High‐Speed Living Polymerization of Polar Vinyl Monomers by Self‐Healing Silylium Catalysts

This contribution describes the development and demonstration of the ambient‐temperature, high‐speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (≤ 0.05 mol % relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal (^RSKA) initiator (I) with a strong Brønsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near‐precise polymer number‐average molecular weight (M_n, controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain‐termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well‐defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst “self‐repair” involved in this living polymerization system have been elucidated, chiefly featuring a propagation “catalysis” cycle consisting of a rate‐limiting C? C bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et₂O)₂]⁺[B(C₆F₅)₄]^? is the most effective activator, which spontaneously delivers the most active R₃Si⁺, reaching a high catalyst turn‐over frequency (TOF) of 6.0×10³ h^?1 for methyl methacrylate polymerization by Me₃Si⁺ or an exceptionally high TOF of 2.4×10⁵ h^?1 for n‐butyl acrylate polymerization by iBu₃Si⁺, in addition to its high (>90 %) to quantitative efficiencies and a high degree of control over M_n and MWD (1.07–1.12). An intriguing catalyst “self‐repair” feature has also been demonstrated for the current living polymerization system.     

Selective deoxygenation of vegetable oils in the presence of Pt–Sn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

We studied deoxygenation of individual fatty esters and fatty acid triglycerides from vegetable oils and lipid extracts from microalgae in the presence of catalysts prepared by deposition of Pt–Sn-containing compounds onto the γ-aluminum oxide surface. Using individual esters as an example, selective reduction of oxygen into water was demonstrated for the first time to proceed on a catalytic system at the 5 : 1 molar ratio of Sn and Pt active components to afford hydrocarbon components of substrates in virtually quantitative yield. Transformation of vegetable oil in the presence of this catalyst affords the C₃–C₁₈ hydrocarbon fraction in yield up to 99% at the content of C₃ and C₁₈ hydrocarbons up to 90%. The fraction of C₁ and C₂ hydrocarbons and carbon oxides is not higher than 0.5%. The possibility of carbon weight loss minimization during transformation of lipids was shown for the first time.     

Catalytic dehydrogenation of propane to propylene over highly active PtSnNa/γ-Al_2O_3 catalyst

This paper reports a new fabrication method of the PtSnNa/γ-Al₂O₃ catalyst through ball milling, which is more stable and active than the commercial catalyst.     

Living ring-opening polymerization of cyclic carbonate using cationic zirconocene complex as catalyst

Living ring-opening polymerization of the cyclic carbonate 1,3-dioxepan-2-one was achieved by using the cationic zirconocene complex [Cp₂ZrMe]⁺[B(C₆F₅)₄]⁻ as catalyst at room temperature. A linear relation between conversion and molecular weight of the obtained polymer was observed. Furthermore, block copolymerization of the cyclic carbonate and ε-caprolactone was successfully performed.     

复合催化剂上CO2加氢合成C2烃类

介绍了由CO₂+H₂合成C2⁺烃的几种复合催化剂体系的研究进展，比较和评价了复合催化剂体系的活性和选择性及对C2⁺烃类生成的影响。着重于复合催化剂体系对C4⁺烃的生成及产物分布的影响并简述反应机理。     

Enhancement of bimetallic Fe-Mn/CNTs nano catalyst activity and product selectivity using microemulsion technique

Bimetallic Fe-Mn nano catalysts supported on carbon nanotubes(CNTs) were prepared using microemulsion technique with water-to-surfactant ratios of 0.4-1.6. The nano catalysts were extensively characterized by different methods and their activity and selectivity in Fischer-Tropsch synthesis(FTS) have been assessed in a fixed-bed microreactor. The physicochemical properties and performance of the nanocatalysts were compared with the catalyst prepared by impregnation method. Very narrow particle size distribution has been produced by the microemulsion technique at relatively high loading of active metal. TEM images showed that small metal nano particles in the range of 3–7 nm were not only confined inside the CNTs but also located on the outer surface of the CNTs. Using microemulsion technique with water to surfactant ratio of0.4 decreased the average iron particle sizes to 5.1 nm. The reduction percentage and dispersion percentage were almost doubled. Activity and selectivity were found to be dependent on the catalyst preparation method and average iron particle size. CO conversion and FTS rate increased from 49.1% to 71.0% and 0.144 to 0.289 gHC/(gcat h), respectively. While the WGS rate decreased from 0.097 to 0.056 gCO2/(gcat h). C5+liquid hydrocarbons selectivity decreased slightly and olefins selectivity almost doubled.     

Synthesis of hydrocarbons from CO and H2 in the presence of Co-Ru and Co-Pd catalysts containing aluminum oxide

The influence of additions of 0.1–0.5% Pd or Ru in a 10% Co/Al₂O₃ catalyst on its activity and selectivity in the synthesis of liquid hydrocarbons from CO and H₂ has been studied. It has been shown that the bimetallic systems make it possible to carry out the synthesis of hydrocarbons with a higher extent of conversion of CO and a higher yield of C ₅ ⁺ carbons in comparison with the original Co catalyst. Co-Ru catalysts exhibit exceptionally high selectivity (up to 80%) with respect to the formation of liquid products. It has been demonstrated by temperature-programmed reduction (TPR) that the introduction of Pd an dRu promotes the reduction of Co at lower temperatures and the formation of cobalt aluminates.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 60–64, January, 1992.     

Analytical method for atmospheric tritium with a portable tritium sampling system

A portable tritium sampler was developed for the stepwise collections of water vapour (HTO), hydrogen (HT) and hydrocarbons (CH₃T) in the atmosphere. First, water vapour was collected in an electronic cooler and an HTO collection column containing 400 g of molecular sieve. Next, dried air was introduced into an HT collection column containing 150 g of palladium catalyst. Hydrogen was then converted to water by catalytic oxidation at room temperature and the resultant water was immediately adsorbed on the molecular sieve bed supporting the catalyst. The remaining gas was finally introduced into a CH₃T collection column containing 100 g of molecular sieve through a platinum catalyst column, in which hydrocarbons were burnt at 400°C. The resultant water was adsorbed in the CH₃T collection column. The collection efficiencies of water in the HTO, HT and CH₃T collection columns were all estimated to be nearly 100%. This newly developed method was found to be useful for the routine tritium monitoring by applying it to actual air samples.     

Catalytic deoxygenation of waste soybean oil over hybrid catalyst for production of bio-jet fuel: in situ supply of hydrogen by aqueous-phase reforming (APR) of glycerol

A one-pot reaction was performed to produce oxygen-free saturated hydrocarbons via the catalytic deoxygenation and hydrogenation of waste soybean oil over a hybrid catalyst (Pd/C and NiO/γ-Al₂O₃). We utilized in situ hydrogen generated from a reforming reaction of glycerol, a byproduct of triglyceride hydrolysis, for the one-pot reaction to produce hydrocarbons. When NiO/γ-Al₂O₃ (2 g) was used along with Pd/C (1 g), most of the unsaturated free fatty acids (FFAs) were hydrogenated into saturated FFAs, and the percentage of desirable hydrocarbons in the liquid product increased, in contrast to the case when only Pd/C (1 g) was used. This result means that using a hybrid catalyst is better for promoting the catalytic deoxygenation reaction than increasing the degree of loading of Pd/C, and suggests that it should be possible to decrease the amount of precious metal catalysts to be used for deoxygenation reaction.     

Hydrodechlorination of Dichloromethane by a Metal-Free Triazole-Porphyrin Electrocatalyst: Demonstration of Main-Group Element Electrocatalysis**

In this work, the electrocatalytic reduction of dichloromethane (CH₂Cl₂) into hydrocarbons involving a main group element-based molecular triazole-porphyrin electrocatalyst H2PorT8 is reported. This catalyst converted CH₂Cl₂ in acetonitrile to various hydrocarbons (methane, ethane, and ethylene) with a Faradaic efficiency of 70 % and current density of −13 mA cm⁻² at a potential of −2.2 V vs. Fc/Fc⁺ using water as a proton source. The findings of this study and its mechanistic interpretations demonstrated that H2PorT8 was an efficient and stable catalyst for the hydrodechlorination of CH₂Cl₂ and that main group catalysts could be potentially used for exploring new catalytic reaction mechanisms.     

Effective tri-metallic TiO2 supported catalyst for hydrocarbon production from carbon dioxide

The current socio-economic issues with concerns on environmental quality and global warming are attributed to high concentrations of atmospheric carbon dioxide due to extensive usage of fossil fuels. Thus, over the last two decades, comprehensive work has been reported on carbon capture and storage and catalytic conversion of carbon dioxide to hydrocarbons. Among these, the reactions with hydrocarbons to form value-added products have been in focus. In this work, an attempt was made to identify the feasibility of the reaction: carbon dioxide and steam to form hydrocarbons of fuel value. After reviewing the literature on the development of various catalysts and their mechanism, a multi-metallic catalyst supported by TiO₂ Nano-needles was explored. The reaction mechanism is expected to proceed with activated CO₂ complex and hydroxyl groups over the metal oxide catalyst. Current reported work on CO₂ and Hydrogen proceeds with activated CO₂ and protons over the catalyst. The characterization techniques mainly XPS, XRD, TGA, FESEM-EDAX, FTIR, and NMR were used to analyze the catalyst activity and to confirm the products formed. The reaction is found to yield methanol and oxygen only. However, the conversion is found to be 0.4% - 3.8% in the temperature range 350°C to 550°C. The reaction of CO₂ with hydroxyl groups from water vapor can be effective as an alternative to the reaction with protons from hydrogen.     

Derivatization of propene/methyloctadiene copolymers: A flexible approach to side‐chain‐functionalized polypropenes

The copolymerization of propene with 7‐methyl‐1,6‐octadiene (MOD) catalyzed by Cp*TiMe₃/B(C₆F₅)₃ ( A ) and rac‐C₂H₄(Ind)₂ZrCl₂/methylaluminoxane ( B ) in toluene under 1 bar propene gave copolymers with unsaturated side chains. Under these conditions, catalyst A produced copolymers with an atactic backbone structure of type 1 , with 3.5–19.6 mol % MOD incorporation and weight‐average molecular weight = 0.7–2.7 × 10⁵. Using catalyst B , copolymers 2 with 0.4–3.8 mol % MOD incorporation were prepared. The comonomer incorporation was a linear function of the feed ratio. The titanium catalyst A had a significantly higher affinity for MOD than the sterically more hindered zirconocene B . Postpolymerization modification of the side‐chain C?C bond allowed the facile introduction of a wide variety of functional groups. Epoxidation and especially ozonolysis of the C?C bond, to give ? CHO and ? COOH functionalized copolymers, proved to be very facile routes to functionalized polypropenes. According to monitoring by NMR, most of these transformations proceed in an essentially quantitative conversion. As an example of potential applications of such polymers, polypropenes with covalently attached dyes were prepared that are suitable for blending. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1484–1497, 2002     

Formation of Pt/C catalysts on various carbon supports

Platinum catalysts with the active component content of 5–40 wt % on various carbon supports have been synthesized by the reductive hydrolysis of platinum chloro complexes. The degree of dispersion of the supported platinum decreases with an increasing weight percentage of the metal in the catalyst. The following mechanism of Pt/C catalyst formation is deduced from experimental data: H₂PtCl₆ adsorption on the support surface generates platinum nuclei, which then grow owing to the deposition of platinum ions under the action of an alkali and a reductant.     

Effect of preliminaey heating on the physicochemical properties of 10% Co/Al2O3 catalyst and its behavior in hydrocarbon synthesis from CO and H2

The effect of preliminary heating of 10% Co/Al₂O₃ in air at 20–600°C on its surface composition, reducibility, and adsorption properties has been studied by programmed thermal reduction (PTR), IR spectroscopy, and DTA. It has been shown that increasing the pretreatment temperature strengthens the interaction between cobalt and the carrier, resulting in an increase in the fraction of weakly bound adsorbed CO on the surface of the reduced catalyst. The activity of Co/Al₂O₃ has been studied in the Fischer-Tropsch synthesis and it has been proposed that the centers of weakly bound linear forms of CO adsorption are involved in the formation of C₂ ⁺ hydrocarbons from CO and H₂.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2444–2450, November, 1991.     

Studies on Phosphorus-Containing Polymers. V. Ring-Opening Polymerization of Tetrahydrofuran Catalyzed by Linear Phosphonitrilic Chloride

It was found that linear phosphonitrilic chloride could be used as a catalyst for ring-opening polymerization of tetrahydrofuran. Bulk polymerizations were carried out in a nitrogen atmosphere. After termination of polymerization, the reaction mixture was poured into water, thereby decomposing the catalyst. The product was dissolved in benzene and then subjected to lyophilization. The polymerization of tetrahydrofuran in the presence of linear phosphonitrilic chloride was found to be an equilibrium and a “living” polymerization. The polymerization product includes little phosphorus, and its infrared absorption spectrum agrees well with that of the polymer obtained with PF₅ catalyst. The results of the polymerization using epichlorohydrin as a promoter show that the number of active sites in the molecule of linear phosphonitrilic chloride is considerably smaller. Consequently it is conceivable that the catalytic activity of the linear phosphonitrilic chloride is attributed to its terminal ～～P⁺Cl₃PCl_?6 structure. Furthermore we presume that the polymerization of tetra-hydrofuran in the presence of this catalyst proceeds through a cationic ring-opening mechanism.     

Comparison of catalytic pyrolysis of biomass with MCM-41 and CaO catalysts by using TGA–FTIR analysis

Pyrolysis of corncob with and without catalyst was investigated using thermogravimetry analyzer coupled with Fourier transform infrared spectroscopy (TGA–FTIR). The effects of two completely different catalysts, acid catalyst (MCM-41) and base catalyst (CaO), on the formation characteristics and composition of pyrolysis vapor were studied. The results show that these two catalysts give different product distributions. For catalytic run with MCM-41, the molality of carbonyl compounds decreases 10.2%, while that of phenols, hydrocarbons and CH₄ increases 15.32%, 4.29% and 10.16% compared with non-catalytic run, respectively. The increase of phenols exhibits in a wide temperature range from about 295 °C to 790 °C in the catalytic run with MCM-41 catalyst. However, the use of CaO in pyrolysis of corncob leads to a huge change of product distribution. The molality of acids decreases 75.88%, while the molality of hydrocarbons and CH₄ increases 19.83% and 51.05% compared with non-catalytic run, respectively. CaO is very effective in deacidification and the conversion of acids promotes the formation of hydrocarbons and CH₄. Catalytic pyrolysis of corncob with CaO shows two main weight-loss stages. The first stage is from 235 °C to 310 °C with a weight loss of 31%. The second stage is from 650 °C to 800 °C with a weight loss of 21%.     

Active‐center equilibrium in Ziegler–Natta butadiene polymerization

The Ziegler–Natta‐catalyzed polymerization of 1,3‐butadiene was investigated at a low aluminum alkyl/cobalt (Al/Co) ratio using two different soluble catalyst systems: cobalt(II) octanoate/diethylaluminum chloride/water and cobalt(II) octanoate/methylaluminoxane/tert‐butyl chloride. When the active‐center concentration was determined by the number‐average molecular weight technique, it was found that the percentage of active cobalt depended on the Al/Co ratio. Subsequently, an equilibrium reaction was proposed to be Co + 2Al ? CoAl₂, where Co is cobalt(II) octanoate, Al is either of the aluminum alkyl‐activator species, and CoAl₂ is the active catalyst. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2256–2261, 2001     

层状K/Mg-Fe-Al催化剂的制备及其CO加氢性能研究

采用共沉淀法制备了系列不同Mg/Fe/Al配比MgFeAl-HTLcs前驱体,经焙烧、浸渍K改性、二次焙烧后用于CO加氢反应。采用N2吸附-脱附、SEM、TG、XRD、H2-TPR、XPS等手段对催化剂进行了表征。结果表明,共沉淀法制备的不同配比MgFeAl-HTLcs类水滑石前躯体均具有典型层状结构;焙烧后生成MgO、Fe2O3以及少量MgFeAlO4物相,三组元间相互作用增强,反应后以MgCO3和Fe3O4物相为主,同时出现较弱的Fe5C2相;K改性后发生结构重构,热稳定性增强,且随Al含量增加,比表面积显著单调下降;与K/Mg-Fe相比,K/Mg-Fe-Al样品中Fe2O3到Fe3O4的还原受到抑制;二次焙烧后,反应前表面相对富Fe,反应后表面富K。在CO加氢反应中,K/Mg-Fe-Al系列催化剂均表现出较高的反应活性以及烯烃选择性,随Fe/Al配比相对增加,C5+含量呈降低趋势,O/P值增加;与K/1.5Mg-0.67Fe相比,K/1.5Mg-0.67Fe-0.33Al催化剂C5+含量由22.17%降至10.90%,C=2-4含量由40.98%提高至47.28%。     

Association of polyacrylonitrile prepared by low-temperature,solution polymerization with an organometallic catalyst

The weight-average molecular weights of polymers of acrylonitrile prepared by a free-radical initiator and an organometallic catalyst have been determined by lightscattering measurements in N,N-dimethylformamide, dimethyl sulfoxide, and dimethylacetamide at 25°C. and in dimethyl sulfoxide at 140°C. The apparent molecular weights of the polymers prepared with the NaAlEt₃S(i-Pr) catalyst in DMF at ?78°C. (referred to as high-melting polymers) changed from 54,800, 82,700, and 480,000 when measured in DMF at 25°C. to 36,000, 41,600, and 225,000 when measured in DMSO at 140°C., whereas the molecular weights of the free-radical polymers remained unchanged. Furthermore, from results obtained in DMSO at 140°C., The intrinsic viscosity–molecular-weight relationships were found to be identical for the high-melting and the free-radical polymer and in substantial agreement with an equation reported by Cleland and Stockmayer. The apparent decrease in molecular weight of the high-melting polymer from 25 to 140°C. indicates rather clearly that the high-melting polymers are associated in DMF at 25°C. The “aggregates,” even though present only at low concentrations, raised the weight-average molecular weight markedly but affected the number-average molecular weight only slightly, thus giving a high M?_w/M?_n ratio. It appears likely that when temperature and solvent are such that association does not occur, linear PAN's will have approximately the same intrinsic viscosity–molecular weight relationship (subject of course to slight change by polydispersity). The often reported abnormal molecular weight of samples prepared by solution polymerization especially at low temperatures, may be attributed to branching, or to an association, as reported here. The nature of association of PAN in dilute solution is also discussed.     

Thermal degradation of polyethylene and polystyrene from the packaging industry over different catalysts into fuel-like feed stocks

Thermal degradation of waste polymers was carried out as a suitable technique for converting plastic polymers into liquid hydrocarbons, which could be used as feed stock materials. The catalytic degradation of waste plastics (polyethylene and polystyrene) was investigated in a batch reactor over different catalysts (FCC, ZSM-5 and clinoptillolite). The effects of catalysts and their average grain size on the properties of main degradation products (gases, gasoline, diesel oil) are discussed. The temperature range of 410-450 °C was used in the process. Both equilibrium FCC catalyst and natural clinoptilolite zeolite catalyst had good catalytic activity to produce light hydrocarbon liquids, and ZSM-5 catalyst produced the highest amount of gaseous products. Gases and liquids formed in cracking reactions were analyzed by gas chromatography. The liquid products consisted of a wide spectrum of hydrocarbons distributed within the C₅-C₂₈ carbon number range depending on the cracking parameters. The composition of hydrocarbons had linear non-branched structure in case of polyethylene, while from polystyrene more aromatics (ethyl-benzene, styrene, toluene, and benzene) were produced. The yields of volatile products increased with increasing degradation temperature. The olefin content of liquids was measured with an infrared technique and an olefin concentration of 50-60% was observed. The concentration of unsaturated compounds increased with decreasing temperature, and in the presence of catalysts. The activation energies were calculated on the basis of the composition of volatile products. The apparent activation energies were decreased by catalysts and catalyst caused both carbon-chain and double bond isomerisation.