Non-trivial temperature effects on the cation exchange chromatography and chelation ion chromatography of metal ions

The effect of column temperature upon the retention of metal ions on sulfonated and mono-, di-, and amino-carboxylated cation exchange columns has been investigated. The retention of alkali, alkaline earth and transition metal ions on each of the above types of cation exchanger was studied over the temperature range 19-65 degrees C. A major difference between the behaviour of mono- and divalent metal ions was shown on each of the above stationary phases, with the monovalent alkali metals exhibiting clearly exothermic behaviour (a decrease in retention with increased temperature) under acidic eluent conditions and an apparent relationship between retention factor and the magnitude of the temperature effect. The effect of temperature upon alkaline earth metal ions was less defined, although strongly endothermic behaviour (increase in retention with temperature) could be seen on all stationary phases through correct choice of eluent. The transition metal ions studied showed endothermic behaviour on all four stationary phases, with the sulfonated column unexpectedly showing the largest increases in retention. The above behaviour can be partially explained through the dominance of the type of solute-stationary phase interaction governing retention. In several of the above columns, both ion-exchange and surface complexation interactions can occur, with the effects of temperature indicating which process dominates under specific eluent conditions.     

Application of multivariate curve resolution methods to on-flow LC-NMR

The application of evolving window factor analysis (EFA), subwindow factor analysis (SFA), iterative target transformation factor analysis (ITTFA), alternating least squares (ALS), Gentle, automatic window factor analysis (AUTOWFA) and constrained key variable regression (CKVR) to resolve on-flow LC-NMR data of eight compounds into individual concentration and spectral profiles is described. CKVR has been reviewed critically and modifications are suggested to obtain improved results. A comparison is made between three single variable selection methods namely, orthogonal projection approach (OPA), simple-to-use interactive self-modelling mixture analysis approach (SIMPLISMA) and simplified Borgen method (SBM). It is demonstrated that LC-NMR data can be resolved if NMR peak cluster information is utilised.     

A new look at the crystallization of polyethylene. III. Crystallization from the melt at high supercoolings

Polyethylene melts normally cannot be crystallized in an isothermally controlled manner below ca. 110°C as crystallization is too fast owing to the presence of preexisting nuclei. We here present a new simple method for producing droplets enabling crystallization to be conducted isothermally down to 75°C and allowing measurements to be performed on them, together with the results of these measurements. We conclude that in contrast to the earlier claims the homogeneous nucleation regime has not been attained even at these low temperatures, the crystal nucleation being dominated by the polymer-substrate interface. The droplets crystallized at these low temperatures have a lamellar morphology as revealed by electron microscopy and grow at rates exceeding 1 m s^?1 [i.e., six orders of magnitude faster than growth at more usual crystallization temperatures previously considered as “low” (110–120°C)]. We have measured the lamellar thickness l as a function of growth temperature, thus extending the fundamentally important l vs. ΔT (supercooling) relation beyond the previously realizable limits towards high ΔT values. The implications of all these results for the existing ideas of polymer crystallization are likely to be far reaching. Further, the new method for achieving high supercoolings opens up new possibilities for the study of annealing phenomena and the effect of nucleating agents.     

Magnesocenophane-Catalyzed Amine Borane Dehydrocoupling

The Lewis acidities of a series of [n]magnesocenophanes ( 1 a – d ) have been investigated computationally and found to be a function of the tilt of the cyclopentadienyl moieties. Their catalytic abilities in amine borane dehydrogenation/dehydrocoupling reactions have been probed, and C[1]magnesocenophane ( 1 a ) has been shown to effectively catalyze the dehydrogenation/dehydrocoupling of dimethylamine borane ( 2 a ) and diisopropylamine borane ( 2 b ) under ambient conditions. Furthermore, the mechanism of the reaction with 2 a has been investigated experimentally and computationally, and the results imply a ligand-assisted mechanism involving stepwise proton and hydride transfer, with dimethylaminoborane as the key intermediate.     

双金属镍-锰/γ-Al2O3催化剂对甲烷二氧化碳重整反应的影响 (cited: 1)

用浸渍法制备γ-Al₂O₃负载的Ni-Mn双金属催化剂．在500～700 oC按照17:17:2的CO₂/CH₄/N₂比例,以36 mL/min的载气流速进行甲烷二氧化碳重整反应, 利用甲烷二氧化碳的转化率、生成的合成气H₂/CO比例以及长期稳定性等指标评价了催化剂的催化性能． 实验表明, 添加Mn提高催化性能并使双金属催化剂的稳定性更高, 比单金属催化剂更好地抑制焦炭生成,Mn最合适的添加量0.5wt％ ．通过BET、CO2-TPD、TGA、XRD、SEM、EDX和FTIR各种技术对催化剂进行了表征．     

Effect of Nano‐support and Type of Active Metal on Reforming of CH4 with CO2

Two series of Co and Ni based catalysts supported over commercial (ZrO₂, CeO₂, and Al₂O₃) nano supports were investigated for dry reforming of methane. The catalytic activity of both Co and Ni based catalysts were assessed at different reaction temperatures ranging from 500—800 °C; however, for stability the time on stream experiments were conducted at 700 °C for 6 h. Various techniques such as N₂ adsorption‐desorption isotherm, temperature‐programmed reduction (H₂‐TPR), temperature‐programmed desorption (CO₂‐TPD), temperature‐programmed oxidation (TPO), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) were applied for characterization of fresh and spent catalysts. The catalytic activity and stability tests clearly showed that the performance of catalyst is strongly dependent on type of active metal and support. Furthermore, active metal particle size and Lewis basicity are key factors which have significant influence on catalytic performance. The results indicated that Ni supported over nano ZrO₂ exhibited highest activity among all tested catalysts due to its unique properties including thermal stability and reducibility. The minimum carbon deposition and thus relatively stable performance was observed in case of Co‐Al catalyst, since this catalyst has shown highest Lewis basicity.     

Neutron activation analysis of IAEA proposed certified reference material IAEA-407 (North Sea Fish Homogenate)

The proposed reference material from the International Atomic Energy Agency, namely IAEA-407 (Fish Homogenate) was analyzed using instrumental neutron activation analysis (INAA). 15 elements, Al, As, Cl, Co, Cr, Fe, Hg, Mg, Mn, K, Na, Sb, Se, V and Zn, were determined using two irradiations (5 minutes and 5 hours) and four countings. IAEA-MA-A-1/TM (Copepoda Homogenate), NIST-SRM-1566 (Oyster Tissue), NIST-SRM-1572 (Citrus Leaves) and NIST-SRM-1577a (Bovine Liver) were utilized as standards in the quantification step.     

Defect-induced increase in the phonon energy involved in the formation of Urbach tail in Cu-ternaries

From a combined analysis of the stoichiometric composition and Urbach tail in samples of CuInSe₂, CuInTe₂, and CuGaTe₂ of the I-III-VI₂ family of chalcopyrite semiconductors, it is found that the energy hν_p involved in the electron/exciton-phonon interaction is a linear function of a parameter Δz which is the sum of the deviations from ideal molecularity Δx and anion to cation ratio Δy. It gives evidence that in the copper ternaries hν_p is associated to the structural defects caused by cation-cation, cation-anion, and other intrinsic disorders. The high value of hν_p found in the studied samples, higher than the highest optical mode, is shown to come from the contribution of the additional phonon energy due to structural defects. This is in agreement with recently proposed models of the temperature dependence of the Urbach energy.