Abstract: A catalyst for hydrotreating heavy hydrocarbon oils comprises a carrier which is a calcined composite of a mixture of a clay mineral consisting mainly of magnesium silicate having a double-chain structure and at least one oxide-forming substance selected from the group consisting of the compounds of the elements belonging to Groups IIA, IIIA, IVA and IVB of the Periodic Table and capable of forming an oxide upon calcination, and at least one catalytic metal component composited with the carrier. The metal of the catalytic metal component is selected from among those belonging to Groups VB, VIB, VIII and IB of the Periodic Table. The catalyst contains about 5 to 80% by weight of the oxide formed from the oxide-forming substance and about 0.1 to 20% by weight of the catalytic metal component in terms of elemental metal. The catalyst has a pore volume of about 0.5 to 2.0 cc/g, an average pore diameter of about 100 to 500 A, and a surface area of about 40 to 400 m.sup.2 /g.

Abstract: A catalyst for hydrotreating heavy hydrocarbon oils comprises a carrier which is a calcined composite of a mixture of a clay mineral consisting mainly of magnesium silicate having a double-chain structure and at least one oxide-forming substance selected from the group consisting of the compounds of the elements belonging to Groups IIA, IIIA, IVA and IVB of the Periodic Table and capable of forming an oxide upon calcination, and at least one catalytic metal component composited with the carrier. The metal of the catalytic metal component is selected from among those belonging to Groups VB, VIB, VIII and IB of the Periodic Table. The catalyst contains about 5 to 80% by weight of the oxide formed from the oxide-forming substance and about 0.1 to 20% by weight of the catalytic metal component in terms of elemental metal. The catalyst has a pore volume of about 0.5 to 2.0 cc/g, an average pore diameter of about 100 to 500 A, and a surface area of about 40 to 400 m.sup.2 /g.