Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - COUPCAT (Coupling dimerisation and metathesis reactions to produce propene from ethanol using heterogeneous catalysts and microreactor systems)

Teaser

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...

Summary

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. Stable reaction rates are used to interpret kinetics in terms of alkene pressure and reaction mechanism in terms of elementary steps using transition state formalisms. Active-site characterization and quantifications 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.

Work performed

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

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

Final results

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.