scholarly journals The synthesis and application of novel Ni(ii) N-alkyl dipyridylaldiminato complexes as selective ethylene oligomerisation catalysts

2014 ◽  
Vol 43 (26) ◽  
pp. 9892-9900 ◽  
Author(s):  
Andrew J. Swarts ◽  
Selwyn F. Mapolie
Keyword(s):  
High Activity ◽  
Catalyst Activity ◽  
Electronic Effects ◽  
Activation Pathways

A series of dinuclear Cl-bridged Ni(ii) complexes, 1a–1e, ligated by N-alkyl 2,2′-dipyridylamine ligands displayed high activity in ethylene oligomerisation, when activated with alkyl aluminium reagents. Steric and electronic effects as well as activation pathways were found to have a significant impact on catalyst activity and selectivity.

Intrinsic composition and electronic effects of multicomponent platinum nanocatalysts with high activity and selectivity for ethanol oxidation reaction

2018 ◽  
Vol 6 (24) ◽  
pp. 11270-11280 ◽  
Author(s):  
Lin-Xiu Dai ◽  
Xin-Yu Wang ◽  
Sheng-Song Yang ◽  
Tao Zhang ◽  
Peng-Ju Ren ◽  
...  
Keyword(s):  
High Activity ◽  
Oxidation Reaction ◽  
Ethanol Oxidation ◽  
Activity Relationship ◽  
Ethanol Electrooxidation ◽  
Electronic Effects ◽  
Ethanol Oxidation Reaction

There exists a volcano-shaped composition–activity relationship for ternary Pt–Rh-based nanoalloys in the ethanol electrooxidation reaction.

scholarly journals Effect of Lewis Acids on the Catalyst Activity for Alkene Metathesis, Z-/E- Selectivity and Stability of Tungsten Oxo Alkylidenes

2021 ◽  
Author(s):  
J. Haydée Merino ◽  
Jesús Bernad ◽  
Xavier Solans-Monfort
Keyword(s):  
Catalytic Activity ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Catalyst Activity ◽  
Electronic Effects ◽  
Activity Increase ◽  
Two Factors ◽  
Hydride Elimination

AbstractLewis acids increase the catalytic activity of classical heterogeneous catalysts and molecular d0 tungsten oxo alkylidenes in a variety of olefin metathesis processes. The formation of labile adducts between the metal complex and the Lewis acid has been observed experimentally and suggested to be involved in the catalyst activity increase. In this contribution, DFT (M06) calculations have been performed to determine the role of Lewis acids on catalyst activity, Z-/E- selectivity and stability by comparing three W(E)(CHR)(2,5-dimethylpyrrolide)(O-2,6-dimesithylphenoxide) (E = oxo, imido or oxo-Lewis acid adduct) alkylidenes. Results show that the formation of the alkylidene—Lewis acid adducts influences the reactivity of tungsten oxo alkylidenes due to both steric and electronic effects. The addition of the Lewis acid on the E group increases its bulkiness and this decreases catalyst Z-selectivity. Moreover, the interaction between the oxo ligand and the Lewis acid decreases the donating ability of the former toward the metal. This is important when the oxo group has either a ligand in trans or in the same plane that is competing for the same metal d orbitals. Therefore, the weakening of oxo donating ability facilitates the cycloaddition and cycloreversion steps and it stabilizes the productive trigonal bipyramid metallacyclobutane isomer. The two factors increase the catalytic activity of the complex. The electron donating tuneability by the coordination of the Lewis acid also applies to catalyst deactivation and particularly the key β-hydride elimination step. In this process, the transition states show a ligand in pseudo trans to the oxo. Therefore, the presence of the Lewis acid decreases the Gibbs energy barrier significantly. Overall, the optimization of the E group donating ability in each step of the reaction makes tungsten oxo alkylidenes more reactive and this applies both for the catalytic activity and catalyst deactivation.

scholarly journals Totally-green Fuels via CO2 Hydrogenation

2020 ◽  
Vol 15 (2) ◽  
pp. 390-404
Author(s):  
Lorenzo Spadaro ◽  
Alessandra Palella ◽  
Francesco Arena
Keyword(s):  
Photoelectron Spectroscopy ◽  
Catalyst Activity ◽  
Single Pulse ◽  
Catalytic Performance ◽  
Surface Reactivity ◽  
Co2 Hydrogenation ◽  
Electronic Effects ◽  
X Ray ◽  
Cerium Content ◽  
Green Fuels

Hydrogen is the cleanest energy vector among any fuels, nevertheless, many aspects related to its distribution and storage still raise serious questions concerning costs, infrastructure and safety. On this account, the chemical storage of renewable-hydrogen by conversion into green-fuels, such as: methanol, via CO2 hydrogenation assumes a role of primary importance, also in the light of a cost-to-benefit analysis. Therefore, this paper investigates the effects of chemical composition on the structural properties, surface reactivity and catalytic pathway of ternary CuO-ZnO-CeO2 systems, shedding light on the structure-activity relationships. Thus, a series of CuZnCeO2 catalysts, at different CuO/CeO2 ratio (i.e. 0.2-1.2) were performed in the CO2 hydrogenation reactions at 20 bar and 200-300 °C, (GHSV of 4800 STP L∙kg∙cat-1∙h-1). Catalysts were characterized by several techniques including X-ray Diffraction (XRD), N2-physisorption, single-pulse N2O titrations, X-ray Photoelectron Spectroscopy (XPS), and Temperature-programmed Reduction with H2 (H2-TPR). Depending on preparation method, the results clearly diagnostics the occurrence of synergistic structural-electronic effects of cerium oxide on copper activity, with an optimal 0.5 copper-to-cerium content. The rise of CuO loading up to 30% drives to a considerable increase of hydrogenation activity: C2Z1-C catalyst obtains the best catalytic performance, reaching methanol yield value of 12% at 300 °C. Catalyst activity proceeds according to volcano-shaped relationships, in agreement with a dual sites mechanism. Copyright © 2020 BCREC Group. All rights reserved 

scholarly journals Selective Hydrogenation Properties of Ni-Based Bimetallic Catalysts

Eng ◽  
2022 ◽  
Vol 3 (1) ◽  
pp. 60-77
Author(s):  
Nobutaka Yamanaka ◽  
Shogo Shimazu
Keyword(s):  
High Activity ◽  
Selective Hydrogenation ◽  
Electronic Structures ◽  
Bimetallic Catalysts ◽  
Bimetallic Nanoparticles ◽  
Ni Catalyst ◽  
Electronic Effects ◽  
Catalytic Systems ◽  
Chemoselective Hydrogenation ◽  
Hydrogenation Reactions

Metallic Ni shows high activity for a variety of hydrogenation reactions due to its intrinsically high capability for H2 activation, but it suffers from low chemoselectivity for target products when two or more reactive functional groups are present on one molecule. Modification by other metals changes the geometric and electronic structures of the monometallic Ni catalyst, providing an opportunity to design Ni-based bimetallic catalysts with improved activity, chemoselectivity, and durability. In this review, the hydrogenation properties of these catalysts are described starting from the typical methods of preparing Ni-based bimetallic nanoparticles. In most cases, the reasons for the enhanced catalysis are discussed based on the geometric and electronic effects. This review provides new insights into the development of more efficient and well-structured non-noble metal-based bimetallic catalytic systems for chemoselective hydrogenation reactions.

scholarly journals Unravelling the key role of surface features behind facet-dependent photocatalysis of anatase TiO2

2019 ◽  
Vol 55 (30) ◽  
pp. 4415-4418 ◽  
Author(s):  
Yung-Kang Peng ◽  
Benedict Keeling ◽  
Yiyang Li ◽  
Jianwei Zheng ◽  
Tianyi Chen ◽  
...  
Keyword(s):  
High Activity ◽  
Anatase Tio2 ◽  
Electronic Effects ◽  
Surface Features

The high activity of the anatase TiO2(001) facet in photocatalytic H2 evolution is due to local electronic effects created by surface F on the facet.

scholarly journals Study on the synthesis of hexene-1 catalyzed by Ziegler-Natta catalyst and polyhexene-1 applications

e-Polymers ◽  
2019 ◽  
Vol 19 (1) ◽  
pp. 511-518 ◽  
Author(s):  
Yibin Yan ◽  
Dengfei Wang ◽  
Shuyan He ◽  
Hegang Ren ◽  
Yongjun Xu
Keyword(s):  
Molecular Weight ◽  
Catalyst Activity ◽  
Catalytic Efficiency ◽  
Electronic Effects ◽  
Reaction Conditions ◽  
Natta Catalyst ◽  
The Common ◽  
Electron Donation ◽  
The Impact ◽  
Ziegler Natta Catalyst

AbstractThis paper presents the synthesis of two aminosilane-based external donors for the Ziegler-Natta catalysis: di(piperidyl) dimethoxysilane (DPPDMS) and dipyrrolyldimethoxysilane (DPRDMS). We compared the electron donation by these two compounds in the MgCl2- supported Ziegler-Natta catalysis of the polymerization of hexene-1 into a polyhexene-1 (PHe) elastomer with that of the common donor cyclohexylmethyldimethoxysilane (CHMMS). The catalytic activity of the system and isotacticity of the polymer (PHe) product improved significantly because of the considerable steric hindrance and strong electronic effects of these aminosilane-based external donors. The effects of different external donors on the catalytic efficiency, polymer isotacticity, molecular weight and molecular weight distribution of the PHe products were investigated. Under the best reaction conditions, the catalyst activity, polymer molecular weight, and glass-transition temperature were determined as 899 g/g Cat·h-1, MW = 252,300 g/mol, and -41.39°C, respectively. The PHe was characterized by FTIR and NMR. This report also describes blending of PHe and low density polyethylene that leads to a significant increase in the impact strength and elongation at breaks.

scholarly journals Pd/HZSM-5 catalyst for n-hexane isomerization: Properties, activities, and deactivation

2020 ◽  
pp. 36-40
Author(s):  
Dao Thi Kim Thoa, Nguyen Kim Trung Dao
Keyword(s):  
High Activity ◽  
Catalyst Activity ◽  
Coke Formation ◽  
Chemical Properties ◽  
Elevated Pressure ◽  
Molar Ratio ◽  
Environment Friendly ◽  
Physico Chemical ◽  
Metallic Catalyst ◽  
Metal Sintering

The activity of n-hexane isomerization with 0,8 %kl Pd/HZSM-5 was studied in a micro reactor in the temperature range of 225-325 oC at 0,1 Mpa with the molar ratio H2/ hydrocarbon of 5.92, n-hexane concentration of 9.2 %mol, GHSV 2698 h-1 at atmospheric pressure. The catalyst owned suitable acidity, reasonable reductivity, good metal dispersion, and appropiate balance between metallic and acidic functions. The catalyst had high activity but low stability. The cause of deactivation was examined via a comparison of physico-chemical properties between a fresh catalyst and a used one. There was no metal sintering. The mono-metallic catalyst performed high activity for n-hexane hydro-isomerization but less stable. Deactivation is mainly attributed to coke formation. Catalyst activity and stability were significantly improved with activity of 0,7 MPa compared to that of 0,1 MPa at elevated pressure. The catalyst Pd-Co/HZSM-5 is capable of resisting against coke, thereby exhibiting high stability at 0,1 MPa. The highly stable and active catalyst helped to form high quality products to result in environment-friendly gasoline.

scholarly journals Enhanced Catalyst Activity ofWO3Using Polypyrrole as Support for Acidic Esterification of Glycerol with Acetic Acid

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Khadijeh Beigom Ghoreishi ◽  
Mohd Ambar Yarmo ◽  
Norasikin Mohamad Nordin ◽  
Mohd Wahid Samsudin
Keyword(s):  
Acetic Acid ◽  
High Activity ◽  
Catalyst Activity ◽  
Reaction Duration ◽  
Ft Ir ◽  
Catalyst Acidity ◽  
Loading Amount ◽  
Average Size ◽  
Glycerol Esterification

A series of polypyrrole supported WO3were fabricated and characterized by FT-IR, XRD, XPS, BET, TGA, and FESEM-EDX. The activity of the catalysts was tested in glycerol esterification with acetic acid, and it found that WO3-Ppy-20 (nanocomposite with 20% WO3loaded) showed the maximum catalyst activity with 98% and selectivity of 70% to triacetin at 110°C with a reaction duration of 10 h and also recorded the highest selectivity (75%) for acetylation of glycerol to monoacetin with about 59% conversion only. The highest acidity of WO3-Ppy-20 is also confirmed using TPD-NH3analysis. The activity and selectivity to triacetin of the catalyst were enhanced by increasing WO3loading amount, resulting in 82% conversion for WO3-Ppy-5 with about 32 and 50% selectivity to monoacetin and diacetin and about 18% selectivity to triacetin; in case of WO3-Ppy-20, these amounts were changed to 5, 25, and 70% selectivity to monoacetin, diacetin, and triacetin, respectively with the conversion of 98%. TPD-NH3analysis found that polypyrrole supported WO3increases the catalyst acidity of WO3. BET and FESEM analyses revealed that WO3particles were well dispersed with the smallest average size in nanocomposite compared to pure WO3, which could contribute to the high activity of WO3-Ppy catalyst for esterification of glycerol.

High-activity samarium-153-EDTMP therapy followed by autologous peripheral blood stem cell support in unresectable osteosarcoma

2001 ◽  
Vol 40 (06) ◽  
pp. 215-220 ◽  
Author(s):  
S. Bielack ◽  
S. Flege ◽  
J. Eckardt ◽  
J. Sciuk ◽  
H. Jürgens ◽  
...  
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
High Activity ◽  
Peripheral Blood ◽  
Peripheral Blood Stem Cell ◽  
Blood Stem Cell ◽  
High Dose ◽  
External Radiotherapy ◽  
Primary Tumor Site ◽  
Hematopoietic Stem

Summary Purpose: Despite highly efficacious chemotherapy, patients with osteosarcomas still have a poor prognosis if adequate surgical control cannot be obtained. These patients may benefit from therapy with radiolabeled phosphonates. Patients and Methods: Six patients (three male, three female; seven to 41 years) with unresectable primary osteosarcoma (n = 3) or unresectable recurrent sites of osteosarcomas (n = 3) were treated with high-activity of Sm-153-EDTMP (150 MBq/kg BW). In all patients autologous peripheral blood stem cells had been collected before Sm-153-EDTMP therapy. Results: No immediate adverse reactions were observed in the patients. In one patient bone pain increased during the first 48 hrs after therapy. Three patients received pain relief. Autologous peripheral blood stem cell reinfusion was performed on day +12 to +27 in all patients to overcome potentially irreversible damage to the hematopoietic stem cells. In three patient external radiotherapy of the primary tumor site was performed after Sm-153-EDTMP therapy and in two of them polychemotherapy was continued. Thirty-six months later one of these patients is still free of progression. Two further patients are still alive. However, they have developed new metastases. The three patients who had no accompanying external radiotherapy, all died of disease progression five to 20 months after therapy. Conclusion: These preliminary results show that high-dose Sm-153-EDTMP therapy is feasible and warrants further evaluation of efficacy. The combination with external radiation and polychemotherapy seems to be most promising. Although osteosarcoma is believed to be relatively radioresistant, the total focal dose achieved may delay local progression or even achieve permanent local tumor control in patients with surgically inaccessible primary or relapsing tumors.

Gastric Fibrinolysis

1975 ◽  
Vol 34 (02) ◽  
pp. 409-418 ◽  
Author(s):  
I. M Nilsson ◽  
S.-E Bergentz ◽  
U Hedner ◽  
K Kullenberg
Keyword(s):  
Gastric Ulcer ◽  
Gastric Juice ◽  
High Activity ◽  
Fibrinolytic Activity ◽  
Duodenal Juice ◽  
Bleeding Tendency ◽  
Local Fibrinolysis ◽  
Heated Plates

SummaryGastric juice from 15 normals, 20 patients with gastric ulcer and 4 patients with erosive haemorrhagic gastroduodenitis was investigated in respect of its activity on unheated and heated fibrin plates and its content of FDP and plasminogen or plasmin with immunochemical methods. Gastric juice from normals showed no activity on unheated and heated fibrin plates, and no FDP or plasminogen could be demonstrated. In the patients with gastric ulcer the gastric juice showed little or no fibrinolytic activity on fibrin plates except in 2, who had regurgitation of duodenal juice and neutral pH of the juice. These patients had equally high activity on heated as on unheated plates and no plasmin could be demonstrated. It was shown that this activity was not due to fibrinolysis, but to non-specific proteolytic activity (probably trypsin). The patients with erosive haemorrhagic gastroduodenitis exhibited quite a different picture. The gastric juice from these patients showed extremely high activity on fibrin plates, the activity was higher on unheated than on heated plates. The activity was inhibited in vitro by addition of EACA and in vivo after administration of AMCA. The occurrence of plasmin could be demonstrated directly immunologically in the gastric juice. By comparison of plasmin and trypsin in various assays it could further be proved that the gastric juice in these cases contained plasminogen activator and plasmin. The patients with erosive haemorrhagic gastroduodenitis showed no increase in fibrinolysis in the blood, but low values for plasminogen and α2M, and the serum contained FDP. These findings in the blood and gastric juice were interpreted as signs of local fibrinolysis in the stomach and duodenum. There is reason to assume that this gastric fibrinolysis contributes substantially to the bleeding tendency. The effect of administration of AMCA on fibrinolytic activity and the haemorrhage lends support to the assumption of such a mechanism.

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