Ceria-supported Cobalt Catalyst Research Articles

Achieving High-Quality Biofuel from Catalytic Upgrading of Sewage Sludge Hydrothermal Liquified Biocrude on Ceria-Supported Cobalt Catalysts

Achieving High-Quality Biofuel from Catalytic Upgrading of Sewage Sludge Hydrothermal Liquified Biocrude on Ceria-Supported Cobalt Catalysts

CO and CO2 Methanation over CeO2-Supported Cobalt Catalysts

CO2 methanation is a promising reaction for utilizing CO2 using hydrogen generated by renewable energy. In this study, CO and CO2 methanation were examined over ceria-supported cobalt catalysts with low cobalt contents. The catalysts were prepared using a wet impregnation and co-precipitation method and pretreated at different temperatures. These preparation variables affected the catalytic performance as well as the physicochemical properties. These properties were characterized using various techniques including N2 physisorption, X-ray diffraction, H2 chemisorption, temperature-programmed reduction with H2, and temperature-programmed desorption after CO2 chemisorption. Among the prepared catalysts, the ceria-supported cobalt catalyst that was prepared using a wet impregnation method calcined in air at 500 °C, and reduced in H2 at 500 °C, showed the best catalytic performance. It is closely related to the large catalytically active surface area, large surface area, and large number of basic sites. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study revealed the presence of carbonate, bicarbonate, formate, and CO on metallic cobalt.

SYNTHESIS, CHARACTERIZATION AND CATALYTIC PERFORMANCE OF CERIA-SUPPORTED COBALT CATALYST FOR METHANE DRY REFORMING TO SYNGAS

In this study the synthesis, characterization and catalytic performance of CeO2 (Ceria) supported Co catalyst was investigated. First, the ceria was synthesized by direct thermal decomposition of Ce(NO3)3.6H2O and subsequently impregnated with 20 wt.% Co using aqueous solution of Co(NO3)2.6H2O as a precursor. The synthesized catalyst was characterized using TGA, N2-adsorption-desorption, X-ray Diffractometry (XRD), Field Emission Scanning Electron Microscope (FESEM-EDX), and Fourier Transformation Infrared (FTIR). The catalytic property of the ceria-supported cobalt catalyst was tested in methane dry reforming using a stainless steel fixed bed reactor. The dry reforming reaction was performed at the temperature range of 923-1023 K under a controlled atmospheric pressure and constant gas hourly space velocity (GHSV) of 30000 h-1. The effects of reactant (CH4 and CO2) feed ratio was investigated on reactants conversion, product yields, and selectivity. The ceria-supported cobalt catalyst recorded highest catalytic activity at a CH4: CO2 ratio of 0.9 and temperature of 1023 K. The highest values of 79.5% and 87.6% were recorded for the CH4 and CO2 conversions respectively. Furthermore, highest yields of 41.98% and 39.76%, as well as selectivity of 19.56% and 20.72%, were obtained for H2 and CO respectively. Syngas ratio of 0.90 was obtained from the dry reforming of methane, making it suitable as feedstock for Fischer-Tropsch synthesis (FTS).

Catalytic performance of ceria-supported cobalt catalyst for CO-rich hydrogen production from dry reforming of methane

Dry reforming of methane was studied over ceria-supported cobalt (20wt%) catalyst prepared via wet-impregnation method. The synthesized catalyst was characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), N2 physisorption and Fourier transform infrared spectroscopy (FTIR). The catalytic methane dry reforming was carried out over the 20wt%Co/80wt%CeO2 catalyst in a fixed-bed reactor. The experiment was performed at atmospheric condition with time-on-stream (TOS) of 4 h, reaction temperatures of 923–1023 K, and CH4:CO2 feed ratios of 0.1–1.0. The XRD pattern showed good dispersion of the cobalt metal on the support. This was corroborated by the FESEM-EDX and FTIR spectrum. The N2 physisorption revealed that the BET specific surface area of the calcined catalyst was more than double the ceria support. The conversions of CH4 and CO2, respectively, as well as the H2 and CO yield, were found to increase with reaction temperature and CH4:CO2 feed ratios. The highest conversions for both CO2 and CH4 were 87.6% and 79.5%, respectively, at 1023 K. Moreover, highest yield of 40% was obtained for CO while that of H2 was 37.6%. Syngas ratio of 0.99 was obtained at a feed ratio of 0.9, which has further cemented the suitability of methane dry reforming over ceria-supported cobalt catalyst for production of syngas meant for Fischer–Tropsch synthesis.

Syngas production from CO2 reforming of methane over ceria supported cobalt catalyst: Effects of reactants partial pressure

The production of syngas from CO2 (dry) reforming of methane is an environmental friendly process since it contributed to the mitigation of CH4 and CO2, the two principal components of greenhouse gases. In this study, ceria-supported cobalt catalyst was synthesized using wet-impregnation method and tested for the production of syngas from methane dry reforming. The main objective of this study is to investigate the effects of partial pressures of the reactants (CH4 and CO2) on the performance of the ceria-supported cobalt catalyst for syngas production via methane dry reforming. The CH4 and CO2 partial pressures were investigated within the range of 5–50 kPa at reaction temperatures of 923–1023 K in a fixed bed reactor at atmospheric pressure and gas hourly velocity of 30,000h−1. The highest conversion of CH4 and CO2 were obtained to be 78 and 80% at CH4 partial pressure of 45 and 25 kPa respectively. Syngas ratio of 1.0 was produced at CH4 partial pressure of 40 kPa (reaction temperature of 1023 K). The maximum yield of 40% and 38% were obtained for H2 and CO, respectively. The used catalyst was characterized by temperature programmed oxidation (TPO) for possible carbon deposition. The TPO analysis revealed the formation of graphitic carbon. The findings from this study show that syngas production from methane dry reforming over ceria-supported cobalt catalyst is significantly influenced by the variation in the partial pressure of the reactants.

Modelling and optimization of syngas production from methane dry reforming over ceria-supported cobalt catalyst using artificial neural networks and Box–Behnken design

In the present study, synthesis gas was produced from dry reforming of methane over ceria supported cobalt catalyst in a fixed bed stainless steel reactor. Artificial neural network (ANN) and Box Behnken design (BBD) were employed to investigate the effects of reactant partial pressures, reactant feed ratios, reaction temperature and their optimum conditions. Good agreement was shown between the predicted outputs from the ANN model and the experimental data. Optimum reactant feed ratio of 0.60 and CH4 partial pressure of 46.85kPa were obtained at 728°C with corresponding conversions of 74.84% and 76.49% for CH4 and CO2, respectively.

Effect of pretreatment on ceria-supported cobalt catalyst for ammonia synthesis

Cerium in a catalyst may affect the catalytic reaction by providing surface hydroxyl groups. In this work, Co/CeO2 catalysts with different properties of hydroxyl groups were prepared using different pretreatment atmospheres during the heat treatment process of the hydroxide gel with metal and cerium. The heat treatment process of Co/CeO2 precipitate in different pretreatment atmospheres was monitored by mass spectrometry. Pulse chemisorption measurements in combination with XRD, TPR, XPS, TEM were used to reveal the relationship between the properties of the as-obtained samples and their catalytic performances in ammonia synthesis. It was found that the pretreatment atmosphere of Co/CeO2 affected the dehydroxylation pathways. Most hydroxyls in CeO2 can release H2O by reacting with atomic hydrogen during the hydrogen reduction process. On the other hand, oxygen treatment resulted in the conversion of hydroxyls to oxides, and further hydrogen reduction promoted the reduction of Ce4+ to Ce3+ and the formation of the stable surface hydroxyl radicals. The active sites available for nitrogen dissociation and ammonia synthesis may decrease because some redundant hydrogen cannot be removed in time by combination with the stable hydroxyls, and thus the catalyst with oxygen treatment showed lower ammonia synthesis activity.

Erratum to: Fischer–Tropsch Synthesis: Studies on the Effect of Support Doping with Si, Mn and Cr on the Selectivity to Alcohols in Ceria Supported Cobalt Catalysts

Mn and Cr doped CeSi mixed oxides were used as supports for Co and tested for CO hydrogenation. Co/CeSi was found to be more active and significantly more selective to n-alcohols/olefins. An increasing selectivity to n-alcohols and decreasing selectivity to olefins as a function of time on stream was also observed, suggesting a trade-off between those two products. Addition of Mn led to similar behavior, although at slightly lower conversions. Addition of Cr, however, considerably suppressed n-alcohol formation, while it kept selectivities to olefins within a 20–30 % range over more than 250 h of testing, indicating either higher alcohol dehydration activity, or that the presence of Cr ions lowered the hydrogenating activity of Co. The present work indicates that enhanced contact area between Co and the reducible support is likely a key factor for enhancing selectivity to alcohols.

Fischer–Tropsch Synthesis: Studies on the Effect of Support Doping with Si, Mn and Cr on the Selectivity to Alcohols in Ceria Supported Cobalt Catalysts

Fischer–Tropsch Synthesis: Studies on the Effect of Support Doping with Si, Mn and Cr on the Selectivity to Alcohols in Ceria Supported Cobalt Catalysts

Effects of metal loading and support for supported cobalt catalyst

Several series of supported cobalt catalysts were synthesized with different loadings and supports. These catalysts were studied by in situ diffuse reflectance Fourier transformed infrared (DRIFT) spectroscopy during the CO2 hydrogenation reaction. The catalysts were also characterized by Ultraviolet visible near-infrared (UV–vis–NIR) spectroscopy and X-ray diffraction (XRD). The nature of interaction between cobalt and the support was determined by calcining the catalysts at elevated temperature and observing changes, if any, by UV–vis–NIR spectroscopy. The reduced catalysts did not possess cobalt oxide phases or cobalt-support compounds, except for the niobia supported cobalt catalyst, where cobalt niobate was readily formed. During reaction adsorbed CO and formate species were observed. The intensity and presence of the adsorbed species was dependent on the specific supported cobalt catalyst. The highest activity was observed for high loadings of cobalt supported on ceria followed by magnesia, alumina, zirconia, silica, titaina and niobia. At low loadings, however, ceria supported cobalt catalyst possessed a lower activity. Thus, the choice of the supports and the loading of the active metal are important while designing the supported cobalt catalysts.

Effect of cobalt precursor on the performance of ceria-supported cobalt catalysts for ethanol steam reforming

The effect of cobalt precursor on the performance of Co/CeO 2 catalysts in ethanol steam reforming was investigated. The catalysts were characterized using various characterization techniques including H 2 chemisorption, temperature-programmed reduction, temperature-programmed desorption, X-ray diffraction, transmission electron microscopy, and diffuse reflectance infrared Fourier transform spectroscopy. The results obtained from steady-state reaction experiments showed a significantly better catalytic performance over the samples prepared by using organometallic Co precursors (especially, cobalt acetyl acetonate). Characterization results suggest that the organic ligands bound to the cobalt species might facilitate its dispersion on the surface of the CeO 2 support, resulting in the improved activity and stability.

Nano- and micro-powder of zirconia and ceria-supported cobalt catalysts for the steam reforming of bio-ethanol

The usefulness of nano- and micro-powders of ceria and zirconia as a support of the cobalt-based catalyst as well as additional modification of zirconia-supported cobalt catalysts with cerium for the production of hydrogen in the steam reforming of bio-ethanol (SRE) for fuel cell applications was studied. It was found that mainly different structural features of the nano- and micro-powder of ceria- and zirconia-supported cobalt catalysts are higher cobalt surface area and much smaller average sizes of cobalt crystallites for the catalysts with high-dispersed support. Similarly, the presence of high-dispersed ceria introduced to the zirconia-supported catalysts simultaneously with the deposition of cobalt increases their total and active surface area as well as decreases the size of cobalt crystallites, regardless of the initial dispersion of zirconia support. The results of the temperature-programmed reduction and the temperature-programmed desorption of hydrogen showed that small crystallites of the cobalt phase strongly interact with high-dispersed ceria. Ceria has a great influence on the effects of the SRE. For the nano-powder ceria-supported cobalt catalyst and for the nano-powder zirconia-supported catalysts with the cobalt–ceria active phase the yield of hydrogen formed from one molecule of ethanol supplied to the SRE process was the highest; even at the relatively low temperature of 420 °C it is close to 5.5 mol H 2/mol EtOH. At the same time there were achieved: complete conversion of ethanol, very close to that of water and 92%, 81–84%, 5–6% selectivities to hydrogen, carbon dioxide and carbon monoxide, respectively.

The role of impregnation medium on the activity of ceria-supported cobalt catalysts for ethanol steam reforming

The effect of impregnation medium on the activity of Co/CeO2 catalysts in ethanol steam reforming was investigated using various characterization techniques including temperature programmed calcination, temperature programmed reduction, X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and diffuse reflectance infrared fourier transform spectroscopy. The steady-state reaction experiments showed that catalysts that were prepared in an organic medium (e.g., ethanol) during impregnation gave higher H2 yields than those prepared in aqueous media. Characterization results showed the presence of oxygenated carbonaceous species left on the surface from the impregnation step. These species, which were stable through oxidation and reduction pre-treatment steps, may possibly contribute to the activity, selectivity and stability of the catalysts by keeping the Co particles segregated and by blocking the sites for side reactions.

Mesoporous CeO2-Supported Co3O4 Catalysts for CO Preferential Oxidation in H2-Rich Gases

Abstract Mesoporous ceria (meso-CeO 2 ) and the mesoporous ceria-supported cobalt catalyst (Co 3 O 4 /meso-CeO 2 ) were synthesized through a surfactant-templated method and used for CO preferential oxidation (PROX) in H 2 -rich gases. The N 2 physical adsorption and X-ray diffraction techniques were used to study the textural properties and crystalline structure of the meso-CeO 2 and Co 3 O 4 /meso-CeO 2 . It was found that Co 3 O 4 /meso-CeO 2 exhibited very good catalytic performance for the PROX reaction at high space velocity, whereas CO 2 and water had negative effects on CO conversion. In addition, the Co 3 O 4 /meso-CeO 2 catalyst had a much wider temperature window for the complete conversion of CO than the Co 3 O 4 /non-mesoporous CeO 2 catalyst.

Cobalt catalysts for the oxidation of diesel soot particulate

Ceria-supported materials prepared by three routes, coprecipitation from aqueous solution containing both Co 2+ and Ce 3+ ions, and impregnation of preformed ceria gel with either cobalt(II) nitrate or cobalt(II) acetate, have been investigated for catalytic activity towards oxidation of diesel soot. All three materials catalyze the conversion of diesel soot particulate to carbon dioxide under a flow of either 6 vol.% O 2 or 0.5 vol.% NO + 6 vol.% O 2 in helium in the temperature range 573–613 K. The temperature of maximum conversion rate shows a small dependence on the particular catalyst and the composition of the oxidant. Raman spectroscopy of the ceria-supported cobalt catalysts indicate that the cobalt is present as Co 3O 4, but its average particle size in Co/CeO 2 impregnated with Co acetate is smaller than the other two Co/CeO 2 preparations. Features in the temperature-programmed reduction (TPR) profiles in the range 500–600 K, coincident with the temperature of catalytic activity, appear to be associated with reduction of the cobalt, suggesting a redox-type mechanism assisted by oxygen spillover on the CeO 2 support. In contrast, cobalt supported on alumina, silica, and tin(IV) oxide obtained by coprecipitation show much lower activity due to the presence of dispersed Co 2+ ions in these materials although small amounts of Co 3O 4 may be present on alumina and tin(IV) oxide.