H₂ and CO Heterogeneous Kinetic Coupling during Combustion of H₂/CO/O₂/N₂ Mixtures over Rhodium

Abstract

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.

Department(s)

Mechanical and Aerospace Engineering

Comments

Support by the Swiss Federal Office of Energy and the EU project HRC-Power is acknowledged.

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)

0010-2180

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2019 The Combustion Institute, All rights reserved.

Publication Date

01 Apr 2019

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