Improvement of catalyst stability during methane dehydroaromatization (MDA) on Mo/HZSM-5 comprising intracrystalline mesopores

[EN] Anew Mo/HZSM-5catalyst (3 wt% Mo, Si/Al = 26) comprising a carbon-templated zeolite having intracrystalline mesopores sizing ca. 10-20nm (HZSM-5-BP) has been prepared. For comparison purposes, an equivalent catalyst has also been prepared from a commercial zeolite (HZSM-5-ref). The materials have been extensively characterized by XRD, ICP-OES, N(2) physisorption, SEM-TEM, (27)Al MAS NMR, FTIR-pyridine, NH(3)-TPD, H(2)-TPR, TG-DTG analyses and TPO, and their catalytic activity evaluated for methane dehydroaromatization (MDA) at 700 degrees C, 1 bar, and 1500 ml/g(cat) h. The hierarchical Mo/HZSM-5-BP catalyst displayed a lower deactivation rate during MDA than the reference one, leading to a higher and stable aromatics yield at T.O.S. above 3 h, despite a higher amount of less reactive coke (associated to the zeolite acid sites) was produced in the former. We hypothesize that the enhanced tolerance to carbon deposits of the carbon-templated zeolite could be related to the intracrystalline mesopores acting as a trap for coke molecules and leaving a higher fraction of acid sites within the channels active for aromatization.Financial support by the Comision Interministerial de Ciencia y Tecnologia (CICYT) of Spain through the projects CTQ2007-66614/PPQ and CTQ2006-28341-E/BQU is gratefully acknowledged. Thanks are also due to the UE Network of Excellence IDECAT (FP6 Programme, NMP3-CT-2005-011730) which promoted the collaboration between the two research institutions.Martinez Feliu, A.; Peris, E.; Derewinski, M.; Burkat-Dulak, A. (2011). Improvement of catalyst stability during methane dehydroaromatization (MDA) on Mo/HZSM-5 comprising intracrystalline mesopores. Catalysis Today. 169(1):75-84. doi:10.1016/j.cattod.2010.11.063S7584169

Rheology of Green Plasticizer/Poly(vinyl chloride) Blends via Time–Temperature Superposition

Plasticizers are commonly added to poly(vinyl chloride) (PVC) and other brittle polymers to improve their flexibility and processing properties. Phthalate plasticizers such as di(2-ethylhexyl phthalate) (DEHP) are the most common PVC plasticizers and have recently been linked to a wide range of developmental and reproductive toxicities in mammals. Our group has developed several replacement compounds that have good biodegradation kinetics, low toxicity profiles, and comparable plasticizer properties to DEHP. Knowledge of the rheology of PVC–plasticizer blends at elevated temperatures is crucial for understanding and predicting the behavior of the compounds during processing. In this work, the time–temperature profiles of PVC blended with our replacement green plasticizers—succinates, maleates, and dibenzoates, of varying alkyl chain length—are compared to blends prepared with DEHP and a commercially available non-phthalate plasticizer, di(isononyl cyclohexane-1,2-dicarboxylate) (Hexamoll® DINCH®). The relationship between the plasticizer molecular structure and viscoelastic response was examined by applying time–temperature superposition. All compounds except the diethyl esters showed a comparable viscoelastic response to DEHP and Hexamoll® DINCH®, and dihexyl succinate exhibited the most effective reduction of the storage modulus G′. All of the dibenzoate blends exhibited a lower stiffness than the DEHP blends. These experiments help to show that the green plasticizers described herein are viable replacements for DEHP, providing a less toxic alternative with comparable processing and rheological performance

Oculoplastic Surgery: Anatomic Foundations, Surgical Techniques, and Enhanced Results

Instruction and Skills Transfer Cours

Exotic shape symmetries around the fourfold octupole magic number N=136N=136: Formulation of experimental identification criteria

International audienceWe employ a realistic nuclear mean-field theory using the phenomenological, Woods-Saxon Hamiltonian with newly adjusted parameters containing no parametric correlations; originally present correlations are removed employing the Monte Carlo approach. We find very large neutron shell gaps at N=136 for all the four octupole deformations α3μ=0,1,2,3. These shell gaps generate well-pronounced double potential-energy minima in the standard multipole (α20,α22,α3μ,α40) representation, often at α20=0, which in turn generate exotic symmetries C2v, D2d, Td, and D3h, discussed in detail. The main goal of the article is to formulate spectroscopic criteria for experimental identification. Calculations employing macroscopic-microscopic method are performed for nuclei with Z≥82 and N≥126 in multidimensional deformation spaces to analyze the expected exotic symmetries and octupole shape instabilities in the mass table “northeast” of the doubly magic Pb208 nucleus. Whereas the proton-unperturbed properties of neutron-generated octupole shell effects are illustrated in detail for exotic Z=82PbN>126 nuclei, our discussion is extended into even-even Z>82 nuclei approaching the less exotic Z/N ratios, to encourage experiments which could identify the predicted exotic symmetries. In addition to the tetrahedral point group symmetry, Td, of which experimental evidence has recently been published, we present D2d symmetry resulting from a superposition of axially symmetric quadrupole and tetrahedral symmetries and two new point group symmetries, D3h and C2v, associated with the octupole α33 and α31 energy minima, respectively. The multidimensional n>2 deformation spaces are treated as usual by projecting the total potential energies onto the n=2 subspace. Using the representation theory of point groups we formulate quantum mechanical criteria for experimental identification of exotic symmetries through analysis of the specific properties of the collective rotational bands generated by the symmetries. The resulting band structures happen to be markedly distinct from the structure of the bands generated by ellipsoidal symmetry quantum rotors; those various rotational properties are discussed in detail

Beyond Regular Model Checking

In recent years, it has been established that regular model checking can be successfully applied to several parameterized verification problems. However, there are many parameterized verification problems that cannot be described by regular languages, and thus cannot be verified using regular model checking. In this study we try to practice symbolic model checking using classes of languages more expressive than the regular languages. We provide three methods for the uniform verification of non-regular parameterized systems