Polymer‐supported half‐titanocene catalysts for the syndiospecific polymerization of styrene

Monocyclopendienyltitanium trichloride (CpTiCl₃) was supported on polymer carriers with different hydroxyl contents, and the supported catalysts were used for styrene polymerization. The supported catalysts exhibited high activity even at low Al/Ti ratios and increased the molecular weight of the products, indicating that polymer carriers could stabilize the active sites. The polymers prepared with unsupported and supported catalysts were extracted with boiling n‐butanone and characterized by carbon nuclear magnetic resonance (¹³C NMR) and differential scanning calorimetry. The polymers obtained by supported catalysts had a high fraction of boiling n‐butanone‐insoluble part and high melting temperatures, but ¹³C NMR results showed that syndiotacticity decreased compared with that of polymers prepared with an unsupported catalyst. ESR study on the supported catalysts confirmed that the active sites supported on the carrier dropped into the solution and formed active sites the same as those in the unsupported system when they reacted with methylaluminoxane. ¹³C NMR analysis showed that the polymerization mechanism of the supported active sites was an active‐site controlled mechanism instead of a chain‐end controlled mechanism of the unsupported active sites. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 127–135, 2000     

共沉淀法和浸渍法制备的HoCeMn/TiO2催化剂的脱硝性能

采用浸渍法和共沉淀法制备了HoCeMn/TiO₂脱硝催化剂并对其结构和性能进行了表征。结果表明共沉淀法增强了活性组分和载体的相互作用，从而增加了 HoCeMnTi-C催化剂表面 Ce³⁺、Mn⁴⁺以及吸附氧的含量，使其表现出优异的低温氧化还原性能。此外，共沉淀法制备的HoCeMnTi-C具有更多的表面酸性位点及更强的表面酸性。催化剂表面酸性和氧化还原性能的提高有助于氨的吸附和活化，从而显著提高其活性。表面酸性位点的增多还抑制了 H₂O和 SO₂在催化剂表面的吸附，提升了催化剂的抗水抗硫性能。催化剂上的选择性催化还原(SCR)反应遵循Eley-Rideal(E-R)机制，催化剂硫中毒是源于形成的硫酸盐覆盖或破坏了催化剂活性位。     

Potential of Supported Copper and Potassium Oxide Catalysts in the Combustion of Carbonaceous Particles

Different oxide carriers (TiO₂ and ZrO₂) as supports for low amounts of Cu²⁺ and K⁺ species (2 wt % as equivalent oxide) were tested in the catalytic oxidation of carbon black. The K-Cu/oxide catalysts were shown to have a lower soot combustion temperature than K/oxide, Cu/oxide, and pure oxide carriers. The K-Cu/ZrO₂ catalyst was found to be the most active; it exhibited activity in a loose contact nearly similar to that obtained in a tight contact mode. Physicochemical characterization by EPR, XPS, and TPR revealed the interaction of K⁺ species with Cu²⁺ species and the ZrO₂ carrier in K-Cu/ZrO₂ as well as a strongly distorted Cu²⁺ species on the ZrO₂ surface. The potassium ions ensure promoting effects towards the contact between the carbon black and the catalyst surface. Although potassium ions were found to lower the reducibility of the cupric oxide species, the oxidation rate of carbon black increased in the presence of K/oxide and K-Cu/oxide.     

共沉淀法和浸渍法制备的HoCeMn/TiO2催化剂的脱硝性能

采用浸渍法和共沉淀法制备了Ho Ce Mn/Ti O₂脱硝催化剂并对其结构和性能进行了表征。结果表明共沉淀法增强了活性组分和载体的相互作用,从而增加了Ho Ce Mn Ti-C催化剂表面Ce³⁺、Mn⁴⁺以及吸附氧的含量,使其表现出优异的低温氧化还原性能。此外,共沉淀法制备的HoCeMnTi-C具有更多的表面酸性位点及更强的表面酸性。催化剂表面酸性和氧化还原性能的提高有助于氨的吸附和活化,从而显著提高其活性。表面酸性位点的增多还抑制了H₂O和SO₂在催化剂表面的吸附,提升了催化剂的抗水抗硫性能。催化剂上的选择性催化还原(SCR)反应遵循Eley-Rideal(E-R)机制,催化剂硫中毒是源于形成的硫酸盐覆盖或破坏了催化剂活性位。     

Isolated Tin(IV) Active Sites for Highly Efficient Electroreduction of CO2 to CH4 in Neutral Aqueous Solution

The development of efficient electrocatalysts with non-copper metal sites for electrochemical CO₂ reduction reactions (eCO₂RR) to hydrocarbons and oxygenates is highly desirable, but still a great challenge. Herein, a stable metal–organic framework (DMA)₄[Sn₂(THO)₂] (Sn-THO, THO⁶⁻ = triphenylene-2,3,6,7,10,11-hexakis(olate), DMA = dimethylammonium) with isolated and distorted octahedral SnO₆²⁻ active sites is reported as an electrocatalyst for eCO₂RR, showing an exceptional performance for eCO₂RR to the CH₄ product rather than the common products formate and CO for reported Sn-based catalysts. The partial current density of CH₄ reaches a high value of 34.5 mA cm⁻², surpassing most reported copper-based and all non-Cu metal-based catalysts. Our experimental and theoretical results revealed that the isolated SnO₆²⁻ active site favors the formation of key *OCOH species to produce CH₄ and can greatly inhibit the formation of *OCHO and *COOH species to produce *HCOOH and *CO, respectively.     

The Effects of M2O3 on Stabilizing Monocopper over the Surface of Cu-ZnO-M2O3 Catalysts for Mathanol Synthesis

The effects of M₃O₃ (M = Al, Sc etc.) in Cu-ZnO-M₂O₃ catalysts on methanol synthesis at low pressure were studied with ESR, XPS and TPR spectroscopy. The results of ESR showed that the generation of monovalent cationic defects was because the valence state and electronic charge on the ZnO lattice lost their balance as M³⁺ doped into ZnO. The induced effect by Sc³⁺ is stronger than that by Al³⁺. The results of XPS and TPR indicated that the amount and stabilization of Cu⁺ on the surface of reduced copper-based catalyst and its catalytic activity were affected by the monovalent cationic defects on the surface of ZnO.     

Catalytic activity of bimetal-containing Co,Pd systems in the oxidation of carbon monoxide

The catalytic activity of low-percentage Co,Pd systems on ZSM-5, ERI, SiO₂, and Al₂O₃ supports in the oxidation of CO was studied. The activity of bimetal-containing catalysts was shown to depend on the nature of the catalyst and the amount and ratio of their active components. According to the results of thermoprogrammed reduction with H₂ (H₂ TPR) and X-ray photoelectron spectroscopy (XPS) data, the metals are distributed as isolated cations or Co^δ+-O-Pd^δ+ clusters with cobalt and palladium cations surrounded by off-lattice oxygen in Co,Pd systems. The 0.8% Co,0.5% Pd-ZSM-5 bimetal catalysts were found to be more active due to the presence of clusters.     

Role of Iron Carbonyls in the Inhibition of Oxygen Activation for the Oxidation of CO Catalyzed by Iron Oxide‐Supported Gold

Iron oxide‐supported gold samples were prepared by co‐precipitation from HAuCl₄ and Fe(NO₃)₃. The activities of the samples as CO oxidation catalysts were tested without thermal treatment and following treatments in flows of He and O₂ at various temperatures. It was found that the untreated samples and those treated in a flow of He at 150 °C were more active than samples that had been treated at 400 °C in either a flow of O₂ or of He. Infrared spectra recorded during CO oxidation catalysis indicate the presence of bonded CO molecules to cationic gold on all samples, whereas spectra of the least active catalysts indicate a predominant presence of Fe²⁺ carbonyls, which were highly stable under the conditions of our experiments. Our results indicate that in the least active samples the Fe²⁺‐bound CO blocks sites that would otherwise be available for oxygen activation.     

Oxidation of CO and hydrocarbons over perovskite-type complex oxides

The catalytic activity of perovskites M^IM^IIO₃ (M^I=La; M^II=Co, Mn, Cr, Al, Ni, and V) and M^ICoO₃ (M=Y, Nd, Sm, and Er) in the oxidation of CO, propylene, and ethylbenzene was investigated. The highest activity was observed for the M^ICoO₃ catalysts with perfect perovskite structure. The nature of the rare-earth element has no influence on the catalytic activity. Deformation of the octahedral coordination of the metal was found for the less active catalysts. The interaction of gases (CO, CO+air) with the catalyst surface was investigated. The more active catalysts adsorb a greater amount of O₂, and the adsorption occurs in the temperature region of the oxidation reaction. The activities of the perovskite- and spinel-type catalysts were compared under similar conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 698–701, April, 1999.     

Interpretation of the difference of optimal Mo density in MoS<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MoS<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> HDS catalysts

The first part of this paper deals with the morphology of the MoS₂ phase and its oxide precursor, the MoO₃ phase, mainly from a geometrical point of view. After giving a brief review of the literature describing the structure of these compounds, Mo densities in both phases were calculated along various crystallographic planes. Further, using structural models recently proposed by others, Mo densities in MoS₂ were also calculated in the case of an epitactic growth on γ-Al₂O₃ and TiO₂ model surfaces. Then, the calculated Mo densities were compared with experimental results (Mo density when HDS activity is maximal) previously obtained for catalysts constituted of MoS₂ supported on a low SSA TiO₂, a high SSA TiO₂ and a conventional γ-alumina. It was suggested that either on alumina or titania the MoS₂ phase is growing as (100) MoS₂ planes. However, while on the alumina the optimal MoS₂ phase might be constituted of dispersed MoS₂ slabs covering only a part of the alumina surface (2.9–3.9 Mo atoms/nm²), on titania the optimal MoS₂ phase might be constituted of a uniform MoS₂ monolayer (5.2 atoms/nm² for the high SSA titania, which is equal to the Mo density of a perfect MoS₂ (100) plane). This difference may originate in the creation of a 'TiMoS' phase enhancing the S atoms mobility over Mo/TiO₂-sulfided catalysts. Indeed, while in the case of a γ-alumina carrier the active sites (labile S atoms) are located on the edge of MoS₂ slabs making the ratio Mo_edge/Mo_total a crucial parameter for the catalytic performances, in the case of a titania carrier the labile sulfur atoms might be statistically distributed all over the TiMoS active phase. Further, the higher Mo density observed over the high SSA titania (5.2 atoms/nm²) when compared to that over the low SSA titania (4.2 atoms/nm²) was supposedly due to the pH-swing method advantageously used to prepare the former carrier. Indeed, this method allows giving a solid with enhanced mechanical properties providing a good stability to the derived catalysts under experimental conditions. In addition, this TiO₂ carrier exhibits a great homogeneity, with a surface structure substantially uniform, which might be adequate for a long-range growth of (100) MoS₂ slabs.     

CuO/Ti0.5Zr0.5O2催化剂对NO+CO反应的催化作用

环境治理是当今社会面临的一大主要问题。目前,城市空气污染日趋严重,特别是工厂和汽车排放的大量未燃烧的烃类、CO、NOx是主要的空气污染物。其中,氮氧化物(NOx)排放状况尤其严重,它的排放会给环境和人们生活带来严重危害,因此,如何有效地消除NOx已成为目前环境保护中一个非常     

Lanthanum-promoted copper-based oxygen carriers for chemical looping combustion process

Copper-based oxygen carriers have high reactivity and favorable thermodynamic properties in the innovative chemical looping combustion (CLC), which results in the inherent capture of CO₂. The major challenge of copper-based oxygen carriers is its low melting point and potential thermal sintering and agglomeration under high-temperature cyclic CLC operations. This study is to verify the beneficial use of a rare earth metal (lanthanum) additive in copper for the enhancements of thermal stability of copper-based oxygen carriers. In both the initial 50-cycle tests using TPR-TPO techniques (temperature-programmed reduction and oxidation, 800 °C) and further extended 840-cycle tests using the micro-reactor system, in over 50 cyclic Redox TPR-TPO tests, the lanthanum-promoted copper-based oxygen carrier showed the substantial resistance to the agglomeration. Thermal analysis studies were also extended into investigations of free oxygen releasing from copper-based oxygen carrier. Characterization of used oxygen carriers revealed the significant interaction between copper and its supporting material, Al₂O₃. The Al₂O₃-supported CuO seemed to indicate a slow release of oxygen. The formation of a new crystal phase (CuAl₂O₄), combining CuO and γ-Al₂O₃, may be a major reason for the stability of copper-based oxygen carrier and the slow oxygen release under oxygen uncoupling condition. The fresh and used oxygen carriers were further characterized by (1) Brunauer–Emmett–Teller for the pore structure analysis, (2) X-ray diffraction for crystal structure analysis, and (3) scanning electron microscopy for surface analysis.     

An IR-Spectroscopic Study of the State of Zirconium in Supported Zirconocene Catalysts

The surface compounds of zirconium in SiO₂/MAO/Cp₂ZrMe₂ (I) and SiO₂/Cp₂ZrMe₂ (II) catalysts were studied by the IR spectroscopy of adsorbed CO at 93-293 K. It was found that the bridging and terminal complexes of CO were formed on the surface of the catalysts at 93 K; the adsorption of CO was reversible. At 293 K, CO was irreversibly inserted into the Zr-Me bond with the formation of various acyl compounds of zirconium; these compounds were characterized by absorption bands in the region 1495-1750 cm^-1 in the IR spectrum. These data suggested the heterogeneity of the surface composition of zirconocene catalysts Iand II. Catalyst I, which was active in ethylene polymerization, contained surface zirconium complexes that can be considered as the precursors of active centers for ethylene polymerization.     

Chloride‐Induced Highly Active Au Catalyst for Methyl Esterification of Alcohols

Chloride is generally regarded as a harmful species for the heterogeneous catalysts, especially Au catalysts. In this work, a series of active Au/NiO_x catalysts were successfully prepared with co‐precipitation method by tracking the concentrations of chloride in the re‐dispersed aqueous solutions. For methyl esterification of alcohols, the highest active Au/NiO_x catalysts could be prepared from aqueous solutions containing 8‐13 ppm chloride, the yield of methyl benzoate of catalyst Au/NiO_x‐9 was 99%. The catalyst structures and the role of chloride in catalysts were explored by ICP, BET, XPS, TEM and EXAFS characterizations. It was found that the appropriate amount of residual chloride in Au catalysts was beneficial to their catalytic activities. Especially for Au/NiO_x‐9, the appropriate amount of residual chloride had positive effects on the physicochemical properties of Au/NiO_x catalyst, the position of Au nanoparticles (NPs) located on NiO_x crystallites and the ratio of Au^δ+/Au⁰ in catalyst, which together resulted in its high reactivity.     

Catalytic Active Site for NO Decomposition Elucidated by Surface Science and Real Catalyst

Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder Pd/Al₂O₃ catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the step sites act as the catalytic active site for NO decomposition on Pd/Al₂O₃. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co₃O₄ serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed in which the reaction is initiated by NO adsorption onto alkali metals to form NO₂⁻ species and then NO₂⁻ species react with the adsorbed NO species to form N₂ over the interface between the alkali metal and Co₃O₄.     

Study of reduced Mo/Al2O3 metathesis catalysts prepared via metal complexes

The Mo/Al₂O₃ catalysts for propene metathesis were prepared both via anchoring Mo complexes of various nuclearities and by conventional method of impregnation. The catalysts from metal complexes were found to be active in metathesis at ambient temperature after reduction with H₂ or CO at 400–500°C. The average oxidation state of Mo in the activated catalysts was determined with regard to oxygen consumption needed for oxidation of the reduced Mo species to Mo⁶⁺.     

Exploring the activation of olefin polymerisation catalysts with density functional theory

Density Functional Theory has been used to study the activation of different olefin polymerisation catalysts by different activators. The results show that biscyclopentadienyl catalyst systems would act as the best catalysts and the activators of the type [CPh₃⁺][A⁻] would be the best at activating such systems. The competition between different species present in solution for the vacant active site in the catalyst was studied for the [(1,2Me₂Cp)₂ZrMe⁺][B(C₆F₅)₃CH₃⁻] system and the pre‐catalyst and AlMe₃ were found to be the compounds most likely to form dormant products in solution.     

Synthesis and physicochemical characterization of palladium-cerium oxide catalysts for the low-temperature oxidation of carbon monoxide

The effect of CeO₂ preparation procedure on the electronic and structural states of the active component of Pd/CeO₂ catalysts and their activity in the low-temperature reaction of CO oxidation was studied. The following two nonequivalent states of palladium were detected in the catalysts having low-temperature activity using XPS and IR spectroscopy: Pd⁰(Pd^δ+) as the constituent of a palladium-reduced interaction phase and Pd²⁺ as the constituent of a palladium-oxidized interaction phase Pd _x CeO_{2 ?δ}. It was found that the procedure used for preparing a CeO₂ support considerably affected the formation of these phases and quantitative ratios between them. It was demonstrated that the palladium-oxidized interaction phase was responsible for low-temperature activity, whereas the palladium-reduced interaction phase was responsible for activity in the region of medium and high temperatures.     

The activation characteristics of the decomposition of H<Subscript>2</Subscript>O<Subscript>2</Subscript> on palladium-carbon catalysts

The kinetics of catalytic decomposition of H₂O₂ on palladium-carbon catalysts with various deposited metal distributions in carrier (active carbon) porous granules was studied. The activation parameters (E _a and A ₀) of the process were calculated by the Arrhenius equation. A determining factor for the catalytic process was found to be the entropy factor (A ₀), which characterized the formation and dissociation of activated transition complexes. A quantum-chemical study of the electronic structure of palladium-carbon catalysts showed the occurrence of electron density transfer from the carbon matrix to metal clusters and collectivization of their electronic systems. This increased the donor-acceptor ability of the synthesized materials and, as a consequence, their catalytic activity.     

Catalytic performance of silica-supported chromium oxide catalysts in ethane dehydrogenation with carbon dioxide

The oxidative dehydrogenation of ethane into ethylene by CO₂ over a series of silica-supported chromium oxide catalysts was investigated. The results showed that the catalysts were effective for the reaction and CO₂ in the feed promoted the catalytic activity. The 5%Cr/SiO₂ catalyst exhibited the excellent performance with 30.7% ethane conversion and 96.5% ethylene selectivity at 700^oC. ESR and UV-DRS were used to probe the active sites and the species with high valent states (Cr⁵⁺ and/or Cr⁶⁺) were found to be important for the reaction.