1070-4272/02/7510-1594 $27.00 C 2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 10, 2002, pp. 1594!1597. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 10, 2002,
Original Russian Text Copyright + 2002 by Zakharchenko.
AND ION-EXCHANGE PROCESSES
Recovery with Calcium Oxide Sorbent of Conversion Products
of Rhodium Catalyst for Ammonia Oxidation
N. I. Zakharchenko
Zhukovsky National Aerospace University, Kharkov, Ukraine
Received June 4, 2002
Abstract-The chemical aspects of recovery with a calcium oxide sorbent of rhodium lost in high-tempera-
ture oxidation of ammonia were studied. The physicochemical properties of this compound and conditions
of its formation were considered.
Catalytic oxidation of ammonia to nitrogen(II) ox-
ide underlies the industrial method for manufacture
of nitric acid . Industrial catalysts (Pt, Rh, and Pd
alloys) undergo physicochemical transformations in
technological processes, with the surface structure
and the chemical composition of the catalysts changed
. A set of such transformations of platinoid cat-
alysts leads to loss of deficient and expensive metals
of the platinum group. An effective way to diminish
the loss of platinum metals is their partial recovery
by sorption masses mainly based on calcium oxide
The mechanism of platinum recovery with calcium-
containing sorbents and the chemical aspect of the
process are rather extensively covered in the scientif-
ic literature [1, 7320]. At the same time, there is no
evidence concerning the mechanism of recovery of
rhodium, entering into the composition of industrial
catalysts for ammonia oxidation (alloy nos. 1 and 5),
with a calcium oxide sorbent; there are no data, either,
on what kind of chemical compounds are formed in
interaction between the products of conversion of
rhodium catalysts and sorbents .
The present communication reports the results ob-
tained in studying the recovery with a calcium oxide
sorbent of rhodium lost in high-temperature oxidation
As a starting compound for preparing the sorbent
was used calcium oxide of chemically pure grade.
The reagent was ground and treated with a 70% aque-
ous solution of ethynol (233% relative to the sorbent
mass) and compacted into pellets under pressure of
150 MPa. After thermal treatment of the mass in air
at 473, 673, 873, and 1253 K (2 h at each tempera-
ture), the sorbent was crashed into grains and a frac-
tion with grain size of 2 0 3 mm was selected.
Since recovery of lost metals and their compounds
is mainly effected by the surface layer of sorbents
[1, 7316, 18320], the sorbent grains were ground af-
ter every 40 h of operation and subjected to repeated
forming and thermal treatment in an inert medium
(Ar) in accordance with the scheme considered above.
The catalytic process of ammonia oxidation was
carried out in a flow-through installation with quartz
reactor 50 cm in diameter. As a catalyst served rho-
dium in the form of a package of five grids with
thread diameter of 0.06 mm. The 17-cm-high bed
of sorbent grains was placed at a distance of 0.8 cm
from the catalyst grids.
The temperature of ammonia oxidation was 1253 K;
the pressure in the system, 0.101 MPa; the content
of ammonia in the ammonia3air mixture, 11.5 vol %;
and the linear flow velocity of the mixture, 0.40 m s
The time of catalyst operation and absorption mass
testing was 600 h. An X-ray phase analysis of the
compounds was made on a Siemens D-500 diffractom-
eter with Cu
radiation. A differential-thermal analy-
sis was done on an MOM Q-derivatograph (Hungary).
The heating rate was 5 deg min
in the temperature
range 29331773 K.
During reactor shutdowns, the system was purged
with dried argon and isolated from air with moisture
absorbers. After being discharged from the reactor,
the sorbent was stored in hermetically sealed vessels
filled with dried argon.
The X-ray phase analysis of the sorbent demon-
strated that it contains CaO and a rhodium compound