Combustion of CH 4 /H 2 /Air Mixtures in Catalytic Microreactors

Conti

2010

Ind. Eng. Chem. Res.

Self Cite

In recent years, catalytic combustion of CH4 has been extensively studied as an alternative option to conventional thermal combustion for the production of heat and energy in view of its capability to achieve effective combustion at much lower temperatures than in conventional oxidation processes, with high efficiency and reduced pollutants such as CO and NO x . In this paper a kinetic study on 2% Pd over Ce x Zr1-x O2 catalyst is presented. The catalyst was prepared by solution combustion synthesis, fully characterized and tested for CH4 catalytic combustion. A kinetic study was carried out in a continuous recycle reactor, operated in differential conditions. Twelve different possible rate equations belonging to Eley−Rideal, Langmuir−Hinshelwood, and Mars van Krevelen models were fitted to the experimental data. The best fitting belonged to a Mars van Krevelen mechanism, considering the concentration of the molecular O2 adsorbed on a single active site, which successively dissociated creating an active site with atomic O2. The obtained kinetic parameters were inside the range reported in literature for similar catalysts (E act,1 = 23.8 kJ mol−1; E act,2 = 31.9 kJ mol−1; E act,1 * = 5.4 kJ mol−1). For comparison, to better assess the catalytic role of Pd in the CH4 combustion, also the kinetic parameters of the sole carrier, Ce x Zr1-x O2, were calculated. The best rate equation for the carrier was based on a different Mars van Krevelen mechanism, a simpler one, involving the surface reaction between adsorbed molecular oxygen and methane from the gas phase (E act,1 = 79.6 kJ mol−1, E act,2 = 114.6 kJ mol−1).

Section: Introductionmentioning

confidence: 99%

Kinetic Studies on Pd/Ce_xZr_1−xO₂ Catalyst for Methane Combustion

Conti

2010

Ind. Eng. Chem. Res.

Self Cite

“…In the literature, catalyst systems composed of Pd, PdO, Pt and their mixtures on a variety of supports (for example, SnO 2 , ZrO 2 , Al 2 O 3 , CeO 2 , TiO 2 , CeO 2 –TiO 2 , ZrO 2 ‐δ‐Al 2 O 3 ) are mainly described for the catalytic combustion of mixtures of CH 4 /CO/H 2 or the individual components 14–22. For lean CH 4 /H 2 /air mixtures, Specchia et al 23 described the catalyst system Pd/NiCrO 4 on ceramic SiC monoliths. Deshpande und Madras 24 described Pd‐ and Pt‐CeO 2 ‐based catalysts for the combustion of off‐gases from fuel cell systems.…”

Section: Introductionmentioning

confidence: 99%

Start‐Up and Load‐Change Behavior of a Catalytic Burner for a Fuel‐Cell‐Based APU for Diesel Fuel

et al. 2014

The catalytic burner CAB 4 was developed for a fuel‐cell‐based diesel‐APU (auxiliary power unit) with a capacity of 14.5 kWth,APU. In order to operate a catalytic burner in such an APU, several requirements must be met. Normal operation involves combustion of anode off‐gas from the fuel cell. If the fuel cell malfunctions or if the gas quality is insufficient, the burner must also be able to fully convert the reformate while by‐passing the fuel cell. It must be possible to catalytically ignite the burner using a reformate with increased CO‐concentration. The burner must fully convert all combustible components in the fuel‐gas at all operating points. The energy contained in the fuel gas is utilized in the CAB to generate superheated steam with no oscillations and to supply this steam to the autothermal reformer. When the fuel processing system is being shut down, the burner should be able to continue providing steam for sweeping the downstream reactors for a limited period of time. Catalytic ignition of the CAB 4 was demonstrated with a reformate containing up to 5 mol.% CO. The behavior of the burner was characterized in steady‐state operation, during load changes, during transitions in the operating mode, and during shut‐down.

“…13 Similarly, a number of different groups have used flame-based synthesis methods to prepare Pd-based combination catalysts, 14,15 as well as supported Pd catalysts. [16][17][18][19][20][21][22] Solution-based methods have frequently used Pd organometallics to prepare Pd-rich nanoparticles that were used in situ to catalyze organic reactions. [23][24][25][26][27][28][29][30] Unsupported Pd particles have previously been shown to be effective combustion catalysts, in the gas phase, however, in those studies the particle generation and catalytic combustion were done separately.…”

Section: Introductionmentioning

confidence: 99%

“…For example Nasibulin et al have demonstrated nanoparticle synthesis using Cu(acac) 2 (copper(II) acetylacetonate) entrained in a N 2 /O 2 flow and passed through a flow tube reactor, whereupon the organic ligands were burned off, leaving behind a vapor of Cu, which then condensed to form copper oxide nanoparticles . Similarly, a number of different groups have used flame-based synthesis methods to prepare Pd-based combination catalysts, , as well as supported Pd catalysts. – Solution-based methods have frequently used Pd organometallics to prepare Pd-rich nanoparticles that were used in situ to catalyze organic reactions. – …”

Section: Introductionmentioning

confidence: 99%

In Situ Generation of Pd/PdO Nanoparticle Methane Combustion Catalyst: Correlation of Particle Surface Chemistry with Ignition

et al. 2009

Decomposition of a fuel-soluble precursor was used for in situ generation of Pd/PdO nanoparticles, which then catalyzed ignition of the methane/O2/N2 flow. To help understand the relationship between particle properties and activity, the composition, structure, and surface chemical state of the particles were determined by a combination of high-resolution transmission electron microscopy (HRTEM), electron diffraction, scanning transmission electron microscopy/energy dispersive X-ray spectroscopy (STEM/EDX), and X-ray photoelectron spectroscopy (XPS). The particles, collected under methane-free conditions, were found to be primarily crystalline, metallic Pd, with TEM results showing a narrow size distribution around 8 nm and scanning mobility particle sizing measurements (SMPS) indicating a median particle size of ∼10 nm. The ignition temperature was lowered ∼150 K by the catalyst, and we present evidence that ignition is correlated with formation of a subnanometer oxidized Pd surface layer.