Modification Of MgO Research Articles

MgO Modified by X2, HX, or Alkyl Halide (X = Cl, Br, or I) Catalytic Systems and Their Activity in Chemoselective Transfer Hydrogenation of Acrolein into Allyl Alcohol.

A new type of catalyst containing magnesium oxide modified with various modifiers ranging from bromine and iodine, to interhalogen compounds, hydrohalogenic acids, and alkyl halides have been prepared using chemical vapor deposition (CVD) and wet impregnation methods. The obtained systems were characterized using a number of methods: determination of the concentration of X- ions, surface area determination, powder X-ray diffraction (PXRD), surface acid-base strength measurements, TPD of probe molecules (acetonitrile, pivalonitrile, triethylamine, and n-butylamine), TPD-MS of reaction products of methyl iodide with MgO, and Fourier transform infrared spectroscopy (FTIR). The catalysts' activity and chemoselectivity during transfer hydrogenation from ethanol to acrolein to allyl alcohol was measured. A significant increase in the activity of modified MgO (up to 80% conversion) in the transfer hydrogenation of acrolein was found, while maintaining high chemoselectivity (>90%) to allyl alcohol. As a general conclusion, it was shown that the modification of MgO results in the suppression of strong basic sites of the oxide, with a simultaneous appearance of Brønsted acidic sites on its surface. Independently, extensive research on the reaction progress of thirty alkyl halides with MgO was also performed in order to determine its ability to neutralize chlorinated wastes.

Stability and efficiency improvement of TiO2-based dye-sensitized solar cells by surface modification of MgO

Stability and efficiency improvement of TiO2-based dye-sensitized solar cells by surface modification of MgO

Some features of the surface modification of MgO–Al2O3–TiO2–SiO2 glass and glass ceramics by Ag diffusion

Diffusion of Ag species into the surface layers of the MgO–Al 2 O 3 –TiO 2 –SiO 2 glass stimulates the crystallization processes therein during subsequent thermal treatment. It was found that the silver doping significantly increases the microhardness of glass and glass ceramics. The effect of the Ag diffusion and the subsequent high-temperature treatment (T > T g ) on the structure and luminescence properties of the MgO–Al 2 O 3 –TiO 2 –SiO 2 glass was studied. The thermal evolution, structure and properties of the glass and glass ceramics were investigated by the DSC method, XRD analysis and luminescence spectroscopy. It was found that the Ag diffusion into the surface layers leads to the formation of numerous different luminescent molecular Ag n clusters. The MgO–Al 2 O 3 –TiO 2 –SiO 2 glass and glass ceramics subjected to the Ag diffusion can operate as effective down-converters of the radiation demonstrating the effective transformation of UV and blue light into the radiation of red and NIR spectral range.

Surface modification of magnesium oxide and its effect on the performance of magnesium phosphate cement

In applying magnesium phosphate cement, controlling its setting time is of great importance, and the activity of the main raw material, magnesium oxide, is the key. In this study, dead-burned magnesia was modified with different amounts of water glass and different thermal treatment temperatures, and the effects of MgO on the macroscopic properties and microstructure of magnesium potassium phosphate cement (MKPC) were studied.The results show that the setting time of MKPC prepared with modified magnesia is prolonged, and the increase of the amount of water glass, the longer the setting time is.The setting time of the sample with 15% water glass and 300 °C treatment increased from 4.3 min to 17.5 min, an increase of 307%.The compressive strength results show that the surface modification of MgO decreased MKPC's early strength, which decreased with an increase in the water glass content and a decrease in the thermal treatment temperature.However, when the curing reached 7 days, the samples' compressive strength exceeded that of the reference group, and the strength development was optimum when the content of water glass was 5% with 300 °C treatment. The 28 d strength increased from 65.8 MPa of the reference group to 72.4 MPa, an increase of 10%.Through scanning electron microscopy (SEM), it was found that new phases were formed in the surface modified samples at the later stage of hydration. Combined with the results of energy-dispersive spectroscopy (EDS), it was confirmed that the magnesium silicate hydrate gels (M-S-H) were formed.The mercury intrusion porosimetry (MIP) test results show that these M-S-H gels can refine the pore size of MKPC, and the porosity of the sample with 5% water glass and 300 °C treatment was reduced from 6.6510% to 6.0429%, which explains the improvement in the MKPC compressive strength. Therefore, the surface modification of magnesium oxide can greatly extend its setting time without adversely affecting its later performance.

β-Cyclodextrin-grafted magnetic graphene oxide nanocomposites in ultrasound-assisted dispersive magnetic solid-phase extraction for simultaneous preconcentration of lead and cadmium ions

This article presents an ultrasound-assisted dispersive magnetic solid-phase extraction method (USA-DMSPE) to preconcentration Cd(II) and Pb(II) simultaneously. The adsorbent (mGO-βCD) was synthesized through three steps with consumption of environmentally friendly materials at room temperature. First graphene oxide (GO) was prepared via modified Hummer’s method and then magnetized by Fe3O4 precipitation (mGO). Finally, β-cyclodextrin was covalently immobilized onto the surface of mGO. X-ray diffraction patterns established pure crystallinity of the materials. Homogenous distribution of magnetic nanoparticles onto GO sheets was confirmed by scanning electron microscopy and transmission electron microscopy. FT-IR spectra proved successful modification of mGO by β-CD. Alternating gradient force magnetometer characterized magnetic property. Brunauer–Emmett–Teller showed porous structure of mGO-βCD and having high surface area. pH (7 ± 0.2), adsorption time (2 min), adsorbent amount (20 mg), eluent kind (HNO3 (3 ml of 2.0 mol L−1)) and desorption time (one minute) were optimum conditions. Sonication disperses adsorbent in sample solution, which accelerates mass transfer, as well as decreasing adsorption time and adsorbent usage amount. Applicability of the method was investigated according to preconcentration factor (Pb(II): 200 and Cd(II): 167), linearity of dynamic range (Pb(II): (2–410) and Cd(II) (3–400 μg L−1), limit of detection (Pb(II): 0.64 and Cd (II): 0.9 μg L−1), relative standard deviation (Pb(II): 1.68% and Cd(II): 2.51%) and adsorption capacity (Pb(II): 188.68 and Cd(II): 78.12). mGO-βCD was reusable for ten times and durable in six months. Selectivity and effect of interference ions were reported. Obtained recoveries for real samples verified the satisfactory performance of the method.

Synthesis of functionalized mesoporous Ni-SBA-16 decorated with MgO nanoparticles for Cr (VI) adsorption and an effective catalyst for hydrodechlorination of chlorobenzene

In this research work the impact of MgO promoter tested on Ni-SBA-16 efficiency in aqueous media as an adsorbent for Cr(VI) and an effective catalyst for hydrodechlorination of chlorobenzene. New hydrothermal procedures were applied for the synthesis of Ni-SBA-16 and MgO/Ni-SBA-16 respectively. Results revealed that nanocomposites containing Ni nanocrystals of an average size distributed homogeneously within the pores of the amorphous silica matrix and also MgO was effectively coated on Ni-SBA-16 mesoporous silica walls, and that the mesoporous Ni-SBA-16 structure has been well preserved upon modification of MgO. The catalyst analysis results showed high interaction of unpromoted and MgO promoted catalyst Ni-SBA-16 as hydrodechlorination of chlorobanzene (≈ 96%) remained stable for 6 hours. The synthesized nanostructures were tested against Cr(VI) removal. 100% Cr(VI) adsorption was noted using 4 g/L and 200 mg/L of nanostructure and Cr(VI) respectively at temperature 75 °C, contact time 100 min and pH 3.

Morphological modification and corrosion response of MgO and Mg3(PO4)2 composite formed on magnesium alloy

During the last decade, much effort has been poured into aiming at controlling the surface morphologies of inorganic layer via plasma electrolysis that exhibited good functional properties. In this work, the 3-dimensional structures were formed on magnesium alloy by means of self-assembly. To this end, the porous inorganic layer was modified additionally by immersion in solutions with different ratios of albumin (ALB) and sodium phosphate (SP). The porous layer was transformed into the flower-like structure when the amount of ALB was relatively higher than SP. As the relative concentration of SP increased, the formation of the rod-like structure was favored, covering the entire surface of porous inorganic layer. These findings were attributed mainly to the electrostatic interactions between albumin and Mg3(PO4)2 where the competitive adsorption between ALB and PO4−3 on oxide surface took place. Since ALB adsorption was hindered by the presence of PO4−3, the rod-like structure controlled at relatively high concentration of SP was responsible for excellent electrochemical stability. The shape-controlled synthesis of either flower- or rod-like structures present provided a green approach desirable for electrochemical applications of magnesium-based alloys.

Improving simultaneous removal efficiency of SO2 and NOx from flue gas by surface modification of MgO with organic component

Using glucose and polyvinylpyrrolidone as raw materials, MgO-organic component materials were prepared by a one-step hydrothermal method. The material is used to improve the efficiency of simultaneous removal of SO2 and NOx, and to reduce the competitive adsorption of both. In the experiments, the adsorption of SO2 and NOx in simulated coal-fired flue gas was tested with MgO-organic component/pure MgO/MgO (PVP modified)/MgO (glucose modified), and the test results were compared. It is very noteworthy that the SO2 dynamic adsorption capacity of the MgO-organic component (the glucose/polyvinylpyrrolidone ratio is 1:3) was 0.3627 mmol/g; while that of NOx was 0.2176 mmol/g, and the adsorption breakthrough time (time taken when the NOx removal rate was 50%) was as long as 60 min (the total flow rate of simulated flue gas is 200 ml/min, the space velocity is 24000 h-1, the reaction temperature is 100 °C, the concentration of SO2 and NOx is 500 ppm and 300 ppm, respectively). In this study, the organic component enhances the simultaneous desulfurization and denitration performance of MgO from three aspects and is verified by different characterization tests. There are an increase in specific surface area, an increase in surface energy and the insert of active functional groups. In particular, the insert of –CO can greatly improve the adsorption efficiency of NOx. Meanwhile, the adsorption process under different operating conditions is discussed in order to provide theoretical support for industrial practice. The work presented here has profound implications for future studies of simultaneous desulfurization and denitration field. Moreover, the economy and sustainability of the technology meet the basic requirements of waste reduction in cleaner production.

Carbon Formation Mechanism of C2H2 in Ni-Based Catalysts Revealed by in Situ Electron Microscopy and Molecular Dynamics Simulations.

Understanding the carbon formation mechanism is critical for designing catalysts in various applications. Here, we report the observation of the carbon formation mechanism on Ni-based catalysts by environmental transmission electron microscopy (ETEM) over a wide temperature range in combination with molecular dynamics simulations and density functional theory calculations. In situ TEM observation performed in a C2H2/H2 atmosphere provides real-time evidence that Ni3C is an intermediate phase that decomposes to graphitic carbon and metallic Ni, leading to carbon formation. Mechanisms of acetylene decomposition and evolution of carbon atom configuration are revealed by molecular dynamics simulations, which corroborate the experimental results. The modification of MgO on NiO can effectively decrease the formation of graphitic layers and thus enhance the catalytic performance of NiO. This finding may provide an insight into the origin of the carbon deposition and aid in developing effective approaches to mitigate it.

Acid strength measurements of Amberlyst 15 resin, p-xylene-2-sulfonic acid and chlorosulfonic and sulfuric acid treated SiO2, Al2O3, TiO2 and MgO

The measurements of the minimum acid strength (HOmin) required for the initiation of cis-stilbene at 303 K and tert-butylbenzene at 313 K, 323 K and 333 K have enabled the establishment of a much more precise acid strength scale based on test reactions. HOmin values obtained were: − 9.0 (cis-stilbene, 303 K), − 9.3, − 9.5 and − 9.9 (tert-butylbenzene, 313 K, 323 K, 333 K). The updated method was used for the determination of the acid strength of different catalysts obtained in the reaction of chlorosulfonic and sulfuric acid on different oxide carriers. It was found that the acid strength values depended on the basicity of the studied supports. For the supports treated with chlorosulfonic acid the values of acid strength were: − 11.5 < HO ≤ − 10.8 in the case of the less basic SiO2 and − 9.3 < HO ≤ − 9.0 for the more basic TiO2, Al2O3 and MgO. For the supports treated with sulfuric acid the acid strength was: -9.3 < HO ≤ -9.0 for the less basic SiO2 and TiO2, − 9.0 < HO ≤ − 7.9 for the more basic Al2O3 and − 7.9 < HO ≤ − 6.9 for the most basic MgO. Silica treated with chlorosulfonic acid possesses higher acid strength than HZSM-5 and amorphous silicaalumina. The catalyst obtained in the modification of TiO2, Al2O3 and MgO with chlorosulfonic acid were of lower acid strength comparable to Amberlyst 15 and HZSM-5 (− 9.3 < HO ≤ − 9.0), but higher than p-xylene-2-sulfonic acid dihydrate (− 7.9 < HO ≤ − 6.9).

Correction to: Simultaneous Modification of Alumina and MgO·Al2O3 Inclusions by Calcium Treatment During Electroslag Remelting of Stainless Tool Steel

Calcium modification of both alumina and MgO·Al2O3 inclusions during protective gas electroslag remelting (P-ESR) of 8Cr17MoV stainless steel and its effect on nitrides and primary carbides were studied by analyzing the transient evolution of oxide and sulfide inclusions in the P-ESR process. The oxide inclusions that were not removed during P-ESR without calcium treatment were found to retain their original state until in as-cast ingot. Calcium treatment modified all MgO·Al2O3 and alumina inclusions that had not been removed in the P-ESR process to liquid/partially liquid CaO-Al2O3-(MgO) with uniformly distributed elements, in addition to a small proportion of partially modified inclusions of a CaO-MgO-Al2O3 core surrounded by a liquid CaO-Al2O3. The modification of low-MgO-containing MgO·Al2O3 inclusions involves the preferential reduction of MgO from the MgO·Al2O3 inclusion by calcium and the reaction of calcium with Al2O3 in the inclusion. It is the incomplete/complete reduction of MgO from the spinel by calcium that contributes to the modification of spinels. Alumina inclusions were liquefied by direct reaction with calcium. Calcium treatment during P-ESR refining also provided an effective approach to prevent the formation of nitrides and primary carbides in stainless steel through modifying their preferred nucleation sites (alumina and MgO·Al2O3 inclusions) to calcium aluminates, which made no contribution to improving the steel cleanliness.

Simultaneous Modification of Alumina and MgO·Al2O3 Inclusions by Calcium Treatment During Electroslag Remelting of Stainless Tool Steel

Simultaneous Modification of Alumina and MgO·Al2O3 Inclusions by Calcium Treatment During Electroslag Remelting of Stainless Tool Steel

Sustainable C–C bond formation through Knoevenagel reaction catalyzed by MgO-based catalysts

A study of the Knoevenagel condensation of p-substituted benzaldehydes with malononitrile or ethyl cyanoacetate over potassium, calcium and lanthanum modified MgO was carried out under thermal and microwave activation. The catalysts were fully characterized to determine their textural, structural and surface acid–base properties. The whole set of catalysts were essayed in propan-2-ol test reaction in order to gain a better understanding of their acid–base properties. As for the surface basic properties of the catalysts, the modification of MgO with Ca and K led to solids with enhanced basicity while La modification slightly reduced the basicity of bare MgO. Inductive and mesomeric effects of the substituent in p-substituted benzaldehydes were coherent with a reaction mechanism in which a nucleophilic attack to the carbon atom of the carbonyl group takes place. Malononitrile or ethyl cyanoacetate were used as the active methylene reagent and the reaction was faster in the case of malononitrile as compared to ethyl cyanoacetate, indicating that the nucleophile formation (carbanion) on the catalyst basic sites is an important issue in this reaction. As for the catalysts, the overall reactivity order in thermal Knoevenagel condensation was \({\text{MgO}}-{\text{K}}\left( {\text{I}} \right)>{\text{MgO}}-{\text{K}}\left( {\text{II}} \right)>{\text{MgO}}-{\text{Ca}}\left( {\text{I}} \right) \approx {\text{MgO}}{-}{\text{La}}\left( {\text{II}} \right) \approx {\text{MgO}}>{\text{MgO}}{-}{\text{La}}\left( {\text{I}} \right)\), which completely agrees with the catalyst basicity extracted from the propan-2-ol test reaction (yield to acetone). The above correlation confirmed that, in Knoevenagel condensation, the carbanion formation on the surface basic sites of the catalysts is a key step in the reaction mechanism. The microwave-activated Knoevenagel reaction was much faster than the conventional, thermally activated reaction. The results indicate that the nucleophilic character of the Knoevenagel condensation also prevails under microwave activation.

Surface modification of polyhedral nanocrystalline MgO with imidazolium carboxylates for dehydration reactions: a new approach

The surface of nanocrystalline MgO was modified with achiral and chiral imidazolium carboxylates which generate MgO–[NHC] complexes. Thus as synthesized complexes were utilized in the dehydration of glucose and also in selective dehydration of (±) nitro alcohol.

The Effect of MgO Precoating on the Perfomance of Ni/MgO-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Catalysts for Carbon Dioxide Reforming of Methane

Ni catalysts supported on γ?-Al2O3 supports modified by different MgO precoating weight were prepared by impregnation method. The surface area, pore diameter and Ni crystallite size were investigated by N2 adsorption/desorption (BET) and X-ray diffraction (XRD) methods. The reducing temperature and quantity information of reducible nickel species were obtained by H2-TPR experiments. The CO2 adsorption/desorption abilities of catalysts were investigated and the activity of catalysts were also measured. The coke resistance performance of catalysts for carbon dioxide reforming of methane (CDRM) was studied by CO2 temperature programmed surface reaction (CO2-TPSR). H2-TPR results revealed that there were three kinds of Ni species on the supports. Appropriate modification amount of MgO could increase the surface nickel active sites which could be easily reduced and prevented the formation of NiAl2O4 spinel species. CO2-TPD indicated that the addition of MgO increased the amount of CO2 adsorption at lower temperatures. N2 adsorption/desorption results disclosed that the excessive modification of MgO would decrease the surface area and pore size of the samples. The reforming reaction results showed that the activity was elevated from 58.62% to 65.95% over the Ni/MgO-Al2O3 when the Mg/Al ratio was 0.05 (wt.) and there was less coke evidenced by the CO2-TPSR results comparing to the Ni/γ?-Al2O3 catalyst.

Modification of MgO as an immobilizing agent for molten electrolyte

This paper describes the synthesis and texture of the MgF2-MgO system used as an immobilizing agent of the electrolyte (KCl-LiCl-RbCl) for high-temperature cells. Preparations containing 20 and 40 mol% MgF2 were characterized by a mesoporous structure and large specific surface areas. It was demonstrated that pellets containing 40–50 mas.% of MgF2-MgO immobilizing agent were good electrolyte immobilizers. The ionic conductivity of pellets investigated in this work ranged from 0.02 to 0.04 S/cm, and it was about 20 times lower than the value set for the pure electrolyte. The difference is due to the tortuosity of the pellet. This mixture remains dimensionally stable at 400 °C and under 60 kPa and reveals good ionic conductivity during tests in a model cell with a 1.32-Ω resistor. During the discharge of the cell, it was observed that the voltage was not less than 1.5 V and current more than 1 A for approximately 100 s. No leakage of the electrolyte was observed.

The effect of impregnation strategy on structural characters and CO2 methanation properties over MgO modified Ni/SiO2 catalysts

Mg-modified Ni/SiO2 catalysts with different MgO contents were prepared by two impregnation methods. The catalysts prepared by co-impregnation method could show better activity and stability than those prepared by sequential impregnation method. The modification of MgO acted as a key factor in enhancing the capacity of CO2 adsorption and accelerating the activation of CO2. Moreover, modified MgO could also increase Ni species dispersion and suppress the metallic Ni sintering and oxidation.

Control of MgO·Al2O3 Spinel Inclusions during Protective Gas Electroslag Remelting of Die Steel

The effect of calcium treatment and/or aluminum-based deoxidant addition on the oxygen control and modification of MgO·Al2O3 spinel inclusions during protective gas electroslag remelting (P-ESR) of H13 die steel with low oxygen content was experimentally studied. It is found that all the inclusions in the consumable electrode are MgO·Al2O3 spinels, besides a few MgO·Al2O3 spinels surrounded by an outer (Ti,V)N or MnS layer. After P-ESR refining combined with proper calcium treatment, all the original MgO·Al2O3 spinels in the electrode (except for the original MgO·Al2O3 spinels having been removed in the P-ESR process) were modified to mainly CaO-MgO-Al2O3 and some CaO-Al2O3 inclusions, both of which have a low melting point and homogeneous compositions. In the case of only Al-based deoxidant addition, all the oxide inclusions remaining in ESR ingots are MgO·Al2O3 spinels. The operation of Al-based deoxidant addition and/or calcium treatment during P-ESR of electrode steel containing low oxygen content is invalid to further reduce the oxygen content and oxide inclusions amount compared with remelting only under protective gas atmosphere. All the original sulfide inclusions were removed after the P-ESR process. Most of the inclusions in ESR ingots are about 2 μm in size. The mechanisms of non-metallic inclusions evolution and modification of MgO·Al2O3 spinels by calcium treatment during the P-ESR process were proposed.

Enhanced cycling stability of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 by surface modification of MgO with melting impregnation method

MgO-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 was synthesized via melting impregnation method followed by a solid state reaction. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) show that the MgO layer is well coated on the surface of the layered oxide particles. Although the initial discharge capacity of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 with proper MgO modification decreases compared to the bare one, the 2wt.% MgO coated cathode exhibits the excellent cycling stability with capacity retention of 96.4% at a current density of 200mAg−1 after 100 cycles at room temperature and 94.3% after 50 cycles at 60°C. Electrochemical impedance spectroscopy (EIS) shows that the thin MgO layer mainly reduces the charge transfer resistance and stabilizes the surface structure of active material during cycling. Melting impregnation method is promising for MgO coating to improving the cycling stability of Li-rich layered oxide cathode for Li-ion batteries.

Formation and Modification of MgO·Al2O3-Based Inclusions in Alloy Steels

The current study performed thermadynamic calculation, laboratory experiments, and industrial trials for the formation and modification of MgO-Al2O3 spinel inclusions in alloy steels. The stability Mg-Al-O diagram was obtained using the thermodymanic study. The resulting MgO-Al2O3-CaO inclusions from MgO-Al2O3 spinel inclusions after the calcium treatment were spherical, and > 5 μm MgO-Al2O3-CaO inclusions have a two-layer structure: an outside CaO-Al2O3 layer and a MgO-Al2O3 core. The modification of > 5 μm MgO·Al2O3 spinel inclusions by calcium treatment includes two steps: (1) reducing MgO in the inclusion into the dissolved magnesium by the dissolved calcium in the steel and (2) generating a liquid xCaO·yAl2O3 layer at the outside of the spinel inclusion. For <2 μm MgO·Al2O3 spinel inclusions, they can possibly be modified into a xCaO·yAl2O3 inclusion by reducing all MgO component in the spinel inclusions with the added calcium.