Surface Reaction Kinetics of the Oxidation and Reforming of Propane over Rh/Al₂O₃ Catalysts

Abstract

A multi‐step surface reaction mechanism for partial oxidation and steam reforming of propane over Rh/Al2O3 catalysts is presented. The mechanism is also applicable to model reactions of the subsystems H2/CO/H2O/CO2/O2/CH4. A stagnation–flow reactor with a catalytically coated disk is used to determine the surface reaction rate and spatial concentration profiles on top of the catalytic plate using a micro‐probe sampling technique. The reactor configuration facilitates one‐dimensional modeling of coupled diffusive and convective transport within the gas‐phase boundary layer coupled with detailed heterogeneous chemistry models of the zero‐dimensional surface. The reaction system is studied at varying inlet concentrations and temperatures. The established reaction kinetics are furthermore tested by simulation of autothermal reforming of propane in an annular reactor previously described by Pagani.

Constrained Chemical Dynamics of CO Dissociation/Hydrogenation on Rh Surfaces

“…Because of the underlying inaccuracies in the density functionala pproximationsa nd the models ystemsu sed in the calculations,hierarchicalr efiningofmechanismsusing semiempirical methods and/or experimental data is anotherc ommon approacht om echanism development. Thisi ncludes the works of Karakayaa nd Deutschmann supported by experimental data, [10,[18][19][20] the workso fV lachos andM aestri [7,[21][22][23] based on a hierarchical approach, the model of Mei et al [6] developed using both DFT and experiments, and our previouss emiempirical work on Rh. [9] Despite these efforts, agreement between the barriers obtained for the studiedp athways can vary considerably (see Ta ble 1), even thought he underlying ab initio and semiempirical methods used are similar.…”

“…The microkinetic modeling of syngas conversion to alcohols over Rh surfaces is severely hindered by the lack of experimental data exploring this process. However, stagnation flow experiments have been performed by Deutschmann and co‐workers for the H 2 +O 2 , CO+O 2 , CO+H 2 +O 2 , CH 4 +O 2 , and C 3 H 6 +O 2 systems. As a consequence, we decided to apply inlet conditions similar to those used in the microkinetic analysis performed by Filot et al., in the stagnation‐flow configuration consistent with the experimental geometry used by Karakaya and Deutschmann for H 2 oxidation over Rh/alumina …”

“…Because of the underlying inaccuracies in the density functional approximations and the model systems used in the calculations, hierarchical refining of mechanisms using semiempirical methods and/or experimental data is another common approach to mechanism development. This includes the works of Karakaya and Deutschmann supported by experimental data, the works of Vlachos and Maestri based on a hierarchical approach, the model of Mei et al . developed using both DFT and experiments, and our previous semiempirical work on Rh .…”

“…Additionally,t he large number of electrons present in the studied systemsl eads to ah igh computational cost. Despite these complications, recent efforts [6][7][8][9][10] have provided the first steps toward truly predictive microkineticm odels applicable to such complex systems.…”

Thermodynamic Considerations on the Oxidation State of Co/γ‐Al2O3 and Ni/γ‐Al2O3 Catalysts under Dry and Steam Reforming Conditions

“…The main challenge in taking dry reforming to the commercial scale is the need for stable and affordable catalysts . Although several noble metals such as Rh, Ru, Ir, and Pd show good catalytic activity and stability, they are hardly suitable for large‐scale applications because of their limited availability and high costs. More affordable transition metals such as Ni and Co are therefore studied for their potential use in dry reforming of methane.…”