-melting properties are always arguable. In this paper, four kinds of sinter containing different MgO and Al2O3 content are investigated. Some observations are obtained. The mechanism of the influence of MgO and Al2O3 on softening properties of sinter are different. Al2O3 has priority over MgO to enter into slag phase and forms low-melting point phase while MgO remains unslagged state and mainly exists in wustite as FeO–MgO solid solution. When sinter melts, the viscosity of the slag generated from sinter containing high MgO and Al2O3 content is low, which could result in low pressure drop. As MgO and Al2O3 content increase, the main minerals of residual slag change from 2CaO•SiO2 to merwinte and melilite. The changes of the minerals in slag phase can well explain the trend of softening-melting characteristic temperatures.

Enhanced Hydrogen Production by Steam Reforming of Acetic Acid over a Ni Catalyst Supported on Mesoporous MgO

A series of Ni-based catalysts supported on different MgO supports were investigated for hydrogen production via steam reforming (SR) of acetic acid (HAc). Three types of NiO and MgO solid solutions were prepared by co-precipitation of Ni(NO3)2 and Mg(NO3)2, impregnation of Ni(NO3)2 on MgO, and impregnation of Ni(NO3)2 on mesoporous MgO (denoted as MgO-m), respectively. The Ni-based catalysts were prepared by reducing these solid solutions at 650 °C in 10% H2/Ar. N2 adsorption results showed that the Brunauer–Emmett–Teller (BET) surface area of NiO/MgO-m solid solution was 3.0 and 2.3 times that of NiO–MgO and NiO/MgO solid solutions, respectively. The Ni/MgO-m catalyst showed the best catalytic performance, and the H2 yield can be enhanced by ∼160% by using the Ni/MgO-m catalyst. Ni/MgO-m kept its high activity up to 20 h of reaction. Thermogravimetry (TG) results indicated that no significant change was observed for the amount of carbon deposits on used Ni/MgO-m after 3 h on stream. Two kind of carbon s...

NiO–MgO Solid Solution Prepared by Sol–Gel Method as Precursor for Ni/MgO Methane Dry Reforming Catalyst: Effect of Calcination Temperature on Catalytic Performance

The influence of calcination temperature (500, 600 and 700 °C) on NiO–MgO solid solution formation and the performance of the resulting catalysts in CO2 reforming of methane was studied. The solid solutions and resulting catalysts were characterized by Brunauer–Emmett–Teller, XRD, temperature-programmed reduction (TPR), TEM and thermal gravimetric analysis techniques. Catalytic performance tests were carried out under 550–750 °C, 1 bar, CO2/CH4 = 1–3 mol/mol and space velocities of 30,000–120,000 ml/(h gcat). The catalyst calcined at 600 °C exhibited the best performance in terms of catalytic activity and stability and showed lowest amount of coke formation after 50 h-on-stream. The effect of calcination temperature on degree of NiO–MgO solid solution formation was demonstrated by both XRD and TPR profiles. The 600 °C calcination temperature was found to be an optimum as it caused modest NiO–MgO interaction, which is responsible for complete formation of the NiO–MgO solid solution with high nickel dispersion and resistant to coke formation.

Steam reforming of ethanol for hydrogen production over MgO—supported Ni-based catalysts

This work studied the effect of preparation method of MgO on the performance of Ni/MgO catalysts for steam reforming of ethanol. Three different MgO were prepared by precipitation and aging, precipitation and decomposition of precursor salt. Depending on the synthesis conditions, the basicity and the type of Ni species significantly varied. TPD of adsorbed CO2 showed that the MgO prepared by precipitation and aging possess the highest amount of basic sites. TPR and XANES revealed the presence of two different Ni species: NiO particles and Ni2+ inserted in the lattice of a NiO–MgO solid solution, which is hardly reducible. Ni supported on MgO obtained by precipitation and aging exhibited the highest reduction degree. The preparation method of MgO also affected the amount of carbon formed during SR of ethanol at 773K under H2O/ethanol molar ratio of 3.0. Increasing basicity decreased the amount of carbon deposits, which was attributed to the increase of carbon gasification rate.