Simultaneous promotion of hydrogenation and direct desulfurization routes in hydrodesulfurization of 4,6-dimethyldibenzothiophene over NiW catalyst by use of SiO2-Al2O3 support in combination with trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid
Effect of novel SiO2-Al2O3 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 WS2-like slabs in the SiO2-Al2O3 supported W and NiW catalysts had higher stacking degree, but smaller basal plane sizes compared with the Al2O3 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 SiO2-Al2O3 support. The SiO2-Al2O3 supported NiW catalyst showed higher activity for hydrogenation (HYD) of 4,6-DMDBT into tetrahydro-DMDBT (THDMDBT) than the Al2O3 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 Al2O3 supported NiW catalyst. On the other hand, the formation of the Ni–W–S phase was promoted when the SiO2-Al2O3 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 WS2-like slabs. Double-layered slabs were predominant in the SiO2-Al2O3 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 Al2O3 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.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (189 K)Download as PowerPoint slideResearch highlights▶ Use of CyDTA and novel SiO2-Al2O3 support for NiW catalyst led to higher HDS activity. ▶ Both DDS and HYD routes were promoted by use of CyDTA and SiO2-Al2O3 support. ▶ Multilayered Ni-W-S phase was selectively formed by use of CyDTA and SiO2-Al2O3 support.
Journal: Applied Catalysis A: General - Volume 383, Issues 1–2, 31 July 2010, Pages 79–88