Abstract:
A process for producing a stable high-temperature catalyst for reduction of nitrogen oxides in combustion exhaust gases at operating temperatures from 300° C. to over 700° C. without the need for exhaust dilution. A zeolite material is steam-treated at a temperature and duration sufficient to partially de-aluminize the zeolite to approximately a steady state, but not sufficient to fully collapse its chemical structure. Iron is added to the zeolite material. The zeolite material is calcined at a temperature, humidity, and duration sufficient to stabilize the zeolite material. Examples and specifications for ranges, order, and durations of steaming, calcining, and other steps are provided.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to catalysts and processes for the reduction of NO x  using a reducing agent such as NH 3  in combustion exhaust at temperatures from 300° C. to over 600° C. 
       BACKGROUND OF THE INVENTION 
       [0002]    Selective catalytic reduction (SCR) is a technology for reduction of nitrogen oxide (NO x ) emissions from combined and simple cycle power plants and coal-fired boilers. The process involves injecting NH 3  into the exhaust gas upstream of a catalytic reactor. Within the catalyst bed, NO x  reacts with adsorbed NH 3  in the presence of O 2  to form primarily N 2  and water. Traditional catalysts employed by the process consist of V 2 O 5  supported on high-surface-area TiO 2 . The process achieves up to 90-95% NO x  reduction efficiency at low to moderate reaction temperatures (300-420° C.). Traditional SCR processes are operated with stoichiometric NH 3 /NO x  ratios consistent with an 80-90% NO x  reduction. Operation with higher NH 3 /NO x  ratios enhances the NO x  reduction efficiency at the expense of ammonia slip, which often needs to be below than 2-5 ppm. NH 3  slip contributes to emissions of nitrogen compound into the atmosphere and leads to the formation of corrosive ammonium sulfates and bisulfates downstream of the SCR. These compounds also may plug heat exchange surfaces in the heat recovery steam generator (HRSG). 
         [0003]    For combined-cycle power plants, the SCR reactor is integrated into the HRSG. In this manner, the catalyst temperature under normal operation conditions of 50-100% load is between 300 and 370° C. However, in simple cycle power plants the temperature of the exhaust leaving a high efficiency gas turbine can exceed 600° C. Absent any heat exchange surfaces in the post turbine enclosure, the reactions between ammonia and NO x  encounter these high temperatures. This requires an SCR catalyst durable to high temperatures and thermal shock, since the temperature in the gas turbine exhaust reaches its maximum in a short period of time, such as 10 minutes. 
         [0004]    High temperature of the exhaust gases requires a reduction in the distance between NH3 injection plane and a face of SCR in order to minimize substantial decomposition of ammonia at temperatures above 500° C. A short distance between ammonia injection grid and the face of SCR dictates the installation of special distribution/mixing devices in order to mitigate maldistribution problems resulting from shrinking zone for ammonia and NOx upstream mixing. 
         [0005]    Locating a V 2 O 5 /TiO 2  SCR catalyst downstream of a gas turbine in temperatures above 550° C. is not feasible, as the temperatures of the flue gas will rapidly deactivate the V 2 O 5 /TiO 2  catalyst, due to a transformation of the TiO 2  from the high surface area anatase phase to the low surface area rutile phase. 
         [0006]    Acidified, metal-impregnated, zeolite-based SCR catalysts have been investigated as an alternative to the V   2   O   5   /TiO   2   SCR catalyst (Farnos et al. 1996; Parvulescu et al. 1998; Stevenson and Vartuli, 2002; Qi and Yang, 2004). Zeolite based catalysts are being investigated because they offer advantages over V2O5/TiO2 SCR catalysts, namely wider operating temperature range, greater thermal stability, and reduced disposal issues associated with the spent catalyst. Although many types of zeolites have been found to facilitate the reactions between NH3 and NOx (Long and Yang, 2002; Delahay et al, 2004; Moreno-Tost et al., 2004; Liu and Teng, 2005), zeolites ZSM-5 and zeolite beta appears to be the most promising. Unlike V 2 O 5 /TiO2 SCR catalysts, the zeolite-based catalyst is unable to effectively oxidize NO. Consequently, a metal function, such as iron, cobalt, etc. is added to the acidified zeolite in order to oxidize NO to NO 2 , which is decomposed according to the following reaction scheme (Long and Yang, 2002): 
         [0000]    
       
                 
         
             
             
         
       
     
         [0007]    The rate-limiting step in the reaction sequence is the oxidation of NO to NO 2 . From equations 1 through 4, ammonia rapidly adsorbs onto the Brønsted acidic sites on the surface of the zeolite to yield adsorbed ammonium ions. NO is oxidized over the metal function (iron oxide) to yield NO 2 . NO 2  interacts with the adsorbed ammonium ions to form an adsorbed ammonium nitrite complex, which decomposes upon reaction with NO to yield N 2  and H 2 O, completing the catalytic cycle. The overall reaction is identical to that of conventional V 2 O 5 /TiO 2  SCR catalysts. 
         [0000]      4 NH3+4 NO+O 2 →4 N 2 +6 H 2 O  (5) 
         [0008]    Tran et al. (U.S. Pat. No. 6,689,709 and U.S. Pat. No. 6,914,026) report the use of iron exchanged zeolite beta and iron/cerium exchanged zeolite beta in the selective catalytic reduction of NOx using NH3. The catalyst was prepared by ion exchange of zeolite beta using cerium, followed by ion exchange with iron. The catalyst achieved enhanced stability over a material prepared without the addition of cerium. Tran et al. also report the improved stability achieved upon steam treatment at 650° C., 10% H 2 O for 2 hours. In all cases, catalytic materials lose activity over time. 
         [0009]    Absil et al. (U.S. Pat. No. 5,710,085) report improved durability of zeolite beta upon treatment using phosphorous. The resulting material displayed enhanced stability and activity during catalytic cracking studies. Exposure of zeolite to water vapor at an elevated temperature results in the removal of framework aluminum. However hydrothermal treatments under some conditions are known to enhance both the structural stability and acidity of zeolites (Kerr et al., 1970, Breck 1974, Chen and McCullen, 1988; Stevenson et al. 2002). 
         [0010]    Despite the above enhancements, prior catalysts do not provide stability and adequate NOx removal efficiency at temperatures above about 550° C. Thus, they cannot efficiently reduce NOx emissions in a direct gas turbine exhaust, such as in simple cycle power plants, without dilution of the exhaust with cooler air. However, dilution of the exhaust significantly reduces the overall gas turbine efficiency, and is not a cost-effective option. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]    The invention is explained in the following description in view of the drawings that show: 
           [0012]      FIG. 1  is a schematic diagram of a gas turbine with exhaust cleaned by selective catalytic reduction. Dashed lines are used for some curves to distinguish them from other crossing curves. 
           [0013]      FIG. 2  compares NO reduction efficiency over time for 8 tested examples of the invention and a baseline example without improvements of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      FIG. 1  illustrates a gas turbine system  20  with an air input  22 , a fuel input  24 , a gas turbine  26 , a combustion exhaust  28 , a reducer (ammonia) input  30 , a selective catalytic reduction bed  32 , and a cleaned exhaust  34 . Ammonia is injected through nozzles installed within an ammonia distribution grid that is located a short distance from the face of the SCR bed  32 . The short distance between the ammonia injection grid and the face of the SCR is required to minimize the decomposition of ammonia at high temperatures of the exhaust above 550° C. As a result, a short NH3/NOx mixing zone can lead to a severe maldistribution effect and can significantly reduce the performance of the SCR downstream. To overcome this problem special distribution/straightening and mixing devices need to be installed upstream of the SCR bed in order to provide a good mixing between NH3 and NOx upstream of the SCR. Such mixing devices are well known from the previous art (e.g. K. J. Rogers, Proceedings of the 2002 Conference on Selective Catalytic Reduction and Selective Non-Catalytic Reduction for NOx Control, US DOE). 
         [0015]    The inventors devised a production process to improve catalytic stability at high temperatures, and achieved dramatic results as shown in  FIG. 2 . A baseline catalyst was produced with known methods as described under example 1 below. NO x  removal efficiency at 605° C. for the baseline sample is represented by curve E 1 . Eight other catalysts were prepared according to examples 2-9 below. Their NO x  removal efficiencies are represented by curves E 2 -E 9  respectively. The baseline curve E 1  dives constantly downward, never stabilizing. In contrast, the inventive examples show full or greatly improved stability over time. Ammonia slip was reduced in the inventive samples, as detailed in tables below. Only catalysts prepared with the following three steps in combination, using certain characteristic ranges in the preparation process, showed the best improvement. 
         [0016]    A basic aspect of the invention is preparing a metal-containing zeolite catalytic material by: (1) steam treatment of the zeolite, (2) addition of iron into the pore volume of the steam-treated zeolite, and (3) high-temperature calcinations. The order and number of the above steps may vary, as exemplified below. In all of the examples high temperature calcination at 750 C-900 C for 1-5 hours was performed at a time after a steam treatment at 500 C-600 C for 5-15 hours. The inventors expected that various alternative base metals or platinum group metals could be used for step 2, and that at least some of them would provide similar efficiencies. However, it was found that at least iron is essential for the best stability at high temperatures. Other metals may be added in addition to iron as later described to provide enhancements. 
         [0017]    According to an aspect of the invention, a zeolite, for example zeolite Y, zeolite beta and/or zeolite ZSM-5, is first treated with steam (e.g. water vapor) at an elevated temperature. Exposure of zeolites to water vapor at temperatures greater than about 400° C. is known to destabilize zeolites (Breck, 1974), so this step of the invention may seem counter-intuitive. Exposure to water vapor results in dealumination (removal of framework aluminum) of the zeolite. Dealumination of a zeolite occurs via the following reaction (Breck, 1974): 
         [0000]    
       
                 
         
             
             
         
       
     
         [0018]    The above treatment results in the formation of aluminum hydroxide and a “hydroxyl nest,” a defect in the lattice of the zeolite resulting in the termination of framework silicon atoms with hydroxyl groups. If the treatment conditions are not excessive, the extent of dealumination upon exposure to steam will reach a steady state, with the residual amount of framework alumina dependent upon the SiO 2 /Al 2 O 3  ratio of the starting zeolite, the temperature of the exposure, the concentration of water vapor in the air, and the duration of the exposure. Should the conditions be excessive, the entire zeolite structure will collapse. Therefore, optimum ranges of temperature, water vapor, and duration are required to provide the results needed herein. 
         [0019]    The present steam treatment of zeolite (e.g. zeolite beta) may be performed at a temperature between about 400° C. and about 800° C., preferably between 500° C. and 600° C., employing between about 5% and 100% water vapor, preferably between about 10% and 25%, for a duration between 30 minutes and 48 hours, preferably between 2 hours and 24 hours, and more preferably between 5 hours and 15 hours. 
         [0020]    Following steam treatment, the zeolite is preferably loaded with iron necessary to catalyze the oxidation of NO to NO 2  as described in equation 2. Promoters, such as tungsten, lanthanum, cerium, barium, vanadium, phosphorous and cesium, may also be added at this time. Techniques used in loading metals into zeolite include, but are not limited to, ion exchange, impregnation, and metal vapor deposition. These techniques are known in the art. 
         [0021]    Alternatively, the catalyst may be prepared by performing the metal loading step first followed by steam treatment. Alternatively, a portion of the metals and/or certain metals may be incorporated prior to steam treatment, with the remaining metals incorporated following steam treatment. 
         [0022]    Following metal loading, the zeolite is stabilized by calcining in dry air (less than 2% H 2 O) at an elevated temperature. High temperature calcination is a key step in the preparation of the catalyst disclosed herein. The calcination is performed at about 500° C.-1100° C., and preferably between about 750° C. and 900° C. The duration of the calcination is between about 30 minutes and about 72 hours, and preferably between about 1 hours and 5 hours. 
         [0023]    This high temperature calcination results in dehydroxylation of the zeolite, i.e., removal of water from the hydroxyl nest. While not wishing to be bound by any theory, it is believed that the high temperature thermal treatment stabilizes the zeolite by closing a “defect” site, thereby reducing the size of the unit cell. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    Further, it is believed that by incorporating metals within the zeolite prior to high temperature calcination, the catalytic metals, or a portion thereof, become incorporated into the defect site, resulting in a highly stabilized metal phase. 
         [0024]    At one point during the preparation of the material, a catalytic metal necessary to oxidize NO to NO 2  (equation 2), especially iron, must be incorporated into the catalyst. Metals may be incorporated at several steps during the manufacture of the catalyst. For example, metals providing either oxidation or stabilizing functions may be incorporated prior to steam treatment or following steam treatment, prior to high temperature calcinations. Although less preferred, metals may be incorporated into the zeolite following high temperature calcinations or added to the binder employed in the washcoating of the zeolite. By this last technique, a metal, or a portion thereof, may become incorporated into the lattice of the binder. Examples of binders include aluminum, zirconium, and silicon-based materials as known in the art. Also less preferred, metal may be added to the catalyst following preparation into formed material, such as for example beads, rings, spheres, extrudates, granules, a monolith, or a washcoated monolith. 
         [0025]    Zeolite beta may be synthesized over a range of silica to alumina (SiO 2 /Al 2 O 3 ) ratios between about 10 to greater than 100, and preferably between about 15 and about 25. The type and concentration of oxidation metal employed in the catalyst may vary. Examples of oxidation metals for equation 2 include base metals such as iron, cobalt, nickel, chromium and copper, and platinum group metals, examples of which include platinum and palladium. Mixtures thereof may also be employed. In selecting metals necessary to facilitate the oxidation of NO to NO 2  as per equation 2, the metal type and metal loading will be dependent upon the operating temperature of the catalyst. As the operating temperature increases, the decomposition of NH3 over the oxidation metal will become significant, especially as the temperature of the process exceeds about 450° C., and more significant as the temperature of the process exceeds about 550° C. 
         [0026]    As a result, the types and concentrations of oxidation metals may vary greatly. Thus, the loading of base metals may be as low as 0.01%, or as high as about 10%. The loading of platinum group metals, known to be more reactive oxidation catalysts, may be as low as 0.001% to as great as 1%. The addition of platinum group metals to the catalyst formulation is also expected to facilitate the decomposition of CO and non-methane hydrocarbons. 
         [0027]    Promoters and stabilizing agents may be added to the catalyst to stabilize the structural integrity of the zeolite, stabilize the Brønsted acidity of the zeolite, stabilize the oxidation metal, enhance the overall acidity of the zeolite, and/or reduce coke formation within the pores of the zeolite during start-up. Such agents may include tungsten, vanadium, lanthanum, cerium, phosphorous, barium, zirconium, and cesium, or mixtures thereof. The concentration and type of metal may vary. For example concentrations may be as low as 0.01% or as high as 10%, preferably between 0.3% and 3%. Promoters may also be added to the binder employed in the preparation of the catalyst in order to enhance the hydrothermal stability of the binder material. 
         [0028]    The catalyst described in this invention may be employed in a variety of geometric forms sufficient to bring about contact between the catalyst and the process stream. These forms include beads, rings, spheres, granules, etc. Alternatively, the catalyst may be either extruded as a monolith, or may be washcoated onto surfaces of geometric forms, such as for example those listed above. Preferably, the catalyst may be washcoated onto the external surface of a ceramic monolith. A monolith may be in a honeycomb form for example, with of a series of straight, non-interconnecting channels. Onto the surface of the monolith, a thin coating of catalytic material is deposited, termed “washcoat” in the art. Monoliths offer several advantages, including low thermal mass, excellent utilization of catalytic material, low pressure drop and predictable flow characteristics. 
         [0029]    The SCR process of the invention that uses the catalyst described herein involves contacting the combustion exhaust stream with the catalyst in a manner necessary to facilitate a reaction between NOx (mixtures of NO and NO 2 ) and a reducing agent such as preferably NH   3 .  The reaction temperature may vary from about 300° C. to over 700° C., preferably 500° C.-650° C., and more preferably 550° C.-620° C. The gas hourly space velocity (GHSV) may vary from about 2,000 volumes per hour to over 150,000 per hour, preferably 6,000-50,000 per hour, and even more preferably 15,000-30,000 volumes per hour. The concentration of NOx in the process stream may range from less than 10 ppm to greater than several hundred ppm. 
       EXAMPLES 
       [0030]    All zeolite beta reported in the following examples was obtained in the ammonium form, and was calcined prior to use in order to remove the organic templating agent. 
       Example 1 
       [0031]    Baseline Zeolite Beta with Fe, No Steam, Minor Calcination 
         [0032]    Baseline iron-containing zeolite beta was prepared by adding 15 g of calcined zeolite beta to a 100 ml beaker. To the beaker was added 60 ml of distilled (DI) water, 15 g of zirconium acetate solution (20% ZrO 2  by weight) and 0.109 g iron (III) nitrate nonahydrate (13.8 wt % iron). The resulting solution was mixed to form a slurry containing 0.001 parts iron per part zeolite beta. The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 21.4 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. The baseline catalyst described above was evaluated for its ability to decompose NO using NH3. The baseline catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 60 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                  2 hrs 
                 93.4% 
                  2.1 ppm 
               
               
                 10 hrs 
                 90.2% 
                  5.2 ppm 
               
               
                 50 hrs 
                 79.0% 
                 13.1 ppm 
               
               
                 100 hrs  
                 71.7% 
                 17.1 ppm 
               
               
                   
               
             
          
         
       
     
       Example 2 
       [0033]    Zeolite beta with 0.6% Fe, steam, calcination, Fe addition. 
         [0034]    18 g of calcined zeolite beta was exposed to 15% H 2 O/Air at 525° C. for 5 hours then calcined at 825° C. for 2 hours in dry air. The resulting zeolite powder was used to prepare a monolithic catalyst. 17.6 g of the above zeolite was added to a 100 ml beaker. To the beaker was added 50 ml DI water, and 0.764 g iron (III) nitrate nonahydrate (13.8 wt % iron). Following 1 hour, 17.6 g of zirconium acetate solution was added to the slurry and then mixed. (20% ZrO 2  by weight). The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 26.2 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. The catalyst described above was evaluated for its ability to decompose NO using NH3. The catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 70 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                  5 hrs 
                 84.7% 
                 5.4 ppm 
               
               
                 25 hrs 
                 84.1% 
                 7.5 ppm 
               
               
                 50 hrs 
                 83.7% 
                 8.6 ppm 
               
               
                   
               
             
          
         
       
     
       Example 3 
       [0035]    Zeolite beta with 0.6% Fe prepared by Fe addition, steam, calcination. 
         [0036]    25 g of calcined zeolite beta was added to a 200 ml beaker. To the beaker was added 50 ml of DI water and the slurry was stirred. To the resulting slurry was added 1.0853 g iron (III) nitrate nonahydrate (13.8 wt % iron). The slurry was then heated to 90° C. Following 3 hours, the slurry was removed and filtered. Resulting material was washed with DI water and filtered again. Dried material was exposed to 15% H 2 O/Air at 525° C. for 5 hours, and then calcined at 825° C. for 2 hours in dry air. Following steam treatment, the material was brown in color. Following high temperature calcinations, the material turned white. 
         [0037]    The resulting material powder was used to prepare a monolithic catalyst. 20.0 g of the above zeolite was added to a 100 ml beaker. To the beaker was added 65 ml DI water, and 20 g zirconium acetate solution (20% ZrO 2  by weight). The resulting solution was mixed to form a slurry. The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 26.2 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. 
         [0000]    The catalyst described above was evaluated for its ability to decompose NO using NH3. The catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 70 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. Note: Compared to example 1, the zeolite is far more stable. Ammonia slip is less than that of Example 2, indicating a more reactive iron phase. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                  5 hrs 
                 83.6% 
                 3.2 ppm 
               
               
                 25 hrs 
                 82.8% 
                 4.4 ppm 
               
               
                 50 hrs 
                 82.1% 
                 4.7 ppm 
               
               
                   
               
             
          
         
       
     
       Example 4 
       [0038]    Zeolite beta with 0.6% Fe prepared by steam, Fe addition, calcination. 
         [0039]    20 g of calcined zeolite beta was steam treated by exposure to 15% H 2 O/Air at 525° C. for 5 hours. The resulting zeolite powder was then added to a 200 ml beaker. To the beaker was added 100 ml of DI water and the slurry was stirred. To the resulting slurry was added 0.8683 g iron (III) nitrate nonahydrate (13.8 wt % iron). The slurry was then heated to 90° C. Following 3 hours, the slurry was removed and filtered. Resulting material was washed with DI water and filtered again. The resulting dried iron-containing zeolite was then calcined at 825° C. for 2 hours in dry air. Following steam treatment, the material was brown in color. Following high temperature calcinations, the material turned white. 
         [0040]    The resulting iron-containing zeolite powder was used to prepare a monolithic catalyst. 15.0 g of the above zeolite was added to a 100 ml beaker. To the beaker was added 50 ml DI water, and 15 g zirconium acetate solution. (20% ZrO 2  by weight). The resulting solution was mixed to form a slurry. The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 26.2 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. 
         [0041]    The catalyst described above was evaluated for its ability to decompose NO using NH3. The catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 70 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                  5 hrs 
                 82.5% 
                 3.2 ppm 
               
               
                 25 hrs 
                 82.4% 
                 4.6 ppm 
               
               
                 50 hrs 
                 82.3% 
                 5.6 ppm 
               
               
                 100 hrs  
                 82.1% 
                 5.8 ppm 
               
               
                   
               
             
          
         
       
     
         [0042]    This catalyst was evaluated for its ability to decompose NOx using NH3 employing 60 ppm as well as 70 ppm NH3 in the process stream as described previously. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 [NH3] 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 60 ppm 
                 76.8% 
                 3.2 ppm 
               
               
                 70 ppm 
                 82.1% 
                 5.8 ppm 
               
               
                   
               
             
          
         
       
     
         [0043]    The catalyst was evaluated for its ability to decompose NOx employing a 60 ppm inlet NH3 at alternative reaction temperatures employing the process stream described above. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Temperature 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 548° C. 
                 87.8% 
                 6.5 ppm 
               
               
                 575° C. 
                 83.5% 
                 4.8 ppm 
               
               
                 590° C. 
                 80.6% 
                 4.0 ppm 
               
               
                 605° C. 
                 76.8% 
                 3.2 ppm 
               
               
                   
               
             
          
         
       
     
       Example 5 
       [0044]    Zeolite beta with 0.6% Fe, 5% W. 
         [0045]    50 g of calcined zeolite beta was added to a 500 ml beaker. To the beaker was added 400 ml of DI water and the slurry was stirred. To the resulting slurry was added 2.6 g of ammonia metatungstate (94.0 wt % WO 3 ). The slurry was then heated to 90° C. Following 4 hours, the slurry was filtered. Resulting solids were washed with DI water, then dried. Dried tungsten-zeolite was then steam treated by exposure to 15% H 2 O/air at 500° C. for 6 hours, then calcined at 825° C. for 2 hours in dry air. 
         [0046]    The resulting tungsten-containing zeolite powder was used to prepare a monolithic catalyst. 15 g of the above zeolite was added to a 100 ml beaker. To the beaker was added 80 ml DI water, 0.661 g iron (III) nitrate nonahydrate (13.8 wt % iron), and 15 g zirconium acetate solution (20% ZrO 2  by weight). The resulting solution was mixed to form a slurry containing 0.006 parts iron per part zeolite beta. The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 25.9 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. 
         [0047]    The catalyst described above was evaluated for its ability to decompose NO using NH3. The catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 60 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                  2 hrs 
                 79.0% 
                 4.6 ppm 
               
               
                 10 hrs 
                 75.8% 
                 5.4 ppm 
               
               
                 50 hrs 
                 74.6% 
                 6.1 ppm 
               
               
                   
               
             
          
         
       
     
         [0048]    The catalyst was evaluated for its ability to decompose NOx using NH3 at alternative reaction temperatures employing the process stream described above. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Temperature 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 550° C. 
                 84.7% 
                 7.7 ppm 
               
               
                 580° C. 
                 80.7% 
                 7.1 ppm 
               
               
                 605° C. 
                 74.6% 
                 6.1 ppm 
               
               
                   
               
             
          
         
       
     
         [0049]    The catalyst was evaluated for its ability to decompose NOx using NH3 at a space velocity of 15,000 and a temperature of 605° C. employing 60 and 70 ppm NH3 in the process stream as described previously. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 [NH3] 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 60 ppm 
                 77.6% 
                 3.9 ppm 
               
               
                 70 ppm 
                 86.8% 
                 6.6 ppm 
               
               
                   
               
             
          
         
       
     
       Example 6 
       [0050]    Zeolite Beta with 0.6% Fe, 5% La 
         [0051]    100 g of calcined zeolite beta was added to an 800 ml beaker. To the beaker was added 700 ml of DI water and the slurry was stirred. To the resulting slurry was added 15.5 g of lanthanum nitrate nonahydrate. The slurry was then heated to 95° C. Following 6 hours, the slurry was removed and filtered. Resulting solids were washed with DI water, then dried. 
         [0052]    25 g of this lanthanum zeolite beta was added to a 200 ml beaker. To the beaker was added 150 ml of DI water and the slurry was stirred. To the resulting slurry was added 1.09 g of iron (III) nitrate nonahydrate (13.8 wt % iron). The slurry was then heated to 90° C. Following 2 hours, the slurry was removed and filtered. Resulting solids washed with DI water, then dried. Dried solids were then steam treated by exposure to 15% H 2 O/Air at 500° C. for 14 hours, then calcined at 825° C. for 2 hours in dry air. 
         [0053]    The resulting iron-lanthanum-containing zeolite powder was used to prepare a monolithic catalyst. 12.25 g of the above zeolite was added to a 100 ml beaker. To the beaker was added 60 ml DI water and 12.25 g zirconium acetate solution (20% ZrO 2  by weight). The resulting solution was mixed to form a slurry. The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 25.9 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. 
         [0054]    The catalyst described above was evaluated for its ability to decompose NO using NH3. The catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 70 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 25 hrs 
                 87.0% 
                 4.3 ppm 
               
               
                 50 hrs 
                 86.1% 
                 5.1 ppm 
               
               
                 100 hrs  
                 84.6% 
                 5.6 ppm 
               
               
                   
               
             
          
         
       
     
       Example 7 
       [0055]    Zeolite Beta with 1.0% Fe, 5% La 
         [0056]    25 g of lanthanum zeolite beta from Example 6 was added to a 200 ml beaker. To the beaker was added 150 ml of DI water and the slurry was stirred. To the resulting slurry was added 1.81 g of iron (III) nitrate nonahydrate (13.8 wt % iron). The slurry was then heated to 90° C. Following 3 hours, the slurry was removed and filtered. Resulting material was washed with DI water, then dried. Dried material was then steam treated by exposure to 15% H 2 O/Air at 525° C. for 5 hours, then calcined at 825° C. for 2 hours in dry air. 
         [0057]    The resulting iron-lanthanum-containing zeolite powder was used to prepare a monolithic catalyst. 15.0 g of the above zeolite was added to a 100 ml beaker. To the beaker was added 60 ml DI water and 15.0 g zirconium acetate solution (20% ZrO 2  by weight). The resulting solution was mixed to form a slurry. The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 25.9 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. 
         [0058]    The catalyst described above was evaluated for its ability to decompose NO using NH3. The catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 82 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                  2 hrs 
                 89.1% 
                 3.4 ppm 
               
               
                 20 hrs 
                 89.0% 
                 5.3 ppm 
               
               
                   
               
             
          
         
       
     
         [0059]    The catalyst was evaluated for its ability to decompose NOx using NH3 employing 60, 70 and 82 ppm NH3 in the process stream as described previously. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 [NH3] 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 60 ppm 
                 73.2% 
                 2.1 ppm 
               
               
                 70 ppm 
                 83.2% 
                 2.1 ppm 
               
               
                 82 ppm 
                 89.0% 
                 5.3 ppm 
               
               
                   
               
             
          
         
       
     
       Example 8 
       [0060]    Zeolite Beta with 1.0% Fe, 2.5% W 
         [0061]    26 g of calcined zeolite beta was exposed to 15% H 2 O/Air at 525° C. for 5 hours. The resulting material was then added to a 200 ml beaker. To the beaker was added 100 ml of DI water and the slurry was stirred. To the resulting slurry was added 1.809 g iron (III) nitrate nonahydrate (13.8 wt % iron) and 1.066 g ammonia metatungstate (94.0 wt % WO 3 ). The slurry was then heated to 90° C. Following 3 hours, the slurry was removed and filtered. Resulting zeolite was washed with DI water and filtered again. The resulting dried iron-tungsten-containing zeolite was then calcined again at 825° C. for 2 hours in dry air. Following steam treatment, the material was brown in color. Following high temperature calcinations, the material turned white. 
         [0062]    The resulting iron-tungsten-containing zeolite powder was used to prepare a monolithic catalyst. 23.0 g of the above zeolite was added to a 100 ml beaker. To the beaker was added 70 ml DI water, and 23 g zirconium acetate solution. (20% ZrO 2  by weight). The resulting solution was mixed to form a slurry. The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 26.2 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. 
         [0063]    The catalyst described above was evaluated for its ability to decompose NO using NH3. The catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 70 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                  5 hrs 
                 85.4% 
                 7.4 ppm 
               
               
                  25 hrs 
                 85.8% 
                 8.5 ppm 
               
               
                  50 hrs 
                 85.9% 
                 9.0 ppm 
               
               
                 100 hrs 
                 85.5% 
                 9.1 ppm 
               
               
                 150 hrs 
                 85.5% 
                 9.1 ppm 
               
               
                 200 hrs 
                 85.5% 
                 9.1 ppm 
               
               
                   
               
             
          
         
       
     
         [0064]    The catalyst was evaluated for its ability to decompose NOx using NH3 at alternative reaction temperatures employing the process stream described above. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Temperature 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 545° C. 
                 92.0% 
                 15.7 ppm 
               
               
                 570° C. 
                 90.1% 
                 12.8 ppm 
               
               
                 585° C. 
                 88.1% 
                 10.7 ppm 
               
               
                 605° C. 
                 85.5% 
                  9.1 ppm 
               
               
                   
               
             
          
         
       
     
         [0065]    The catalyst was evaluated for its ability to decompose NOx employing a 60 ppm inlet NH3 at alternative reaction temperatures employing the process stream described above. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Temperature 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 545° C. 
                 88.8% 
                 8.8 ppm 
               
               
                 570° C. 
                 86.2% 
                 7.1 ppm 
               
               
                 585° C. 
                 83.5% 
                 6.1 ppm 
               
               
                 605° C. 
                 79.6% 
                 5.0 ppm 
               
               
                   
               
             
          
         
       
     
         [0066]    The catalyst was then evaluated at a space velocity of 15,000 hr −1  employing a process stream described above with a 70 ppm inlet NH3 inlet at a temperature of 605° C. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 GHSV 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 15,000 
                 88.4% 
                 5.5 ppm 
               
               
                   
               
             
          
         
       
     
         [0067]    The catalyst was then evaluated at a space velocity of 15,000 hr −1  employing a process stream described above with a 60 ppm inlet NH3 inlet at a temperature of 605° C. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 GHSV 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                 15,000 
                 84.2% 
                 3.1 ppm 
               
               
                   
               
             
          
         
       
     
       Example 9 
       [0068]    Zeolite Beta with 1% Fe,1% P 
         [0069]    25 g of calcined zeolite beta was steam treated by exposure to 15% H 2 O/Air at 525° C. for 5 hours. The resulting zeolite powder was then added to a 200 ml beaker. To the beaker was added 100 ml of DI water and the slurry was stirred. To the resulting slurry was added 1.881 g iron (III) nitrate nonahydrate (13.8 wt % iron) and 1.066 g ammonium phosphate (23.4% phosphorous by weight). The slurry was then heated to 90° C. Following 3 hours, the slurry was removed and filtered. Resulting zeolite was washed with DI water and filtered again. The resulting dried iron-phosphorous-containing zeolite was then calcined again at 825° C. for 2 hours in dry air. Following steam treatment, the material was brown in color. Following high temperature calcinations, the material turned white. 
         [0070]    The resulting iron-phosphorous-containing zeolite powder was used to prepare a monolithic catalyst. 22.44 g of the above zeolite was added to a 100 ml beaker. To the beaker was added 70 ml DI water, and 22.44 g zirconium acetate solution. (20% ZrO 2  by weight). The resulting solution was mixed to form a slurry. The slurry was used to washcoat a piece of monolith having a cell density of 230 cells/in 2  and a volume of 25.9 cm 3 . Following washcoating, the monolith was dried, then calcined at 525° C. for 1 hour. 
         [0071]    The catalyst described above was evaluated for its ability to decompose NO using NH3. The catalyst was evaluated at 605° C. at a space velocity of 20,000 hr −1  employing a feed stream consisting of 10% O 2 , 6.8% H 2 O, 50 ppm NO, 70 ppm NH3, balance N 2 . The table below reports the conversion of NO and the effluent concentration of NH3 as a function of time. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Time-on-stream 
                 NO Conversion 
                 Effluent [NH3] 
               
               
                   
               
             
             
               
                  5 hrs 
                 90.4% 
                 1.7 ppm 
               
               
                 25 hrs 
                 89.9% 
                 2.8 ppm 
               
               
                 50 hrs 
                 88.5% 
                 3.6 ppm 
               
               
                 100 hrs  
                 86.7% 
                 5.3 ppm 
               
               
                   
               
             
          
         
       
     
         [0072]    These examples demonstrate that the invented catalyst offers improved stability over prior art in treating high temperature combustion gases. Unlike prior catalysts it can be used to reduce emissions of NOx to about 2-5 ppm during stable and long-term operations at over 550 C. Applications include, but are not limited to, treatment of stationary sources of combustion exhaust such as power plants, and mobile sources such as diesel exhaust. 
         [0073]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.