Effects of Ti oxidation state on ethylene, 1-hexene comonomer polymerization by MgCl<Subscript>2</Subscript>-supported Ziegler–Natta catalysts

In this study, the influences of the Ti oxidation state on the catalytic properties of MgCl₂-supported Ziegler–Natta catalysts in ethylene homo- and co-polymerization with 1-hexene were investigated. Three catalysts having different Ti oxidation states were synthesized by milling TiCl₄, TiCl₃, or TiCl₂ together with MgCl₂. With these catalysts having different Ti oxidation states, the polymerization conditions such as the Al concentration, temperature, and 1-hexene concentration were varied to figure out their catalytic abilities in ethylene homo- and co-polymerization. The Ti oxidation state affected the catalyst activity largely, having unique dependences on the polymerization conditions. A higher oxidation state led to a higher activity, slightly larger comonomer incorporation, and lower molecular weight as well as its narrower distribution. However, rough characteristics of copolymers were similar among the different Ti oxidation states.     

Effect of the pretreatment with oxygen and/or oxygen-containing compounds on the catalytic performance of Pd-Ag/Al2O3 for acetylene hydrogenation

Catalytic performance of Pd-Ag/-Al₂O₃ was studied for the selective hydrogenation of acetylene in the presence of excess ethylene. The catalyst activation was undertaken prior to the reaction test by the pretreatment with oxygen and/or oxygen-containing compounds, i.e. O₂, NO, N₂O, CO and CO₂. The enhancement of catalytic performances by the pretreatment was a consequence of an increase in accessible Pd sites responsible for acetylene hydrogenation to ethylene. Furthermore, the sites involving direct ethane formation from acetylene could be suppressed by NO_x treatment.     

Effects of various poisoning compounds on the activity and stereospecificity of heterogeneous Ziegler–Natta catalyst

A TiCl₄/ethylbenzoate/MgCl₂ Ziegler–Natta catalyst was pretreated with chemically different poisoning compounds to investigate their effects on the catalyst activity and stereospecificity for propylene polymerization. The poisoning power on the activity was in the order of methanol > acetone > ethyl acetate. A kinetic analysis using the stopped-flow method revealed that addition of the poisoning materials decreased the activity through the reduction of the number of active sites, whereas the catalyst isospecificity was hardly affected by these materials.     

Synthesis of nanocrystalline alumina by thermal decomposition of aluminum isopropoxide in 1-butanol and their applications as cobalt catalyst support

Nanocrystalline alumina powders were prepared by thermal decomposition of aluminum isopropoxide (AIP) in 1-butanol at 300 °C for 2 h and employed as cobalt catalyst supports. The crystallization of alumina was found to be influenced by the concentration of AIP in the solution. At low AIP content, wrinkled sheets-link structure of γ-Al₂O₃ was formed, while at high AIP concentrations, fine spherical particles of χ-Al₂O₃ were obtained. It was found that using these fine particles alumina as cobalt catalyst supports resulted in much higher amounts of cobalt active sites measured by H₂ chemisorption and higher CO hydrogenation activities.     

Observation on different reducing power of cocatalysts on the Ziegler–Natta catalyst containing alkoxide species for ethylene polymerization

In this work, the effects of three types of cocatalyst having different alkyl groups, such as triethylaluminium (TEA), triisobutylaluminum (TiBA), and trioctylaluminium (TnOA), and their concentrations on the catalytic activity and polymer properties were investigated for the Ziegler–Natta catalyst containing alkoxide species. The drastic escalation of catalytic activity was observed when the ratio of Al/Ti was increased only for TEA because of its good diffusivity as proven by the electron spin resonance technique. Moreover, it was found that the characteristic of the alkyl group in cocatalyst affected on the chain transfer ability. The chain transfer ability of TnOA was found to be equal to the TiBA in spite of its concentration was higher. By the way, the cocatalyst types and their concentrations did not affect on the variety of active sites as seen in molecular weight distribution of polymer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40884.     

Effect of aging on the properties of mesoporous niobium oxide

Using niobium(V) chloride and F127 in a water–ethanol system, this work reports the effect of aging of niobium-surfactant gel at 40 and 110 °C on the final product properties. The aging at low temperature of 40 °C showed small modification of the textural properties of the mesoporous niobium oxide. On the other hand, the hydrothermal aging at 110 °C showed significant increase in BET surface area, pore volume, pore size and microporosity with additional thermal and structural properties deviation. The process of hydrothermal aging at 110 °C is believed to lock chlorides in the niobium structure and cause the structural modification of the niobium skeleton leading to distinct developed crystalline structure and phase transformation behavior. The result also showed that hydrothermal aging at 110 °C could also enhance Lewis acidity of the product after calcination at 500 °C.     

Effect of nano-SiO2 particle size on the formation of LLDPE/SiO2 nanocomposite synthesized via the in situ polymerization with metallocene catalyst

Here, we revealed the effect of particle size of the nanoscale SiO₂ on catalytic and characteristic properties of LLDPE/nano-SiO₂ composites synthesized via the in situ polymerization with a zirconocene/MAO catalyst. In the experiment, SiO₂ (10 and 15 nm) was first impregnated with MAO. Then, copolymerization of ethylene/1-hexene was performed in the presence of nano-SiO₂/MAO to produce LLDPE/nano-SiO₂ composites. It was found that the larger particle exhibited higher polymerization activity due to fewer interactions between SiO₂ and MAO. The larger particle also rendered higher insertion of 1-hexene leading to decreased melting temperature (T_m). There was no significant change in the LLDPE molecular structure by means of ¹³C NMR.     

New concepts in material and energy utilization

New criteria in material and energy utilization are proposed. The potential index (Θ*) is assigned to explain some natural processes in the world and to identify reasonably the preferable process instead of the efficiency. In addition, this term can first integrate the independent knowledge of the fields of mechanical, electrical and chemical engineering. It not only describes satisfactorily the transformation processes that are well-known in mechanical and electrical engineering, but also the increasing potential processes familiar in chemical engineering.     

Impact of Boron Modification on MCM-41-Supported Cobalt Catalysts for Hydrogenation of Carbon Monoxide

Boron modification on MCM-41-supported cobalt (Co) catalysts was found to decrease the catalyst activity during CO hydrogenation. The decreased activities were due to stronger support interaction between Co oxide species and the support with the presence of boron resulting in lower reducibility. However, based on methanation the selectivity to C₂–C₄ products slightly increased with low loading of boron.     

Observation of bimodal polyethylene derived from TiO2-supported zirconocene/MAO catalyst during polymerization of ethylene and ethylene/1-hexene

The bimodal polyethylene obtained from TiO₂-supported zirconocene/MAO catalyst was observed during polymerization of ethylene and ethylene/1-hexene. By means of XPS, it revealed that TiO₂ consisted of Ti³⁺ (BE = 462.6 eV) and Ti⁴⁺ (BE = 464.9 eV). The dual catalytic sites were attributed to the presence of Ti³⁺ and Ti⁴⁺ in TiO₂.