Influence of peroxometallic intermediaries present on polyoxometalates nanoparticles surface on the adipic acid synthesis

The cyclohexene oxidation by hydrogen peroxide catalysed by polyoxometalates (POM) has been shown as an adequate green route for the adipic acid synthesis. In this study, it has been demonstrated that POM's salts are effective catalysts for this reaction and how peroxopolyoxometalates intermediaries are the truly responsible species of the POM's salts catalytic activity and solubility. However, the latter can be reduced by calcining the catalyst previously. Polyoxomolybdates salts generally present a higher activity than polyoxotungstenates salts. Finally, it must be remarked the positive effect exerted by the acetic acid stabilising the peroxide of hydrogen against its decomposition.The authors thank the Generalitat Valenciana and FEDER (PROMETEO/2009/047), and MICINN and Plan E (CTQ2012-31762) for the financial support

Zirconia-supported 11-molybdovanadophosphoric acid catalysts: effect of the preparation method on their catalytic activity and selectivity

The oxidation of adamantane with hydrogen peroxide catalyzed by zirconia-supported 11-molybdovanadophosphoric acid is shown to be a suitable green route for the synthesis of adamantanol and adamantanone. This work evaluates how the catalyst activity and selectivity are affected by some of its preparative parameters, such as the method for supporting the catalytically active heteropoly acid over the zirconia matrix or the pretreatments applied to the resulting materials before being used as heterogeneous catalysts. Our results indicate that the most effective catalysts able to maintain their activity after several reaction runs are those prepared by following the sol-gel route, whereas the most selective catalysts are those obtained by impregnation methods. Moreover, the calcination temperature has also been identified as a relevant parameter influencing the performance of catalysts based on supported heteropoly acids. The increasing catalytic activity observed over several consecutive reaction runs has been attributed to the formation of peroxo derivatives of polyoxometalate clusters at the surface of the catalyst and their accumulation after each reaction cycle.Funding for this research was provided by: Generalitat Valenciana (grant No. PROMETE/2018/076); Ministerio de Economía, Industria y Competitividad (grant No. CTQ2015– 64801-R); Obra Social la Caixa, Fundación Caja Navarra and Universidad Pública de Navarra (contract to SR in the framework of the program ‘Captación de Talento’)

Chemical Activation of Lignocellulosic Precursors and Residues: What Else to Consider?

This paper provides the basis for understanding the preparation and properties of an old, but advanced material: activated carbon. The activated carbons discussed herein are obtained from “green” precursors: biomass residues. Accordingly, the present study starts analyzing the components of biomass residues, such as cellulose, hemicellulose, and lignin, and the features that make them suitable raw materials for preparing activated carbons. The physicochemical transformations of these components during their heat treatment that lead to the development of a carbonized material, a biochar, are also considered. The influence of the chemical activation experimental conditions on the yield and porosity development of the final activated carbons are revised as well, and compared with those for physical activation, highlighting the physicochemical interactions between the activating agents and the lignocellulosic components. This review incorporates a comprehensive discussion about the surface chemistry that can be developed as a result of chemical activation and compiles some results related to the mechanical properties and conformation of activated carbons, scarcely analyzed in most published papers. Finally, economic, and environmental issues involved in the large-scale preparation of activated carbons by chemical activation of lignocellulosic precursors are commented on as well.This research was funded by Generalitat Valenciana (PROMETEO/2018/076), European Commission/FEDER, and the University of Alicante (VIGROB-136)

Effect of the stabilisation time of pitch fibres on the molecular sieve properties of carbon fibres

The stabilisation of pitch fibres (PFs) is the most important step for their subsequent use in the preparation of carbon fibres (CFs) and their resulting characteristics. The present work studies the influence that the stabilisation time has on the porosity of the CFs, and on the subsequent properties as carbon molecular sieve (CMS). The increase of the stabilisation time carried out at 573 K, from 2 to 8 h favours their CMS properties producing a decrease in the microposity accessible to N2, which gets completely blocked after 6 and 8 h, while the narrow microporosity (V-DR CO2) remains accessible. Adsorption kinetic studies with CH4 and CO2 were performed to assess the possibility of using these CFs as CMS by comparing them with Takeda 3A CMS. The results suggest that there is an optimal stabilisation time which allows the preparation of CFs from an abundant raw precursor with properties similar to Takeda 3A CMS.MCYT (PPQ2003-03884)

Unusual pre-oxidized polyacrylonitrile fibres behaviour against their activation with CO2: carbonization effect

The CF-PAN activation process with CO2 has been analysed. Activation of CF-PAN with CO2 leads to unusual results both, activation percentage evolution over the time and generated porosity development. In the explanation has been highlighted the role of the carbonization step in the CF-PAN activation process. The analysed results point to the fact that part of the released nitrogen-containing compounds during PANOX fibres carbonization are deposited on the CF surface, which affects to carbonized PAN fibres, decreasing actives sites, or acting as inhibitors of the gasification reaction.The authors thank the Generalitat Valenciana and FEDER (PROMETEO2/2014/010), and MICINN and Plan E (CTQ2012-31762) for the financial support

Zirconia-supported tungstophosphoric heteropolyacid as heterogeneous acid catalyst for biodiesel production

A series of materials based on the immobilization of the 12-tungstophosphoric heteropolyacid over zirconia supports have been prepared and applied as heterogeneous acid catalysts in the esterification of palmitic acid with methanol as a model reaction for the preliminary stage of the biodiesel production. The title materials have been obtained through the sol-gel method combined with a subsequent hydrothermal treatment at mild conditions, which affords catalysts with larger porosity and higher thermal and chemical stability under the esterification reaction conditions than other preparative approaches. Generating the zirconia support by hydrolysis of an alkoxyde precursor in the presence of the heteropolyacid leads to materials with homogeneously well-dispersed clusters, as well as to an increasing contribution of the tetragonal ZrO2 crystalline phase, a decreasing size of the nanoparticles and larger microporous volumes as the loading of the Keggin-type species increases. The 12-tungstophosphoric acid retains its catalytic activity in the esterification of palmitic acid with methanol at 60 °C upon immobilization over zirconia and conversions even higher than those observed under homogeneous conditions are obtained due to the active contribution of the support. The sample with a 30% mass percentage of heteropolyacid has been identified as the most efficient catalyst because it affords conversions above the 90% and shows the lower loss of activity over successive reaction runs among all of our materials. This loss of activity has been analyzed on the basis of the leaching of the catalyst and the fouling of the materials.This work was financially supported by Generalitat Valenciana through FEDER funds (grant PROMETEO2/2014/010) and by the Spanish Ministerio de Economia y Competitividad (grant CTQ2015-64801-R). S.R. acknowledges financial support from InaMat and from the program “Ayudas para la Captación del Talento adscritas a los Institutos de Investigación de la UPNA” funded by a collaboration agreement with Obra Social la Caixa and Fundación Caja Navarra

A Simple Approach To Develop Tailored Mesoporosity in Nanostructured Heteropolysalts

In this study, we describe a very simple approach to the development of tailored mesoporosity in any nanostructured heteropolysalt with control over both the mesoporous volume and the pore size. This approach, which consists in the treatment of a solid microporous precursor with a basic agent, has been tested on the ammonium salt of the Keggin-type [PMo12O40]3− heteropolyanion and constitutes a novel procedure for the preparation of mesoporous solids with no precedents. The results obtained in this study allow two main conclusions to be drawn: 1) the micro- and mesoporous structures in the heteropolysalt nanoparticles are independent from each other and 2) the development of mesoporosity in the solid material must be related to a process of alkaline degradation within the core of the nanocrystals that aggregate into the particles. These results afford valuable additional information to the present model of porosity that has been established for heteropolysalts.This work was financially supported by Generalitat Valenciana (grant PROMETEO2/2014/010) and Ministerio de Economia y Competitividad (grant CTQ2015-64801-R) through FEDER funds. S.R. acknowledges financial support from the program “Ayudas para la Captación del Talento adscritas a los Institutos de Investigación de la Universidad Pública de Navarra” funded by a collaboration agreement between Universidad Pública de Navarra, Fundación Bancaria la Caixa and Fundación Bancaria Caja Navarra

Trabajo de coordinación para la implementación del cuarto curso del Grado en Química

En el curso 2013-14 se implantará el cuarto y último curso del Grado en Química. La experiencia adquirida durante la implementación de los tres primeros cursos ha puesto de manifiesto la conveniencia de realizar un proceso de coordinación entre los profesores de las diferentes asignaturas que garantice la consecución de las competencias previstas en la memoria del título. Por ello, se ha creado en la Facultad de Ciencias de la Universidad de Alicante una red de investigación en docencia universitaria que ha estado trabajando desde el inicio del presente curso académico en este tema. Dicha red está constituida por el Vicedecano de Ordenación Académica de la Facultad de Ciencias, la Coordinadora Académica de Química y los profesores coordinadores de todas las asignaturas del 4º curso del grado (excepto Prácticas Externas y Trabajo Fin de Grado). En esta comunicación se presentarán los resultados del trabajo de investigación realizado por estos profesores que ha permitido elaborar las guías docentes de las asignaturas, planificar y coordinar las actividades a realizar para que los alumnos adquieran las competencias transversales, realizar un cronograma de actividades de evaluación y otro de prácticas de laboratorio que asegure la distribución homogénea del trabajo del alumno durante el curso académico

Assessment of Ultramicroporosity on Carbon Molecular Sieves by Water Adsorption

This work is focused on the application of water adsorption to the characterisation of the narrow microporosity (ultramicroporosity) in carbon molecular sieves (CMS). In addition, the mechanism of water adsorption in carbonaceous solids was analysed. Despite the presence of surface groups in these materials, they exhibited low adsorption at low relative pressures (P/P 0 < 0.2), indicating the significant role of micropore size in the commencement of water adsorption. Interestingly, it was observed that water adsorbed on samples that did not exhibit CO 2 adsorption