Industrial Ziegler-type hydrogenation catalysts made from Co(neodecanoate)2 or Ni(2-ethylhexanoate)2 and AlEt3: evidence for nanoclusters and sub-nanocluster or larger Ziegler-nanocluster based catalysis

Ziegler-type hydrogenation catalysts are important for industrial processes, namely, the large-scale selective hydrogenation of styrenic block copolymers. Ziegler-type hydrogenation catalysts are composed of a group 8-10 transition metal precatalyst plus an alkylaluminum cocatalyst (and they are not the same as Ziegler-Natta polymerization catalysts). However, for ～50 years two unsettled issues central to Ziegler-type hydrogenation catalysis are the nature of the metal species present after catalyst synthesis, and whether the species primarily responsible for catalytic hydrogenation activity are homogeneous (e.g., monometallic complexes) or heterogeneous (e.g., Ziegler nanoclusters defined as metal nanoclusters made from combination of Ziegler-type hydrogenation catalyst precursors). A critical review of the existing literature (Alley et al. J. Mol. Catal. A: Chem. 2010, 315, 1-27) and a recently published study using an Ir model system (Alley et al. Inorg. Chem. 2010, 49, 8131-8147) help to guide the present investigation of Ziegler-type hydrogenation catalysts made from the industrially favored precursors Co(neodecanoate)(2) or Ni(2-ethylhexanoate)(2), plus AlEt(3). The approach and methods used herein parallel those used in the study of the Ir model system. Specifically, a combination of Z-contrast scanning transmission electron microscopy (STEM), matrix assisted laser desorption ionization mass spectrometry (MALDI MS), and X-ray absorption fine structure (XAFS) spectroscopy are used to characterize the transition metal species both before and after hydrogenation. Kinetic studies including Hg(0) poisoning experiments are utilized to test which species are the most active catalysts. The main findings are that, both before and after catalytic cyclohexene hydrogenation, the species present comprise a broad distribution of metal cluster sizes from subnanometer to nanometer scale particles, with estimated mean cluster diameters of about 1 nm for both Co and Ni. The XAFS results also imply that the catalyst solutions are a mixture of the metal clusters described above, plus unreduced metal ions. The kinetics-based Hg(0) poisoning evidence suggests that Co and Ni Ziegler nanoclusters (i.e., M(≥4)) are the most active Ziegler-type hydrogenation catalysts in these industrial systems. Overall, the novelty and primary conclusions of this study are as follows: (i) this study examines Co- and Ni-based catalysts made from the actual industrial precursor materials, catalysts that are notoriously problematic regarding their characterization; (ii) the Z-contrast STEM results reported herein represent, to our knowledge, the best microscopic analysis of the industrial Co and Ni Ziegler-type hydrogenation catalysts; (iii) this study is the first explicit application of an established method, using multiple analytical methods and kinetics-based studies, for distinguishing homogeneous from heterogeneous catalysis in these Ziegler-type systems; and (iv) this study parallels the successful study of an Ir model Ziegler catalyst system, thereby benefiting from a comparison to those previously unavailable findings, although the greater M-M bond energy, and tendency to agglomerate, of Ir versus Ni or Co are important differences to be noted. Overall, the main result of this work is that it provides the leading hypothesis going forward to try to refute in future work, namely, that sub, M(≥4) to larger, M(n) Ziegler nanoclusters are the dominant, industrial, Co- and Ni- plus AlR(3) catalysts in Ziegler-type hydrogenation systems.     

Synthesis and characterization of novel substituted and cyclic benzoquinone derivatives

Novel substituted benzoquinone compounds were synthesized from the reactions of p-chloranil and p-fluoranil with some thiols, amines, and diols in different reaction media. Interesting cyclic compounds like crown ether structures were obtained. The structures of all compounds were characterized by spectroscopic methods and microanalysis.     

Ziegler-type hydrogenation catalysts made from group 8–10 transition metal precatalysts and AlR3 cocatalysts: A critical review of the literature

Ziegler-type hydrogenation catalysts (group 8–10 transition metal precatalysts plus AlR₃ cocatalysts) are one of the most important families of industrial hydrogenation catalysts, especially for polymer hydrogenation. Despite their ～40 year history of industrial use, there is a need for improved fundamental understanding in order to make further, rationally directed improvements in these catalysts. This review examines the existing literature on Ziegler-type hydrogenation catalysts, specifically: (i) the variables important to catalyst synthesis, (ii) the catalyst formation reaction mechanism, (iii) the compositional and structural nature of the active catalyst species, and (iv) the mechanism of catalytic hydrogenation. This review also (v) discusses the current approaches to the homogeneous versus heterogeneous catalysis question, with the goal of identifying if Ziegler-type hydrogenation catalysts are homogeneous (e.g., monometallic) versus heterogeneous (e.g., nanoclusters) as the true catalyst(s). A summary of the main insights from each section of the review is also given.     

Incorporating the pricing decisions into the dynamic fleet management problem

This paper presents a model to coordinate the pricing and fleet management decisions of a freight carrier. We consider a setting where the loads faced by the carrier over a certain time horizon are deterministic functions of the prices. We want to find what prices the carrier should charge so that its pricing and fleet management decisions jointly maximize the profits. Our solution approach is an iterative one. At each iteration, we solve the fleet management problem with fixed prices, and then, adjust these prices by using the primal-dual solution to the fleet management problem so as to obtain ‘better’ prices. Computational experiments show that our approach yields high-quality solutions and can efficiently be applied on large problems.     

Study of phosphorus distribution in coastal surface sediment by sequential extraction procedure (NE Mediterranean Sea, Antalya-Turkey)

The paper presents the results of the distribution of phosphorus (P) bioavailability (total P, organic and inorganic P) in marine surface sediments collected from four coasts that are under different anthropogenic pressures of NE Mediterranean Sea (Alanya, Serik, Kemer, Finike — Antalya, Turkey) in May, 2009. Speciation of inorganic phosphorus (IP) was carried out using a method on sequential extractions, with each releasing four forms of IP — loosely bound P, phosphorus bound to aluminum (P-Al), phosphorus bound to iron (P-Fe), and phosphorus bound to calcium (P-Ca) and determined by the inductively coupled plasma-optical emission spectrometer (ICP-OES). The total P contents ranged from 152.18 to 275.12 mg/kg. It was found that more than 96% of the total P is IP. Among the four forms of IP, IP distribution ranges were 1.20-3.59% for loosely bound P, 2.38-4.74% for P-Fe, 4.43-8.55% for P-Al, and 84.36-91.99% for P-Ca. The region of Alanya was characterized by the highest total P concentration in the surface sediment than Serik, Kemer, Finike sediments. For all the marine surface sediment samples, the rank order of inorganic P-fractions was Ca-P > Al-P > Fe-P > loosely bound P.     

MOL solution of DOM for transient radiative transfer in 3-D scattering media

A methodology based on the method of lines solution of discrete ordinates method for solution of the 3-D transient radiative transfer equation is introduced. The method is applied to the prediction of transient and steady state transmittances in a cubical enclosure containing purely scattering medium and validated against Monte Carlo solutions from the literature. The flexibility of the method for implementation of linear spatial differencing schemes, flux limiters and weighted essentially non-oscillatory methods is demonstrated. Van Leer flux limiter is found to provide stable, accurate and efficient solutions.     

Effect of PNA backbone modifications on cyanine dye binding to PNA-DNA duplexes investigated by optical spectroscopy and molecular dynamics simulations

Optical spectroscopy and molecular dynamics simulations have been used to study the interaction between a cationic cyanine dye and peptide nucleic acid (PNA)-DNA duplexes. This recognition event is important because it leads to a visible color change, signaling successful hybridization of PNA with a complementary DNA strand. We previously proposed that the dye recognized the minor groove of the duplex, using it as a template for the assembly of a helical aggregate. Consistent with this, we now report that addition of isobutyl groups to the PNA backbone hinders aggregation of the dye when the substituents project into the minor groove but have a weaker effect if directed out of the groove. UV-Visible and circular dichroic spectroscopy were used to compare aggregation on the different PNA-DNA duplexes, while molecular dynamics simulations were used to confirm that the substituents block the minor groove to varying degrees, depending on the configuration of the starting amino acid. In addition to a simple steric blockage effect of the substituent, the simulations suggest that directing the isobutyl group into the minor groove causes the groove to narrow and the duplex to become more rigid, structural perturbations that are relevant to the growing interest in backbone-modified PNA for applications in the biological and materials sciences.     

A stochastic approximation method for the single-leg revenue management problem with discrete demand distributions

We consider the problem of optimally allocating the seats on a single flight leg to the demands from multiple fare classes that arrive sequentially. It is well-known that the optimal policy for this problem is characterized by a set of protection levels. In this paper, we develop a new stochastic approximation method to compute the optimal protection levels under the assumption that the demand distributions are not known and we only have access to the samples from the demand distributions. The novel aspect of our method is that it works with the nonsmooth version of the problem where the capacity can only be allocated in integer quantities. We show that the sequence of protection levels generated by our method converges to a set of optimal protection levels with probability one. We discuss applications to the case where the demand information is censored by the seat availability. Computational experiments indicate that our method is especially advantageous when the total expected demand exceeds the capacity by a significant margin and we do not have good a priori estimates of the optimal protection levels.     

Ultrasonic destruction of bisphenol-A: the operating parameters

Degradation of bisphenol-A (BPA) by ultrasonic irradiation at 300 kHz was investigated at varying substrate concentrations, pH, hydroxyl radical scavengers and sparge gases. It was found that increases in BPA initial concentration slowed down the reaction rate, but enhanced the sonochemical product yield. Both the rate of reaction and the product yield were adversely affected by pH elevation above the neutral level. The degree of BPA decay was fastest in the presence of air due to the formation of acids and excess radicals, and slowed down as the gas was replaced by argon and oxygen. The impact of large concentrations of hydroxyl radical scavengers such as carbonate and t-butanol was to decrease the rate of degradation, particularly when the scavenger concentration was considerably larger than that of BPA, and the deceleration was more remarkable in the presence of t-butanol than in that of carbonate.     

Determination of lead separated selectively with ion exchange method from solution onto BCW in Sirnak, East Anatolia of Turkey

There are approximately 82 million of tons asphaltites reserves in ?irnak, East Anatolia of Turkey. The present study was investigated to employ ashes of S?rnak BCW (burned coal waste) as an ion exchange in removal of important toxic metal, Lead (Pb), in high yields by adsorption. The ion exchange characteristics of lead onto BCW from aqueous solution were investigated with respect to the changes in pH of solution, adsorbent dosage, initial metal ion concentration, contact time and temperature of solution. For the adsorption of lead, the Langmuir isotherm model fitted to equilibrium data better than the Freundlich isotherm model. Thermodynamic functions, the change of free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) of adsorption were also calculated for lead. These parameters showed that the adsorption was feasible, spontaneous and exothermic at 293–333 K. Experimental data were also evaluated in terms of kinetic characteristics of adsorption. The batch kinetic data were correlated to the pseudo-first order and pseudo-second order models. The data fitted better to the pseudo-second order equation. The activation energy of systems was determined. Experimental data have shown that BCW that was used in unmodified form; as low cost, readily available ion exchange; can be used for removal of lead from industrial waste waters. Analysis was determined using Flame Atomic Absorption Spectrometry (FAAS).