Tungsten oxide-type compound having a new crystalline structure and method for preparing same
The compound according to the invention is a compound of formula (1) A x W 1-y MO y O 3 , wherein A is chosen from the group comprising the Li, Na, NH 4 , K and H cations, and it is characterized in that x and y verify the relationships 0≤x≤1 and 0≤y≤0.5, and in that it has a crystalline structure of the hexagonal type with a base of WO 6 octahedra, said structure having tunnels delimited by 6, 4 and 3 of said octahedra and oriented along the axis c.
1. A compound of formula (1) A x W 1-y Mo y O 3 wherein A is selected from the group consisting of the Li, Na, NH 4 , K and H cations, wherein 0≤x≤1 and 0≤y≤0.5, and wherein the compound exhibits a crystalline structure of hexagonal type which is based on WO 6 octahedra, said structure having tunnels delimited by 6, 4 and 3 of said octahedra and oriented along the axis c.
2. The compound as claimed in claim 1 , wherein 0≤x≤0.2.
3. The compound as claimed in claim 1 , wherein 0.5≤x≤1.
4. The compound as claimed in claim 1 , wherein x and/or y=0.
5. The compound as claimed in claim 1 , wherein the compound exhibits a crystalline structure with lattice parameters a: 10.0(1) Å and c: 3.9(1) Å and space group P6/mmm.
6. The compound as claimed in claim 1 , characterized in that it is composed of particles in the shape of platelets of from 50 to 500 nm in diameter and from 2 to 50 nm thick.
7. A process for preparing a compound as claimed in claim 1 , the process comprising:
(a) contacting an aqueous solution of a salt of W (VI) and, where appropriate, of a salt of Mo(VI), with a reducing agent to form a first medium;
(b) adjusting the pH of the first medium to a value of at most 7 to form a suspension,
wherein a cation A is introduced in one of steps (a) or (b);
(c) maturing the suspension to form a second medium;
(d) heating the second medium to form a third medium;
(e) separating and drying a solid from the third medium to form a compound A x W 1-y Mo y O 3 , wherein x>0;
(f) optionally, eliminating the cation A from the compound A x W 1-y Mo y O 3 to form a compound W 1-y Mo y O 3 .
8. The process as claimed in claim 7 , wherein the aqueous solution in step (a) comprises a salt of tungsten and of the cation A.
9. The process as claimed in claim 7 , wherein step (b) comprises adjusting the pH to a value of at most 2.
10. The process as claimed in claim 7 , wherein step (c) comprises maturing the suspension at a temperature of at most 80° C.
11. The process as claimed in claim 7 , wherein step (d) comprises heating the third medium at a temperature of at least 95° C.
12. The process as claimed in claim 7 , wherein the reducing agent is at least one reducing agent selected from hydrazine, sugars and ascorbates.
13. The process as claimed in claim 7 , wherein A is NH 4 or H and wherein step (f) comprises heating under air.
14. The process as claimed in claim 7 , wherein A is Li, Na, K, NH 4 or H and wherein step (f) comprises an electrochemical oxidation.
15. The process as claimed in claim 7 , wherein A is Li, Na, K or NH 4 and wherein step (f) comprises an ion exchange to replace Li, Na, K or NH 4 with H followed by heating under air or electrochemical oxidation of the compound resulting from the ion exchange.
16. The process as claimed in claim 9 , wherein step (b) comprises adjusting the pH to a value of between 1 and 2.
17. The process as claimed in claim 10 , wherein step (c) comprises maturing the suspension at ambient temperature.
18. The process as claimed in claim 11 , wherein step (d) comprises heating the third medium at a temperature of at least 120° C.