Magnesium Oxide Surface Research Articles

ChemInform Abstract: Dehydroxylation and Formation of Coordinatively Unsaturated Ions on Magnesium Oxide Surface.

AbstractAnhand der IR‐Spektren von OH‐‐Gruppen an MgO‐Oberflächen wird gezeigt, daß beim Abbau von freien OH‐‐Gruppen unter Entwicklung von H2 bei 1000 K hauptsächlich 3fach koordinierte Ionen gebildet werden, während überwiegend 4‐ (und 5‐)fach koordinierte Ionen entstehen, wenn mit H‐Brücken verknüpfte OH‐‐Gruppen unter Freisetzung von H2O‐Dampf bei 750 K abgebaut werden.

Reaction of adsorbed carbon monoxide with hydrogen on magnesium oxide

The reactivity of carbon monoxide adsorbed on magnesium oxide surfaces towards hydrogen has been examined by the temperature-programmed desorption (t.p.d.) technique and by i.r. spectroscopy. The surface species resulting from the reaction of adsorbed CO with H2 in the temperature range 343–583 K gave t.p.d. peaks for CO and H2 at 773 K. The t.p.d. profiles were in agreement with that of adsorbed formaldehyde but were totally different from that of adsorbed formic acid. The surface species showed i.r. features in the C—H stretching region and in the region 1700–1000 cm–1. One set of the features in the latter region appearing at 1604 and 1370 cm–1 could be attributed to formate.Based on the t.p.d. profiles and i.r. spectra it is concluded that CO adsorbed on the MgO surface reacts with H2 to form formyl (HCO) which is then adsorbed on the surface oxygen atoms to give formate (HCOO).

The segregation of calcium ions at the surface of magnesium oxide: theory and calculation

Atomistic simulation methods have been used to calculate the energetics of substitution and segregation of calcium ions near and at the {001} and {110}¦ surfaces of magnesium oxide at thermal equilibrium. Defect clusters and complete planes of segregating ions have been considered, thereby including impurity-impurity interaction terms. Calculated enthalpies of segregation of −0.42 and −0.78 eV, derived from different interatomic potentials, are in good agreement with the experimental heat of segregation of −0.78±0.22 eV reported recently by Wynblatt and McCune. A simple statistical mechanical theory leads to an Arrhenius expression for large crystals and the deviation from this behaviour expected in microcrystallites.

Intensity anomalies of auger electron signals observed by incident beam rocking method for magnesium oxide (001) surface

Auger electron yields of Mg(KLL), Mg(LVV) and O(KLL) from the magnesium oxide (001) surface are measured for various glancing angles of 10 kV incident electron beams in the [010] azimuth. The Auger electron yields are sharply enhanced at the surface wave resonance (SWR) conditions for vacuum cleaved clean surface. The rocking curve of the Mg(LVV) signal intensity is very sensitive to the surface conditions. For a surface contaminated by less than one monolayer of carbon atoms, the rocking curve profile of Mg(LVV) has a large dip at the SWR condition, while the KLL rocking curve profiles are enhanced at the SWR condition. It is considered that the change of the Mg(LVV) rocking curve profile by the contamination is caused by a change of electronic state of the valence electrons at the surface.

Dehydroxylation and Formation of Coordinatively Unsaturated Ions on Magnesium Oxide Surface

Dehydroxylation and Formation of Coordinatively Unsaturated Ions on Magnesium Oxide Surface

Diffusion in phases with several components and sublattices

Alkali metal-based sorbents are potential for oxidized mercury (Hg2+) selective adsorption but show hardly effect to elemental mercury (Hg0) in flue gas. Density functional theory (DFT) was employed to investigate the Hg0 and HgCl2 adsorption mechanism over alkali metal-based sorbents, including calcium oxide (CaO), magnesium oxide (MgO), potassium chloride (KCl) and sodium chloride (NaCl). Hg0 was found to weakly interact with CaO (001), MgO (001), KCl (001) and NaCl (001) surfaces while HgCl2 was effectively adsorbed on top-O and top-Cl sites. Charge transfer and bond population were calculated to discuss the covalency and ionicity of HgCl2 bonding with the adsorption sites. The partial density of states (PDOS) analysis manifests that HgCl2 strongly interacts with surface sites through the orbital hybridizations between Hg and top O or Cl. Frontier molecular orbital (FMO) energy and Mulliken electronegativity are introduced as the quantitative criteria to evaluate the reactivity of mercury species and alkali metal-based sorbents. HgCl2 is identified as a Lewis acid and more reactive than Hg0. The Lewis basicity of the four alkali metal-based sorbents is predicted as the increasing order: NaCl < MgO < KCl < CaO, in consistence with the trend of HgCl2 adsorption energies.

Reactivity of low-coordination sites on the surface of magnesium oxide

Photoluminescent and electron spin resonance studies of MgO smoke powders show that etching of the smoke cubes by water vapour leads to an increase in the number of reactive sites of low coordination on the surface without a parallel increase in the surface area. The formation of anion radicals after adsorption of oxygen and nitrobenzene was used as a monitor of the number of sites of low coordination and it is suggested that 3-coordinated surface O2– ions are involved in the formation of radical ions from both adsorbates.

Evidence from inelastic electron tunnelling spectroscopy for vibrational mode reassignments in simple aliphatic carboxylate ions

Tunnelling studies of the vibrational spectra of formate- and acetate-, including 18O-enriched acetate-, anions adsorbed on plasma-grown aluminium and magnesium oxide surfaces show that the CO 2 − symmetric stretch mode can be clearly distinguished from the CH modes in the same region of the spectra. This CO 2 − mode of the formate ion is at 1456 cm −1 on aluminium oxide and at 1348 cm −1 on magnesium oxide; for the acetate ion the corresponding values are 1463 and 1445 cm −1

Inelastic electron tunnelling spectroscopy of 1,3-diketones and related molecules on plasma-grown aluminium oxide

Inelastic electron tunnelling (IET) spectra are reported for 2,4-pentanedione and other 1,3-diketones, β-ketoester, methyl-2-hydroxybenzoate and 2-hydroxybenzaldehyde adsorbed from the vapour on to plasma-grown aluminium oxide. These adsorbates are shown to exist as the corresponding anions chelated to surface-exposed aluminium cations with the chelate ring held approximately perpendicular to the local surface. The IET spectrum of the corresponding 2,4-pentanedione: magnesium-oxide surface complex is also discussed as is the surface protonation–dehydration reaction which leads to the formation of the chemisorbed chelates.

Surface reactions of oxygen ions. 5. Oxidation of alkanes and alkenes by O2- on magnesium oxide

The superoxide ion on the magnesium oxide surface was produced by reacting oxygen with magnesium oxide containing trapped electrons. Four different superoxide species on different sites were identified by NMR spectroscopy and differential thermal analysis. Stoichiometric reactions of the superoxide ion with C/sub 1/-C/sub 4/ alkanes and alkenes at 175/sup 0/C were slower than the corresponding reactions with O(-1) and O/sub 3/(-1) on magnesium oxide. Methane and ethylene reacted only at temperatures above 300/sup 0/C and yielded mainly carbon dioxide. Propylene gave no gaseous products at 175/sup 0/C, but IR spectroscopy revealed that it adsorbed as formate and acetate ions which were converted to carbonates at higher temperatures and desorbed as acetaldehyde and methanol. The 1-butene formed 2-butanol, methanol, acetaldehyde, and acrolein above 300/sup 0/C. The analyses of the oxygen-containing and hydrocarbon products suggested that the initial step of the surface reaction is hydrogen abstraction and that the resulting radicals react with lattice oxygen to form carboxylate ions or with HO/sub 2/(-1) to form alkoxy or epoxide intermediates.

CNDO Calculations of the g tensors and spin densities of small paramagnetic sulfur-containing anions on magnesium oxide

Using a CNDO semiempirical calculation principal values of g tensors and spin densities have been determined for the sulfur-containing molecules SO 2 −. SSO −, S 3 −, SCO −, and CS 2 −,as well as CO 2 −. Bond angles and bond lengths were varied independently. The calculated values were compared with the experimentally determined values for the ions formed on the surface of magnesium oxide. Good agreement was achieved between the calculated and experimental g values: the former was often within experimental error. For SO 2 −, S 3 −, and SCO − the agreement was unique for a particular bond angle and bond length, thus providing a means of estimating the geometric structure for these paramagnetic ions. For S 2O −, CS 2 −,and CO 2 − several structures gave acceptable g values. Where possible, agreement between spin densities in the respective atomic orbitals was used as a secondary criterion to select the best structure. According to the calculations the d-orbital contribution to the total spin density never exceeded 11%.

The characterization of magnesium oxide surfaces prepared by electron beam cleavage

Abstract The surface of freshly electron beam cleaved MgO was analyzed by in situ gold decoration experiments. The depositions were performed under controlled vacuum, temperature and supersaturation conditions. Particular attention was directed to the influence of ion and electron irradiation of the substrate surface prior to the depositions. Several significant results were obtained. The decoration behavior on electron beam cleaved (001)MgO is substantially different from published data obtained on mechanically cleaved (001)MgO surfaces. The differences are believed to be due to the extreme temperature conditions during the electron beam cleavage process. No such unusual behavior was found for the (111)-oriented MgO surfaces which are also generated during the electron beam cleavage process. Furthermore, the MgO surface is noticeably susceptible to electron irradiation damage under normal transmission electron microscope imaging conditions, and very small doses of noble gas ion bombardment induce strong structural surface damage which annihilates the differences in nucleation behavior between (100) and (111) substrate areas.

Reaction between ethylene and O– ions on the surface of magnesium oxide

Download options Please wait... Article information DOI https://doi.org/10.1039/F19777301149 Article type Paper Download Citation J. Chem. Soc., Faraday Trans. 1, 1977,73, 1149-1152 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Reaction between ethylene and O– ions on the surface of magnesium oxide Y. B. Taarit, M. C. R. Symons and A. J. Tench, J. Chem. Soc., Faraday Trans. 1, 1977, 73, 1149 DOI: 10.1039/F19777301149 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Younes Ben Taarit Martyn C. R. Symons Anthony J. Tench

The adsorption of hydrogen and oxygen on magnesium oxide: The effect of γ-irradiation

The adsorption of hydrogen and oxygen on magnesium oxide surfaces with and without the influence of continuous γ-irradiation has been investigated. The temperature range for hydrogen was 294-773 K, and for oxygen 294-973 K. In the absence of radiation little adsorption of oxygen was detected below 573 K, but above this temperature an activated process requiring an Ea of 60.6�5.0 kJ mol-1 was obtained. At all temperatures, continuous γ-irradiation enhanced the adsorption, and a mechanism involving (e-|□-)s defect centres has been proposed. Hydrogen adsorption was detected at all temperatures in the absence of radiation and an enhancement of the uptake was noted during radiation at all temperatures above 294 K. ��� The Gads for oxygen decreased with increasing temperature whilst that for hydrogen increased with temperature. A mechanism for this marked difference has been proposed.

Quantum mechanical approach to the chemisorption of molecular hydrogen on defect magnesium oxide surfaces

Quantum mechanical theoretical calculations have been performed on the linear atomic chain \((MgOHV_{\ddot Mg} HOMg)^{2 + } \) in order to simulate the interaction of molecular hydrogen with the defects present at the surface of activated MgO. The total energy of the system, the relative energy of the various molecular orbitals, and the electronic charge distribution have been computed for various lattice parameters (dO-O = 4.0–4.8 A) as a function of the H-H (or O-H) separation. A symmetrical motion of the hydrogen nuclei with respect to the central Mg2+ vacancy was assumed. It is shown that chemisorption of hydrogen on surface O−ions sites results in the formation of pseudo-hydroxyl groups. For a small lattice parameter (4.0 A), no stable state of molecular hydrogen has been found while an increase in the lattice parameter results in a uniform increase of the calculated activation energy for the molecular hydrogen activation process. A mechanism is proposed which is not so different from that put forward for the hydrogen activation by transition metal complexes. Molecular hydrogen is found to act as an electron donor.

Influence De L'exposant De Slater Sur La Stabilité De Structures Simples De L'oxyde De Magnesium

AbstractWithin the framework of the SCF model using a minimal basis set one examines the influence of varying the Slater exponents on simple systems used to similate a magnesium oxide surface.

Free radical properties of the magnesium oxide surface, I

Free radical properties of MgO catalysts obtained by thermal decomposition of Mg(OH)2 in nitrogen, hydrogen and oxygen have been investigated. All the oxides show one-electron donor properties (reduction of adsorbed tetracyanoethylene and trinitrobenzene). Only the MgO calcined in oxygen shows one-electron acceptor properties (oxidation of adsorbed perylene). Acetaldehyde transformations were studied on the above catalysts. The MgO calcined in oxygen appeared to be the most active. Presumably, its activity is due to one-electron acceptor centers on the surface.

Infrared study of the adsorption of methyl fluorosulphate vapour on the surface of magnesium oxide

The adsorption of methyl fluorosulphate vapour onto magnesium oxide has been studied by infrared spectroscopy. Isolated surface hydroxyl groups form hydrogen bonds with adsorbed methyl fluorosulphate molecules. Slow chemisorptive interactions give MgOSO2OMe groups and hydrogen fluoride, which itself reacts with the surface to give water and fluoride ions. Subsequent evacuation at high temperatures caused the decomposition of MgOSO2OMe groups to MgOMe groups, sulphur trioxide, and surface sulphato complexes. The treated surface could be completely dehydroxylated by evacuation at lower temperatures than could the untreated pure oxide surface.

Photooxidation of sulfur dioxide on the surface of magnesium oxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotooxidation of sulfur dioxide on the surface of magnesium oxideM. J. Lin and J. H. LunsfordCite this: J. Phys. Chem. 1975, 79, 9, 892–897Publication Date (Print):April 1, 1975Publication History Published online1 May 2002Published inissue 1 April 1975https://doi.org/10.1021/j100576a010RIGHTS & PERMISSIONSArticle Views92Altmetric-Citations15LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (602 KB) Get e-Alerts

Infra-red study of the interaction of hydrogen sulphide and water with a magnesium oxide surface

The interaction of hydrogen sulphide with an anhydrous magnesium oxide surface has been examined by infra-red spectroscopy. Hydrogen sulphide appears to react first with the surface to form a water molecule in a configuration which immediately reacts to form hydroxyl groups; thionyl groups are not observed during the early stages of adsorption. These results led to a study of the rehydration of magnesium oxide by water vapour. A detailed analysis of the results shows a more complex situation than previously reported with two types of hydroxyl group and two conformations of water molecules present on the surface in equilibrium with water vapour.