Aluminium and zirconium-based mixed oxide

A mixed oxide composition comprising a mixed oxide of aluminium, of zirconium, of lanthanum and optionally of at least one rare-earth metal other than cerium and other than lanthanum (denoted REM), wherein the proportions by weight of these elements expressed as oxide equivalent with respect to a total weight of the mixed oxide composition are as follows:

• between 20.0 wt% and 45.0 wt% of aluminium;
• between 1.0 wt% and 15.0 wt% of lanthanum;
• between 0 and 10.0 wt% of at least one REM, on condition that if the mixed oxide composition comprises more than one REM, this proportion applies to each of these rare-earth metals;
• and
• between 50.0 wt% and 70.0 wt% of zirconium;
• wherein the mixed oxide composition is characterized in that after calcination in air at 1100° C. for 5 hours, has a specific surface area (BET) ranging from at least 25 m2/g to at most 40 m2/g;
• and wherein after calcination in air at 950° C. for 3 hours, a porosity of the mixed oxide composition determined by N2 porosimetry is such that:
• in a domain of the pores with a size lower than 100 nm, a porogram of the mixed oxide composition exhibits a peak which is located at a diameter Dp, 950°C/3 h between 10 and 25 nm;
• a ratio V<30 nm, 950°C/3h / Vtotal, 950°C/3h is greater than or equal to 0.85;
• Vtotal, 950°C/3h is greater than or equal to 0.35 ml/g;
• wherein V<30 nm, 950°C/3h and Vtotal, 950°C/3h denote a pore volume for the pores with a size lower than 30 nm and a total pore volume of the mixed oxide composition after calcination in air at 950° C. for 3 hours, respectively.