Silica-stabilized ultrafine anatase titania, vanadia catalysts, and methods of production thereof

Abstract

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.

What is claimed is: 
     
         1 . A method of producing a silica-stabilized titania catalyst support material, comprising:
 providing a TiO 2  slurry comprising TiO 2  particles;   providing a particulate silica source;   combining the TiO 2  slurry with the particulate silica source to form a TiO 2 —SiO 2  mixture; and   adjusting the TiO 2 —SiO 2  mixture to a pH<8.5 and a temperature <80° C. wherein the particulate silica source is dissolved and reprecipitated on the TiO 2  particles to form the silica-stabilized titania catalyst support material.   
     
     
         2 . The method of  claim 1  further comprising the step of combining the silica-stabilized titania catalyst support material with WO 3  to form a silica-stabilized titania tungsten catalyst support material. 
     
     
         3 . The method of  claim 2  further comprising washing and sintering the silica-stabilized titania tungsten catalyst support material. 
     
     
         4 . The method of  claim 2  wherein the silica-stabilized titania tungsten catalyst 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 primarily comprises a surface area of at least 80 m 2 /gm before sintering. 
 
     
     
         5 . The method of  claim 1  wherein the TiO 2  particles of the TiO 2  slurry comprise preformed titanium hydroxide, titanium oxy-hydroxide or titanium dioxide particles. 
     
     
         6 . The method of  claim 1  wherein the TiO 2  particles of the TiO 2  slurry are not produced in the presence of urea. 
     
     
         7 . The method of  claim 1 , wherein the SiO 2  of the TiO 2 —SiO 2  mixture, after dissolving, comprises silicon atoms which are substantially in the Q 3 , Q 2 , Q 1  and Q 0  coordination environments. 
     
     
         8 . The method of  claim 1  wherein the SiO 2  on the TiO 2  particles substantially comprises patches which are ≦5 nm in depth after redistribution of the SiO 2  as seen by scanning electron microscopy or by transmission electron microscopy. 
     
     
         9 . The method of  claim 2  comprising combining the TiO 2 —WO 3 —SiO 2  mixture with V 2 O 5  to form a vanadia catalyst. 
     
     
         10 . The method of  claim 9  wherein the vanadia catalyst comprises 0.5%-3% dry weight of V 2 O 5 . 
     
     
         11 . The method of  claim 9  wherein the V 2 O 5  of the vanadia catalyst is present at a fractional monolayer value of less than 1.0 before sintering. 
     
     
         12 . The method of  claim 9  comprising the additional step of sintering the vanadia catalyst at ≧650° C.