Search results for "NAD"
showing 10 items of 2033 documents
Relationship between bulk phase, near surface and outermost atomic layer of VPO catalysts and their catalytic performance in the oxidative dehydrogen…
2017
Abstract A set of vanadium phosphorous oxide (VPO) catalysts, mainly consisting of (VO) 2 P 2 O 7 , VO(PO 3 ) 2 or VOPO 4 ·2H 2 O bulk crystalline phases, has been investigated for the oxidative dehydrogenation (ODH) of ethane to ethylene, a key potential reaction for a sustainable industrial and socioeconomic development. The catalytic performance on these VPO catalysts has been explained on the basis of the main crystalline phases and the corresponding surface features found by XPS and LEISS at 400 °C, i.e. within the temperature range used for ODH reaction. The catalysts based on (VO) 2 P 2 O 7 phase presented the highest catalytic activity and productivity to ethylene. Nevertheless, the…
Molybdenum–vanadium supported on mesoporous alumina catalysts for the oxidative dehydrogenation of ethane
2006
Abstract Vanadium and/or molybdenum oxides supported on mesoporous alumina have been prepared by a “wet” impregnation method, characterized (by using several physico-chemical techniques TPR, DR-UV–vis, Raman spectroscopies) and tested in the oxidative dehydrogenation (ODH) of ethane. For comparison Mo–V-mixed oxides supported on γ-Al2O3 have also been studied. The characterization results indicate that the main vanadium species in both Mo-free and Mo-containing V-based samples present low aggregation and coordination, whereas molybdenum is present as monomeric or polymeric tetrahedral molybdenum species. Interestingly, no apparent interaction between molybdenum and vanadia takes place. The …
Copolymerization of ethylene with norbornene or 1-octene using supported ionic liquid systems
2016
Copolymerization of ethylene with norbornene (E/NB) and ethylene with 1-octene (E/Oct) is performed using supported ionic liquid (SIL) systems, in which metallocene (Cp2VCl2) or post-metallocene [VCl2(salenCl2)] vanadium catalysts are immobilized in pyridinium chloroaluminate ionic liquid supported on silica. The studied SIL catalysts show higher activities as well as stability than their non-supported analogues. In addition, higher activities and better comonomer incorporation are observed for norbornene (above 30 mol%). The comonomer incorporation has considerable influence on copolymer molecular weight (M w), melting temperature, crystallinity degree, and microstructure of the copolymers…
The effect of the comonomer on the copolymerization of ethylene with long chain α-olefins using Ziegler–Natta catalysts supported on MgCl2(THF)2
2000
Abstract The effect of the type of the comonomer (1-pentene, 1-hexene, 1-octene, 1-decene and 1-dodecene) on the copolymerization of ethylene with α-olefin over vanadium (VOCl3 and VCl4) and titanium (TiCl4) catalysts supported on MgCl2(THF)2 and activated by Et2AlCl was studied. The results show that the introduction of a longer α-olefin in the ethylene polymerization feed depresses the catalytic activity of all investigated catalysts. The catalyst activity does not depend on the type of the comonomer applied but changes with the comonomer concentration in the feed. The incorporation of α-olefin in the polymer chain was found to be dependent on the type and concentration of the comonomer i…
Vanadium complex with tetradentate [O,N,N,O] ligand supported on magnesium type carrier for ethylene homopolymerization and copolymerization
2009
Immobilization of 1,2-cyclohexylenebis(5-chlorosalicylideneiminato)vanadium dichloride on the magnesium support obtained in the reaction of MgCl 2 .3.4EtOH with Et 2 AlCl gives a highly active precursor for ethylene homopolymerization and its copolymerization with 1-octene. This catalyst exhibits the highest activity in conjunction with MAO, but it is also highly active with AlMe 3 as a cocatalyst. On the other hand, when combined with chlorinated alkylaluminum compounds, Et 2 AlCl and EtAlCl 2 , it gives traces of polyethylene. Moreover, its catalytic activity is strongly affected by the reaction temperature: it increased with rising polymerization temperature from 20 °C to 60 °C, The kine…
Organometallic vanadium‐based heterogeneous catalysts for ethylene polymerization. Study of the deactivation process
1998
Slurry polymerizations of ethylene over vanadium catalysts (based on VCl4 and VOCl3) and their MgCl2(THF)2-supported equivalents were studied. Unsupported vanadium catalysts were found to be unstable while the vanadium active sites deposited on the MgCl2(THF)2 complex are stable. A sharply outlined correlation was found between the concentration of vanadium(III) and catalyst productivity. The high activity and stability of the vanadium catalyst when supported on the magnesium complex is attributed to the increase of resistance to reduction of active vanadium(III) to inactive vanadium(II) by an organoaluminium co-catalyst.
Dichlorovanadium(IV) diamine-bis(phenolate) complexes for ethylene (co)polymerization and 1-olefin isospecific polymerization
2018
Abstract Two vanadium complexes bearing amine-bis(phenolate) ligands with the amino side-arm donor, [V{Me2NCH2CH2N(CH2-2-O-3,5-tBu2-C6H2)2}Cl2] (1) and [V{Me2NCH2CH2N(CH2-2-O-3,5-tBu2-C6H2)(CH2-2-O-C6H4)}Cl2] (2), were synthesised and characterized by FTIR and 1H NMR spectroscopy. Upon activation with Al(iBu)3/Ph3CB(C6F5)4, these complexes became active catalysts for 1-octene polymerization giving highly stereoregular polymers (mmmm ∼ 90%) having regioirregularly arranged units. The catalytic activity of the catalysts in ethylene homo- and copolymerization, and their ability to incorporate a comonomer were highly dependent on both the activator type and the complex structure. 1/EtAlCl2 exhi…
Instytucjonalny wymiar ochrony granic zewnętrznych Unii Europejskiej w kontekście bezpieczeństwa państw członkowskich
2018
Celem artykułu jest analiza problemu funkcjonowania instytucji zapewniających ochronę zewnętrznych granic Unii Europejskiej pod kątem zagwarantowania bezpieczeństwa jej państwom w kontekście współczesnych wyzwań. Do chwili, kiedy zaistniał kryzys migracyjny istniało bowiem przekonanie, że Unia Europejska stworzyła instytucjonalne warunki dla skutecznego zapewnienia bezpieczeństwa swoich granic. UE to przestrzeń, w obrębie której realizowana jest swoboda przemieszczania się obywateli, wyrażona poprzez swobodę podróżowania, podejmowania pracy, studiowania czy zamieszkiwania w wybranym kraju Unii. Realizacja tej swobody nastąpiła w wyniku zniesienia kontroli na wewnętrznych granicach UE. Jedna…
Bezpieczeństwo granic Unii Europejskiej w kontekście kryzysu migracyjnego 2015/2016
2016
The European Union is a space within which the freedom of movement of citizens, expressed through freedom to travel. work, study or live in a chosen EU country, is realized. The implementation of this freedom was a result of the abolition of Controls at internal borders of the Union. However. for a Member of the EU, the price of this freedom is the necessity to ensure national security, which makes the protection of external borders a special task. The European Union, through the Schengen Agreement, created institutions for the protection of external borders in terms of ensuring the national security of Member States, The current migration crisis is a serious verification of the effectivene…
Instytucja granic zewnętrznych Unii Europejskiej a zapewnienie bezpieczeństwa państw członkowskich w warunkach współczesnego kryzysu migracyjnego
2017
Unia Europejska to przestrzeń w obrębie której realizowana jest swoboda przemieszczania się obywateli. Realizacja tej swobody nastąpiła w wyniku zniesienia kontroli na wewnętrznych granicach Unii. Jednak dla państwa unijnego ceną tej wolności jest zapewnienie bezpieczeństwa narodowego co czyni szczególnym ochronę granic zewnętrznych. Unia Europejska, głównie poprzez Układ z Schengen stworzyła instytucje dla ochrony granic zewnętrznych pod kątem zapewnienia bezpieczeństwa narodowego państw członkowskich i ich obywateli. Obecny kryzys migracyjny stanowi poważną weryfikację dla oceny skuteczności działania tych instytucji. Celem niniejszego artykułu jest analiza problemu funkcjonowania zewnętr…