γ-radiation grafting: A novel approach for the preparation of robust and highly selective supported metal complex catalysts

The technique of γ radiation grafting is shown to be of value in functionalising mechanically strong, chemically simple and chemically inert polymers such as polypropylene. The technique leads to the incorporation of several functional groups at a single site on the polymer which is of value in creating a three-dimensional catalytically active site. Such sites enable the local environment to further enhance the natural selectivity arising from the molecular nature of a metal complex catalyst. Accordingly, supported metal complex catalysts prepared in this way have higher selectivities than their homogeneous analogues. The approach is illustrated by reference to cobalt and rhodium(I) olefin hydroformylation catalysts; in both cases the supported catalysts show greater selectivity towards the formation of normal as opposed to branched aldehydes than their homogeneous analogues.     

A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts

Catalytic partial oxidation of methane has been reviewed with an emphasis on the reaction mechanisms over transition metal catalysts. The thermodynamics and aspects related to heat and mass transport is also evaluated, and an extensive table on research contributions to methane partial oxidation over transition metal catalysts in the literature is provided.Presented are both theoretical and experimental evidence pointing to inherent differences in the reaction mechanism over transition metals. These differences are related to methane dissociation, binding site preferences, the stability of OH surface species, surface residence times of active species and contributions from lattice oxygen atoms and support species.Methane dissociation requires a reduced metal surface, but at elevated temperatures oxides of active species may be reduced by direct interaction with methane or from the reaction with H, H₂, C or CO.The comparison of elementary reaction steps on Pt and Rh illustrates that a key factor to produce hydrogen as a primary product is a high activation energy barrier to the formation of OH. Another essential property for the formation of H₂ and CO as primary products is a low surface coverage of intermediates, such that the probability of O–H, OH–H and CO–O interactions are reduced.The local concentrations of reactants and products change rapidly through the catalyst bed. This influences the reaction mechanisms, but the product composition is typically close to equilibrated at the bed exit temperature.     

Transition metal complexes bound to macroporous resins carrying nitrile groups. Effect of matrix structure on the activity of supported catalysts

Two groups of resins bearing nitrile (CN) groups based on macroporous copolymers of acrylonitrile and divinylbenzene (AN/DVB) and terpolymers of styrene, acrylonitrile and divinylbenzene (S/AN/DVB) have been used as polymer matrices for the immobilization of Rh(I), Pt(II) and Pd(II) complexes. A group of four S/DVB resins functionalized with the CN ligands have been prepared and used for comparison. The resins differ in their chemical and physical structure, local concentration of the CN groups and their availability. Characterization of the heterogeneous complexes by IR spectroscopy confirmed the coordination of the metal ions to the polymer-CN ligands. The catalytic behaviour of the immobilized complex catalysts was tested in the hydrosilylation of 1-hexene. The activity of the polymer-bound catalysts strongly depends on the structure of the support used. The largest effect of the chemical structure of the polymer was found for the catalysts immobilized on the AN/DVB resins, while the polymer morphology played the major role in the high activity of the catalysts attached to the S/N/DVB resins. Lower activity was found for the systems bound to the functionalized S/DVB resins. Both polymer-supported Pt and Rh systems appeared to be highly effective for the hydrosilylation of the CC double bonds, but the platinum catalysts proved to be considerably more active. The rhodium catalysts were found efficient in the hydrosilylation of ketones. The immobilized Pd(II) complex was reduced to the metallic Pd by hydrosilanes. The supported Pt catalyst remained active when recycled 5 times, while the activity of the rhodium systems gradually decreased. The results offer the possibility of choosing the most suitable polymer matrix for the immobilization of metal complex catalysts for use in hydrosilylation and other catalytic reactions.     

Ni supported on sepiolite catalysts for the hydrogenation of furfural to value-added chemicals: influence of the synthesis method on the catalytic performance

Topics in Catalysis - Nickel-based catalysts supported on sepiolite catalysts, with a nickel loading between 1 and 10 wt%, have been synthesized by several synthetic strategies...     

Single crystal flow reactor for studying reactivities on metal oxide model catalysts at atmospheric pressure to bridge the pressure gap to the adsorption properties determined under UHV conditions

A flow reactor for the investigation of heterogeneous catalytic reactions on single crystalline metal oxide model catalysts has been designed. It is located in a high pressure cell attached to an UHV analysis chamber where the model catalysts can be prepared and characterized by surface science techniques. It can also be run in a batch modus. After sample transfer the high pressure cell can be completely separated from the UHV chamber and it can be used for oxidation treatments and reaction studies at gas pressures up to 1 bar. A new heating system provides direct heating of the sample by laser light up to 1200 K. Product analysis is done by gas chromatography coupled with mass spectrometry, which allows detection in the ppb range. The single crystal flow reactor provides new insight into the atomic scale surface chemistry of metal oxides under real catalysis conditions and bridges the pressure gap for model systems prepared and characterized under UHV conditions. Results on the dehydrogenation of ethylbenzene to styrene over epitaxial potassium–iron oxide films are presented and correlated to thermal desorption measurements on the same films under UHV conditions.     

Selective hydrogenation of benzene to cyclohexene catalyzed by Ru supported catalysts: Influence of the alkali promoters on kinetics, selectivity and yield

The selective hydrogenation of benzene to cyclohexene in the presence of Ru supported catalysts has been investigated in a tetraphase slurry reactor at 423 K, at 5 MPa of pressure, in the presence of two liquid phases: benzene and an aqueous solution of ZnSO₄ (0.6 mol l⁻¹). A study of the influence of the transport phenomena on the reactivity of the catalyst has been carried out. But no correlation between Carberry and Wheeler–Weisz numbers and the selectivity of the catalysts has been found. The main features of the catalysts are the strong dependence between the catalysts preparation procedure and their activity and selectivity. The best results have been observed with Ru/ZrO₂ catalysts. The influence of the bases employed in the precipitation of the catalysts precursor has also been investigated. KOH is the most effective, yield of 41% and initial selectivity of 80% of cyclohexene has been observed.     

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 3. Drying process

In the present part of the group study on the preparation of 13 wt% MoO₃/Al₂O₃, the effects of drying processes were investigated on the physicochemical and catalytic properties. Two series of catalysts were prepared by a conventional impregnation technique and by an equilibrium adsorption method using a common extrudate support. XPS and EPMA results demonstrated that the distribution of Mo oxide species in extrudates was strongly affected by drying processes. A rapid drying, in particular at a reduced pressure, was found to induce a strong segregation of Mo oxides on the outer surface of the extrudates, forming a sharp egg shell type distribution of Mo. On the other hand, drying under static conditions produced a moderate egg shell type distribution, suggesting that a slow drying rate is favorable for a homogeneous distribution of Mo. The equilibrium adsorption technique was found to provide considerably flat Mo profiles inside the extrudates except for the utmost surfaces where Mo concentrations increased steeply.     

A comparative study on catalytic performances of chromium incorporated and supported mesoporous MSU-x catalysts for the oxidehydrogenation of ethane to ethylene with carbon dioxide

Two kinds of Cr-based mesoporous materials, Cr incorporated and supported silicate MSU-1, were synthesized at room temperature and characterized with XRD, N₂ adsorption–desorption, FT-IR, DR UV–vis and H₂-TPR techniques. Both Cr-based catalysts exhibited similar mesoporous channels and textural properties. The catalytic performances of two catalysts for the oxidative dehydrogenation of ethane to ethylene with CO₂ were investigated. They both showed high activities, providing 58.0 and 68.1% ethane conversion and 53.4 and 55.6% ethylene yield at 700 °C, respectively. The catalysts were prone to deactivate in the reaction but could be partially regenerated by oxygen. Cr species formed in high oxidation state were reduced during the reaction. It was proposed that these high-valent Cr species were responsible for the high activities of catalysts.     

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 1. Surface area of alumina

This is the first report of a group study on the preparation of a MoO₃/Al₂O₃ catalyst to find predominant preparation parameters for better and reproducible catalyst preparations. Variously prepared MoO₃/Al₂O₃ catalysts possessing 13 wt% MoO₃ were subjected to multiprong characterizations and catalytic tests. It was found that the surface area of the support was the most predominant preparation parameter for the dispersion of Mo oxide species; the dispersion increased as the surface area of the support increased. The formation of crystalline MoO₃ was observed at a surface Mo concentration higher than 3.2 Mo nm⁻². With sulfided MoO₃/Al₂O₃, it was established that the dispersion of Mo sulfide species increased with increasing surface area of the support and was in proportion to that of Mo oxide precursor species. The hydrodesulfurization activity of sulfided MoO₃/Al₂O₃ was proportional to the NO adsorption capacity. It is suggested that a homogeneous distribution of Mo oxide species is attained by an equilibrium adsorption technique. However, it was revealed that the surface area of the catalyst and Mo distribution were considerably modified by preparation parameters, such as drying processes, other than the surface area.     

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 2. Volume of an impregnation solution

Ten types of 13 wt% MoO₃/Al₂O₃ catalysts were prepared by a conventional impregnation or equilibrium adsorption method using a common extrudate support. These catalysts were subjected to a comprehensive characterization and catalytic reactions to find important preparation parameters in practical preparations. It was demonstrated in the present group study that the formation of crystalline MoO₃ was strongly correlated with the Mo segregation on the outer surface of the extrudate. When the amount of the impregnation solution was large (ca. 10 cm³ g-Al₂O₃⁻¹), a considerably homogeneous distribution and high dispersion of Mo oxide species were attained irrespective of the other preparation parameters. It is suggested that when a pore volume impregnation or incipient wetness technique is employed, drying processes strongly affect the dispersion and distribution of Mo oxide species. Drying at a reduced pressure is suggested to result in a segregation of Mo oxides on the outer surface of the extrudate, and accordingly a formation of crystalline MoO₃.     

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 4. Preparation parameters and impact index

The effects of the volume and pH of the impregnation solution and of the calcination conditions were examined on the physicochemical and catalytic properties of a 13 wt% MoO₃/Al₂O₃ extrudate catalyst. The Al₂O₃ support and drying procedures (static conditions without flowing air) were fixed in the preparations. In the present series of catalysts, the amount of crystalline MoO₃ was marginally small. It was found that the dispersion of Mo oxide species increased as the volume of the impregnation solution increased, gradually approaching a maximum value. The increase in pH (2–8) of the impregnation solution was found to reduce the dispersion of Mo oxide species. The Mo dispersion increased slightly for the impregnation catalysts as the calcination temperature increased (673–873 K), whereas it decreased for the equilibrium adsorption catalysts. The effects of the calcination atmosphere (with or without flowing air, or with flowing humid air) were very small on the dispersion of Mo oxide species under the present preparation conditions. On the other hand, the methanol oxidation activity of MoO₃/Al₂O₃ was sensitive to the preparation parameters examined here. It was demonstrated by means of EPMA and XPS that a considerable migration of Mo took place during the calcination.

In the present study on the preparation of a 13 wt% MoO₃/Al₂O₃ catalyst, an impact index is proposed to measure the magnitude of the effects of the respective parameter(s) on the physicochemical and catalytic properties. With the Mo dispersion, the effects of the preparation parameter decreased in the order, surface area of the support >> drying process > volume of the impregnation solution > pH, calcination temperature and atmosphere. The size of the impact index for the dispersion of Mo sulfide species is 70–75% of that for the Mo oxide species. The HDS activity of the catalyst was less affected by the preparation parameters than the Mo sulfide dispersion. The preparation parameters affected the segregation of Mo on the outer surface of extrudates in a decreasing order: drying process > volume of the impregnation solution > pH, calcination conditions. It was found that the oxidation of methanol was affected most intensely by the drying procedures. The volume of the impregnation solution, calcination conditions and pH of the impregnation solution also strongly affected the oxidation activity. The impact index suggests that the sensitivity to the preparation variables of the physicochemical and catalytic properties of MoO₃/Al₂O₃ decreases in the order, methanol oxidation activity > surface Mo segregation > Mo oxide dispersion > Mo sulfide dispersion > HDS activity.     

Structure–reactivity relationships in supported VOx catalysts for the oxyhydrative scission (OHS) of 1-butene and n-butane to acetic acid: A comprehensive catalytic and in situ study

A pure and an antimony-modified VO_x/TiO₂ catalyst have been catalytically tested in a total pressure range of 1–17 bar and studied by in situ FTIR, in situ UV/vis and operando-EPR spectroscopy at normal pressure in the oxyhydrative scission (OHS) of 1-butene and n-butane to acetic acid (AA). While 1-butene OHS follows the sequence butene → butoxide → ketone → acetate/AA with a multitude of trace side products also formed, n-butane OHS leads to AA, CO_x and H₂O only. Adding water to the feed improves AA selectivity by favouring the hydrolysis of the ketone intermediate. Doping by Sb was found to improve AA selectivity being due, among other reasons, to deeper V reduction under steady-state conditions. Activity in n-butane OHS decreases continuously with rising total pressure while both activity and selectivity in 1-butene OHS pass a maximum at 7 bar.     

Selective oxidation of aromatic compounds on zeolites using N2O as a mild oxidant: A new approach to design active sites

Dehydroxylated ZSM-5 type zeolites are used for selective oxidation of aromatic compounds, including benzene, chlorobenzene, styrene, difluorobenzenes, phenol, alkylbenzenes into corresponding phenols and diphenols using nitrous oxide as a mild oxidant. In the case of benzene, the yield of phenol reaches 70–80%. Extremely high selectivity (98–100%) in the case of benzene and 85% in the case of difluorobenzenes and high regioselectivities are observed on the dehydroxylated HZSM-5 zeolite. The active sites are shown to be the strong Lewis acid–base pair sites formed upon dehydroxylation of the zeolites. The reaction mechanism that is alternative to the proposed iron-mediated mechanism is discussed.     

A chemometric approach to understanding the bioelimination of anionic,water‐soluble dyes by a biomass—Part 3: Direct dyes**

Using a new, rapid and robust laboratory method for assessing the bioelimination of water‐soluble dyes, the level of bioelimination of a series of direct dyes has been determined and a chemometric analysis has been conducted on the bioelimination results to correlate bioelimination with chemical structure. Bioelimination varies from 0 to 95% and correlates, for the majority of the direct dyes studied, with their size/charge ratio. The bioelimination of direct dyes is enhanced by large size/charge ratios, the presence of aromatic amino functions and extended azo (naphthalene) chromophores.     

A chemometric approach to understanding the bioelimination of anionic,water‐soluble dyes by a biomass ‐ Part 4: Reactive dyes**

The bioelimination of a series of hydrolysed reactive dyes of known chemical structure has been determined using a new, rapid and robust laboratory method and a chemometric analysis conducted on the bioelimination results. The level of bioelimination varies from 0% up to only 25% and the chemometric analysis indicates that if either the number of aromatic rings increases or the number of 2‐hydroxyethylsulphone groups decreases, then the bioelimination increases. To maximise the bioelimination of reactive dyes, large, planar triazine‐based dyes should be used.     

Effects of functionalization conditions of sulfonic acid grafted SBA-15 on catalytic activity in the esterification of glycerol to monoglyceride: a factorial design approach

A series of propyl sulfonic acid-modified SBA-15 catalysts (SBA-15SO₃H) was prepared under various conditions using post-functionalization approach. A factorial design coupled with response surface analysis were employed to evaluate the effects of the preparation conditions on the catalyst activity. Optimization of the conditions to find the most active SBA-15SO₃H catalyst with the highest activity in glycerol esterification with lauric acid at 160?°C for 6?h was also made. Amount of 3-(mercaptopropyl)trimethoxysilane (MPTMS) and reflux time were chosen as parameters of the preparation conditions. The presence of propyl sulfonic acid groups in SBA-15SO₃H catalysts was confirmed by FT-TIR method. The catalysts were also characterized by means of surface analysis, XRD, TEM and TGA. The results obtained from the statistical models suggested that the amount of MPTMS was more important parameter to influence the activity compared to the reflux time. The optimum preparation condition was achieved at a reflux time of 20?h and an MPTMS amount of 1?mL/gram SBA-15 to obtain the SBA-15SO₃H(1) with the highest monoglyceride selectivity (70.2%) and corresponding lauric acid conversion (95%) in the esterification process.     

Anodic oxidation of Co(II) complexes with amines on a rotating Au electrode: Ligand effects in relation to the application for autocatalytic metal deposition

For the comparison of the electrochemical activity of Co(II)-amine complexes, the electrochemical response of an Au rotating disk electrode in alkaline Co(II)-glycine solutions to six amines: ethylenediamine (en), propane-1,2-diamine (pn-1,2), propane-1,3-diamine (pn-1,3), cyclohexane-1,2-diamine (chn), butane-1,4-diamine (bn), diethylenetriamine (dien), was studied. Addition of amines tested (except for bn) in mM levels shifts the open-circuit potential to more negative values by up to 0.5 V and enhances dramatically the anodic Co(II) oxidation current, as a result of Co(II) complex transformation into more stable and electrochemically active Co(II)-amine species. The effect of amines on the open-circuit potential changes in the line: dien ∼ en > pn-1,2 ∼ chn > pn-1,3 ? bn, and on the anodic current in the sequence: dien ∼ en > pn-1,2 > chn > pn-1,3 ? bn. The procedure described helps to select ligands for Co(II) complexes used as reducing agents in electroless plating solutions. The amines of high electrochemical response: dien, en, pn-1,2, and possibly, chn, are suitable for electroless copper deposition, pn-1,3 (a lower response), for electroless silver deposition, and bn (no response), not suitable for electroless plating solutions.     

Propylene polymerization over MgCl2‐supported TiCl4 catalysts bearing different amounts of a diether internal electron donor: Extrapolation to the role of internal electron donor on active site

In this work, the composition of MgCl₂‐supported Ziegler‐Natta (ZN) catalysts bearing different amounts of 9,9‐bis(methoxymethyl)fluorine (BMMF) and the propylene polymerization over these catalysts are investigated. Based on the experimental results, the models of active sites suitable for ZN catalysts with/without internal donor BMMF are established, and they can be described as follows: atactic site (I)—isolated TiCl₄ monomeric species on the (110) lateral cut (around which there is no complexes), weakly isospecific site (II)—semi‐isolated and surrounded TiCl₄ monomeric species on the (110) lateral cut (in the vicinity of which BMMF or other TiCl₄ is adsorbed), and highly isospecific site (III)—dimeric TiCl₄ species (Ti₂Cl₈) on the (104) lateral cut. Meanwhile, the mechanism underlying the role of BMMF on active sites is revealed (i) convert atactic sites (I) to weakly isospecific site (II) by occupying either or both of L₁ or/and L₂ vacancies around site; (ii) improve the isotacticity of weakly isospecific site (II) in donor‐free ZN catalyst by adsorbing at L₂ vacancy or/and replacing the Cl for TiCl₄ at L₁; and (iii) replace highly isospecific site (III). In addition, these roles of BMMF are successively achieved according to the amount of BMMF added. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A systematic approach to the study of multicomponent polymerization kinetics: butyl acrylate/methyl methacrylate/vinyl acetate. III. Emulsion homopolymerization and copolymerization in a pilot plant reactor

A systematic study of the terpolymerization of butyl acrylate/methyl methacrylate/vinyl acetate (BA/MMA/VAc) is being conducted. In this third stage of the study,

1 Parts 1 and 2: Dubé, M. A. & Penlidis, A., Polymer, 36 (1995) 587. Dubé, M. A. & Penlidis, A., Macromol. Chem. Phys., 196 (1995) 1101.

emulsion homopolymerizations and copolymerizations of the monomers comprising the BA/MMA/VAc system were performed in a 5 litre stainless steel pilot plant reactor, mainly for troubleshooting purposes and as a precursor to the detailed terpolymerization experiments to follow. First, a search for a stable emulsion recipe was conducted. At the same time, experimental procedures were established for the 5 litre pilot plant reactor along with product characterization techniques. Finally, selective emulsion homopolymerizations and copolymerizations were run for each of the three monomers and each combination of the three monomers, respectively. The polymers produced were characterized for conversion, composition, molecular weight and particle size. Although the emphasis of the experiments was to establish recipes, techniques, and procedures for emulsions terpolymerization, several useful observations were made regarding the kinetics even from these troubleshooting experiments.