Catalyst carriers for purification of waste gas and process for preparing the same

Disclosed are a catalyst carrier for purification of waste gas which comprises a carrier comprising a calcined clay material composed of 1 to 5% by weight of lithium oxide (Li.sub.2 O), not less than 20% by weight of aluminum oxide (Al.sub.2 O.sub.3) and not less than 60% by weight of silicon dioxide (SiO.sub.2), the total thereof being substantially 100; an aluminum oxide supported on the surface of the said clay material; and a platinum group element having further supported on said aluminum oxide; and a process for preparing the same.

This invention relates to a catalyst carrier for purification of waste gas 
and a process for preparing the same. More particularly, it is concerned 
with a catalyst carrier for purification of waste gas having a superior 
catalytic effect at a lower temperature, a prolonged life as a catalyst 
and a superior thermal shock resistance. 
As space-closed type dwellings have recently been popularized and cooking 
manner changed, heating instruments, cooking instruments and the like have 
become diversified. On the other hand, there has been presented a problem 
wherein such harmful combustion waste gases as carbon monooxide, a 
hydrocarbon, nitrogen oxide, lampblack and the like, which are produced 
from these heating instruments, cooking instruments and the like, tend to 
contaminate dwelling environments. 
Therefore, there have been studied various means for purification of such 
waste gases. For instance, one of such means is directed to the studies on 
a catalyst carrier capable of converting harmful substances in waste gas 
to harmless substance by decomposition. 
As such catalyst carrier, there have been hitherto proposed, for example, 
those catalyst carriers comprising at least one of noble metals such as, 
for example, platinum, palladium and the like or metal oxides such as, for 
example, copper, chromium, iron, zinc or nickel oxides and the like, which 
is supported on a carrier such as, for example, a honeycomb-like, 
sphere-like or pellet-like porous material comprising, e.g. alumina, 
alumina-silica or cordierite or glass fiber. 
In these catalyst carriers, however, it has been very difficult to make the 
catalyst homogeneously and effectively supported on the carrier and, as a 
result, a high catalytic effect could not have been accomplished with a 
small amount of the catalyst. Consequently, it has been previously 
attempted to make active alumina first supported on the carrier and then 
make a catalyst supported thereon (Japanese Patent Publication No. 
3635/1977), but this method could not always provide a satisfactory 
catalytic effect and further presented a problem on its cost. 
In particular, considering a catalytic effect, the prior art catalyst 
carrier when contacted with, for example, carbon monooxide show a removal 
rate for carbon monooxide of as low as not more than 40% at a temperature 
of not higher than 200.degree. C. and then, if heating instruments or 
cooking instruments have just been on firing and are under still lower 
temperature as a whole, there is presented the problem that its catalytic 
effect would not be expectable. Moreover, it has been practically not 
satisfactory owing to its shortened catalyst life, and a removal rate for 
carbon monooxide is lowered even after application over, for instance, 
approximately 500 hours. In addition, the prior art catalyst carrier, 
especially its carrier has disadvantages that it tends to readily undergo 
damage on vibration, shock or the like owing to its low mechanical 
strength and also to readily produce crack or breakage in rapid heating or 
quenching. 
It is a primary object of this invention to provide a catalyst carrier 
which can be readily prepared inexpensively, solve the above-mentioned 
disadvantages, show a non-reduced catalytic effect even in a small amount 
of the catalyst supported, still maintain a high catalytic effect at a 
lower temperature, have a superior thermal shock resistance and keep a 
prolonged life as a catalyst, as well as a process for preparing the same. 
Other objects and advantages of this invention will be apparent from the 
following description. 
The present inventors have been intensive studies and, as a result, have 
found out that the above objects can be accomplished by using as a carrier 
for a catalyst a calcined clay material and thereby providing a catalyst 
carrier comprising alumina and platinum group metal supported on the said 
carrier. This invention has been completed upon this finding. 
More specifically, the catalyst for purification of waste gas according to 
this invention comprises a carrier which comprises a calcined clay 
material having a composition of 1 to 5% by weight of lithium oxide 
(Li.sub.2 O), not less than 20% by weight of aluminum oxide (Al.sub.2 
O.sub.3) and not less than 60% by weight of silicon dioxide, a total of 
these ingredients being substantially 100, an aluminum oxide supported on 
the surface of said calcined clay material, and a platinum group metal 
supported further on said aluminum oxide. 
The clay material, which may be employed as a starting material for the 
present catalyst carrier, is meant to refer to those materials having 
incorporated therein a LiO.sub.2 -containing composition. 
In general, a clay is a soil-like composite of natural ore containing as 
main ingredients aluminum oxide (Al.sub.2 O.sub.3), silicon dioxide 
(SiO.sub.2) as well as, for instance, iron oxide (Fe.sub.2 O.sub.3), 
calcium oxide (CaO), magnesium oxide (MgO), sodium oxide (Na.sub.2 O), 
potassium oxide (K.sub.2 O) and the like. It may produce plasticity when 
its fine powder is moistened with water and then be molded into various 
types of forms. Such molded product may be converted to a calcined product 
having a porous structure and a prescribed mechanical strength where 
calcined at a suitable temperature. 
Any clay containing at least 15% by weight of Al.sub.2 O.sub.3 and at least 
35% by weight of SiO.sub.2 may be employed in this invention; there may be 
mentioned, for example, kaolin, china clay, acid clay, diaspore clay, 
Gairome (ga-iro-me) clay*, Kibushi (Ki-bu-shi) clay**, ball clay, mullite, 
bentonite, agalmatolite, alluvial soil, and the like. It is preferable to 
use a suitable blend of two or more of the clays selected from the 
above-recited members. 
FNT *A Japanese naming of a clay belonging to a kind of kaolin clay; a white or 
slightly grayish green clay containing in a scattering state a great 
amount of quarts particles having particle size of from 1 to 3 mm; 
available principally from the soil of Seto area of Aichi Prefecture, 
Tajimi area of Gifu Prefecture or Ueno area of Mie Prefecture, Japan; and 
having composition, for example, of 50.75% SiO.sub.2, 32.55% Al.sub.2 
O.sub.3, 0.22% TiO.sub.2, 1.69% Fe.sub.2 O.sub.3, 0.14% MgO, 0.90% CaO, 
0.83% Na.sub.2 O+K.sub.2 O, 2.19% H.sub.2 O(+) and 10.71% H.sub.2 O(-). 
FNT **A Japanese naming of a clay belonging to a kind of kaolinite-containing 
clay; available principally from the soil of Seto area of Aichi 
Prefecture, Tajimi area of Gifu Prefecture or Ueno area of Mie Prefecture, 
Japan; and having composition, for example, of 43.58% SiO.sub.2, 33.94% 
Al.sub.2 O.sub.3, 1.63% Fe.sub.2 O.sub.3, 0.12% MgO, 0.10% CaO, 0.46% 
Na.sub.2 O, and 20.02% ignition loss. 
As the Li.sub.2 O-containing composition which may be incorporated in the 
aforesaid clay, there may be employed any of those containing Li.sub.2 O, 
but usually and preferably spondumene (Li.sub.2 O.Al.sub.2 
O.sub.3.4SiO.sub.2), petalite (Li.sub.2 O.Al.sub.2 O.sub.3.8SiO.sub.2) or 
lithium feldspar (Li.sub.2 O.Al.sub.2 O.sub.3.6SiO.sub.2). 
In this invention, the clay material may be prepared as stated 
hereinbefore, by adding and blending the Li.sub.2 O-containing composition 
into the clay: In this instance, it is requisite that the ingredient ratio 
in the resultant clay material be controlled so as to be not less than 20% 
by weight of Al.sub.2 O.sub.3, not less than 60% by weight of SiO.sub.2 
and 1 to 5% by weight of Li.sub.2 O, the total thereof being substantially 
100. 
In the case where the ingredient ratios of Al.sub.2 O.sub.3 and SiO.sub.2 
in the clay material are not more than 20% by weight and not more than 60% 
by weight, respectively (in other words, where the amounts of Fe.sub.2 
O.sub.3, CaO, MgO, Na.sub.2 O, K.sub.2 O and so on, inter alia, CaO, MgO, 
Na.sub.2 O, K.sub.2 O incorporated are larger), support of the catalyst on 
the resultant carrier (the calcined product) is not smoothly accomplished, 
nor a catalytic effect at a low temperature improved. 
Moreover, in the case where the ingredient ratio of Li.sub.2 O in the clay 
material is not more than 1% by weight, improved thermal shock resistance 
of the resulting carrier (the calcined product) can not be obtained. If 
the ingredient ratio of Li.sub.2 O is more than 5% by weight, thermal 
shock resistance of the resulting carrier (the calcined product) can be 
improved, but the carrier tends to become brittle, show reduced mechanical 
strength and then become worn and torn. Consequently, the upper limit of 
the ingredient ratio of Li.sub.2 O in the clay material should be 
preferably 5% by weight. 
As the Al.sub.2 O.sub.3 source which may be supported on the 
above-mentioned carrier, there may be mentioned, for example, alumina sol, 
.gamma.-alumina, other Al.sub.2 O.sub.3 -containing mixture and the like 
and one or more of those as stated above may be selected and employed. 
As the platinum group element, there may be mentioned, for example, 
platinum, palladium, rhodium, ruthenium and the like and one or more of 
those as stated above may be selected and employed. 
Then, the preparation of the said catalyst will be explained more fully 
hereinbelow. 
The process for preparing a catalyst carrier for purification of waste gas 
according to the present invention comprises admixing at least two powdery 
clay materials containing as main ingredients Al.sub.2 O.sub.3 and 
SiO.sub.2 but having different compositions, so as to be 1 to 5% by weight 
of Li.sub.2 O, not less than 20% by weight of Al.sub.2 O.sub.3 and not 
less than 60% by weight of SiO.sub.2, the total thereof being 
substantially 100; subjecting the resultant mixture to calcination; 
coating Al.sub.2 O.sub.3 over the surface of the resulting calcined 
product by dipping into a solution containing 55 to 90% by weight of 
alumina sol having a solid content of approximately 10% or a solution 
containing 30 to 50% by weight of an equal amount mixture of the said 
alumina sol and .gamma.-alumina; subjecting the resulting product to heat 
treatment and then making a platinum group element supported thereon. 
The present process may be conducted by first admixing at least two of the 
afore-said powdery clay materials to prepare a prescribed composition and, 
after, for example, kneading with addition of water, molding into a 
honeycomb-like, sphere-like or pellet-like shape by means of a molding 
device. Thereafter, the molded product thus formed is subjected to 
calcination under atmosphere. 
Calcination condition is preferably set to a calcination temperature of 
500.degree. to 1400.degree. C. over a calcination period of 1 to 2 hours, 
especially the calcination temperature of 1000.degree. to 1400.degree. C. 
so that the resulting calcined product may have a porous structure with an 
adequate mechanical strength (usually and preferably a bending strength of 
50 to 300 kg/cm.sup.2) and an adequate specific surface area (usually and 
preferably 50 to 200 m.sup.2 /g). 
Then, a carrier comprising the resulting calcined product is carried with 
Al.sub.2 O.sub.3. The procedures therefore may be effected first by 
dipping the calcined product into a solution containing 55 to 90% by 
weight of alumina sol having a solid content of approximatey 10% or a 
solution containing 30 to 50% by weight of a mixture of the said alumina 
sol with .gamma.-alumina in an equal amount or by spray-coating or 
brushing the above solution onto the calcined product. The solution to be 
used in this instance is prepared, for example, by dissolving or 
dispersing the said alumina in water, a solvent containing 5% of 
hydrochloric acid and the like. The calcined product having Al.sub.2 
O.sub.3 impregnated and coated over the porous surface layer thereof is 
then subjected to heat treatment. Such heat treatment is accomplished by 
heating, for example, at 400.degree. to 800.degree. C. under atmosphere or 
hydrogen atmosphere over 1 to 2 hours. If the heating temperature is lower 
than 400.degree. C., a sufficient adherence of alumina onto the calcined 
product after molding can not be attained, while if the temperature is 
higher than 800.degree. C., alumina tends to agglomerate to provide a 
poorly dispersed state of alumina on the molded product surface and also a 
poor adherence of the platinum group element is obtained. 
Further, the platinum group element is made supported on the so treated 
calcined product. The procedures therefor is effected by impregnating or 
adhering a solution of the platinum group element onto the surface and/or 
internal pores (herein, often referred to as a surface layer) of the so 
treated carrier by dipping method, spray-coating method or brushing 
method, and then heating, for example, at a temperature of 200.degree. to 
500.degree. C. to thermally decompose the said element and make it 
supported on the carrier in the form of its metal or oxide. In this 
instance, it is preferably to employ a dipping method wherein the carrier 
is dipped into a solution of the platinum group element in order to make 
the platinum group element homogeneously supported on the carrier. The 
platinum group element is usually employed in the form of an approximately 
0.2% aqueous solution of chloroplatinic acid (H.sub.3 PtCl.sub.6) or a 
solution or dispersion thereof in water or other solvent. 
The present catalyst carrier thus produced has the following advantages; 
namely, (1) a higher catalytic effect can be shown even with a less amount 
of the catalyst supported, since an influence of the component having an 
inhibitory action on a catalytic effect in the carrier is inhibited, (2) a 
less reduction in a catalytic effect is seen with a prolonged catalyst 
life, (3) a higher catalytic effect can be seen at a low temperature, (4) 
a superior thermal shock resistance is seen, (5) the carrier may be 
available inexpensively, since its raw material is readily available clay 
and there is no need to use a specific binder. The catalyst carrier for 
purification of waste gas thus obtained according to this invention is 
very useful for deodorization and purification of the combustion waste gas 
exhausted from heating instruments such as portable oilstoves, oil hot 
air-type heaters and the like, cooking instruments and so on.

EXAMPLE 1 
A mixed clay powder A was prepared by admixing Kibushi clay powder 
containing as main ingredients 35% by weight of Al.sub.2 O.sub.3 and 48% 
by weight of SiO.sub.2 with Gairome clay powder containing as main 
ingredients 34% by weight of Al.sub.2 O.sub.3 and 50% by weight of 
SiO.sub.2 at a weight ratio of 1:1. 
Thereafter, a powdery mullite (3Al.sub.2 O.sub.3.2SiO.sub.2) containing as 
main ingredients 53% by weight of Al.sub.2 O.sub.3 and 45% by weight of 
SiO.sub.2 was admixed with a powdery petalite to form 3 types of mixed 
clay powder B containing 2, 6 and 10% by weight of the petalite (see page 
5, lines 9-10), respectively. 
The said mixed clay powder A was admixed with the said mixed petalite 
powder B at a weight ratio of 1:1 to form a starting material for clay 
material. Conventional chemical analysis established that all clay 
material powders contain not less than 20% by weight of Al.sub.2 O.sub.3 
and not less than 60% by weight of SiO.sub.2, with the content of Li.sub.2 
O being 1% by weight, 3% by weight and 5% by weight, respectively. 
The clay material powder was kneaded with a proper volume of water for one 
hour and the resultant kneaded product was press-molded into a 
honeycomb-like disc with a diameter of 130 mm and a thickness of 5 mm. The 
disc was dried and cured under atmosphere and then calcined at 
1200.degree. C. over one hour to form a calcined product. 
Each of the three calcined products thus obtained was dipped into a 55% by 
weight solution of alumina sol (manufactured by NISSAN CHEMICAL 
INDUSTRIES, LTD., having an Al.sub.2 O.sub.3 solid content of 10% to 
prepare a carrier having Al.sub.2 O.sub.3 coated over the surface layer 
thereof. The carrier was allowed to be dried and heated at 600.degree. C. 
for one hour. Then, it was dipped into chloroplatinic acid solutions 
having concentrations of 0.20, 0.15, 0.10 and 0.05% for one minute to 
prepare four samples having different chloroplatinic acid contents, 
respectively. Thereafter, these samples were air-dried and heated at 
600.degree. C. for one hour to produce the catalyst carrier of this 
invention. 
Conventional analysis on a supported platinum amount on the resulting 
catalyst carrier showed that a supported platinum amount (g) to apparent 
volume of the catalyst (l) is 0.90 g/l, 0.70 g/l, 0.45 g/l, and 0.25 g/l, 
respectively. 
EXAMPLE 2 
Following the substantially same procedures, as in Example 1 except that a 
solution containing 15% by weight each of the said alumina sol and 
.gamma.-alumina was employed for supporting Al.sub.2 O.sub.3 on calcined 
product, there was prepared a catalyst carrier. The supported platinum 
amount on the resulting catalyst carrier was equal to that of Example 1. 
Experiment 1 
Measurement of Carbon Monooxide Removal Rate 
Four catalysts, which were prepared from the starting carrier material of a 
clay material containing 3.0% by weight of Li.sub.2 O according to Example 
1 and had different supported platinum amounts, were measured for carbon 
monooxide removal rate. 
Each of the four catalyst carriers was independently placed in a ventilated 
reaction equipment and a gas containing carbon monooxide of 250 ppm with 
an air balance so controlled that S.V. value (space velocity value) may be 
10000 (1/hr) was fed therethrough at a flow quantity of 11.1 l/min. Carbon 
monooxide concentrations before and after the gas passes through the 
catalyst carrier were measured by means of a CO analytical instrument 
according to a N.D.I.R method and a CO removal ratio (%) was calculated. 
Measurement temperature was 200.degree. C. 
The results are shown in FIG. 1 in terms of CO removal ratio to supported 
platinum amount (g/l). As apparent from FIG. 1, the catalyst carrier of 
this invention was found to show the less supported platinum amount of 0.3 
to 1.0 g/l and the CO removal ratio of above 90% even at a relatively 
lower temperature of 200.degree. C. 
Then, the present catalyst with the supported platinum amount of 0.90 g/l 
prepared according to Example 1 was measured under the same condition as 
stated above for CO removal ratio (%) at inlet gas temperatures of 
100.degree. C., 150.degree. C. and 200.degree. C., respectively. For 
comparison, measurement was similarly effected on the prior art 
commercially available catalyst having 1 to 2 g/l of platinum supported on 
a carrier made of cordierite [composition: 2Mg.0.5SiO.sub.2.2Al.sub.2 
O.sub.3 ]. 
These results are summarized in the following Table 1 and also illustrated 
in FIG. 2 wherein the curve (a) is for the present catalyst carrier and 
the curve (b) is for the said prior art catalyst carrier. As apparent from 
Table 1 and FIG. 2, the present catalyst carrier was found to have a 
superior catalytic effect even at a lower temperature as compared with the 
prior art commercially available catalyst carrier. 
Similar results were obtained with the catalyst carrier prepared according 
to Example 2. 
TABLE 1 
______________________________________ 
CO 
gas temp. (.degree.C.) 
Catalyst 100 150 200 
______________________________________ 
Present catalyst (Pt: 0.9 g/l) 
38 77 97 
Prior art catalyst (Pt: 1 to 2 g/l) 
0 0 40 
______________________________________ 
Experiment 2 
Catalyst Life 
A catalyst carrier having a platinum amount of 0.92 g/l supported on a 
carrier containing 3% by weight of Li.sub.2 O according to Example 1 was 
assembled into a portable oilstove and removal index of carbon monoxide 
with lapse of time was investigated. 
Measurement was effected by using a catalyst with an outer diameter of 130 
.phi. and a thickness of 5 mm and setting a wick height of the oilstove 
under the best combustion condition, and purification degree of carbon 
monooxide was determined in terms of index under the condition that the 
maximum temperature was about 570.degree. C. when the catalyst actually 
charged. The results are shown in FIG. 3. 
At the same time, similar measurement was done with the prior art 
commercial catalyst carrier comprising the cordierite carrier having 1 to 
2 g/l of platinum supported thereon, in a similar manner to Experiment 1, 
for comparison. 
As apparent from FIG. 3, the catalyst carrier of this invention [as shown 
with the curve (a)] was found to exert a more stable catalytic effect over 
a prolonged period of time, as compared with the prior art catalyst 
carrier [as shown with the curve (b)]. 
Also, the catalyst carrier prepared according to Example 2 was similarly 
found to show a prolonged catalyst life. 
Experiment 3 
Thermal Shock Resistance Test 
Respective fifty carriers were prepared from each of clay materials 
containing Li.sub.2 O at 1% by weight, 3% by weight and 5% by weight, 
respectively, and respective fifty catalyst carrier, each having a 
supported platinum amount of 0.9 g/l, were prepared from the said carriers 
according to Example 1. 
These catalyst carriers were placed in a portable oilstove with a caloric 
value of 2140 K cal/hr at the position of about 7.5 cm above its radiator 
net, heated under stationary combustion state for 30 minutes to one hour 
and immediately thereafter thrown into water (25.degree. C.). Immediately 
before thrown into water, central temperature of the catalyst carrier was 
530.degree. to 570.degree. C. and peripheral temperature thereof 
450.degree. to 500.degree. C. 
When the catalyst carrier was quenched in water, the number of broken 
catalysts as well as the number of catalysts having fissures such as 
cracks and the like were calculated out, respectively. 
Also, similar test was effected with the commercially available catalyst as 
used in Experiment 1, for comparison. 
These results are summarized in the following Table 2, wherein also shown 
are average values for vending strength, specific surface area and linear 
expansion coefficient measured in respect of each catalyst carrier. 
TABLE 2 
______________________________________ 
Sort of catalyst carrier 
Li.sub.2 O content in catalyst carrier of 
Prior art 
the invention (wt. %) 
catalyst 
Test item 
1 3 5 carrier 
______________________________________ 
Number 20 0 0 40 
of broken 
ones 
Number 30 0 0 50 
of fissured ones 
Vending 180.about.230 
150.about.200 
70.about.130 
70.about.110 
strength 
(kg/cm.sup.2) 
Specific 10.about.90 
50.about.150 
20.about.100 
40.about.110 
surface 
area (m.sup.2 /g) 
Linear 2.0.about.4.0 
0.76.about.0.96 
-0.10.about.0.20 
2.5.about.4.2 
Expansion 
coefficient 
(.times. 10.sup.-6 /.degree.C., 
20.about.800.degree. C.) 
______________________________________ 
As apparent from Table 2, the catalyst carrier of this invention was found 
to have a remarkably superior thermal shock resistance, as compared with 
the prior art catalyst carrier. It was also found that the larger the 
component ratio of Li.sub.2 O becomes, the lower mechanical strength of 
the catalyst carrier is. 
Substantially same results were obtained with the catalyst carrier prepared 
according to Example 2.