Abstract
Hot gas-clean up will improve the efficiency of emerging gasification
technologies. Selective catalytic oxidation (SCO) of ammonia is a
promising approach for dealing with the main fixed nitrogen species. The
work presented here comprises both laboratory scale experimental
measurements of potential SCO catalysts, as well as the development of a
simple four-step reaction model to describe the behaviour of one of the
more promising catalysts. A range of transition metal oxides supported
on γ-alumina were studied for their activity in the SCO of ammonia in a
simulated gasification gas mixture containing CO, H2O, H2, CO2, CH4, H2S
and toluene as model tar species. Both copper and chromium based
catalysts demonstrated a window of operating temperature over which they
were resistant to poisoning by H2S; Cu/Al2O3 was in fact promoted by this gas for the SCO reaction. The ammonia conversion over 7% Cu/Al2O3
was studied in more detail, and this data was further used to develop a
kinetic model for the reactions taking place over the temperature range
723–906 K. Excellent conversion and selectivity to N2 was found in the temperature window 973–1173 K and 2.6 vol% O2. However, it also catalyses a rapid H2O2
reaction. This reaction consumes all remaining available oxygen so that
no other oxidation reactions take place (e.g. of methane or ‘tar’). The
four-step reaction model was developed using the PLUG application of
Chemkin and Surface Chemkin software coupled with the gas-phase
mechanism Kilpinen 97. Rates for the heterogeneous oxidation of ammonia
and hydrogen are included as well as forward and reverse reactions of
the water gas shift. Over the temperature range in question, the surface
reaction rates are much faster than the gas-phase reactions. The model
is applicable for the 723–906 K temperature range using a gas mixture containing 0.4 vol% ammonia and 0.01 vol% H2S in the presence of O2 (0–2.6 vol%).
Original language | English |
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Pages (from-to) | 139 - 146 |
Number of pages | 8 |
Journal | Applied Catalysis B: Environmental |
Volume | 60 |
Issue number | 1-2 |
DOIs | |
Publication status | Published - 2005 |
MoE publication type | A1 Journal article-refereed |
Keywords
- Ammonia (selective catalytic oxidation)
- Gasification (biomass)
- Modelling (kinetics, ammonia oxidation)