Titania-supported Cobalt Research Articles

Elucidating deactivation of titania-supported cobalt Fischer-Tropsch catalysts under simulated high conversion conditions

The study of titania-supported cobalt nanoparticles is relevant for industrial Fischer-Tropsch synthesis (FTS). Herein, we report about various deactivation pathways of cobalt supported on P25 titania (cobalt loading 2–8 wt%) under simulated high conversion conditions using in situ Mössbauer spectroscopy. A fraction of metallic cobalt was oxidized under humid FTS conditions. The absolute amount of oxidized cobalt was ∼ 1.2 wt% independent of the cobalt loading, indicating that specific cobalt-titanol interactions are involved in the oxidation process. The formation of cobalt-titanate-like compounds was only observed under very high water-to-hydrogen ratios in the absence of carbon monoxide. Steam considerably enhances cobalt sintering under FTS conditions. As such, deactivation under humid FTS conditions is not only caused by cobalt oxidation but also by enhancing sintering of the active phase.

Tuning the Metal–Support Interaction and Enhancing the Stability of Titania-Supported Cobalt Fischer–Tropsch Catalysts via Carbon Nitride Coating

Supported metal catalysts have found numerous applications in many catalytic reactions, including Fischer–Tropsch (FT) synthesis. Metal dispersion, metal reducibility, catalytic performance, and ca...

Hydrogenation of Pyridines on Titania-Supported Cobalt Nanoparticles

Key words hydrogenation - pyridines - cobalt catalysis - nanoparticles - titanium dioxide

Morphological transformations during Fischer-Tropsch synthesis on a titania-supported cobalt catalyst

Deactivation mechanisms for a rhenium-promoted titania-supported cobalt catalyst are investigated during Fischer-Tropsch (FT) synthesis. Bench-scale reactor tests, chemisorption studies, thermogravimetric analyses (TG), and transmission electron microscopy (TEM) are used to probe environmental effects on catalytic activity.Bench-scale reactor studies show a steady decrease in activity with time. While a fraction of this loss can be recovered with a low temperature reduction (rejuvenation) inside the reactor, multiple data indicate this phenomenon is primarily attributable to water-induced oxidation of small cobalt particles.Data from long-term FT runs indicate the presence of three non-rejuvenable deactivation mechanisms: metal agglomeration, strong metal-support interaction (SMSI), and mixed metal oxide formation. High conversion studies implicate byproduct water in the agglomeration process, and ex-situ TEM data conclusively reveals that growth occurs via a coalescence mechanism. Combined kinetic and chemisorption studies reveal that SMSI results from the gradual buildup of titania decoration on the surface of the active cobalt and is exacerbated with multiple rejuvenation cycles. TGA data indicate that mixed metal oxide formation occurs in long-duration, pilot plant runs. In all cases, the aggregate of reactor kinetic, chemisorption, TG, and TEM results point to chemically-assisted deactivation phenomena attributable to the byproduct water.

Effects of loading and synthesis method of titania-supported cobalt catalysts for Fischer–Tropsch synthesis

Because of their high activity and selectivity to C5+ hydrocarbons in the Fischer–Tropsch, process, titania-supported cobalt catalysts have received great interest from industrial and academic, institutions. Here, we report on three catalyst preparation procedures, incipient wetness impregnation (IWI), deposition precipitation using urea hydrolysis (DPU) or ammonia evaporation (DPA) to prepare, Co/TiO2 catalysts with 4–24wt.% Co. The results reveal a strong impact of the catalyst preparation, procedure on dispersion and distribution of cobalt over the titania surface. IWI led to clustered cobalt, oxide particles of ∼10nm, while for the DPA catalysts, similarly sized nanoparticles were found to be, well-distributed over the support surface. Co/TiO2 catalysts prepared by DPU showed the presence of, ∼2nm supported cobalt oxide particles beside large unsupported particles. Catalytic tests under, industrially relevant conditions show that the DPA catalysts displayed a superior activity and C5+, selectivity for the entire cobalt loading range studied.

Zirconia Modification on Nanocrystalline Titania-Supported Cobalt Catalysts for Methanation

In this present study, the zirconia-modified different crystallite sizes of TiO 2 (11, 13 and 16 nm) as support for the cobalt catalysts were investigated. The different TiO 2 crystallites derived from the sol-gel method was obtained by varying the water:alkoxide molar ratio from 165 to 4 to gain the different nanocrystallite sizes of TiO 2 . Then, the TiO 2 supports were used to yield various Co/TiO 2 catalysts. It was found that the sizes of cobalt oxides species dispersed on TiO 2 were corresponding to TiO 2 sizes. Based on XPS study, the binding energy of Co 2p3/2 was not affected by the size of TiO 2 . The catalytic activity was measured via CO hydrogenation under methanation condition. In case of unmodified TiO 2 support, the smaller TiO 2 crystallites (Co/TiO 2 _11 nm) exhibited higher activity than other larger ones. Moreover, the zirconia modification also resulted in increased in activity for all samples. For both cases, it can be attributed to increased cobalt dispersion with small crystallite size of TiO 2 support coupled with the zirconia modification as measured by CO chemisorption.

Kinetic study of Fischer–Tropsch process on titania-supported cobalt–manganese catalyst

An active cobalt–manganese catalyst was prepared by co-precipitation method, and was also tested for hydrogenation of carbon monoxide to light olefins. The catalyst was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area techniques. The kinetic experiments on a well-characterized Co–Mn/TiO 2 catalyst were performed in a fixed-bed micro-reactor, and were also conducted in a temperature range of 190–280 °C, pressure range of 1–10 bar, H 2/CO feed ratio (mol/mol) range of 1–3 and a space velocity range of 2700–5200 h −1. Two kinetic expressions based on Langmuir–Hinshelwood–Houngen–Watson (LHHW) mechanism were observed to fit the experimental data accurately for Fischer–Tropsch synthesis reaction. The kinetic parameters were estimated with non-linear regression method. Activation energies obtained were 35.131 and 44.613 kJ/mol for optimal kinetics models.

Fischer–Tropsch Synthesis on Lanthanum Promoted Co/TiO2 Catalysts

Lanthanum promoted titania-supported cobalt catalysts were prepared using incipient wetness impregnation method. The catalysts were characterized by XRD, TPR and TPD. The catalytic activity for Fischer–Tropsch synthesis was evaluated in a fixed-bed reactor. The activity increased with increasing La content except at high loadings. Furthermore, La promoter increased methane and CO2 selectivity, suppressed the formation of C5+ products. TPR profiles of prepared catalysts. (a) Co–Ti–0La; (b) Co–Ti–1/2000La; (c) Co–Ti–1/200La; (d) Co–Ti–1/120La; (e) Co–Ti–1/20La; (f) Co–Ti–1/20La recalcined at 673 K for 6 h.

Cobalt Fischer-Tropsch synthesis: Deactivation by oxidation?

Cobalt catalysts as used in the Fischer-Tropsch synthesis (FTS) are relatively expensive (as compared to iron) and need to have a high metal dispersion and long life to be able to offer a good balance between cost and performance. The oxidation of nano-sized metallic cobalt to cobalt oxide during Fischer-Tropsch synthesis has long been postulated as a major deactivation mechanism. However, to date there is no consistent picture. This paper presents an extensive overview of the literature on this topic of deactivation by means of oxidation for unsupported as well as silica-, alumina- and titania-supported cobalt catalysts. Furthermore, it presents results on the deactivation of an industrial Co/Al2O3 catalyst as obtained by pseudo in situ X-ray diffraction, magnetic measurements and X-ray absorption near-edge spectroscopy. These analyses were performed to study the oxidation state of spent industrial Co/Al2O3 catalyst samples withdrawn from a slurry reactor operating under realistic FTS conditions, and it was concluded that oxidation can be ruled out as a major deactivation mechanism. Finally, these data together with all relevant literature were used to create a common view on the oxidation behaviour of metallic cobalt during FTS. The apparent discrepancies in literature on the oxidation behaviour of cobalt are most likely due to the lack of direct characterisation of the cobalt oxidation state and due to the comparison of catalysts with varying cobalt crystallites sizes, compared at different reactor partial pressures of hydrogen and water (PH2O/PH2). It was shown that the oxidation of cobalt can be prevented by selecting the correct combination of the reactor partial pressures of hydrogen and water (PH2O/PH2) and the cobalt crystallite size.

Effects of manganese oxide promoter on the CO and H 2 adsorption properties of titania-supported cobalt Fischer–Tropsch catalysts

The adsorption properties of manganese-promoted Co/TiO 2 Fischer–Tropsch (FT) catalysts were investigated by diffuse reflectance infrared spectroscopy (DRIFTS) using CO and H 2 as probe molecules. Manganese was found to be closely associated to the FT active Co 0 sites at the surface of the catalysts. With increased MnO loading, CO preferentially binded linearly to surface metal sites. Manganese also decreased the extent of Co–TiO 2 interactions, increasing the Co 0 dispersion, resulting in higher H 2 chemisorption uptake. Furthermore, with increasing MnO loading, FT catalytic tests at 1 bar and 220 °C revealed an increase in C 5+ selectivity and olefinic products. These findings suggest that MnO species induce both structural and electronic promotion effects, resulting in higher metal dispersions and lower hydrogenation activity of the catalyst, ultimately enhancing the overall FT catalytic performance. The findings also suggest that MnO catalyzes the water–gas shift reaction, thereby changing the syngas feed composition and affecting overall catalyst performance.

Promoting effect of fluorine on titania-supported cobalt–molybdenum hydrodesulfurization catalysts

Abstract The species of a series of F–TiO2 support containing various amounts of fluorine (0–4.30 wt.%) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and pyridine-adsorbed IR. The results show that the addition of fluorine has a large effect on titania support and two kinds of fluorides are found to be formed in titania support after titania support is treated by NH4F. The state of the fluoride depends on the fluorine content. With lower fluorine content (≤0.94 wt.%) only one kind of fluoride is formed. Further increase in the fluorine content (≥2.07 wt.%) results in the formation of two kinds of fluorides. ESR analysis confirmed the formation of Ti3+ species after fluorine-modification, which actually exists as Ti4+ species containing an oxygen vacancy with an electron trapped in. Co–Mo catalysts supported on fluorine-modified titania presented higher HDS activities than Co–Mo catalyst supported on untreated titania. The hydrodesulfurization mechanism on sulfided fluorine-promoted cobalt–molybdenum/titania catalysts was discussed in this report.

Titania-supported cobalt and nickel bimetallic catalysts for carbon dioxide reforming of methane

Titania-supported cobalt and nickel bimetallic catalysts were investigated for CO 2 reforming of methane to synthesis gas at 1023 K under ambient pressure. Bimetallic Co–Ni/TiO 2 catalysts with an appropriate Co/Ni ratio showed highly stable activities without carbon deposition. Whereas the monometallic Co/TiO 2 catalyst deactivated rapidly because of the oxidation of metal, 10 mol% substitution of nickel for cobalt suppressed the oxidation of metal, providing a high catalytic stability. However, the catalysts with excess nickel content (>80 mol%) underwent carbon formation. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses revealed that a homogeneous alloy of cobalt and nickel was formed from bulk to the surface by the H 2 reduction, and the alloy was stable during reforming. The advantages of the bimetallic catalysts are high resistance to undesirable metal oxidation and coking, through the control of reactions between CH 4 and CO 2.

Co-Support Compound Formation in Titania-Supported Cobalt Catalyst

Co-support compound formation (Co-SCF) in Co/TiO2 was found during standard reduction resulting in a lower reducibility of the catalyst. The compound formed is considered to be non-reducible at temperatures <800°C during TPR and different from CoTiO3. The characteristics of Co-SCF were investigated using BET surface area, XRD, Raman spectroscopy, SEM/EDX, and TPR.

Shell GTL fuels ‘green’ London bus

Cobalt catalysts as used in the Fischer-Tropsch synthesis (FTS) are relatively expensive (as compared to iron) and need to have a high metal dispersion and long life to be able to offer a good balance between cost and performance. The oxidation of nano-sized metallic cobalt to cobalt oxide during Fischer-Tropsch synthesis has long been postulated as a major deactivation mechanism. However, to date there is no consistent picture. This paper presents an extensive overview of the literature on this topic of deactivation by means of oxidation for unsupported as well as silica-, alumina- and titania-supported cobalt catalysts. Furthermore, it presents results on the deactivation of an industrial Co/Al2O3 catalyst as obtained by pseudo in situ X-ray diffraction, magnetic measurements and X-ray absorption near-edge spectroscopy. These analyses were performed to study the oxidation state of spent industrial Co/Al2O3 catalyst samples withdrawn from a slurry reactor operating under realistic FTS conditions, and it was concluded that oxidation can be ruled out as a major deactivation mechanism. Finally, these data together with all relevant literature were used to create a common view on the oxidation behaviour of metallic cobalt during FTS. The apparent discrepancies in literature on the oxidation behaviour of cobalt are most likely due to the lack of direct characterisation of the cobalt oxidation state and due to the comparison of catalysts with varying cobalt crystallites sizes, compared at different reactor partial pressures of hydrogen and water (PH2O/PH2). It was shown that the oxidation of cobalt can be prevented by selecting the correct combination of the reactor partial pressures of hydrogen and water (PH2O/PH2) and the cobalt crystallite size.

Characterization of Alumina, Silica, and Titania Supported Cobalt Catalysts

A multiple technique approach was used to characterize the structural, chemical, and electronic properties of Co catalysts supported on Al 2O 3, SiO 2, and TiO 2 as well as Co/Mn catalysts on TiO 2. The morphology of the catalysts was studied by transmission electron microscopy followed by X-ray diffraction to determine the phase composition and the distribution of the crystallite size. The electronic properties of the calcined catalysts were investigated by X-ray photoelectron spectroscopy. Comparison with reference data allows identification of the cobalt-containing species in the surface. In agreement with adsorption experiments, the signal intensities yield the dispersion of the applied catalysts in the sequence Co/Al 2O 3>Co/TiO 2>Co/SiO 2. Temperature-programmed reduction and oxidation reveal the formation of various oxides in dependence on temperature as well as, in case of the alumina- and titania-supported cobalt catalysts, the formation of high-temperature compounds CoAl 2O 4 and CoTiO 3, respectively. Dynamic and static adsorption studies and BET measurements complete the characterization of the supported catalysts.

Kinetics of Fischer—Tropsch synthesis on titania-supported cobalt

The objective of this work was to obtain kinetic data on a well-characterized, titania-supported catalyst under commercially-representative reaction conditions. Effects of water partial pressure on the activity of Co/titania were also considered.

Titania-Supported Cobalt and Cobalt–Phosphorus Catalysts: Characterization and Performances in Ethane Oxidative Dehydrogenation

TiO2-supported Cobalt and cobalt–phosphorus catalysts prepared by impregnation are characterized by XRD, XPS, Laser Raman Spectroscopy (LRS), and Diffuse Reflectance Spectroscopy (DRS) and investigated in ethane oxidative dehydrogenation (ODH). At low cobalt loadings, the carrier is essentially covered by octahedral Co2+ ions, whereas at concentrations superior to 3.7 wt% formation of the Co3O4 spinel is observed. The best performance in ethane ODH is achieved at 550°C with the sample containing 7.6 wt% Co. The reaction begins with a conversion of 33% and a selectivity around 75%, then it decreases to reach after 150 min on stream a stationary state at 22% of conversion and 60% selectivity. This loss of 30% of the initial activity may be associated with a decrease of the specific surface area and the concomitant formation of CoTiO3 and Co2TiO4, as revealed by LRS, in situ DRS, and XPS analysis. The activity in ethane ODH seems to be mainly related to the presence of Co2+ ions octahedral sites. Addition of phosphorus to Co(7.6)/TiO2 catalysts results in the reduction of Co3+ ions and a growth of amorphous cobalt–phosphorus compounds which provoke a severe decrease of the catalyst performance.

Kinetics of Fischer–Tropsch synthesis on titania-supported cobalt

Rate data have been obtained for CO hydrogenation on a well-characterized 11.7% Co/TiO 2 catalyst in a differential fixed bed reactor at 20 atm, 180–240°C, and 5% conversion over a range of reactant partial pressures. The resulting kinetic parameters can be used to model precisely and accurately the kinetics of this reaction within this range of conditions. Turnover frequencies and rate constants determined from this study are in very good to excellent agreement with those obtained in previous studies of other cobalt catalysts, when the data are normalized to the same conditions of temperature and partial pressures of the reactants. Based on this comparison CO conversion and the partial pressure of product water apparently have little effect on specific rate per catalytic site. The data of this study are fitted fairly well by a simple power law expression of the form − r CO= kP H 2 0.74 P CO −0.24, where k=5.1×10 −3 s −1 at 200°C, P=10 atm, and H 2/CO=2/1; however, they are best fitted by a simple Langmuir–Hinshelwood (LH) rate form − r CO= aP H 2 0.74 P CO/(1+ bP CO) 2 similar to that proposed by Yates and Satterfield.

Dispersion and electronic structure of titania-supported cobalt and cobalt oxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDispersion and electronic structure of titania-supported cobalt and cobalt oxideY. Shao, W. Chen, E. Wold, and J. PaulCite this: Langmuir 1994, 10, 1, 178–187Publication Date (Print):January 1, 1994Publication History Published online1 May 2002Published inissue 1 January 1994https://doi.org/10.1021/la00013a027RIGHTS & PERMISSIONSArticle Views364Altmetric-Citations22LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts