Abstract:
Two types of catalysts are disclosed. They are: 
     1. Catalyst for oxidation of carbon monoxide, nitrogen monoxide or sulfur dioxide, comprising manganese dioxide, calcium aluminate, iron oxyhydroxide and copper hydroxycarbonate; and 
     2. Catalyst for oxidation of carbon monoxide, nitrogen monoxide or sulfur dioxide, prepared by heating a mixture of manganese dioxide calcium aluminate, iron oxyhydroxide and copper hydroxycarbonate.

Description:
BACKGROUND OF THE INVENTION 
     The same inventors as those of the present invention proposed a catalyst for use in purifying exhaust gas, said catalyst comprising manganese dioxide, calcium aluminate and heat resistant aggregate. This catalyst has been disclosed in U.S. Pat. No. 3,905,917. The inventors have found that a catalyst comprising a mixture of manganese dioxide, calcium aluminate, iron oxyhydroxide and copper hydroxycarbonate and a catalyst prepared by heating said mixture are superior to the catalyst disclosed in U.S. Pat. No. 3,905,917 in the catalytic action of oxidation of carbon monoxide, nitrogen monoxide or sulfur dioxide. The present invention is based on this discovery. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a catalyst for use in treating gas, and more particularly to a catalyst for the oxidation of carbon monoxide (CO), nitrogen monoxide (NO) or sulphur dioxide (SO 2 ) and process of preparing the catalyst. 
     The catalysts of the present invention are used for oxidizing CO, NO or SO 2  contained in air or oxygen-containing gas to CO 2 , NO 2  or SO 3 , respectively. 
     The catalysts of the present invention are as follows: 
     1. Composition A comprising a mixture of manganese dioxide, calcium aluminate, iron oxyhydroxide and copper hydroxycarbonate. 
     2. Composition B prepared by heating a mixture of manganese dioxide, calcium aluminate, iron oxyhydroxide and copper hydroxycarbonate at a temperature between 220° C and 850° C for 1 to 5 hours. 
     The range of the ingredients of Composition A are as follows: 
     
         ______________________________________            % by weight______________________________________Manganese dioxide  45 - 75Calcium aluminate  15 - 25Iron oxyhydroxide   5 - 15Copper hydroxycarbonate               2 - 10______________________________________ 
    
     Manganese dioxide is preferably γ-MnO 2  having pH values of from 4 to 8. 
     Calcium aluminate comprises principally xCaO.Al 2  O 3 , and calcium aluminate comprising from 60 to 85% of Al 2  O 3  and from 40 to 15% of CaO is suitably used. Cements commercially available under the names of Alumina cement or High alumina cement, may be used instead of calcium aluminate as shown above. Calcium aluminate is used as a binder of the catalysts. 
     Iron oxyhydroxide is FeO (OH). 
     Copper hydroxycarbonate is CuCO 3 .Cu(OH) 2  or 2C u  CO 3 .Cu(OH) 2 . 
     The catalyst of the present invention are prepared as follows: 
     1. Composition A is prepared by the steps of: 
     a. adding water to a mixture of manganese dioxide, calcium aluminate, iron oxyhydroxide and copper hydroxycarbonate, 
     b. forming the mixture into the desired shape, 
     c. carrying out preliminarily curing of the shaped body in air, and 
     d. accomplishing the curing of the shaped body in the presence of water to solidify the shaped body. 
     2. Composition B is prepared by heating the solidified body obtained by the steps as shown above, at a temperature between 220° C and 850° C for 1 to 5 hours. 
     The catalysts of the present invention (Compositions A and B) can be used over a wide temperature range of from 100° C to 850° c to oxidizing CO, NO and SO 2  contained in air or oxygen-containing gas to CO 2 , NO 2  and SO 3 , respectively. 
     When the catalyst of Composition A is used at temperatures above 220° l C, copper hydroxycarbonate changes to CuO, and when the catalyst is used above 275° C, iron oxyhydroxide changes to α-Fe 2  O 3 . When the catalysts (Compositions A and B) are heated at temperatures of about 300° C and 600° C, they have the following compositions: 
     β-MnO 2  - xCaO.Al 2  O 3  - ¢-Fe 2  O 3  - CuO (300° C) 
     α-mn 2  O 3  -xCaO.Al 2  O 3  - α-Fe 2  O 3  - CuO (600° C) 
     When Composition A is used at temperatures above 220° C, the catalyst of Composition A changes to a composition of the catalyst of Composition B prepared by heating previously Composition A. 
     The catalyst of Composition B can be used also at temperatures of 220° C and below 220° C instead of the catalyst of Composition A. 
     As stated above, the catalysts of the present invention (Compositions A and B) effectively oxidize CO, NO or SO 2  to change CO, NO or SO 2  to CO 2 , NO 2  or SO 3 , respectively, and SO 3  is combined with MnOx (x = 1 or 2) and CaO in the catalysts to produce finally CaSO 4 . Accordingly, these catalysts are suitably used in treating gas (oxygen-containing gas) containing CO, No or SO 2 . 
     The superiority of the catalysts of the present invention will be shown in the examples. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is illustrated by the following examples. Unless otherwise set forth, all proportions (%) in this specification are by weight. 
     EXAMPLE 1 
     Samples Nos. 1, 2, 3, 4, 5, 6 and 7 were provided, which comprise various weight percentages of the ingredients as shown in Table 1, as follows: 
     
                       Table 1______________________________________            Sample No.Ingredient (%)     1     2     3   4   5   6   7______________________________________γ-MnO.sub.2  65    65    65  65  70  75  60Calcium aluminate  20    20    20  20  20  20  20Iron oxyhydroxide  10    15Copper hydroxycarbonate              5           15Ferric oxide                       10  10Copper oxide                       5       5______________________________________ 
    
     The ingredients were mixed, and to 100 parts (by weight) of the mixture was added 10 parts of water. Columnar shaped bodies having a size of 5 mmφ × 5 mm were made of the mixtures. The shaped bodies were dried in air and then subjected to the curing in steam having a temperature of 65° C to 95° C for 1 hour. 
     65 g of each of the cured shaped bodies was filled in a quartz tube having an inside diameter of 30 mm. A gas including oxygen (15%) and nitrogen (84%), containing 1,500 ppm of carbon monoxide, was passed through the quartz tube at a space velocity of 10,000 hr -1 . Percentages of oxidation of carbon monoxide are shown in FIG. 1. 
     From the results as shown in FIG. 1, it is evident that Sample No. 1 including iron oxyhydroxide and copper hydroxycarbonate is superior to other catalysts (Sample Nos. 2-7) and Sample No. 3 including copper hydroxycarbonate is superior to other catalysts of Sample Nos. 2 and 4-7 in the catalytic action of oxidation of carbon monoxide. 
     Calcium aluminate in this Example comprises alumina (54%), calcium oxide (38%), ferric oxide and titanium oxide (remainder). Calcium aluminate including 15 to 40% of calcium oxide may be used. 
     EXAMPLE 2 
     Sample Nos. 11, 12, 13, 14 and 15 were provided, which comprise various weight percentages of the ingredients as shown in Table 2, by repeating the same procedure as that of Example 1 and then heating the cured shaped bodies at a temperature of 800° C for 4 hours. 
     
                       Table 2______________________________________           Sample No.Ingredient (%)    11     12     13   14   15______________________________________γ-MnO.sub.2 65     65     75   75   80Calcium aluminate 20     20     20   20   20Iron oxyhydroxide 10     --     --   --   --Copper hydroxycarbonate              5      5      5   --   --Ferxic oxide             10Copper oxide                          5______________________________________ 
    
     Percentages of oxidation of carbon monoxide were measured in the same manner as that of Example 1. The results obtained are shown in FIG. 2. In FIG. 2, Curve No. 1 of FIG. 1 also is shown with a view to comparing Sample No. 1 (Composition A) with Sample No. 11 (Composition B). 
     From the results as shown in FIG. 2, it is evident that Sample No. 11 (catalyst of the present invention, Composition B) is superior to other catalysts (Sample Nos. 12, 13, 14 and 15) in the catalytic action of oxidation of carbon monoxide at elevated temperatures and that Sample No. 1 (Composition A) is superior to Sample No. 11 (Composition B) in the catalytic action at lower temperatures than 200° C. 
     EXAMPLE 3 
     The same procedure as shown in Example 2 was repeated except that Sample No. 1 was heated at temperatures of 120° C, 300° C and 500° C, respectively, for 4 hours to obtain Sample Nos. 21, 22 and 23. 
     Percentages of oxidation of carbon monoxide of Sample Nos. 21, 22 and 23 were measured in the same manner as that shown in Example 1. The results are shown in FIG. 3. As seen from the results, the catalysts of the present invention are excellent in the catalytic action of oxidation of carbon monoxide also when they have been heated previously at temperatures of 120° C, 300° C and 500° C. Curve No. 11 of FIG. 3 is the same as Curve No. 11 of FIG. 2. 
     EXAMPLE 4 
     Sample Nos. 31-36 were provided, which comprise various weight percentages of the ingredients as shown in Table 3, by repeating the same procedure as that of Example 1. 
     
                       Table 3______________________________________        Sample No.Ingredient (%) 31     32     33   34   35   36______________________________________γ-MnO.sub.2          75     73     70   65   60   55Calcium aluminate          20     20     20   20   20   20Iron oxyhydroxide          --      2      5   10   15   20Copper hydroxycarbonate           5      5      5    5    5    5______________________________________ 
    
     As shown above, iron oxyhydroxide is contained in an amount of from zero % to 20%. 
     Percentages of oxidation of carbon monoxide were measured at a temperature of 300° C in the same manner as that of Example 1, and the results obtained are shown in FIG. 4. From the results, it is evident that catalysts containing iron oxyhydroxide of 5 to 15% are excellent in the catalytic action of oxidation of carbon monoxide. 
     EXAMPLE 5 
     Sample Nos. 41-48 were provided, which comprise various weight percentages of the ingredients as shown in Table 4, by repeating the same procedure as that of Example 2 except that the shaped bodies were heated at a temperature of 500° C, instead of 800° C, for 4 hours. 
     
                       Table 4______________________________________          Sample No.Ingredient (%)   41    42    43  44  45  46  47  48______________________________________γ-MnO.sub.2            70    69    68  67  65  60  55  50Calcium aluminate            20    20    20  20  20  20  20  20Iron oxyhydroxide            10    10    10  10  10  10  10  10Copper hydroxycarbonate            --    1     2   3   5   10  15  20______________________________________ 
    
     As shown above, copper hydroxycarbonate is contained in an amount of from zero % to 20%. 
     Percentages of oxidation of carbon monoxide were measured at a temperature of 200° C, and the results obtained are shown in FIG. 5. From the results obtained, it is evident that catalysts containing copper hydroxycarbonate of 2 to 10% are excellent in the catalytic action of oxidation of carbon monoxide. 
     EXAMPLE 6 
     In this example, removal of SO 2  by the catalyst of the present invention is illustrated. In FIG. 6, a front view of a home oil heater is shown. 
     An oil (refined kerosene) is burned in the cylinder of heat resisting glass 1 having a inside diameter of 165 mm, in which the wire netting 2 and the metallic cylinder 3 are equipped with. A waste gas rises and passes through the layer of catalyst 4 which is held between two metallic screens 5 and 6, said screens being of 10 meshes. The layer of catalyst 4 consists of 127 pieces of Sample No. 11 in Example 2. The space velocity of the waste gas was about 10,000 hr -1 . 
     In FIG. 7 Curve a shows an amount of SO 2  which has been produced in the oil heater and Curve b shows an amount of SO 2  which has been removed by the catalyst. As shown by the curves, SO 2  can completely be removed by the catalyst over 600 hours after the start of using the catalyst. 
     In this catalytic action, SO 2  contained in an exhaust gas first is oxidized to SO 3  and then SO 3  is changed to MnSO 4  and CaSO 4  by the interaction with MnOX (x = 1 or 2) and CaO in the catalyst. 
     EXAMPLE 7 
     A home oil heater as shown in FIG. 6 was worked in a room of 2 m 3 . Fifteen minutes after the start, the content of CO in the room reached 40 ppm. On the contrary, the content of CO reached over 400 ppm in an oil heater not provided with the catalyst. 
     EXAMPLE 8 
     In this example, oxidation of NO is illustrated. 
     Sample No. 51 was prepared by repeating the same procedure as that of Example 2 except that cobalt hydroxycarbonate was used instead of copper hydroxycarbonate of Sample No. 1. 
     Oxidations of NO by using Samples No. 1, No. 51 and granular platinum (Pt) catalyst were compared in the same manner as that of Example 1 by using nitrogen gas containing 3% of oxygen and 1,000 ppm of NO at a space velocity of 8,000 hr -1 . 
     The results obtained are shown in FIG. 8. As seen from the results, excellent catalyst for oxidation of NO at lower temperatures can be obtained by adding cobalt hydroxycarbonate in an amount up to 10% to the catalysts of the present invention. 
     Oxides of cobalt, copper, vanadium and silver also may be added to the catalysts of the present invention. 
     EXAMPLE 9 
     Mechanical strength of the catalysts of the present invention may be improved by adding reinforcing fillers to the catalysts. 
     Silica, asbestos, ceramic fibers (i.g. dealkalizated glass fiber) and metallic wire (i.g. iron or copper wire having a size of 0.5 mmφ × 30 mm) may be used as the reinforcing fillers. 
     Test pieces of the catalysts were prepared as follows: 
     Ingredients and reinforcing filler as shown in the following Table 5 were mixed with a small amount of water, and the mixtures were molded at a pressure of 0.5 ton/cm 2  to obtain shaped bodies having a size of 40 × 20 × 5 mm. Bending strength of the test pieces were measured at a room temperature and after heating at a temperature of 500° C for 4 hours. The results obtained are shown in Table 5. 
     
                       Table 5______________________________________In-gredientreinforcing filler          Test piece No.(parts by weight)          61     62     63     64    65______________________________________γ-MnO.sub.2          65     65     65     65    65Calcium aluminate          20     20     20     20    20Iron oxyhydroxide          10     10     10     10    10Copper hydroxycarbonate           5      5      5      5     5                 silica Asbestos                               Glass IronReinforcing filler          --                   fiber wire                 10      5      2     5   RoomBending temperature              290    310  340    340   370strength(kg/cm.sup.2)   After   heating at 250    260  290    300   320   500° C______________________________________ 
    
     As seen from the results, mechanical strength of the catalyst can be improved by adding reinforcing fillers to the catalysts.