Phosgene (Cl2C=O) is a black spot for the chemical industry. On the one hand, phosgene is the key electrophilic reagent in the production of organic carbonates, polycarbonates and polyurethanes. On the other hand, its intrinsic toxicity and the HCl emissions from its utilization induce a dramatic additional cost for economy, environment, and people.
CO2 is an electrophilic analogue of phosgene and could replace it in these processes, with many advantages: soon provided by industrial carbon capture, CO2 is only mildly toxic, abundant, renewable, concentrated, and cheap. However, CO2 will be a real alternative to phosgene only if chemists find how to activate this very stable C1 source in nucleophilic additions (AN) with low-energy reactants (alcohols, amines). Today, CO2 activation still appears as a real scientific challenge. Beyond "trial and error" approaches, the challenge will be met when we have built a new knowledge corpus, which accurately describes each transformation route with its specific mechanisms and key parameters.
AN on CO2 will provide powerful processes for the production of valuable chemicals when two main obstacles have been overcome: the low yields in addition products and the slowness of the reaction. Indeed, with the best solid inorganic catalysts available and 100 bar of CO2, the synthesis of diethylcarbonate (DEC) from ethanol and CO2 typically proceeds in 1h with a final yield of around 1%. The yield is limited by the reaction thermodynamics, which favors the hydrolysis of the DEC by the co-produced water.
The yield can be improved with chemical engineering approaches displacing water from the reaction medium. These approaches largely dominate in the scientific literature about AN on CO2, but they do not improve the kinetics of the reaction. For improving the kinetics, most of previous investigations have focused on catalyst screening, yet the major reviews on CO2 transformation stress that the field cruelly needs a deeper understanding of the catalytic action from fundamental studies. Indeed, converting AN on CO2 into an industrial flow catalytic process will only be possible if the time of reaction goes down to a few minutes. With heterogeneous catalysis in flow reactor, the processes improving the yield will then be easy to implement. The main purpose of the present project is to directly address the kinetics of AN on CO2 in heterogeneous catalysis.
This ANR project aims to understand at a molecular level how AN on CO2 can be catalyzed by inorganic solids. It is a fundamental investigation in heterogeneous catalysis. It focuses on a catalytic system that combines the main characteristics of the attractive AN reactions (simple nucleophile, water production) and the simplicity of a model: zirconia-catalyzed synthesis of dimethylcarbonate from CO2 and methanol.
The ultimate deliverable of the project will be a molecular description of the active sites with structural parameters allowing the design of better catalysts for CO2 activation. This description will be brought by a dual experimental-theoretical approach. Experimentally, we will look for structure-activity relationships from kinetic measurements and characterizations. Theoretically, we will model the various surface sites of the catalysts to study their properties in spectroscopy, adsorption and catalysis. Comparison between experiments and modeling will give a better assignment of experimental signals and an explanation of the catalytic action.
Institut de chimie moléculaire et des matériaux - Institut Charles Gerhardt Montpellier (Laboratoire public)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Institut de chimie moléculaire et des matériaux - Institut Charles Gerhardt Montpellier
Help of the ANR 211,906 euros
Beginning and duration of the scientific project: November 2017 - 36 Months