Driving Research in the Field of Industrial Carbon Capture and Utilization -
A Practical NMR Case Study

WACKER is pursuing ambitious climate-protection measures: It aims to halve its greenhouse gas emissions by 2030 and achieve net-zero by 2045. The conversion of carbon dioxide into high-value chemical feedstocks by electrochemical CO2 reduction (ECO2R) is a promising technology being explored by WACKER’s corporate R&D team. As of today, research is still ongoing as multiple challenges for the ECO2R process, e.g. selectivity, efficiency and long-term stability, need to be solved before its operation on an industrial scale is feasible ¹. 

The first step towards meaningful research is the correct quantification of the formed products. During the ECO2R up to 16 different products can be formed with most of them in a liquid state ² . For liquid products (ethanol, propanol, formic acid, and others) nuclear magnetic resonance (NMR) spectroscopy is the main and established method for quantification as it offers multiple advantages in comparison to other methods. NMR allows to quantify at different pH values without the necessary removal of the conductive salt in the electrolyte. Furthermore, optional solvent suppression can be used to decrease the H₂O peak making smaller product concentrations visible ³. 

Stefan Haufe Ph.D., Director Electrochemistry; Philipp Altmann Ph.D., Head of Analytical Laboratory; 
Daniel Rottmann, M.Sc., Doctoral Student Electrochemistry; WACKER Group, Munich, Germany

Joerg Koehler Ph.D., Senior Director for the Cleantech, Industrial and Applied Markets, Bruker BioSpin GmbH, Ettlingen, Germany

Head of Analytical Laboratory, Corporate Research & Development, WACKER Group

The Advanced Chemical Profiling Module helps to generate robust, reproducible quantifications of the measured data. As soon as a database is set up accordingly, the process of using the new software module does not require NMR expert knowledge. This procedure should be well suited for production environments where the contents of the samples are comparable and the sample matrices are not too complex.

Bruker BioSpin Group is developing cutting edge technologies in the field of NMR since more than 60 years

Bruker’s Avance series floor-standing Nuclear Magnetic Resonance (NMR) spectrometers are widely applied in various industrial market segments. The worldwide installed base covers analytical tasks at a variety of value chain positions with having a focus on product innovation environments. Data processing, interpretation, and report filing is a process bottleneck especially when it comes to repeated analyses such as formulation screening tasks. This is fundamental in high-through-put set-ups like in production affiliated laboratories, company-internal analytical testing service hubs, R&D centers, and pilot-upscaling support functions of centers of excellence. Sample handling, data acquisition, and initial raw data processing is fully automated with Bruker’s Avance series NMR spectrometers. Bruker’s industry-standard NMR software TopSpin® and fully integrated modules such as IconNMR™ are matching various customer needs for analytical data acquisition. The interpretation of NMR data and the translation into the answer to the initial analytical questions is still often dependent on highly skilled spectroscopic experts. A comprehensive software-based automated end-to-end workflow from sample to actionable information intelligence without the need of any spectroscopic expert interaction addresses this process bottleneck and would allow the experts focusing on more sophisticated tasks. Bruker’s new Advanced Chemical Profiling Solution is addressing the task of data processing, interpretation, and report filing for NMR data of chemical mixtures. Identification and quantification of constituents in incoming goods, process intermediates, and final product formulations is essential for improving both, quality, and efficiency in R&D lab-scale, pilot, and volume production processes. The Advanced Chemical Profiling Solution fully integrates into TopSpin® and IconNMR™ allowing for creation of comprehensive and fully automated workflows from sample to report. This on-premises solution also features optimized intellectual property security and data integrity. The database driven solution is customizable by in-house NMR experts meeting needs for a variety of use cases.

WACKER’s CO₂ electrolysis meets Bruker NMR

The initial step for the analysis of a typical set of ECO2R experiments generally involved the evaluation of the expected identities of electrolysis products by the electrolysis team, either by means of experimental and analytical data or theoretical considerations. The resulting list of compounds was subsequently communicated to the NMR department of the “Consortium für elektrochemische Industrie”, WACKER’s corporate R&D facility in Munich. Accordingly, a spectral database of all pure substances to be expected in the output media of the CO2 electrolysis process was created with a Bruker Avance III HD 500 MHz NMR spectrometer equipped with a SampleXpress. Additionally, different internal standards were screened and the most suitable was then picked for the respective purpose, e.g., chemical shift, pH stability. In the case of ECO2R sodium trimethylsilylpropanesulfonate (DSS) and potassium hydrogen phthalate (KHP) in D₂O turned out to be the best fits. The final concentrations of DSS and KHP in the prepared samples were 0.1 mg/mL and 1.0 mg/mL, respectively. The most accurate quantification was established by referencing peaks on the left side of the water signal to KHP, and peaks on the right side of the water peak to DSS.

Each individual sample was analyzed as duplicate. In a typical experiment 540 µL of the sample was mixed with 60 µL internal standard (either DSS or KHP) to give an overall sample volume of 600 µL. The samples were measured with the water suppression pulse sequence noesygppr1d (1D NOESY with pre-saturation and spoil gradients) to facilitate the evaluation. One experiment consisted of 64 scans with a delay time (d1) of 60 seconds to ensure quantitative relaxation of all relevant nuclei. The spectra were quantified individually running the Advanced Chemical Profiling Module by hand or the processing was integrated into the automation of Topspin. The new software module generated the report in PDF Form with a table of the calculated concentrations, a visual representation of the identified peaks and a visualization of the accuracy of the measurement.

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