Disentangling catalysis and mass transport: Using diffusion measurements by pulsed field gradient NMR to reveal the microkinetics of CO oxidation over nanoporous gold

Baniani, Amineh; Wild, Stefan; Forman, Evan M.; Risse, Thomas; Vasenkov, Sergey; Bäumer, Marcus

doi:10.1016/j.jcat.2022.08.020

Cited by 2 publications

(11 citation statements)

References 43 publications

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“…Applying a suitable procedure for this process (which does not deteriorate the fragile porous structure) provided conversions being 50% higher than those achieved with the larger discs, in accord with the predictions (see Fig. 7, blue trace) [43]. Figure 8 also reveals that for samples of the latter kind, the thickness sensitively influences the productivity.…”

Section: Optimization Of a Catalysts' Performance By Reducing Mass Tr...supporting

confidence: 85%

“…The applicability of this technique was clearly demonstrated not only for measurements of self-diffusion in bulk gases, but also within porous matter, such as zeolites and oxides [2,18]. In contrast, nanostructured metal materials have not been studied until very recently at the example of npAu [43], possibly because they have been considered not to be accessible by PFG-NMR. Specifically, the induction of eddy currents has to be expected for metallic specimen which can potentially lead to measurement artefacts.…”

Section: Direct Measurement Of Gas Diffusivities By Pfg Nmrmentioning

confidence: 99%

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New Perspectives for Evaluating the Mass Transport in Porous Catalysts and Unfolding Macro- and Microkinetics

et al. 2022

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In this article we shed light on newly emerging perspectives to characterize and understand the interplay of diffusive mass transport and surface catalytic processes in pores of gas phase metal catalysts. As a case study, nanoporous gold, as an interesting example exhibiting a well-defined pore structure and a high activity for total and partial oxidation reactions is considered. PFG NMR (pulsed field gradient nuclear magnetic resonance) measurements allowed here for a quantitative evaluation of gas diffusivities within the material. STEM (scanning transmission electron microscopy) tomography furthermore provided additional insight into the structural details of the pore system, helping to judge which of its features are most decisive for slowing down mass transport. Based on the quantitative knowledge about the diffusion coefficients inside a porous catalyst, it becomes possible to disentangle mass transport contributions form the measured reaction kinetics and to determine the kinetic rate constant of the underlying catalytic surface reaction. In addition, predictions can be made for an improved effectiveness of the catalyst, i.e., optimized conversion rates. This approach will be discussed at the example of low-temperature CO oxidation, efficiently catalysed by npAu at 30 °C. The case study shall reveal that novel porous materials exhibiting well-defined micro- and mesoscopic features and sufficient catalytic activity, in combination with modern techniques to evaluate diffusive transport, offer interesting new opportunities for an integral understanding of catalytic processes. Graphical Abstract

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Section: Optimization Of a Catalysts' Performance By Reducing Mass Tr...supporting

confidence: 85%

Section: Direct Measurement Of Gas Diffusivities By Pfg Nmrmentioning

confidence: 99%

New Perspectives for Evaluating the Mass Transport in Porous Catalysts and Unfolding Macro- and Microkinetics

et al. 2022

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Section: Gas Phase Catalysismentioning

confidence: 99%

“…Recently, pulsed field gradient (PFG) NMR spectroscopy was employed to evaluate to which extent NPG’s tortuosity slows down the diffusive transport. For CO and CO 2 , as reactant and product molecules of CO oxidation, as well as for CH 4 , included in the study as an inert gas for reference purposes, consistently, a mean pathway elongation by a factor of about 2 was derived in all cases . On the basis of this result, representing the first experimental assessment of NPG’s (diffusive) tortuosity factor, and the mean pore diameter to take the contribution of Knudsen diffusion into account, it was possible to quantitatively describe the macrokinetics, i.e., the experimentally observable and obtainable catalytic CO conversion rates, as a function of the diffusive mass transport and the microkinetics of the surface reactions.…”

Section: Gas Phase Catalysismentioning

confidence: 99%

“…When, however, breaking up the discs into smaller platelets (of the same thickness) so that their diameters decrease to just about a few 100 micometers, the efficiency can be increased to almost 100%in agreement with the predictions of the Thiele modulus formalism and NPG’s structural characteristics (see solid line in Figure ). This result demonstrates that the well-defined and well-controllable features of NPG in conjunction with options to adapt the macroscopic shape of the material to a particular set of reaction conditions provides a good basis for predicting and optimizing its performance in a given catalytic application …”

Section: Gas Phase Catalysismentioning

confidence: 99%

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Nanoporous Gold: From Structure Evolution to Functional Properties in Catalysis and Electrochemistry

et al. 2023

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Nanoporous gold (NPG) is characterized by a bicontinuous network of nanometer-sized metallic struts and interconnected pores formed spontaneously by oxidative dissolution of the less noble element from gold alloys. The resulting material exhibits decent catalytic activity for low-temperature, aerobic total as well as partial oxidation reactions, the oxidative coupling of methanol to methyl formate being the prototypical example. This review not only provides a critical discussion of ways to tune the morphology and composition of this material and its implication for catalysis and electrocatalysis, but will also exemplarily review the current mechanistic understanding of the partial oxidation of methanol using information from quantum chemical studies, model studies on single-crystal surfaces, gas phase catalysis, aerobic liquid phase oxidation, and electrocatalysis. In this respect, a particular focus will be on mechanistic aspects not well understood, yet. Apart from the mechanistic aspects of catalysis, best practice examples with respect to material preparation and characterization will be discussed. These can improve the reproducibility of the materials property such as the catalytic activity and selectivity as well as the scope of reactions being identified as the main challenges for a broader application of NPG in target-oriented organic synthesis.

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Disentangling catalysis and mass transport: Using diffusion measurements by pulsed field gradient NMR to reveal the microkinetics of CO oxidation over nanoporous gold

Cited by 2 publications

References 43 publications

New Perspectives for Evaluating the Mass Transport in Porous Catalysts and Unfolding Macro- and Microkinetics

New Perspectives for Evaluating the Mass Transport in Porous Catalysts and Unfolding Macro- and Microkinetics

Nanoporous Gold: From Structure Evolution to Functional Properties in Catalysis and Electrochemistry

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