Gregor Jenzer | Swiss Federal Institute of Technology (ETH) (original) (raw)
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Papers by Gregor Jenzer
Applied Catalysis A: General, 2001
Propylene epoxidation over a Pd-Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carrie... more Propylene epoxidation over a Pd-Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carried out in a fixed bed reactor under high pressure conditions. The continuous operation allowed the study of catalyst deactivation and changes in product distribution with time-on-stream. The initial propylene oxide selectivity was very high, 99% at 3.5% conversion, but the catalyst deactivated rapidly with time-on-stream and successively the formation of methyl formate became the prevalent reaction. Using carbon dioxide, instead of nitrogen, had a beneficial effect on the formation of propylene oxide, and even higher yields were obtained when increasing the pressure from 50 to 120 bar (supercritical fluid phase). Thermal analysis (TA-MS and TA-FTIR) indicated that catalyst regeneration requires oxidation at elevated temperature; washing with an organic solvent is less efficient. The serious catalyst deactivation and the striking shift in the selectivity pattern of the catalyst is traced to competing alcohol oxidation on platinum metal.
Catalysis Lett, 2001
ABSTRACT
Journal of Catalysis, 2001
Noble metal catalyzed aerobic oxidation of alcohols to carbonyl compounds or carboxylic acids is ... more Noble metal catalyzed aerobic oxidation of alcohols to carbonyl compounds or carboxylic acids is an efficient method, but the frequently observed catalyst deactivation and flammability of organic solvents in the case of water-insoluble alcohols limit the application range. We applied "supercritical" (dense) carbon dioxide as the solvent, a cheap and nonflammable medium with fair and tunable solubility in particular for weakly polar water-insoluble alcohols. The experiments were carried out in a continuous fixed bed reactor, over 0.5 wt% Pd/alumina, at 80-140 • C and 75-125 bar. A comparative study of oxidation of 1-and 2-octanols to carbonyl compounds, chosen as model reactions, demonstrated that the method is well suited for the partial oxidation of secondary alcohols with molecular oxygen, whereas for primary alcohols the selectivity is low. In the oxidation of 2-octanol the selectivity was excellent (>99.5%) and independent of conversion. No significant catalyst deactivation was observed and the rate in CO 2 was higher by a factor of up to 2-4 compared to the rate of oxidation in nitrogen. The complex effects of pressure and oxygen concentration on the reaction rate have been interpreted by studying the phase behavior in a high-pressure view cell under reaction conditions.
Chemical Communications, 2000
ABSTRACT
Catalysis letters, 1999
The one-step procedure of amination of bifunctional secondary alcohols to diamines has been inves... more The one-step procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixed-bed reactor. Application of supercritical NH 3 as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8-10%). The main reason for the low diamine selectivity of 1,3dihydroxy compounds is water elimination leading to undesired monofunctional products via α, β-unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4-dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3-propanediol.
Applied Catalysis A: General, 2001
Propylene epoxidation over a Pd-Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carrie... more Propylene epoxidation over a Pd-Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carried out in a fixed bed reactor under high pressure conditions. The continuous operation allowed the study of catalyst deactivation and changes in product distribution with time-on-stream. The initial propylene oxide selectivity was very high, 99% at 3.5% conversion, but the catalyst deactivated rapidly with time-on-stream and successively the formation of methyl formate became the prevalent reaction. Using carbon dioxide, instead of nitrogen, had a beneficial effect on the formation of propylene oxide, and even higher yields were obtained when increasing the pressure from 50 to 120 bar (supercritical fluid phase). Thermal analysis (TA-MS and TA-FTIR) indicated that catalyst regeneration requires oxidation at elevated temperature; washing with an organic solvent is less efficient. The serious catalyst deactivation and the striking shift in the selectivity pattern of the catalyst is traced to competing alcohol oxidation on platinum metal. : S 0 9 2 6 -8 6 0 X ( 0 0 ) 0 0 6 8 9 -X
Applied Catalysis A: General, 2001
Propylene epoxidation over a Pd-Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carrie... more Propylene epoxidation over a Pd-Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carried out in a fixed bed reactor under high pressure conditions. The continuous operation allowed the study of catalyst deactivation and changes in product distribution with time-on-stream. The initial propylene oxide selectivity was very high, 99% at 3.5% conversion, but the catalyst deactivated rapidly with time-on-stream and successively the formation of methyl formate became the prevalent reaction. Using carbon dioxide, instead of nitrogen, had a beneficial effect on the formation of propylene oxide, and even higher yields were obtained when increasing the pressure from 50 to 120 bar (supercritical fluid phase). Thermal analysis (TA-MS and TA-FTIR) indicated that catalyst regeneration requires oxidation at elevated temperature; washing with an organic solvent is less efficient. The serious catalyst deactivation and the striking shift in the selectivity pattern of the catalyst is traced to competing alcohol oxidation on platinum metal.
Catalysis Lett, 2001
ABSTRACT
Journal of Catalysis, 2001
Noble metal catalyzed aerobic oxidation of alcohols to carbonyl compounds or carboxylic acids is ... more Noble metal catalyzed aerobic oxidation of alcohols to carbonyl compounds or carboxylic acids is an efficient method, but the frequently observed catalyst deactivation and flammability of organic solvents in the case of water-insoluble alcohols limit the application range. We applied "supercritical" (dense) carbon dioxide as the solvent, a cheap and nonflammable medium with fair and tunable solubility in particular for weakly polar water-insoluble alcohols. The experiments were carried out in a continuous fixed bed reactor, over 0.5 wt% Pd/alumina, at 80-140 • C and 75-125 bar. A comparative study of oxidation of 1-and 2-octanols to carbonyl compounds, chosen as model reactions, demonstrated that the method is well suited for the partial oxidation of secondary alcohols with molecular oxygen, whereas for primary alcohols the selectivity is low. In the oxidation of 2-octanol the selectivity was excellent (>99.5%) and independent of conversion. No significant catalyst deactivation was observed and the rate in CO 2 was higher by a factor of up to 2-4 compared to the rate of oxidation in nitrogen. The complex effects of pressure and oxygen concentration on the reaction rate have been interpreted by studying the phase behavior in a high-pressure view cell under reaction conditions.
Chemical Communications, 2000
ABSTRACT
Catalysis letters, 1999
The one-step procedure of amination of bifunctional secondary alcohols to diamines has been inves... more The one-step procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixed-bed reactor. Application of supercritical NH 3 as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8-10%). The main reason for the low diamine selectivity of 1,3dihydroxy compounds is water elimination leading to undesired monofunctional products via α, β-unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4-dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3-propanediol.
Applied Catalysis A: General, 2001
Propylene epoxidation over a Pd-Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carrie... more Propylene epoxidation over a Pd-Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carried out in a fixed bed reactor under high pressure conditions. The continuous operation allowed the study of catalyst deactivation and changes in product distribution with time-on-stream. The initial propylene oxide selectivity was very high, 99% at 3.5% conversion, but the catalyst deactivated rapidly with time-on-stream and successively the formation of methyl formate became the prevalent reaction. Using carbon dioxide, instead of nitrogen, had a beneficial effect on the formation of propylene oxide, and even higher yields were obtained when increasing the pressure from 50 to 120 bar (supercritical fluid phase). Thermal analysis (TA-MS and TA-FTIR) indicated that catalyst regeneration requires oxidation at elevated temperature; washing with an organic solvent is less efficient. The serious catalyst deactivation and the striking shift in the selectivity pattern of the catalyst is traced to competing alcohol oxidation on platinum metal. : S 0 9 2 6 -8 6 0 X ( 0 0 ) 0 0 6 8 9 -X