In situ reaction monitoring in heterogeneous catalysts by a benchtop NMR spectrometer

Abstract

Understanding the reactivity and mass transport properties of porous heterogenous catalysts is important for the development of new materials. Whereas MRI has previously been used to correlate chemical kinetics and hydrodynamics under operando conditions, this paper demonstrates that a modern benchtop NMR spectrometer is a suitable alternative to obtain diverse reaction information in porous heterogeneous catalyst materials on a smaller scale. Besides information about the chemical conversion within the pores, it can also be used to study changes of surface interaction by T 1 /T 2 NMR relaxometry techniques and changes in mass transport by PFG NMR from a single chemical reaction.

Pulsed field gradient NMR diffusion measurement in nanoporous materials

“…with uniform concentrations all over the sample. More detailed information, with the option of measuring the evolution of concentration profiles over the sample, is provided by the application of magnetic resonance tomography (MRT) [5,6,203,204], see also (Price et al in this issue). However, starting with already the very first attempts of such studies in uptake measurements with beds of zeolite crystallites [205], see also Sect.…”

“…However, combination with magnetic resonance imaging (MRI, see, e.g. [5][6][7] and Price et al this volume) also opens up the option of spatially resolved measurement.…”

Recent Applications of Benchtop Nuclear Magnetic Resonance Spectroscopy

“…In particular, benchtop NMR spectrometers have remarkably high potential, as they are sufficiently compact and portable to be operated even in a fume hood (Table 4). Comparison of offline gas-chromatographic method and online NMR method for monitoring toluene hydrogenation MHz 1 H NMR [62] Online monitoring of transfer hydrogenation of acetophenone to phenylethanol MHz 1 H NMR [63] Online monitoring of Grignard reagent preparation using fluid-bed Mg column MHz 1 H NMR [64] Chemical reaction (Fischer esterification, Suzuki coupling, oxime reaction) monitoring using a flow cell MHz 1 H NMR [65] In-and online monitoring of hypervalent I(III)-mediated cyclopropanation with solvent switching system MHz 1 H NMR COSY [66] Continuous monitoring of esterification using bypass method in flow cell to control temperature and pressure MHz 1 H NMR [67] Inline monitoring of complex nitration in flow using multivariate analysis MHz 1 H NMR [68] Bayesian approach for automated quantitative analysis using mixtures of alcohols and acetates MHz 1 H NMR [69] Exploration of data acquisition parameter selection such as flow and mixing behavior of continuous Reaction monitoring of porous heterogeneous catalysts using reduction of 1-octene over Pd/TiO 2 as example reaction MHz 1 H NMR T 1 /T 2 NMR relaxometry [80] Online monitoring of biocatalytic synthesis of aromatic amino alcohols MHz 1 H NMR [81] Real-time monitoring of highly enriched parahydrogen production MHz 1 H NMR [82] As real-time measurements using benchtop NMR spectroscopy become possible in "inline" or "online" methods, the number of related works and industrial applications gradually increases [61,83,84]. "Inline" means that the NMR probe and the reaction system are directly connected in series so that all reaction matrices are continuously analyzed by the NMR device (Figure 5), while "online" means that the NMR probe and the reaction system are not directly connected, with samples periodically collected during the reaction transmitted to the analysis system.…”

Ultrafast Laplace NMR to study metal–ligand interactions in reversible polarisation transfer from parahydrogen

“…Laplace NMR has been used to monitor chemical processes that result in changes in T 1 , T 2 or D, 54,55 although the technique is most typically applied to detection of bulk water at M concentrations. 36,56,57 Here, monitoring of chemical reactions involving species at tens of mM concentrations using ultrafast LNMR has been demonstrated.…”