Role of Hydroxyl Groups in the Basic Reactivity of MgO: a Theoretical and Experimental Study

Abstract

Résumé -Rôle des groupes hydroxyles sur la réactivité basique de MgO : étude expérimentale et théorique -Des surfaces propres (exemptes de carbonates et d'hydroxyles) et hydroxylées de MgO de différentes morphologies sont utilisées pour étudier la corrélation entre basicité thermodynamique de Brønsted (évaluée par le pouvoir déprotonant vis à vis du méthanol et du propyne suivi par FTIR) et réac-tivité basique (évaluée par le test de conversion du 2-methyl-but-3-yn-2-ol (MBOH)). Si une corrélation est obtenue dans le cas des surfaces propres, par contre pour les surfaces hydroxylées, les groupes OH bien que bases faibles de Brønsted sont plus actifs que les ions oxydes O 2-. Ces groupes OH donnent en infra-rouge une bande étroite ν OH à haute fréquence. Afin de les identifier, des surfaces impliquant des ions O 2-LC et Mg 2+ LC de basse coordinence (low coordination = LC) ont été modélisées par calculs DFT. Tous les sites dissocient l'eau : excepté pour les crans et bilacunes où les OH formés peuvent être considérés comme isolés, dans tous les autres cas, les OH formés sont liés par pont hydrogène. Les fréquences infra-rouge obtenues par calculs sont en accord avec le spectre expérimental qui présente deux domaines : l'un, large et situé à basse fréquence (ν OH < 3700 cm -1 ), est attribué aux hydroxyles donneurs Study -Clean (i.e., carbonate-and hydroxyl-free) and hydroxylated MgO surfaces of various morphologies were used to study the correlation between thermodynamic Brønsted basicity (evaluated by the deprotonation of methanol and propyne followed by FTIR) and basic reactivity (evaluated by the conversion of Abstract -Role of Hydroxyl Groups in the Basic Reactivity of MgO: a Theoretical and Experimental

Fourier-transform infrared and X-ray diffraction analyses of the hydration reaction of pure magnesium oxide and chemically modified magnesium oxide

“…45 The peak at 3696 cm À1 was assigned to the OH groups (that exhibited low coordination numbers) present on the surface edges and/or corner sites. [63][64][65][66]68 Knözinger et al 65 assigned it to the isolated mono-coordinated OH groups. Chizallet et al 66,68 assigned it to the hydrogen-bonded mono-coordinated OH groups.…”

“…The hydration properties of pure MgO and doped MgO have rarely been investigated using the FT-IR technique. This study provides information on hydration based on previously reported results [63][64][65][66][67][68] obtained by studying the characteristics of OH groups on the MgO surface. We aim to determine the effects of the addition of LiCl and/or LiOH on the hydration properties (heat output operation) of MgO using two characterization techniques: X-ray diffraction (XRD) and FT-IR.…”

“…They proposed a stoichiometric equation for the adsorption and dissociation reactions involving molecular H 2 O. The equation can be represented as follows (eqn (1) [63][64][65][66][67][68] ): (1) where LC represents the low coordinate.…”

Predominant role of grafted iron(III) Schiff-base complex in oxidation of gaseous and aqueous reactants: A visible light responsive photocatalyst

“…These play a vital role in the reactions, especially the ones that the surface involved. As it is known, the interaction of a cation and anion leads to the formation of the acid-base pair [54] that results in the stabilisation of counterparts whether anions or cations [55,56]. In order to tackle the issue, water may be regarded as a suitable molecule in surface chemistry.…”

Characterization of surface acidity and catalytic ability of natural clay minerals by means of test catalytic reaction

“…The MBOH conversion was used for testing of zeolites by Huang and Kaliaguine (1993), as well as by Meyer and Hoelderich (1999), hydrotalcite-derived metal oxides by Kustrowski et al (2004), whereas MgO by Chizallet et al (2006). However, there are very few applications of the test reaction of methyl butynol conversion for investigation of natural clays and clay minerals (Novikova et al, 2006;AlSawalha et al, 2011).…”