Silica-stabilized ultrafine anatase titania, vanadia catalysts, and methods of production thereof
View Patent ↗The invention is directed to compositions and processes for the production of silica-stabilized ultrafine anatase titanias and which may further comprise tungsten and vanadia. The surface stabilization may be by treatment of the TiO 2 particles with a low molecular weight and/or small nanoparticle form of silica such as, in preferred embodiments, a tetra(alkyl)ammonium silicate or silicic acid, which serves to efficiently maintain the anatase phase and prevent crystal growth under severe thermal and hydrothermal conditions, even in the presence of vanadia. The vanadia catalysts produced from the novel titanias have equal or improved catalytic activity for selective catalytic reduction of NOx compared to conventional vanadia supported silica-titania based catalysts. The invention is further directed to diesel emission catalytic devices comprising the novel titania-based catalyst compositions.
1. A method of producing a catalyst support material, comprising:
providing a slurry comprising TiO 2 ;
combining the TiO 2 slurry with (1) a silica precursor solution comprising SiO 2 nanoparticles having a diameter of less than 5 nm and with (2) WO 3 , to form a TiO 2 —WO 3 —SiO 2 mixture; wherein the silica precursor solution is combined with the TiO 2 slurry before, after, or while the WO 3 is combined with the TiO 2 slurry; and
sintering the TiO 2 —WO 3 —SiO 2 mixture to form a silica-stabilized titania support material.
2. The method of claim 1 wherein the silica-stabilized titania support material, comprises:
86%-94% dry weight of TiO 2 , 3%-9% dry weight of a SiO 2 , and 3%-7% dry weight of WO 3 ; and wherein the titania support material has a surface area of at least 80 m 2 /gm before sintering.
3. The method of claim 1 wherein the TiO 2 of the slurry comprise preformed titanium hydroxide, titanium oxy-hydroxide or titanium dioxide particles.
4. The method of claim 1 wherein the TiO 2 of the slurry is not produced in the presence of urea.
5. The method of claim 1 wherein the SiO 2 of the silica precursor solution comprises a diameter of less than 4 nm.
6. The method of claim 1 wherein the silica precursor solution comprises a tetra(alkyl)ammonium silicate solution or silicic acid.
7. The method of claim 1 wherein the SiO 2 substantially comprises patches which are ≦5 nm in depth after redistribution as seen by scanning electron microscopy or by transmission electron microscopy.
8. The method of claim 1 comprising combining the TiO 2 —WO 3 —SiO 2 mixture with V 2 O 5 to form a vanadia catalyst.
9. The method of claim 8 wherein the vanadia catalyst comprises 0.5%-3% dry weight of V 2 O 5 .
10. The method of claim 8 wherein the V 2 O 5 of the vanadia catalyst is present at a fractional monolayer value of less than 1.0 before sintering.
11. The method of claim 8 comprising the additional step of sintering the vanadia catalyst at ≧650° C.
12. A method of producing a catalyst support material, comprising:
providing a slurry comprising TiO 2 and combining the TiO 2 slurry with (1) a silica precursor solution comprising SiO 2 , wherein at least 50% of the SiO 2 of the silica precursor solution comprises silicon atoms in the Q 3 , Q 2 , Q 1 and Q 0 coordination environments, and with (2) WO 3 , to form a TiO 2 —WO 3 —SiO 2 mixture; wherein the silica precursor solution is combined with the TiO 2 slurry before, after, or while the WO 3 is combined with the TiO 2 slurry and; and sintering the TiO 2 —WO 3 —SiO 2 mixture to form a silica-stabilized titania support material.
13. A method of producing a catalyst support material, comprising:
providing a slurry comprising TiO 2 and combining the TiO 2 slurry with (1) a silica precursor solution comprising silicic acid and with (2) WO 3 , to form a TiO 2 —WO 3 —SiO 2 mixture; wherein the silica precursor solution is combined with the TiO 2 slurry before, after, or while the WO 3 is combined with the TiO 2 slurry and; and sintering the TiO 2 —WO 3 —SiO 2 mixture to form a silica-stabilized titania support material.