Ziegler-type hydrogenation catalysts, those made from a group 8-10 transition metal precatalyst and an AlR(3) cocatalyst, are often used for large scale industrial polymer hydrogenation; note that Ziegler-type hydrogenation catalysts are not the same as Ziegler-Natta polymerization catalysts. A review of prior studies of Ziegler-type hydrogenation catalysts (Alley et al. J. Mol. Catal. A: Chem. 2010, 315, 1-27) reveals that a approximately 50 year old problem is identifying the metal species present before, during, and after Ziegler-type hydrogenation catalysis, and which species are the kinetically best, fastest catalysts--that is, which species are the true hydrogenation catalysts. Also of significant interest is whether what we have termed "Ziegler nanoclusters" are present and what their relative catalytic activity is. Reported herein is the characterization of an Ir Ziegler-type hydrogenation catalyst, a valuable model (vide infra) for the Co-based industrial Ziegler-type hydrogenation catalyst, made from the crystallographically characterized [(1,5-COD)Ir(mu-O(2)C(8)H(15))](2) precatalyst plus AlEt(3). Characterization of this Ir model system is accomplished before and after catalysis using a battery of physical methods including Z-contrast scanning transmission electron microscopy (STEM), high resolution (HR)TEM, and X-ray absorption fine structure (XAFS) spectroscopy. Kinetic studies plus Hg(0) poisoning experiments are then employed to probe which species are the fastest catalysts. The main findings herein are that (i) a combination of the catalyst precursors [(1,5-COD)Ir(mu-O(2)C(8)H(15))](2) and AlEt(3) gives catalytically active solutions containing a broad distribution of Ir(n) species ranging from monometallic Ir complexes to nanometer scale, noncrystalline Ir(n) nanoclusters (up to Ir(approximately 100) by Z-contrast STEM) with the estimated mean Ir species being 0.5-0.7 nm, Ir(approximately 4-15) clusters considering the similar, but not identical results from the different analytical methods; furthermore, (ii) the mean Ir(n) species are practically the same regardless of the Al/Ir ratio employed, suggesting that the observed changes in catalytic activity at different Al/Ir ratios are primarily the result of changes in the form or function of the Al-derived component (and not due to significant AlEt(3)-induced changes in initial Ir(n) nuclearity). However (iii), during hydrogenation, a shift in the population of Ir species toward roughly 1.0-1.6 nm, fcc Ir(0)(approximately 40-150), Ziegler nanoclusters occurs with, significantly, (iv) a concomitant increase in catalytic activity. Importantly, and although catalysis by discrete subnanometer Ir species is not ruled out by this study, (v) the increases in activity with increased nanocluster size, plus Hg(0) poisoning studies, provide the best evidence to date that the approximately 1.0-1.6 nm, fcc Ir(0)(approximately 40-150), heterogeneous Ziegler nanoclusters are the fastest catalysts in this industrially related catalytic hydrogenation system (and ...

We show that the noncrystalline-to-crystalline transition of supported Pt nanoparticles (NPs) in the subnanometer to nanometer size range is statistical in nature, and strongly affected by particle size, support, and adsorbates (here we use H2). Unlike in the bulk, a noncrystalline phase exists and is stable in small NPs, reflecting a general mesoscopic feature. Observations of >3000 particles by high-resolution transmission electron microscopy show a noncrystalline-to-crystalline transition zone that is nonabrupt; there is a size regime where disordered and ordered NPs coexist. The NP size at which this transition occurs is strongly dependent on both the adsorbate and the support, and this effect is general for late 5d transition metals. All results are reconciled via a statistical description of particle-support-adsorbate interactions.

The values of density, surface tension, and refractive index were measured for a classic series of air and water stable ionic liquids (ILs) based on tetrafluoroborate, [C n mim][BF 4 ](n = 2,3,4,5,6)(1-alkyl-3-methylimidazolium tetrafluoroborate) in the temperature range of (298.15 to 338.15 ± 0.02) K. In terms of Glasser's theory, the standard molar entropy and lattice energy of the ILs were calculated. Using Kabo's method, the molar enthalpy of vaporization of the IL, Δ l g H m 0 (298 K), was estimated. According to the interstice model, the thermal expansion coefficient of ILs [C n mim][BF 4 ] (n = 2,3,4,5,6), α, were calculated, and in comparison with experimental value, their magnitude order is in good agreement. To test this new concept of ionic parachor, [BF 4 ] − was chosen as a reference ion and its individual value of ionic parachor was determined in terms of extrathermodynamic assumption. Then, using ionic parachor of [BF 4 ] − , the ionic parachors for all corresponding imidazolium cations, [C n mim] + , were calculated and in good agreement with those obtained by Guan's estimation, and the 17 anion ionic parachors were also obtained. In terms of ionic parachor, the surface tension and refractive index of the investigated ionic liquids were estimated, and the estimated values correlate quite well with their matching experimental values.

No abstract

Jellylike phase (JLP) is usually harmful to the process of crystallization. The special state of cefotaxime sodium (CTX) jellylike phase and its spontaneous transition to crystals is investigated in this paper. The crystals transformed from JLPs containing different solvents have distinct habits and forms. The solvent used in JLP formation and crystallization was very important. The results show that the polarity and hydrogen bonding ability of the solvent plays a decisive role in the JLP formation and its crystallization. Combined with Fourier transform infrared spectra, in situ Raman spectroscopy monitoring experiment indicates that the orientational hydrogen bonding between the solvent and CTX molecule facilitates the construction of the CTX crystal structure. JLP crystallization offers a new way for novel polymorph development and crystal habit modification, especially for drugs that are difficult to crystallize from solution.