Rather than start a new thread, here is a patent of interest to those contemplating (or electroplating!) Ostwald process catalysts...
Catalyst for production of nitric acid by oxidation of ammonia
US 5336656 A
http://www.google.com/patents/US5336656
Example #4 caught my eye... No noble metals. A catalyst and substrate that a sophisticated amateur might make at reasonable cost. LOW PRESSURE
OPERATION WITH HIGH EFFICIENCY.
Now about finding a cheap source of ammonia gas?
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EXAMPLE 4 A foam structure 8 inches in diameter and 0.8 inches thick and containing 30 pores per inch was produced by immersing a polyurethane
expanded foam into a ceramic slurry of cordierite (magnesia alumina silicate) powder, After firing to temperatures in excess of 1300° C. the ceramic
foam was dipped into an aqueous colloidal dispersion of alumina containing about 20% by weight of Al2 O3. The sample was dried and calcined to 500°
C. for one hour, The foam was found to have picked up 8% by weight alumina. The alumina coated foam was dipped onto a solution of 12% zinc as zinc neo
decanoate in toluene. The weight pick up measured after calcination to 500° C. was 5%. This zinc oxide and alumina coated foam was then dipped into a
12% cobalt as cobalt neo decanoate in toluene and dried and calcined at 500° C. The weight pick up was 15% as cobalt oxide. This catalyst was placed
in the ammonia oxidation reactor and ignited with the electric spark ignitor. The reactor was run for two weeks before evaluation, Analysis of the
ammonia input to the reactor showed 10% ammonia in air, The output was measured at between 9.1 and 9.4% NO giving a corrected conversion of 92 to 95%.
Pilot Plant Trial Experience (comparison with Pt gauze) The reactor chamber of the pilot unit utilizes 16, 8 inch diameter gauzes. The flow rate is
600 scfm which gives a linear velocity of 1.355 meters per second and an approximate pressure drop of 1.9 inches of water. The feed is approximately
6.7% ammonia in air. The reactor operates at 4 psig and atmospheric pressure is about 13 psig. A platinum catalyst on foam was prepared with 10.5% Pt
on an 8 inch diameter 0.80 inches thick, 30 pores per linear inch alumina foam. This catalyst loading had a platinum loading of 1.38 troy ounces in
the reactor. (The metal contained in the gauzes pack was 9.94 troy ounces.) At this metal loading the metallized ceramic catalyst is electrically
conductive with a resistance of about 0.4 ohms per inch. This metallized foam was placed on a non metallized alumina support segment and mounted in
the reactor. The gauze reactor was operated at 760°-800° C. The performance of the catalyst was checked by taking samples of the reacted gases and
titrating for nitric acid and ammonia. Twelve samples were taken over a six hour run. The results showed that the gauze converted 95% of the ammonia
to nitric acid and furthermore in the absorption system used approximately 45-46% acid was produced. The metallized foam converted up to 96% of the
ammonia to nitric acid and for unexplained reasons gave a stronger acid strength of about 50%. After these tests were completed only the acid strength
was used to monitor the performance and nitric acid was produced for an additional 60 days. At the end of the 60 days, the catalyst was performing
acceptably, with no evidence of reduced activity and the run was stopped only to recover the catalyst for analysis. Assay showed that there was no
metal loss (assay in 10.50% assay out 10.54%) and there was no loss of performance was detected. TABLE
2______________________________________Comparisons of Foams to Gauze Thickness of Foamto Match Gauze(Surface Area of 80 mesh gauze is 1.53 Square
meters of wire persquare meter gauze) Pressure Drop at 1.355 m/sec, (inPores Per Linear Inch Thickness of Foam H2
O)______________________________________10 0.229 cm 0.7220 0.114 cm 1.3830 0.076 cm 1.9050 0.046 cm 6.11______________________________________ From
about 12 to 15% Pt by weight the metallized structure has a continuous and electrically conductive film. The ceramic surface is substantially coated.
Table 3 below shows the platinum reduction achievable by using the coated form. This made possible because the ceramic makes up the core and the
platinum is on the surface where it is effective as a catalyst. TABLE 3______________________________________Comparisons of Pt loadings on Gauze and
MetallizedCeramic Foams(Coated at 12% by weight)(80 mesh wire gauze has 1.78 troy ounce per square footof gauze)Pores per linear inch TO/Sq
Ft______________________________________10 0.114520 0.057230 0.038250 0.0229______________________________________ It is estimated that the catalysts
and process according to the present invention, if substituted for the conventional platinum gauze can reduce the metal content of the catalyst charge
over 90%.
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