A new MAS NMR probe for in situ investigations of hydrocarbon conversion on solid catalysts under continuous-flow conditions

Hunger, Michael; Horvath, Thomas D.

doi:10.1039/c39950001423

Cited by 115 publications

(78 citation statements)

References 3 publications

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“…In the future, we can expect that (i) these approaches have the potential for further improvements and applications, for example increase in the sensitivity of in situ MAS NMR spectroscopy by employing the dynamic nuclear polarization (DNP) technique etc. ; (ii) since many active sites in/on heterogeneous catalysts are low-g nuclei, such as 95 Mo, 107 Ag, 47,49 Ti, their direct NMR measurements under reaction conditions should go to the ultra-high field magnet using the Carr-Purcell-Meiboom-Gill (CPMG) sequence and/or twodimensional MQ MAS NMR technique etc. to increase the detection resolution; (iii) joint in situ MAS NMR experiments and quantum chemical calculations and simulations using DFT, Monte Carlo etc.…”

Section: Discussionmentioning

confidence: 99%

“…In spite of these technical difficulties, a few laboratories have developed flow MAS probes that have yielded promising results. [12][13][14][46][47][48] Among these protocols, the most widely used one was designed by Hunger and Horvath 47 who first reported a MAS flow probe allowing reactant gas to flow over a catalyst. This equipment consists of a MAS rotor with an axially placed tube inserted into the rotor via a hole in the rotor cap.…”

Section: Continuous-flow Conditionsmentioning

confidence: 99%

“…In order to investigate the heterogeneous catalysis in large-scale industrial processes, many attempts have been made to develop in situ solid-state NMR under continuous-flow conditions. [10][11][12][13][14] The most successful and practical design is that reported by Hunger et al directly utilizing the NMR rotor as a fix-bed reactor with continuous flowing of reactants under magic-angle spinning. 11 In some cases, continuous-flow MAS NMR spectroscopy is combined with other analytical techniques such as gas chromatography, 15,16 UV/Vis spectroscopy 17 or laser hyperpolarized xenon 18 to give additional information on the reaction intermediates, products and kinetics.…”

Section: Introductionmentioning

confidence: 99%

“…[10][11][12][13][14] The most successful and practical design is that reported by Hunger et al directly utilizing the NMR rotor as a fix-bed reactor with continuous flowing of reactants under magic-angle spinning. 11 In some cases, continuous-flow MAS NMR spectroscopy is combined with other analytical techniques such as gas chromatography, 15,16 UV/Vis spectroscopy 17 or laser hyperpolarized xenon 18 to give additional information on the reaction intermediates, products and kinetics. In this review, firstly the experimental setups for in situ MAS NMR are briefly described, then more recent research progress on the applications of in situ MAS NMR in the acidity characterizations, reaction mechanisms and kinetics of some important organic reactions mainly catalyzed by zeolites are summarized.…”

Section: Introductionmentioning

confidence: 99%

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In situsolid-state NMR for heterogeneous catalysis: a joint experimental and theoretical approach

et al. 2012

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In situ solid-state NMR is a well-established tool for investigations of the structures of the adsorbed reactants, intermediates and products on the surface of solid catalysts. The techniques allow identifications of both the active sites such as acidic sites and reaction processes after introduction of adsorbates and reactants inside an NMR rotor under magic angle spinning (MAS). The in situ solid-state NMR studies of the reactions can be achieved in two ways, i.e. under batch-like or continuous-flow conditions. The former technique is low cost and accessible to the commercial instrument while the latter one is close to the real catalytic reactions on the solids. This critical review describes the research progress on the in situ solid-state NMR techniques and the applications in heterogeneous catalysis under batch-like and continuous-flow conditions in recent years. Some typical probe molecules are summarized here to detect the Brønsted and Lewis acidic sites by MAS NMR. The catalytic reactions discussed in this review include methane aromatization, olefin selective oxidation and olefin metathesis on the metal oxide-containing zeolites. With combining the in situ MAS NMR spectroscopy and the density functional theoretical (DFT) calculations, the intermediates on the catalyst can be identified, and the reaction mechanism is revealed. Reaction kinetic analysis in the nanospace instead of in the bulk state can also be performed by employing laser-enhanced MAS NMR techniques in the in situ flow mode (163 references).

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Section: Discussionmentioning

confidence: 99%

Section: Continuous-flow Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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In situsolid-state NMR for heterogeneous catalysis: a joint experimental and theoretical approach

et al. 2012

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“…One example is the following. Starting from a standard Bruker 7 mm MAS probe, a PFA capillary tube is accommodated inside the probe to ensure the injection of the gas mixture [69]. It is connected to a glass tube which delivers the gas mixture to the sample, carefully packed inside a 7 mm rotor, through a hole drilled in the rotor cap.…”

Section: Spin Exchange Optical Pumping (Seop)mentioning

confidence: 99%