Modified Co3O4/ZrO2 catalysts for VOC emissions abatement

The catalytic activity study of cobalt oxides dispersed on different supports evidenced first the highest performances of zirconia based catalysts in the reaction of toluene oxidation. The influence of the presence of ethylenediamine (en) during the preparation of Co/ZrO₂ and the ZrO₂ support modification by Y₂O₃ were then studied and compared with reference catalyst prepared conventionally by impregnation of ZrO₂ with an aqueous solution of Co(NO₃)₂. Addition of an aqueous solution of ethylenediamine to a cobalt nitrate solution led to a strong increase on the catalytic activity of the activated solids in the toluene deep oxidation as compared with the reference catalyst. The best catalytic results were explained in terms of cobalt oxides dispersion but also in terms of Co–support interaction. The generated cobalt species were reducible at much lower temperatures and then were more active in the toluene total oxidation. Finally an efficient catalyst for VOC oxidation was produced combining the modifications of ZrO₂ by yttrium and of the precursor.     

助剂在钴基催化剂F-T合成重质烃反应中的应用

煤 /天然气经合成气生产洁净二次能源和化学品将在本世纪初成为重要的能源化过程 .在新的过程观念 ( SMDS法 )中 ,新型钴基催化剂的制备是 F- T合成重质烃反应中的关键问题 ,其中助剂可以对催化剂的活性和选择性进行调变 .概述了专利中常用的助剂如金属钌、氧化锆、氧化镧对钴基催化剂 F- T反应性能的影响及作用机制 ,指出添加适当的助剂可以在不影响催化剂的F- T反应活性的前提下 ,提高产物的长链烃 ( C5 )选择性 .     

Cobalt Particle Size Effects in the Fischer–Tropsch Synthesis and in the Hydrogenation of CO2 Studied with Nanoparticle Model Catalysts on Silica

We have investigated the effect of cobalt nanoparticle size in Fischer–Tropsch synthesis (CO/H₂) and have compared it to data obtained for carbon dioxide hydrogenation (CO₂/H₂) using model catalysts produced by colloidal methods. Both reactions demonstrated size dependence, in which we observed an increase of the turnover frequency with increasing average particle size. In both case, a maximum activity was found for cobalt particles around 10–11 nm in size. Regarding the selectivity, no size-dependent effect has been observed for the CO₂ hydrogenation, whereas CO hydrogenation selectivity depends both on the temperature and on the size of the particles. The hydrogenation of CO₂ produces mainly methane and carbon monoxide for all sizes and temperatures. The Fischer–Tropsch reaction exhibited small changes in the selectivity at low temperature (below 250 °C) while at high temperatures we observed an increase in chain growth with the increase of the size of cobalt particles. At 250 °C, large crystallites exhibit a higher selectivity to olefin than to the paraffin equivalents, indicating a decrease in the hydrogenation activity.     

Preparation and properties of supported cobalt catalysts for Fischer-Tropsch synthesis

Alumina-supported cobalt catalysts have been prepared from different cobalt precursors to study the influence of the precursor on the ultimate metal particle size. Furthermore, the effect of the particle size on the catalytic performance (activity and selectivity) during Fischer-Tropsch synthesis has been investigated. The preparation of low-loaded cobalt catalysts (2.5 wt%) by incipient wetness impregnation using cobalt EDTA and ammonium cobalt citrate precursors resulted initially in very small cobalt oxide particles, as determined by XPS. The small oxide particles reacted during the thermal treatment in a reducing gas flow with the alumina support to cobalt aluminate, which was neither active nor selective during Fischer-Tropsch synthesis. The catalysts prepared with cobalt nitrate had larger particles that could be easily reduced to metallic cobalt. These catalysts were active under reaction conditions. High-loaded cobalt catalysts (5.0 wt%) prepared using ammonium cobalt citrate showed a larger particle size than the low-loaded catalyst prepared from the citrate precursor. The extent of reduction to metallic cobalt that could be achieved with the high-loaded catalyst was significantly higher than that with the low-loaded catalyst, as shown by magnetic measurements. Accordingly, the high-loaded catalyst exhibited a reasonable activity and, in addition, an interesting and remarkably high selectivity toward higher hydrocarbons, and also a very high Schultz-Flory parameter.     

Oxidative Dehydrogenation of Propane on V2O5/ZrO2 Catalyst

The performance of zirconia supported vanadia catalyst has been investigated for the oxidative dehydrogenation of propane. Vanadia loading was varied from 1.6 to 22.7 wt%, both below and well above monolayer coverage. The turnover frequency was highest for the catalyst with a vanadia surface density of 5 VO _x /nm². The effect of vanadia loading on the redox behavior of the catalysts was investigated by temperature-programmed reduction and temperature-programmed oxidation. The specific activity increased with ease of reducibility of the catalyst. The extent of reduction and ease of reoxidizability of the catalysts were also found to depend on the surface vanadia structure and to influence the catalytic activity. The effect of vanadia loading on the basicity of the catalysts was also investigated.     

Fischer-Tropsch synthesis by reduced graphene oxide nanosheets supported cobalt catalysts: role of support and metal nanoparticle size on catalyst activity and products selectivity

In this paper,a series of cobalt catalysts supported on reduced graphene oxide(rGO)nanosheets with the loading of 5,15 and 30 wt-%were provided by the impregnation method.The activity of the prepared catalysts is evaluated in the Fischer-Tropsch synthesis(FTS).The prepared catalysts were carefully characterized by nitrogen adsorption-desorption,hydrogen chemisorption,X-ray diffraction,Fourier transform infrared spectroscopy,Raman spectroscopy,temperature programmed reduction,transmission electron microscopy,and field emission scanning electron microscopy techniques to confirm that cobalt particles were greatly dispersed on the rGO nanosheets.The results showed that with increasing the cobalt loading on the rGO support,the carbon defects are increased and as a consequence,the reduction of cobalt is decreased.The FTS activity results showed that the cobalt-time yield and turnover frequency passed from a maximum for catalyst with the Co0 average particle size of 15 nm due to the synergetic effect of cobalt reducibility and particle size.The products selectivity results indicated that the methane selectivity decreases,whereas the C5+selectivity raises with the increasing of the cobalt particle size,which can be explained by chain propagation in the primary chain growth reactions.     

Effect of fluorine on hydrogenation of cyclohexene on sulfided Ni (or Co)Mo/Al2O3 catalysts

The effect of fluorine incorporation on alumina support on the surface structure of unpromoted molybdenum, promoted cobalt—molybdenum and nickel—molybdenum catalysts, and their activity for hydrogenation of cyclohexene has been studied. The incorporation of 0.2 and 0.8 wt.-% fluorine on the alumina was carried out by impregnation with NH₄F solutions. The catalysts in the oxidic state were characterized by X-ray diffraction and ammonia adsorption and in the sulfide state by X-ray photoelectron spectroscopy (XPS) and infra-red spectroscopy (IR) of adsorbed NO. The absence of significant changes in the binding energy values of Mo3d and Ni2p (or Co2p) levels in the XPS spectra of the fluorine-containing catalysts as compared to the fluorine-free counterpart does not support the existence of an electronic effect of fluorine. The quantitative XPS results showed, however, that fluorine clearly increases the dispersion of molybdenum and promoter, this being linearly correlated to surface fluorine content. The IR results of adsorbed NO also indicate that fluorine incorporation leads generally to minor sizes of MoS₂ slabs, and more exposed promoter atoms, except for the cobalt in the CoMo/F(0.2)A catalyst. It is suggested that the increase in the dispersion of the supported active phase is a secondary effect of fluorine incorporation, which may result from the observed textural changes of the alumina and its small partial solubilization provoked by NH₄F solution. It was found that the incorporation of fluorine enhances appreciably, moderately and considerably the hydrogenation activity of molybdenum, cobalt—molybdenum an nickel—molybdenum catalysts, respectively. Such increase in hydrogenation activity is not directly correlated to the exposed atoms probed by NO adsorption, and is only loosely related to molybdenum dispersion for the molybdenum and cobalt—molybdenum catalysts. The lack of similar reliable correlations for the nickel—molybdenum catalysts suggests that other structural parameters such as extent of reduction-sulfidation and certain configurations of molybdenum ions and sulfur vacancies may govern hydrogenation activity.     

Zirconia: Selective oxidation catalyst for removal of tar and ammonia from biomass gasification gas

Catalysts containing zirconia and alumina were tested for their activity in the selective oxidation of tar and ammonia in biomass gasification gas. Their performance was compared with that of nickel and dolomite catalysts. Synthetic gasification gas with toluene as tar model compound was used as feed. In the presence of oxygen, zirconia and alumina-doped zirconia gave high toluene and ammonia conversions even below 600 °C. They were the most active catalysts for toluene oxidation below 700 °C and for ammonia oxidation below 650 °C. At higher temperatures than these, the impregnated ZrO₂/Al₂O₃ catalysts performed better: oxidation selectivity was improved and toluene and ammonia conversions were higher. The presence of both zirconia and alumina in the catalyst promoted toluene and ammonia conversions at low temperatures: zirconia enhanced the oxidation activity, while alumina improved the oxidation selectivity. The presence of H₂S had little effect on the activity of alumina-doped zirconia.     

Thermogravimetric analyses and catalytic behaviors of zirconia-supported nickel catalysts for carbon dioxide reforming of methane

Carbon dioxide reforming of methane has been performed over zirconia-supported nickel catalysts. Temperature-programmed surface reactions (TPSR) with CH₄ and CO₂ have also been investigated over the catalysts by means of thermogravimetric analysis technique to explore the behavior of carbon formation during the reaction. The effect of the modification of the zirconia support on supported Ni catalysts reveals that the ceria-doped zirconia support exhibits high catalyst stability against high temperature aging test as well as high resistance to coke formation. Moreover, simultaneous alteration of the support and Ni surface of Ni/ZrO₂ with a Ce modifier and a Ca promoter led to a high performance catalyst, Ni-Ca/Ce-ZrO₂, revealing high activity as well as high stability in the CO₂ reforming of methane.     

Partial oxidation of methane to synthesis gas over Co/Ca/Al2O3 catalysts

A series of calcium-modified alumina-supported cobalt catalysts were prepared with a two-step impregnation method, and the effect of calcium on the catalytic performances of the catalysts for the partial oxidation of methane to syngas (CO and H₂) was investigated at 750 °C. Also, the catalysts were characterized by XRD, TEM, TPR and (in situ) Raman. At 6 wt.% of cobalt loading, the unmodified alumina-supported cobalt catalyst showed a very low activity and a rapid deactivation, while the calcium-modified catalyst presented a good performance for this process with the CH₄ conversion of 88%, CO selectivity of 94% and undetectable carbon deposition during a long-time running. Characterization results showed that the calcium modification can effectively increase the dispersion and reducibility of Co₃O₄, decrease the Co metal particle size, and suppress the reoxidation of cobalt as well as the phase transformation to form CoAl₂O₄ spinel phases under the reaction conditions. These could be related to the excellent catalytic performances of Co/Ca/Al₂O₃ catalysts.     

Cobalt supported on carbon nanotubes — A promising novel Fischer–Tropsch synthesis catalyst

An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNT) supported and γ–alumina-supported cobalt catalysts with different amounts of cobalt are reported. Up to 40 wt.% of cobalt is added to the supports by the impregnation method. The effect of the support on the reducibility of the cobalt oxide species, dispersion of the cobalt, average cobalt clusters size, water–gas shift (WGS) activity and activity and selectivity of FTS is investigated. Using carbon nanotubes as cobalt catalyst support was found to cause the reduction temperature of cobalt oxide species to shift to lower temperatures. The strong metal-support interactions are reduced to a large extent and the reducibility of the catalysts improved significantly. CNT aided in well dispersion of metal clusters and average cobalt clusters size decreased. Results are presented showing that the hydrocarbon yield obtained by inventive CNT supported cobalt catalyst is surprisingly much larger than that obtained from cobalt on alumina supports. The maximum concentration of active surface Co° sites and FTS activity for alumina and CNT supported catalysts are achieved at 34 wt.% and 40 wt.% cobalt loading respectively. CNT caused a slight decrease in the FTS product distribution to lower molecular weight hydrocarbons.     

Cobalt and iron oxide modified mesoporous zirconia: Preparation, characterization and catalytic behaviour in methanol conversion

Mesoporous zirconia materials with different textural characteristics and degrees of crystallinity were obtained by various procedures and modified with cobalt and iron oxide nanoparticles. The obtained materials were characterized by N₂-physisorption, XRD, TEM, FTIR, Mössbauer spectroscopy, TPR-TG and methanol conversion as a catalytic test. Formation of finely dispersed iron and cobalt oxide species, hosted in the zirconia matrix, was observed after the modification. The obtained composites possess higher catalytic activity and different in comparison with the corresponding zirconia supports dehydration and dehydrogenation ability. It was demonstrated that the variations in the textural and surface features of zirconia support and the deposition of different metal oxides on it provided a great opportunity for the preparation of catalysts with tunable bi-functional acidic and redox properties.     

CO oxidation catalysts based on copper and manganese or cobalt oxides supported on MgF2 and Al2O3

The catalytic activity of a mixed phase of copper–cobalt and copper–manganese oxides supported on magnesium fluorine or alumina has been studied in low temperature CO oxidation at 30 °C. During calcination, the oxides studied partially react to form different type spinels depending on the calcination temperature. These spinels have different effect on the catalytic activity. In low temperature CO oxidation the copper–manganese catalysts are more active than the copper–cobalt ones.     

The Water-Gas Shift Reaction Over Au-Based, Bimetallic Catalysts. The Au-M (M=Ag, Bi, Co, Cu, Mn, Ni, Pb, Ru, Sn, Tl) on Iron(III) Oxide System

The bimetallic Au-M/Fe₂O₃ catalysts were prepared by deposition coprecipitation method with Au/M atomic ratio of 1. All the catalysts were measured for WGS reaction and characterized by TPR/TPO studies. Ruthenium- and nickel-modified catalysts showed higher WGS activities compared to the other systems including unmodified Au/Fe₂O₃ at low temperature (100 °C). At higher temperature (240 °C), ruthenium-, nickel-, bismuth-, lead-, copper-, silver-, thallium- and tin-modified catalysts were more active than unmodified Au/Fe₂O₃. Manganese- and cobalt-modified catalysts were less active than unmodified Au/Fe₂O₃. TPR analyses indicated a shift in reduction temperature in the bimetallic catalysts, suggesting a degree of interaction between gold and the second metal.     

Effect of calcination atmosphere and temperature on γ-Al2O3 supported cobalt Fischer-Tropsch catalysts

The effect of calcination temperature and atmosphere on the properties of γ-Al₂O₃ supported cobalt Fischer-Tropsch catalysts has been investigated. One common precursor for all the catalysts was prepared by incipient wetness impregnation of γ-Al₂O₃ with an aqueous solution of cobalt nitrate hexahydrate. It was subjected to four different calcination atmospheres (air/50% steam: 30 mL/min, air: 30 mL/min, air: 50 mL/min, N₂: 30 mL/min) and eight different calcination temperatures (range: 473–723 K), making the total number of samples 32. Both the post calcination nitrogen content and the cobalt dispersion were measured. The results demonstrated that in order to maximise the cobalt dispersion, it is necessary to use low calcination temperatures and remove the precursor decomposition products (NO, NO₂, H₂O) efficiently. The Fischer-Tropsch synthesis performance of two catalysts calcined at the same temperature, but at different air flow rates was evaluated. No significant effect of the air flow rate was found on the turnover frequency or C₅₊ selectivity, but a high flow rate resulted in 30% higher activity per gram catalyst.     

Hydrogenation of Sunflower Oil over M/SiO2 and M/Al2O3 (M = Ni,Pd, Pt,Co, Cu) Catalysts

This work is aimed at evaluating the performance of several catalysts in the partial hydrogenation of sunflower oil. The catalysts are composed of noble (Pd and Pt) and base metals (Ni, Co and Cu), supported on both silica and alumina. The following order can be proposed for the effect of the metal on the hydrogenation activity: Pd > Pt > Ni > Co > Cu. At a target iodine value of 70 (a typical value for oleomargarine), the production of trans isomers is minimum for supported nickel catalysts (25.7–32.4 %, depending on the operating conditions). Regarding the effect of the support, Al₂O₃ allows for more active catalysts based on noble metals (Pd and Pt) and Co, the effect being much more pronounced for Pt. Binary mixtures of catalysts have been studied, in order to strike a balance between catalyst activity and product distribution. The results evidence that Pd/Al₂O₃–Co/SiO₂ mixture has a good balance between activity and selectivity, and leads to a very low production of trans isomers (11.8 %) and a moderate amount of saturated stearic acid (13.5 %). Consequently, the utilization of cobalt‐based catalysts (or the addition of cobalt to other metallic catalysts) could be considered a promising alternative for the hydrogenation of edible oil.     

Catalytic behavior of nanostructured sulfated zirconia promoted by alumina: Butane isomerization

Promotion of sulfated zirconia with alumina (ASZ) improves its catalytic activities in n-butane isomerization. The activity and stability of the sulfated zirconia catalysts are investigated in three different nanostructures: ASZ supported on MCM-41, ASZ nanoparticles, and Al-promoted mesoporous sulfated zirconia. The increase of activity was determined primarily by the amount of aluminum addition and the temperature of calcination. The remarkable activity and stability of the Al-promoted catalysts are due to an improved distribution of acid sites strength. The Al loadings in all three catalysts can be adjusted so that optimum catalytic activities for butane isomerization could be found. The increase of butane conversion can be as high as 6 times of that in un-promoted SZ catalysts. This is due to an enhanced amount of weak Brønsted acid sites with intermediate strength on the optimal catalysts. For nanoparticle form of sulfated zirconia, the activity is most steady which is related to the optimum distribution of weak Brønsted acid. On the other hand, too much strong Brønsted acid leads to rapid decay of activity because of coking and cracking. The overall reaction mechanism of the isomerization of n-butane over sulfated zirconia was discussed to understand the details in product distribution.     

Effect of preparative conditions of Fe and Mn sulfated zirconia catalysts on their activities for η‐butane isomerization

This work investigates the effect of preparative conditions of Fe‐ and Mn‐promoted sulfated zirconia catalysts on their activities for low‐temperature η‐butane isomerization. It was found that the active species on a promoted catalyst can be successfully regenerated in an oxidative treatment at 450°C after the catalyst was deactivated either during the reaction or under a high‐temperature treatment in helium. The loading sequence of Fe and Mn does not significantly affect the catalyst activity. Both Fe and Mn can individually promote the activity of sulfated zirconia catalysts. However, the promoting effect of Fe is much stronger than that of Mn; the catalyst containing only Fe is significantly more active than that containing both Fe and Mn and does not deactivate any more rapidly. The optimum Fe content was found to be 4 wt%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Role of the support and of the preparation method for copper-based catalysts in the 2-propanol decomposition

Pure copper oxide and mixed CuO/ZnO catalysts with different Cu:Zn atomic ratios were tested for the 2-propanol decomposition in order to investigate the nature of the active site and the role of the ZnO support. Fresh catalysts as well as catalysts oxidized in pure oxygen did not exhibit any catalytic activity below 373 K. When reduced either in pure hydrogen or in reaction mixture (helium plus alcohol) both copper oxide and mixed two-phase catalysts showed a dehydrogenating activity in the temperature range 323–423 K. The apparent activation energy for both reduced CuO and reduced CuO/ZnO catalysts was 60 ± 8 kJ mol^–1. The first order rate constants were found to be a linear function of the exposed zero-valent copper area. The comparison of Cu(0) turnover frequency in unsupported Cu(0) and in Cu(0)/ZnO samples did not show any synergic effect of the support. The role of the preparation method on the Cu(0) dispersion is also discussed.     

Gold catalysts supported on ceria-modified mesoporous zirconia for low-temperature water–gas shift reaction

New gold catalytic system prepared on ceria-modified mesoporous zirconia used as water–gas shift (WGS) catalyst is reported. Mesoporous zirconia was synthesized using surfactant templating method through a neutral [C₁₃(EO)₆-Zr(OC₃H₇)₄] assembly pathway. Ceria modifying additive was deposited on mesoporous zirconia by deposition–precipitation method. Gold-based catalysts with different gold content (1–3 wt. %) were synthesized by deposition–precipitation of gold hydroxide on mixed metal oxide support. The supports and the catalysts were characterized by powder X-ray diffraction, high-resolution transmission electron microscopy, N₂ adsorption analysis and temperature programmed reduction. The catalytic behavior of the gold-based catalysts was evaluated in WGS reaction in a wide temperature range (140–300 °C) and at different space velocities and H₂O/CO ratios. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new Au/ceria-modified mesoporous zirconia catalysts was compared with that of gold catalysts supported on simple oxides CeO₂ and mesoporous ZrO₂, revealing significantly higher catalytic activity of Au/ceria-modified mesoporous zirconia. A high degree of synergistic interaction between ceria and mesoporous zirconia and a positive modification of structural and catalytic properties by ceria have been achieved. It is clearly revealed that the ceria-modified mesoporous zirconia is of much interest as potential support for gold-based catalyst. The Au/ceria-modified mesoporous zirconia catalytic system is found to be effective catalyst for WGS reaction.