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Flame spray synthesis of CoMo/Al2O3 hydrotreating catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
41722 45897 2011 8 PDF Available
Title
Flame spray synthesis of CoMo/Al2O3 hydrotreating catalysts
Abstract

The first alumina supported and unsupported cobalt molybdenum hydrotreating catalysts have been prepared by one-step flame spray pyrolysis (FSP) by spraying and combusting tris(acetylacetonato)aluminum, cobalt 2-ethylhexanoate and molybdenum 2-ethylhexaoate dissolved in toluene. The oxide particles produced contained varying amounts of transition metals (8, 16, 24 and 32 wt.% Mo with atomic ratio Co/Mo = 1/3 and 16 wt.% Mo with atomic ratios Co/Mo = 2/3 and 1/1) with alumina constituting the balance. In addition, an unsupported reference catalyst (atomic ratio Co/Mo = 1/3) was produced. The particles obtained consisted mostly of γ-Al2O3 with some CoAl2O4, as evidenced by X-ray diffraction (XRD) and UV–vis spectroscopy. Bulk MoO3 was not detected by XRD, except at the highest molybdenum content (32 wt.%) and in the unsupported sample, indicating that molybdenum is well dispersed on the surface of the support. The specific surface area as measured by nitrogen adsorption (BET) decreased from 221 to 90 m2/g when going from the lowest loading supported catalyst (8 wt.%) to the unsupported reference. Transmission electron microscopy (TEM) images showed that at low molybdenum loadings nanoparticle agglomerates with 5–10 nm primary particles were produced. As the molybdenum loading on the alumina was increased from 8 to 32 wt.% and for the unsupported reference the primary particle size increased to up to 20 nm and the morphology became more irregular due to primary particle sintering and aggregation.After activation by sulfidation the activity of the catalysts were measured for the three hydrotreating reactions hydrodesulfurization, hydrodenitrogenation and hydrogenation using a model oil containing dibenzothiophene, indole and naphthalene in n-heptane solution. The best catalyst was the FSP-produced material containing 16 wt.% Mo (atomic ratio Co/Mo = 1/3), which did not contain crystalline MoO3 and only small amounts of CoAl2O4. The hydrotreating activity was approximately 75% of that of commercial cobalt molybdenum catalysts prepared by wet impregnation of pre-shaped alumina extrudates. Since the commercial catalyst is the product of years of development, this shows the potential of the flame spray pyrolysis technique.The Co–Mo–S phase, active for hydrotreating, is formed upon sulfidation of the flame made oxide precursor. TEM images of the spent catalysts showed that as the metal loading was increased from 8 to 32 wt.% Mo the average length of supported MoS2 entities increased from 3 to 4 nm (for the unsupported catalyst it was 8.5 nm), while the average number of MoS2 layers per particle increased from 1.1 to 2.5. The increase in MoS2 particle size resulted in lower activity.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (189 K)Download as PowerPoint slideHighlights► Preparation: CoMo on alumina catalysts prepared from Co–Mo–Al-precursor solution by flame synthesis. ► One step synthesis results in mostly γ-alumina, some CoAl2O4 spinel and XRD-amorphous MoO3. ► High surface area due to 5–10 nm sized oxide nanoparticles. ► Catalysis: excellent hydrotreating activities similar to those of impregnated catalysts. ► Flame synthesis is a promising method for preparation of hydrotreating catalysts.

Keywords
Flame spray pyrolysis; Cobalt; Molybdenum sulfide; Hydrotreating; Nanomaterial; Catalysis
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Flame spray synthesis of CoMo/Al2O3 hydrotreating catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 397, Issues 1–2, 30 April 2011, Pages 201–208
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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Any Questions? feel free to contact us