Abstract: Disclosed is a process for hydroconverting a heavy hydrocarbon oil in a reactor under high-temperature and high-pressure conditions,wherein said hydroconversion is carried out through using at least three desulfurization catalysts which each contains as active metals transition metals of Group VI and VIII in the Periodic Table supported on an alumina carrier and which have different SI of 40 or higher, 30 or higher and below 40, and lower than 30, respectively,and wherein said at least three catalysts are packed into the reactor in a descending order of SI from the inlet to the outlet of the reactor, with the proportion of the catalyst having SI of 40 or higher is at least 10% by volume, that of the catalyst having SI of 30 or higher and below 40 is at least 20% by volume, and that of the catalyst having SI of lower than 30 is at least 30% by volume.

Abstract: A catalyst composition for the hydrogenation of heavy hydrocarbon oil comprising at least one active ingredient for hydrogenation supported on a porous refractory oxide carrier and which has the following characteristics:(1) the mean pore diameter of the pores thereof is in the range of 130 to 250 .ANG.;(2) the volume of pores having a pore diameter within .+-.30 .ANG. of the mean pore diameter is in the range of from not less than 30% to less than 60% of the total volume of the pores;(3) the volume of pores having a pore diameter of not larger than 80 .ANG. is not more than 13% of the total volume of the pores;(4) the volume of pores having a pore diameter of not smaller than 350 .ANG. is not more than 25% of the total volume of the pores; and(5) the ratio (mm.sup.2 /mm.sup.3) of the outer surface of a molded catalyst particle to the volume thereof is in the range of 3 to 8.

Abstract: A hydrogen treating catalyst comprising alumina, 3 to 7% by weight of nickel calculating as NiO and 10 to 20% by weight of molybdenum calculating as MoO.sub.3, which has a total pore volume of 0.55 to 1.0 ml/g, an average pore diameter of 50 to 250 .ANG., and factor P of 3 to 4, wherein the volume of pores having a diameter of larger than the average pore diameter+10 .ANG. and smaller than the average pore diameter+500 .ANG. is 10 to 30% of the total pore volume in catalyst pore distribution, wherein the factor P is represented by the following formula:P=PD/Swherein PD represents an average pore diameter measured by a mercury porosimeter which is the pore diameter (.ANG.) corresponding to the pressure at which 1/2 of the total pore volume is saturated with mercury, and S represents a proportion (%) of volume of pores in a range of PD.+-.5 .ANG..