Periodic Reporting for period 2 - COUPCAT (Coupling dimerisation and metathesis reactions to produce propene from ethanol using heterogeneous catalysts and microreactor systems)
Période du rapport: 2017-04-01 au 2018-03-31
This project addresses fundamental and applied questions on the production of high value-added molecules from linear C4-C8 olefins. These molecules are important in petrochemistry, production of polymers or as precursors for fuel additives. Among these, heterogeneous catalysts present the advantage of significant reduction post-reaction catalyst and product separation costs, which also favors a significant reduction on waste streams containing environmentally hazardous homogeneous catalysts.
Nickel and molybdenum based catalysts have shown promising data on the dimerization of ethene to butenes and on the metathesis reactions of ethene and 2-butenes to propene, respectively. The reported catalysts, however, deactivate very rapidly, which limits their potential application in future industrial processes. Moreover, such conditions difficult a proper identification of active dimerization or metathesis metal species and kinetic data for mechanistic interpretations.
The main objective of this period is to study the mechanistic aspects of dimerization and metathesis reactions, using heterogeneous catalysts with systematic changes in metal content. The study will prioritize stability over reactivity, as stable rate conditions allow the proper elucidation of the kinetic role of active-site. Kinetic terms and reaction mechanism are defined in terms of elementary steps using transition state formalisms. Active-site characterization and quantification are supported by the use of selective titrants for Lewis and Bronsted acid-sites. This information is relevant for the design of more active catalysts or their application at industrial reaction conditions.
Several conclusions of this action can be highlighted herein:
- Mechanistic understanding of Ni-based catalysts active for light olefin dimerization reactions
- Development of new experimental methods for the stabilization of catalysts showing strong deactivation in the presence of olefins
- New reaction methods that can open scientific opportunities in the field of oligomerization, catalysis or theoretical methods
- Training to become an independent researcher and establish own research projects
- International experience and collaboration with world-class experts in multidisciplinary fields related to catalysis
Nickel and molybdenum based catalysts have shown promising data on the dimerization of ethene to butenes and on the metathesis reactions of ethene and 2-butenes to propene, respectively. The reported catalysts, however, deactivate very rapidly, which limits their potential application in future industrial processes. Moreover, such conditions difficult a proper identification of active dimerization or metathesis metal species and kinetic data for mechanistic interpretations.
The main objective of this period is to study the mechanistic aspects of dimerization and metathesis reactions, using heterogeneous catalysts with systematic changes in metal content. The study will prioritize stability over reactivity, as stable rate conditions allow the proper elucidation of the kinetic role of active-site. Kinetic terms and reaction mechanism are defined in terms of elementary steps using transition state formalisms. Active-site characterization and quantification are supported by the use of selective titrants for Lewis and Bronsted acid-sites. This information is relevant for the design of more active catalysts or their application at industrial reaction conditions.
Several conclusions of this action can be highlighted herein:
- Mechanistic understanding of Ni-based catalysts active for light olefin dimerization reactions
- Development of new experimental methods for the stabilization of catalysts showing strong deactivation in the presence of olefins
- New reaction methods that can open scientific opportunities in the field of oligomerization, catalysis or theoretical methods
- Training to become an independent researcher and establish own research projects
- International experience and collaboration with world-class experts in multidisciplinary fields related to catalysis
1. Overview of the results
The experimental evidences show a direct route for the formation of propene from ethene, achieved via dimerization and metathesis reactions. This has been achieved using novel catalysts and characterization spectroscopic methods. Moreover, developed catalysts and reaction conditions allowed to develop new reaction engineering concepts, which lead to very stable catalyst performance and opens new research opportunities in the field of heterogeneous catalysis. The following sections provide details for each specific task:
a. Dimerization reactions using alkenes
- Synthesis of nickel exchanged sites on H+ sites on MCM-41
- Stabilization of active Ni sites at subambient temperatures and in the presence of hydrocarbon mixtures
- Unprecedented Ni site reactivity compared to reported Ni-based heterogeneous and homogeneous catalysts
- Linear increase of dimerization rates with Ni to H+ ratio
- Identification of kinetically relevant isolated Ni sites exchanged at stoichiometric quantities, also identified using selective titrants
- Accurate description of reaction kinetics using transition state formalisms in non-ideal media
- Unprecedented primary 1-alkene and dimer selectivity obtained at subambient temperatures compared to >400K
- Preparation of microreactors
- Catalysts characterization and comparison to state-of-the-art
- Proof of concept using more complex organometallic compounds
b. Metathesis reactions with propene
- Enhanced metathesis reactivity through controlled Mo site activation at high temperature
- Linear relationship with metathesis rates and Mo content
- Enhanced stability under zero-order reaction kinetics, deactivation under empty surface Mo sites
2. Exploitation and dissemination of results
The scientific results have been disseminated through 3 different channels:
a. Publications, so far published in 2 articles and 2 more in preparation. Especially the article in Journal of Catalysis (2017) represents a landmark showing new reaction engineering concepts.
b. Dissemination in scientific conferences (North American Catalysis Society, Denver, USA and European Catalysis Society, Florence, Italy) and invited lectures (American Chemical Society conference 2018 and Haldor Topsoe, Denmark, 2018). This allowed to expose the results to researchers in the field of catalysis and chemical engineering, which has definitely allowed to open new research lines and projects. Indeed, the results obtained in this work allowed to apply for a EU consortium project (call CE-NMBP-24-2018, with an objective for Circular Economy) involving 12 international partners.
c. Outreach articles (at University magazines) and activities (with students in Chemical Engineering, training sessions) allowed to expose the results to the open public and socialize on the importance of catalysis and science in our society.
The experimental evidences show a direct route for the formation of propene from ethene, achieved via dimerization and metathesis reactions. This has been achieved using novel catalysts and characterization spectroscopic methods. Moreover, developed catalysts and reaction conditions allowed to develop new reaction engineering concepts, which lead to very stable catalyst performance and opens new research opportunities in the field of heterogeneous catalysis. The following sections provide details for each specific task:
a. Dimerization reactions using alkenes
- Synthesis of nickel exchanged sites on H+ sites on MCM-41
- Stabilization of active Ni sites at subambient temperatures and in the presence of hydrocarbon mixtures
- Unprecedented Ni site reactivity compared to reported Ni-based heterogeneous and homogeneous catalysts
- Linear increase of dimerization rates with Ni to H+ ratio
- Identification of kinetically relevant isolated Ni sites exchanged at stoichiometric quantities, also identified using selective titrants
- Accurate description of reaction kinetics using transition state formalisms in non-ideal media
- Unprecedented primary 1-alkene and dimer selectivity obtained at subambient temperatures compared to >400K
- Preparation of microreactors
- Catalysts characterization and comparison to state-of-the-art
- Proof of concept using more complex organometallic compounds
b. Metathesis reactions with propene
- Enhanced metathesis reactivity through controlled Mo site activation at high temperature
- Linear relationship with metathesis rates and Mo content
- Enhanced stability under zero-order reaction kinetics, deactivation under empty surface Mo sites
2. Exploitation and dissemination of results
The scientific results have been disseminated through 3 different channels:
a. Publications, so far published in 2 articles and 2 more in preparation. Especially the article in Journal of Catalysis (2017) represents a landmark showing new reaction engineering concepts.
b. Dissemination in scientific conferences (North American Catalysis Society, Denver, USA and European Catalysis Society, Florence, Italy) and invited lectures (American Chemical Society conference 2018 and Haldor Topsoe, Denmark, 2018). This allowed to expose the results to researchers in the field of catalysis and chemical engineering, which has definitely allowed to open new research lines and projects. Indeed, the results obtained in this work allowed to apply for a EU consortium project (call CE-NMBP-24-2018, with an objective for Circular Economy) involving 12 international partners.
c. Outreach articles (at University magazines) and activities (with students in Chemical Engineering, training sessions) allowed to expose the results to the open public and socialize on the importance of catalysis and science in our society.
The main impact of the developed catalyst synthesis and reaction conditions lie on the enhancement of Ni site stability, which has a direct impact on several aspects:
- To increase the reactivity of active Ni sites, thus reducing catalyst preparation or re-use (if regenerable) costs. This has direct on a significant improvement of the environmental costs of alkene oligomerization processes.
- Addresses fundamental questions on the active site nature, which opens new research horizons to catalysts and reactions that have not been industrially applied due to technical constraints caused by rapid active Ni deactivation.
- This is a clear example of how reaction pathways can be altered at subambient temperatures in heterogeneous catalysts, without the use of additional solvents and higher primary product selectivity, which reduces post-reaction catalyst and product separation costs.
- This work rigorously describes the fundamental questions on reaction kinetics involved in alkene oligomerization using transition-state theory. Moreover, and due to the developed reaction conditions, this work aims to have a direct impact on the processes that already make use of alkenes to produce oligomers or future processes that aim to use renewable sources, such as ethanol, to produce higher value-added oligomers.
- More importantly, the results from these studies open new research lines (in which the researcher will continue) that can lead to breakthroughs in terms of solid-catalyst stability and reactivity. Published studies were the first compelling evidences on the effects of intrapore liquids altering specific reaction intermediates, but the impact can be even bigger if stabilization effects are also achieve in terms of active-site reactivity.
- To increase the reactivity of active Ni sites, thus reducing catalyst preparation or re-use (if regenerable) costs. This has direct on a significant improvement of the environmental costs of alkene oligomerization processes.
- Addresses fundamental questions on the active site nature, which opens new research horizons to catalysts and reactions that have not been industrially applied due to technical constraints caused by rapid active Ni deactivation.
- This is a clear example of how reaction pathways can be altered at subambient temperatures in heterogeneous catalysts, without the use of additional solvents and higher primary product selectivity, which reduces post-reaction catalyst and product separation costs.
- This work rigorously describes the fundamental questions on reaction kinetics involved in alkene oligomerization using transition-state theory. Moreover, and due to the developed reaction conditions, this work aims to have a direct impact on the processes that already make use of alkenes to produce oligomers or future processes that aim to use renewable sources, such as ethanol, to produce higher value-added oligomers.
- More importantly, the results from these studies open new research lines (in which the researcher will continue) that can lead to breakthroughs in terms of solid-catalyst stability and reactivity. Published studies were the first compelling evidences on the effects of intrapore liquids altering specific reaction intermediates, but the impact can be even bigger if stabilization effects are also achieve in terms of active-site reactivity.