A process for producing alumina, the process having a seeding phase and a precipitation phase. During the seeding phase a seed mixture is produced by adding an aluminium salt to an aqueous solution and then adding an alkaline metal aluminate to the mixture while maintaining the seed mixture at generally neutral pH. The precipitation phase produces precipitated alumina by simultaneously adding aluminium salt and alkaline metal aluminate to the seed mixture while maintaining a pH from 6.9 to 7.8. The recovered precipitated alumina has at least one, preferably all the following characteristics: i) a crystallite size of 33-42 Ang.: in the (120) diagonal plane (using XRD).; ii) a crystallite d-spacing (020) of between 6.30-6.59 Ang.; iii) a high porosity with an average pore diameter of 115-166 Ang.; iv) a relatively low bulk density of 250-350 kg/m.sup.3; v) a surface area after calcination for 24 hours at 1100 C. of 60-80 m.sup.2/g; and vi) a pore volume after calcination for one hour at 1000 C. 0.8-1.1 m.sup.3/g.

A catalyst comprising a calcined oxide matrix which is mainly alumina and an active phase comprising nickel, said active phase being at least partially co-mixed within said calcined oxide matrix which is mainly alumina, the nickel content being in the range 5% to 65% by weight of said element with respect to the total mass of catalyst, said active phase not comprising any metal from group VIB, the nickel particles having a diameter of less than 15 nm, said catalyst having a median mesopore diameter in the range 12 nm to 25 nm, a median macropore diameter in the range 50 to 300 nm, a mesopore volume, measured by mercury porosimetry, of 0.40 mL/g or more and a total pore volume, measured by mercury porosimetry, of 0.45 mL/g or more. The process for the preparation of said catalyst, and its use in a hydrogenation process.

A process for the preparation of an alumina in the form of beads with a sulphur content in the range 0.001% to 1% by weight and a sodium content in the range 0.001% to 1% by weight with respect to the total mass of said beads is described, said beads being prepared by shaping an alumina gel having a high dispersibility by drop coagulation. The alumina gel is itself prepared using a specific precipitation preparation process in order to obtain at least 40% by weight of alumina with respect to the total quantity of alumina formed at the end of the gel preparation process right from the first precipitation step, the quantity of alumina formed at the end of the first precipitation step possibly even reaching 100%. The invention also concerns the use of alumina beads as a catalyst support in a catalytic reforming process.

There is described a hydroprocessing process of at least one gas oil cut having a weighted mean temperature (TMP) between 240 C. and 350 C. using a catalyst comprising at least one metal of the group VIB and/or at least one metal of the group VIII of the periodic classification and a support comprising an amorphous mesoporous alumina having a connectivity (Z) greater than 2.7, the hydroprocessing process operating at a temperature between 250 C. and 400 C., at a total pressure between 2 MPa and 10 MPa with a ratio of hydrogen volume to volume of hydrocarbon-containing feedstock between 100 and 800 litres per litre and at an Hourly Volume Rate (HVR) which is defined by the ratio of the volume flow rate of liquid hydrocarbon-containing feedstock to volume of catalyst fed into the reactor between 1 and 10 h.sup.1.

The invention relates to the preparation of a catalyst containing: a mainly aluminium oxide calcined support; a hydro-dehydrogenating active phase containing at least one metal of group VIB, the process including: a) a first precipitation step of at least one basic precursor and at least one acidic precursor, b) a heating step, c) a second precipitation step by addition to the suspension of at least one basic precursor and at least one acidic precursor, d) a filtration step; e) a drying step, f) a moulding step, g) a heat treatment step; h) an impregnation step of the hydro-dehydrogenating active phase on the support obtained in the step g).

A novel alumina gel is described having an elevated dispersibility index, and in particular a dispersibility index greater than 70%, a crystallite size between 1 and 35 nm, and a sulphur content between 0.001% and 2% by weight, and a sodium content between 0.001% and 2% by weight, the weight percentages being expressed in relation to the total mass of alumina gel.

The present invention also discloses the method for preparing said gel comprising at least one step of precipitating at least one aluminium salt, at least one step of heating the suspension obtained and a final heat treatment step for forming the alumina gel.