Chemical and geometric effects of Ce and washcoat addition on catalytic partial oxidation of CH4 on Rh probed by spatially resolved measurements

Donazzi, Alessandro; Michael, Brian C.; Schmidt, L.D.

doi:10.1016/j.jcat.2008.09.028

Cited by 58 publications

(26 citation statements)

References 21 publications

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“…The presence of a hot zone at the entrance of packed bed CH 4 -CPO reactors was also identified by Basini et al [10,11] using IR-thermography. The recent introduction of the so-called ''spatially resolved sampling technique'', first applied by Horn et al [12,13] to characterize the temperature and concentration profiles in Rh-coated foams under working CPO conditions and later assessed in other studies [14][15][16][17], has completed the picture. A sharp peak of temperature establishes on the catalyst surface at the reactor entrance, while a smoother maximum is presented by the gas-phase temperature.…”

Section: Introductionmentioning

confidence: 99%

“…Within this very entrance region, O 2 is completely consumed; this is the reason why it has been identified as an ''oxidation zone''. Methane consumption, however, occurs along the whole length of the monolith (especially in the case of catalysts with little Rh dispersion [16]) and a ''reforming zone'' has been identified downstream of the oxidation zone, indicating the presence of an oxygen-depleted reacting system.…”

Section: Introductionmentioning

confidence: 99%

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Optimal Design of A CPO-Reformer of Light Hydrocarbons with Honeycomb Catalyst: Effect of Frontal Heat Dispersions on the Temperature Profiles

et al. 2011

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This paper extends a previous investigation on the thermal behavior of CH 4 -CPO reformers with honeycomb catalysts. Modeling and experimental studies on the short contact time catalytic partial oxidation (CPO) of CH 4 to syngas from our and from other groups have shown that Rh-catalysts rapidly deactivate at the very high temperatures, close to 1000°C, that establish in the inlet zone of the reactor. We have previously shown that a significant reduction of the surface hot-spot temperature can be obtained by properly designing the catalyst: beneficial effects are observed at increasing opening of the honeycomb channels, which decreases the rate of O 2 inter-phase mass transfer, and at increasing catalyst activity, which promotes the rate of the endothermic reactions. In this work, we explore the effect of the reactor configuration, namely the effect of heat dispersion from the glowing front face of the monolith. Three reactor configurations were compared in CH 4 -CPO experiments: (i) a configuration with perfect continuity between the front heat shield (FHS) and the catalytic module, which behaved close to an ideal adiabatic reactor, (ii) a configuration where the FHS was separated from the catalytic monolith and (iii) a configuration where the FHS was at large distance from the catalytic module. State of the art experimental tools, including the spatially resolved measurement of temperature and concentration profiles were used to characterize the thermal behavior of the various configurations. Detailed kinetic modeling supported the analysis of data. The results showed that, at the expense of a small loss of thermal efficiency, a very moderate loss of performance in terms of conversion and selectivity, but, remarkably, an important reduction of the surface inlet temperatures were achieved. Preliminary experiments with propane/air mixtures suggest that the adoption of a moderately dispersive reactor can represent a promising solution for the stable operation of catalytic units treating heavier fuels than methane.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Optimal Design of A CPO-Reformer of Light Hydrocarbons with Honeycomb Catalyst: Effect of Frontal Heat Dispersions on the Temperature Profiles

et al. 2011

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“…Qualitatively, this behavior is what our and other research groups have observed also in the case of a CH 4 -CPO experiment on rhodium, and can be fully explained by the catalytic production of syngas on rhodium. [4,[9][10][11] Thus, integral measurements (i.e., measurements of temperature and composition collected exclusively at the reactor outlet) would have suggested the unique existence of a heterogeneous process. A purely catalytic process was, for instance, inferred by Deutschmann and co-workers, [12] who analyzed integral data of iso-octane partial oxidation over Rh at O/C > 1.…”

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confidence: 99%

Synergy of Homogeneous and Heterogeneous Chemistry Probed by In Situ Spatially Resolved Measurements of Temperature and Composition

et al. 2011

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The interaction between heterogeneous and homogeneous chemistries is a crucial issue for high-temperature catalytic processes. In particular, the assessment of the main routes that control the selectivity to the desired products is essential for the design and safe operation of reaction units. This assessment is particularly true for the ultrafast conversion of hydrocarbons in short-contact-time (SCT) reactors that play a pivotal role in the effort to cope with the worldwide growing demand for more efficient exploitation of energy and material resources. Examples are the catalytically assisted combustion for gas turbines with ultralow emissions, the catalytic partial oxidation (CPO) of hydrocarbons to H 2 or CO/H 2 mixtures (i.e., syngas), [1] and the oxidative dehydrogenation (ODH) of light alkanes to olefins. [2,3] As a common feature, these processes operate in autothermal and compact reactors, with noble-metal catalysts (palladium, rhodium, and platinum). An enormous energy intensity is peculiar to the SCT autothermal conversion of hydrocarbons over noble metals. Strongly exothermic and endothermic reactions proceed on the catalyst surface at extremely high rates. As a consequence, sharp gradients of temperature (up to 200 8C mm À1 ) and concentration are established within the small reactor volumes. Temperatures ranging from 250 to 1100 8C are generally experienced within a few millimeters. Such a level of severity-in terms of power density and extent of temperature and concentration gradients-is typical of flames and gas-phase oxidation processes in general. For a catalytic process, however, these conditions represent a thoroughly unconventional kinetic regime. To best grasp the intensity and the speed of the involved phenomena, we need to think of SCT conversion of light alkanes as the catalytic equivalent of a flame. This analogy can clearly depict the complexity of the process and emphasize the related scientific issues: To what extent does a catalytic process "stick" to the catalyst surface at these very high temperatures, where the adsorption of species is thermodynamically unfavored? Can the gas-phase activation of C À H bonds (e.g., the formation and propagation of radicals) cooperate or compete with the catalytic process?In this respect, it is largely accepted that in the case of CH 4 CPO over rhodium the gas-phase paths are negligible at atmospheric pressure and the catalytic route dominates. [4][5][6] Conversely, the SCT-ODH of short alkanes over platinum proceeds mainly in the gas phase, thus giving rise to the production of olefins and other hydrocarbon species. [7,8] On the basis of these examples, we could conclude that either catalytic or gas-phase chemistry governs the SCT conversion of hydrocarbons, depending only on the stability of the CÀH bond in the gas phase.Herein, by using novel techniques for collecting spatially resolved temperature and concentration profiles, we show that the partial oxidation of short-chain alkanes over rhodium breaks the paradigmatic compartments of heterogeneou...

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“…In addition, this method is extended to prepare a structured catalyst using structured carbon nanofiber (SCNF) supported Cu-CeO 2 as an example. For the Zr x Ce 1-x O 2 (x = 0, 0.5, 0.75, 1)/Al 2 O 3 nanocomposites (as a promising catalyst support for catalytic partial oxidation of methane [28][29][30]), an excessive solvent impregnation (ESI) method is used; For the SCNFs supported Cu-CeO 2 catalysts (as a promising catalyst for preferential oxidation of CO in hydrogenrich gases [31,32]), incipient wetness impregnation is used. IR, TEM, XRD, TGA-DTA-MS experiments are performed to investigate the chemical reaction and structure evolution during the impregnation, drying and calcination procedures, in order to understand the interaction between the active components and the surface of the solid matrices.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Supported Catalysts by Impregnation and Calcination of Low-Temperature Polymerizable Metal-Complexes

Zhao

Boullosa-Eiras

et al. 2011

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The low-temperature polymerizable metal complex solution has been used as an active component precursor to prepare supported (structured) catalysts by a straight-forward sequence of impregnation, drying and calcination. Two typical samples, 5 wt% Zr x Ce 1-x O 2 / Al 2 O 3 nanocomposite and structured carbon nanofiber supported Cu-CeO 2 catalyst, are prepared to explore the potential of this method in the controlled synthesis of catalysts and catalyst supports. The interaction between the active component precursor and the surface of the solid matrices during impregnation and drying is investigated by infrared spectroscopy (IR) and transmission electron microscopy (TEM), demonstrating that the in situ polymerization process is crucial for the deposition of the active component on the surface of solid matrices. The evolution of the phase transformation and the structure of the produced materials during the calcination step is studied by coupling thermal gravimetric analysis-differential thermal analysis-mass spectroscopy (TGA-DTA-MS), TEM and X-ray diffraction (XRD) measurements, indicating that higher thermal stable particles or smaller particles can be obtained with the presence of the Al 2 O 3 or structured carbon nanofibers (SCNF), respectively, after calcination. This method combines the advantages of sol-gel and impregnation, representing a promising route for preparing supported catalysts and catalyst supports. The limitations of the method are also discussed.

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Chemical and geometric effects of Ce and washcoat addition on catalytic partial oxidation of CH4 on Rh probed by spatially resolved measurements

Cited by 58 publications

References 21 publications

Optimal Design of A CPO-Reformer of Light Hydrocarbons with Honeycomb Catalyst: Effect of Frontal Heat Dispersions on the Temperature Profiles

Optimal Design of A CPO-Reformer of Light Hydrocarbons with Honeycomb Catalyst: Effect of Frontal Heat Dispersions on the Temperature Profiles

Synergy of Homogeneous and Heterogeneous Chemistry Probed by In Situ Spatially Resolved Measurements of Temperature and Composition

Synthesis of Supported Catalysts by Impregnation and Calcination of Low-Temperature Polymerizable Metal-Complexes

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