Selective conversion of alcohols to aldehydes over metal oxide catalysts
(2013)- Abstract
- Nowadays, transition metal oxide catalysts are employed to a large extent in many chemical processes for the selective production of chemicals and intermediates. Although metal oxides are mostly known as oxidation catalysts, they can successfully catalyze a wide range of reactions, such as dehydration.
Two different processes have been studied in the present work: the selective oxidation of methanol over V-Mo-based catalysts and the dehydration of glycerol over supported Nb- and W-oxide catalysts.
Since the iron molybdate catalyst commercially employed in the selective conversion of methanol to formaldehyde suffers from deactivation by Mo volatilization, alternative catalysts such as supported Fe-V-oxide and unsupported... (More) - Nowadays, transition metal oxide catalysts are employed to a large extent in many chemical processes for the selective production of chemicals and intermediates. Although metal oxides are mostly known as oxidation catalysts, they can successfully catalyze a wide range of reactions, such as dehydration.
Two different processes have been studied in the present work: the selective oxidation of methanol over V-Mo-based catalysts and the dehydration of glycerol over supported Nb- and W-oxide catalysts.
Since the iron molybdate catalyst commercially employed in the selective conversion of methanol to formaldehyde suffers from deactivation by Mo volatilization, alternative catalysts such as supported Fe-V-oxide and unsupported V-Mo-oxide spinel-type catalysts were studied. The supported catalysts were found to be less selective than the commercial one, their showing a far more severe volatilization due to the limited amount of active metal they contain. At the same time, a spinel-type structure containing V, Mo or both was found to be flexible and stable under both reducing and oxidizing conditions, enabling the cations to change valence while preserving the spinel-type structure. In addition, the spinel structure was found to be stable with regard to volatilization during methanol oxidation. Nevertheless, V-Mo-oxide spinel-type catalysts, despite their excellent structural and stability properties, were found to be less selective than the commercial one and to not be suitable for replacing it without further improvement.
In the production of biodiesel large amounts of glycerol are formed as a major by-product. Because of its low market demand, glycerol can represent a sustainable feedstock for producing chemicals and intermediates, such as acrolein, which is presently a fossil derivative obtained commercially from propene. The gas-phase dehydration of glycerol to acrolein over Al2O3-, SiO2-, TiO2- and ZrO2-supported Nb- and W-oxide catalysts was investigated here, tests regarding it being carried out under both anaerobic and aerobic conditions. ZrO2- and TiO2-supported W-oxides were found to be the catalysts that performed best under anaerobic and aerobic conditions, respectively, in terms of both their activity and their acrolein selectivity. A clear dependence of the activity and acrolein selectivity on the total acid site and Brønsted acid site concentration, respectively, was also observed. All of the catalysts were found to undergo deactivation due to poisoning of the active sites by coke molecules and heavy compounds. The deactivation phenomenon was found to be reduced considerably in the presence of oxygen. (Less) - Abstract (Swedish)
- Popular Abstract in English
Alcohols and aldehydes are used in the chemical industry largely as a starting material for the manufacture of a wide range of products. They are also used as such in various industrial applications. The flexibility is due mainly to the functionalities of the alcohols and aldehydes being hydroxylic and carbonylic, respectively. Much interest is directed nowadays at converting alcohols into aldehydes, which can easily be done by either oxidizing or dehydrating the alcoholic groups. Since in the absence of a catalyst such conversion is very unlikely, more severe reaction conditions are required, such as high temperature or high pressure or both. This can lead to an excessive breakage of bonds in... (More) - Popular Abstract in English
Alcohols and aldehydes are used in the chemical industry largely as a starting material for the manufacture of a wide range of products. They are also used as such in various industrial applications. The flexibility is due mainly to the functionalities of the alcohols and aldehydes being hydroxylic and carbonylic, respectively. Much interest is directed nowadays at converting alcohols into aldehydes, which can easily be done by either oxidizing or dehydrating the alcoholic groups. Since in the absence of a catalyst such conversion is very unlikely, more severe reaction conditions are required, such as high temperature or high pressure or both. This can lead to an excessive breakage of bonds in the reactant molecules and also to combustion. A catalyst is a substance that promotes the reaction towards a route that involves a lower potential barrier, so that more severe reaction conditions are no longer needed.
In the work carried out here two types of chemical reactions were investigated, each in a separate study: the oxidation of methanol to formaldehyde and the dehydration of glycerol to propenal (acrolein). The objective of the first study was to explore the use of catalysts alternative to the one in commercial use today. The second study, in turn, concerned a reaction that was seen to possibly represent a sustainable one able to replace a commercial process making use of a fossil derivative as a starting material. Both types of reactions were studied in the gas-phase and in the presence of metal oxide catalysts. Such catalysts are a combination of oxygen with what are usually transition metals that form solid structures in a long-range order. The active sites for the chemical reaction are usually located at the surface of these structures, where the metals are unsaturated and thus more reactive.
Formaldehyde is the first in the series of aliphatic aldehydes. It is used mainly for the manufacture of such condensates as adhesives, molding compounds and coating resins. Currently, formaldehyde is obtained from methanol oxidation by two competitive processes: the silver process and the oxide process. The latter technology achieves a high degree of efficiency through use of an Fe-Mo-based catalyst, enabling a high degree of formaldehyde selectivity (~93%) at nearly complete methanol conversion. Nevertheless, the catalytic performance on stream is negatively affected by the volatilization of molybdenum, which causes deactivation and the need for frequent replacement of the catalyst. In line with this, the first part of the thesis is concerned with the stability towards volatilization of alternative oxidating metals, such as vanadium, during methanol oxidation. Account is also taken of the structure-activity relationships involved.
Acrolein is a valuable intermediate in the synthesis of acrylic acid, which in turn is employed as a monomer for the manufacture of acrylates in the polymer industry. At present, acrolein is produced commercially by the gas-phase oxidation of propene over a Bi-Mo-based catalyst. Due to the limited reservoir of fossil resources from which propene is derived, there has been strong interest in developing a process for making acrolein from renewable feedstocks. A potential candidate for this is glycerol, obtained in large amounts as a major by-product in biodiesel production. The second part of the thesis concerns the gas-phase dehydration of glycerol to acrolein over supported catalysts containing Nb- and W-oxides as active species. Particular attention is directed here at the structure, acid properties and stability of the catalysts. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/4001888
- author
- Massa, Mariano LU
- supervisor
- opponent
-
- Dr. Millet, Jean-Marc M., Institut de Recherches sur la Catalyse et l’Environnement de Lyon, IRCELYON, UMR5256 CNRS-Université Claude Bernard Lyon 1, 2 avenue A. Einstein, F-69626 Villeurbanne cedex. France
- organization
- publishing date
- 2013
- type
- Thesis
- publication status
- published
- subject
- pages
- 67 pages
- defense location
- Lecture Hall F, Center for Chemistry and Chemical Engineering, Getingevägen 60, Lund
- defense date
- 2013-10-25 13:15:00
- ISBN
- 978-91-7422-328-6
- language
- English
- LU publication?
- yes
- id
- bd072f60-774c-418a-b2e0-df07dbbb6d06 (old id 4001888)
- date added to LUP
- 2016-04-04 13:21:22
- date last changed
- 2018-11-21 21:13:26
@phdthesis{bd072f60-774c-418a-b2e0-df07dbbb6d06,
abstract = {{Nowadays, transition metal oxide catalysts are employed to a large extent in many chemical processes for the selective production of chemicals and intermediates. Although metal oxides are mostly known as oxidation catalysts, they can successfully catalyze a wide range of reactions, such as dehydration.<br/><br>
Two different processes have been studied in the present work: the selective oxidation of methanol over V-Mo-based catalysts and the dehydration of glycerol over supported Nb- and W-oxide catalysts.<br/><br>
Since the iron molybdate catalyst commercially employed in the selective conversion of methanol to formaldehyde suffers from deactivation by Mo volatilization, alternative catalysts such as supported Fe-V-oxide and unsupported V-Mo-oxide spinel-type catalysts were studied. The supported catalysts were found to be less selective than the commercial one, their showing a far more severe volatilization due to the limited amount of active metal they contain. At the same time, a spinel-type structure containing V, Mo or both was found to be flexible and stable under both reducing and oxidizing conditions, enabling the cations to change valence while preserving the spinel-type structure. In addition, the spinel structure was found to be stable with regard to volatilization during methanol oxidation. Nevertheless, V-Mo-oxide spinel-type catalysts, despite their excellent structural and stability properties, were found to be less selective than the commercial one and to not be suitable for replacing it without further improvement.<br/><br>
In the production of biodiesel large amounts of glycerol are formed as a major by-product. Because of its low market demand, glycerol can represent a sustainable feedstock for producing chemicals and intermediates, such as acrolein, which is presently a fossil derivative obtained commercially from propene. The gas-phase dehydration of glycerol to acrolein over Al2O3-, SiO2-, TiO2- and ZrO2-supported Nb- and W-oxide catalysts was investigated here, tests regarding it being carried out under both anaerobic and aerobic conditions. ZrO2- and TiO2-supported W-oxides were found to be the catalysts that performed best under anaerobic and aerobic conditions, respectively, in terms of both their activity and their acrolein selectivity. A clear dependence of the activity and acrolein selectivity on the total acid site and Brønsted acid site concentration, respectively, was also observed. All of the catalysts were found to undergo deactivation due to poisoning of the active sites by coke molecules and heavy compounds. The deactivation phenomenon was found to be reduced considerably in the presence of oxygen.}},
author = {{Massa, Mariano}},
isbn = {{978-91-7422-328-6}},
language = {{eng}},
school = {{Lund University}},
title = {{Selective conversion of alcohols to aldehydes over metal oxide catalysts}},
year = {{2013}},
}