Achieving Highly Efficient, Selective, and Stable CO2 Reduction on Nitrogen-Doped Carbon Nanotubes

The challenge in the electrosynthesis of fuels from CO2 is to achieve durable and active performance with cost-effective catalysts. Here, we report that carbon nanotubes (CNTs), doped with nitrogen to form resident electron-rich defects, can act as highly efficient and, more importantly, stable catalysts for the conversion of CO2 to CO. The unprecedented overpotential (-0.18 V) and selectivity (80%) observed on nitrogen-doped CNTs (NCNTs) are attributed to their unique features to facilitate the reaction, including (i) high electrical conductivity, (ii) preferable catalytic sites (pyridinic N defects), and (iii) low free energy for CO2 activation and high barrier for hydrogen evolution. Indeed, DFT calculations show a low free energy barrier for the potential-limiting step to form key intermediate COOH as well as strong binding energy of adsorbed CON and weak binding energy for the adsorbed CO. The highest selective site toward CO production is pyridinic N, and the NCNT-based electrodes exhibit no degradation over 10 h of continuous operation, suggesting the structural stability of the electrode.

Hydrogen storage in CO2-activated amorphous nanofibers and their monoliths

Amorphous carbon nanofibers (CNFs), produced by the polymer blend technique, are activated by CO2 (ACNFs). Monoliths are synthesized from the precursor and from some ACNFs. Morphology and textural properties of these materials are studied. When compared with other activating agents (steam and alkaline hydroxides), CO2 activation renders suitable yields and, contrarily to most other precursors, turns out to be advantageous for developing and controlling their narrow microporosity (< 0.7 nm), VDR(CO2). The obtained ACNFs have a high compressibility and, consequently, a high packing density under mechanical pressure which can also be maintained upon monolith synthesis. H2 adsorption is measured at two different conditions (77 K / 0.11 MPa, and 298 K / 20 MPa) and compared with other activated carbons. Under both conditions, H2 uptake depends on the narrow microporosity of the prepared ACNFs. Interestingly, at room temperature these ACNFs perform better than other activated carbons, despite their lower porosity developments. At 298 K they reach a H2 adsorption capacity as high as 1.3 wt.%, and a remarkable value of 1 wt.% in its mechanically resistant monolith form.

Applications for CO2-Activated Carbon Monoliths: I. Gas Storage

Carbon monoliths with high densities are studied as adsorbents for the storage of H2, CH4, and CO2 at ambient temperature and high pressures. The starting monolith A3 (produced by ATMI Co.) was activated under a CO2 flow at 1073 K, applying different activation times up to 48 h. Micropore volumes and apparent surface areas were deduced from N2 and CO2 adsorption isotherms at 77 K and 273 K, respectively. CO2 and CH4 isotherms were measured up to 3 MPa and H2 up to 20 MPa. The BET surface area of the starting monolith (941 m2/g) could be significantly increased up to 1586 m2/g, and the developed porosity is almost exclusively comprised of micropores <1 nm. Total storage amounts take into account the compressed gas in the void space of the material, in addition to the adsorbed gas. Remarkably, high total storage amounts are reached for CO2 (482 g/L), CH4 (123 g/L), and H2 (18 g/L). These values are much higher than for other sorbents with similar surface areas, due to the high density of the starting monolith and of the activated ones, for which the density decreases only slightly (from 1.0 g/cm3 to 0.8 g /cm3 upon CO2 activation). The findings reveal the suitability of high density activated carbon monoliths for gas storage application. Thus, the amounts of stored gas can be increased by more than a 70 % in the case of H2 at 20 MPa, almost 5.5 times in the case of CH4 at 3 MPa, and more than 7.5 times in the case of CO2 at 3 MPa when adsorbents are used for gas storage under the investigated conditions rather than simple compression. Furthermore, the obtained results have been recently confirmed by a scale-up study in which 2.64 kg of high density monolith adsorbent was filled a tank cylinder of 2.5 L (Carbon, 76, 2014, 123).

Carbon dioxide/propylene oxide coupling reaction catalyzed by chromium salen complexes

A series of chromium/Schiff base complexes N,N'-bis(salicylidene)-1,2-phenylenediamino chromium(III) X were prepared and employed for the alternating copolymerization of carbon dioxide with racemic propylene oxide in the presence of (4-dimethylamino)pyridine. The effect of the complex structure and reaction conditions on the catalytic activity, the poly(propylene carbonate)/cyclic carbonate (PPC/PC) selectivity, and the polymer head-to-tail linkages was examined. The experiments indicated that N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamino chromium(III) (NO3) exhibited the highest PPC/PC selectivity as well as polymer head-to-tail linkages and N,N'-bis(3,5-dichlorosalicylidene)-1,2-phenylenediimino chromiu(III) (NO3) possessed the highest catalytic activity among these chromium/Schiff base complexes. The structure of the produced copolymer was characterized by the IR, H-1 NMR, and C-13 NMR measurements.

The control of porosity at nano scale in resorcinol formaldehyde carbon aerogels

Organic aerogels were synthesized by sol–gel polymerization of resorcinol (R) with formaldehyde (F) catalyzed by sodium carbonate (C) followed by vacuum drying. The influence of the resorcinol/sodium carbonate ratio (R/C) on the porous structure of the resultant aerogels was investigated. The nitrogen adsorption–desorption measurements show that the aerogels possess a well developed porous structure and mesoporosity was found to increase with increasing the R/C ratio. Carbon aerogels were obtained by carbonization of RF aerogels. The carbonization temperature impacts the microstructure of the aerogels by pore transformations during carbonization probably due to the formation of micropores and shrinkage of the gel structure. The results showed that a temperature of 1073 Kis more effective in the development of the pore structure of the gel. Activated carbon aerogels were obtained from the CO2 activation of carbon aerogels. Activation results in an increase in the number of both micropores and mesopores, indicative of pore creation in the structure of the carbon. Activation at higher temperatures results in a higher degree of burn off and increases the pore volume and the surface area remarkably without change of the basic porous structure, pore size, and pore size distribution.

Reforming of a model biogas on Ni and Rh-Ni catalysts: Effect of adding La

Ni catalysts supported on gamma-Al2O3 modified by Rh and La were prepared and evaluated on the reforming of a model biogas. The catalysts were characterized by EDS, XRD, TPR, XANES and surface area estimation (BET). The results showed that in the original Ni catalyst, the Ni interacted strongly with the alumina support, exhibiting high reduction temperatures in TPR tests. In the catalytic tests, the addition of Rh on Ni catalysts improved CH4 conversion but also increased carbon deposition, possible by causing the segregation of Ni species under the reaction conditions. The presence of La on Ni catalysts reduced the carbon deposition by favoring the gasification of carbon species. Addition of synthetic air to the process improved the CH4 conversion and also decreased the carbon formation. The catalysts Ni, Rh-NiLa, and Rh showed good results in the conversion of model sulfur-free biogas, which suggests that they are promising catalysts to be tested in conversion of real biogas. (C) 2012 Elsevier B.V. All rights reserved.

A density functional theory study on CO2 capture and activation by graphene-like boron nitride with boron vacancy

First principle calculations for a hexagonal (graphene-like) boron nitride (g-BN) monolayer sheet in the presence of a boron-atom vacancy show promising properties for capture and activation of carbon dioxide. CO2 is found to decompose to produce an oxygen molecule via an intermediate chemisorption state on the defect g-BN sheet. The three stationary states and two transition states in the reaction pathway are confirmed by minimum energy pathway search and frequency analysis. The values computed for the two energy barriers involved in this catalytic reaction after enthalpy correction indicate that the catalytic reaction should proceed readily at room temperature.

Anionic migration reactions in aromatic systems effected by collisional activation : Deprotonated anilides containing methoxycarbonyl substituents

Long-range cross-ring reactions are of minor importance in the collision-induced mass spectra (MS/MS) of [M - H]- ions of CH2OCO-C6H4-NHCOR systems: e.g. the loss of 'CD3CO2CH3' from CH3OCO-C6H4-(N) over bar COCD3. Major processes involve (i) losses of radicals to form stable radical anions, e.g. loss of a ring hydrogen atom and losses from the ester (CH3 ., CH3O . and . CO2CH3), (ii) losses of neutral molecules from the amide moiety [e.g. CO (R = H) and CH2CO (R = CH3), and proximity effects when the two substituents are ortho [e.g. loss of (CH3OD+CO2) from o-CH3OCO-C6H4 (N) over bar COCD3].

Activation of Lattice Oxygen of TiO2 by Pd2+ Ion: Correlation of Low-Temperature CO and Hydrocarbon Oxidation with Structure of Ti1-xPdxO2-x (x=0.01-0.03)

Lattice oxygen of TiO2 is activated by the substitution of Pd ion in its lattice. Ti1-xPdxO2-x (x = 0.01-0.03) have been synthesized by solution combustion method crystallizing in anatase TiO2 structure. Pd is in +2 oxidation state and Ti is in +4 oxidation state in the catalyst. Pd is more ionic in TiO2 lattice compared to Pd in PdO. Oxygen storage capacity defined by ``amount of oxygen that is used reversibly to oxidize CO'' is as high as 5100 mu mol/g of Ti0.97Pd0.03O1.97. Oxygen is extracted by CO to CO2 in absence of feed oxygen even at room temperature which is more than 20 times compared to pure TiO2. Rate of CO oxidation is 2.75 mu mol g(-1) s(-1) at 60 degrees C over Ti0.97Pd0.03O1.97 and C2H2 gets oxidized to CO2 and H2O at room temperature. Catalyst is not poisoned on long time operation of the reactor. Such high catalytic activity is due to activated lattice oxygen created by the substitution of Pd ion as seen from first-principles density functional theory (DFT) calculations with 96 atom supercells of Ti32O64, Ti31Pd1O63, Ti30Pd2O62, and Ti29Pd3O61. The compounds crystallize in anatase TiO2 structure with Pd2+ ion in nearly square planar geometry and TiO6 octahedra are distorted by the creation of weakly bound oxygens. Structural analysis of Ti31Pd1O63 which is close to 3% Pd ion substituted TiO2 shows that oxygens associated with both Ti and Pd ions in the lattice show bond valence sum of 1.87, a low value characteristic of weak oxygen in the lattice compared to oxygens with valence 2 and above in the same lattice. Exact positions of activated oxygens have been identified in the lattice from DFT calculations.

Síntesis de carbonato de glicerol a partir de glicerol, CO2 y sus derivados

209 p. : il., gráf.

Effects of metal catalysts on CO2 gasification reactivity of biomass char

The effects of five metal catalysts (K, Na, Ca, Mg, and Fe) on CO2 gasification reactivity of fir char were studied using thermal gravimetric analysis. The degree of carbonization, crystal structure and morphology of char samples was characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The CO2 gasification reactivity of fir char was improved through the addition of metal catalysts, in the order K>Na>Ca>Fe>Mg. XRD analysis indicated that Na and Ca improved the formation of crystal structure, and that Mg enhanced the degree of carbon structure ordering. SEM analysis showed that spotted activation centers were distributed on the surface of char samples impregnated with catalysts. Moreover, a loose flake structure was observed on the surface of both K-char and Na-char. Finally, the kinetic parameters of CO2 gasification of char samples were calculated mathematically.

Copolymerization of CO2 and propylene oxide under rare earth ternary catalyst: design of ligand in yttrium complex

Copolymerization of carbon dioxide and propylene oxide was carried out employing (RC6H4COO)(3)Y/glycerin/ZnEt2 (R = -H, -CH3, NO2, -OH) ternary catalyst systems. The feature of yttrium carboxylates (ligand, substituent and its position on the aromatic ring) is of great importance in the final copolymerization. Appropriate design of substituent and position of the ligand in benzoate-based yttrium complex can adjust the microstructure of aliphatic polycarbonate in a moderate degree, where the head-to-tail linkage in the copolymer is adjustable from 68.4 to 75.4%. The steric factor of the ligand in the yttrium complex is crucial for the molecular weight distribution of the copolymer, probably due to the fact that the substituent at 2 and 4-position would disturb the coordination or insertion of the monomer, lead the copolymer with broad molecular distribution. Based on the study of ultraviolet-visible spectra of the ternary catalyst in various solvents, it seems that the absorption band at 240-255 nm be closely related to the active species of the rare earth ternary catalysts.

Study on the Adsorption and Activation of NO and CO over Mixed Oxide Catalysts Containing Cu by Means of TPSR

Adsorption and activation of small molecules NO, CO and CO+ NO on LaSrCuO4, La2CuO4 and La1.7Th0.3CuO4 which are typical samples in the sence of nonstoichiometric oxygen(lambda) anrong the series of La2-x(SrTh)(x)CuO4 +/-lambda mixed oxide catalysts were studied by means of MS- TPD (TPSR ), XRD, chemical analysis and so on. It was shown that the adsorption amount of NO can be correlated with the content of oxygen vacancy while the types and strength of adsorption of NO could be related to the oxidation state of the metallic ion. It was also found that CO molecule was first converted into CO32- and then desorbed in the form of CO2 at high temperature during the adsorption and desorption of CO on the mixed oxide with oxygen vacancy. The fact that the profiles of TPD(TPSR) of NO in co-adsorption of NO+CO and in single NO adsorption are similar shows that the adsorption of NO molecule not only has some priority to that of CO but also is stronger than that of CO. It seems that the adsorption of NO plays a dominate role in the activation and decomposition of NO.