Control of hydrodesulfurization and hydrodearomatization properties over bimetallic Pd-Pt catalysts supported on Yb-modifed USY zeolite

Increasingly stringent regulations on the removal of aromatic and sulfur compounds in diesel fuel require the development of new catalysts and processes. Here, control of hydrodesulfurization (HDS) and hydrodearomatization (HDA) properties was studied by preparing bimetallic Pd-Pt catalysts supported on ytterbium-modified ultrastable Y (USY) zeolite by impregnation and subsequent calcination under different temperatures. Catalytic performances of the prepared catalysts, such as HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and RDA of tetralin, were investigated in a high-pressure continuous-flow reactor. With changing calcination temperature, the HDS activity is only slightly affected, although the maximum HDS conversion was obtained at 300degreesC. In contrast, the HDA activity decreased significantly, with hydrogenation selectivity remaining relatively constant as confirmed by the weak variation of the trans-decalin to cis-decalin ratio. A low calcination temperature of 200degreesC simultaneously favored both deep HDS and deep HDA, whereas a high calcination temperature of 500degreesC favored selective HDS reactions with minimal HDA reactions (i.e. saving of expensive hydrogen). These results clearly indicate that the selectivity of HDS to HDA can be controlled by simply changing the calcination temperature of Pd-Pt/Yb/USY zeolite catalysts. (C) 2001 Elsevier Science Ltd. All rights reserved.