Davidâ w. Knight | Cardiff University (original) (raw)
Papers by Davidâ w. Knight
A method for regioselective alkylation of the 3-thiono-1,2,4-triazinone 10 at the sulfur atom is ... more A method for regioselective alkylation of the 3-thiono-1,2,4-triazinone 10 at the sulfur atom is reported. Subsequent Claisen rearrangements, triggered either thermally or using a palladium catalyst, deliver N-alkylated products, while acid-catalysed rearrangements of examples where a tertiary carbenium ion can be generated, result in formation of N-thioalkyl derivatives.
Topics in Catalysis, 2006
ChemSusChem, 2000
Glycolic acid is an important chemical that has uses as a cleaning agent as well as a chemical in... more Glycolic acid is an important chemical that has uses as a cleaning agent as well as a chemical intermediate. At present glycolic acid is manufactured from either chloroacetic acid or from formaldehyde hydrocyanation, both routes being nongreen and using nonsustainable resources. We investigate the possibility of producing glycolate from the oxidation of glycerol, a sustainable raw material. We show that by using 1 % wt Au/carbon catalysts prepared using a sol-immobilization method glycolate yields of ca. 60 % can be achieved, using hydrogen peroxide as oxidant in an autoclave reactor. We describe and discuss the reaction mechanism and consider the reaction conditions that maximize the formation of glycolate.
Catalysis Today, 2007
We report the preparation of Au-Pd nanocrystalline catalysts supported on TiO(2) and carbon prepa... more We report the preparation of Au-Pd nanocrystalline catalysts supported on TiO(2) and carbon prepared via a sol-immobilisation technique using three different preparation strategies; namely, simultaneous formation of the sols for both metals or initial formation of a seed sol of one of the metals followed by a separate step in which a coating sol of the second metal is added. The catalysts have been structurally characterised using a combination of transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts have been evaluated for the oxidation of benzyl alcohol under solvent-free conditions. The catalysts prepared using the sol immobilisation technique show higher activity when compared with catalysts prepared by impregnation, particularly as lower metal concentrations can be used. The Au-Pd catalysts were all more active than the corresponding monometallic supported Au or Pd catalysts. For 1 wt% Au-Pd/TiO(2) the order of metal addition in the preparation was not observed to be significant with respect to selectivity or activity. However, the 1 wt% Au-Pd/carbon catalysts are more active but less selective to benzaldehyde than the TiO(2)-supported catalysts when compared at iso-conversion. Furthermore, for the carbon-supported catalyst the order of metal addition has a very marked affect on activity. The carbon-supported catalysts are also more significantly affected by heat treatment, e.g. calcination at 400 degrees C leads to the activity being decreased by an order of magnitude, whereas the TiO(2)-supported catalysts show a 50% decrease in activity. Toluene is observed as a by-product of the reaction and conditions have been identified that minimise its formation. It is proposed that toluene and benzaldehyde are formed by competing parallel reactions of the initial benzyl intermediate via an adsorbed benzylidene species that can either be hydrogenated or oxidised. Hence, conditions that maximise the availability of oxygen on the catalyst surface favour the synthesis of benzaldehyde.
Catalysis Letters, 2006
The oxidation of benzyl alcohol to benzaldehyde has been investigated in the absence of solvent u... more The oxidation of benzyl alcohol to benzaldehyde has been investigated in the absence of solvent using zeolite-supported Au and Au-Pd catalysts. Three zeolites were investigated, ZSM-5, zeolite b and zeolite Y, and these were contrasted with the titanoslicalite TS-1 and TiO 2 as supports. For the Au catalysts the best results are obtained with zeolite b as the support and the conversions were comparable or better than those observed with TiO 2 in terms of turn over frequencies. However, the selectivities observed with the acidic zeolites were lower than the non-acidic TS-1 and TiO 2 . This is due to the subsequent reaction of benzaldehyde via acid catalysed reactions to give benzyl benzoate and its dibenzyl acetal, and, in some cases dibenzylether. Initial catalysts were evaluated with a gold loading of 2 wt% and increasing this to 4 wt% showed the expected increase in activity, indicating that there is scope to improve the performance of these catalysts. The most active catalysts were prepared by impregnation and catalysts prepared by deposition precipitation were considerably less active. Introduction of Pd into the catalyst improved the activity without significantly affecting the selectivity.
A method for regioselective alkylation of the 3-thiono-1,2,4-triazinone 10 at the sulfur atom is ... more A method for regioselective alkylation of the 3-thiono-1,2,4-triazinone 10 at the sulfur atom is reported. Subsequent Claisen rearrangements, triggered either thermally or using a palladium catalyst, deliver N-alkylated products, while acid-catalysed rearrangements of examples where a tertiary carbenium ion can be generated, result in formation of N-thioalkyl derivatives.
Topics in Catalysis, 2006
ChemSusChem, 2000
Glycolic acid is an important chemical that has uses as a cleaning agent as well as a chemical in... more Glycolic acid is an important chemical that has uses as a cleaning agent as well as a chemical intermediate. At present glycolic acid is manufactured from either chloroacetic acid or from formaldehyde hydrocyanation, both routes being nongreen and using nonsustainable resources. We investigate the possibility of producing glycolate from the oxidation of glycerol, a sustainable raw material. We show that by using 1 % wt Au/carbon catalysts prepared using a sol-immobilization method glycolate yields of ca. 60 % can be achieved, using hydrogen peroxide as oxidant in an autoclave reactor. We describe and discuss the reaction mechanism and consider the reaction conditions that maximize the formation of glycolate.
Catalysis Today, 2007
We report the preparation of Au-Pd nanocrystalline catalysts supported on TiO(2) and carbon prepa... more We report the preparation of Au-Pd nanocrystalline catalysts supported on TiO(2) and carbon prepared via a sol-immobilisation technique using three different preparation strategies; namely, simultaneous formation of the sols for both metals or initial formation of a seed sol of one of the metals followed by a separate step in which a coating sol of the second metal is added. The catalysts have been structurally characterised using a combination of transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts have been evaluated for the oxidation of benzyl alcohol under solvent-free conditions. The catalysts prepared using the sol immobilisation technique show higher activity when compared with catalysts prepared by impregnation, particularly as lower metal concentrations can be used. The Au-Pd catalysts were all more active than the corresponding monometallic supported Au or Pd catalysts. For 1 wt% Au-Pd/TiO(2) the order of metal addition in the preparation was not observed to be significant with respect to selectivity or activity. However, the 1 wt% Au-Pd/carbon catalysts are more active but less selective to benzaldehyde than the TiO(2)-supported catalysts when compared at iso-conversion. Furthermore, for the carbon-supported catalyst the order of metal addition has a very marked affect on activity. The carbon-supported catalysts are also more significantly affected by heat treatment, e.g. calcination at 400 degrees C leads to the activity being decreased by an order of magnitude, whereas the TiO(2)-supported catalysts show a 50% decrease in activity. Toluene is observed as a by-product of the reaction and conditions have been identified that minimise its formation. It is proposed that toluene and benzaldehyde are formed by competing parallel reactions of the initial benzyl intermediate via an adsorbed benzylidene species that can either be hydrogenated or oxidised. Hence, conditions that maximise the availability of oxygen on the catalyst surface favour the synthesis of benzaldehyde.
Catalysis Letters, 2006
The oxidation of benzyl alcohol to benzaldehyde has been investigated in the absence of solvent u... more The oxidation of benzyl alcohol to benzaldehyde has been investigated in the absence of solvent using zeolite-supported Au and Au-Pd catalysts. Three zeolites were investigated, ZSM-5, zeolite b and zeolite Y, and these were contrasted with the titanoslicalite TS-1 and TiO 2 as supports. For the Au catalysts the best results are obtained with zeolite b as the support and the conversions were comparable or better than those observed with TiO 2 in terms of turn over frequencies. However, the selectivities observed with the acidic zeolites were lower than the non-acidic TS-1 and TiO 2 . This is due to the subsequent reaction of benzaldehyde via acid catalysed reactions to give benzyl benzoate and its dibenzyl acetal, and, in some cases dibenzylether. Initial catalysts were evaluated with a gold loading of 2 wt% and increasing this to 4 wt% showed the expected increase in activity, indicating that there is scope to improve the performance of these catalysts. The most active catalysts were prepared by impregnation and catalysts prepared by deposition precipitation were considerably less active. Introduction of Pd into the catalyst improved the activity without significantly affecting the selectivity.