Iron oxide supported sulfated TiO2 nanotube catalysts for NO reduction with propane

Sulfated TiO₂ nanotubes and a series of iron oxide loaded sulfated TiO₂ nanotubes catalysts with different iron oxide loadings (1 wt%, 3 wt%, 5 wt% and 7 wt%) were prepared and calcined at 400 °C. The physico-chemical properties of the catalysts were studied by using XRD, N₂-physisorption, Raman spectroscopy, SEM-EDX, TEM, XPS, and pyridine adsorption using FTIR and H₂-TPR techniques. It was observed that iron oxide was highly dispersed on the sulfated TiO₂ nanotube support due to its strong interaction. The activity of these catalysts in the catalytic removal of NO with propane was also studied in the temperature range of 300–500 °C. Highest activity (90% NO conversion) was observed with 5 wt% iron oxide supported on sulfated TiO₂ catalyst at 450 °C. Selective catalytic reduction of NO activity of the catalysts was correlated with iron oxide loading, reducibility, and the Brönsted and Lewis acid sites of the catalysts. The catalyst also showed good stability under studied reaction conditions that no deactivation was observed during the 50 h of reaction.     

Comparison of the activity of Au/CeO2 and Au/Fe2O3 catalysts for the CO oxidation and the water-gas shift reactions

We compare the activity and relevant gold species of nanostructured gold–cerium oxide and gold–iron oxide catalysts for the CO oxidation by dioxygen and water. Well dispersed gold nanoparticles in reduced form provide the active sites for the CO oxidation reaction on both oxide supports. On the other hand, oxidized gold species, strongly bound on the support catalyze the water-gas shift reaction. Gold species weakly bound to ceria (doped with lanthana) or iron oxide can be removed by sodium cyanide at pH ≥12. Both parent and leached catalysts were investigated. The activity of the leached gold–iron oxide catalyst in CO oxidation is approximately two orders of magnitude lower than that of the parent material. However, after exposure to H₂ up to 400 °C gold diffuses out and is in reduced form on the surface, a process accompanied by a dramatic enhancement of the CO oxidation activity. Similar results were found with the gold–ceria catalysts. On the other hand, pre-reduction of the calcined leached catalyst samples did not promote their water-gas shift activity. UV–Vis, XANES and XPS were used to probe the oxidation state of the catalysts after various treatments.     

Kinetics of the dehydrogenation of ethylbenzene to styrene over unpromoted and K-promoted model iron oxide catalysts

The dehydrogenation of ethylbenzene to styrene over unpromoted and potassium-promoted model iron oxide catalysts has been studied using ultrahigh vacuum techniques in conjunction with elevated pressure reaction kinetics. Model iron oxide catalysts were prepared by oxidizing a polycrystalline Fe sample that was subsequently dosed with metallic potassium. At 875 K the unpromoted catalyst exhibited a turnover frequency of 5×10^–4 molecules/ site s and an activation energy of 39 kcal/mol, both in excellent agreement with the results found for an analogous iron oxide powder catalyst. Potassium promotion increased the turnover frequency to 1.0×10^–3 molecules/site s and lowered the activation energy to 36 kcal/mol for the dehydrogenation reaction. Similarities between the activation energies on the unpromoted and promoted catalysts indicate that the active site is the same on both catalysts. Creation of the active site was dependent upon the formation of an Fe³⁺ metastable species, consistent with the formation of a KFeO₂ phase, upon the addition of potassium.     

The Balance Between Reactivity and Stability of Modified Oxide Surfaces Illustrated by the Behavior of Sulfated Zirconia Catalysts

The stability of a series of sulfated zirconia catalysts, promoted with up to 2 wt% iron or manganese, in their calcined state was investigated. Phase composition, nature of surface sulfate species, degree of hydroxylation, and butane isomerization activity changed during aging over months in various atmospheres and during milling. The metastability of small oxide particles is discussed, including literature data on alumina, titania and other oxides. Catalytically active fractions of a material easily transition into more stable, less active forms.     

The influence of alkali metals on the activity of supported ruthenium catalysts for the water-gas shift reaction

This paper presents the results of the studies on the influence of alkali metals on the activity of ruthenium catalysts, which were supported on the products of α- and δ-iron oxide-hydroxide calcination. Modification of these supports with alkali metals, in particular potassium, rubidium and cesium, prior to deposition of ruthenium was found to increase the activity of Ru/Fe₂O₃ catalysts in the water-gas shift reaction. It was also established that the activity and stability of catalysts prepared on iron oxide obtained from α-FeOOH increased when the latter was modified with sodium ions. The favourable effect of sodium on the activity of the catalysts was shown to appear at a certain proportion of the base to the active component, i.e. ruthenium. This revised version was published online in July 2006 with corrections to the Cover Date.     

ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> Mixed Oxides Xerogel and Aerogel as Solid Acid Catalysts for Solvent Free Isomerization of α-Pinene and Dehydration of 4-Methyl-2-Pentanol

Abstract  

Sulfated and non-sulfated ZrO₂–SiO₂ mixed oxide xerogel and aerogel samples having varied Zr/Si molar ratio were evaluated as solid acid catalysts for the isomerization of α-pinene and dehydration of 4-methyl-2-pentanol. Sulfation resulted into enhancement in the catalytic activity of both xerogel and aerogel samples towards the studied reactions. For example, sulfated catalysts showed 86–98% conversion of α-pinene and 8–35% conversion of 4-methyl-2-pentanol. The selectivity data for camphene and limonene indicated the requirement of moderate acidity. The correlation with cyclohexanol dehydration showed that isomerization of α-pinene is a Br?nsted acid catalyzed reaction. The relationship of 4-methyl-2-pentanol conversion with acid site density and sulfur per unit area was found to be linear.     

Solid superacid catalysis: kinetics of butane isomerization catalyzed by a sulfated oxide containing iron,manganese, and zirconium

Kinetics of the isomerization ofn-butane and of isobutane catalyzed by sulfated zirconium oxide containing 1.5 wt% Fe, 0.5 wt% Mn, and 4.0 wt% sulfate at 60°C are well represented by a Langmuir-Hinshelwood equation accounting for the reaction equilibrium and for adsorption of both butanes. The adsorption equilibrium constants estimated from the kinetics data are nearly the same for the two butanes. The form of the rate equation and the observation that disproportionation accompanies isomerization suggest that the reaction proceeds via a C_g intermediate.     

n-Butane isomerization over transition metal-promoted sulfated zirconia catalysts: effect of metal and sulfate content

n-Butane isomerization has been investigated over transition metal-promoted sulfated zirconia catalysts. Fe alone was a more efficient promoter than Mn and Cr, and mixtures of Fe–Mn, Fe–Cr, and Fe–V. Promotion of a commercial sulfated zirconia (4.8% sulfate) with iron amounts in excess of 2% depressed the conversion and increased the deactivation rate. Increasing reaction temperatures improved the conversion and decreased the induction period. At 70°C and above, the induction period was suppressed. The influence of activation temperature was studied over a Fe-sulfated zirconia catalyst (with 2% Fe and 4.8% SO₄²⁻ pre-calcined at 600°C). The best conversion was achieved when the catalyst was activated at 350°C in air. This temperature was apparently sufficient to generate the redox sites active at low reaction temperature. Activation in flowing helium depressed the catalytic activity and increased the induction period. The sulfate content had a significant effect on the catalyst performance. For 2% Fe-promoted zirconia, a maximum conversion was found for 7.5% SO₄²⁻, probably related with a better balance (or synergism) of the redox and acid sites involved in a bimolecular mechanism. The time required to reach a maximum of conversion (induction period) decreased with increasing total acidity, i.e. with sulfate content. The series of catalysts with different amounts of sulfate has been characterized by X-ray diffraction, nitrogen adsorption–desorption isotherms, TGA, ammonia-TPD, DRIFT, Raman, and X-ray photoelectron spectroscopy.     

Kinetics and catalysis of the reaction of coal char and steam

The kinetics and catalysis of the reaction between steam and two different coal chars were investigated in a small fixed-bed reactor. Atmospheric pressure and temperatures between 600 and 850 °C were used. Various possible catalysts were tested, and the effect of catalyst concentration was examined. Of the catalysts used, potassium carbonate was the most effective. It was followed in order of decreasing effectiveness by sodium carbonate, lithium carbonate, potassium chloride, sodium chloride, and copper (II) oxide. Calcium oxide and iron (III) oxide were totally ineffective. The catalysts were more effective at higher concentration. Also, addition of 10% potassium carbonate to the coal char lowered the apparent activation energy of the reaction from 254.2 to 144.5 kJ/mol and the frequency factor from 2.41 × 10⁸ to 1.32 × 10⁴ s^?1. The water-gas shift reaction reached equilibrium during gasification in the presence of alkali-metal carbonates and the product gas was primarily carbon dioxide and hydrogen. Without catalyst present, the water-gas shift reaction was far from equilibrium.     

云母氧化铁珠光颜料的制备

以硫酸法钛白副产物硫酸亚铁为原料，制得云母氧化铁，然后用三氯化钛包覆云母氧化铁，制得各色云母氧化铁珠光颜料。讨论了云母氧化铁和云母氧化铁珠光颜料的生成条件对产品性能的影响。确定了最佳的反应条件。     

Neopentane cracking catalyzed by iron- and manganese-promoted sulfated zirconia

Cracking of neopentane was catalyzed by a sulfated oxide of zirconium promoted with iron and manganese. Reaction at 300–450°C, atmospheric pressure, and neopentane partial pressures of 0.00025–0.005 bar gave methane as the principal product, along with C₂ and C₃ hydrocarbons, butenes, and coke. The order of reaction in neopentane was determined to be 1, consistent with a monomolecular reaction mechanism and with the formation of methane andt-butyl cations; the latter was presumably converted into several products, including only little isobutylene. At 450°C and a neopentane partial pressure of 0.005 bar, the rate of cracking at 5 min onstream was 5×10^–8 mol/(g of catalyst s). Under the same conditions, the rates observed for unpromoted sulfated zirconia and USY zeolite were 3×10^–8 and 6×10^–9 mol/ (g of catalyst s), respectively. The observation that the promoted sulfated zirconia is not much more active than the other catalysts is contrasted to published results showing that the former catalyst is more than two orders of magnitude more active than the others forn-butane isomerization at temperatures <100°C. The results raise a question about whether the superacidity attributed to sulfated zirconia as a low-temperature butane isomerization catalyst pertains at the high temperatures of cracking.     

Interaction of hydrogen and n‐pentane with sulfated zirconia

Interaction of hydrogen with sulfated zirconia catalysts was studied in situ at 473 K. Interaction of hydrogen with the sample evacuated at 673 K leads to the formation of new hydroxyl groups (wide bands near 3330 cm⁻¹) and water (1620 cm⁻¹). In the case of the sample evacuated at 873 K, SOH groups (3660 cm⁻¹) and zirconium hydrides (1555 cm⁻¹) form. Adsorption of n‐pentane on sulfated zirconia catalysts in the range of 253–383 K was studied. It was shown that hydrides and protonated cyclopentadienes form at low temperatures. At higher temperatures, aromatic compounds are formed mainly. The reaction mechanism is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of iron on the properties of sulfated zirconia

Sulfated zirconia has found several industrial applications, mainly for catalyzing reactions which require acidic sites. In order to control the properties of this solid, the effect of iron on the sulfated zirconia properties was studied in this work. Samples with different iron to zirconium molar ratios were prepared by the sol–gel method, followed by sulfation and characterization by several techniques. It was found that all iron ions go into zirconia when Fe/Zr ≤ 0.4. However, when higher amounts of iron (Fe/Zr ≥ 0.8) are added, hematite is segregated. Different phases can be obtained depending on the iron content and on the sulfur presence. Iron increases the specific surface areas of both sulfated and pure zirconia but does not affect the incorporation of sulfate groups as compared to pure zirconia. Iron also makes the solids thermally more stable and modifies the sulfated zirconia surface creating acidic sites with medium strength. Therefore, it is possible to control the acidity of the solid doping the sulfated zirconia with iron. All these changes are very useful for catalytic applications.     

Catalytic liquefaction of coal with supercritical water/CO/solvent media

This paper describes studies of the catalytic activity of cobalt molybdenum sulphide, cobalt molybdenum oxide, iron sulphate, iron acetate dibasic and H₂S during the reaction between supercritical CO and water, and during liquefaction of coal using supercritical CO-water-solvent mixtures. The kinetics of the water gas shift reaction was studied first and was found to be first order in all the catalysts studied. The activity of the catalysts decreased in the following order: cobalt molybdenum sulphide > cobalt molybdenum oxide > iron salts. The presence of toluene, tetralin, and THQ decreased the CO conversion on the cobalt catalysts but increased CO conversion in the presence of iron salts catalysts. Moderate coal conversion of toluene soluble products (25%–35%) were obtained in the presence of supercritical water and water/CO mixtures. Addition of organic solvents to a supercritical water/CO medium increased conversion of toluene soluble products to 70–80% for THQ, to 50–60% for tetralin, and to 35–40% for toluene. Addition of H₂S to the solvent/water/CO medium increased conversion to toluene soluble products even further. In the presence of H₂S/solvent/water/CO, the presence of catalysts had only a minor effect on coal conversion and were not required to achieve high coal conversions. The optimum operating conditions for an Illinois No. 6 coal were obtained using a H₂S/THQ/CO/water medium at 3600 psi, and 400 °C. Higher conversions were attained with a subbituminous Wyodak coal. These studies clearly demonstrate that high conversions to soluble products can be attained using a supercritical water/Co/solvent medium.     

Catalytic decomposition of biomass tars with iron oxide catalysts

Catalytic gasification of wood (Cedar) biomass was carried out using a specially designed flow-type double beds micro reactor in a two step process: temperature programmed non-catalytic steam gasification of biomass was performed in the first (top) bed at 200–850 °C followed by catalytic decomposition gasification of volatile matters (including tars) in the second (bottom) bed at a constant temperature, mainly 600 °C. Iron oxide catalysts, which transformed to Fe₃O₄ after use possessed catalytic activity in biomass tar decomposition. Above 90% of the volatile matters was gasified by the use of iron oxide catalyst (prepared from FeCl₃ and NH_3aq) at SV of 4.5 × 10³ h^?1. Tar was decomposed over the iron oxide catalysts followed by water gas shift reaction. Surface area of the iron oxide seemed to be an important factor for the catalytic tar decomposition. The activity of the iron oxide catalysts for tar decomposition seemed stable with cyclic use but the activity of the catalysts for the water gas shift reaction decreased with repeated use.     

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.     

Catalytic acylation of aromatics with carboxylic anhydrides over sulfated zirconia

Two sulfated zirconia samples have been synthesized using different preparation procedures. Textural and acid properties of these catalysts have been characterized and compared with commercial zeolite Hβ by means of nitrogen low-temperature adsorption, temperature-programmed desorption of ammonia and microcalorimetry. The two sulfated zirconias proved to be appropriate catalysts for acylations of aromatic compounds containing electron donating substituents, e.g., for syntheses of several aromatic ketones. This revised version was published online in June 2006 with corrections to the Cover Date.     

Catalytic decomposition of methylene chloride by sulfated oxide catalysts

Catalytic decomposition of methylene chloride in air with a concentration of 959 ppm and temperature ranges from 160 to 275°C were studied. Three different sulfated oxide catalysts, TiO₂(SO₄), ZrO₂(SO₄), CeO₂(SO₄) were prepared and their activities and selectivities were measured. The catalytic activity decreased in the order: TiO₂(SO₄) > ZrO₂(SO₄) > CeO₂(SO₄). Complete catalytic decomposition of methylene chloride was achieved at low temperature (275°C) over a sulfated titanium dioxide catalyst. The oxygen adsorption (pick-up) and the acidity values of three catalysts showed the same trend as their activities. The presence of water (2% in volume) in the feed stream reduced the activities remarkably and raised the activation energies for the decomposition reaction. The selectivities among all three catalysts were similar, with HCl, CO and CO₂ being the products. A bifunctional catalyst comprising sulfated titanium dioxide with copper oxide was developed to improve the selectivity of catalytic oxidation of methylene chloride towards carbon dioxide.     

Reactions of conjugated fatty acids. III. Kinetics of the Diels-Alder reaction

Summary The kinetics of a Diels-Alder-type reaction between diethylazodicarboxylate andt,t-9,11-octadecadienoic acid has been studied in various solvent systems and with acidic catalysts. The rate of the reaction was found to vary as follows: a) the reaction rate is faster in polar solvents than in nonpolar solvents; b) addition of acidic catalysts to nonpolar solvents increases the rate of the reaction, and acidic catalysts appear to have no effect on the rate of reaction in polar solvents; c) when compatibility can be maintained, addition of water to polar solvent systems appears to increase the reaction rate in proportion to the amount of water added. The reaction follows second-order or pseudo second-order kinetics. Probably it is more complex than the over-all reaction kinetics indicate. Certain reactions were studied at two temperatures, and information on activation energy of the reaction has been obtained. Presented at fall meeting, American Oil Chemists’ Society, Philadelphia, Pa., Oct. 10–12, 1955.     

Utilization of waste containing rare-earth elements

The sulfuric acid method of dissolving metallic waste containing rare-earth elements and iron with the obtainment of a sulfate rare-earth concentrate and an iron-containing solution is described. The distribution of the components into solid and liquid reaction products has been studied. The conditions of the conversion of rare-earth sulfate elements into hydroxide and fluoride compounds have been found. The principal possibility of utilizing iron-containing sulfuric acid filtrates with the obtainment of iron oxide pigments of a wide range of colors, catalysts, and coating components of welding electrodes is shown.