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1. A process for oligomerization of an olefinic feedstock containing olefinic hydrocarbon molecules having 2 to 10 carbon atoms per molecule, said process comprising bringing said olefinic feedstock into contact with a catalyst comprising at least one amorphous material having hierarchized and organized porosity and including at least two elementary spherical particles, wherein each of said particles comprises a mesostructured silicon-oxide-based matrix having a uniform diameter of mesopores of between 1.5 and 30 nm and having amorphous and microporous walls with a thickness of between 1 and 50 nm, said elementary spherical particles having a maximum diameter of 200 microns, said amorphous walls consisting of protozeolitic entities and the preparation of said catalyst comprising:
a) preparing a clear solution that contains precursor elements of protozeolitic entities, wherein said precursor elements are at least one structuring agent, at least one silicic precursor, and at least one precursor of at least one element X; wherein the element X is aluminum, iron, germanium, titanium, or boron; wherein the reaction mixture is aqueous or aqua-organic; wherein the structuring agent is basic or the reaction medium additionally includes alkaline metal hydroxide; wherein said reaction mixture is treated under hydrothermal conditions under autogenous pressure at a temperature between ambient temperature and 200° C. until the formation of a clear solution; b) mixing at least one surfactant and at least said clear solution that is obtained according to a) in a solution wherein the ratio of the volumes of inorganic and organic materials is between 0.26 and 4, wherein said solution has a pH that is greater than 9; c) atomizing said solution that is obtained in stage b) by generating an aerosol and forming spherical droplets of said solution; d) drying said droplets; and e) eliminating said structuring agent and said surfactant for obtaining an amorphous material with hierarchized porosity in the range of microporosity and mesoporosity and organized within the range of mesoporosity.
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