Preparation of activated carbon-metal (hydr) oxide materials by thermal methods. Thermogravimetric-mass spectrometric (TG-MS) analysis

[EN] tActivated carbon (AC)-metal (hydr) oxide (MO) materials prepared by wet impregnation of a commercialAC with Al3+, Fe3+, Zn2+, SnCl2, TiO2and WO42−in water at pH between 1.37 and 9.54 in two successivesoaking and oven-drying steps are analysed by thermogravimetry-mass spectrometry (TG-MS) between25 and 900◦C. Under identical conditions, a blank sample (ACB) was first prepared using deionized waterand then thermally analyzed. The mass loss in the TG analysis is 1.35 wt% for AC, 2.12 wt% for ACB, andbetween 2.47 and 23.20 wt% for the AC-MO materials. For these materials, it depends on the impregnationagent and varies by SnCl2> Fe3+> Al3+> Zn2+> WO42−> TiO2. The number of thermal effects giving off CO2and CO is larger with the Al3+, Fe3+and Zn2+ions than with SnCl2, TiO2and WO42−. It is so in particular forCO2with the Fe3+ion and for CO with the Al3+ion. In general, the release of CO at high temperature hasbeen associated with the carbothermal reduction of metal oxides. As a result of the reaction low-meltingpoint metals such as Al, Zn and Sn, unlike Fe and W, are formed which vaporize and thereby contribute tothe mass loss. Only with Fe3+and TiO2, the amount of desorbed water is larger by dehydroxylation thanby dehydration. The masses of evolved H2O, CO2and CO are by far higher with SnCl2, whereas they arelower with TiO2and WO42−

Physico-chemical characterization of activated carbon–metal oxide photocatalysts by immersion calorimetry in benzene and water

[EN] From a commercial activated carbon (AC) and Al3?, Fe3?, Zn2?, SnCl2, TiO2 and WO4 2- in water, three series of AC–metal (hydr)oxide (MO) samples prepared by wet impregnation in two successive steps of soaking at 80 ºC and oven-drying at 120 ºC (S1) and subsequent heat treatment at 200 (S2) or 850 C (S3) were characterized texturally by N2 adsorption at -196 C and by immersion calorimetry in benzene and water. The mass changes associated with the preparation of the samples are usually stronger for S1 and S3 than for S2. The incorporation of MO to AC causes a greater decrease in the micropore volume and pore narrowing only for the SnCl2-impregnated sample. The opposite effects on the microporous structure are noted for most S2 and S3, as compared to S1. For AC, -DiH(C6H6) is 114.0 J g-1 and -DiH(H2O) is 30.5 J g-1. For the AC–MO samples, -DiH(C6H6) and Stot(C6H6) are generally lower than for AC and vary by S3[S2[S1. However, -DiH(H2O), Stot(H2O) and [O] are usually lower for S3. Stot(C6H6) is higher for the samples prepared using the metal ions. The results of immersion calorimetry for AC and AC–MO samples provide one with valuable information concerning the dependence of the hydrophobicity and hydrophilicity of the samples on the method used in their preparation

Preparation and Microstructural Characterization of Activated Carbon-Metal Oxide Hybrid Catalysts: New Insights into Reaction Paths

[EN] In catalysis processes, activated carbon (AC) and metal oxides (MOs) are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and MO nanoparticles in a single hybrid material usually entails both chemical and microstructural changes, which may largely influence the potential catalytic suitability and performance of the resulting product. Here, the preparation of a wide series of AC MO hybrid catalysts is studied. Three series of such catalysts are prepared by support first of MO (Al2O3, Fe2O3, SnO2, TiO2, WO3, and ZnO) precursors on a granular AC by wet impregnation and oven-drying at 120 ºC, and by subsequent heat treatment at 200 or 850 ºC in inert atmosphere. Both the chemical composition and microstructure are mainly investigated by powder X-ray diffraction. Yield and ash content are often strongly dependent on the MO precursor and heat treatment temperature, in particular for the Sn catalysts. With the temperature rise, trends are towards the transformation of metal hydroxides into metal oxides, crystallinity improvement, and occurrence of drastic composition changes, ultimately leading to the formation of metals in elemental state and even metal carbides. Reaction paths during the preparation are explored for various hybrid catalysts and new insights into them are provided

FT-IR Analysis of Pyrone and Chromene Structures in Activated Carbon

[EN] The behavior of activated carbon in many catalysis processes is determined by the basic character of its surface. Using FT-IR spectroscopy, an attempt is made here to identify not only pyrone and chromene type structures but also their isomers in a commercial activated carbon (Merck; AC). The infrared analysis between 400 and 4000 cm−1 focuses on the keto (−CO) group in pyrones, methylene (−CH2−) group in chromenes, and enol ether group (O−CC) in both kinds of structures. Although overlapping bands are frequent in the AC spectrum, occurrence of most significant pyrone and chromene absorptions proves their presence in AC. This is so in particular for 2-pyrone and 4H-chromene, whereas 4-pyrone is less amenable to the infrared analysis

Preparation of activated carbon-metal oxide hybrid catalysts: textural characterization

[EN] In catalysis processes, activated carbon (AC) and metal oxides (MOs) are used as catalysts and catalyst supports because of their textural and chemical properties. A combination of AC andMO properties in a single catalyst entails changes in the catalytic activity and behaviour which would redound to the number of applications. The present study aims at preparing AC-MO hybrid catalysts by chemical interaction of MO precursors in aqueous medium with AC and at carrying out the textural characterization of the samples. From a commercial AC and six MO precursors (i.e. Fe3+, Al3+, Zn2+, SnCl2, TiO2, andWO4 2 −), three series of hybrid catalysts were prepared by wet impregnation and oven-drying at 120 °C and subsequent heat treatment of the resulting products at 200 or 850 °C in inert atmosphere. The samples were characterized texturally by N2 adsorption at−196 °C, mercury porosimetry, and density measurements. Therefore, the influence of theMO precursor and heating conditions on the porous texture is studied. Yield varies more widely for the samples prepared at 120 °C and 850 °C than at 200 °C. The mass increase after oven-drying at 120 °C and the mass decrease after heating at 850 °C are much greater for the Sn catalysts. Because of the support ofMO precursors on AC, in general, macro-, meso-, and microporosity significantly decrease. The effects on the texture of AC are by far more important for the Sn catalyst and also, though less, for the Fe catalyst. However, they are weaker for theW and Ti catalysts. In general, the heat treatment at 200 °C only causes small changes in the porous texture of the samples. By heating at 850 °C the pore size distribution becomes more uniform in the three porosity regions. Microporosity develops chiefly for the Sn catalyst, whereas mesoporosity does mainly for the Sn and Fe catalysts. The textural modifications have been associated with mass, composition, and structural modifications

Particle size distribution and morphological changes in activated carbon‐metal oxide hybrid catalysts prepared under different heating conditions

[EN] In catalysis processes, activated carbon (AC) andmetal oxides (MOs) are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and a MO in a single hybrid material entails changes not only in the composition, microstructure and texture but also in the morphology, whichmay largely influence the catalytic behaviour of the resulting product. Thiswork isaimedat investigating the modifications in themorphology and particle size distribution (PSD) for AC-MO hybrid catalysts as a result of their preparation under markedly different heating conditions. From a commercial AC and six MO (Al2O3, Fe2O3, ZnO, SnO2, TiO2 andWO3) precursors, two series of such catalysts are prepared by wet impregnation, oven-drying at 120ºC, and subsequent heat treatment at 200ºC or 850ºC in inert atmosphere. The resulting samples are characterized in terms of theirmorphology andPSDby scanning electronmicroscopy and ImageJ processing program. Obtained results indicate that the morphology, PSD and degree of dispersion of the supported catalysts are strongly dependent both on the MO precursor and the heat treatment temperature. With the temperature rise, trends are towards the improvement of crystallinity, the broadening of the PSD and the increase in the average particle size, thus suggesting the involvement of sinteringmechanisms. Such effects aremore pronounced for the Fe, Sn andWcatalysts due to the reduction of the corresponding MOs by AC during the heat treatment at 850ºC

Surface morphological characterization of activated carbon-metal (hydr)oxide composites: some insights into the role of the precursor chemistry in aqueous solution

[EN] Morphological features of metal (hydr)oxide (MO) particles supported on activated carbon (AC) largely influence the performance of these composite materials in most of their applications, particularly in heterogeneous catalysis. Furthermore, the MO precursor as well as the preparation method and conditions strongly determine these morphological features. Thus, the present work is aimed at shedding light on the role of the precursor chemistry on the surface morphology of a series of AC-MO composites prepared by wet impregnation of a commercial AC with Al(NO3)3, Fe(NO3)3, and Zn(NO3)2 in aqueous solution. These materials are characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The microstructure, morphology, size distribution and degree of dispersion of the supported MO (nano)particles strongly depend on the chemical transformations undergone by the precursors not only in the impregnation solutions after their contact with AC but also during the oven-drying step. Al3þ, Fe3þ and Zn2þ species in aqueous medium are involved in hydrolysis and polymerization processes, which notably modify the pH of the starting precursor solutions. Upon their contact with AC, pH markedly increases due to the strong basic character of the carbon surface (pHpzc 10.50), leading to the precipitation of the metal hydroxides or oxyhydroxides. Both supported bayerite (a-Al(OH)3) and goethite (a-FeO(OH)) are essentially amorphous; however, the former grows in micrometric particles while the latter does as nanoparticles. By contrast, the higher crystallinity and larger particle size of supported w€ulfingite (e-Zn(OH)2) are connected with an additional transformation of the as-precipitated amorphous hydroxide during the heating step at 120 C

Preparación de fotocatalizadores carbón activado-(hydr) oxidos metálicos en diferentes condiciones de calentamiento. Aspectos químicos

Se estudia la preparación de materiales de carbón activado (AC)-(hydr)oxide de metales (MO) a partir de un carbón activado comercial y de Al3+, Fe3+, Zn2+, SnCl2, TiO2 y WO4 2- en disolución/suspensión acuosa, con especial énfasis en los cambios químicos producidos a lo largo del proceso. En total se han preparado tres series de muestras mediante remojo at 80 ºC y secado en estufa a 120 ºC (S1) y posterior calentamiento de estas muestras bien a 200 ºC (S2) o a 850 ºC (S3) en N2. El pH del líquido de impregnación fue 2.91 con Al3+, 1.54 con Fe3+,5.16 con Zn2+, 1.37 con SnCl2, 5.84 con TiO2 y 9.54 con WO4 2-. Se aportan los datos del rendimiento del proceso y el contenido de cenizas de las muestras. Para las muestras de la serie S1, el rendimiento del proceso varía según SnCl2>> Fe3+ > WO42- > Zn2+ = TiO2 > Al3+.This study deals with the preparation of activated carbon (AC)-metal (hydr)oxide (MO) photocatalysts from commercial AC and Al3+, Fe3+, Zn2+, SnCl2, TiO2 and WO4 2- in water, with special emphasis on the chemical changes produced along the process. Overall, three series of samples were obtained by first soaking at 80 ºC and oven-drying at 120 ºC (S1) and by subsequent heating at 200 ºC (S2) or 850 ºC (S3) in N2 atmosphere. pH of the impregnation solution/suspension was 2.91 with Al3+, 1.54 with Fe3+, 5.16 with Zn2+, 1.37 with SnCl2, 5.84 with TiO2 and 9.54 with WO4 2-. Data of the process yield at the three temperatures and of the ash content are reported. For S1, yield varies by SnCl2 >>Fe3+> WO4 2-> Zn2+ = TiO2> Al3+.Trabajo financiado por: Junta de Extremadura y Fondos FEDER Ministerio de Educación, Cultura y Deportes. Beca FPU AP2010-2574peerReviewe

Activated carbon surface chemistry: Changes upon impregnation with Al(III), Fe(III) and Zn(II)-metal oxide catalyst precursors from NO3¯ aqueous solutions

Debido a la importancia de la catálisis heterogénea, se han analizado los cambios producidos en la química de superficie por impregnación del carbono activado (AC) con iones de Al3+, Fe3+ y Zn2+ de solución acuosa NO3¯ sales con pH 2,91 por Al3+ , 1,54 para el Fe3+ y 5.16 para Zn2+ en dos etapas sucesivas de remojo y horno-secado son estudiados. Las muestras (A120, F120 y Z120) a partir de la composición elemental y por la energía dispersiva de rayos X (EDX), por análisis de espectroscopia FT-IR, espectroscopia de fotoelectrones de rayos X (XPS) y por la medición del pH del punto de carga cero (pHpzc). El proceso rendimiento fue de 102% para un WT120, 114 wt% para F120 y 103 wt% para Z120. Y pyrone Chromene, Las estructuras tipo Cromeno, pirona y éter son predominantes en AC. La hidrólisis de los iones metálicos influye marcadamente en el pH de la solución de impregnación y también en la oxidación de superficie de los grupos funcionales de AC por O2 y NO3¯ disueltos en una solución de ese tipo. El grado de oxidación de CA es mayor con el Fe3+ que con la solución Al3+ y Zn2+. Los grupos de ácido carboxílico para F120 y grupos hidroxilo fenólico para Z120 y especialmente para el A120 se forman a partir de la reducción de las estructuras de la AC. El contenido de nitrógeno es superior por Z120 A120 > >F120 > AC. pHpzc es 10.50 para CA, 5,20 para el A120, 4.00 para F120 y 6,30 para Z120.Because of the relevance in heterogeneous catalysis, the changes produced in the surface chemistry of activated carbon (AC) upon impregnation with the Al3+, Fe3+ and Zn2+ ions from aqueous solution of NO3¯ salts at pH 2.91 for Al3+, 1.54 for Fe3+ and 5.16 for Zn2+ in two successive soaking and oven-drying steps are studied. The samples (A120, F120 and Z120) were analyzed in terms of elemental composition and by energy dispersive X-ray analysis (EDX), FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and measurement of pH of the point of zero charge (pHpzc). The process yield was 102 wt% for A120, 114 wt% for F120, and 103 wt% for Z120. Chromene, pyrone and ether type structures are by far predominant in AC. The hydrolysis of metal ions markedly influences the pH of the impregnation solution and thereby the oxidation of surface functional groups of AC by O2 and NO3¯ dissolved in such a solution. The degree of AC oxidation is larger with the Fe3+ solution than with the Al3+ and Zn2+ solutions. Carboxylic acid groups for F120 and phenolic hydroxyl groups for Z120 and especially for A120 are formed from reducing structures of AC. The nitrogen content is higher by Z120 > A120 >F120 > AC. pHpzc is 10.50 for AC, 5.20 for A120, 4.00 for F120 and 6.30 for Z120.Trabajo financiado por: Gobierno de Extremadura; y Fondos Europeos FEDER. Ministerio de Educación, Cultura y Deportes. Beca FPU para Adrián Barroso Bogeat. AP2010-2574peerReviewe

Temperature dependence of the electrical conductivity of activated carbons prepared from vine shoots by physical and chemical activation methods

[EN] A broadly varied series of activated carbons (ACs) was prepared from vine shoots (VS) by the method of physical activation in air, CO2 and steam, and by the method of chemical activation with H3PO4, ZnCl2 and KOH aqueous solutions. Here, the temperature dependence of the dc electrical conductivity for the ACs is studied from room temperature up to 200ºC. The bulk electrical conductivity of the carbon samples is found to be the result of a complex interplay between several factors, texture and surface chemistry likely being the most relevant ones. The best conductivity values are obtained for sample carbonized at 900ºC. The physical activation stage has been proved to decrease the conductivity of the carbonized products, the reduction being more pronounced for air than for CO2 and steam. Such a detrimental effect of physical activation on conductivity has been associated with the formation of oxygen groups and structures on carbon surface rather than with the porosity development. The conductivity of ACs prepared by chemical activation is even lower than for physically activated samples, likely due to the higher degree of porosity development. All carbon samples, irrespective of the activation method and activating agent, behave as semiconductor materials and therefore the electrical conduction is related to an energy gap (Eg). The Eg values widely vary from 0.084 eV for the sample carbonized at 900ºC up to 0.659 eV for the AC prepared by physical activation in air