Adsorption and diffusion of propane and propylene in Ag+-impregnated MCM-41

Equilibrium data and diffusion characteristics of propane and propylene were determined on mesoporous adsorbents modified with an organic molecule (APTES) and/or impregnated with AgNO₃, in order to obtain a separation by adsorption via π-complexation. Adsorption capacities were determined by a gravimetric technique, while diffusion characteristics were evaluated by the ZLC technique. The equilibrium isotherms data showed that the modification with an organic molecule will weaken the π-interaction between Ag⁺ and double C=C bond. On the other hand slightly higher adsorption capacities for propylene (about 1.5 mol/kg) were obtained for the sample prepared by a direct impregnation with larger amounts of AgNO₃ (M4 sample). Diffusion runs confirmed that the propane desorption rate on M4 sample was much higher compared to propylene. This evidence leads to a potential application of that adsorbent material for a kinetic separation.     

Bimetallic Ru?Cu over ZSM5 zeolites in propane hydrogenolysis

Bimetallic Ru–Cu catalysts supported on ZSM5 have been prepared using RuCl₃ or Ru(NO) (NO₃)₃ as precursors. Co chemisorption, TPR measurements and catalytic activity in propane hydrogenolysis have shown that the degree of Ru–Cu interaction depends on the Ru precursor used.

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Ru–Cu, ZSM-5, RuCl₃ Ru(NO) (NO₃)₃ . CO, , Ru–Cu .

     

Mechanisms of the reactions of propane with CBr3+ cation and superelectrophilic complex CBr4+·AlBr3- containing a bromine-centered cationic center: a theoretical study

Fragments of the potential energy surfaces (PES) of the systems [C₃H₈ + CBr₃ ⁺] and [C₃H₈ + Br₂CBr⁺·Br₂AlBr₂ ^–] were simulated by the MNDO/PM3 method. Energy minima corresponding to weakly bound adducts of propane molecule with the CBr₃ ⁺ cation or neutral complex CBr₃ ⁺·AlBr₄ ^– were found on the PES's of both systems. These are adducts with the coordination of a H atom of the methylene group of the propane molecule to the electrophile at the Br atom carrying the largest positive charge. As the fragments of the adducts are brought close together, the coordinated H atom migrates to the C atom of the CBr₃ ⁺ fragment. The potential barriers of these migrations were found to be low for both systems. The reactions proceed without formation of cyclic intermediates or transition states typical of the Olah mechanism.     

Pathways for C-H bond cleavage of propane σ-complexes on PdO(101)

We used dispersion-corrected density functional theory (DFT-D3) calculations to investigate the initial C-H bond cleavage of propane σ-complexes adsorbed on the PdO(101) surface. The calculations predict that propane molecules adsorbed in η(1) configurations can undergo facile C-H bond cleavage on PdO(101), where the energy barrier for C-H bond activation is lower than that for desorption for each molecular complex. The preferred pathway for propane dissociation on PdO(101) corresponds to cleavage of a primary C-H bond of a so-called staggered p-2η(1) complex which initially coordinates with the surface by forming two H-Pd dative bonds, one at each CH(3) group. Among all of the adsorbed propane complexes, the staggered p-2η(1) complex has the highest binding energy and must overcome the lowest energy barrier for C-H bond scission. Analysis of the atomic charges reveals that propane C-H bond cleavage occurs heterolytically on PdO(101), and suggests that primary C-H bond activation is favored because a more stabilizing charge distribution develops within the 1-propyl transition state structures. Lastly, we conducted kinetic simulations using microkinetic models derived from the DFT-D3 structures, and find that the models reproduce the apparent activation energy for propane dissociation on PdO(101) to within 14% of that determined experimentally. We show that the entropic contributions of the adsorbed transition structures greatly exceed those predicted by the harmonic oscillator model, and that quantitative agreement with the apparent dissociation pre-factor may be obtained by approximating two of the frustrated adsorbate motions as free motions while treating the remaining modes as harmonic vibrations.     

Adduct Formation Between γ-Cyclodextrin and the Bifluorophore 1,3-Bis(1-pyrenyl)propane

The complexation of the bifluorophore 1,3-bis(pyrenyl)propane with γ-cyclodextrin in water has been studied by means of steady state and time-resolved fluorescence spectroscopy. It was found that in the association with γ-cyclodextrin the propane chain of 1,3-bis(pyrenyl)propane folds and the two pyrene units enter the same cyclodextrin cavity where they form weakly bound ground state dimers, which upon excitation emit excimer fluorescence. In addition to this 1:1 excimer emitting complex, two more complexes were detected, which emit monomer pyrene fluorescence. One has 1:1 stoichiometry, i.e. isomeric to the previous complex, and the other, with 2:1 stoichiometry, is comprised of two γ-cyclodextrin units and one 1,3-bis(pyrenyl)propane.     

Vapour–liquid equilibrium measurements and correlation of the difluoromethane (R32) + propane (R290) + 1,1,1,2,3,3,3-heptafluoropropane (R227ea) ternary mixture at temperatures from 269.85 to 328.35 K

Vapour–liquid equilibrium (VLE) data of the ternary mixture composed of difluoromethane (R32), propane (R290) and 1,1,1,2,3,3,3-heptafluoropropane (R227ea) have been measured for three compositions at temperatures between 269.85 and 328.35 K. The experimental method is a synthetic one with a variable volume cell. Our results about each of the three corresponding binary systems are compared to literature data using a Soave–Redlich–Kwong (SRK) equation of state with MHV1 mixing rules involving the NRTL model.     

Vapor–liquid equilibrium data for the propane+1,1,1,2,3,3,3-heptafluoropropane (R227ea) system at temperatures from 293.16 to 353.18 K and pressures up to 3.4 MPa

Isothermal vapor–liquid equilibrium (VLE) data for the propane+1,1,1,2,3,3,3-heptafluoropropane (R227ea) binary system were measured at 293.16, 303.14, 313.14, 333.15, 343.16 and 353.18 K and pressures up to 3.5 MPa. The experimental method, used in this work, is of the static-analytic type. It takes advantage of two pneumatic capillary samplers (Rolsi™, Armines’ patent) developed in the Cenerg/TEP laboratory. The peculiarity of R227ea–propane binary system is to present azeotropic behavior at each studied temperature.The six sets of isothermal P, x, y data are represented with the Soave–Redlich–Kwong (SRK) equation of state (EoS) and several mixing rules involving the NRTL model.     

Characterization of a heavy oil–propane system in the presence or absence of asphaltene precipitation

When a light hydrocarbon solvent is injected into a heavy oil reservoir under a sufficiently high reservoir pressure, asphaltene precipitation occurs so that the heavy oil is in situ deasphalted during a hydrocarbon solvent-based heavy oil recovery process. The physicochemical properties of this in situ deasphalted heavy oil are rather different from those of the original crude oil in the heavy oil reservoir. In this paper, a heavy oil sample is saturated with a typical light hydrocarbon solvent (i.e., propane) under different saturation pressures in a see-through windowed high-pressure saturation cell. The heavy oil–propane system is characterized by measuring and comparing several important physicochemical properties of the propane-saturated heavy oil samples under different saturation pressures and the flashed-off heavy oil samples, such as the solubility, oil-swelling factor, density, viscosity, asphaltene content, hydrogen and carbon aromaticities. When the heavy oil is saturated with propane at P ≤ 780 kPa and T = 20.8 °C, there is no observable asphaltene precipitation and deposition under a microscope camera. The respective properties of the propane-saturated heavy oil samples taken from the upper and lower parts of the saturation cell are measured and found to be essentially the same within the experimental errors so that the entire system is considered to be almost homogeneous. If the saturation pressure is increased to P = 850 kPa, strong asphaltene precipitation occurs and some large asphaltene particles are deposited onto the bottom of the saturation cell. In this case, the heavy oil is deasphalted and the flashed-off heavy oil has lower density, viscosity, asphaltene content, hydrogen and carbon aromaticities than those of the original heavy crude oil.     

Crystal Structure of Di[bis(diphenylphosphino)propane]Copper(Ⅰ) Perchlorate Complex

1INTRODUCT1oNIthasbeenwellknownthatthereactionofcopper(E)saltswithditertiaryphosphinesorarsinesisoftenaconvenientroutetocopper(I)analogues.8-dimethylarsinoquinolinee,3-methylthiopropyldimethylarsineand(o-diphenylarsi-nophenyl)diphenylphosphinesulphideallonlyyieldcopper(I)complexesofthiskindofligandsfromreactioninvolvingcopper(I)salts.Insimilarmanner,copper(I)nitratecomplexesofstoichiometryCu(dppm)(NO,),Cu2(dppe)3(NO,)2,Cu-(dppe),(NO,),andCu(dppe)(NO,)havebeenprepared.ltappearsthatthe…     

Catalytic dehydrogenation of propane to propylene over highly active PtSnNa/γ-Al_2O_3 catalyst

This paper reports a new fabrication method of the PtSnNa/γ-Al₂O₃ catalyst through ball milling, which is more stable and active than the commercial catalyst.     

Aging and activation of α-NiMoO4 catalyst for selective propane oxydehydrogenation into propene

Increase in catalytic activity performance of a stoichiometric NiMoO₄ system has been studied using a periodic flow reactor system. Aging results in an increase of selectivity, a decrease in BET surface area, a weak decrease in activity and a change in surface morphological properties. α-Nickel molybdate exposed to the reaction gases and temperature tends to transform progressively toward an α-aged phase more and more like to the most selective β-phase.     

High selectivity for primary C-H bond cleavage of propane σ-complexes on the PdO(101) surface

We investigated regioselectivity in the initial C-H bond activation of propane σ-complexes on the PdO(101) surface using temperature programmed reaction spectroscopy (TPRS) experiments. We observe a significant kinetic isotope effect (KIE) in the initial C-H(D) bond cleavage of propane on PdO(101) such that the dissociation yield of C(3)H(8) is 2.7 times higher than that of C(3)D(8) at temperatures between 150 and 200 K. Measurements of the reactivity of (CH(3))(2)CD(2) and (CD(3))(2)CH(2) show that deuteration of the methyl groups is primarily responsible for the lower reactivity of C(3)D(8) relative to C(3)H(8), and thus that 1° C-H bond cleavage is the preferred pathway for propane activation on PdO(101). By analyzing the rate data within the context of a kinetic model for precursor-mediated dissociation, we estimate that 90% of the propane σ-complexes which dissociate on PdO(101) during TPRS do so by 1° C-H bond cleavage.     

Triangular ruthenium acetate clusters containing the bis(pyridyl)propane ligand and their inclusion chemistry with β-cyclodextrin

The triruthenium carboxylate cluster [Ru₃O(OAc)₆(py)₂(bpp)]⁺ (OAc = acetate) containing the bridging 1,3-bis(4-pyridyl)propane (bpp) ligand, and its dimeric species [{Ru₃O(OAc)₆(py₂)}₂(μ-bpp)]²⁺ were synthesized in order to investigate their inclusion compounds with β-cyclodextrin (β-CD). Characterization of the complexes was carried out based on spectroscopic, electrochemical and spectroelectrochemical techniques, while the formation of inclusion complexes was evaluated using ¹H NMR/NOESY spectroscopy. Since bpp is a flexible ligand, a DFT study was carried out in order to characterize its conformational isomers and their possible role in the host–guest chemistry with β-CD. Instead of observing the formation of inclusion compounds with different stoichiometries, we observed the formation of 1:1 bpp/β-CD compounds in which the bpp ligand assumes different conformations. The assembly of polymetallic rotaxane species was successfully demonstrated by monitoring the ¹H NMR spectra of the monomeric cluster species in the presence of aquapentacyanoferrate(II) ions and β-CD.     

Mean potential statistical theory of the H+ + D2 → HD + D+ reaction

The reactive collision process H(+) + D(2)(ν = 0, j = 0) → HD + D(+) is theoretically analyzed for collision energies ranging from threshold up to 1.3 eV. It is assumed that the reaction takes place via formation of a collision complex. In calculations, a statistical theory is used, based on a mean isotropic potential deduced from a full potential energy surface. Calculated integral cross sections, opacity functions, and rotational distributions of the HD products are compared with recent statistical and quantum mechanical calculations performed using a full potential energy surface. Satisfactory agreement between the results obtained using the two statistical methods is found, both of which however overestimate the existing quantum mechanical predictions. The effects due to the presence of identical particles are also discussed.     

Synthesis of a new ordered mesoporous NiMoO4com-plex oxide and its efficient catalytic performance foroxidative dehydrogenation of propane

Highly ordered mesoporous NiMoO4material was successfully synthesized using mesoporous silica KIT-6 as hard template via vacuum nanocasting method. The structure was characterized by means of XRD, TEM, N2adsorption-desorption, Raman and FT-IR. The mesoporous NiMoO4with the coexistence of α-NiMoO4and β-NiMoO4showed well-ordered mesoporous structure, a bimodal pore size distribution and crystalline framework. The catalytic performance of NiMoO4was investigated for oxidative dehydrogenation of propane. It is demonstrated that the mesoporous NiMoO4catalyst with more surface active oxygen species showed better catalytic performance in oxidative dehydrogenation of propane in comparison with bulk NiMoO4.     

Temperature-dependent Polymorphism in Co（II） Coordination Polymers from 5-Nitroisophthalate and 1,3-Bis（4-pyridyl）propane

The solvothermal reaction of 5-nitroisophthalic acid （H2nip）, 1,3-bis（4-pyridyl）pro- pane （bpp） and Co（NO3）2·6H：O at 130 and 160 ℃ gave rise to two polymorphic complexes [Co（bpp）（H20）（nip）], （1, 2）. Complex I belongs to monoclinic, space group C2/c with a = 14.489（6）, b = 18.242（8）, c = 19.414（9） A, β = 123.09（3）°, V = 4299（3） A3, Z = 8, C21H19CoN3O7, Mr = 484.32, Dc= 1.497 g/cm3, F（000） = 1992,/l = 0.847 mm-1. In complexes I and 2, bpp connects Co（II） into different 1D chains which are bridged by nip to form similar two-fold interpenetrating 3D frameworks.     

Honeycomb-shaped PtSnNa/γ-Al2O3/cordierite monolithic catalyst with improved stability and selectivity for propane dehydrogenation

A novel honeycomb-shaped PtSnNa/γ-Al₂O₃/cordierite monolithic catalyst was developed. It was found that, the unique structure of the material led to the improved catalyst performances versus the conventional granule catalyst.     

Effect of preparation method on structural characteristics and propane steam reforming performance of Ni–Al2O3 catalysts

Propane steam reforming was studied over Ni–Al₂O₃ catalysts that were prepared by a conventional impregnation (IM) method and a one-step sol–gel (SG) technique. Both Ni–Al₂O₃ catalysts showed similar initial activity. However, IM-Ni–Al₂O₃ deactivated severely with time-on-stream of propane steam reforming. The catalyst prepared using a SG technique demonstrated stable catalytic performance. The two catalysts also showed major differences in product distribution, with SG catalyst giving much higher yields of hydrogen. Catalysts were characterized with temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. It was revealed that, with sol–gel preparation, highly dispersed small Ni crystallites are formed with a strong interaction with the support. This is shown to be important for coke suppression and catalyst stability.     

Ab Initio Study on the Reaction of La~+ + CH_4→La+-CH~2 + H_2

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