Oxidative Coupling of Methane Over Lithium-Doped Ultrafine Crystalline Magnesium Oxide

Matsuura, Ikuya; Utsumi, Yasuhide; Doi, Toshiya; Yoshida, Yasushi

doi:10.1016/s0166-9834(00)83235-2

Cited by 30 publications

(10 citation statements)

References 4 publications

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“…The effect of Li addition on MgO could, therefore, be rationalized as a roughening of the MgO surface on an atomic level, leading to exposition of more low coordinated O 2À surface ions and higher index planes, in agreement with previous experimental studies [10][11][12][13] starting from preformed MgO contacted with Li precursors and theoretical predictions. The effect of Li addition on MgO could, therefore, be rationalized as a roughening of the MgO surface on an atomic level, leading to exposition of more low coordinated O 2À surface ions and higher index planes, in agreement with previous experimental studies [10][11][12][13] starting from preformed MgO contacted with Li precursors and theoretical predictions.…”

Section: Chemical Characterization By Using Xrd Tg-ms and Ir Spectrsupporting

confidence: 87%

“…By adding Li to the combustion precursor, Li-induced changes in the morphology and defect structure of MgO could be studied systematically. Also, Matsuura et al [12] and Anpo et al [13] studied the effect of Li doping on ultrafine MgO and confirmed the exposure of lower coordinative surface sites by using TEM and photoluminescence spectroscopy. At higher Li loadings, the primary MgO particles grow even further, to up to 500 nm, causing the three-dimensional pore network to collapse.…”

Section: Introductionmentioning

confidence: 95%

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Lithium as a Modifier for Morphology and Defect Structure of Porous Magnesium Oxide Materials Prepared by Gel Combustion Synthesis

et al. 2011

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Defect rich MgO nanocrystals arranged in a hierarchic three‐dimensional pore network were synthesized by using gel combustion synthesis (GCS). By adding Li to the combustion precursor, Li‐induced changes in the morphology and defect structure of MgO could be studied systematically. At low Li loadings (up to 1 wt %), the three‐dimensional pore network was resistant to temperatures up to 800 °C, even though the primary MgO nanoparticles had changed their morphology from on average 8 nm size {100} terminated nanocubes to up to 250 nm large complex polyhedral, exposing more and more {111} facets. At higher Li loadings, the primary MgO particles grow even further, to up to 500 nm, causing the three‐dimensional pore network to collapse. After describing the GCS method, detailed structural characterizations of all of the materials synthesized were conducted by means of XRD, BET and pore size analysis, and electron microscopy. IR and thermogravimetric mass spectroscopy (TG‐MS) in combination with XRD were used to investigate the formation and decomposition of carbonate species during synthesis and calcination. Diffuse reflectance UV/Vis (DR‐UV/Vis) spectroscopy was used to characterize surface defects, such as low coordinated O2− ions at edges, corners, and kinks of the MgO surface. Bulk defects were studied by using electron paramagnetic resonance (EPR) spectroscopy. Morphology and defect concentration of the Li/MgO materials were found to be strongly dependent on the fuel‐to‐oxidizer ratio used in the combustion synthesis, the Li concentration, and the calcination atmosphere.

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Section: Chemical Characterization By Using Xrd Tg-ms and Ir Spectrsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 95%

Lithium as a Modifier for Morphology and Defect Structure of Porous Magnesium Oxide Materials Prepared by Gel Combustion Synthesis

et al. 2011

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“…This is in agreement with the previous results showing that the Li addition on MgO leads to the formation of higher index planes. 41,46,47 3.2. Steady State PL Measurements.…”

Section: Resultsmentioning

confidence: 99%

Blue and Orange Photoluminescence and Surface Band-Gap Narrowing in Lithium-Doped MgO Microcrystals

Soma

Uchino

2017

J. Phys. Chem. C

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Structure and properties of Li-doped MgO have been extensively studied during the past decades in view of the effect of aliovalent doping on the catalytic, optical absorption and magnetic properties. However, the photoluminescence (PL) properties of Li-doped MgO have not been systematically investigated previously. In this work, we prepared micrometer-sized Li-doped MgO crystals using solid-phase redox reaction between B2O3 and metals of Mg and Li under argon atmosphere. The resulting Li-doped MgO microcrystals exhibit blue (2.8 eV or 440 nm) and orange PL (2.1 eV or 580 nm) emissions under excitation with photons of energies of ∼5 and ∼3 eV, respectively. The blue PL is attributed to the bulk oxygen vacancies, or F-type centers, whose emission energy levels are modified by the Li ions incorporated into the MgO structure. On the other hand, the orange PL presumably results from the oxygen vacancies at the near surface regions where a substantial bandgap narrowing down to visible range of ∼3 eV occurs. It is also found that the photoexcited electrons generated by surface interband transition can be transferred to the surface emission states via thermal activation, resulting in temperature antiquenching of the orange PL emission. Hence, the present method provides a simple and effective way to prepare visible luminescent Li-doped MgO microcrystals with an intriguing effect of aliovalent doping both on the bulk and surface electronic structures.

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“…% of MnO2. On the other hand, although the use of lithium as a catalyst in wastewater treatment was not reported, it could promote the catalytic efficiency of some metal oxides such as MgO for the oxidative coupling of methane (Matsuura et al, 1989).…”

Section: Effect Of Catalystsmentioning

confidence: 99%

A study on ozonation and ozone based advanced oxidation processes for the removal of naphthenic acids from water: kinetic studies modelling and optimal control

jibouri¹

2021

Preprint

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Industrial wastewater is one of the largest environmental challenges of this century. Most of these wastewaters contain non-biodegradable pollutants which need special treatment methods. Advanced oxidation processes (AOP’s), such as, ozonation, catalytic ozonation and ozone/ hydrogen peroxide have proved their effectiveness on the degradation of bio-recalcitrant pollutants. The main drawback in these processes is the high operating cost. The objective of this study was to develop innovative continuous ozonation and ozone based processes that can effectively degrade industrial non-biodegradable pollutants. Naphthenic acids (NAs) was used as the model pollutant in this study due to its importance as a major pollutant in oil and oil sands industries. The target was to convert bio-recalcitrant NAs into biodegradable substances with minimum consumption of ozone gas (operating cost). These processes can be followed by the biodegradation process to fully remove the rest of the pollutants. This research passed through several stages including screening of operating parameters, kinetic studies, and modeling, followed by optimal control of these processes. It was found that ozone concentration had the most significant effect on the NAs degradation compared to other parameters. The kinetics of direct and indirect (radical) ozonation of NAs were investigated and rate constants and activation energies of these reactions were determined. Catalytic ozonation of NAs was explored using alumina supported metal oxides and unsupported catalysts. Activated carbon was found to be the most effective catalyst. The addition of hydrogen peroxide into the ozonation systems significantly improved the removal of NAs compared with the ozonation only process. Models based on mass balance for the ozonation and ozone/ hydrogen peroxide processes were developed to predict the concentration profiles of reacting species. Optimal control policies of ozone/oxygen gas flow rate versus time were developed and validated to minimize NAs concentration in the liquid outlet stream from the continuous ozonation and ozone/ hydrogen peroxide processes. The experimental results demonstrated that the optimal control policies successfully minimized NAs concentration in the outlet stream. At the same time, ozone gas consumption was reduced to its minimum, i.e., just enough to minimize the concentration of NAs in the outlet stream.

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Oxidative Coupling of Methane Over Lithium-Doped Ultrafine Crystalline Magnesium Oxide

Cited by 30 publications

References 4 publications

Lithium as a Modifier for Morphology and Defect Structure of Porous Magnesium Oxide Materials Prepared by Gel Combustion Synthesis

Lithium as a Modifier for Morphology and Defect Structure of Porous Magnesium Oxide Materials Prepared by Gel Combustion Synthesis

Blue and Orange Photoluminescence and Surface Band-Gap Narrowing in Lithium-Doped MgO Microcrystals

A study on ozonation and ozone based advanced oxidation processes for the removal of naphthenic acids from water: kinetic studies modelling and optimal control

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