M. Ferrandon et al., Thermal stability of metal-supported catalysts for reduction of cold-startemissions in a wood-fired domestic boiler, CATAL TODAY, 53(4), 1999, pp. 647-659
The aim of the present work is to develop a catalyst based on a mixture of
manganese oxides and platinum supported on a metallic monolith for abatemen
t of emissions from wood combustion, particularly during the cold-start pha
se. The activity and the thermal stability of the catalysts have been studi
ed in the laboratory, before performing tests in a wood-stove. The effect o
f the hydrothermal treatment at 900 degrees C on the adherence of the washc
oat onto a metallic substrate was studied using scanning electronic microsc
ope. It revealed well-adhering washcoat onto the metallic support due to th
e growth of the alumina whiskers during the treatment. The influence of the
amount of washcoat, as well as the influence of the concentration of manga
nese oxides in it (Mn: 5 to 20 mol%/Al2O3) on the activity of fresh and hyd
rothermally-treated catalysts were studied. The activity tests were carried
out using a mixture of carbon monoxide, naphthalene and methane in the pre
sence of air, steam and carbon dioxide to resemble the flue gases from wood
combustion. On the fresh catalysts, containing the same total amount of ma
nganese, a high concentration of manganese oxides in the washcoat favoured
the oxidation of carbon monoxide and naphthalene, whereas a lower concentra
tion of manganese oxides in the washcoat gave higher activity for the oxida
tion of methane. An increased total amount of manganese oxides in the catal
ysts, which had the same amount of washcoat, resulted in an increase in act
ivity for the oxidation of the three combustibles. After thermal treatment
at 900 degrees C for 270 h in steam, most of the manganese oxide catalysts
were activated for the oxidation of carbon monoxide and naphthalene while o
nly being slightly deactivated for the oxidation of methane. The addition o
f manganese oxides in the washcoat, however, lowers the temperature of the
gamma- to alpha-alumina phase transformation. Platinum (0.5 mol%) was added
to the manganese oxide (10 mol%) catalyst to improve its activity. A plati
num catalyst was also tested for comparison. The platinum and the mixed cat
alysts showed similar activity for the oxidation of carbon monoxide and nap
hthalene, while the mixed catalysts were more active for the oxidation of m
ethane. A similarly mixed MnOx-Pt (10-0.5 mol%) catalyst supported on Al2O3
stabilised with 3% lanthanum, but at larger scale, was tested in a wood-st
ove. The possibility of pre-heating the catalyst during the start-up phase
was studied. The tests revealed a strong decrease of the carbon monoxide an
d unburned hydrocarbons emissions during the start-up phase when the cataly
st was pre-heated with hot air compared with no pre-heating or no catalyst.
(C)1999 Elsevier Science B.V. All rights reserved.