Silica containing alumina supports, catalysts made therefrom and processes using the same

1. An alumina catalyst support composition which comprises calcined precipitated alumina comprising from about 3 to about 10 wt % silica, said composition having a pore volume of about 0.60 cc/g or greater, a median pore diameter ranging from about 70 Å to about 120 Å, a pore size distribution such that at least about 90% of the total pore volume falls within the range of about 20 Å to about 250 Å, a pore size distribution width of about 40 Å or greater, wherein the term “pore size distribution width” is used to indicate the smallest range of pore diameters of the pores of the silica containing alumina composition in which is present two-thirds of the total pore volume of the silica containing alumina material, and a unimodal pore distribution, the distribution expressed as a function of the difference in pore volume, dV, divided by the difference in pore size, dA, and referred to as incremental pore volume, dV/dA, is plotted versus pore size measured in Angstroms (Å), the unimodal distribution having a single or primary peak mode and exhibiting a shoulder on the primary peak mode, indicating the presence of a secondary peak of diminished size relative to the primary peak mode and present at a pore diameter greater than the median pore diameter;

wherein pore volume and pore size distribution properties are determined by mercury penetration porosimetry at a pressure range from atmospheric to about 60,000 psi, a contact angle Θ=140° and a mercury surface tension of 474 mN/m at 25° C.; and

wherein a unimodal pore distribution of the alumina composition is characterized by the presence of no more than one maximum peak when incremental pore volume of the alumina is plotted as a function of pore diameter; and

wherein the support composition does not contain catalytically active metals.

2. The alumina catalyst support composition of claim 1 , wherein the composition has a total pore volume of about 0.60 cc/g to about 1.0 cc/g.

3. The alumina catalyst support composition of claim 2 , wherein the pore size distribution width ranges from about 40 Å to about 120 Å.

4. The alumina catalyst support composition of claim 3 , wherein from about 90 to about 95% of the total pore volume falls within the range of about 20 Å to about 250 Å.

5. The alumina catalyst support composition of claim 1 , wherein the pore volume and pore size distribution properties are determined by mercury penetration porosimetry using a mercury porosimeter at a pressure range from about atmospheric pressure to about 60,000 psi, with a contact angle, θ=140° and a mercury surface tension of 474 mN/m at 25° C.

6. A catalyst composition suitable for use in the hydroconversion of a middle distillate or a heavy hydrocarbon feedstock, said catalyst composition comprising a support comprised of calcined precipitated alumina composition comprising from about 3 to about 10 wt % SiO 2 , wherein the support has a pore volume of about 0.60 cc/g or greater, a median pore diameter ranging from about 70 to about 120 Å, a pore size distribution such that at least about 90% of the total pore volume falls within the range of about 20 Å to about 250 Å, and a pore size distribution width of about 40 Å or greater, wherein the term “pore size distribution width” is used to indicate the smallest range of pore diameters of the pores of the silica containing alumina composition in which is present two-thirds of the total pore volume of the silica containing alumina material, and a unimodal pore distribution, the distribution expressed as a function of the difference in pore volume, dV, divided by the difference in pore size, dA, and referred to as incremental pore volume, dV/dA, is plotted versus pore size measured in Angstroms (Å), the unimodal distribution having a single or primary peak mode and exhibiting a shoulder on the primary peak mode, indicating the presence of a secondary peak of diminished size relative to the primary peak mode and present at a pore diameter greater than the median pore diameter; and at least one impregnated catalytically active component selected from the group consisting of: (i) an oxide of a Group VIB metal component selected from Mo and W; (ii) an oxide of a Group VIII metal component selected from Ni and Co; and combinations thereof, said catalytically active component containing an oxide of a phosphorous component;

wherein pore volume and pore size distribution properties are determined by mercury penetration porosimetry at a pressure range from atmospheric to about 60,000 psi, a contact angle θ=140° and a mercury surface tension of 474 mN/m at 25° C.; and

wherein a unimodal pore distribution of the alumina composition is characterized by the presence of no more than one maximum peak when incremental pore volume of the alumina is plotted as a function of pore diameter.

7. The catalyst composition of claim 6 , wherein the support material has a total pore volume of about 0.60 to about 1.0 cc/g.

8. The catalyst composition of claim 7 , wherein said Group VIB metal component is present as an oxide in said catalyst composition in the range of from about 10 wt % to about 40 wt %; said Group VIII metal component is present as an oxide in said catalyst composition in the range of from about 1 wt % to about 15 wt %; and said phosphorus component is present as an oxide in said catalyst composition in the range of from about 0.1 wt % to about 10 wt %, as oxide, and all wt % being based on the total weight of said catalyst composition.

9. The catalyst composition of claim 6 , wherein from about 90 to about 95% of the total pore volume falls within the range of about 20 Å to about 250 Å.

10. The catalyst composition of claim 9 , wherein the pore size distribution width ranges from about 40 Å to about 120 Å.

11. A method of hydroprocessing a middle distillate or a heavy hydrocarbon feedstock, said method comprising contacting under hydrodesulfurization and hydrodenitrogenation conditions said feedstock with a catalyst of claim 6 .