Since their discovery in 2004, carbon dots (CDs), with particle sizes < 10 nm, have found use ... more Since their discovery in 2004, carbon dots (CDs), with particle sizes < 10 nm, have found use in various applications, mainly based on the material’s fluorescent properties. However, other potential uses of CDs remain relatively unexplored when compared to other carbon-based nanomaterials. In particular, the use of CDs as catalysts and as supports for use in catalytic reactions, is still in its infancy. Many studies have indicated the advantages of using CDs in catalysis, but there are difficulties associated with their stability, separation, and aggregation due to their small size. This small size does however allow for studying the interaction of small catalyst particles with small dimensional supports, including the inverse support interaction. However, recent studies have indicated that CDs are not stable under high temperature conditions (especially >250 °C; with and without a catalyst) suggesting that the CDs may agglomerate and transform under some reaction conditions. ...
Herein, the influence of the counter anion on the structural properties of hollow carbon spheres ... more Herein, the influence of the counter anion on the structural properties of hollow carbon spheres (HCS) support was investigated by varying the nickel metal precursor salts applied. TEM and SEM micrographs revealed the dimensional dependence of the HCS shell on the Ni precursor salt, as evidenced by thick (~42 nm) and thin (~23 nm) shells for the acetate and chloride-based salts, respectively. Importantly, the effect of the precursor salt on the textural properties of the HCS nanosupports (~565 m2/gNi(acet)) and ~607 m2/gNiCl), influenced the growth of the Ni nanoparticles, viz for the acetate-(ca 6.4 nm)- and chloride (ca 12 nm)-based salts, respectively. Further, XRD and PDF analysis showed the dependence of the reduction mechanism relating to nickel and the interaction of the nickel–carbon support on the type of counter anion used. Despite the well-known significance of the counter anion on the size and crystallinity of Ni nanoparticles, little is known about the influence of such...
Editorial on the Research Topic 15 years of the Federation of African Societies of Chemistry (FAS... more Editorial on the Research Topic 15 years of the Federation of African Societies of Chemistry (FASC) This Research Topic of Frontiers in Chemistry is produced to celebrate the 15th anniversary of the Federation of African Societies of Chemistry (FASC). Established on the 23rd of February 2006, FASC was set up to promote the advancement of chemical sciences and the practice of chemistry that could be instrumental to the fulfillment of the development aspiration and objective of the people in Africa. In order to achieve the above aim, FASC set up the following objectives:
2D layered carbon nanostructures made by annealing 0D carbon dots, have been used as ethanol/meth... more 2D layered carbon nanostructures made by annealing 0D carbon dots, have been used as ethanol/methanol sensors.
Liquid insulation is used in high voltage equipment such as power transformers as both dielectric... more Liquid insulation is used in high voltage equipment such as power transformers as both dielectric medium and coolant. Breakdown in liquid insulation tends to be governed either by streamer initiation under more uniform fields, or by streamer propagation under more non-uniform fields. A model streamer propagation study, which screens the effectiveness of additives based on cyclohexane and mixtures with diethylaniline (DEA) and toluene, is presented in this paper. The effect of additives, at different concentrations, on streamer propagation velocity in cyclohexane under an applied lightning impulse voltage of positive polarity is studied. Cyclohexane (ionisation potential 9.88 eV) was chosen because, being a hydrocarbon, it shares similarities with the constituents of common insulating liquids. Previous studies have also shown how, in general, the addition of additives of lower ionization potential than the bulk liquid can slow down streamer propagation in insulating liquids. A point-...
Nanocomposites are new generation electrical insulation made up of nano-fillers mixed in a host i... more Nanocomposites are new generation electrical insulation made up of nano-fillers mixed in a host insulation matrix. Such insulation technology has a potential for tailor engineering the properties to desired specifications. This paper presents a review of the nanocomposites insulation technology followed by an account of the experimental method and results of a methodology used in synthesising mesoporous hollow carbon nano-sphere (MHCNs) fillers. The obtained nanoparticles are characterised using SEM, TEM, Raman spectra, Banauer Emmett-Teller (BET), and thermogravimetric analysis techniques. The MHCNs have a diameter of $383 \pm 14\ \text{nm}$ and BET surface area of 341.5 m2/g. In the ongoing research, the synthesized MHCNs are then used as fillers to fabricate a C\Epoxy nanocomposite.
The effect of cobalt precursor (nitrate, acetate and chloride salts) on the catalyst reducibility... more The effect of cobalt precursor (nitrate, acetate and chloride salts) on the catalyst reducibility and dispersion, as well as the catalytic activity of the Fischer-Tropsch (FT) synthesis, of boron-modified titania-supported cobalt catalysts (0.1%B/10%Co/TiO 2) has been investigated. FT studies were performed on both calcined and uncalcined catalysts prepared from the three cobalt sources. The uncalcined nitrate catalyst showed a higher activity for FT synthesis compared to the uncalcined acetate and chloride catalysts. For the calcined catalysts, the acetate and nitrate catalysts exhibited higher FT activity. The low activity associated with the chloride catalyst related to poisoning by residual chloride ions. Calcination was found to enhance the extent of cobalt bulk reduction and FT activity for all three of the catalysts. The FT reaction rate increased with increasing percentage cobalt dispersion while the turnover frequency (TOF) was found be near independent of cobalt source.
The addition of sulfide ions (500 — 20000 ppm) to iron/carbonate solutions over a range of pH val... more The addition of sulfide ions (500 — 20000 ppm) to iron/carbonate solutions over a range of pH values generates iron hydroxo precipitates containingS2– These materials show different physical parameters (pore characteristics, colour and particle size) as well as catalytic properties. Chemical speciation studies using M1NTEQA2 reveal that the pH and sulfide concentrations influence the type and amount of the solution
... 20%) in the amount of cobalt species dispersed on the titania support was observed when cobal... more ... 20%) in the amount of cobalt species dispersed on the titania support was observed when cobalt acetate precursor salts were used in the catalyst preparation instead of cobalt nitrate salts ( Table 1 ). Similar results were obtained by Kraum and Baerns [5] . The use of cobalt ...
Abstract A series of Co/B/TiO2 ( B = ammonium borate , boric acid, o-carborane, 0.01–1.5 wt.% B) ... more Abstract A series of Co/B/TiO2 ( B = ammonium borate , boric acid, o-carborane, 0.01–1.5 wt.% B) catalysts were synthesized. The addition of boron decreased the reducibility of the Co as determined from temperature-programmed reduction studies and H2 reduction/O2back titration studies. This in turn decreased the FT activity but not the turnover frequency of the Co catalyst.
A range of 5% Fe/5% Co bimetallic catalysts supported on TiO 2 was promoted with 0.1%, 0.5% and 1... more A range of 5% Fe/5% Co bimetallic catalysts supported on TiO 2 was promoted with 0.1%, 0.5% and 1.0% potassium, chromium and manganese respectively, and their physical properties and Fischer-Tropsch (FT) CO hydrogenation capabilities were evaluated. Low level promotion (0.1% and 0.5%) by K and Cr modestly improved the activity, decreased the selectivity to methane and increased the +C 5 fraction of the FT product while the Mn promoted catalysts retarded activity and reduced selectivity.
A series of novel sulfur-containing precipitated-iron catalysts were prepared by the addition of ... more A series of novel sulfur-containing precipitated-iron catalysts were prepared by the addition of 2000-20000 ppm sulfur (Na2S, (NH4)2S, (NH4)2S 5) to iron, during the precipitation reaction. XPS characterization of the highly sulfided catalyst (20000 ppm) after calcination at 200°C and 400°(2 did not reveal the presence of surface sulfur (160-170 eV region). However, low temperature calcination (200°C) followed by reduction (300°C) revealed surface S 2-(162.3 eV), while high temperature calcination (400°C) gave rise to SO~-(169.4 eV) species. Use of a higher reduction temperature (400°C) increased the surface sulfide concentration to 15.6 at% S 2-as compared to 1.3 at% after reduction at 300°C. At lower S loadings (2000, 5000 ppm) only sulfate species were observed under analogous conditions. The addition of polysulfide ((NH4)2S 5) instead of S 2-, resulted in the formation of a surface polysulfide and SO42-surface species. A mechanism for the surface segregation of sulfur after reduction in terms of site competition with oxygen is consistent with the data.
A pilot plant Fischer-Tropsch synthesis reaction was performed in a fixed bed reactor containing ... more A pilot plant Fischer-Tropsch synthesis reaction was performed in a fixed bed reactor containing a precipitated iron catalyst. Sections were taken from the reactor and tested for Fischer-Tropsch activity in micro reactors. The catalyst sections were subjected to SEM, SIMS and XRD analysis and revealed catalyst deactivation due to (i) sulphur poisoning in the top portion of the reactor bed and (ii) magnetite formation and crystallite growth in the bottom portion of the reactor bed.
A new range of sulfided iron catalysts has been synthesised by adding small amounts of Na 2 S (50... more A new range of sulfided iron catalysts has been synthesised by adding small amounts of Na 2 S (500-20 000 ppm) to precipitated iron. The new materials, after calcination (400 • C, 16 h) and reduction (400 • C, 16 h), were subjected to syngas (2 : 1 H 2 : CO) at 250 • C at 8 bar pressure for up to 8 days. Catalysts with low sulfide concentrations were up to four times more active in the Fischer-Tropsch reaction than a sulfur-free catalyst, while catalysts with high sulfide loadings were apparently poisoned. Increased olefin/paraffin ratios were also obtained at the low sulfide loadings. The new sulfided materials were studied by a combination of BET, DRIFTS, XRD, TPR and SEM and the results indicate that the surface area and reducibility of the iron catalyst are affected by the presence of S 2− ions and that SO 2− 4 acts as a promoter in the Fischer-Tropsch reaction.
TiO 2 was treated with boron (0.05, 0.1%; boric acid source) to give B/TiO 2. Co(NO 3) 2 •6H 2 O ... more TiO 2 was treated with boron (0.05, 0.1%; boric acid source) to give B/TiO 2. Co(NO 3) 2 •6H 2 O (10% Co) was then added to both TiO 2 and B/TiO 2 (incipient wetness) and the materials were then sulfided with 100, 200 and 500 ppm (NH 4) 2 S. The sulfided Co/TiO 2 catalysts with and without boron were characterised by TPR and O 2 titration and evaluated for Fischer-Tropsch synthesis. Low-level sulfur addition (100, 200 ppm S) did not significantly influence the activity and selectivity of the catalysts. The addition of a higher-level loading of sulfur (500 ppm S) resulted in severe sulfur poisoning of catalysts (80% decrease in reaction rate), but the modification of Co/TiO 2 by boron retarded this poisoning (35% decrease in reaction rate). A shift in the product distribution to light molecular weight hydrocarbons (α = 0.32) was observed for the 500 ppm S loaded catalyst (no boron addition) while boron addition retarded this shift (α = 0.47). The effect of boron on the sulfur poisoning resistance of the Co/TiO 2 catalysts is discussed.
... 19]. Zinc also plays a role as a promoter on catalysts used in the hydrodesulfurisation react... more ... 19]. Zinc also plays a role as a promoter on catalysts used in the hydrodesulfurisation reaction [20], [21] and [22]. In earlier studies we reported on the use of Co/Zn/TiO 2 catalysts in the FT reaction [25], [26], [27] and [28]. In the ...
The sol-gel method was used to prepare Co(10 wt%)/Zn(x)/TiO 2 (x = 0, 1, 5 and 10 wt%) catalysts.... more The sol-gel method was used to prepare Co(10 wt%)/Zn(x)/TiO 2 (x = 0, 1, 5 and 10 wt%) catalysts. Two methods were used to gel the catalyst precursors (Co, Zn, TiO 2): (i) co-gelling all the components and (ii) gelling the titania support alone followed by the impregnation of zinc and cobalt precursors. The catalysts prepared by co-gelling all the catalysts components together were tested for Fischer-Tropsch (FT) activity and <5% conversion was obtained using standard FT conditions. This finding correlates with the strong interaction between the support and the Co, even in the presence of zinc. Impregnation of the sol-gel prepared titania support with zinc and cobalt precursors resulted in different degrees of interaction between the support and cobalt catalysts (due to the presence of zinc) as determined from TPR and XPS measurements. However, the modified sol-gel prepared catalysts also showed low activity towards Fischer-Tropsch (FT) when compared to the catalysts prepared using Degussa titania as support.
A series of Co/Zn/TiO 2 catalysts have been synthesized and their Fischer-Tropsch (FT) activity s... more A series of Co/Zn/TiO 2 catalysts have been synthesized and their Fischer-Tropsch (FT) activity studied. The effect of changing the sequence of impregnating zinc (5%) and cobalt (10%) onto the titania support as well as the effect of calcination of the catalyst in-between the impregnation steps have generated a range of new catalysts. Results obtained from XPS, AES and chemisorption (with hydrogen) techniques suggest that a 'sandwich' layer of zinc is formed in-between the cobalt and the titania even when the zinc was impregnated after the cobalt. The study reveals that Zn forms agglomerates on the TiO 2 surface and that the Co sits on top of the non-crystalline Zn particles. The presence of zinc was found to have both beneficial as well as detrimental effects on Fischer-Tropsch activity that was determined by the amount of Zn added and the preparation procedures used to make the Co/Zn/TiO 2 catalysts. Zinc was found to increase the dispersion of cobalt, but uncovered zinc particles were found to be active under the FT synthesis conditions forming mostly methane.
Self-condensation of propanol was carried out at atmospheric pressure over MgO as catalyst. The r... more Self-condensation of propanol was carried out at atmospheric pressure over MgO as catalyst. The reaction gave 2-methylpentanol and propionaldehyde as the major products. The introduction of hydrogen before and during the reaction enhanced the catalyst selectivity to 2methylpentanol. The effect of possible reaction intermediates on the catalyst selectivity and the mechanism of the reaction were investigated over MgO and indicated the important role of hydrogen transfer in the reaction. The highest selectivity (69%) was achieved in the presence of hydrogen at 450 8C with propanol conversion of 24%.
Since their discovery in 2004, carbon dots (CDs), with particle sizes < 10 nm, have found use ... more Since their discovery in 2004, carbon dots (CDs), with particle sizes < 10 nm, have found use in various applications, mainly based on the material’s fluorescent properties. However, other potential uses of CDs remain relatively unexplored when compared to other carbon-based nanomaterials. In particular, the use of CDs as catalysts and as supports for use in catalytic reactions, is still in its infancy. Many studies have indicated the advantages of using CDs in catalysis, but there are difficulties associated with their stability, separation, and aggregation due to their small size. This small size does however allow for studying the interaction of small catalyst particles with small dimensional supports, including the inverse support interaction. However, recent studies have indicated that CDs are not stable under high temperature conditions (especially >250 °C; with and without a catalyst) suggesting that the CDs may agglomerate and transform under some reaction conditions. ...
Herein, the influence of the counter anion on the structural properties of hollow carbon spheres ... more Herein, the influence of the counter anion on the structural properties of hollow carbon spheres (HCS) support was investigated by varying the nickel metal precursor salts applied. TEM and SEM micrographs revealed the dimensional dependence of the HCS shell on the Ni precursor salt, as evidenced by thick (~42 nm) and thin (~23 nm) shells for the acetate and chloride-based salts, respectively. Importantly, the effect of the precursor salt on the textural properties of the HCS nanosupports (~565 m2/gNi(acet)) and ~607 m2/gNiCl), influenced the growth of the Ni nanoparticles, viz for the acetate-(ca 6.4 nm)- and chloride (ca 12 nm)-based salts, respectively. Further, XRD and PDF analysis showed the dependence of the reduction mechanism relating to nickel and the interaction of the nickel–carbon support on the type of counter anion used. Despite the well-known significance of the counter anion on the size and crystallinity of Ni nanoparticles, little is known about the influence of such...
Editorial on the Research Topic 15 years of the Federation of African Societies of Chemistry (FAS... more Editorial on the Research Topic 15 years of the Federation of African Societies of Chemistry (FASC) This Research Topic of Frontiers in Chemistry is produced to celebrate the 15th anniversary of the Federation of African Societies of Chemistry (FASC). Established on the 23rd of February 2006, FASC was set up to promote the advancement of chemical sciences and the practice of chemistry that could be instrumental to the fulfillment of the development aspiration and objective of the people in Africa. In order to achieve the above aim, FASC set up the following objectives:
2D layered carbon nanostructures made by annealing 0D carbon dots, have been used as ethanol/meth... more 2D layered carbon nanostructures made by annealing 0D carbon dots, have been used as ethanol/methanol sensors.
Liquid insulation is used in high voltage equipment such as power transformers as both dielectric... more Liquid insulation is used in high voltage equipment such as power transformers as both dielectric medium and coolant. Breakdown in liquid insulation tends to be governed either by streamer initiation under more uniform fields, or by streamer propagation under more non-uniform fields. A model streamer propagation study, which screens the effectiveness of additives based on cyclohexane and mixtures with diethylaniline (DEA) and toluene, is presented in this paper. The effect of additives, at different concentrations, on streamer propagation velocity in cyclohexane under an applied lightning impulse voltage of positive polarity is studied. Cyclohexane (ionisation potential 9.88 eV) was chosen because, being a hydrocarbon, it shares similarities with the constituents of common insulating liquids. Previous studies have also shown how, in general, the addition of additives of lower ionization potential than the bulk liquid can slow down streamer propagation in insulating liquids. A point-...
Nanocomposites are new generation electrical insulation made up of nano-fillers mixed in a host i... more Nanocomposites are new generation electrical insulation made up of nano-fillers mixed in a host insulation matrix. Such insulation technology has a potential for tailor engineering the properties to desired specifications. This paper presents a review of the nanocomposites insulation technology followed by an account of the experimental method and results of a methodology used in synthesising mesoporous hollow carbon nano-sphere (MHCNs) fillers. The obtained nanoparticles are characterised using SEM, TEM, Raman spectra, Banauer Emmett-Teller (BET), and thermogravimetric analysis techniques. The MHCNs have a diameter of $383 \pm 14\ \text{nm}$ and BET surface area of 341.5 m2/g. In the ongoing research, the synthesized MHCNs are then used as fillers to fabricate a C\Epoxy nanocomposite.
The effect of cobalt precursor (nitrate, acetate and chloride salts) on the catalyst reducibility... more The effect of cobalt precursor (nitrate, acetate and chloride salts) on the catalyst reducibility and dispersion, as well as the catalytic activity of the Fischer-Tropsch (FT) synthesis, of boron-modified titania-supported cobalt catalysts (0.1%B/10%Co/TiO 2) has been investigated. FT studies were performed on both calcined and uncalcined catalysts prepared from the three cobalt sources. The uncalcined nitrate catalyst showed a higher activity for FT synthesis compared to the uncalcined acetate and chloride catalysts. For the calcined catalysts, the acetate and nitrate catalysts exhibited higher FT activity. The low activity associated with the chloride catalyst related to poisoning by residual chloride ions. Calcination was found to enhance the extent of cobalt bulk reduction and FT activity for all three of the catalysts. The FT reaction rate increased with increasing percentage cobalt dispersion while the turnover frequency (TOF) was found be near independent of cobalt source.
The addition of sulfide ions (500 — 20000 ppm) to iron/carbonate solutions over a range of pH val... more The addition of sulfide ions (500 — 20000 ppm) to iron/carbonate solutions over a range of pH values generates iron hydroxo precipitates containingS2– These materials show different physical parameters (pore characteristics, colour and particle size) as well as catalytic properties. Chemical speciation studies using M1NTEQA2 reveal that the pH and sulfide concentrations influence the type and amount of the solution
... 20%) in the amount of cobalt species dispersed on the titania support was observed when cobal... more ... 20%) in the amount of cobalt species dispersed on the titania support was observed when cobalt acetate precursor salts were used in the catalyst preparation instead of cobalt nitrate salts ( Table 1 ). Similar results were obtained by Kraum and Baerns [5] . The use of cobalt ...
Abstract A series of Co/B/TiO2 ( B = ammonium borate , boric acid, o-carborane, 0.01–1.5 wt.% B) ... more Abstract A series of Co/B/TiO2 ( B = ammonium borate , boric acid, o-carborane, 0.01–1.5 wt.% B) catalysts were synthesized. The addition of boron decreased the reducibility of the Co as determined from temperature-programmed reduction studies and H2 reduction/O2back titration studies. This in turn decreased the FT activity but not the turnover frequency of the Co catalyst.
A range of 5% Fe/5% Co bimetallic catalysts supported on TiO 2 was promoted with 0.1%, 0.5% and 1... more A range of 5% Fe/5% Co bimetallic catalysts supported on TiO 2 was promoted with 0.1%, 0.5% and 1.0% potassium, chromium and manganese respectively, and their physical properties and Fischer-Tropsch (FT) CO hydrogenation capabilities were evaluated. Low level promotion (0.1% and 0.5%) by K and Cr modestly improved the activity, decreased the selectivity to methane and increased the +C 5 fraction of the FT product while the Mn promoted catalysts retarded activity and reduced selectivity.
A series of novel sulfur-containing precipitated-iron catalysts were prepared by the addition of ... more A series of novel sulfur-containing precipitated-iron catalysts were prepared by the addition of 2000-20000 ppm sulfur (Na2S, (NH4)2S, (NH4)2S 5) to iron, during the precipitation reaction. XPS characterization of the highly sulfided catalyst (20000 ppm) after calcination at 200°C and 400°(2 did not reveal the presence of surface sulfur (160-170 eV region). However, low temperature calcination (200°C) followed by reduction (300°C) revealed surface S 2-(162.3 eV), while high temperature calcination (400°C) gave rise to SO~-(169.4 eV) species. Use of a higher reduction temperature (400°C) increased the surface sulfide concentration to 15.6 at% S 2-as compared to 1.3 at% after reduction at 300°C. At lower S loadings (2000, 5000 ppm) only sulfate species were observed under analogous conditions. The addition of polysulfide ((NH4)2S 5) instead of S 2-, resulted in the formation of a surface polysulfide and SO42-surface species. A mechanism for the surface segregation of sulfur after reduction in terms of site competition with oxygen is consistent with the data.
A pilot plant Fischer-Tropsch synthesis reaction was performed in a fixed bed reactor containing ... more A pilot plant Fischer-Tropsch synthesis reaction was performed in a fixed bed reactor containing a precipitated iron catalyst. Sections were taken from the reactor and tested for Fischer-Tropsch activity in micro reactors. The catalyst sections were subjected to SEM, SIMS and XRD analysis and revealed catalyst deactivation due to (i) sulphur poisoning in the top portion of the reactor bed and (ii) magnetite formation and crystallite growth in the bottom portion of the reactor bed.
A new range of sulfided iron catalysts has been synthesised by adding small amounts of Na 2 S (50... more A new range of sulfided iron catalysts has been synthesised by adding small amounts of Na 2 S (500-20 000 ppm) to precipitated iron. The new materials, after calcination (400 • C, 16 h) and reduction (400 • C, 16 h), were subjected to syngas (2 : 1 H 2 : CO) at 250 • C at 8 bar pressure for up to 8 days. Catalysts with low sulfide concentrations were up to four times more active in the Fischer-Tropsch reaction than a sulfur-free catalyst, while catalysts with high sulfide loadings were apparently poisoned. Increased olefin/paraffin ratios were also obtained at the low sulfide loadings. The new sulfided materials were studied by a combination of BET, DRIFTS, XRD, TPR and SEM and the results indicate that the surface area and reducibility of the iron catalyst are affected by the presence of S 2− ions and that SO 2− 4 acts as a promoter in the Fischer-Tropsch reaction.
TiO 2 was treated with boron (0.05, 0.1%; boric acid source) to give B/TiO 2. Co(NO 3) 2 •6H 2 O ... more TiO 2 was treated with boron (0.05, 0.1%; boric acid source) to give B/TiO 2. Co(NO 3) 2 •6H 2 O (10% Co) was then added to both TiO 2 and B/TiO 2 (incipient wetness) and the materials were then sulfided with 100, 200 and 500 ppm (NH 4) 2 S. The sulfided Co/TiO 2 catalysts with and without boron were characterised by TPR and O 2 titration and evaluated for Fischer-Tropsch synthesis. Low-level sulfur addition (100, 200 ppm S) did not significantly influence the activity and selectivity of the catalysts. The addition of a higher-level loading of sulfur (500 ppm S) resulted in severe sulfur poisoning of catalysts (80% decrease in reaction rate), but the modification of Co/TiO 2 by boron retarded this poisoning (35% decrease in reaction rate). A shift in the product distribution to light molecular weight hydrocarbons (α = 0.32) was observed for the 500 ppm S loaded catalyst (no boron addition) while boron addition retarded this shift (α = 0.47). The effect of boron on the sulfur poisoning resistance of the Co/TiO 2 catalysts is discussed.
... 19]. Zinc also plays a role as a promoter on catalysts used in the hydrodesulfurisation react... more ... 19]. Zinc also plays a role as a promoter on catalysts used in the hydrodesulfurisation reaction [20], [21] and [22]. In earlier studies we reported on the use of Co/Zn/TiO 2 catalysts in the FT reaction [25], [26], [27] and [28]. In the ...
The sol-gel method was used to prepare Co(10 wt%)/Zn(x)/TiO 2 (x = 0, 1, 5 and 10 wt%) catalysts.... more The sol-gel method was used to prepare Co(10 wt%)/Zn(x)/TiO 2 (x = 0, 1, 5 and 10 wt%) catalysts. Two methods were used to gel the catalyst precursors (Co, Zn, TiO 2): (i) co-gelling all the components and (ii) gelling the titania support alone followed by the impregnation of zinc and cobalt precursors. The catalysts prepared by co-gelling all the catalysts components together were tested for Fischer-Tropsch (FT) activity and <5% conversion was obtained using standard FT conditions. This finding correlates with the strong interaction between the support and the Co, even in the presence of zinc. Impregnation of the sol-gel prepared titania support with zinc and cobalt precursors resulted in different degrees of interaction between the support and cobalt catalysts (due to the presence of zinc) as determined from TPR and XPS measurements. However, the modified sol-gel prepared catalysts also showed low activity towards Fischer-Tropsch (FT) when compared to the catalysts prepared using Degussa titania as support.
A series of Co/Zn/TiO 2 catalysts have been synthesized and their Fischer-Tropsch (FT) activity s... more A series of Co/Zn/TiO 2 catalysts have been synthesized and their Fischer-Tropsch (FT) activity studied. The effect of changing the sequence of impregnating zinc (5%) and cobalt (10%) onto the titania support as well as the effect of calcination of the catalyst in-between the impregnation steps have generated a range of new catalysts. Results obtained from XPS, AES and chemisorption (with hydrogen) techniques suggest that a 'sandwich' layer of zinc is formed in-between the cobalt and the titania even when the zinc was impregnated after the cobalt. The study reveals that Zn forms agglomerates on the TiO 2 surface and that the Co sits on top of the non-crystalline Zn particles. The presence of zinc was found to have both beneficial as well as detrimental effects on Fischer-Tropsch activity that was determined by the amount of Zn added and the preparation procedures used to make the Co/Zn/TiO 2 catalysts. Zinc was found to increase the dispersion of cobalt, but uncovered zinc particles were found to be active under the FT synthesis conditions forming mostly methane.
Self-condensation of propanol was carried out at atmospheric pressure over MgO as catalyst. The r... more Self-condensation of propanol was carried out at atmospheric pressure over MgO as catalyst. The reaction gave 2-methylpentanol and propionaldehyde as the major products. The introduction of hydrogen before and during the reaction enhanced the catalyst selectivity to 2methylpentanol. The effect of possible reaction intermediates on the catalyst selectivity and the mechanism of the reaction were investigated over MgO and indicated the important role of hydrogen transfer in the reaction. The highest selectivity (69%) was achieved in the presence of hydrogen at 450 8C with propanol conversion of 24%.
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