Simultaneous promotion of hydrogenation and direct desulfurization routes in hydrodesulfurization of 4,6-dimethyldibenzothiophene over NiW catalyst by use of SiO 2-Al 2O 3 support in combination with trans-1,2-diaminocyclohexane- N, N, N′ ,N′-tetraacetic acid

Abstract

Effect of novel SiO 2-Al 2O 3 support on surface structure and hydrodesulfurization (HDS) activity of the NiW catalyst prepared using trans-1,2-diaminocyclohexane- N, N, N′ ,N′-tetraacetic acid (CyDTA) was investigated by combination of quasi in situ TEM, in situ diffuse reflectance FTIR spectroscopy (DRIFTS) coupled with NO adsorption, and 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS activity measurement. When the catalysts were prepared without using CyDTA, quasi in situ TEM observation showed that WS 2-like slabs in the SiO 2-Al 2O 3 supported W and NiW catalysts had higher stacking degree, but smaller basal plane sizes compared with the Al 2O 3 supported counterparts. In situ DRIFTS coupled with NO adsorption further revealed that the formation of the Ni–W–S phase was suppressed by use of SiO 2-Al 2O 3 support. The SiO 2-Al 2O 3 supported NiW catalyst showed higher activity for hydrogenation (HYD) of 4,6-DMDBT into tetrahydro-DMDBT (THDMDBT) than the Al 2O 3 supported counterpart. However, this catalyst failed to promote the HYD route because of lower activity for C–S bond cleavage of THDMDBT, and showed lower HDS activity than the Al 2O 3 supported NiW catalyst. On the other hand, the formation of the Ni–W–S phase was promoted when the SiO 2-Al 2O 3 supported NiW catalyst was prepared using CyDTA, which was accompanied with further increase of stacking degree and decrease of the basal plane size of the WS 2-like slabs. Double-layered slabs were predominant in the SiO 2-Al 2O 3 supported NiW catalyst prepared with using CyDTA. This catalyst showed higher activity for both HYD of 4,6-DMDBT, and C–S bond cleavage of 4,6-DMDBT and THDMDBT. The HYD route and direct desulfurization (DDS) route were promoted simultaneously over this catalyst, leading to three times higher HDS activity than the Al 2O 3 supported NiW catalyst. These results suggest that the formation of the multi-layered Ni–W–S phase with the smaller basal plane size is crucial for promoting the HYD route in HDS of 4,6-DMDBT.