STUDIES ON TiCI4/Mg (OEt)_2/EB SUPPORTED CATALYSTS FOR PROPYLENE POLYMERIZATION

The supported catalysts for propylene polymerization were prepared by milling Mg (OEt)_2 with EB (ethylbenzoate) and treating with TiCl_4 solution. When TiCl_4/(Mg(OEt)_2/EB) (mol.) ratio was increased, decrease in contents of-OEt and Ti of the catalysts was observed, while the content of EB increased. It is proved by analyses of IR, X-ray and XPS that during co-milling Mg(OEt)_2 with EB no reactions have taken place. But after treatment with TiCl_4 solution, Mg(OEt)_2 converts into MgCl_2 and EB coordinates on the resulting MgCl_2 carrier, a surface complex forms.The activity of catalysts,isotacticity and vicosimetric molecular weight of polypropylene increase with the decrease of the content of ethoxyl group. The kinetic curves of propene polymerization obtained with present catalysts system display decay curves. It is found from the triad tacticity calculated from the expanded spectra of methyl carbon region that, ethoxyl group in catalyst has an effect on the configuration of polymer chain.

Endeavors on the development of efficient and sustainable supported metal catalysts for chemical synthesis on solid-liquid interfaces

Supported metal catalysts,particularly for precious metals,have gained increasing attention in green synthetic chemistry.They can make metal-catalyzed organic synthesis more sustainable and economical due to easy separation of product with less metal residue,as well as reusability of the high-cost catalysts.Although great effort has been spent,the precise catalytic mechanism of supported metal-catalyzed reactions has not been clearly elucidated and the development of efficient and stable recyclable catalysts remains challenging.This highlight reveals a“molecular fence”metal stabilization strategy and discloses the metal evolution in Pd-catalyzed C-C bond formation reactions using Nheterocyclic carbene(NHC)-functionalized hypercrosslinked polymer support,wherein the polymeric skeleton isolates or confines the metal species involved in the catalytic reactions,and NHC captures free low-valent metal species in solution and stabilizes them on the support via strong metal-support coordination interaction.This strategy creates a novel route for the development of supported metal catalysts with high stability and provides insights into the reaction mechanism of heterogeneous catalysis.

Enhanced stability of nitrogen-doped carbon-supported palladium catalyst for oxidative carbonylation of phenol

Enhancing the stability of supported noble metal catalysts emerges is a major challenge in both science and industry.Herein,a heterogeneous Pd catalyst(Pd/NCF)was prepared by supporting Pd ultrafine metal nanoparticles(NPs)on nitrogen-doped carbon;synthesized by using F127 as a stabilizer,as well as chitosan as a carbon and nitrogen source.The Pd/NCF catalyst was efficient and recyclable for oxidative carbonylation of phenol to diphenyl carbonate,exhibiting higher stability than Pd/NC prepared without F127 addition.The hydrogen bond between chitosan(CTS)and F127 was enhanced by F127,which anchored the N in the free amino group,increasing the N content of the carbon material and ensuring that the support could provide sufficient N sites for the deposition of Pd NPs.This process helped to improve metal dispersion.The increased metal-support interaction,which limits the leaching and coarsening of Pd NPs,improves the stability of the Pd/NCF catalyst.Furthermore,density functional theory calculations indicated that pyridine N stabilized the Pd^(2+)species,significantly inhibiting the loss of Pd^(2+)in Pd/NCF during the reaction process.This work provides a promising avenue towards enhancing the stability of nitrogen-doped carbon-supported metal catalysts.

Partial oxidation of methane over SiO2 supported Ni and NiCe catalysts

Nickel and nickel-ceria catalysts supported on high surface area silica, with 6 wt% Ni and 20 wt% CeO2 were prepared by microwave assisted(co) precipitation method. The catalysts were investigated by XRD,TPR and XPS analyses and they were tested in partial oxidation of methane(CPO). The catalytic reaction was carried out at atmospheric pressure in a temperature range of 400–800℃ with a feed gas mixture containing methane and oxygen in a molecular ratio CH4/O2=2. The Ni catalyst exhibited 60% methane conversion with 60% selectivity to CO already at 500℃. On the contrary, the Ni–Ce catalyst was inert to CPO up to 700℃. Moreover, the former catalyst reproduced its activity at the descending temperatures maintaining a good stability at 600℃, over a reaction time of 80 h, whereas the latter one completely deactivated. Test of CH4 temperature programmed surface reaction(CH4-TPSR) revealed a higher methane activation temperature(> 100℃) for the Ni–Ce catalyst as compared to the Ni one. Noticeable improvement of the ceria containing catalyst occurred when the reaction test started at a temperature higher than the methane decomposition temperature. In this case, the sample achieved the same catalytic behavior of the Ni catalyst. As confirmed by XPS analyses, the distinct electronic state of the supported nickel was responsible for the differences in catalytic behavior.

Supported catalysts for simultaneous removal of SO_(2),NO_(x),and Hg^(0)from industrial exhaust gases:A review

The simultaneous removal of SO_(2),NO_(x)and Hg^(0)from industrial exhaust flue gas has drawn worldwide attention in recent years.A particularly attractive technique is selective catalytic reduction,which effectively removes SO_(2),NO_(x)and Hg^(0)at low temperatures.This paper first reviews the simultaneous removal of SO_(2),NO_(x)and Hg^(0)by unsupported and supported catalysts.It then describes and compares the research progress of various carriers,eg.,carbon-based materials,metal oxides,silica,molecular sieves,metal-organic frameworks,and pillared interlayered clays,in the simultaneous removal of SO_(2),NO_(x)and Hg^(0).The effects of flue-gas components(such as O_(2),NH3,HCl,H2 O,SO_(2),NO and Hg^(0))on the removal of SO_(2),NOx,and Hg^(0)are discussed comprehensively and systematically.After summarizing the pollutantremoval mechanism,the review discusses future developments in the simultaneous removal of SO_(2),NOx and Hg^(0)by catalysts.

SILICA-SUPPORTED NICKEL AND ZIRCONIUM CATALYSTS FOR BRANCHED POLYETHYLENE

8-Aminoquinoline nickel dichloride and bis(cyclopentadienyl)zirconium dichloride (Cp_2ZrCl_2) were supportedsimultaneously on silica to produce branched polyethylene successfully by combined polymerization. The supportedpolymerization results showed that the molecular weight of polyethylene increased while the molecular weight distributionbecame wider and the molecular chains of oligomers remaning in the final solution became shorter as compared to theoligomers obtained in polymerization processes with pure 8-aminoquinoline nickel dichloride catalysis, as well as theCp_2ZrCl_2 and nickel combination system. With decreasing amount of Ni catalyst in the supported catalyst, the molecular chains of oligomers in the resulting solution became shorter, while α-olefin selectivity increased.

Simultaneous catalytic removal of NOx and diesel soot particulate over perovskite-type oxides and supported Ag catalysts

A series of perovskite type oxides and supported Ag catalysts were prepared, and characterized by X ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS). The catalytic activities of the catalysts as well as influencing factors on catalytic activity have been investigated for the simultaneous removal of NOx and diesel soot particulate. An increase in catalytic activity for the selective reduction of NOx was observed with Ag addition in these perovskite oxides, especially with 5% Ag loading. This catalyst could be a promising candidate of catalytic material for the simultaneous elimination of NOx and diesel soot.

Ultrafine Pt nanoparticles supported on double-shelled C/TiO2 hollow spheres material as highly efficient methanol oxidation catalysts

Catalyst support is extremely important for future fuel cell devices.In this work,we developed doubleshelled C/TiO2(DSCT)hollow spheres as an excellent catalyst support via a template-directed method.The combination of hollow structure,TiO2 shell and carbon layer results in excellent electron conductivity,electrocatalytic activity,and chemical stability.These uniformed DSCT hollow spheres are used as catalyst support to synthesize Pt/DSCT hollow spheres electrocatalyst.The resulting Pt/DSCT hollow spheres exhibited high catalytic performance with a current density of 462 mA mg^-1 for methanol oxidation reaction,which is 2.52 times higher than that of the commercial Pt/C.Furthermore,the increased tolerance to carbonaceous poisoning with a higher If/Ibratio and a better long-term stability in acid media suggests that the DSCT hollow sphere is a promising C/TiO2-based catalyst support for direct methanol fuel cells applications.

PREPARATION OF NOVEL POLYETHYLENE-graft-POLY(4-VINYLPYRIDINE)-SUPPORTED METALLOCENE CATALYSTS FOR ETHYLENE POLYMERIZATION

Polyethylene (PE) grafting 4-vinylpyridine copolymers has been produced as powders of different rushes by theirradiation method. After treatment with methylaluminoxane (MAO), the copolymers were used as supports for Cp_2ZrCl_2catalyst Results of X-ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, ultraviolet spectroscopy andscanning electron microscope measurements show that the catalytic sites have been linked through MAO on the PE-graft-4-vinylpyridine (PEVP). The percentages of grafting 4-vinylpyridine and supported Cp_2ZrCl_2 depend on the size ofpolyethylene powder. The smaller the polyethylene powder, the more percent of 4-vinylpyridine groups and Cp_2ZrCl_2 existon the polyethylene chains, and the PEVP-supported catalyst has a relatively high activity for ethylene polymerization.

Low-temperature conversion of methane to oxygenates by supported metal catalysts: From nanoparticles to single atoms

Direct cost-effective conversion of abundant methane to high value-added oxygenates(methanol,formic acid,acetic acid,etc.)under mild conditions is prospective for optimizing the structure of energy resources.However,the CAH bond of products is more reactive than that of high thermodynamic stable methane.Exploring an appropriate approach to eliminate the‘‘seesaw effect"between methane conversion and oxygenate selectivity is significant.In this review,we briefly summarize the research progress in the past decade on low-temperature direct conversion of methane to oxygenates in gas-solid-liquid phase over various transition metal(Fe,Cu,Rh,Pd,Au Pd,etc.)based nanoparticle or single-atom catalyst.Furthermore,the prospects of catalyst design and catalysis process are also discussed.

Oxidative desulfurization of diesel fuel oil using supported Fenton catalysts and assisted with ultrasonic energy

An ultrasound-assisted heterogeneous catalytic oxidation process was applied to eliminate sulfur from commercial diesel fuel oil.The studied variables were catalyst concentration,type of catalyst(homogeneous or heterogeneous),oxidizing agent concentration,and the application of ultrasound energy.Supported catalysts were prepared by impregnation of coal fly ash with an iron(Ⅱ)sulfate aqueous solution using ultrasound energy.After drying,the catalyst was calcined at 500℃for 4 h.The oxidizing agent was hydrogen peroxide.Ultrasound energy was applied with a frequency of 47 kHz and an intensity of 147 W.Ethanol was employed for extracting the oxidized compounds from the hydrocarbon mixture.Coal fly ash and ethanol were used with the purpose of applying low-cost raw materials in chemical processes.It was found that under the studied conditions,increasing oxidizing agent concentration and the application of ultrasound energy can enhance the sulfur removal from commercial diesel fuel oil.Catalyst concentration did not play a significant role in the process.Similar results were obtained using homogeneous or heterogeneous catalyst,which is important since the heterogeneous catalyst could be recovered,reactivated,and used in many cycles.

Hydrochlorination of acetylene using expanded multilayered vermiculite(EML-VMT)-supported catalysts

Catalyst supports have very important effects on catalyst performance.A novel expanded multilayered vermiculite（EML-VMT） is successfully used as the catalyst support for the acetylene hydrochlorination.By mixing carbon on the surface of EML-VMT[i.e.,EML-VMT-C）,the HgCl2/EML-VMT-C achieved a high acetylene conversion of 97.3%,a vinyl chloride selectivity of 100%and a turn over frequency（TOF） value of 8.83 × 10^-3s^-1 at a temperature of 140 C,an acetylene gas hourly space velocity（GHSV） of 108 h^-1,and a feed volume ratio V（HC1）/V（C2H2） of 1.15.Moreover,the HgCl2/EML-VMT-C shows good stability.The EML-VMT also shows potential in the preparation of other EML-VMT-supported catalysts.

EFFECTS OF AMINO GROUPS AND MICROSTRUCTURE OF ORGANIC MESOPOROUS SILICA SUPPORTED METALLOCENE CATALYSTS ON ETHYLENE POLYMERIZATION

Mesoporous silica （MS）, 3-aminopropyltriethoxysilane （APTES） modified mesoporous silica （AMS）, bis（3- trimethoxysilylpropyl）amine modified mesoporous silica （BAMS） and APTES modified solid spherical silica （AS） were prepared and used to immobilize metallocene catalysts for ethylene polymerization. Gel permeation chromatography results showed that polyethylenes （PEs） catalyzed by AMS （or BAMS） supported metallocene catalysts at the molar ratios of Al/Zr = 100, 300 and 500 were of bimodal molecular weight distribution （BMWD）; while PEs catalyzed by the above catalysts at the molar ratios of Al/Zr 〉 800 were of monomodal molecular weight distribution （MMWD）. However, MS （or AS） supported metallocene catalysts could only produce PEs with MMWD in spite of the molar ratio of Al/Zr. It was because that AMS （or BAMS） supported catalysts possessed two active sites for ethylene polymerization at low molar ratios of Al/Zr due to the combination effects of mesopore geometrical constraint and amino groups of the supports, which was confirmed by X-ray photoelectron spectroscopy. This brings forward a novel and easy method for the synthesis of polyolefin with BMWD.

Simultaneous formation of sorbitol and gluconic acid from cellobiose using carbon-supported ruthenium catalysts

A carbon-supported Ru catalyst, Ru/BP2000, is able to simultaneously convert cellobiose into sorbitol and gluconic acid. This reaction occurs as the result of hydrolytic disproportionation in water at 393 K under an Ar atmosphere, without bases or sacrificial reagents. In-situ XANES measurements suggest that the active Ru species involved is composed of partially oxidized Ru metal.

In situ IR, pulse reaction and TPD-ITD study of catalytic performance of room-temperature carbon monoxide oxidation on supported gold catalysts

With in situ IR, two different CO adsorption bands were detected on various chemical state gold catalysts. One band is attributed to the linear CO on an oxidized gold catalyst(2100 cm -1 ), the other one is ascribed to the bridged CO on metallic gold (2085 cm -1 ). CO pulse reaction showed that Au/Fe 2O 3 catalyst had a room temperature activity even in the presence of moisture. The produced CO 2 was detained and more easily desorbed from supported gold catalyst than support oxide. TPD IDT results indicated that the O - 2 superoxide ions are the possible active oxygen species.

Stabilizing supported gold catalysts in acetylene hydrochlorination by constructing an acetylene–deficient reaction phase

In the process of acetylene hydrochlorination,the rapid deactivation of supported gold(Au)catalysts by acetylene is still a huge challenge.Here,we provide an innovative strategy for constructing an acetylene–deficient reaction phase on the active site by coating an ionic liquid film on the Au(H2O)/C surface.The reactant ratio of C2H2 to HCl in this acetylene–deficient reaction phase is 1:132,in contrast to the 1:1 M ratio in the gas phase,thus boosting the catalytic stability of Au(H2O)/C catalysts.The kinetic and theoretical analysis showed that the reduction of cationic gold by C2H2 and the generation of carbon deposition can be inhibited in this constructed reaction phase during reaction.The current work not only broadens the scope of supported Au catalysts in acetylene hydrochlorination,but also verifies the perspective of the tunability of stoichiometric balance,which can be used in other catalytic applications.

DEPENDENCE OF THE DISTRIBUTION OF ACTIVE CENTERS ON MONOMER IN SUPPORTED ZIEGLER-NATTA CATALYSTS

Distribution of active centers(ACD)of ethylene or 1-hexene homopolymerization and ethylene-1-hexene copolymerization with a MgCl_2/TiCl_4 type Z-N catalyst were studied by deconvolution of the polymer molecular weight distribution into multiple Flory components.Each Flory component is thought to be formed by a certain type of active center. ACD of ethylene-1-hexene copolymer with very low 1-hexene incorporation was compared with that of ethylene homopolymer to see the effect of introducingα-olefin on ethyle...

Methane Dry Reforming over Alumina Supported Co Catalysts

A series of Co/γ-Al_2O_3 catalysts were prepared with the impregnation method and characterized by means of the BET specific surface area, X-ray diffraction(XRD), thermogravimetric analysis(TGA) and Laser Raman spectroscopy. The Co/γ-Al_2O_3 catalysts were activated by using H_2, 20%CH_4/H_2 or CH_4, respectively. There was no obvious difference between the activities of the Co/γ-Al_2O_3 catalyst activated by using the different activation methods for methane dry reforming. The catalytic properties of the Co/γ-Al_2O_3 catalysts with different Co loadings were also investigated. The optimized Co loading for the Co/γ-Al_2O_3 catalyst pretreated with 20% CH_4/H_2 is around 12%(mass fraction).

Importance of Metal－Oxide Support Wettingandinteractions on Understanding of Physical and Chemical Behaviours of Supported Metal Catalysts

It has been generally recognised that the metal catalysts supported on oxide ceramic and non-oxide ceramic supports exhibit completely different characteristics as compared with the homogeneous ones. The na-ture of bonding and interactions occurring at the metal / ceramic interfaces are believed to be of importancefor the characteristics of such catalysts. The recently developed microscopic theory of adhesion and wettingin metal/ ceramic systems is briefly presented here with the emphasis on the ionocovalent oxide ceramics.and its consequence on the understanding of the physical and chemical behaviours of supported metal cata-lysts is exploited.