Promoting Synergy in CoW Sulfide Hydrotreating Catalysts by Chelating Agents

doi:10.1006/jcat.2001.3203

Journal of Catalysis

Volume 200, Issue 1, 15 May 2001, Pages 194-196

https://doi.org/10.1006/jcat.2001.3203 Get rights and content

Abstract

Adding chelating agents such as 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CyDTA) and triethylenetetraaminehexa acetic acid (TTHA) to the aqueous solution of cobalt nitrate and ammonium metatungstate used for impregnating the silica support results in enhanced activities for the hydrodesulfurization of thiophene after the catalysts have been sulfided. These chelating agents serve to retard the sulfidation of cobalt with respect to that of tungsten, which facilitates the formation of a phase in which Co atoms decorate the edges of WS₂, analogous to the well-known CoMoS phase.

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Highly active and stable CoWS<inf>2</inf> catalysts in slurry phase hydrocracking of vacuum residue: XAFS studies
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The bimetallic CoWS₂ catalysts were prepared in situ during the slurry phase hydrocracking (HCK) of vacuum residue (VR) using W(CO)₆ and Co-octoate as oil soluble precursors to investigate the promotional effect of Co promoters on the dispersed WS₂ catalyst for the VR HCK. The morphologies and structural properties of dispersed catalysts were characterized by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS). The bimetallic CoWS₂ catalyst was observed to form well-dispersed monolayers in the size range of 7–11 nm, which showed higher turn-over frequency values (TOF) and C₇-asphaltene (C₇-ASP) conversions than monometallic WS₂ or Co₉S₈ catalysts in the VR HCK at 693 K and 10.0 MPa H₂. Moreover, the extended X-ray fine absorption structure spectroscopy (EXAFS) coupled with the density functional theory (DFT) calculations successfully verified the formation of the Co-W-S phase.
Surface-dependent activity of model CoMoS hydrotreating catalysts
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Citation Excerpt :
Trans-2-butene accounts for 18–20% of all HDS products while the cis isomer ranges from 8 to 14%. This higher selectivity towards the trans isomer was also consistently reported by Kishan et al. [47] and studies involving traditional catalysts [49,50]. Finally, n-butane appears as the lowest concentration product, making up from 3 to 7% of thiophene HDS products.
The current environmental and industrial contexts require constant revision and improvement of hydrotreating processes for obtaining cleaner (bio)fuels through the development of supported transition metal sulfide (TMS) catalysts. The present work proposes a surface-science approach to describe the surface-dependent genesis of the cobalt-promoted active phase (CoMoS) supported on α-Al₂O₃ single crystals used as surrogates of the industrial γ-Al₂O₃ support. Co-Mo precursor solutions are deposited by aqueous-phase impregnation onto four α-Al₂O₃ single crystals of C(0001), A $(11 \bar{2} 0)$ , M $(10 \bar{1} 0)$ , and R $(1 \bar{1} 02)$ orientations, which display specific OH sorption sites. The model catalysts are characterized in the oxide and sulfide states by XPS, AFM, and TEM revealing a surface dependent sulfidation and dispersion as a result of metal-support interactions of diverse nature. The surfaces can be ranked following metal-support interactions of increasing strength C(0001) < A $(11 \bar{2} 0)$ , M $(10 \bar{1} 0)$ < R $(1 \bar{1} 02)$ in good agreement with model non-promoted catalysts. However, AFM and TEM imaging also reveal that cobalt incorporation leads to an increase in the stacking of CoMoS particles with respect to non-promoted catalysts. The activity of the model catalysts in thiophene hydrodesulfurization cannot be simply related to the common features of the active phase (sulfidation, dispersion, promotion extent) but a volcano-shape curve is obtained when plotting the activity as a function of metal-support interactions. These results suggest that high activity is obtained on surfaces with intermediate metal-support interactions that lead to an optimal metal-sulfur bond energy in agreement with the Sabatier principle. Transposing these results to the traditional γ-Al₂O₃ support suggests an enhanced activity of the (1 0 0) facet, which can lead to the development of improved supports for hydrotreating catalysts.
Organic additives for hydrotreating catalysts: A review of main families and action mechanisms
2021, Catalysis Today
Ever more active hydrotreating (HDT) catalysts should be developed to meet the growing demand for cleaner fuels. With each novel generation of HDT catalysts the requirements of performance, stability and possibility of regeneration become more sophisticated. Versatile types of organic molecules are applied to improve the HDT catalysts, and to activate regenerated catalysts. The additives improve the dispersion of the active phase, the degree of promotion and modify the interactions with the support. Complex chemical and physical processes are involved in the mechanisms of action, which are different from one family of additives to another. In this review we summarize recent advances on the main types of additives, the current state of understanding of the mechanisms of their action as well as challenges and perspectives in developing novel additives for highly performing novel generations of HDT catalysts in a sustainable way.
Improved NiMoSA catalysts: Analysis of EDTA post-treatment in the HDS of 4,6-DMDBT
2020, Catalysis Today
To optimize the performance of HDS catalysts prepared with an improved support and a chelating agent, the present work analyzes the variations in HDS activity and hydrogenation/desulfurization selectivity when different protocols are applied in the preparation of a NiMo HDS catalyst with EDTA as chelating agent and silica-modified alumina (SA) as support. It was shown that grafting 6 wt. % SiO₂ on the alumina support favors the formation of Mo⁶⁺_Oh and decreases the presence of Mo⁶⁺_Td, which is difficult to reduce and sulfide, resulting in SA supported catalysts with increased HDS activity. The use of both SA and EDTA improves the hydrogenation rate constant and not the direct desulfurization one. Successive impregnation Ni+Mo (Mo first) leads to higher dispersion of edge sites in the MoS₂ crystallites. Post-treatment of the oxide catalysts with EDTA gives rise to a better promotion associated to the removal of Ni from inactive compounds, favoring additional formation of NiMoS phase. The post-treatment is more effective in catalysts prepared by successive impregnation. The successively-prepared EDTA+Ni+Mo/SA catalyst presents the highest activity in the HDS of 4,6-DMDBT.
Activation of regenerated CoMo/Al<inf>2</inf>O<inf>3</inf> hydrotreating catalysts by organic additives – The particular case of maleic acid
2019, Applied Catalysis A: General
Activation of hydrodesulfurization (HDS) catalysts through sulfidation of oxide precursors is a critical procedure required to achieve preparation of the Co(Ni)-promoted Mo(W)S₂ sulfides commonly used for performing sulfur removal from transportation fuels. Better optimized preparation of HDS catalysts can be reached if organic additives, glycol-type compounds or chelating agents, are used during the activation process. Moreover, comprehension of the role of the organic additives during activation has become even more essential with the increasing necessity to regenerate satisfactorily the last generation of HDS catalysts, more sensitive to the harsh conditions used during the oxidative regeneration treatment. In this respect, maleic acid (MA) was recently found to be an efficient additive for the activation of regenerated HDS catalysts.
In the present study, deeper understanding of the role played by maleic acid for restoring the HDS activity was determined at different steps of the preparation of a regenerated CoMo-Al₂O₃ (here called CoMo-R) catalyst. Comparison was first performed to two other additives, a chelating agent, ethylenediaminetetraacetic acid (EDTA) and a glycol-type compound, triethyleneglycol (TEG), after impregnation and drying steps, using UV–vis diffuse reflectance spectroscopy, ex situ and in situ X-ray diffraction and thermal analysis. Results emphasized that maleic acid is the most efficient additive for extracting cobalt from cobalt molybdate species leading after sulfidation to much better HDS catalytic properties in the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and of a straight run gasoil.
The sulfidation step was also carefully analyzed during the activation of CoMo-R in the presence of MA using inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron, Raman and electron paramagnetic resonance spectroscopies, mass spectrometry analysis and transmission electron microscopy. This detailed analysis allows proposing a complete description of the sulfidation mechanism in the presence of MA leading to a better understanding of the key aspects to be reached during the activation process.
Comparison of citric acid and glycol effects on the state of active phase species and catalytic properties of CoPMo/Al<inf>2</inf>O<inf>3</inf> hydrotreating catalysts
2017, Applied Catalysis B: Environmental
CoPMo/Al₂O₃ catalysts were prepared using H₃PMo₁₂O₄₀ and Co complexes with citric acid (CA) or non-complexing organic additives such as ethylene glycol (EG), diethylene glycol, triethylene glycol (TEG), glycerol, and a mixture of EG and CA. The catalysts were characterized by low-temperature N₂ adsorption, Raman spectroscopy, thermogravimetric analysis, temperature-programmed reduction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The prepared samples were tested in hydrodesulfurization (HDS) of dibenzothiophene (DBT). The addition of either CA or glycols led to several beneficial effects such as weakening of the slab-support interaction at enhancing the promotion degree, dispersion and stacking number of the CoMoS species. It has been shown that the promotion degree of CoMoS edges increased with a pore volume gain by the additive-impregnated catalysts after their sulfidation. Catalysts with CA, TEG or the EG-CA mixture demonstrated higher activity in DBT HDS. Probable reasons for the found relationships are discussed.

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Research NotePromoting Synergy in CoW Sulfide Hydrotreating Catalysts by Chelating Agents

Abstract

J. Catal.

J. Catal.

J. Catal.

J. Catal.

J. Catal.

Hydrotreating Catalysis

Research Note
Promoting Synergy in CoW Sulfide Hydrotreating Catalysts by Chelating Agents