HONEYCOMB SUPPORTED PEROVSKITE CATALYSTS FOR AMMONIA
OXIDATION PROCESSES
L. A. Isupova, N.A. Kulikovskaya, E.F. Sutormina, S. V. Tsybulya, N.A.Rudina, I.A. Ovsyannikova,
I.A. Zolotarskii, V.A. Sadykov
Boreskov Institute of Catalysis SB RAS, pr. Lavrentieva, 5, Novosibirsk, Russia, 630090
Introduction
High-temperature catalytic processes such as deep and partial oxidation of
methane, its autothermal reforming, fuels combustion, ammonia oxidation into NO etc are
now among the most rapidly developing fields in heterogeneous industrial catalysis. Complex
oxides with perovskite structure were shown to be promising for such applications. For those
processes occurring at short contact times, the monolith honeycomb shape of catalysts is often
required. There are two types of monolith catalysts – bulk (consisting of active component
mainly) and supported (impregnated on an inert substrate). Early a monolith honeycomb
perovskite catalysts for ammonia oxidation process was developed in Boreskov Institute of
catalysis SB RAS and is used now in UKL-7 plants in Russia [1]. Another traditional
approach in technology of monolithic catalysts preparation consists in supporting the active
components on the refractory monolithic carrier. The method developed by Pechini [2] seems
to be promising for catalysts preparations with strong surface active component enrichment
(with formation of active film) [3]. This paper present data on supported perovskites on
cordierite honeycomb carrier characterized with low thermal expansion coefficient that is very
important for catalyst stability to thermal cycles.
Experimental
Supported perovskites LaMeO3 (Me = Mn, Co, Fe, Ni, Cu) were prepared by
impregnation of thin wall (wall thickness ~ 0.25 mm) monolithic cordierite support with
square or triangular channels ~ 1-1.5 mm, specific surface area ~2 m2/g and mean pore radius
~ 0.12 microns by solutions of nitrates salts in the ethylene glycol with added citric acid.
After drying at 100-200 oC, a film of polymerized metal-ether complexes strongly adhering to
the monolithic support walls is formed. After annealing at temperatures exceeding 500 oC, the
organic residue is burned, and porous perovskite supported layer emerges. For comparison,
supported 3d oxides were also prepared. To prevent interaction between the active component
and support as well as to increase the active component content a secondary sublayer was
coated. Chemical compositions of the layers are given in the Table 1. The structural and
textural features of supported perovskites were studied by XRD, SEM, X-ray microanalysis,
thermal analysis and adsorption measurements. Catalytic properties were investigated in NH3
oxidation process in the flow installation at 700-900 oC and atmospheric pressure. Samples in
the form of fragments of honeycomb catalysts with diameter ~26 mm and lenght of ~50 mm
were tested. Gas mixture (5% ammonia in the air) was feed with 7.5 l/min flow rate. The
ammonia content was determined with on-line spectrophotometer analysis.
Results and discussions
According to the thermal analysis data, the processes of the gases evolution from the
amorphous precursors formed by oxidative decomposition of polymerized organometallic
composites formed at the drying stage, are completed only at temperatures exceeding 800 oC.
Hence the calcination at 900 oC was usually used for catalysts preparation. The amount of
supported oxide was varied in the range 2-10%. Data on pore size distribution show decrease
in the pore volume value of supported catalysts as compared with carrier that may be due to a
partial entering of active component into the carrier pores. X-ray microanalysis revealed that
active component was distributed uniformly across the wall thickness and formed a 2-3 µm
grainy layer which repeated a surface relief. This porous layer was composed by separate
grains, and its morphology is nearly independent upon the calcination temperature.
In the reaction of ammonia oxidation, the most active catalysts were found to be those
supported on the secondary layer or impregnated with active component twice. Perovskites
are more active than corresponding simple 3d oxides. Cobaltite, magnites and cuprites of
lanthanum are the most efficient at their content ~ 5-6% (Table 1). Stability of prepared
catalysts was proved by catalyst testing after 3 months run in UKL-7 plant. The catalyst has
retained 70% of its initial activity. Hence new perovskite catalysts supported by Pechini route
on cordierite honeycomb substrate have been developed for ammonia oxidation process.
Table 1. Influence of the chemical composition of active component (LaCoO 3 or LaMnO3) and
secondary sublayer on the maximal NO x yield in ammonia oxidation process.
LaCoO3
Secondary layer
No
Ln2O3
ZrO2
Co3O4
LaCoO3
NO output
35.2 %
76.3 %
81.8 %
78.5 %
79.5 %
LaMnO3
Secondary layer
No
Ln2O3
ZrO2
MnO2
LaMnO3
References
1.
2.
3.
V.A. Sadykov, L.A. Isupova et all. Appl. Catal.:A General, 204 Issue 1 (2000) 59.
M. P. Pechini. U.S. Patent No 3,330,697.
L.A. Isupova et al., Catal. Today. 75/1-4 (2002) 305.
NO output
13.7 %
51.0 %
64.2 %
65.1 %
59.4 %