Method for Selectively Producing Ordered Carbon Nanotubes

Abstract

The invention relates to a method for selectively producing nanotubes made of carbon ordered by decomposing a gaseous carbon source in contact with at least one solid catalyst in the form of catalyst grains which are made of an alumina porous support provided with a metallic ferrous non-oxidised deposit and whose mean grain-size ranges from 25 μm to 2.5 mm and on which said metallic ferrous deposit covers more than 75% of the surface of the microscopic alumina support and is embodied in the form of at least one cluster formed by a plurality of metallic agglutinated bulbs.

1 . A process for the selective manufacture of ordered carbon nanotubes by decomposition of a carbon source in the gaseous state brought into contact with catalyst particles comprising at least one supported solid catalyst in the form of particles consisting of a porous alumina support bearing an unoxidized ferrous metal coating of at least one transition metal, including iron, characterized in that said supported catalyst particles:
 have a mean particle size of between 25 μm and 2.5 mm; and   said ferrous metal coating covers more than 75% of the surface of the macroscopic form of the porous alumina support.   
     
     
         2 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating is in the form of at least one cluster formed from a plurality of agglutinated metal bulbs. 
     
     
         3 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating forms a homogeneous continuous ferrous metal surface layer formed from metal bulbs. 
     
     
         4 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating is designed to cover the alumina support in such a way that its pores are made inaccessible. 
     
     
         5 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating results from elemental metal deposition carried out in a single step on the alumina support. 
     
     
         6 . The process as claimed in  claim 1 , characterized in that the bulbs have a mean dimension of between 10 nm and 1 μm. 
     
     
         7 . The process as claimed in  claim 1 , characterized in that the unoxidized ferrous metal coating on each catalyst particle extends superficially with a developed overall mean dimension of greater than 35 μm. 
     
     
         8 . The process as claimed in  claim 7 , characterized in that the unoxidized ferrous metal coating of each catalyst particle extends superficially with a developed overall mean dimension of between 200 μm and 400 μm. 
     
     
         9 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating of each catalyst particle extends superficially with a mean apparent area of each catalyst particle greater than 2×10 3  μm 2 . 
     
     
         10 . The process as claimed in  claim 9 , characterized in that the ferrous metal coating of each catalyst particle extends superficially with a mean apparent area of between 10 4  μm 2  and 1.5×10 5  μm 2 . 
     
     
         11 . The process as claimed in  claim 1 , characterized in that a supported catalyst is used in the form of particles whose shapes and dimensions are adapted so as to allow the formation of a fluidized bed of these catalyst particles, in that a fluidized bed of the catalyst particles is formed in a reactor and in that the carbon source is continuously delivered into the reactor, contacting the catalyst particles under conditions suitable for fluidizing the bed of catalyst particles and for ensuring that the decomposition reaction and the formation of nanotubes take place. 
     
     
         12 . The process as claimed in  claim 1 , characterized in that a supported catalyst having a mean particle size of between 100 μm and 200 μm is used. 
     
     
         13 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating covers 90% to 100% of the surface of the particles. 
     
     
         14 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating forms a metal shell covering the entire surface of the porous alumina support and making its pores inaccessible. 
     
     
         15 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating extends over a thickness of greater than 0.5 μm. 
     
     
         16 . The process as claimed in  claim 1 , characterized in that the alumina core has a specific surface area of greater than 100 m 2 /g and in that the supported catalyst has a specific surface area of less than 25 m 2 /g. 
     
     
         17 . The process as claimed in  claim 1 , characterized in that a supported catalyst comprising more than 20% by weight of unoxidized ferrous metal coating is used. 
     
     
         18 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating consists mainly of iron. 
     
     
         19 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating consists exclusively of iron. 
     
     
         20 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating is formed from iron and from at least one metal chosen from nickel and cobalt. 
     
     
         21 . The process as claimed in  claim 1 , characterized in that a quantity of carbon source such that the ratio of the mass of carbon of the initial carbon source introduced per hour to the mass of metal of the supported catalyst is greater than 100 is used. 
     
     
         22 . The process as claimed in  claim 1 , characterized in that the carbon source is ethylene. 
     
     
         23 . The process as claimed in  claim 1 , characterized in that the bulbs have a mean dimension of between 30 nm and 100 nm. 
     
     
         24 . The process as claimed in  claim 1 , characterized in that the ferrous metal coating extends over a thickness of around 2 to 20 μm.