Synthesis of attrition-resistant heterogeneous catalysts using templated mesoporous silica

Abstract

A method and composition of matter relating to mesoporous structures. The inventive method and inventive structures relate to, for example, attrition-resistant heterogeneous catalysts. A preferred embodiment makes use of a liquid-crystal template mechanism to create a silica structure where insoluble nanoparticles (generally submicron particles) are trapped inside. Such a structure provides controlled porosity for transport of reactants to and products from the catalytically active phase, respectively. Catalytically active structures of the present invention are useful for Fischer-Tropsch synthesis where the breakup and attrition of the catalytically active phase ordinarily hinders performance. The method of the present invention is generally applicable to other mesoporous materials and active phase combinations.

What is claimed is:  
     
         1 . A method for encapsulating a dispersed insoluble compound in a mesoporous structure comprising the steps of: 
 a) combining a soluble oxide precursor, a solvent and a surfactant to form a mixture;    b) dispersing an insoluble compound in the mixture;    c) spray-drying the mixture to produce dry powder; and    d) calcining the powder to yield a porous structure comprising the dispersed insoluble compound.    
     
     
         2 . The method of  claim 1  further comprising the step of introducing a precipitation control agent to the mixture to control precipitation of the oxide precursor.  
     
     
         3 . The method of  claim 2  wherein the agent comprises at least one agent selected from the group consisting of HCl and HNO 3 .  
     
     
         4 . The method of  claim 1  further comprising the step of cooling the mixture to control precipitation of the oxide precursor.  
     
     
         5 . The method of  claim 1  wherein the oxide precursor comprises an alkoxide of silicon.  
     
     
         6 . The method of  claim 5  wherein the alkoxide of silicon comprises tetraethyl orthosilicate.  
     
     
         7 . The method of  claim 1  wherein the oxide precursor comprises at least one precursor selected from the group consisting of silicic acid, zirconium alkoxide, titanium alkoxide, aluminum alkoxide.  
     
     
         8 . The method of  claim 1  wherein the surfactant comprises at least one ammonium ion.  
     
     
         9 . The method of  claim 1  wherein the surfactant comprises at least one surfactant selected from the group consisting of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride.  
     
     
         10 . The method of  claim 1  further comprising at least one step of adjusting pH of the mixture.  
     
     
         11 . The method of  claim 10  wherein the at least one adjusting step adjusts the pH of the mixture to a pH less than approximately pH 5.  
     
     
         12 . The method of  claim 1  wherein the insoluble compound comprises at least one oxide.  
     
     
         13 . The method of  claim 12  wherein the at least one oxide comprises at least one oxide selected from the group consisting of iron oxide, titanium oxide, cobalt oxide and vanadium oxide.  
     
     
         14 . The method of  claim 1  wherein the insoluble compound comprises at least one zeolite.  
     
     
         15 . The method of  claim 14  wherein the at least one zeolite comprises ZSM-5 zeolite.  
     
     
         16 . The method of  claim 1  wherein the insoluble compound comprises at least one non-oxide phase.  
     
     
         17 . The method of  claim 16  wherein the at least one non-oxide phase comprises at least one non-oxide phase selected from the group consisting of nitride and carbide.  
     
     
         18 . The method of  claim 17  wherein the at least one non-oxide phase comprises molybdenum nitride.  
     
     
         19 . The method of  claim 16  wherein the at least one non-oxide phase comprises at least one carbide selected from the group consisting of iron carbide and molybdenum carbide.  
     
     
         20 . The method of  claim 1  wherein the dispersing step comprises sonication.  
     
     
         21 . The method of  claim 1  wherein the mixture of the combining step forms a template for templating a mesoporous structure.  
     
     
         22 . The method of  claim 1  wherein the precipitation control agent of the introducing step allows for formation of a template for templating a mesoporous structure by delaying precipitation of the oxide precursor.  
     
     
         23 . The method of  claim 1  wherein the insoluble compound of the dispersing step comprises colloidal dimensions.  
     
     
         24 . The method of  claim 1  wherein the calcining step substantially removes the surfactant.  
     
     
         25 . A composition of matter comprising the porous structure comprising the dispersed insoluble compound of  claim 1 .  
     
     
         26 . A composition of matter comprising a porous structure comprising a dispersed insoluble compound wherein said porous structure comprises pores formed by an oxide precursor templated on a surfactant template.  
     
     
         27 . The composition of matter of  claim 26  wherein said pores allow gas to access said dispersed insoluble compound.  
     
     
         28 . The composition of matter of  claim 26  wherein said dispersed insoluble compound comprises a catalyst.  
     
     
         29 . The composition of matter of  claim 28  wherein said catalyst comprises iron oxide.  
     
     
         30 . The composition of matter of  claim 26  wherein said porous structure comprises an ordered porosity.  
     
     
         31 . The composition of matter of  claim 30  wherein said ordered porosity corresponds to an order from a surfactant template.  
     
     
         32 . The composition of matter of  claim 26  comprising resistance to attrition.  
     
     
         33 . The composition of matter of  claim 26  comprising a Fischer-Tropsch catalyst.  
     
     
         34 . A composition of matter comprising a porous structure comprising a phase-changed dispersed insoluble compound comprising nanoparticles wherein said porous structure comprises pores formed by an oxide precursor templated on a surfactant template.  
     
     
         35 . The composition of matter of  claim 34  wherein said pores comprise an average pore size that retains phase-changed nanoparticles of said dispersed insoluble compound within said porous structure.  
     
     
         36 . The composition of matter of  claim 34  comprising resistance to attrition.