Polymerization of cyclohexene oxide with aluminum complex/silanol catalyst. VI. Oligomer and polymer effects

The activity of an aluminum complex/polysilanol polymerization catalyst was examined in order to confirm the dependence of catalytic activation on silanol chain length. Tris (acetylacetonato)–aluminum/silanol increased when silanols with an intramolecular hydrogen bond such as the trimer of diphenylsilanediol, polydiphenyl(4-vinylphenyl)silanol, and polymeric silanol of silicone were used. However, when tris(ethylacetoacetato)aluminum or tris(salicylaldehydato)aluminum was used, the product obtained from the reaction of a part of the aluminum complex with the polysilanols had to be considered in any explanation of the catalytic activation. The active catalyst with such aluminum complexes was obtained when the silanols that had intramolecular hydrogen bonds and gave the appropriate ratio of the reaction between the aluminum complex and silanol were used.     

Polymerization of cyclohexene oxide with Al(acac)3- silanol catalyst

The polymerization of cyclohexene oxide was investigated with a new catalyst system of Al(acac)₃- silanol compounds. Catalyst activity varied with the ratio of silanol/Al(acac)₃ and the structure of silanol compounds. Catalyst deactivation appeared to be caused by self-condensation of silanol and the addition of silanol to the epoxy ring. Polymer structure was investigated by ¹³C-NMR spectroscopy and x-ray diffraction. The mechanism of the polymerization appears to be cationic.     

The catalytic activity of Ni?V oxide catalysts

The activity and selectivity of Ni–V oxide catalysts in relation to the phase composition were investigated. The catalytic activity was measured in the oxidative dehydrogenation of methanol to formaldehyde and in the oxidation of SO₂ to SO₃.The oxide with the atom ratio gives the highest yield of formaldehyde and the slowest rate of SO₂ oxidation. The above phase, as shown by X-ray and IR measurements, has a specific structure characterized by a weakened V=O double bond.

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Ni–V . SO₂ SO₃. SO₂. , , , V=O

     

Bi-Mo-Nb复合氧化物的结构与对丙烯氧化的催化活性

本文用XRD, IR, Raman, SEM和ESR等方法研究了系列氧化物Bi~2Mo~3-3XNb~2xO~12-4X(X=0.00, 0.02, 0.05, 0.10, 0.15, 0.20, 0.25) 的结构和对丙烯氧化的催化活性。结果表明, 在X<0.25范围内, 催化剂基本保持典型的α-Bi~2Mo~3O~12结构, 少量Nb^5+的掺杂, 可取代晶格中的Mo^6+, 产生氧空位,无序分布的氧空位的浓度先随X值的增加而增加, 当X=0.15时达到最大值, 催化剂对丙烯氧化的催化活性与这种氧空位的浓度成正比, 反应遵循Redox机理。     

Photopolymerization of cyclohexene oxide by use of o-nitrobenzyl triphenylsilyl ether/aluminum compound catalyst. Dependence of catalyst activity on the structure of the silyl ether

o-Nitrobenzyl triphenylsilyl ehther/aluminum compound has been previously shown by the authors to act as catalyst in the photopolymerization of epoxides. The dependence of the structure of the silyl ether on the catalyst activity was examined. There were two steps in the photopolymerization. The first step (“Step 1”) is photodecomposition of the silyl ether to silanol. The second step (“Step 2”) is the initiation of polymerization by silanol and the aluminum compound. The introduction of an electron withdrawing group, Cl, CF₃, on the benzene ring bonded to Si made the quantum yield of Step 1 low, however, the rate of Step 2 was increased. The low quantum yield of Step 1 was explained in terms of the rate of electron transfer that is controlled by the relative electron density between the CH₂ and NO₂ in the o-nitrobenzyl group. The acceleration of Step 2 was explained in terms of an increase in silanol acidity that was promoted by the introduction of an electron withdrawing group. The overall rate of the photopolymerizatiol depends to a greater degree on the rate of Step 2 than on that of Step 1.     

Polymerization of styrene with nickel complex/methylaluminoxane catalytic systems

Polymerization of styrene using catalytic systems based on nickel derivatives and methylaluminoxane (MAO) was studied. Among tested catalysts, nickel bis(acetylacetonate) and nickel dichloride show the maximum activity. Bis(phosphine)nickel dichlorides exhibit lower activity, depending on the nature of the phosphine ligand. Polymer yields decrease by lowering the catalyst concentration, by increasing the reaction temperature, or by carrying out the polymerization in a polar donor solvent. Weight average molecular weight of most of the prepared polystyrenes ranges from 9000 to 25,000, with polydispersity indexes of 1.6–3.8. However, polystyrene prepared in dioxane solvent exhibits a small fraction of very high molecular weight (about 140,000). From NMR analysis, the products seem generally to be constituted of two polymers with different steric microstructure: atactic polystyrene and partially isotactic polystyrene (ca. 75–85% meso diads). Catalytic site specificity is correlated with the type of nickel ligand, while the effect of reaction temperature is less defined. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2119–2126, 1998     

Transformation of carbon compounds on graphimet catalysts, VII. Investigation of the catalytic activity of Pt-graphimet in cyclohexene hydrogenation

Pd-graphimet was an efficient catalyst in cyclohexene hydrogenation. Despite atomic Pd dispersion, thermal treatment of the sample resulted in complete deactivation, which is attributed to surface carbon deposition.     

A new amidoimidomalonate zinc complex with a sedecameric solid state structure catalyzing the copolymerization of CO2 and cyclohexene oxide

A new amidoimidomalonate ligand was synthesized in a short and effective way and the zinc acetate complex thereof was prepared. XRD investigation revealed an unprecedented solid state structure, where the sedecameric complex [(lig)₂Zn₄(OAc)₄]₄ builds the edges of a square cavity. Each edge is made up by a similar unit [(lig)₂Zn₄(OAc)₄] with four zinc atoms. The complex is an active catalyst in the copolymerization of CO₂ and cyclohexene oxide and produces polyethercarbonates with broad molecular weight distributions.     

Investigation on the catalytic activity of doped low-percentage oxide catalysts Mn/ZnO obtained from oxalate precursor

The precursors with a low manganese content ≤ 0.07% Mn were synthesized by spontaneous crystallization from Zn²⁺, Mn²⁺ and C₂O₄ ²⁻-containing solutions. The initial ratio Zn²⁺:C₂O₄ ²⁻ = 1:1 and 1:2 influences the morphology and prevailing orientations of the crystallites in the oxalate samples. The presence of such small Mn content in the samples does not change the morphology or size of the crystals. The ZnO and Mn/ZnO oxides with manganese content from 0.51×10⁻² to 15.1×10⁻² Wt % are obtained after thermal decomposition of the oxalates. The oxides preserved the morphology of the precursors. The catalytic tests show that the pure ZnO has a poor activity for CO oxidation reaction. Its doping with Mn promotes the catalytic activity (up from twice to five times) in spite of the very low contents of the dopants. The observed increase of the activity depends on both dopant concentration and Zn²⁺:C₂O₄ ²⁻ ratio, probably due to the different mechanism of the manganese inclusion and different morphology of the oxides. The catalysts of the 1:2 series are more active in CO oxidation reaction.      

Formation,composition, and catalytic activity of multicomponent oxide structures on aluminum

Possibility is considered of obtaining multicomponent oxide systems as afterburning catalysts for automobiles by flame-electrolytic oxidation and impregnation of oxide structures on aluminum.     

Tin oxide dependence of the CO2 reduction efficiency on tin electrodes and enhanced activity for tin/tin oxide thin-film catalysts

The importance of tin oxide (SnO(x)) to the efficiency of CO(2) reduction on Sn was evaluated by comparing the activity of Sn electrodes that had been subjected to different pre-electrolysis treatments. In aqueous NaHCO(3) solution saturated with CO(2), a Sn electrode with a native SnO(x) layer exhibited potential-dependent CO(2) reduction activity consistent with previously reported activity. In contrast, an electrode etched to expose fresh Sn(0) surface exhibited higher overall current densities but almost exclusive H(2) evolution over the entire 0.5 V range of potentials examined. Subsequently, a thin-film catalyst was prepared by simultaneous electrodeposition of Sn(0) and SnO(x) on a Ti electrode. This catalyst exhibited up to 8-fold higher partial current density and 4-fold higher faradaic efficiency for CO(2) reduction than a Sn electrode with a native SnO(x) layer. Our results implicate the participation of SnO(x) in the CO(2) reduction pathway on Sn electrodes and suggest that metal/metal oxide composite materials are promising catalysts for sustainable fuel synthesis.     

Influence of cobalt precursors on the catalytic activity of the cobalt oxide/Al2O3 catalysts

Cobalt acetate and cobalt nitrate were employed as precursors to prepare different kinds of Co₃O₄/Al₂O₃ catalysts. The catalysts were used to decompose VOC's such as xylene, isopropyl alcohol and butyl acetate. This revised version was published online in June 2006 with corrections to the Cover Date.