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Polyethylene glycol stabilized platinum nanoparticles were immobilized on solid supports such as γ-Al2O3, SBA-15, TiO2 and active carbon, forming supported polyethylene glycol stabilized platinum nanoparticles (SPPNs). In the hydrogenation of p-chloronitrobenzene (p-CNB) in supercritical carbon dioxide (scCO2), the SPPN showed high selectivity to p-chloroaniline (>99.3%) in the whole range of conversion. Such high selectivity to corresponding haloanilines (HANs) (>99.1%) was also obtained in the hydrogenation of o-CNB, m-CNB, 2-chloro-6-nitrotoluene, p-bromonitrobenzene and m-iodonitrobenzene. The dehalogenation and the accumulation of intermediates were fully inhibited simultaneously in scCO2. The SPPN catalysts could be reused several times without loss of high selectivity in present reaction system., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The utilization of CO2 as a renewable and cheap carbon resource to produce fuels, chemicals and polymers has attracted more attention. This review will summarize the developments in the production of polymers like polyureas and polyurea hybrids with CO2 as a monomer directly or indirectly. The influences of catalyst and the structure of diamine monomer on the molecular weight, thermal stability and mechanical properties of polyureas are discussed. In addition, the general properties and applications of functional CO2‐based polyureas are also described. A few examples of CO2‐based polyurea hybrids are also introduced. Finally, the future research priorities as well as the development trend of polyurea materials are depicted. [ABSTRACT FROM AUTHOR]

The fabrication of self-healing and recyclable CO2-based polymeric materials meets the requirement of sustainable development. By introducing reversible hydrogen bonds and heat-responsive Diels–Alder bonds, a new, environmentally friendly, self-healing and recyclable polyurethane-urea Diels–Alder adduct (PUUa-DA) was successfully synthesized using CO2 and furfuryl amine as renewable feedstocks. PUUa-DA was semi-crystalline and exhibited high thermal stability, 5% weight loss temperature being above 220 °C. Moreover, PUUa-DA with a cross-linked structure showed a tensile stress of 18.5 MPa, a modulus of 151 MPa and an elongation at break of 136%. The dynamic Diels–Alder bonds and hydrogen bonds provide the self-healing response and contribute to 94% recovery of the tensile strength upon heating. Therefore, PUUa-DA will have potential applications as a functional material in a wide range of practical fields. The synthesis of PUUa-DA using CO2 and bio-based furfuryl amine will be of importance in green and sustainable chemistry. [ABSTRACT FROM AUTHOR]

A non‐noble heterogeneous catalyst of Cu/TiO2 was prepared for N‐methylation of N‐methylaniline (MA) with CO2 and H2. 5 wt.–% Cu loaded TiO2 (P25) catalyst exhibited a high performance, with 82 % MA conversion and 98 % N,N‐dimethylaniline (DMA) selectivity under the reaction conditions used (4 MPa H2, 2 MPa CO2, 180 °C, 36 h). The Cu/TiO2 catalyst was more effective with respective to the total conversion and the DMA selectivity as compared to 5 wt.–% Cu loaded catalysts on CeO2, ZnO and activated carbon materials. The possible active species of Cu/TiO2 catalyst should be both Cu+ and Cu0 which contributed to the high activity as the reaction conversion increased linearly with them exposed on the surface of catalyst. Moreover, the reaction pathways involved were studied; it was likely that the reaction took place via an intermediate of formaldehyde that was formed from CO2 and H2, as confirmed by in situ diffuse reflectance Fourier‐transform infrared spectroscopy, then it reacted with MA to give N‐methylformanilide (MFA), and finally MFA was hydrogenated to DMA. [ABSTRACT FROM AUTHOR]

A series of polyureas were synthesized with CO 2 as the carbonyl building block, which consist of a hard segment of CO 2 -based oligourea and a soft segment of soluble polyether diamine. The hard segment was formed from 1,3-bis(3-aminopropyl) tetramethyl disiloxane with CO 2 , and the soft segment was obtained through polyaddition of polyether diamine with an extender agent. The Number-average Molecular Weight (Mn) and Weight-average Molecular Weight (Mw) were estimated by Gel permeation chromatography (GPC). The properties of the synthesized polyureas such as thermo-stability and the tensile strength were examined, and these properties could be adjusted by varying the molecular weight of polyether diamine and oligourea segments. The synthesized polyureas have an amorphous structure and presented satisfied thermo-stability (∼250 °C) and the high tensile strength (22.4 MPa). [ABSTRACT FROM AUTHOR]

Using CO2 as a carbonyl building block to synthesize valuable chemicals is an important issue in the field of green and sustainable chemistry. Herein, the conversion of CO2 with glycerol to glycerol carbonate was investigated in the presence of 2-cyanopyridine. It was found that 2-cyanopyridine not only acts as the dehydrating agent to break the thermodynamic limit of the reaction, but also activates the carbonyl bond of CO2 to catalyze the present carbonylation as confirmed by FTIR experimental spectra. Moreover, the activation closely depends on the stereo-structure of cyanopyridine, in that 3-cyanopyridine and 4-cyanopyridine do not have such activating function. The theoretical calculation demonstrated that 2-cyanopyridine could bond CO2 through the conjugating nitrogen to form a five-membered ring, thus CO2 is activated and then reacts with glycerol to produce glycerol carbonate. The reaction parameters were examined and evaluated for the reaction catalyzed with 2-cyanopyridine in the absence of any metal catalysts and additives. With increasing CO2 pressure, the yield of glycerol carbonate increases, and under the optimum conditions an 18.7% yield is obtained which is one of the best results reported up to now. The present work provides a new way for activation of CO2. [ABSTRACT FROM AUTHOR]

Highlights: [•] The addition of CO2 remarkably affected the reaction rate and product selectivity. [•] The decreased reaction rate is due to the formation of solid carbamate in the presence of CO2. [•] The yield of benzylamine was increased to >94.4% in the presence of CO2. [•] The presence of CO2 could prohibit the formation of dibenzylamine in organic solvents. [•] The acidic nature of H2O–CO2 benefited the elimination of NH3. [Copyright &y& Elsevier]

Abstract: Water as a clean solvent and promoter in the organic synthesis have attracted more attention, herein the effect of water was studied for the hydrogenation of o-chloronitrobenzene (o-CNB) over Pt/C and Pd/C catalysts in ethanol, n-heptane and compressed CO2. Very interesting, the reaction rate decreased in ethanol, but increased in n-heptane and compressed CO2 with the addition of water. The role of water in the reaction was mainly discussed from the experimental data and phase behavior analysis, one is to activate the functional group of NO2 through the interactions via a hydrogen bonding, and the other is to affect the solubility of hydrogen in ethanol and n-heptane. The positive effect of the interaction between water and reactants may be counteracted by the negative effect of hydrogen solubility in ethanol. However, the concentration of o-CNB and hydrogen changed slightly in n-heptane with the addition of water, so the interaction of water with reactants may play a main role in improving the TOF. The combination of H2O and CO2 is more efficient than the pure H2O, CO2 and H2O–n-heptane systems. The phase behavior may play important role also for the improved activity except for the interactions of H2O and CO2 with the reactants. o-CNB phase was expanded in the compressed CO2 and so the concentration of H2 in o-CNB phase increased due to the miscible of CO2 and H2, resulting in the enhancement of reaction rate and the maximum conversion at pressure of 9MPa CO2, at which the volume was expanded to the largest one. The similar results were also obtained in the compressed CO2 system without H2O. In addition, the stability of Pt/C and Pd/C was studied in H2O–n-heptane and H2O–CO2. As a result, the H2O–CO2 media and Pt/C catalyst is one of the most effective systems for the hydrogenation of o-CNB. [Copyright &y& Elsevier]

Abstract: The hydrogenation of chloronitrobenzene to chloroaniline was investigated over Ni/TiO2 at 35°C in supercritical CO2 (scCO2), ethanol, and n-hexane. The reaction rate followed the order of scCO2 > n-hexane>ethanol. In scCO2, the selectivity to chloroaniline and to aniline over Ni/TiO2 were 97–99.5% and <1%, respectively, in the conversion range of 9–100%. The high chemoselectivity to chloroaniline cannot be achieved over Ni/TiO2 in ethanol and n-hexane. In situ high-pressure Fourier transform infrared measurements were made to study the molecular interactions of CO2 with the following reactant and reaction intermediates: chloronitrobenzene, chloronitrosobenzene, and N-chlorophenylhydroxylamine. The molecular interaction modifies the reactivity of each species and accordingly the reaction rate and the selectivity. The influence of Cl substituent on the interaction modes of CO2 with these reacting species is discussed. Possible reaction pathways for the hydrogenation of chloronitrobenzene in scCO2 over Ni/TiO2 are also proposed. [Copyright &y& Elsevier]

Abstract: Hydrogenation of maleic anhydride (MAH) with Pd/C catalysts in supercritical carbon dioxide (scCO2) was investigated. The selectivity for γ-butyrolactone (GBL) reached 97.3% in scCO2 at 100% conversion of MAH, which was notably higher than that of 77.4% obtained in organic solvent of ethylene glycol dimethyl ether (EGDME). The particle size of Pd exhibited large influence on the reaction rate and selectivity of GBL. Higher selectivity of GBL was obtained with Pd/C catalyst of smaller Pd particle size, and the rate of GBL selectivity increase as a function of CO2 pressure was found to be significantly correlated with Pd particle size. [Copyright &y& Elsevier]

The selective hydrogenation of nitrobenzene (NB) over Ni/γ-Al2O3 catalysts was investigated using different media of dense phase CO2, ethanol, and n-hexane. In dense phase CO2, the total rate of NB hydrogenation was larger than that in organic solvents under similar reaction conditions; the selectivity to the desired product, aniline, was almost 100% over the whole conversion range of 0–100%. The phase behavior of the reactant mixture in/under dense phase CO2 was examined at reaction conditions. In situ high-pressure Fourier transform infrared measurements were made to study the molecular interactions of CO2 with the following reactant and reaction intermediates: NB, nitrosobenzene (NSB), and N-phenylhydroxylamine (PHA). Dense phase CO2 strongly interacts with NB, NSB, and PHA, modifying the reactivity of each species and contributing to positive effects on the reaction rate and the selectivity to aniline. A possible reaction pathway for the hydrogenation of NB in/under dense phase CO2 over Ni/γ-Al2O3 is also proposed. [Copyright &y& Elsevier]

Abstract: The reaction rates of the hydrogenation of maleic anhydride (MAH) and succinic anhydride (SAH) were significantly accelerated and the selectivity to γ-butyrolactone (GBL) was enhanced largely when the reaction mixture was pressurized by a non-reactant of CO2. Above 99% selectivity to GBL was achieved in 14MPa CO2, the superior selectivity in scCO2 was attributed to that MAH and/or SAH could be extracted to CO2 phase and separated from H2O, the hydrolysis were thus minimized and so the selectivity to GBL was improved. [Copyright &y& Elsevier]

Abstract: Hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) with Pd/C has been investigated in supercritical carbon dioxide (scCO2) at 308K. The influences of several parameters such as CO2, H2 pressures, Pd metal particle size and reaction time have been discussed. CO2 pressure presented markedly effects on the reaction rate and product selectivity under the reaction conditions used, the selectivity to o-CAN at CO2 pressure from 8 to 13MPa (supercritical region) was larger than that at CO2 pressure below 6MPa (subcritical region). Moreover, the larger selectivity to o-CAN was obtained in scCO2 compared with that in ethanol. [Copyright &y& Elsevier]

Chemoselective hydrogenation of water-insoluble aromatic nitro compounds can be achieved over Ni catalysts in a H2O–compressed CO2system at 35–50 °C without using any environmentally harmful solvent. The effective CO2pressure is much lower than the critical pressure of CO2. The hydrogenation of nitro group should be the rate-determining step. [ABSTRACT FROM AUTHOR]

Abstract: The fabrication of nanostructured materials from hydrous inorganic metal salt processed in supercritical CO2 (scCO2) expanded liquids has advantages to obtain good results. However, the behavior of the inorganic salts and the detailed reaction mechanism are still unknown up to now. In this work, the actual behavior of hydrous inorganic metal salts in CO2 expanded ethanol at the temperature of 50–200°C, including the phase behavior, deposition mechanism, reaction rate and the effect of templates on the deposition were systematically investigated by using XRD, FTIR, CHN-analysis, TGA, ICP-AES. A series of experimental parameters such as CO2 flow rate, expand procedure, reaction temperature and time have been discussed, as well as the roles of CO2 and H2O (often originated from salts and/or solvent but always neglected) were studied in this contribution. Significantly, a coordination–decomposition (C–D) was proved to be the converting mechanism for the precipitation of the hydrous inorganic metal salts, rather than the fuzzy decomposition. [Copyright &y& Elsevier]

Protein nanoparticles represent a promising system for the encapsulation and delivery of bioactive compounds or highly sensitive ingredients. In this study, whey protein isolate nanoparticles (WPINs) were prepared by using supercritical carbon dioxide (scCO 2) treatment. The effects of scCO 2 on the size and stability of the WPINs were investigated. The average particle diameter ranged from 100 to 300 nm when the WPIN solution was treated with scCO 2 at 8–24 MPa and 45 °C for 30 min. ScCO 2 -treated WPINs had more uniform size distribution and smaller particles than WPINs prepared without scCO 2. However, particle aggregation was observed during heating to 55–75 °C. Fluorescence and differential thermogravimetric analysis showed that CO 2 pressure did not cause secondary and tertiary structure changes or denaturation of WPINs. The change in WPINs size was likely caused by the high diffusibility of scCO 2 , which could slightly modify WPINs local structure, affecting hydrophobic interactions and hydrogen bonding within the molecule. These results indicate that the size of nano-particles can be modulated by adjusting CO 2 pressure, which may facilitate WPINs use in food and biomedical products. • Whey protein isolate nanoparticles (WPIN) were prepared using supercritical carbon dioxide (scCO 2) treatment. • The impact of scCO 2 treatment on the structures of WPINs. • The size of the nanoparticles can be regulated by adjusting the CO 2 pressure. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogenation of o-chloronitrobenzene over Au/TiO2 was investigated in supercritical carbon dioxide (scCO2), ethanol, H2O, and H2O/CO2 at 140°C. The reaction rate followed the order of H2O>H2O/CO2 >ethanol>scCO2. Au/TiO2 was deactivated in the systems containing CO2. Changes of Au/TiO2 catalysts were investigated by means of transmission electron microscopy (TEM), in situ infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance ultraviolet-visible spectra (DR-UV/Vis). Aggregation of Au particles was excluded from origins of deactivation by TEM. Carbonate-like species formed on gold in the presence of CO2 and H2 were detected by in situ IR spectroscopy. The results of XPS and DR-UV/Vis reveal that the active species of Au0 was oxidized in the presence of CO2. The possible formation of CO and its influence on the activity of Au/TiO2 were also discussed. Accordingly, the formation of carbonates, the oxidation of surface Au0 by CO2, and the CO formation are proposed to be the possible factors for the deactivation of Au/TiO2. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenation of phenol to cyclohexanone and cyclohexanol in/under compressed CO2 was examined using commercial Rh/C and Rh/Al2O3 catalysts to investigate the effects of CO2 pressurization on the total conversion and the product selectivity. Although the total rate of phenol hydrogenation with Rh/C was lowered by the presence of CO2, the selectivity to cyclohexanone was improved at high conversion levels >70%. On the other hand, the activity of Rh/Al2O3 was completely lost in an early stage of reaction. The features of these multiphase catalytic hydrogenation reactions using compressed CO2 were studied in detail by phase behavior and solubility measurements, in situ high-pressure FTIR for molecular interactions of CO2 with reacting species and formation/adsorption of CO on the catalysts, and simulation of reaction kinetics using a simple model. The CO2 pressurization was shown to suppress the hydrogenation of cyclohexanone to cyclohexanol, improving the selectivity to cyclohexanone. The formation and adsorption of CO were observed for the two catalysts at high CO2 pressures in the presence of H2, which was one of important factors retarding the rate of hydrogenation in the presence of CO2. It was further indicated that the adsorption of CO on Rh/Al2O3 was strong and caused the complete loss of its activity. [Copyright &y& Elsevier]