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Angelini A.,University of Bari | Dibenedetto A.,University of Bari | Fasciano S.,CIRCC | Aresta M.,National University of Singapore
Catalysis Today | Year: 2016

The synthesis of di-n-butyl carbonate has been studied starting from n-butanol and either CO2 or urea. A comparison of the two synthetic routes is reported. Several mixed oxides have been synthesized and tested with the aim of finding a catalyst active in mild conditions (T, t), recoverable and reusable. Different strategies to push the reaction toward the formation of the target product (di-n-butylcarbonate) have been applied and adapted to each case. The pervaporation membrane and chemical water traps are compared as techniques for water elimination and equilibrium shift in the direct carboxylation. Among the tested catalysts, 0.03Nb2O5/CeO2 is the best in the case of the direct carboxylation of butanol, whereas 0.5MgO/ZnO results the best in terms of activity and robustness for the alcoholysis of urea. © 2016 Elsevier B.V.


Aresta M.,National University of Singapore | Aresta M.,University of Bari | Dibenedetto A.,CIRCC | Dibenedetto A.,University of Bari | And 2 more authors.
Journal of Catalysis | Year: 2016

The need to reduce the emission of carbon dioxide into the atmosphere is pushing toward the use of "renewable carbon", so to avoid as much as possible burning "fossil carbon". It would be possible to complement the natural "carbon cycle" by developing man-made industrial processes for "carbon recycling", converting, thus, "spent carbon" as CO2 into "working carbon", as that present in valuable chemicals or fuels. Such practice would fall into the utilization of "renewable carbon", as the man-made process would perfectly mimic the natural process. An order of complexity higher would be represented by the integration of biotechnology and catalysis for an effective CO2 conversion, using selective catalysts such as enzymes, or even whole microorganisms, coupled to chemical technologies for energy supply to enzymes, using perennial sources as sun or wind or geothermal as primary energy.These days all the above approaches are under investigation with an interesting complementarity of public-private investment in research. This paper aimed at making the state of the art in CO2 conversion and giving a perspective on the potential of such technology. Each atom of C we can recycle is an atom of fossil carbon left in the underground for next generations that will not reach the atmosphere today. © 2016 Elsevier Inc.


Ventura M.,CIRCC | Aresta M.,National University of Singapore | Aresta M.,University of Bath | Dibenedetto A.,CIRCC | Dibenedetto A.,University of Bari
ChemSusChem | Year: 2016

A simple, cheap, and selective catalyst based on copper/cerium oxides is described for the oxidation of 5-(hydroxymethyl)furfural (5-HMF) in water. An almost quantitative conversion (99 %) with excellent (90 %) selectivity towards the formation of 5-formyl-2-furancarboxylic acid, a platform molecule for other high value chemicals, is observed. The catalyst does not require any pretreatment or additives, such as bases, to obtain high yield and selectivity in water as solvent and using oxygen as oxidant. When a physical mixture of the oxides is used, low conversion and selectivity are observed. Air can be used instead of oxygen, but a lower conversion rate is observed if the same overall pressure is used, and the selectivity remains high. The catalyst can be recovered almost quantitatively and reused. Deactivation of the catalyst, observed in repeated runs, is due to the deposition of humins on its surface. Upon calcination the catalyst almost completely recovers its activity and selectivity, proving that the catalyst is robust. Aerobic workout: A mixed oxide of copper and cerium (CuOCeO2) is prepared by a milling method. The catalyst shows high activity towards the selective conversion of 5-(hydroxymethyl)furfural (5-HMF) in water, using O2 as oxidant and without any external additives. Deposition of humins during reaction causes deactivation, but upon calcination the original activity is mostly restored. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


PubMed | CIRCC and National University of Singapore
Type: Journal Article | Journal: ChemSusChem | Year: 2016

A simple, cheap, and selective catalyst based on copper/cerium oxides is described for the oxidation of 5-(hydroxymethyl)furfural (5-HMF) in water. An almost quantitative conversion (99%) with excellent (90%) selectivity towards the formation of 5-formyl-2-furancarboxylic acid, a platform molecule for other high value chemicals, is observed. The catalyst does not require any pretreatment or additives, such as bases, to obtain high yield and selectivity in water as solvent and using oxygen as oxidant. When a physical mixture of the oxides is used, low conversion and selectivity are observed. Air can be used instead of oxygen, but a lower conversion rate is observed if the same overall pressure is used, and the selectivity remains high. The catalyst can be recovered almost quantitatively and reused. Deactivation of the catalyst, observed in repeated runs, is due to the deposition of humins on its surface. Upon calcination the catalyst almost completely recovers its activity and selectivity, proving that the catalyst is robust.


Dibenedetto A.,University of Bari | Aresta M.,CIRCC | Pastore C.,CIRCC | Pastore C.,CNR Water Research Institute | And 3 more authors.
RSC Advances | Year: 2015

In this paper, we present the results of a study on 5-HMF production from fructose by means of heterogeneous catalysts in aqueous media. Mild conditions were used, setting the temperature between 393 K and 443 K. Cerium(iv) phosphates, different from other metal(iv)-phosphates, such as titanium and zirconium, have been characterized only recently. Ce-phosphates are quite complex structures as they show several arrangements. They undergo leaching of the phosphate group as phosphoric acid with consequent slow de-activation of the catalysts. The leaching rate depends on the nature and on the temperature of the calcination of the original phosphates. This opened the question whether the conversion was driven by the heterogeneous catalysts or by the soluble phosphoric acid. A specific test has demonstrated that the solid catalysts are responsible for the conversion of fructose into 5-HMF, more than the liquid phase. We have also demonstrated that the leached phosphate is substituted by fructose on the solid catalyst. A best yield of 52% with selectivity of 93% in batch and 24% in a flow reactor at 443 K (single pass) with a selectivity also >95% were obtained. © The Royal Society of Chemistry 2015.


Aresta M.,CIRCC | Dibenedetto A.,CIRCC | Dibenedetto A.,University of Bari | Angelini A.,CIRCC | Angelini A.,University of Bari
Chemical Reviews | Year: 2014

The utilization of CO2 is a strategy that can be efficiently combined with a more intelligent use of fossil-C, guaranteeing the availability of the latter for a longer term and avoiding large volumes of CO2. The business as usual (BAU) model based on the use of fossil-C as source of energy for carrying out thermal reactions can contribute to a limited extent to the conversion of CO2and recycling of carbon, also in the long term. Chemicals such as carbonates, carbamates, ureas, and carboxylates will be the real target, reaching a volume on the order of <300 Mt/y of used CO 2with a best wish of volume of avoided CO2 lower than 1 Gt/y. The discovery of efficient systems for solar energy capture, two-photon use for two-electron transfer to CO2 for an easy and fast reduction, efficient charge separation systems, space separation of oxidation and reduction processes on photocatalysts, preferable production of non-water-soluble organics from CO2, and many more needs to be studied.


Aresta M.,CIRCC | Dibenedetto A.,CIRCC | Dibenedetto A.,University of Bari | Angelini A.,CIRCC | Angelini A.,University of Bari
Journal of CO2 Utilization | Year: 2013

CO2 is today at the centre of the attention of scientists and technologists for its potential as source of carbon in the synthesis of chemicals and fuels. The actual utilization of CO2 although significant for the chemical industry (ca. 200 Mt/y) represents a minor fraction of the anthropogenic emission (32,000 Mt/y). So far, only thermal routes were exploited, based on the use of fossil carbon as source of energy. This has brought to the exploitation of low-energy reactions, making a few chemicals. The changing paradigm in the use of perennial energy sources such as solar-, wind- and geothermal-energy, makes possible the exploitation of reactions that are more energy intensive and bring to products such as fuels that have a large market. This paper makes an analysis of the potential of several applications, highlighting barriers to a large scale conversion and identifying technologies that can make possible and economically acceptable the conversion of CO 2 into fuels. Cycling large volumes of CO2 represents a way to control both its immission into the atmosphere and the extraction of fossil fuels. © 2013 Elsevier Ltd. All rights reserved.


Aresta M.,CIRCC | Dibenedetto A.,University of Bari | Angelini A.,University of Bari
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2013

The need to cut CO2 emission into the atmosphere is pushing scientists and technologists to discover and implement new strategies that may be effective for controlling the CO2 atmospheric level (and its possible effects on climate change). One option is the capture of CO2 from power plant flue gases or other industrial processes to avoid it entering the atmosphere. The captured CO2 can be either disposed in natural fields (geological cavities, spent gas or oil wells, coal beads, aquifers; even oceans have been proposed) or used as a source of carbon in synthetic processes. In this paper, we present the options for CO2 utilization and make an analysis of possible solutions for the conversion of large volumes of CO 2 by either combining it with H2, that must be generated from water, or by directly converting it into fuels by electrolysis in water using solar energy. A CO2-H2-based economy may address the issue of reducing the environmental burden of energy production, also saving fossil carbon for future generations. The integration of CO2 capture and utilization with CO2 capture and storage would result in a more economically and energetically viable practice of CO2 capture. Copyright © The Royal Society 2013.


Aresta M.,CIRCC | Dibenedetto A.,CIRCC | Dibenedetto A.,University of Bari | Angelini A.,CIRCC | And 2 more authors.
Topics in Catalysis | Year: 2015

Dialkylcarbonates, (RO)2CO, can be prepared from alcohols and CO2. Such reaction is clean (water is the co-product) but thermodynamically disfavored. In principle, the reaction mechanism of formation of carbonates requires the acid-base activation of alcohols. Existing data support that the first step is the formation of the alkoxo group RO- that reacts with CO2 to give the hemicarbonate moiety ROC(O)O-. The latter converts into the relevant carbonate (RO)2CO following different pathways depending on the catalyst used. DFT calculations have been used in a few cases to support the reaction mechanism. Transition states relevant to various mechanistic scenarios have been identified. The results indicated that the relative energies of these transition states depend on the nature of the alkyl group and the molecularity of the reactive step. Organic catalysts, homogeneous-, heterogenized- and heterogeneous-metal systems are discussed in this paper and the known relevant mechanisms compared. Water represents a serious limitation to equilibrium shift to the right and can affect the catalysts. Techniques used to remove water are also discussed. © 2014 Springer Science+Business Media New York.


PubMed | CIRCC and University of Bari
Type: Journal Article | Journal: ChemSusChem | Year: 2016

We describe a process for the selective conversion of C6 -polyols into 5-hydroxymethylfurfural (5-HMF) in biphasic systems of organic carbonate/water (OC/W), with cerium(IV) phosphates as catalysts. Different reaction parameters such as the OC/W ratio, catalyst loading, reaction time, and temperature, were investigated for the dehydration of fructose. Under the best reaction conditions, a yield of 67.7% with a selectivity of 93.2% was achieved at 423K after 6h of reaction using [(Ce(PO4)1.5 (H2 O)(H3 O)0.5 (H2 O)0.5)] as the catalyst. A maximum yield of 70% with the same selectivity was achieved after 12h. At the end of the reaction, the catalyst was removed by centrifugation, the organic phase was separated from water and evaporated in vacuo (with solvent recovery), and solid 5-HMF was isolated (purity >99%). The recovery and reuse of the catalyst and the relationship between the structure of the OC and the efficiency of the extraction are discussed. The OC/W system influences the lifetime of the catalysts positively compared to only water.

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