United States Patent 7,641,887 reveals Institut Francias du Petrole’s (Rueil Malmaison Cedex, FR) nano-porous alumina-on-alumina composite supports which allow catalysts to be produced for carrying out a large range of reactions on hydrocarbon cuts.
In the patent, inventors Renaud Revel, Stephane Morin, Lars Fischer and Christophe James detail manufacturing methods for porous alumina-on-alumina catalyst supports which have a pore volume with at least bimodal distribution, thus defining a main porosity and a secondary porosity, the main porosity being of an average size greater than the secondary porosity. Optionally a tertiary or quaternary porosity may also be formed.
90% of the total pore volume corresponds to pores larger than 15 nm, and in that at least 3%-5% of the total pore volume corresponds to pores smaller than 12 nm. Ab ordered relationship between the main porosity and the secondary porosity is defined by the fact that any element in the main porosity is connected either to the outside of the particle, or to at least one element in the secondary porosity, this expression to be taken in a non-exclusive sense.
The main porosity is supported by a solid mostly constituted by a mixture of theta and alpha alumina, inside which there is deposited a layer of amorphous alumina or crystallized alumina with crystalline forms chosen from the following forms: gamma, delta, theta, chi or kappa, said layer supporting the secondary porosity.
This layer supporting the secondary porosity is generally created from a preformed solid composed of a mixture of theta or alpha aluminas, followed in a first variant by a stage of impregnation of an aluminum salt or, in a second variant, by total or partial dissolution of the alumina in the preformed solid using a solubilizing agent, followed by a stage of precipitation of said aluminum salt.
The support thus formed has a specific surface area of less than 90 m2/g, preferably less than 80 m2/gm, very preferably less than 75 m2/gm a pore volume with an at least bimodal structure, having an interconnected main porosity and secondary porosity, this pore structure being moreover ordered in the sense defined by the rule "any element in the main porosity is connected either to the outside, or to at least one element in the second porosity".
