Abstract:
A process for producing nitrous oxide comprises reacting ammonia with nitric oxide and/or oxygen in the presence of a catalyst comprising a Group VIB metal oxide, to produce a reaction mixture comprising nitrous oxide, and optionally recovering the nitrous oxide from the effluent mixture.

Description:
FIELD OF THE INVENTION 
     This invention is directed to the production of nitrous oxide, N 2 O, from ammonia and nitric oxide, NO, over a catalyst comprising a Group VIB metal oxide. Specifically, the catalyst of this invention comprises an oxide of a Group VIB metal such as molybdenum oxide, that may optionally be supported on a Group VIB metal oxide support such as zirconia, or on a solid support material such as silica, and that may optionally comprise a Group VIIIB metal oxide component such as iron oxide. 
     BACKGROUND OF THE INVENTION 
     One commercial process for making nitrous oxide involves the thermal decomposition of ammonium nitrate when heated from 200 to 260° C. according to the following equation: 
     
       
         NH 4 NO 3 —N 2 O+2H 2 O 
       
     
     However, extreme caution must be used in handling ammonium nitrate, which may be highly explosive under extreme shock or elevated temperatures. Therefore, improved methods for controlling the thermal decomposition of ammonium nitrate have been disclosed. For example, the thermal decomposition of ammonium nitrate in the presence of a melt containing ammonium hydrogen sulfate and ammonium sulfate is described in U.S. Pat. No. 4,154,806; the thermal decomposition of ammonium nitrate into an aqueous, strongly acid reaction liquor containing chloride ions as a catalyst is described in U.S. Pat. No. 4,102,986; and the thermal decomposition of ammonium nitrate in a chloride-containing aqueous solution of nitric acid and the presence of catalytically active ions of manganese, copper, cerium, lead, bismuth, cobalt or nickel, is described in U.S. Pat. No. 3,656,899. 
     Another commercial process for producing nitrous oxide involves the reaction of ammonia and air using Mn and Bi oxides as catalysts. For example, Japanese Patent No. 6122507 describes a process for preparing nitrous oxide by the oxidation of ammonia with oxygen in the presence of steam and a CuO/MnO 2  catalyst. Other methods for producing nitrous oxide include the reaction of a molten nitrate salt with ammonium chloride and the reaction of ammonia with at least one molten nitrate salt of an alkaline earth metal, as described in U.S. Pat. No. 4,720,377. 
     The present invention is directed to the conversion of ammonia with nitric oxide and/or oxygen into nitrous oxide using a catalyst comprising a Group VIB metal oxide. Accordingly, the present invention avoids the dangers associated with the use and handling of ammonium nitrate and is an alternative and novel nitrous oxide synthesis method that is inexpensive and safe. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a process for producing nitrous oxide comprising the step of reacting ammonia with nitric oxide and/or oxygen in the presence of a catalyst comprising a Group VIB metal oxide, to produce an effluent mixture comprising nitrous oxide. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The Catalyst 
     One embodiment of the present invention utilizes the Group VIB metal oxide alone as the catalyst for reaction. 
     A second embodiment utilizes a catalyst that comprises the Group VIB metal oxide in combination with the Group VIIIB metal oxide. 
     A third embodiment utilizes a catalyst that comprises the Group VIB metal oxide, in combination with the Group IVB metal oxide as a support. 
     A fourth embodiment utilizes a catalyst that comprises the Group VIB and Group VIIIB metal oxides, in combination with the Group IVB metal oxide as a support. 
     A fifth embodiment utilizes a catalyst that comprises the Group VIB metal oxide, in combination with a solid support material. 
     A sixth embodiment utilizes a catalyst that comprises the Group VIB and Group VIIIB metal oxides, in combination with the solid support material. 
     The Group VIB metal oxide of the present invention may be an oxide of chromium, molybdenum or tungsten. Preferably, the Group VIB metal oxide is molybdenum oxide, MoO 3 . Sources of the Group VIB metal oxide may include pure molybdenum oxide MoO 3 , ammonium heptamolybdate tetrahydrate (NH 4 ) 6 Mo 7 O 24 . 4H 2 O, and molybdenum halides and oxyhalides. 
     The Group IVB metal oxide of the present invention may be an oxide of titanium, zirconium or hafnium. Preferably, the Group IVB metal oxide is zirconia. Sources of the Group IVB metal oxide may include zirconyl chloride and zirconyl nitrate. When the Group IVB metal oxide is used in combination with the Group VIB metal oxide, the weight ratio of the Group VIB metal oxide to Group IVB metal oxide is from about 0.001:1 to 0.5:1, and preferably from about 0.1:1 to 0.3:1. 
     Examples of the solid support materials include silica and the material designated M41S, which is described in U.S. Pat. No. 5,102,643. A particular example of such an M41S material is a material designated MCM-41, which is described in U.S. Pat. No. 5,098,684. When the Group VIB metal oxide is used in combination with the solid support material, the weight ratio of the Group VIB metal oxide to the solid support material is from about 0.05:1 to 0.8:1, and preferably from about 0.15:1 to 0.6:1. 
     The Group VIIIB metal oxide may be an oxide of iron. Preferably, the Group VIIIB metal oxide is iron oxide. Sources of the Group VIIIB metal oxide may include iron (II) sulfate heptahydrate FeSO 4 .7H 2 O, iron halides and iron nitrate. When the Group VIIIB metal oxide is used in combination with the Group VIB metal oxide alone, the Group VIB and Group IVB metal oxides, or the Group VIB metal oxide and the solid support material, the molar ratio of the Group VIIIB metal oxide to the Group VIB metal oxide is from about 0.001:1 to 0.1:1, and preferably from about 0.005:1 to 0.05:1. 
     Preparation of the Catalyst 
     The catalyst of the present invention may be prepared, for example, by combining a first liquid solution comprising a source of the Group VIB metal oxide, and a second liquid solution comprising a source of the Group IVB metal and/or a third liquid solution comprising a source of the Group VIIIB metal oxide, under conditions sufficient to cause precipitation of the catalyst Examples of the precipitating reagent include ammonium hydroxide, alkylammonium hydroxide and alkaline hydroxides such as sodium hydroxide. Water is a preferred solvent for these solutions. 
     Optionally, the liquid solution from which the catalyst is precipitated may comprise a solid support material, in which case the components of the catalyst may be precipitated directly onto the solid support material. For example, the Group VIIIB metal oxide may optionally be co-precipitated from the liquid solution, along with the Group VIB metal oxide, directly onto the solid support material. 
     The temperature at which the liquid solution is maintained during precipitation may be less than about 200° C., e.g., from about 0° to 200° C. A particular range of such temperatures is from about 50° to 100° C. The pH range of the liquid solution during precipitation is from about 4 to 11. 
     The catalyst may be recovered from the liquid solution by filtration, followed by drying. The catalyst may be subjected to a final calcination as described below to dehydrate the catalyst and to confer the required mechanical strength on the catalyst. 
     Calcination of the catalyst may be carried out, preferably in an oxidizing atmosphere, at about atmospheric pressure to 6890 kPa (about 1000 psi); and at temperatures from about 500° to 850° C. The calcination time may be up to 48 hours, e.g., for about 0.5 to 24 hours, e.g., for about 1.0 to 10 hours. 
     The Process 
     Nitric oxide and ammonia are converted to nitrous oxide in the present invention by a reaction which may be described by the following equation: 
     
       
         4NH 3 +4NO+3O 2 —4N 2 O+6H 2 O, 
       
     
     although other reactions may also occur. 
     An additional reaction that occurs when oxygen is present is the oxidation of ammonia with oxygen to form nitrous oxide which may be described by the following equation: 
     
       
         2NH 3 +2O 2 —N 2 O+3H 2 O 
       
     
     The molar feed ratio of nitric oxide to ammonia ranges from about 0.01:1 to 10:1; the amount of oxygen fed to the reaction unit ranges from about 0.01 to 35 molar %. 
     The method according to the present invention is carried out at a temperature ranging from about 200 to 600° C., and preferably from about 300 to 500° C.; a pressure ranging from about 0.1 to 100 atmospheres, and preferably from about 0.5 to 5 atmospheres. The gas hourly space velocity for the reaction ranges from about 1,000 to 10,000,000 hr −1 , and preferably from about 20,000 to 1,000,000 hr −1 . 
     The effluent mixture comprises nitrogen, oxygen, nitric oxide, ammonia and the desired product, nitrous oxide. The nitrous oxide may be separated and recovered from the effluent mixture by conventional means known to skilled artisans or the entire effluent may be used as a feed to a separate reactor. Alternatively, the nitrous oxide can be utilized in situ as a selective oxidant for various substrates. For example, benzene could be co-fed with the reactants and phenol product recovered. 
    
    
     The invention will now be more particularly described with reference to the Examples, each of which discloses the conversion of a gaseous mixture containing ammonia together with nitric oxide and/or oxygen, with the balance in each case being helium. 
     EXAMPLE I 
     Five hundred grams of ZrOCl 2 .8H 2 O were dissolved with stirring in 6.0 liters of distilled water. To this, a solution containing 33 grams of (NH 4 ) 6 Mo 7 O 24 .4H 2 O in 500 ml of H 2 O was added. Finally, a solution containing 263 ml of conc. NH 4 OH and 500 ml of distilled H 2 O was added dropwise over a 30-45 minute period. The pH of the solution was approximately 9. This slurry was then placed in a steambox for 72 hours. The product formed was recovered by filtration, washed with excess water, and dried overnight at 85° C. The material was then calcined in air at 700° C. for 3 hours. Chemical analysis of the dried materials showed an Mo/Zr ratio of 0.11 (weight basis); this corresponds to a water-free sample composition of approximately 7.3% Mo. 
     Table 1 shows the activity and selectivity of this sample for the conversion of 500 ppm each of ammonia and nitric oxide into N 2 O at a space velocity of approximately 600,000 hr −1 . At 500° C., about 60% of the inlet ammonia and nitric oxide is converted. The selectivity to N 2 O is approximately 61%; the remaining 39% of the material is converted to N 2 . 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example I. 
               
               
                 0.050 g catalyst used. Space velocity˜600,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O 
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 448 
                 447 
                 45 
                 5 
                 9.9% 
               
               
                 350 
                 1 
                 500 
                 500 
                 399 
                 397 
                 84 
                 14 
                 14.4% 
               
               
                 400 
                 1 
                 500 
                 500 
                 345 
                 345 
                 105 
                 44 
                 29.6% 
               
               
                 450 
                 1 
                 500 
                 500 
                 273 
                 288 
                 109 
                 107 
                 49.7% 
               
               
                 500 
                 1 
                 500 
                 500 
                 173 
                 230 
                 115 
                 180 
                 61.1% 
               
               
                   
               
             
          
         
       
     
     EXAMPLE II 
     This catalyst was prepared in a manner identical to Example I except that it was calcined in air at 830° C. for 3 hours. Table 2 shows that calcination of this material at a higher temperature gives higher selectivity to N 2 O at temperatures of 400° C. and below than the catalyst of Example I, but a lower selectivity at 500° C. The selectivity of this sample is much less affected by temperature than that of the catalyst used in Example I. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example II. 
               
               
                 0.050 g catalyst used. Space velocity˜600,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O 
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 465 
                 473 
                 14 
                 16 
                 52.7% 
               
               
                 350 
                 1 
                 500 
                 500 
                 397 
                 432 
                 37 
                 47 
                 55.7% 
               
               
                 400 
                 1 
                 500 
                 500 
                 291 
                 397 
                 70 
                 85 
                 54.8% 
               
               
                 450 
                 1 
                 500 
                 500 
                 193 
                 378 
                 101 
                 110 
                 52.2% 
               
               
                 500 
                 1 
                 500 
                 500 
                 132 
                 378 
                 124 
                 117 
                 48.5% 
               
               
                   
               
             
          
         
       
     
     EXAMPLE III 
     Five hundred grams of ZrOCl 2 .8H 2 O were dissolved with stirring in 6.0 liters of distilled water. To this, a solution containing 66 grams of (NH 4 ) 6 Mo 7 O 24 .4H 2 O in 500 ml of H 2 O was added. Finally, a solution containing 263 ml of conc. NH 4 OH and 500 ml of distilled H 2 O was added dropwise over a 30-45 minute period. The pH of the solution was adjusted to approximately 9 by the addition of 146 grams of concentrated NH 4 OH. This slurry was then placed in a steambox for 72 hours. The product formed was recovered by filtration, washed with excess water, and dried overnight at 85° C. The material was then calcined in air at 600° C. for 3 hours. Chemical analysis of the dried materials showed an Mo/Zr ratio of 0.19 (weight basis); this corresponds to a water-free sample composition of approximately 11.4% Mo. Table 3 shows the activity and selectivity of this sample for N 2 O formation. The higher concentrations of molybdenum gives both higher activities and selectivities than observed in Example I. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example III. 
               
               
                 0.050 g catalyst used. Space velocity˜600,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O 
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 385 
                 385 
                 91 
                 15 
                 14.5% 
               
               
                 350 
                 1 
                 500 
                 500 
                 322 
                 321 
                 121 
                 50 
                 29.0% 
               
               
                 400 
                 1 
                 500 
                 500 
                 252 
                 269 
                 109 
                 125 
                 53.5% 
               
               
                 450 
                 1 
                 500 
                 500 
                 167 
                 228 
                 95 
                 205 
                 68.4% 
               
               
                 500 
                 1 
                 500 
                 500 
                 92 
                 211 
                 99 
                 250 
                 71.7% 
               
               
                   
               
             
          
         
       
     
     EXAMPLE IV 
     Five hundred grams of ZrOCl 2 .8H 2 O were dissolved with stirring in 6.0 liters of distilled water. To this, a solution containing 66 grams of (NH 4 ) 6 Mo 7 O 24 .4H 2 O in 500 ml of H 2 O was added. Another solution containing 7.5 grams of FeSO 4 .7H 2 O in 500 ml of H 2 O was added. Finally, a solution containing 263 ml of conc. NH 4 OH and 500 ml of distilled H 2 O was added dropwise over a 30-45 minute period. The pH of the solution was adjusted to approximately 9. This slurry was then placed in a steambox for 72 hours. The product formed was recovered by filtration, washed with excess water, and dried overnight at 85° C. The material was then calcined in air at 600° C. for 3 hours. Chemical analysis of the dried materials showed an Mo/Zr ratio of 0.20 (weight basis) and an Fe/Zr ratio of 0.012; this corresponds to a water-free sample composition of approximately 12.1% Mo and 0.72% Fe. Table 4 shows the activity and selectivity of this iron-containing sample. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example IV. 
               
               
                 0.052 g catalyst used. Space velocity˜600,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O 
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 387 
                 382 
                 90 
                 19 
                 17.2% 
               
               
                 350 
                 1 
                 500 
                 500 
                 310 
                 314 
                 117 
                 62 
                 34.4% 
               
               
                 400 
                 1 
                 500 
                 500 
                 220 
                 259 
                 110 
                 145 
                 56.9% 
               
               
                 450 
                 1 
                 500 
                 500 
                 132 
                 226 
                 101 
                 216 
                 68.1% 
               
               
                 500 
                 1 
                 500 
                 500 
                 70 
                 222 
                 106 
                 246 
                 69.8% 
               
               
                   
               
             
          
         
       
     
     EXAMPLE V 
     250 grams of ZrOCl 2 .8H 2 O were dissolved with stirring in 1.5 liters of distilled water. This solution was heated to approximately 60° C. To this, a solution containing 33 grams of (NH 4 ) 6 Mo 7 O 24 .4H 2 O and 130 grams of conc. NH 4 OH in 1250 ml of H 2 O was added. This solution was also heated to approximately 60° C. The solution containing the zirconyl chloride was slowly added to the second solution with mixing. The pH of the solution was approximately 7. This slurry was then placed in a steambox for 72 hours. The product formed was recovered by filtration, washed with excess water, and dried overnight at 85° C. The material was then calcined in air at 600° C. for 3 hours. Chemical analysis of the dried materials showed an Mo/Zr ratio of 0.24 (weight basis); this corresponds to a water-free sample composition of approximately 14.1% Mo. Table 5 shows that catalyst synthesis at a higher temperature results in a sample with slightly higher selectivity to N 2 O, especially at temperatures of 400° C. and below, as compared to Example III. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example V. 
               
               
                 0.064 g catalyst used. Space velocity˜450,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O 
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 371 
                 362 
                 90 
                 30 
                 25.3% 
               
               
                 350 
                 1 
                 500 
                 500 
                 272 
                 279 
                 117 
                 93 
                 44.2% 
               
               
                 400 
                 1 
                 500 
                 500 
                 162 
                 223 
                 112 
                 185 
                 62.2% 
               
               
                 450 
                 1 
                 500 
                 500 
                 78 
                 202 
                 106 
                 246 
                 69.9% 
               
               
                 500 
                 1 
                 500 
                 500 
                 32 
                 208 
                 108 
                 265 
                 71.1% 
               
               
                   
               
             
          
         
       
     
     EXAMPLE VI 
     This catalyst was prepared in a manner identical to Example V except that it was calcined in air at 700° C. for 3 hours. Table 6 shows that calcining at 700° C. lowers overall activity somewhat compared to Example V; selectivities to N 2 O are higher at 400° C. and below but are lower at 450 and 500° C. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example VI. 
               
               
                 0.054 g catalyst used. Space velocity˜600,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O 
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 402 
                 403 
                 62 
                 30 
                 32.8% 
               
               
                 350 
                 1 
                 500 
                 500 
                 306 
                 330 
                 89 
                 85 
                 49.0% 
               
               
                 400 
                 1 
                 500 
                 500 
                 197 
                 280 
                 98 
                 157 
                 61.7% 
               
               
                 450 
                 1 
                 500 
                 500 
                 111 
                 260 
                 106 
                 204 
                 65.9% 
               
               
                 500 
                 1 
                 500 
                 500 
                 57 
                 261 
                 115 
                 220 
                 65.8% 
               
               
                   
               
             
          
         
       
     
     EXAMPLE VII 
     This catalyst was prepared in a manner identical to Example V except that it was calcined in air at 830° C. for 3 hours. Table 7 shows that calcining at 830° C. lowers both activity and selectivity to N 2 O. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example VII. 
               
               
                 0.052 g catalyst used. Space velocity ˜600,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O  
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 449 
                 453 
                 29 
                 21 
                 41.7% 
               
               
                 350 
                 1 
                 500 
                 500 
                 376 
                 401 
                 54 
                 57 
                 51.1% 
               
               
                 400 
                 1 
                 500 
                 500 
                 276 
                 361 
                 77 
                 102 
                 57.0% 
               
               
                 450 
                 1 
                 500 
                 500 
                 183 
                 336 
                 97 
                 140 
                 59.2% 
               
               
                 500 
                 1 
                 500 
                 500 
                 115 
                 327 
                 112 
                 161 
                 59.0%  
               
               
                   
               
             
          
         
       
     
     EXAMPLE VIII 
     A solution containing 41.4 grams of (NH 4 ) 6 Mo 7 O 24 .4H 2 O and 200 grams of H 2 O was prepared. The solution was slowly added to 150 grams of silica (HiSil 233) and placed in a polypropylene bottle. This mixture was mixed using a roller overnight. The product formed was recovered by filtration, washed with minimum water, and dried overnight at 85° C. The material was then calcined in air at 540° C. for 3 hours. From the preparation we expect this sample to contain approximately 15% Mo by weight. Table 8 shows that this Mo/SiO 2  catalyst can also convert nitric oxide and ammonia into N 2 O, although in this case with a lower selectivity than most of the examples described above. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example VIII. 
               
               
                 0.147 g catalyst used. Space velocity ˜200,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O  
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 471 
                 472 
                 21 
                 10 
                 31.1% 
               
               
                 350 
                 1 
                 500 
                 500 
                 442 
                 442 
                 40 
                 18 
                 31.3% 
               
               
                 400 
                 1 
                 500 
                 500 
                 392 
                 401 
                 66 
                 32 
                 32.8% 
               
               
                 450 
                 1 
                 500 
                 500 
                 323 
                 351 
                 100 
                 54 
                 35.2% 
               
               
                 500 
                 1 
                 500 
                 500 
                 205 
                 280 
                 150 
                 92 
                 38.1%  
               
               
                   
               
             
          
         
       
     
     EXAMPLE IX 
     Table 9 shows that bulk MoO 3 , obtained from the Aldrich Chemical Company, is also an effective catalyst for converting nitric oxide and ammonia into N 2 O. Compared to the supported catalysts, selectivities at 350° C. and below are higher, but fall steadily as temperature increases. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example IX. 
               
               
                 0.266 g catalyst used. Space velocity ˜120,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O  
               
               
                   
               
             
          
           
               
                 300 
                 1 
                 500 
                 500 
                 462 
                 466 
                 10 
                 33 
                 76.0% 
               
               
                 350 
                 1 
                 500 
                 500 
                 386 
                 415 
                 29 
                 73 
                 71.4% 
               
               
                 400 
                 1 
                 500 
                 500 
                 243 
                 353 
                 72 
                 128 
                 63.9% 
               
               
                 450 
                 1 
                 500 
                 500 
                 32 
                 340 
                 151 
                 148 
                 49.5% 
               
               
                 500 
                 1 
                 500 
                 500 
                 0 
                 449 
                 194 
                 61 
                 23.8%  
               
               
                   
               
             
          
         
       
     
     EXAMPLE X 
     The data shown in Table 10 were collected using the catalyst described in Example III. They show that selectivity to N 2 O is not a strong function of inlet nitric oxide and ammonia concentration when nitric oxide and ammonia are fed in equimolar amounts. There is no reason to believe that feeding much higher concentrations of nitric oxide and ammonia would not also result in the formation of correspondingly high concentrations of N 2 O. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example III. 
               
               
                 Effect of variations in inlet NO and NH 3  concentrations. 
               
               
                 0.050 g catalyst used. Space velocity ˜600,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O  
               
               
                   
               
             
          
           
               
                 500 
                 1 
                 500 
                 500 
                 242 
                 311 
                 63 
                 157 
                 71.4% 
               
               
                 500 
                 1 
                 200 
                 200 
                 84 
                 132 
                 25 
                 68 
                 73.4% 
               
               
                 500 
                 1 
                 350 
                 350 
                 163 
                 220 
                 45 
                 114 
                 71.7% 
               
               
                 500 
                 1 
                 750 
                 750 
                 387 
                 463 
                 95 
                 230 
                 70.9% 
               
               
                 500 
                 1 
                 907 
                 907 
                 481 
                 560 
                 115 
                 277 
                 71.6%  
               
               
                   
               
             
          
         
       
     
     EXAMPLE XI 
     The data shown in Table 11 were collected using the catalyst described in Example V. They show that significant amounts of N 2 O are formed even if nitric oxide and ammonia are not fed in equimolar amounts. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example V. 
               
               
                 Effect of variations in inlet NO and NH 3  concentrations. 
               
               
                 0.064 catalyst used. Space velocity ˜450,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O  
               
               
                   
               
               
                 500 
                 1 
                 500 
                 500 
                 32 
                 208 
                 108 
                 265 
                 71.1% 
               
               
                 500 
                 1 
                 625 
                 375 
                 54 
                 108 
                 148 
                 260 
                 63.7%  
               
               
                   
               
             
          
         
       
     
     EXAMPLE XII 
     The data shown in Table 12 were collected using the catalyst described in Example IV. They show that some N 2 O is formed even when no nitric oxide is fed, i.e., when only ammonia and oxygen are fed. Selectivities are lower, however, than when equimolar amounts of nitric oxide and ammonia are fed. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 Conversion of NO and NH 3  to N 2 O over catalyst described in Example IV. 
               
               
                 Effect of feeding only NH 3 . 
               
               
                 0.050 g catalyst used. Space velocity ˜600,000 hr −1 . 
               
             
          
           
               
                   
                 inlet concentrations 
                 outlet concentrations 
                 selectivity to 
               
             
          
           
               
                 T(° C.) 
                 O 2 (%) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 N 2 O  
               
               
                   
               
             
          
           
               
                 445 
                 1 
                 500 
                 0 
                 211 
                 0 
                 119 
                 17 
                 12.5% 
               
               
                 445 
                 2 
                 500 
                 0 
                 212 
                 0 
                 124 
                 20 
                 13.9% 
               
               
                 445 
                 3 
                 500 
                 0 
                 214 
                 0 
                 127 
                 22 
                 14.5% 
               
               
                 550 
                 1 
                 500 
                 0 
                 48 
                 16 
                 149 
                 61 
                 29.0% 
               
               
                 550 
                 3 
                 500 
                 0 
                 51 
                 19 
                 143 
                 78 
                 35.3% 
               
               
                 550 
                 0.6 
                 500 
                 0 
                 54 
                 14 
                 146 
                 58 
                 28.5% 
               
               
                 550 
                 0.6 
                 1000 
                 0 
                 145 
                 12 
                 316 
                 90 
                 22.2% 
               
               
                 550 
                 0.6 
                 1840 
                 0 
                 337 
                 9 
                 606 
                 125 
                 17.1%  
               
               
                   
               
             
          
         
       
     
     EXAMPLE XIII 
     The data shown in Table 13 were collected using the catalyst described in Example 3 calcined at 600° C. They show that the conversion and N 2 O selectivity are increased as increasing amounts of oxygen in the 1-4.5% range are fed 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 13 
               
             
             
               
                   
               
               
                 Effect of oxygen concentration on conversion of NO and NH 3  over Mo/ZrO 2   
               
               
                 calcined at 600 C. 
               
               
                 GHSV: 1,375,000 hr −1   
               
               
                 Feed: NH 3 (500 ppm); NO(500 ppm); O 2 (1-4.5%) 
               
             
          
           
               
                   
                   
                   
                 selectivity 
               
               
                   
                 outlet concentrations 
                 percent 
                 to 
               
             
          
           
               
                 T(° C.) 
                 inlet O 2 (ppm) 
                 NH 3 (ppm) 
                 NO(ppm) 
                 N 2 (ppm) 
                 N 2 O(ppm) 
                 conversion* 
                 N 2 O† 
               
               
                   
               
             
          
           
               
                 450 
                 1 
                 319 
                 347 
                 52 
                 111 
                 32.5 
                 68.3 
               
               
                 450 
                 4.5 
                 319 
                 342 
                 53 
                 116 
                 33.8 
                 68.6 
               
               
                 475 
                 1 
                 278 
                 326 
                 58 
                 137 
                 38.9 
                 70.4 
               
               
                 475 
                 4.5 
                 276 
                 320 
                 57 
                 145 
                 40.4 
                 71.8 
               
               
                 500 
                 1 
                 247 
                 310 
                 62 
                 159 
                 44.2 
                 72.0 
               
               
                 500 
                 2 
                 240 
                 306 
                 61 
                 167 
                 45.6 
                 73.5 
               
               
                   
               
               
                 *defined as (N 2  + N 2 O)(inlet NH 3  + inlet NO)  
               
               
                 †defined as (N 2 O)(N 2  + N 2 O)