scholarly journals Effect of Drying Temperature on Iron Fischer-Tropsch Catalysts Prepared by Solvent Deficient Precipitation

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Michael K. Albretsen ◽  
Baiyu Huang ◽  
Kamyar Keyvanloo ◽  
Brian F. Woodfield ◽  
Calvin H. Bartholomew ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Phase I ◽  
Pore Structure ◽  
Catalytic Properties ◽  
Catalytic Performance ◽  
Phase Iii ◽  
Fischer Tropsch ◽  
Two Phase ◽  
Methane Selectivity ◽  
Physical Changes

A novel solvent deficient precipitation (SDP) method to produce nanoparticles was studied for its potential in Fischer-Tropsch synthesis (FTS) catalysis. Using Fe(NO3)3·9H2O as the iron-containing precursor, this method produces ferrihydrite particles which are then dried, calcined, reduced, and carbidized to form the active catalytic phase for FTS. Six different drying profiles, including final drying temperatures ranging between 80 and 150°C, were used to investigate the effect of ammonium nitrate (AN), a major by-product of reaction between Fe(NO3)3·9H2O and NH4HCO3 in the SDP method. Since AN has two phase-transitions within this range of drying temperatures, three different AN phases can exist during the drying of the catalyst precursors. These AN phases, along with physical changes occurring during the phase transitions, may affect the pore structure and the agglomeration of ferrihydrite crystallites, suggesting possible reasons for the observed differences in catalytic performance. Catalysts dried at 130°C showed the highest FTS rate and the lowest methane selectivity. In general, better catalytic performance is related to the AN phase present during drying as follows: phase III > phase II > phase I. However, within each AN phase, lower drying temperatures led to better catalytic properties.

scholarly journals Etude par resonance magnetique des mouvements moléculaires dans l'acrylonitrile solide

1973 ◽  
Vol 51 (23) ◽  
pp. 3889-3900 ◽  
Author(s):  
Buu Ban ◽  
C. CHACHATY
Keyword(s):  
Phase Transitions ◽  
Phase I ◽  
Phase Ii ◽  
Phase Iii ◽  
Solid Matrix ◽  
Peroxy Radicals ◽  
Γ Irradiation ◽  
Rotational Oscillation ◽  
Résonance Magnétique ◽  
Oxygen Addition

Phase transitions and molecular motions in solid acrylonitrile and its deuterated homologue CH2=CDCN, have been studied between 100 and 191 °K (m.p.) by wide line n.m.r. and by T1 relaxation time measurements. Phase I (164 °K < T < 191 °K) is trapped and becomes metastable by quick cooling of acrylonitrile at 77 °K. It changes into the phase II, stable between 113 °K and 164 °K by a long duration annealing at 155–160 °K. The phase II → phase III transition occurs at 113 °K. It may be assumed that phase III, stable below this temperature, is rigid at T < 105 °K. Phase II may be characterized by a rotational oscillation of molecules around an axis defined by the N atom and the middle of the vinyl double bond. In phase I, acrylonitrile molecules undergo a binary reorientation motion around this axis with an activation energy of 4.2 kcal mol−1. The motion of peroxy radicals, trapped in acrylonitrile has been also studied by e.s.r. These radicals were produced by oxygen addition to free radicals previously formed by γ irradiation of acrylonitrile at 77 °K. The g anisotropy variation with temperature, shows no discontinuities at phase transitions, the activation of reorientation of peroxy radicals being 0.65 kcal mol−1. This result suggests that we are dealing in fact with macroradicals, the internal rotation of which is only observable in a solid matrix.

Phase transitions and ferroelectricity in NaSb3F10

2008 ◽  
Vol 42 (1) ◽  
pp. 58-62 ◽  
Author(s):  
R. J. Christie ◽  
P. K. Wu ◽  
P. Photinos ◽  
S. C. Abrahams
Keyword(s):  
Phase Transitions ◽  
Phase I ◽  
Thermal Hysteresis ◽  
Entropy Change ◽  
Pyroelectric Coefficient ◽  
Phase Iii ◽  
Space Group ◽  
Heating And Cooling ◽  
Order Of Magnitude ◽  
First Order Phase

Atomic coordinate analysis allows materials with appropriate but previously unrecognized dielectric properties to be predicted as new ferroelectrics if their crystal structure is known. An earlier such prediction that NaSb3F10is ferroelectric is confirmed herein without ambiguity. Its spontaneous polarizationPsis found to exhibit reproducible dielectric hysteresis at room temperature, withPs≃ 60 µC m−2, under the application of a field of 0.3 MV m−1or greater. The pyroelectric coefficient 〈p〉 = 17 (5) µC m−2 K−1at 298 K. NaSb3F10undergoes a phase transition atTC≃ 461 K, on correction for thermal hysteresis, with entropy change ΔS= 5.7 (3) J mol−1 K−1. The colorless crystals melt atTm ≃ 515 K and decompose above ∼600 K. The thermal hysteresis of ∼35 K inTC, on heating and cooling at 5–25 K min−1, is typical of first-order phase transitions. The space group in ferroelectric phase III isP63, and that in phase II is predicted to beP6322, a nonpolar supergroup ofP63; the supergroup expected in the prototypic nonferroic phase I isP63/mmc. The space group of phase III isnota direct subgroup of phase I. The dielectric permittivity ∊′ at 1 kHz increases over an order of magnitude between 300 K and a major inflection atTC, continuing to increase steadily thereafter toTm.

Isolated versus Condensed Anion Structure II; the Influence of the Cations (1,3-propanediammonium, 1,4-phenylendiammonium, and n-propylammonium) on Structures and Phase Transitions of CdBr2-4Salts A 79,81Br NQR and X-ray Structure Analysis

1996 ◽  
Vol 51 (12) ◽  
pp. 1216-1228 ◽  
Author(s):  
Hideta Ishihara ◽  
Shi-qi Dou ◽  
Keizo Horiuchi ◽  
V. G. Krishnan ◽  
Helmut Paulus ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Phase I ◽  
Chain Structure ◽  
Phase Iii ◽  
X Ray ◽  
Dsc Measurements ◽  
Structure Determinations ◽  
A Chain ◽  
Successive Phase ◽  
Phase Iv

Abstract The influence of the cations on the condensation of anions CdBr42- in salts (A')CdBr4 (II) and (A)2CdBr4 (II) is studied by 79,81Br NQR and X-ray crystal structure determinations. (A')CdBr4 : A' = [H3N(CH2)3NH3]2+ (1) crystallizes with a layer-type anion structure at 298 K and A' = [1,4-(H3N)2C6H4]2+ (2) crystallizes with a chain-type anion structure at 298 K. (A)2 CdBr4 : A = [n-H3C(CH2)2NH3]+ (3) crystallizes with a layer-type anion structure at 293 K. (1) shows successive phase transitions at 328, 363, and 495 K according to the NQR and DSC measurements. Phase IV of (1): at 298 K orthorhombic, Pnma, Z = 4,a = 772.1 (4), b = 1905.4(9), c = 789.8(4) pm. 81Br NQR spectrum showed a doublet at 77 K (phase IV) with ν1= 61.177 and ν2 = 45.934 MHz and also a doublet at 350 K (phase III) with ν1= 57.581 and ν2 = 48.747 MHz. (2): at 295 K orthorhombic, Pnma, Z = 4, a = 802.5(3), b = 1775.1(6), c = 881.9(3) pm; the five-coordinated Cd atom and one-dimensional [CdBr4]2- anion chain structure was observed. This coordination and chain structure are very rare for (A')CdX4 (II) or (A)2CdX4 (II). Two 81Br NQR lines were observed at 77 K: ν1= 70.159 and ν3 = 40.056 MHz. One more line appeared at 85 K: ν2 = 53.622 MHz. A 81Br NQR triplet was observed at 273 K: ν1 = 67.919, ν2 = 56.317, and ν3 = 40.907 MHz. (3) shows successive phase transitions at 121, 135, 165, and 208 K according to the NQR, DSC, and DTA measurements. Phase I of (3): at 293 K orthorhombic, Cmca, Z = 4, a = 783.4(4), b = 2480.2(10), c = 806.5(4) pm. 81Br NQR doublet was observed at 77 K (phase V) and at 300 K (Phase I) with ν1 = 61.060 and ν2 = 54.098 MHz (77 K); v1 = 55.835 and ν2 = 55.964 MHz (373 K). No NQR line could be observed in phases II, III, and IV.

scholarly journals High-pressure neutron diffraction study of L-serine-I and L-serine-II, and the structure of L-serine-III at 8.1 GPa

2006 ◽  
Vol 62 (5) ◽  
pp. 815-825 ◽  
Author(s):  
Stephen A. Moggach ◽  
William G. Marshall ◽  
Simon Parsons
Keyword(s):  
Hydrogen Bonds ◽  
Phase I ◽  
Phase Ii ◽  
Neutron Diffraction Study ◽  
Neutron Powder Diffraction ◽  
Hirshfeld Surface ◽  
Phase Iii ◽  
Two Phase ◽  
Carboxylate Groups ◽  
The Cost

The hydrostatic compression of L-serine-d 7 has been studied to 8.1 GPa by neutron powder diffraction. Over the course of this pressure range the compound undergoes two phase transitions, the first between 4.6 and 5.2 GPa, yielding L-serine-II, and the second between 7.3 and 8.1 GPa, yielding L-serine-III. All three polymorphs are orthorhombic, P212121, and feature chains of serine molecules connected via head-to-tail ND...O hydrogen bonds formed between ammonium and carboxylate groups. The chains are linked into a ribbon by a second set of ND...O hydrogen bonds. The hydroxyl moieties are distributed along the outer edges of the ribbon and in phase I they connect the ribbons into a layer by chains of OD...OD hydrogen bonds. The layers are connected together by a third set of ND...O hydrogen bonds, forming R^3_4(14) rings with substantial voids at their centres. In the transition from phase I to II these voids begin to close up, but at the cost of breaking the OD...OD chains. The OD...OD hydrogen bonds are replaced by shorter OD...O hydrogen bonds to carboxylate groups. At 7.3 GPa the O...O distance in the OD...O hydrogen bonds measures only 2.516 (17) Å, which is short, and we propose that the phase transition to phase III that occurs between 7.3 and 8.1 GPa relieves the strain that has built up in this region of the structure. The hydroxyl D atom now bifurcates between the OD...O contact that had been present in phase II and a new OD...O contact formed to a carboxylate in another layer. Hirshfeld surface fingerprint plots show that D...D interactions become more numerous, while hydrogen bonds actually begin to lengthen in the transition from phase II to III.

Activated Carbon Supported Iron Catalyst for the Fischer-Tropsch Synthesis

2013 ◽  
Vol 805-806 ◽  
pp. 232-235 ◽  
Author(s):  
Hong Yan Ban ◽  
Zi Wei Wang ◽  
Zhi Qiang Wang ◽  
Zhi Gang Fang
Keyword(s):  
Activated Carbon ◽  
Surface Chemistry ◽  
Iron Catalyst ◽  
Catalytic Performance ◽  
Physical Structure ◽  
Fischer Tropsch ◽  
Syngas Conversion ◽  
Ft Synthesis ◽  
Reaction Performance ◽  
Methane Selectivity

The catalyst prepared using the AC as support showed remarkably improvement of reaction performance. The improvement of the reaction performance obtained for the AC is probably ascribed to the physical structure and surface chemistry of AC. The support and corresponding catalyst are characterized by N2 adsorption. Catalytic performance of the catalyst during FT synthesis was excellent. Syngas conversion was about 74%, whereas methane selectivity was low (~2 %).

scholarly journals Orientational disorder and phase transitions in crystals of (NH4)2NbOF5

2008 ◽  
Vol 64 (5) ◽  
pp. 527-533 ◽  
Author(s):  
Anatoly A. Udovenko ◽  
Natalia M. Laptash
Keyword(s):  
Phase Transitions ◽  
Phase Ii ◽  
Central Atom ◽  
Crystal Form ◽  
Partial Ordering ◽  
Phase Iii ◽  
X Ray Diffraction ◽  
Dynamic Nature ◽  
Two Phase ◽  
X Ray

Ammonium oxopentafluoroniobate, (NH4)2NbOF5, was synthesized in a single-crystal form and the structures of its different phases were determined by X-ray diffraction at three temperatures: phase (I) at 297 K, phase (II) at 233 K and phase (III) at 198 K. The distorted [NbOF5]2− octahedra are of similar geometry in all three structures, with the central atom shifted towards the O atom. The structure of (I) is disordered, with three spatial orientations of the [NbOF5]2− octahedron related by a jump rotation around the pseudo-threefold local axis such that the disorder observed is of a dynamic nature. As the temperature decreases, the compound undergoes two phase transitions. The first is accompanied by full anionic ordering and partial ordering of the ammonium groups (phase II). The structure of (III) is completely ordered. The F and O atoms in the structures investigated were identified via the Nb—X (X = O and F) distances. The crystals of all three phases are twinned.

Model for the crystal packing and conformational changes of biphenyl in incommensurate phase transitions

2004 ◽  
Vol 60 (2) ◽  
pp. 228-237 ◽  
Author(s):  
Alexander Dzyabchenko ◽  
Harold A. Scheraga
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Phase I ◽  
Crystal Packing ◽  
Twist Angle ◽  
Basic Structure ◽  
Incommensurate Phase ◽  
Phase Iii ◽  
Temperature Structure ◽  
High Temperature Structure

Standard atom–atom potentials for hydrocarbons and a torsional potential to account for the π-electron conjugation energy were used to model the crystal structures and phase transitions of biphenyl. The model describes the high-temperature phase (I) with its planar molecule as a stationary point of the energy hypersurface. Phase I represents a low-energy barrier between the symmetry minima of the ground state (phase III), in which the molecule is twisted with torsion angles of opposite sign. Global-energy minimization was carried out by considering both regular structures, with one or two independent molecules, and quasi-one-dimensional superstructures built of N cells (N up to 16) of the high-temperature structure. The various energy-minimized biphenyl structures demonstrate remarkable similarity in their crystal packing; in particular, there are characteristic rows of cooperatively twisted molecules parallel to the superstructure dimension b. The structures built of centrosymmetric rows (P\bar 1, Z = 4 and 8) are almost as low in energy as the basic structure (an N = 2 superstructure, Pa, Z = 4); moreover, one of them is isostructural with the low-temperature p-quaterphenyl structure. With N > 8, structures of lower energy than that of the basic structure (N = 2) were found; their common feature is an M-fold modulation of the twist angle over the supercell period, with M smaller than N and generally not a simple fraction of it. The global minimum was found to conform to the ratio k = M/N = 6/14, which is close to the experimentally observed k = 6/13 in the incommensurate phase III. Enthalpy minimization showed an overall decrease in the magnitude of the twist angle down to τ ≃ 0°, as well as the evolution of the modulated structures towards the high-temperature structure with increasing pressure, in agreement with evidence for the high-pressure limit of the incommensurate biphenyl phases.

X-ray studies of the phase transitions of bis(guanidinium)zirconium bis(nitrilotriacetate) hydrate, (C(NH2)3)2Zr(N(CH2COO)3)2 · H2O

1999 ◽  
Vol 214 (3) ◽  
Author(s):  
J. Schreuer ◽  
E. Haussühl
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Phase I ◽  
Phase Iii ◽  
Group Symmetry ◽  
Translational Symmetry ◽  
X Ray Diffraction ◽  
Space Group Symmetry ◽  
X Ray ◽  
Structural Differences

AbstractThe structural differences of phase I (at 193 K) and phase III (293 K) of bis(guanidinium)zirconium bis(nitrilotriacetate) hydrate were investigated by means of X-ray diffraction. The phase transition III → I is characterised by a loss of translational symmetry as it is indicated by the change of space group symmetry from

Activated Carbon Supported Iron Catalyst for the Fischer-Tropsch Synthesis

2011 ◽  
Vol 335-336 ◽  
pp. 161-164
Author(s):  
Hong Yan Ban ◽  
Jiao Wei ◽  
Xiao Zhi Sun ◽  
Zhi Gang Fang
Keyword(s):  
Activated Carbon ◽  
Iron Catalyst ◽  
Catalytic Performance ◽  
Physical Structure ◽  
Tropsch Synthesis ◽  
Fischer Tropsch ◽  
Fischer Tropsch Synthesis ◽  
Syngas Conversion ◽  
Reaction Performance ◽  
Methane Selectivity

The application of activated carbon (AC) supported Fe-Cu-K catalyst for Fischer-Tropsch synthesis (FTS) is studied. The catalyst prepared using the AC as support showed remarkably improvement of reaction performance. The improvement of the reaction performance obtained for the AC is probably ascribed to the physical structure and surface chemistry of AC. The support and corresponding catalyst are characterized by N2 adsorption. Catalytic performance of the catalyst during FT synthesis was excellent. Syngas conversion was about 74%, whereas methane selectivity was low (~2 %).

Catalytic performance of Co/Zn–Al2O3 Fischer–Tropsch catalysts: a comparative study of zinc introduction methodologies

RSC Advances ◽  
2015 ◽  
Vol 5 (74) ◽  
pp. 60534-60540 ◽  
Author(s):  
Juan Du ◽  
Junkun Yan ◽  
Jingping Hong ◽  
Yuhua Zhang ◽  
Sufang Chen ◽  
...  
Keyword(s):  
Comparative Study ◽  
Pore Structure ◽  
Supported Catalyst ◽  
Catalytic Performance ◽  
Fischer Tropsch

Co-precipitated Zn–Al2O3 showed improved pore structure, and the supported catalyst presented the best FTS performance.

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