Towards the insights into the deactivation behavior of acetylene hydrogenation catalyst

A series of model catalysts were obtained by treating commercial fresh and spent catalysts unloaded from the factory with different methods, including green oil dipping, extraction and high-temperature regeneration;finally, the deactivation behavior of the commercial catalyst for acetylene hydrogenation were studied. The influence of various possible deactivation factors on the catalytic performance was elucidated via detailed structural characterization, surface composition analysis, and activity evaluation.The results showed that green oil, carbon deposit and sintering of active metal were the main reasons for deactivation, among which green oil and carbon deposit led to rapid deactivation, while the activity could be recovered after regeneration by high-temperature calcination. The sintering of active metal components was attributed to the high-temperature regeneration in hydrothermal conditions, which was slow but irreversible and accounted for permanent deactivation. Thus, optimizing the regeneration is expected to extend the service life of the commercial catalyst.

A facile and precise method for quantifying small–large/light-weighted molecular interaction system

It is significant to quantify the intermolecular physisorption extent in biomedical field.By taking the advantage of a significant difference from either sizes or weights,we introduced a combination of Scatchard equation and either ultracentrifugation or size exclusion chromatography to obtain both the binding constant and the number of binding sites by using bovine serum albumin and eosin B as models.Compared to the photoluminescence quenching-based methods like Stern-Volmer and Hill equations,the introduced method is not only more precise but also simpler and more straightforward for the operation.Moreover,the protein conformational changes and the corresponding theoretical binding mode with an atomic resolution were also studied by using three-dimensional fluorescence spectroscopy and molecular docking method,respectively.These comparative results could help scientists select right methods to study any interactions between two molecules with significant differences from either sizes or weights.

SYNTHESIS OF BIMODAL POLYETHYLENE WITH UNSYMMETRICAL α-DIIMINE NICKEL COMPLEXES: INFLUENCE OF LIGAND BACKBONE AND UNSYM-SUBSTITUTED ANILINE MOIETY

A series of unsymmetrical a-diimine nickel complexes with various backbones and substituted aniline moieties were synthesized and characterized. The crystallographic analysis of the nickel complexes confirmed the existence of meso-and rac-configuration in solid structure. Nickel complexes after activation by MAO were screened for ethylene polymerization to evaluate backbone substituent effect on synthesis of bimodal PE. Acenaphthyl nickel complex with planar backbone afforded a bimodal PE with a broad polydispersity, whereas camphyl nickel complex with rigid and bulky backbone afforded a monomodal PE with a narrow polydispersity. Steric effect of aniline moiety for acenaphthyl nickel complex was also examined, and bimodal PE with dominant high-molecular-weight fraction was obtained by modifying substituents on aniline moiety.

Regioselective Polymerizations of α-Olefins with an α-Diamine Nickel Catalyst

Polymerizations of linear α-olefins(CnH2n, CH2=CH―R, R = Cn-2) catalyzed by early transition metals typically afford amorphous polymers with alkyl chains(Cn-2), while chain-straightening polymerizations of α-olefins with nickel-based catalysts produce semicrystalline polyolefins. Polymerizations of various α-olefins were carried out using an α-diamine nickel catalyst with a significantly distorted chelating ring. The influences of temperature, monomer concentration, and chain length of α-olefins on polyolefin microstructure were examined in detail. The α-diamine nickel catalyst realized highly regioselective 2,1-insertion of α-olefins regardless of reaction temperature and monomer concentration. Increased chain length of α-olefins led to the formation of more linear polyolefin.Semicrystalline polyolefins with high melting temperatures(Tm) were made from α-olefins through highly regioselective 2,1-insertion and precise chain-straightening.

Synthesis, Characterization, and Catalytic Ethylene Oligomerization of Pyridine-imine Palladium Complexes

Two neutral five-membered pyridine-imine palladium complexes with the bulky dibenzhydryl（CH（Ph）2） substituted aniline were synthesized and fully characterized by nuclear magnetic resonance（NMR） and X-ray crystal diffraction. Well-defined cationic palladium complexes were further obtained by treatment of chloromethylpalladium complexes with sodium tetrakis（3,5-bis（trifluoromethyl）phenyl）borate（NaBArF） in CH3CN. Cationic palladium complexes were capable of catalyzing ethylene oligomerization without any cocatalysts. The influences of catalyst structure, reaction temperature, and ethylene pressure on ethylene oligomerization were studied in detail. The introduction of bulky benzhydryl（CH（Ph）2） on the ortho position of the aniline moiety enhanced catalytic activity, thermal stability of the catalyst, and molecular weight of the obtained products. Highly branched oligomers with molecular weights of 600-800 g/mol and narrow polydispersities（1.03-1.12） were produced.

Synthesis of Isotactic Polystyrene-block-Polyethylene by the Combination of Sequential Monomer Addition and Hydrogenation of 1,4-Trans-polybutadiene Block

Herein, we demonstrate the synthesis of a well-defined diblock copolymer consisting of isotactic polystyrene （iPS） and linear polyethylene, isotactic polystyrene-block-polyethylene （iPS-b-PE）, by the combination of sequential monomer addition and hydrogenation. Isospecific living polymerization of styrene and living trans-1,4-polymerization of 1,3-butadiene were catalyzed by 1,4-dithiabutandiyl-2,2＇-bis（6-cumenyl-4-methylphenoxy） titanium dichloride （complex 1） activated by triisobutyl aluminum modified methylaluminoxane （MMAO） at room tempera^xre to provide highly isotactic polystyrene （iPS） and 1,4-trans-polybutadiene （1,4-trans-PBD） with narrow molecular weight distribution. Furthermore, the iPS-b-I,4- trans-PBD was synthesized via sequential monomer addition in the presence of complex 1 and MMAO. The hydrogenation of the 1,4-trans-PBD block was promoted by RuC12（PPh3）3 used as a catalyst to produce iPS-b-PE.

Crystallization-driven Self-assembly of Isotactic Polystyrene in N,N-Dimethylformamide

Herein we demonstrate crystallization-driven self-assembly ofisotactic polystyrene （iPS） with high isotacticity and narrow molecular weight distribution and crystallization-induced switching of the morphology of iPS aggregates in N, N-dimethylformamide （DMF）. The formation and morphology switching of the self-assembled aggregates of iPS are investigated by means of dynamic light scattering （DLS）, scanning electron microscopy （SEM）, differential scanning calorimetry （DSC） and wide angle X-ray diffraction （WXRD）. The results reveal that cooling DMF solution of iPS promotes iPS chains to self-assemble into spherical aggregates with a gelled core cross-linked by microcrystals, which is surrounded by solvent-swollen corona. Furthermore, crystallization induces the deformation of iPS aggregates from spherical to plate-like or nest-like.

Polymer-free versus permanent polymer drug eluting stents in coronary artery disease: A meta-analysis of 10 RCTs with 6575 patients

Background:Permanent polymer drug eluting stents (PP-DES) may induce inflammation of the vessel wall due to the existence of the polymer,which may delay intimal healing.Polymer-free DES (PF-DES) that eliminate the polymeric carrier may potentially lead to safer DES.However,the safety and efficacy of PF-DES remains controversial.Methods:Randomized controlled trials comparing PF-DES with PP-DES were searched in online database including MEDLINE,Excerpta Medica Database (EMBASE) and Cochrane Library.Studies reporting late lumen loss (LLL),all-cause death,myocardial infarction (MI),target lesion revascularization (TLR) and late stent thrombosis (LST) were enrolled and quantitatively analyzed.Results:Ten studies enrolling 6575 patients were included in this meta-analysis.The PF-DES showed a benefit in reducing all-cause death (OR =0.77,95％ CI:0.61 to 0.98,P =0.03) and long-term LLL (weighted mean difference (WMD)-0.16 mm,95％ CI:-0.22 to -0.11 mm,P ＜ 0.001),while no superiority was found in reducing short-term LLL (WMD 0.03 mm,95％ CI:-0.07-0.13 mm,P =0.57),MI (OR =1.12,95％ CI:0.19 to 23.18,P=0.39),TLR (OR =1.19,95％ CI:0.42 to 3.38,P=0.83)and LST (OR =0.92,95％CI:0.05 to 5.71,P =0.74).Conclusion:PF-DES showed benefits in reducing long-term LLL and mortality compared with PP-DES,but no superiority was found in short-term LLL,MI,TLR and LST.These findings provide a sound basis for the wide application of PF-DES in the future.