M. J. Holgado

Characterization of Ni–Mg–Al mixed oxides and their catalytic activity in oxidative dehydrogenation of n-butane and propene

Abstract Hydrotalcite-type materials with different Ni:Mg:Al ratios have been prepared and characterized by different methods (powder X-ray diffraction, differential thermal analysis and thermogravimetric analysis, FT-IR and VIS–UV/diffuse reflectance spectroscopies and specific surface area and pore size distribution assessment). Samples calcined at 600°C, where the layered structure has been destroyed, are formed by non-stoichiometric NiO–MgO oxides, and their catalytic activity in n -butane and propene oxidative dehydrogenation has been studied; production of methane and ethylene, in addition to CO 2 and H 2 O, is observed. The sample without Ni is not active in these reactions, but, among those containing Ni, that with the lowest content exhibits the largest activity.

Hexacyanoferrate-interlayered hydrotalcite

Abstract Hexacyanoferrate(II) and hexacyanoferrate(III) hydrotalcites have been synthesized by exchange of originally existing carbonate ions at pH = 4.5. The samples have been characterized by elemental chemical analysis, powder X-ray diffraction, FT-IR and X-ray absorption spectroscopies, nitrogen adsorption for specific surface area and porosity assessment, and their thermal stability has been characterized by Differential Thermal Analysis and Thermogravimetric Analysis. It has been found that during exchange hexacyanoferrate(II) is partially oxidized to hexacyanoferrate(III), a constant oxidation percentage being already attained after 3 h stirring during synthesis. Hexacyanoferrate(III) ions, however, are partially reduced during the same preparation process, but the reduction degree increases with the stirring time. Decomposition takes place in three consecutive partially overlapped steps: dehydration, decomposition of the interlayer cyanide ligands and dehydroxylation of the brucite-like layers. Upon calcination at 600 °C, a mixture of an AlMgO solid solution is formed, together with MgFe 2 O 4 spinel.

Thermal evolution of V(III)-containing layered double hydroxides

Abstract A study is reported on the thermal evolution of Mg, V layered double hydroxides with interlayer carbonate anions and different Mg/V molar ratios (from 1 to 4). Decomposition in O2 occurs at lower temperature than that in N2; the stability of the layered structure decreases as the V content increases. Oxidation of layer V3+ cations occurs in the same temperature range as dehydroxylation and decarbonation. The nature of the crystalline phases formed upon calcination at high temperatures strongly depends on the Mg/V molar ratio in the initial solid.

Electronic Spectra of Titania-Supported First Transition Series Cations

Abstract Titanium dioxide is one of the most throughly investigated chemicals for photochemical conversion of solar energy through splitting of the water molecule. However, its photoresponse is mainly located in the near u. v. region, and so dopants are generally used to extend its photoresponse towards the visible range of the solar spectrum1–4.

Hydrogenolysis of light hydrocarbons on Rh/TiO2. Catalysts reduced at high temperature

Hydrogenolysis of C2 to C4 hydrocarbons has been studied on Rh/TiO2 (2.5wt. % Rh) reduced in H2 at 773 K. Activity for this reaction is observed above 480 K, leading to lower hydrocarbons as the reaction temperature is increased.AbstractГидрогенолиз углеводородов состава C2 до C4 исследован на Rh/TiO2 (2,5 вес .% Rh), восстановленном в H2 при 773 К. Активность катализатора в этой реакции наблюдалась выше 480 К, приводя к образованию более низких углеводородов с увеличением температуры реакции.

Li/MgO catalysts. III. Effect of precursor salts on the catalytic activity in methane oxidative coupling

Oxidative coupling of methane has been studied on Li/MgO catalysts prepared from three different MgO precursors and from lithium carbonate or nitrate. In samples prepared from Li2CO3, the persistence of this on the support surface favors formation of carbon oxides.AbstractРеакции окислительного соединения метана исследовали на катализаторах Li/MgO, приготовленных из трёх различных предшественников MgO и карбоната или нитрата лития. В образцах, приготовленных из Li2CO3, остатки последнего на поверхности носителя благоприятствуют образованию окислов углерода.

Li/MgO catalysts, I. Effect of precursor salts on their structural and surface properties

Li/MgO solids have been prepared from MgO, by thermal decomposition of Mg5(OH)2(CO3)4·4H2O or by precipitation from aqueous solutions of magnesium nitrate, and then impregnating the solid thus obtained with aqueous solutions of lithium carbonate or nitrate. Non-porous solids are obtained in all cases. Specific surface area development depends on the nature of the precursors, the MgO→Mg(OH)2→MgO process being topotactic.AbstractТвердые Li/MgO получены из MgO с помощью термического разложения Mg5(OH)2(CO3)4·4H2O или высаждением водных растворов нитрата магния с дальнейшим импрегнированием полученного осадка водными растворами карбоната или нитрата лития. Во всех случаях были получены непористые вещества. Удельная поверхностная площадь зависит от природы прекурсоров, а процесс MgO→Mg(OH)2→MgO является топотактическим.

Carbonaceous residues in Rh/TiO2-catalyzed hydrogenolysis of short alkanes

Abstract Hydrogenolysis of ethane, propane, n-butane and isobutane has been studied on a Rh/ TiO 2 catalyst after reduction at 773 K. The results have been analyzed following the Kempling-Anderson formalism and a kinetic analysis has been also performed. Positive reaction orders with respect to hydrogen have been found, probably due to removal of carbonaceous residues from the catalyst surface by hydrogen during the reaction, thus overcoming the negative effect that hydrogen usually has in hydrogenolysis.

A simple conductivity study of decavanadate intercalation in hydrotalcite

Conductivity measurements have been carried out in order to follow the anion exchange process in layered double hydroxides. Measurements during chloride/decavanadate exchange have shown that it takes place through a first-order mechanism, without defoliation of the layered material.

Li/MgO catalysts: II. A DTA and TG study of precursors

The thermal decomposition of precursors of Li/MgO catalysts prepared from different Mg and Li compounds is reported. Dehydration and dehydroxylation is observed in both cases, in addition to decomposition of LiNO3, but not of Li2CO3. The properties of the solids are related to the melting and spreading of LiNO3 or Li2CO3 before or after Mg(OH)2 dehydroxylation.AbstractОписывают термическое разложение прекурсоров катализаторов Li/MgO, приготовленных их различных соединений Mg и Li. Помимо разложения LiNO3, а не Li2CO3, в обоих случаях наблюдается дегидратация и дегидроксилирование. Свойства твердых веществ коррелируют с плавлением и распределением LiNO3 или Li2CO3 на поверхности перед или после дегидроксилирования Mg(OH)2.