Heterogenisation of selective ethylene tetramerisation catalysts.

Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.The aim of the study was to heterogenise existing tetramerisation catalysts by supporting the bis(diphenylphosphino)amine ligands on polymer. The polymer of choice was Merrifield’s resin which was functionalized to enable attachment of the ligands. These supported ligands were characterized via ATR, solid-state NMR, SEM and TGA-DSC. In order to compare activity of the supported and unsupported ligands, homogeneous bis(diphenylphosphino)amine ligands were synthesized and characterized via NMR, elemental Analysis, ATR and GC-MS. Tetramerisation reactions were carried out in a Parr pressure reactor using Cr(acac)₃as the precursor and MMAO-3A as the activator. The homogeneous ligands proved active in the tetramerisation of ethylene, with the selectivity of 1-octene in the C8 fraction being comparable with that mentioned in literature (> 98 wt%). When comparing the homogeneous ligands with their heterogeneous counterparts, the heterogeneous ligands performed poorly due to steric effects caused by the polymer chain. The activity dropped by more than four times that of their homogeneous counterparts and the selectivity towards the main product, 1-octene, was very low (< 10 wt%). These ligands seemed to create a system that favoured the formation of the C6 products more than any other product, with the C6 cyclics being the most dominant

Synthesis and characterization of amine-functionalized supported phosphine catalysts and their application in ethylene oligomerization

A series of phosphorus and nitrogen-based ethylene oligomerization ligands of the type Ph2PN(X)PPh2 where X = i-propyl, n-butyl, ethylbenzene and&nbsp; cyclohexyl substituents are reported. These ligands were functionalized to enable tethering on amino-silica. The free ligands, amino-silica and the&nbsp; tethered ligands were characterized by BET, XRD, IR, TGA and NMR. The catalysts were tested for ethylene oligomerization using Cr(acac)3 (acac =&nbsp; acetylacetonate) as the precursor and MMAO (modified methylaluminoxane) as the activator. The activity and selectivity of these catalysts to 1-octene was&nbsp; monitored at 45 bar ethylene in the temperature range of 45–100 °C. The activity of the supported catalysts was comparable to their homogeneous&nbsp; counterparts, surpassing them in some cases and selectivities to 1-octene in the C8 products were as high as 99 wt%. The steric effect of the substituent&nbsp; on the ligand as well as that of the support was found to influence the activity and product distribution

Ethylene Trimerization over Supported SNS and PNP Chromium Catalysts

Chromium(III) complexes with sulphur, nitrogen and phosphorus tridentate ligands were synthesized and characterized. These complexes were&nbsp; supported on SiO2 and characterized by BET surface area measurements, XRF, SEM-EDX and FTIR. The complexes were tested for activity and selectivity in&nbsp; the trimerization of ethylene. The substituent’s effect and influence on the sulphur on the supported catalysts were studied using the ethyl and the&nbsp; decyl substituted catalysts. The influence of temperature on catalytic performance was evaluated using the PPP supported system. The most active&nbsp; supported catalyst, the decyl substituted SNS catalyst, showed good activity of up to 19 500 g/g Cr h–1 and selectivity of 97.3 % to C6 products (98.2 %&nbsp; 1-hexene). This activity and selectivity were comparable to the homogeneous counterpart’s performance that achieved 22 000 g/g Cr h–1 and 98.2 % C6&nbsp; products (96.7 % 1-hexene), which surpassed the ethyl substituted catalyst, which was not supported, under the same reaction conditions. The supported&nbsp; PPP catalyst activities showed it was sensitive to higher temperatures, but this depends on the supporting technique

Mathematical investigations of a kinetic model for glycerol hydrogenolysis via heterogeneous catalysis

In this paper we report on some mathematical investigations of the chemical process for the hydrogenolysis of glycerol over a heterogeneous metal catalyst. The main interest of this process is related to the fact that glycerol is produced as a by-product in the production of biodiesel in huge amounts that are expected to exceed the projected demands. This makes the sustainability of biodiesel production depend on the conversion of the glycerol into useful products hence it is a desirable goal to have effective conversion methods. A reaction model from literature is used to derive a system of ordinary differential equations (ODE) which is then analysed using methods from qualitative analysis of ODEs. Numerical solutions of the system are simulated to try and find out the solution’s behaviour in the chemistry point of view. It was found that all solutions of the model converge to some stable limit point in a 2-dimensional plane in the positive cone of the R5 phase space, and the limit point depends on the values of rate constants ki as well as on the hydrogen to glycerol initial ratios. Even though the results are based on a specific kinetic model, it is hoped that they may help in providing tools for better understanding and description of the reaction.The authors acknowledge the African Institute for Mathematical Sciences (AIMS)-ZA and The MasterCard foundation for funding this work. FPdC was partially supported by FCT/Portugal through CAMGSD, IST-ID , projects UIDB/04459/2020 and UIDP/04459/2020.info:eu-repo/semantics/publishedVersio

Oxidation of styrene to benzaldehyde and styrene oxide over nickel and copper ceria solution combustion catalysts

CeO2, Cu0.05Ce0.95O2-δ, Ni0.04Ce0.96O2-δ, Cu0.05Ni0.05Ce0.90O2-δ, catalysts were synthesised via solution combustion technique using urea as a fuel. The as pre-preared catalysts were characterised via X-ray powder diffraction, Brunauer-Emmett-Teller surface area analysis, transmission and scanning electron microscopy analysis. The characterisation techniques strongly suggested that all the catalysts were prepared successfully, and that copper and nickel were successfully incorporated into the lattice structure of ceria. The effect of the reaction conditions on the catalytic properties of the synthesised material were studied in detail using Cu0.05Ni0.05Ce0.90O2-δ as the model catalyst. The effect of temperature, solvents and co-oxidants was investigated in optimisation studies. A combination of acetonitrile, tert-butyl hydroperoxide and a temperature of 60 °C were found to be optimal after 24 hours and used for all catalysts. All catalysts were found to be active in styrene oxidation under these conditions, with styrene conversion as high as 69% over Ni0.04Ce0.96O2-δ, and selectivity to benzaldehyde and styrene oxide 38 and 26% respectively

Hydrogenolysis of glycerol to monoalcohols over supported Mo and W Catalysts

MoO3 and WO3 were supported on γ-Al2O3 and SiO2 with nominal loadings of 10 wt % via wet impregnation. The catalysts were characterized using XRD, TPR, Pulse TPD, Raman, TEM, and BET surface area. The alumina supported catalysts were found to contain higher Brønsted acidity compared to those supported on silica. These catalysts were evaluated in the hydrogenolysis of glycerol in a continuous flow fixed bed reactor in a temperature range of 250–325 °C and a H2 pressure of 60 bar. All catalysts were active, with activity increasing with temperature as well as Brønsted acidity. The selectivity to ethylene glycol and 1,2-propanediol decreased with increase in temperature. In parallel, the selectivity to lower alcohols such as methanol, ethanol, 2-propanol, and 1-propanol increased with temperature as the ethylene glycol and 1,2-propanediol reacted further to these products due to C–C bond cleavage. The total selectivity to lower alcohols was 34.6, 64.8, 70.6, and 54.6% over Mo/Al2O3, Mo/SiO2, W/Al2O3, and W/SiO2 respectively. The total selectivity to lower alcohols increased to 73.6, 72.8, 85.3, and 66.1% over Mo/Al2O3, Mo/SiO2, W/Al2O3, and W/SiO2 respectively when the H2:glycerol ratio was doubled

Catalysis for fuels: general discussion

SCI(E)EDITORIAL MATERIAL165-20519

Theory as a driving force to understand reactions on nanoparticles: general discussion

International audienc

Gas-Phase Oxidative Dehydrogenation of <i>n</i>-Octane over Metal Oxide Catalysts: A Review

The oxidative dehydrogenation (ODH) of alkanes, whereby hydrogen is removed to form unsaturated compounds, is an important process, particularly in the petrochemical industry. The ODH of lighter alkanes (C3–C6) is well-reported in the literature, and while there are several reports on the ODH of n-octane (C8), there is no reported review of the important findings in the literature. This review discusses the gas-phase ODH of n-octane occurring at high temperatures (300–550 °C). The mechanisms via which the n-octane ODH of occurs are also briefly discussed. The oxidants (mainly O2 and CO2) and catalysts (supported and unsupported metal oxides) are discussed as well as the effect of these and the temperature on the type of products formed and their various distributions. Furthermore, the review looks at the acid–base and redox properties of the catalysts and how they affect product formation. Some challenges as well as perspectives of the ODH process are also highlighted