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The need to decrease the concentration of CO

This paper discusses the epochal change in the reputation of carbon dioxide, which is now considered as a raw material alternative to fossil C for the synthesis of chemicals, materials and fuels, as opposed to a waste material that must be confined underground. In particular, its use as renewable C is compared to biomass. In this paper, a specific point is discussed: is ethanol (or any fuel) produced via the catalytic conversion of atmospheric CO

Olive pomace is a semisolid by-product of olive oil production and represents a valuable source of functional phytocompounds. The valorization of agro-food chain by-products represents a key factor in reducing production costs, providing benefits related to their reuse. On this ground, we herein investigate extraction methods with supercritical carbon dioxide (SC-CO2) of functional phytocompounds from olive pomace samples subjected to two different drying methods, i.e., freeze drying and hot-air drying. Olive pomace was produced using the two most common industrial olive oil production processes, one based on the two-phase (2P) decanter and one based on the three-phase (3P) decanter. Our results show that freeze drying more efficiently preserves phytocompounds such as &alpha, tocopherol, carotenoids, chlorophylls, and polyphenols, whereas hot-air drying does not compromise the &beta, sitosterol content and the extraction of squalene is not dependent on the drying method used. Moreover, higher amounts of &alpha, tocopherol and polyphenols were extracted from 2P olive pomace, while &beta, sitosterol, chlorophylls, and carotenoids were more concentrated in 3P olive pomace. Finally, tocopherol and pigment/polyphenol fractions exerted antioxidant activity in vitro and in accelerated oxidative conditions. These results highlight the potential of olive pomace to be upcycled by extracting from it, with green methods, functional phytocompounds for reuse in food and pharmaceutical industries.

The Capture and Storage of Carbon Dioxide (CCS) is illustrated in this chapter. CO2 can be captured from point sources (power plants and industries) or directly from the atmosphere (Direct Air Capture (DAC)) or even from mobile sources. Technologies for the capture are illustrated here and some examples of disposal in natural fields are described, together with fixation into long-lasting materials, such as inorganic carbonates.

The basic aspects of the reactivity of carbon dioxide are featured, related to the electronic structure of the molecule. The phase diagram of CO2 is also discussed for understanding how CO2 exists in different conditions of temperature and pressure.

In this chapter, the relevance of Carbon Dioxide Utilization (CCU) to Innovation and Sustainability of the Chemical Industry and to the strategy of the Circular Economy is discussed. A number of examples are presented of processes which may convert CO2 into added-value chemicals, polymeric materials, and fuels which have each a market higher than 1 Mt/y, causing a significant reduction of CO2 emission. Only thermal processes are considered here, while solar-driven processes are discussed in Chap. 10 and the integration of Chemical Catalysis and Biotechnology is presented in Chap. 11.

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 CO 2 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 CO 2 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 CO 2 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.

New catalytic systems based on ceria have been used in the direct carboxylation of ethanol. The catalytic behavior of Al(2)O(3) and Nb(2)O(5) loaded ceria is compared, the latter showing a better performance. A morphological and structural study has been carried out on Nb(2)O(5)/CeO(2) catalysts in order to explain their behavior in catalysis. Pervaporation membranes have been used for water separation. The synthesis of diethylcarbonate (DEC) has been carried out either in a liquid phase (ethanol) pressurized with CO(2) or in supercritical conditions. A set-up has been developed that allows the production of quite pure DEC (>90%) with recycling of CO(2) and ethanol.

In this chapter the direct, non-metal-mediated interaction of carbon dioxide with electron-rich elemental or molecular species is discussed. Anionic species such as H−, OH−, and R3C− and covalent species such as amines have been taken into consideration, in view of their relevance to systems of potential or real industrial interest.

A p-type semiconductor, CuI, has been synthesized, characterized, and tested as a photocatalyst for CO2 reduction under UV/Vis irradiation in presence of isopropanol as a hole scavenger. Formation of CO, CH4 , and/or HCOOH was observed. The photocatalytic activity of CuI was attributed to the very low potential of the conduction band edge (i.e., -2.28 V vs. NHE). Photocurrents generated by the studied material confirm a high efficiency of the photoinduced interfacial electrontransfer processes. Our studies show that p-type semiconductors may be effective photocatalysts for CO2 reduction, even better than extensively studied n-type titanium dioxide, owing to the low potential of the conduction band edge.

The modes of coordination of carbon dioxide (CO2) to metal centres are presented in this chapter. The coordination at both room temperature and low temperature in gas matrices is discussed with the reactivity of the coordinated cumulene. X-ray diffraction structural data are presented and discussed together with spectroscopic properties of the complexes.

Chemical reducing agents (sodium dithionite) or bioglycerol (as H and e−-donor under irradiation in the presence of ZnS-A as photocatalyst) are able to back-convert NADP+ into NADPH, which is used as e−-donor in the enzymatic reduction of CO_{2} into CH_{3}OH. In doing so, the molar ratio CH_{3}OH/CO_{2} has been increased (without recycling of NADP+) using the photocatalyst.

Aqueous glycerol was used as the hydrogen source for the reduction of CO(2) to the hydrogen carrier formic acid in the presence of the catalyst [RuCl(2)(PPh(3))(3)]. All intermediates were identified and characterized. Glycerol was converted into glycolic acid, HO-CH(2)-COOH, that was identified by using (1)H and (13)C NMR spectroscopy.

The development of a new synthetic approach to acrylates based on the formation of alkyl esters of acrylic acids has been studied. A preformed Pd-COOMe moiety is used as a model system to investigate the insertion of an olefin into the Pd--C bond. The fast elimination of acrylate is observed. Density functional calculations support the experimental findings and allow the characterization of transition states along the reaction pathway. The first example of olefin/CO(2) coupling with facile release of ethyl acrylate is also presented.

Glycerol was reacted with CO 2 (5 MPa) at 450 K in presence of Sn-catalysts ( n -Bu 2 Sn(OMe) 2 1 , n -Bu 2 SnO 2 or Sn(OMe) 2 3 ), using either glycerol or tetraethylene glycol dimethyl ether (tedmg) as reaction medium. 1 was much more active than 2 . 1 was demonstrated to convert into n -Bu 2 Sn(glycerol-2H) 4 upon reaction with glycerol and elimination of MeOH. Monomeric 4 is proposed to be the active species in catalysis. It converted into a polymeric material with time with consequent reduction of its catalytic activity. Also, after the first catalytic cycle 4 was converted into an oligomeric material that did not contain glycerol. This also caused the reduction of the catalytic activity. 3 was able to uptake CO 2 but was not able to promote the carboxylation of glycerol. 1 and 2 also promoted the trans -esterification of dimethylcarbonate (DMC) with glycerol to afford glycerol carbonate, but at a lower rate than the direct carboxylation of glycerol. This fact seems to rule out that the carboxylation of glycerol may proceed through the preliminary formation of DMC and its subsequent trans -esterification.

We have investigated the dependence of the rate of the production of biogas upon the concentration of nickel, cobalt and iron at sub-toxic concentration and monitored its composition as amount of hydrogen, methane and carbon dioxide. The distribution of the added metals between the liquid and solid phase has also been monitored. The results of our investigations show that the addition of any of the listed metals to the sludge may cause the production of a higher amount of biogas and influence the methane or carbon dioxide percentage. Conversely, the effect on the hydrogen production depends upon the metal added, the age of the active sludge used, and its adaptation to the susbtrate. As a general feature, during the acidogenesis phase, nickel reduces, while iron increases, the percentage of dihydrogen in the biogas, while cobalt has no influence.

In this paper the synthesis of a cyclic organic carbonate by a halogen-free route is described. The ketal formed from cyclohexanone and 1,2-ethanediol was reacted with carbon dioxide, either in SC-CO2 or in organic solvents under CO2 pressure. Transition-metal complexes with functionalized fluorinated di-ketone ligands were used as catalyst. The synthetic methodology based on SC-CO2 is effective for the synthesis of ethylene carbonate. The use of methanol as co-solvent in SC-CO2 prevents the formation of the ethylene carbonate and only the alcoholysis of the ketal is observed. In organic solvents, no reaction takes place.

The reactivity of industrially relevant silylalkylamines towards CO2 and dialkyl/arylcarbonates is discussed. The kinetics of uptake of carbon dioxide at various temperatures shows that at 295 K, silylalkylmonoamines react with carbon dioxide in a 2∶1 molar ratio, affording classic intermolecular ammonium carbamates of formula RNHCOO−+NH3R, while at 273 K, dimeric carbammic acids, (RNHCOOH)2, are formed. Conversely, silylalkyldiamines react at 297 K with carbon dioxide to afford zwitterionic intramolecular six-membered cyclic ammonium carbamates of formula RNH2+CH2CH2NHCOO−, a unique example of CO2 uptake by an amine with a 1∶1 molar ratio. Such systems may have a potential application in CO2 separation. The catalytic role of carbon dioxide in the carbamation of the above mentioned amines by reaction with organic carbonates is described.

Carboxylation reactions widely occur in nature by the direct use of carbon dioxide or hydrogen carbonate and are mediated by enzymes, which may or may not have a metal as an active center. Such direct carboxylation reactions have found only very few applications for synthetic purposes at industrial level. In this paper we review a part of the work we have done on the use of carbon dioxide and describe: (i) the use of a carboxylation enzyme for the conversion of phenol into 4-OH benzoic acid; and (ii) the potential of biomimetic mixed anhydrides for the synthesis of compounds of industrial interest. The enzymatic production of acetic acid from carbon dioxide is compared with known and new transition metal catalyzed reactions that are fully biomimetic.

This article summarizes a number of applications of CO2 in the synthesis of molecular compounds, materials and fuels. The actual and perspective amount of used CO2 is given for 2016 and 2030. Barriers to a full exploitation are discussed and future areas of major interest are highlighted. Keywords: carbon dioxide; building block for chemicals; source of carbon for fuels; synthesis of polymers

CO 2 is today at the center of the attention of scientists and technologists for its potential as a source of carbon. The actual utilization of CO 2 although significant “per se” (ca. 200 Mt/y) represents a minor fraction of the anthropogenic emission (32,000 Mt/y). This chapter describes old and new uses of carbon dioxide in synthetic chemistry, with an analysis of the potential of several applications, highlighting barriers to a large-scale conversion and identifying technologies, which enable the conversion into fuels. Cycling large volumes of CO 2 represents a way to control both its emission into the atmosphere and the extraction of fossil fuels.

The coordination chemistry of phenoxide ligands, such as C6H5O–, 4-(CH3)-C6H4O–, 3,5-(CH3)2-C6H3O–, 2,6-(tert-butyl)2-C6H3O–, 2,6-(CH3)2-C6H3O–, to Mn(II) has been investigated because of the possible implication of Mn(II)–phenoxide complexes as intermediates in the phenylphosphate carboxylase enzyme, a protein which catalyses the selective carboxylation of phenylphosphate to 4-OH-benzoic acid using CO2. We report here the synthesis and characterization of [CpMn(µ-OAr)(THF)]2 (ArO = C6H5O–, 4-(CH3)-C6H4O–, 3,5-(CH3)2-C6H3O–, 2,6-(CH3)2-C6H3O–) and [CpMn(η5-ArO)] (ArO = 2,6-(tert-butyl)2-C6H3O– and 2,6-(CH3)2-C6H3O–) complexes, the first examples of mixed-sandwich complexes with Cp and phenate as π-ligands. The latter bear the 2,6-substituted phenoxide π-coordinated to the [Mn(Cp)]+ moiety. The different mode of bonding of the phenoxide ligands to Mn(II), substantiated by 1H NMR and electron spin resonance (ESR) spectroscopy, is controlled by the steric hindrance of substituents at the 2- and 6-position. The reactivity of the π-bonded ligand towards CO2 is also reported as a quite rare example of nucleophilic attack at the cumulene by the ring-carbon of the phenoxide, which is driven by electron density localization at the 4-position generated upon π-coordination to Mn(II).Key words: Mn(II)-complexes, phenoxide ligands, 1H NMR spectroscopy, ESR spectroscopy, reaction with carbon dioxide.

The reduction of carbon dioxide emission into the atmosphere requires the implementation of several convergent technologies in different production sectors. The chemical industry can contribute to the issue with innovative synthetic technologies, which implement the principles of atom-economy, dematerialization, energy saving, and raw material diversification with carbon recycling. Such methodologies based on carbon dioxide utilization merge two issues, namely, avoiding the production of CO 2 and carbon recycling. In this paper, some options are discussed, such as the synthesis of carboxylic acids, organic carbonates, and carbamates/isocyanates. Synthetic processes of methanol from either CO 2 or CO are compared. The results of application of LCA to selected cases are discussed.

The synthesis, analytical and spectroscopic characterisation, and reactivity of three new Rh(I)–phenoxide complexes of formula Rh 2 (μ-OPh) 2 (C 2 H 4 ) 4 ( 1 ), Rh(C 2 H 4 ) 2 (η 5 -OPh) ( 2 ) and Rh(diphos)(η 5 -OPh) ( 4 ) [diphos=1,2-bis(diphenylphosphino)ethane] are reported. Both the η 5 - and μ-(O) modes of bonding have been found. The η 5 -complexes are quite air-sensitive. The reactivity towards carbon dioxide is described and the formation of an emicarbonate is reported with the O-bonded phenoxide. A ring carboxylation occurs with η 5 -complexes.

The mitigation of carbon dioxide is one of the scientific and technological challenges of the 2000s. Among the technologies that are under assessment, the recovery of carbon dioxide from power plants or industrial flue gases plays a strategic role. Recovered carbon dioxide can be either disposed in natural fields or used. The availability of large amounts of carbon dioxide may open new routes to its utilisation in biological, chemical and innovative technological processes. In this paper, the potential of carbon dioxide utilisation in the short-, medium-term is reviewed.

This chapter presents the efforts from recent years in carbon dioxide conversion under homogeneous catalysis. Several different compounds are considered, from fine chemicals to products of the energy industry, showing the high potential that CO 2 chemistry has in the development of a sustainable chemical industry. References to published reviews and old works produce a panoramic view of the huge work done so far that is the basis for new developments and applications to target syntheses.

The recovery of carbon dioxide from concentrated sources is currently under evaluation as a technology for the control of the emission into the atmosphere. In order this option would be operative it is necessary to define the fate of recovered carbon dioxide. Two ways are open forward: 1. - disposal in natural fields (oceans, aquifers, deep geological cavities); 2. - utilisation (technological use or chemical conversion). The fixation in chemicals can contribute both to reduce the use of fossil carbon and to cut the emission of carbon dioxide into the atmosphere.

A new method of synthesis of both aliphatic and aromatic alkali-metal carbamates and anhydrous alkylammonium tetraphenylborates by reaction, at room temperature, of amines with alkali-metal tetraphenylborates in the presence of CO2(0.1 MPa) has been determined. This reaction represents the first step of a new very selective synthetic route to alkali-metal carbamates from amines, carbon dioxide and alkali-metal hydroxides at room temperature and pressure. It is also the first example of the isolation of aromatic amine alkali-metal carbamates through a non-isocyanate route.

One of the many goals of the green chemistry movement is to eliminate the use of phosgene (COCl{sub 2}), an extremely hazardous compound used in many syntheses, including the production of carbamates, organic carbonates, and polymers. One of the most interesting options for eliminating this compound is to replace it with CO{sub 2}. In addition to carbon dioxide`s abundance and benign nature, it has the benefits of recycling carbon and of reducing the amount of CO{sub 2} released into the atmosphere when its use is linked with other processes that emit CO{sub 2}. Several synthetic strategies that do not use phosgene are under development. The authors briefly review the most interesting ones and then expand on the use of CO{sub 2} as a potential building block for organic carbamates, carbonates, and isocyanates. One of these routes, polycarbonate synthesis, is already in industrial-scale operation: PAC Polymers Inc. currently produces CO{sub 2}-epoxide copolymers. The synthesis of carbamates and substituted ureas has been developed, and this process awaits industrial exploitation.