Hydrogen spillover effects on noble metal-promoted Co/HPS (high porous saponite) catalysts have been investigated by temperature-programmed reduction (TPR) studies and batch autoclave reactor trials. Pt and Rh noble metals were used to introduce hydrogen spillover on Co/HPS. TPR studies showed that Pt-Rh combination has more significant effects on the reducibility of Co species on HPS catalysts than the unpromoted and single noble metal (Pt, Rh individually)-promoted catalysts. The Pt-Rh combination shifts the TPR peaks to lower temperatures. Two Pt-Rh-promoted catalysts were evaluated in batch autoclave reactor (at 400 degreesC and 140 kg/cm(2)) Using vacuum gas oil (VGO) as the feedstock. Pt-Rh-promoted catalysts showed higher activity for both hydrocracking and hydrodesulfurization of the heavy feed than the unpromoted Co/HPS catalyst. (C) 2003 Elsevier B.V. All rights reserved.