While there are many procedures to make catalysts for GTL technologies both in the experimental and commercial phase, the purpose of this page will serve to review some notes on reactions that are typically used in the field.

Nitric acid Passivation

Although chromium (Cr), iron (Fe) and aluminium (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal oxide layer that protects the metal from further oxidation, which is called passivation. Typical passivation concentrations range from 18% to 22% by weight. (Reference: Wikipedia 09/09/10)

Ferric/Ferrous nitrate

"Ferric nitrate (nitrate of iron) is generally made by dissolving scrap iron in nitric acid of 1.30 sp. gr. '1'he reaction is as follows:

- 2 Fe +8 HN03 = 2 Fe(N03)3 + 2 NO +4 H20.

By concentrating the solution, colorless crystals, containing six or nine molecules of crystal water, are obtained.
The aqueous solution will dissolve ferric hydroxide, and this basic solution is much used in textile coloring. By using an excess of iron, and permitting the reaction to continue slowly, after all the acid has been acted upon, a precipitate of insoluble basic ferric nitrate ultimately forms. The solution obtained in this way is of a red-brown color and indefinite composition. It is chiefly used for blacks in silk dyeing, and for iron-buff on cotton.
Ferrous nitrate is prepared by dissolving iron in cold dilute nitric acid (1.10 sp. gr.). But a considerable amount of ammonium nitrate is also formed in the solution, according to the reaction:-

4 Fe + 10 HN03 =4 Fe(N03)2 +NH4NO3 + 3 H20.

This solution is very unstable and decomposes when heated even slightly, forming basic ferric nitrate and liberating nitric oxide. To prepare a pure ferrous nitrate, decomposition of a ferrous sulphate solution by barium or lead nitrate is employed:-

FeS04 + Ba(NO3)2 = BaS04 + Fe(NO3)2

The solution is filtered or decanted from the precipitated barium sulphate.
There is a preparation sold as "nitrate of iron," (probably so called because some nitric acid is used in making it), which is not a nitrate, but a basic ferric sulphate and sulphate-nitrate solution. -A solution of ferrous sulphate (copperas) is oxidized by nitric acid, according to the following equations:-

1) 6 FeS04 + 2 H:X0a + 2 H20 = 3 Fe2(S04)2' (OH)2 + 2 NO.
2) 6 FeS04 +5 noxoa = 3 FelS04)2' (NOa) • (OU) + 2 NO + H20.
3) 6 FeS04 + 8 IIXOa = 3 Fe2(S04)2' (NOa)2 + 2 NO +4 H20.
4) 12 FeS04 + 3 H2SO. + 4 HNOa = 3 FeiS04)5' (OI-J)2+ 4 NO
+ 2 H20.

Equation 4 gives the best product. The solution of basic ferric sulphate and sulphate-nitrates IS a dark brown-red liquid, and is much used in silk dyeing. It is only mentioned· here because of the frequent confusion of names in the commercial article. Silver nitrate is made by dissolving the metal in dilute nitric acid: - 6 Ag + 8 UNOa = 6 AgNOa + 4 H20 + 2 NO.
If the silver contains copper, the resulting solution of nitrates is evaporated to dryness and then heated cautiously to about 2500 C., at which temperature the copper nitrate is decomposed into copper oxide, nitric oxide, and oxygen, while the silver salt is not altered. By extracting the residue with water, the silver nitrate is dissolved, leaving the copper oxide. The solution is then evaporated to crystallize the silver nitrate.
The salt fuses unchanged at 225⁰ C., but decomposes if heated nearly to redness; it is cast in small sticks, and is much used in medicine for a cautery, under the name of lunar caustic.
Silver nitrate has a very corrosive action on organic matter. It is largely used in photography, and to a lesser degree in pharmacy, in the manufacture of mirrors, in preparing" indelible inks," and as a chemical reagent.
Read more: http://www.lenntech.com/chemistry/nitrates.htm#ixzz0z4NZTchc"

Reference: http://www.lenntech.com/chemistry/nitrates.htm