Transformation of carbon dioxide

The free-radical chemistry of polyethylene glycol: organic reactions in compressed carbon dioxide

The thermal oxidative degradation of polyethylene glycol (PEG) is known to occur in an oxygen atmosphere at elevated temperatures. In this study, PEG radicals assumed to result from thermal oxidative degradation are successfully applied, in combination with compressed CO(2), to initiate a range of free-radical reactions, such as selective formylation of primary and secondary aliphatic alcohols, oxidation of benzylic alcohols, benzylic C==C bond cleavage, and benzylic sp(3) C--H oxidation, demonstrating enormous synthetic potential in a cost-efficient, practically useful, and environmentally friendly manner; not requiring any catalyst or additional free-radical initiator. We find that both PEG and molecular oxygen are prerequisites in order to perform these reactions smoothly. Given that dense CO(2) is immune to free-radical chemistry; it is an ideal solvent for such reactions. As a result, compressed CO(2) allows reactions initiated by PEG radicals to be tuned by subtly adjusting reaction parameters such as the CO(2) pressure, thereby enhancing the product selectivity. By attaining a high selectivity towards the desired products this methodology is practical for organic syntheses.

Investigations of the conversion of inorganic carbonates to methane

Inorganic carbonates, which occur abundantly on earth, constitute an inexpensive natural source of carbon. Therefore, the direct conversion of these carbonates into methane is of considerable importance. Thermal decomposition of transition metal carbonates with the composition MCa(CO(3))(2) (where M=Co, Ni, or Fe, and M/Ca is 1:1) and M(1)M(2)Ca(CO(3))(3) (where M(1)M(2)=CoNi, NiFe, or FeCo, and M(1)/M(2)/Ca is 1:1:2) shows that the reduced transition metals in combination with metal oxide nanoparticles (e.g., Co/CoO/CaO) act as catalysts for the conversion of CO(2) (produced from the carbonates) into methane. The favorable decomposition conditions include heating at 550 degrees C in an H(2) atmosphere for 5-6 h. These catalysts are found to be excellent for the methanation of CaCO(3), exhibiting high efficiency in the utilization of H(2) with 100 % conversion and 100 % selectivity. The best catalyst for conversion of CaCO(3) into CH(4) is Co/CoO/CaO. There are also indications that similar catalysts based on Fe may yield higher hydrocarbons.

Nickel-catalyzed reductive carboxylation of styrenes using CO2

A nickel-catalyzed reductive carboxylation of styrenes using CO2 has been developed. The reaction proceeds under mild conditions using diethylzinc as the reductant. Preliminary data suggests the mechanism involves two discrete nickel-mediated catalytic cycles, the first involving a catalyzed hydrozincation of the alkene followed by a second, slower nickel-catalyzed carboxylation of the in situ formed organozinc reagent. Importantly, the catalyst system is very robust and will fixate CO2 in good yield even if exposed to only an equimolar amount introduced into the headspace above the reaction.

Carbon dioxide hydrogenation on Ni(110)

We demonstrate that the key step for the reaction of CO 2 with hydrogen on Ni(110) is a change of the activated molecule coordination to the metal surface. At 90 K, CO 2 is negatively charged and chemically bonded via the carbon atom. When the temperature is increased and H approaches, the H-CO 2 complex flips and binds to the surface through the two oxygen atoms, while H binds to the carbon atom, thus yielding formate. We provide the atomic-level description of this process by means of conventional ultrahigh vacuum surface science techniques combined with density functional theory calculations and corroborated by high pressure reactivity tests. Knowledge about the details of the mechanisms involved in this reaction can yield a deeper comprehension of heterogeneous catalytic organic synthesis processes involving carbon dioxide as a reactant. We show why on Ni the CO 2 hydrogenation barrier is remarkably smaller than that on the common Cu metal-based catalyst. Our results provide a possible interpretation of the observed high catalytic activity of NiCu alloys.

CO2 coordination by inorganic polyoxoanion in water

Two inorganic polyoxoanions react with carbon dioxide in aqueous solution to yield two polymeric chainlike complexes, where an activated CO2 molecule covalently bonds to polyoxoanions in a linear mu-eta1,eta1-OCO style. For the first time, the CO2 coordination is realized by an economic and environmentally friendly approach.