A diesel oxidation catalyst comprising a honeycomb substrate washcoated with a mixture of clay, a refractory oxide and a zeolite is disclosed. The washcoated substrate is subsequently deposited with a precious metal catalyst and a sulfur oxidation suppressant. In a preferred embodiment, the clay is acid-leached bentonite, the refractory oxide is zirconia or titania, the zeolite is beta-zeolite or Y-zeolite or ZSM-5 or mordenite, the precious metal catalyst is preferably platinum, and the sulfur oxidation suppressant is vanadium or vanadium oxide or a combination thereof