Basicity Of MgO Research Articles

Upgrading biogas into syngas via bi-reforming of model biogas over ruthenium-based nano-catalysts synthesized via mechanochemical method

The upgrading of biogas to value-added syngas via reforming of biogas is of great significance from the perspective of green carbon science. A series of Ru based nano-catalysts (Ru/MgO, Ru/La2O2CO3, Ru/CeO2) with relatively low Ru loading and high dispersion were successfully prepared by mechanochemical method, and applied in the bi-reforming of model biogas reaction. The representative catalysts were comprehensively characterized by XRD, N2 physical adsorption, ICP-OES, SEM, XPS, H2-TPR, CO2-TPD, HRTEM, FTIR of CO adsorption, TPSR, TG, and Raman spectroscopy, etc. Ascribed to the appropriate basicity of MgO, homogeneous Ru dispersion with ultra-small particle size, and strong interaction between Ru ultra-small nano particles and MgO support, Ru/MgO exhibit higher CO2 adsorption and activation, higher CH4 activation and dissociation, compared with Ru/La2O2CO3, Ru/CeO2, which facilitate the formation of active oxygen species and intermediate coke removal, thus enhance the resistance to coke deposition and sintering. At reaction conditions of T = 750 °C and weight hourly space velocity = 32,400 mLgCat−1 h−1, 0.5Ru/MgO catalyst exhibit satisfying catalytic activity (initial CH4/CO2 conversation rate of 87/48%) and superior stability (stable for 150 h) with negligible deactivation rates.

Mechanistic investigation on ethanol‐to‐butadiene conversion reaction over metal oxide clusters

AbstractDensity functional theory (DFT) calculations were conducted to investigate mechanistic details of ethanol‐to‐butadiene conversion reaction over MgO or ZnO catalyst. We evaluated the Lewis acidity and basicity of MgO and ZnO and found that ZnO had the stronger Lewis acidity and basicity than MgO. Potential energy surfaces of ethanol‐to‐butadiene conversion, which included relevant transition states and intermediates, were computed in detail following the generally accepted mechanism reported in the literature, where such mechanism included ethanol dehydrogenation, aldol condensation, Meerwein‐Pondorf‐Verley reduction, and crotyl alcohol dehydration. DFT results showed that ethanol dehydrogenation was the rate‐limiting step of overall reaction when the reaction was catalyzed by MgO. Also, DFT results showed that ethanol dehydrogenation occurred more easily on ZnO than on MgO, where such a result correlated with the stronger Lewis acidity of ZnO. In addition, we computed ethanol dehydration, which generates ethylene, one of the major undesired side reaction products for butadiene formation. DFT results showed that ZnO favored dehydrogenation over dehydration, while MgO favored dehydration.

Elaboration and mastering of technology of semiproduct smelting in EAF under magnesia slags

Technology of magnesia slags forming provides increase of electric energy utilization efficiency and furnace lining resistance due to early formation of stable slag foam and decrease of aggressive slag impact on the lining. At the same time the practice of operation with magnesia slags shows, that excessive over-saturation them by magnesium oxide results in heterogenization, decrease of refining properties and deterioration of some technological, technical and economic process indices. Therefore, study and elaboration technology of rational composition magnesia slags forming by periods of a heating in EAF is an actual task. Results of numerical simulation of slag temperature and chemical composition effect on MgO saturation concentration during different melting periods in EAF presented. Besides, results of analysis of refining abilities of magnesia slags depending on MgO saturation degree also presented study of magnesia slags viscosity effect depending on MgO basicity and saturation concentration, as well as magnesia slag chemical and phase composition effect on foaming efficiency. Results of theoretical and experimental study were used as a base of elaboration rational slag composition by periods of melting in the EAF and technological techniques of their formation. A technology elaborated and implemented at PAO “Seversky pipe plant” EAF shop by leaving some amount of high-magnesia slags of the previous heat and addition in two stages high-magnesia flux of “Magma” grade during the oxidizing period. This resulted in a record resistance of the refractory EAF lining, exceeding 1900 heats within a campaign and a high level of technological, technical and economic process indices.

Consequences of MgO activation procedures on its catalytic performance for acetone self-condensation

A new procedure for increasing surface area and basicity of MgO has been developed in this work, leading to a tailored catalyst for the self-condensation of acetone. The preparation method, consisting on the hydration/dehydration of periclase, was optimized varying the activation procedures. The effect of the precursor (magnesium oxide or magnesium carbonate) and the thermal treatment on the morphological properties and the basic sites distribution was characterized. In particular, CO2 calorimetry data attributed the increase of basic sites mainly to the increase in surface area. The material was tested for the base-catalyzed self-condensation of acetone, obtaining high conversions and selectivities towards the products of most industrial value, the isophorones. The selectivity reached to trimers at 723K was almost 50%, and towards isophorones, of more than 30%.

Chemical regeneration of magnesium oxide used as a sorbent for fluoride

► Use of MgO in repeated calcination regarding its sorption of F − and chemical stability was tested. ► The principal mechanism to immobilize F − is based on formation of Mg(OH)2. ► The basicity of MgO was considered to be responsible for the removal of F − through hydration. ► NaMgF 3 and Mg were evaporated by the calcination at 1273 K of the solid residues after sorption of F − . Use of MgO for repeated calcination with regard to its sorption density for F − and chemical stability was examined. Magnesium oxide was produced by the calcination of MgCO 3 at 1273 K for 1 h. The sorption of 9.82 mM F − on the calcined product and the calcinations of solid residues were carried out five times to evaluate trends in sorption density for F − and the stability of the chemically regenerated sorbents. The order of sorption density of F − ( Q /mol g −1 ) apparently seems to depend on the specific surface area. However, Q′ values after normalization of the sorption density for the specific surface area ( Q′ /mmol m −2 ) were found to be correlated with the solid basicities of the calcined products which were derived from CO 2 -TPD curves for the calcined products. The number of weak base sites, calculated from the peak intensity at 373 K in CO 2 -TPD, was considered to be responsible for the removal of F − through hydration. Large quantities of NaMgF 3 and elemental Mg were evaporated by the calcination at 1273 K of the solid residues formed after sorption of F − .

MgO-supported Cu nanoparticles for efficient transfer dehydrogenation of primary aliphatic alcohols

Abstract Basic MgO-supported Cu nanoparticles showed exceptionally high activity for transfer dehydrogenation of 1-octanol and the yield of 1-octanal was as high as 58% at 423 K. The Cu/MgO catalyst was also sufficiently active for aromatic, secondary aliphatic and cyclic alcohols, and the yields of the corresponding aldehydes or ketones approached almost 100%. Structure–reactivity correlation revealed that the synergistic effect between the basicity of MgO and the hydrogen spillover of Cu nanoparticle contributed significantly to the extremely high activity in transfer dehydrogenation of alcohols.

Proton Conductivity and Solid Acidity of Mg-, In-, and Al-Doped SnP2O7

Mg-, In-, and Al-doped were synthesized, and their potential as electrolytes for fuel cells was evaluated in terms of their performance and durability. The overall conductivity of Mg-doped increased with increasing content and reached a maximum at 10 mol %. However, this was smaller than that obtained for doping with 10 mol % and 5 mol % , especially at temperatures below . This result was interpreted to be a consequence of lower proton mobility rather than of smaller proton concentration in Mg-doped , probably due to the electrostatic restriction by against proton transport. Moreover, to investigate the influence of the doping on the fuel-cell properties, fuel-cell tests were conducted using , , and as electrolytes at a temperature of . Compared with and cells, the cell showed a somewhat higher Ohmic resistance but exhibited a comparable polarization resistance, which is the main component of the total electrical resistance. More importantly, the doping led to an improved stability of the Pt catalyst and carbon support at high potentials. This beneficial effect was attributed to a large reduction in the acidity of resulting from the basicity of MgO.

Solid base and their performance in synthesis of propylene glycol methyl ether

The base strength and basicity of MgO, CaO and Mg–Al oxide were studied for the synthesis of propylene glycol methyl ether from methanol and propylene oxide. The results showed that solid base with moderate strength such as MgO facilitated the formation of propylene glycol methyl ether. FTIR illustrated that methanol dissociated to methoxide species on MgO surface, while no dissociation took place on CaO. The moderate base strength and weak Lewis acid sites on MgO were very important for the methanol dissociation and then the synthesis of propylene glycol methyl ether.

Synthesis and characterization of Pt/MgO catalysts and their use in n-hexane conversion

Abstract Eight of magnesium oxide-supported Pt catalysts were prepared by impregnation following synthesis of the oxide by calcination of magnesium hydroxide and subsequent rehydration–calcination of the solid obtained. This procedure substantially increases both the specific surface area and the basicity of MgO. The Pt catalysts thus obtained were characterized in terms of structure and surface properties by use of various instrumental techniques (XRD, TPD, TPR and gas adsorption). The catalysts contained variable amounts of Pt and were tested in n -hexane conversion, where, as expected from basic solids, they proved specially selective towards dehydrogenation and cyclization products.

Further evidence of responsibility of impurities in MgO for variability in its basicity and catalytic performance in oxidative coupling of methane

Further evidence was delivered that certain impurities, which could be contained in MgO samples, might be responsible for observed variability in MgO basicity and catalytic performance in oxidative coupling of methane. The surface basicity/base strength distribution of a series of MgO samples containing or not containing Ca and Na impurities was determined by a temperature-programmed desorption of CO 2. It was revealed that samples containing Ca and Na impurities have much more medium, strong and very strong basic sites. The surface basicity of MgO samples containing added alkali or alkaline earth compounds or water was characterized by a test reaction of transformation of 2-butanol. It was confirmed that the introduction of these compounds to a pure MgO enhanced both its basicity and activity in oxidative coupling of methane.

INFLUENCE OF MgO IN THE CO2 – STEAM REFORMING OF METHANE TO SYNGAS BY NiO/MgO/α-Al2O3 CATALYST

Simultaneous steam and CO2 reforming of methane to syngas (H2and CO) over NiO/MgO/a-Al2O3 catalyst have been investigated at different MgO wt.%. The catalyst has been characterized by temperature-programmed reduction and XRD techniques. Addition of MgO reduced the carbon deposition and energy consumption. The stability and less coking on MgO-promoted catalysts are attributed to the lewis basicity of MgO.

On the active site of MgO/CaO mixed oxide for oxidative coupling of methane

The catalytic performance of Mg/Ca mixed oxides for oxidative coupling of methane and their physical properties were studied. It was found that while the activity for formation of carbon oxides was not influenced by the ratio MgO/CaO, both selectivity and activity to CZ hydrocarbons were maximum (67% and 14.5 C-mmol · h −1 · g −1, respectively) with 85% MgO/CaO at 1023 K. The values increased with increasing reaction temperature. Physical properties such as the strain in the MgO lattice and the amount of strongly adsorbed CO 2 were also maximum at the same composition. It was found that most of the surface species was MgO for Mg-rich oxides. Surface basicity, which was estimated by the wavenumber difference of the asymmetric and symmetric IR absorption bands of surface carbonates, was associated with these properties. The basicity of MgO, which was promoted by incorporated CaO, is considered to be the main factor for promoting the coupling activity.

PbO-SiO<SUB>2</SUB>系におけるMgOおよびNiOの挙動

The behavior of MgO and NiO in PbO-SiO2 melts, respectively, has been investigated through the measurements of electrical conductivity, viscosity and far-infrared absorption spectra.In the PbO-SiO2-MgO system, the addition of MgO decreases both electrical conductivity and viscosity in the basic slag region (PbO/SiO2=3/2∼2/3) while no such a contribution is found in the acid slag (PbO/SiO2=3/7). These facts can be interpreted as proof that the basicity of MgO is weaker than that of PbO and increases with MgO content. The amphoteric behavior of MgO in the melts is substantiated by the far-infrared spectra of MgO.In the PbO-SiO2-NiO system, the addition of NiO to the melts of PbO/SiO2=1∼2/3 increases electrical conductivity up to 10 mol% of NiO but decreases it thereafter. In the meanwhile, no such an increasing effect is observed on the viscosity. NiO in the melts behaves as an amphoteric oxide, although it seems to be a rather mild base in the higher NiO region. The far-infrared spectra of the high NiO slag that shows no contribution of NiO to the electrical conductivity is substantially the same as that of pure NiO. This suggests the existence of molecular type of NiO (no dissociation to Ni2+ and O2−) in the melts of the higher NiO region.

Surface property and catalytic activity of MgOTiO 2

The acid-base and reducing properties of MgOTiO 2 of various compositions—binary mixtures of a basic oxide (MgO) and an acidic oxide (TiO 2)—were studied and compared with their catalytic activities for the decomposition of diacetone alcohol, the dehydration of 4-methyl-2-pentanol, and the alkylation of phenol with methanol. The acidity of TiO 2 decreased upon addition of MgO, whereas the basicity of MgO was found to increase upon addition of 10 wt% TiO 2. The decomposition rate of diacetone alcohol was correlated well with the basicity of MgO-TiO 2 of different compositions, while the dehydration of 4-methyl-2-pentanol was correlated with the acidity. On the other hand, a maximum conversion of the alkylation was observed over MgOTiO 2 (weight ratio, 1:1) which has both basicity and acidity. No correlation was found between the reducing property and catalytic activity. The hydrogen exchange reaction of propylene with D 2O or D 2 over MgOTiO 2 (1:1) was shown by microwave spectroscopy to proceed via π-allyl carbanion or isopropyl carbenium ion intermediates, indicating that the active sites are basic and acidic, respectively.

Synthesis of 2,3,6-Trimethyl Phenol From m-Cresol Over MgOa

2,9,6- Trimethyl phenol is an important starting material for synthetic Vitamin E. This paper describes the vapour phase catalytic alkylation of m-cresol with methanol over MgO at different conditions of temperature (779-899 K) and pressure (1-90 bar). The reaction depends on the basicity of MgO which is maximum around 779 K as measured by benzoic acid titration. At 779 K and 20-90 bar the m-cresol conversion is 95-100% and 2,9,6-trimethyl phenol selectivity is 80-90%.