Adsorption mechanism of carbon dioxide in faujasites: grand canonical monte carlo simulations and microcalorimetry measurements

Molecular simulations have been coupled with adsorption microcalorimetry measurements in order to understand more deeply the interactions between carbon dioxide and various types of faujasite surfaces. The modeling studies, based on newly derived interatomic potentials for describing the interactions within the whole system, provide isotherms and evolutions of the differential enthalpy of adsorption as a function of coverage for DAY, NaY, and NaLSX which are in very good accordance with those obtained experimentally. The microscopic mechanism of CO2 adsorption was carefully analyzed, with different behaviors proposed, depending on the energetic characteristics of each faujasite surface, which are consistent with the trends observed for the differential enthalpies of adsorption.     

Acetyl nitrate nitrations in [bmpy][N(Tf)2] and [bmpy][OTf], and the recycling of ionic liquids

In this work we have examined the nitration by acetyl nitrate of a range of activated and deactivated aromatic substrates in two ionic liquids and compared the results to the same reaction in dichloromethane. Both ionic liquids are stable to the reaction conditions, and in both ionic liquids the yields of reaction are higher after unit time than the same reactions in dichloromethane, although the regioselectivity is little affected by solvent choice. This result gives further support to the suggestion that in the ionic liquid, acetyl nitrate dissociates to give the nitronium ion, and that this is the effective nitrating agent here. However, it is shown that [bmpy][N(Tf)(2)] is a better solvent for aromatic nitration than [bmpy][OTf]. This is due to the ease of formation of nitronium ion in the former ionic liquid, and is consistent with the fact that [bmpy][N(Tf)(2)] is a weaker hydrogen bond acceptor solvent than [bmpy][OTf]. Finally, a method by which [bmpy][N(Tf)(2)] may be recovered and reused for aromatic nitration has been demonstrated.     

Crystal structure of tetraphenylarsonium aquatetracyanonitridorhenate(V), (AsPh4)2 [ReN(H2O)(CN)4]·5H2O

The crystal structure of (AsPh₄)₂[ReN(H₂O)(CN)₄]·5H₂O has been determined from three-dimensional X-ray diffraction data. The yellow crystals are monoclinic, space group P2₁/n with cell dimensionsa=15.482(1),b=19.950(2),c=16.999(1)? and β=101.69(6)^o,Z=4,D _expt=1.48(1)g cm⁻³ andD _calc=1.52g cm⁻³. The anisotropic refinement of 7858 observed reflections converged toR=0.055. The [ReN(H₂O)(CN)₄]²⁻ ion has a distorted octahedral geometry. Bond distances: Re≡N=1.639(8), Re−OH₂=2.496(7) and Re−C_(av)=2.11(1) ?. The rhenium atom is displaced by 0.35 ? out of the plane formed by the four carbon atoms of the cyano ligands towards the terminal nitrido ligand. TMC 2479     

Calorimetry by immersion into liquid nitrogen and liquid argon: a better way to determine the internal surface area of micropores

The aim of this work is to assess the internal surface area of a set of samples (either carbons or oxides, either porous or nonporous, either microporous or mesoporous) by microcalorimetry via immersion into liquid nitrogen or argon. We have made use of an isothermal, heat-flux microcalorimeter, initially designed and built in our laboratory for the sake of gas adsorption experiments at 77 or 87 K. It seems that immersion calorimetry into liquid nitrogen and argon makes it possible to go one step further in the determination of the internal surface area of micropores.     

Nucleophilicity in ionic liquids. 3. Anion effects on halide nucleophilicity in a series of 1-butyl-3-methylimidazolium ionic liquids

We have continued the study of halide nucleophilicity in ionic liquids, concentrating on the effect of changing the anion ([BF(4)](-), [PF(6)](-), [SbF(6)](-), [OTf](-), and [N(Tf)(2)](-)) when the cation is [bmim](+) (where bmim = 1-butyl-3-methylimidazolium). It was found that the nucleophilicities of all the halides were lower in all of the ionic liquids than in dichloromethane. Changing the anion affected the order of halide nucleophilicity, e.g., in [bmim][BF(4)] the order of nucleophilicity was Cl(-)>Br(-)>I(-) while in [bmim][N(Tf)(2)] the order was Cl(-)相似文献   

Microcalorimetric investigation of high-surface-area mesoporous titania samples for CO2 adsorption

Mesoporous titania powders were synthesized using the triblock copolymer F127 (PEO(106)PPO(70)PEO(106)) as a surfactant template. Two different procedures (ammonia and/or low-temperature treatment at 393 K) were successfully applied to stabilize the mesoporous structure, resulting in significantly increased surface areas and pore volumes with respect to those of the untreated titania powders. Three of these samples were chosen for further investigation by adsorption microcalorimetry. These samples are characterized by high surface areas (varying between 340 and 141 m (2) g (-1)) and a varying degree of crystallization (anatase phase). The samples were compared to nanosized anatase particles treated to 873 K. The adsorption microcalorimetry was carried out using nitrogen and carbon dioxide at 77 and 303 K, respectively, to gain complementary information about the surfaces. Nitrogen at 77 K showed, for the three samples, adsorption enthalpies at low coverage of similar values, approximately -19 to -22 kJ mol (-1), indicating that the probe gas interacts with similar energetic surface sites. Two distinct energetic regions are observed, the first of which increases with increasing pretreatment temperature, which can be related to increased sample crystallinity. The adsorption of carbon dioxide at 303 K showed high adsorption enthalpies (up to approximately 65-80 kJ mol (-1)), highlighting strong interactions of the carbon dioxide with the titania surface at low pressures. Finally, the CO(2) adsorption properties of the titania samples (adsorbed amount and enthalpies of adsorption) are compared with those of other nanosized adsorbents. This comparison shows the potentiality of mesoporous titania powders for the adsorption of CO(2).     

Structural Transformations and adsorption of fuel-related gases of a structurally responsive nickel phosphonate metal-organic framework, Ni-STA-12

The structure of the nickel N,N'-piperazinebismethylenephosphonate, Ni-STA-12 (St. Andrews porous material-12), has been determined in the hydrated (Ni2L x 8 H2O, L = O3PCH2NC4H8NCH2PO3), partially dehydrated (Ni2L x 2 H2O), and fully dehydrated (Ni2L) forms from high-resolution synchrotron X-ray powder diffraction. The framework structures of Ni2L x 8 H2O and Ni2L x 2 H2O are almost identical (R, a = 27.8342(1) A, c = 6.2421(2) A; R, a = 27.9144(1) A, c = 6.1655(2) A) with additional physisorbed water of the as-prepared Ni-STA-12 present in an ordered hydrogen-bonded network in the channels. Ab initio structure solution of the fully dehydrated solid indicates it has changed symmetry to triclinic (P1, a = 6.03475(5) A, b = 14.9157(2) A, c = 16.1572(2) A, alpha = 112.5721(7) degrees, beta = 95.7025(11) degrees, gamma = 96.4950(11) degrees) as a result of a topotactic structural rearrangement. The fully dehydrated solid possesses permanent porosity with elliptical channels 8 A x 9 A in free diameter. The structural change results from the loss of water coordinated to the nickel cations, so that the nickel coordination changes from edge-sharing octahedral NiO5N to edge- and corner-sharing five-fold NiO4N. During this change, two out of three phosphonate groups rotate to become fully coordinated to nickel cations, leaving the remainder of the phosphonate groups coordinated to nickel cations by two oxygen atoms and with a P=O bond projecting into the channels. This transformation, which is completely reversible, causes substantial changes in both vibrational and electronic properties as shown by IR, Raman, and UV-visible spectroscopies. Complementary adsorption, calorimetric, and infrared studies of the probe adsorbates H2, CO, and CO2 reveal the presence of several distinct adsorption sites in the solid, which are attributed to their interactions with nickel cations which are weak Lewis acid sites, as well as with P=O groups that project into the pores. At 304 K, the adsorption isotherms and enthalpies of adsorption on dehydrated Ni-STA-12 have been measured for CO2 and CH4: Ni-STA-12 gives adsorption uptakes of CO2 of 2.5 mmol g(-1) at 1 bar, an uptake ca. 10 times that of CH4.     

High energy behaviour and gauge symmetry

The imposition of unitarity bounds is shown to lead to a Yang-Mills structure in a wide class of theories involving vector mesons. Scalar fields are needed and, at least in simple cases, the unique unitary theory is of the Higgs type.     

A new proposal for Monte Carlo simulation of fermions on a lattice

With F flavours of matter fields extrapolation to negative F effectively changes bosons into fermions and vice-versa. Extrapolatingresults of calculations performed with bosonic quarks we reproduce results obtained by evaluating the fermion determinant in some simple examples. We find an example of a long computer run apparently converging to the wrong answer when systematic lattice site access is used.