X-ray absorption spectroscopy under reaction conditions: suitability of different reaction cells for combined catalyst characterization and time-resolved studies

Grunwaldt, Jan‐Dierk; Caravati, Matteo; Hannemann, Stefan; Baiker, Alfons

doi:10.1039/b403071k

Cited by 231 publications

(221 citation statements)

References 57 publications

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“…In situ spectroscopic studies have been found vital to understand the structure of heterogeneous catalysts and to optimize activity, selectivity and lifetime of catalytic processes [1][2][3][4][5][6][7][8][9][10][11]. Nowadays, a number of in situ techniques such as infrared, Raman, NMR and X-ray absorption, spectroscopy or X-ray diffraction are available.…”

Section: Introductionmentioning

confidence: 99%

Axial variation of the oxidation state of Pt-Rh/Al2O3 during partial methane oxidation in a fixed-bed reactor: An in situ X-ray absorption spectroscopy study

Grunwaldt

Baiker

2005

Catal Lett

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Probing the structure of materials in situ is of central importance in heterogeneous catalysis. Mostly, this is done in an integral manner, that is without spatial resolution. However, at high conversion in a catalyst bed prominent concentration and/or temperature profiles may exist which can result in significant spatial variation of the catalyst structure. In the present study, X-ray absorption spectroscopy combined with on-line mass spectrometry was used to monitor the structural changes of a Pt-Rh/Al 2 O 3 catalyst in a fixed-bed reactor during partial oxidation of methane. The reaction ignited at 310°C and integral X-ray absorption spectroscopy showed that the Rh-Pt-particles were reduced at the same time. However, monitoring with a beam of 1 mm Â 0.6 mm size along the axial position of the catalyst bed uncovered that Rh and Pt were still in oxidized state in the entrance region, whereas they were in reduced state in the zone at the end of the catalyst bed. The gradual transition from the reduced to the oxidized state was found to shift towards the bed entrance if the temperature was slightly increased.

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Section: Introductionmentioning

confidence: 99%

Axial variation of the oxidation state of Pt-Rh/Al2O3 during partial methane oxidation in a fixed-bed reactor: An in situ X-ray absorption spectroscopy study

Grunwaldt

Baiker

2005

Catal Lett

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“…Hence it is particularly useful for the study of complexation reactions from solution (Brown and Sturchio, 2002), the very beginnings of precipitation (Waychunas, 2001), and studies of localized reactive complexes in biochemical systems (Naqui et al, 1986;Kisker et al, 1997). It is also possible to employ XAS methods for extreme surface sensitivity by use of grazing-incidence synchrotron beams (Waychunas, 2002), for fast reaction processes using flow reactors (Grunwaldt et al, 2004), and at extreme conditions of pressure and temperature (Bassett et al, 2000;Badro et al, 1997).…”

Section: Xasmentioning

confidence: 99%

Nucleation, Growth, and Aggregation of Mineral Phases: Mechanisms and Kinetic Controls

Benning

Waychunas

2008

Kinetics of Water-Rock Interaction

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The formation of any phase, whether natural or synthetic (Fig. 7.1), is usually a disequilibrium process that follows a series of steps until a thermodynamically stable state (equilibrium) is achieved. The first step in the process of creating a new solid phase from a supersaturated solution (either aqueous or solid) is called nucleation. A particle formed by the event of nucleation usually has a poorly ordered and often highly hydrated structure. This particle is metastable with respect to ordering into a well-defined phase, which can accompany growth of the particle. This process of initiation of a new phase is defined as a first order transition and can follow various pathways involving a host of mechanisms. One of these pathways occurs when individual nuclei coalesce into larger clusters, a process defined as aggregation, which itself can follow a series of different pathways. The new phase is thermodynamically defined when the growing nucleus or aggregate has distinct properties relative to its host matrix; for example, a well-defined crystal structure, composition and/or density. These processes depend on a plethora of chemical and physical parameters that control and strongly affect the formation of new nuclei, the growth of a new crystal, or the aggregation behavior of clusters, and it is these issues that will be the focus of this chapter. We will discuss the mechanisms and rates of each process as well as the methods of quantification or modeling from the point of view of existing theoretical understanding. Each step will be illustrated with natural examples or laboratory experimental quantifications. Complementary to the information in this chapter, a detailed analysis of the mechanisms and processes that govern dissolution of a phase are discussed in detail in Chap. 5 and more detailed information about molecular modeling approaches are outlined in Chap. 2.

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“…Hence, not the chemical reaction but mass transfer of the reactants/products is rate-limiting. Recent calculations [5] showed that the internal mass transfer, which can be described by the effective diffusion coefficient D e in the bulk material is ratelimiting. For round-shaped particles the reaction time τ can be calculated according to the formula: with the size of the particles R p .…”

Section: Figurementioning

confidence: 99%

Time-Resolved and Operando XAS Studies on Heterogeneous Catalysts — From the Gas Phase Towards Reactions in Supercritical Fluids

Grunwaldt

Baiker

2007

AIP Conference Proceedings

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Abstract. X-ray absorption spectroscopy is a well-suited technique to uncover the structure of heterogeneous catalysts under reaction conditions. Different aspects of in situ cell design suitable for dynamic and catalytic studies are discussed. In addition, criteria are presented that allow estimating the influence external and internal mass transfer. Starting with studies on gas-solid reactions, including structure-activity relationships, this concept is extended to liquid-solid reactions, reactions at high pressure and in supercritical fluids. The following examples are discussed in more detail: partial oxidation of methane over Pt-Rh/Al 2 O 3 , reduction of a Cu/ZnO catalyst, alcohol oxidation over Bi-promoted Pd/Al 2 O 3 in liquid phase and over Pd/Al 2 O 3 in supercritical CO 2 , and batch reactions (e.g. CO 2 -fixation over zinc-based catalysts).

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X-ray absorption spectroscopy under reaction conditions: suitability of different reaction cells for combined catalyst characterization and time-resolved studies

Cited by 231 publications

References 57 publications

Axial variation of the oxidation state of Pt-Rh/Al2O3 during partial methane oxidation in a fixed-bed reactor: An in situ X-ray absorption spectroscopy study

Axial variation of the oxidation state of Pt-Rh/Al2O3 during partial methane oxidation in a fixed-bed reactor: An in situ X-ray absorption spectroscopy study

Nucleation, Growth, and Aggregation of Mineral Phases: Mechanisms and Kinetic Controls

Time-Resolved and Operando XAS Studies on Heterogeneous Catalysts — From the Gas Phase Towards Reactions in Supercritical Fluids

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