H₂ and CO Heterogeneous Kinetic Coupling during Combustion of H₂/CO/O₂/N₂ Mixtures over Rhodium
The chemical interactions between CO and H2 over rhodium were investigated for H2/CO/O2/N2 mixtures with H2:CO volumetric ratios 1:5-3:1, overall fuel-lean equivalence ratios φ = 0.13 and 0.23, a pressure of 5 bar, and surface temperatures 510-610 K. This temperature range was particularly important for catalytic ignition in hybrid hetero-/homogeneous combustion concepts of large gas-turbines operating at part-load or idling conditions and in recuperative micro-turbine-based microreactors at normal operation. In situ Raman measurements of major gas-phase species concentrations were carried out over the catalyst boundary layer, while 2-D simulations were performed with a detailed catalytic reaction scheme. Comparisons of simulations and measurements assessed the performance of the catalytic reaction mechanism for the oxidation of pure CO, pure H2 and H2/CO fuel blends. Transition temperatures were identified below (above) which H2 inhibited (promoted) the oxidation of CO. For a given equivalence ratio, the transition temperatures decreased significantly with increasing H2:CO volumetric ratio (595 K for H2:CO = 1:5 and less than 535 K for H2:CO = 3:1, at φ = 0.13) while for a given H2:CO volumetric ratio they dropped moderately with decreasing φ. This behavior was fundamentally different to that of platinum catalysts, whereby transition temperatures depended weakly on H2:CO volumetric ratio and stronger on equivalence ratio. The strong dependence of the transition temperatures on H2:CO volumetric ratio over rhodium pointed to the advantage of this catalyst when used for high-hydrogen-content ( > 80% volume) fuels in power generation applications. The promotion effect of H2 on CO oxidation above the transition temperatures was a result of the increased importance of the indirect CO oxidation route via surface COOH.
R. Sui et al., "H₂ and CO Heterogeneous Kinetic Coupling during Combustion of H₂/CO/O₂/N₂ Mixtures over Rhodium," Combustion and Flame, vol. 202, pp. 292-302, Elsevier Inc., Apr 2019.
The definitive version is available at https://doi.org/10.1016/j.combustflame.2019.01.021
Mechanical and Aerospace Engineering
Keywords and Phrases
Chemical interactions of H2 and CO over rhodium; In situ Raman measurements; Inhibition of CO oxidation by H2; Syngas catalytic combustion for power generation; Transition temperatures
International Standard Serial Number (ISSN)
Article - Journal
© 2019 The Combustion Institute, All rights reserved.
01 Apr 2019