New NiMo catalysts supported on ZrO2-modified SBA-15 materials for 4,6-dimethyldibenzothiophene hydrodesulfurization

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Zr-SBA-15 supports with different ZrO2 loadings (12.5, 25, 37.5 and 50 wt. %) were prepared by incipient wetness impregnation of pure siliceous SBA-15. ZrO2 species were found to be well-dispersed on SBA-15 surface (DRS, XRD) at low ZrO2 loading (below 25 wt. %). At high ZrO2 loadings the formation of tetragonal and monoclinic crystalline zirconia phases was observed. In the catalysts supported on ZrO2-modified SBA-15 materials, the dispersion of Mo oxide species was found to be much better than on corresponding pure SBA-15 and ZrO2. For Zr-SBA-15-supported NiMo catalysts the formation of crystalline MoO3 was not detected by XRD. Catalytic activity tests in hydrodesulfurization of 4,6-dimethyldibenzothiophene showed that the modification of SBA-15 supports with Zr(IV) species significantly improves the performance of NiMo catalysts in HDS of refractory dibenzothiophenes.

Introduction

SBA-15-type materials are novel well-ordered mesoporous molecular sieves with high surface area and narrow distribution of pores of about 60-100 Å in diameter [1]. These materials have already been tested in a variety of applications, such as adsorbents, molecular sieves, catalysts and catalytic supports. However, up to now only purely siliceous SBA-15 materials were tested in hydrodesulfurization (HDS) and published information is limited to a few papers 2., 3., 4.. The incorporation of heteroatoms (Al, Ti, Zr, etc.) on the pure siliceous SBA-15 surface should modify dispersion and coordination of the deposited active metal species (Mo, W) and subsequently their efficiency and selectivity in HDS reaction. In the present work, with the aim of searching for new, highly effective HDS catalysts, a series of ZrO2-modified SBA-15 supports and the respective NiMo catalysts were prepared, characterized and evaluated in the 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS reaction.

Section snippets

Experimental

Purely siliceous SBA-15 was synthesized according to the well-known procedure [1] using the triblock copolymer Pluronic P123 as the structure-directing agent and tetraethyl orthosilicate (TEOS) as the silica source. ZrO2-modified SBA-15 supports with different ZrO2 loadings (12.5, 25, 37.5 and 50 wt %) were prepared by incipient wetness impregnation of zirconium (IV) propoxide solution in dry 1-propanol on pure siliceous parent SBA-15. Zr-containing solids were calcined in air at 550°C for 6 h.

Results and Discussion

The results from textural characterization of the supports indicate that zirconia incorporation on the SBA-15 surface produces a decrease in the SBA-15 textural properties, which is more pronounced at high ZrO2 loading (Table 1). The pore size distributions calculated from the desorption branch of the isotherms show a narrow distributions of mesopores with the maxima at the values shown in Table 1. It can be observed from this table that ZrO2 incorporation into SBA-15 results in a notable

Conclusions

It can be concluded that the modification of SBA-15 supports with ZrO2 species results in high-performance NiMo catalysts for hydrodesulfurization of hindered dibenzothiophenes. Zirconia loading in the catalyst support leads to an increase in the dispersion of oxidic Mo species and promotes the HYD pathway of 4,6-DMDBT hydrodesulfurization.

Acknowledgements

Financial support for this work by CONACyT-Mexico (grant 46354) is gratefully acknowledged. The authors thank I. Puente-Lee, M. Aguilar-Franco and C. Salcedo-Luna for assistance in TEM and XRD characterizations.

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