Versatile Procedures for Reliable NMR Quantification of CO₂ Electroreduction Products

Abstract

Electrochemical reduction can capture and utilize CO2 through its conversion to small chemicals and fuels. Analytical standard operating procedures for the accurate quantification of short chain acids, aldehydes, and alcohols by HPLC, GC-MS or NMR are not well established. Electrochemical reduction of CO2 produces the smallest conceivable organic compounds, which necessitates slow NMR quantifications due to slow T1 relaxation towards equilibrium magnetization. It is shown that the use of paramagnetic contrast agents or cooling of water/DMSO provides T1-optimized measurements with attractive sensitivity and speed. 1 H NMR experiments that are widely used in the study of biological mixtures are found unsuitable for quantitative analyses of T1-optimized samples.

Probing the Role of Individual OH Sites in Carbohydrate Conversion Suggests Strategies for Increasing Product Selectivity and Avoiding Humins

“…In this experiment, 2 mM Gd(III) complex was added to the reaction mixture to increase the signal-to-noise ratio of the experiment. 56 Time series of S3). Compounds were identified using a suite of homo-and heteronuclear 2D NMR assignment spectra including 1 H− 1 H COSY, 1 H− 1 H TOCSY, 1 H− 1 H ROESY, 1 H− 13 C HSQC, and 1 H− 13 C HMBC spectra on samples of reaction mixtures that had been stabilized by reducing the temperature to 30 °C.…”

“…A time series of 13 C NMR spectra using natural abundance substrate (and 30° flip angle and inverse gated decoupling of 1 H) was acquired for tracking the conversion of 900 mM xylose by 30 mM SnCl 4 in DMSO/water (85/15%) at 70 °C by accumulating 256 transients with an interscan relaxation delay of 3.3 s and sampling the FID for 0.68 s (32,768 complex data points). In this experiment, 2 mM Gd­(III) complex was added to the reaction mixture to increase the signal-to-noise ratio of the experiment …”

A Guideline to Determine Faradaic Efficiency in Electrochemical CO2 Reduction

“… The detection limit of NMR varies depending on the product and instrument used (Table S2). ,, Recently it has been shown that the detection limit can be further improved by using the WATERGATE suppression method . A drawback of NMR is that highly volatile products such as acetaldehyde cannot be detected, when formed in very low concentrations.…”

Pathways and their usage in the conversion of carbohydrates by aqueous barium hydroxide: insights from hyperpolarized and quantitative NMR

“…Required waiting times in quantitative experiments were shortened through the addition of paramagnetic additives to improve sensitivity and shorten time demand. 2,37,38 Careful qNMR quantifications of the detected species after varying reaction times and temperatures are shown in Fig. 5 (and S4-S7, ESI †).…”

“…Such insights can remain challenging, as isomeric forms of carbohydrates and their dehydration or cleavage products need to be distinguished. Fortunately, ever-improving methodologies for guiding biomass conversion are being developed and encompass for instance NMR spectroscopy, [2][3][4][5][6][7][8][9][10] optical operando spectroscopy, [11][12][13] X-ray diffraction or absorption spectroscopy, 14 inelastic neutron scattering, 15,16 and DFT calculations. [17][18][19][20] Among the chemicals that can be derived from hexoses are lactic acid (2-hydoxypropanoic acid) and its esters.…”