SHS-produced β-sialons as supports for oxidation catalysts

SHS-produced β-sialons Si_6−z Al _z O _z N_8−z (z = 1, 3, 4) were tested as supports for oxidation catalysts comprising of unary, binary or ternary mixtures of transition metal (Cr, Mn, Fe, Co, Ni, Cu) oxides and also KMnO₄ and K₂Cr₂O₇. In oxidation of CO and propane (C₃H₈), the highest activity was exhibited by the catalysts based on cobalt oxides. Suggested are some methods for activation of the above catalysts.      

Titania supported Co-Mn-Al oxide catalysts in total oxidation of ethanol

Catalytic activity of the Co-Mn-Al mixed oxide catalysts (Co:Mn:Al molar ratio of 4:1:1) supported over titania was examined in total oxidation of ethanol. The prepared catalysts were characterized by chemical analysis (AAS), surface area measurements, and temperature programmed techniques (TPR, TPD). In ethanol oxidation, the catalysts activity gradually increased with increasing active phase content. Low concentration of Co-Mn-Al oxides in the catalyst negatively affected formation of reaction byproducts: carbon monoxide production steeply increased when Co + Mn metals concentration were lower than 5 wt.%. On the other hand, formation of the second main reaction intermediate, acetaldehyde was limited, when acidity of the catalyst was not high, i.e. concentration of Co-Mn metals over titania was low.     

Investigation of palladium interaction with cerium oxide and its state in catalysts for low-temperature CO oxidation

Palladium catalysts supported on nanosized CeO₂ supports were synthesized by different methods. The catalysts showed high low-temperature activity (LTA) in CO oxidation. The synthesized palladium–ceria catalysts for low-temperature CO oxidation were investigated by a complex of physicochemical methods, and their catalytic performance was determined in the light-off regime. It was shown using high-resolution transmission electron microscopy (HRTEM) and EDX microanalysis that the catalysts with high LTA are characterized by exceptionally high dispersity of palladium on the surface of the supports. Two different states of palladium were observed by XPS. They correspond to the surface interaction phases (SIPs) as Pd_xCeO_2−δ and small metal clusters (<10 Å). According to diffraction images obtained by HRTEM, the latter have flattened shape due to epitaxial binding between (1 1 1) facets of palladium and CeO₂. Two types of CO adsorption sites (Pd²⁺ and Pd⁰) were distinguished by FTIR. They can be attributed to SIP (Pd²⁺) and palladium in flat metal clusters (Pd^δ+ and Pd⁰). The drop of LTA in CO oxidation is related to the loss of the palladium chemical interaction with the surface of the support and palladium sintering to form PdO nanoparticles. The formation of PdO particles is stimulated by crystallization of CeO₂ particle surface due to the calcination of support at temperatures above 600 °C. The XPS, HRTEM and FTIR data give reliable evidence that PdO particles are not responsible for LTA in CO oxidation.In this work, the structure of the active sites consisting of two phases: atomically dispersed palladium within the SIP and palladium metal nanoclusters is proposed. The catalyst pretreatment in hydrogen was found to improve significantly its catalytic (LTA) properties. The effect of the hydrogen pretreatment was supposed to be related to the formation of hydroxyl groups and their effect on the electronic and geometrical state of the surface active sites and their possible direct participation in CO oxidation.     

Total oxidation of ethanol and propane over Mn-Cu mixed oxide catalysts

Mn-Cu mixed oxides were prepared by co-precipitation varying the aging time for 4, 18 and 24 h. The catalytic performance in propane and ethanol total oxidation on these samples was better than on Mn₂O₃ and CuO pure oxides. The increase of the aging time enhanced the activity and the selectivity to CO₂. The nature and disposition of the phases forming the catalytic system as well as the effect of the precipitated aging time was determined by means of specific surface area measurements, X-ray diffractometry (XRD), infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and temperature programmed desorption of oxygen (O₂-TPD). The catalytic behaviour seems related to the existence of a Cu_1.5Mn_1.5O₄ mixed phase and the easier reducibility of the catalysts.     

Carbon fibres as supports for transition metal catalysts in hydrocarbon oxidation reactions

The potential use of carbon fibres as catalyst supports for transition metal oxides in the complete oxidation of 1-butene and ethane by nitrous oxide has been assessed. The extent of catalyst activity was clearly related to the preparative procedures adopted and the activity sequence shown by the fibre-supported materials in 1-butene oxidation matched that measured on bulk oxides in the same reaction, namely: Co₂O₃ >CuO >NiO >Mn₂O₃.     

Vanadium oxide catalysts on structured microfiber supports for the selective oxidation of hydrogen sulfide

Vanadium(V) oxide catalysts for the selective oxidation of hydrogen sulfide to sulfur on a nonporous glass-fiber support with a surface layer of a porous secondary support (SiO₂) are studied. The catalysts are obtained by means of pulsed surface thermosynthesis. Such catalysts are shown to have high activity and acceptable selectivity in the industrially important region of temperatures below 200°C. A glass-fiber catalyst containing vanadium oxide (10.3 wt % of vanadium) in particular ensures the complete conversion of H₂S at a temperature of 175°C and a reaction mixture hourly space velocity (RMHSV) of 1 cm³/(g_cat s) with a sulfur yield of 67%; this is at least 1.35 times higher than for the traditional iron oxide catalyst. Using a structured glass-fiber woven support effectively minimizes diffusion resistance and greatly simplifies the scaleup of processes based on such catalysts. Such catalysts can be used for the cleansing of tail gases from Claus units and in other processes based on the selective oxidation of H₂S.     

Catalytic wet air oxidation of stearic acid on cerium oxide supported noble metal catalysts

Catalytic wet air oxidation (CWAO) of stearic acid was carried out in a batch reactor over noble metals (Ru, Pd, Pt, Ir) catalysts supported on ceria. The influence of reaction conditions such as temperature, oxygen pressure and stearic acid concentration were investigated. The reaction occurs via a complex mechanism. The molecule of stearic acid can be oxidized by successive carboxy–decarboxylation (R_nCOOH + O₂ → R_n−1COOH +CO₂) yielding essentially CO₂ (route A). It may also be oxidized after CC bond rupture within the alkyl chain, which gives rise to significant amounts of acetic acid besides CO₂ (route B). Pt/CeO₂ is a very active catalyst in the conversion of stearic acid and extremely selective to carbon dioxide (route A), while the mechanism via CC bond splitting is much more marked on Ru/CeO₂. The catalyst characterization indicates that both noble metal and CeO₂ particles remain stable during the reaction.     

Selective gas-phase oxidation of ethanol by molecular oxygen over oxide and gold-containing catalysts

The rapid increase in the production rates of bioalcohols (in particular bioethanol) gives grounds for regarding them as a promising renewable chemical raw material for obtaining a number of useful organic synthesis products. In order to develop new green technologies for processing ethanol into value-added products, a systematic study of selective conversion of ethanol under conditions of oxidation by molecular oxygen in the flow gas-phase mode over such catalysts as V₂O₅-TiO₂, mixed oxides V-Mo-Te, V-Mo-Nb and V-Mo-Te-Nb, and gold supported on oxide supports is performed. The catalytic activity is determined under conditions of temperature-programmed reaction under atmospheric pressure using a gas mixture (composition, mol %: EtOH, 2; O₂, 18; He, 80) at a hourly space velocity of the mixture of 3600 h^?1 over 0.25–0.5 mm catalyst fraction. The possibility of the efficient conversion of ethanol to products of partial oxidation and accompanying conversions (acetaldehyde, 90–99% yield; acetic acid, 92-98% yield; productive capacity >3 g g-cat^?1 h^?1) and acetic acid-ethyl acetate mixtures (1: 1 ratio, total yield >90%) in a number of cases is demonstrated.     

Nafion-H as catalyst for isobutane/2-butene alkylation compared with a cerium exchanged Y zeolite

A solid superacidic Nafion-H polymer was examined as a catalyst for isobutane/2-butene alkylation and compared with a cerium-exchanged Y zeolite. Both catalysts demonstrate initial alkylation activity with rapid decrease in alkylation selectivity. The total product distributions were found to be significantly different after three hours of reaction. Nafion-H showed less selectivity towards iso-octanes, but formed relatively more 2,2,4-trimethylpentane. The differences between the two catalysts suggest dissimilar favoured reaction mechanisms.     

Gallium oxide promoted zeolite catalysts for oxidehydrogenation of propane

Novel gallium-containing catalysts for oxidehydrogenation of propane, based on zeolite Beta, ZSM-5 and ferrierite, have been prepared and characterised by scanning electron microscopy, IR, MAS NMR and Raman spectroscopies. The catalytic properties of zeolitic matrixes with B, Al, and both ions at tetrahedral sites have been studied. Transformation of propane on pure zeolites and promoted with gallium (III) oxide depended on the structure of the matrix, its morphology and the type of cations occupying zeolite framework sites. Formation of new hydroxyl groups has been evidenced for some MFI zeolites promoted with Ga₂O₃.     

Mesoporous Co-Al oxide nanosheets as highly efficient catalysts for CO oxidation

We report mesoporous Co-Al oxide nanosheets (Co_xAl-Ns, where x denotes the Co/Al ratio in the samples) prepared by calcination of CoAl-hydrotalcite and subsequent alkaline treatment. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements show that the prepared Co-Al oxide nanosheets (Co_xAl-Ns) are very thin (10–15 nm) and exhibit high mesoporosity (3–5 nm). Catalytic CO oxidation tests reveal that the Co_xAl-Ns exhibit excellent catalytic performances at relatively low temperatures: for example, the Co_2.5Al-Ns catalyst could achieve 99% CO conversion at −98°C. Kinetic studies and experimental investigations indicate that the high activity of the Co_2.5Al-Ns sample is strongly related to the abundance of active sites associated with the large Brunauer–Emmett–Teller surface area. The Co_2.5Al-Ns catalyst also achieves full conversion of CO in tests performed with a gas mixture simulating automobile exhaust gas at 200°C. After loading the Co_2.5Al-Ns on a porous ceramic substrate, the obtained Co_2.5Al-Ns/PC shows high activity and stability in CO oxidation process. These features are potentially important for future industrial applications of these catalysts.     

Novel supports for nickel-based catalysts for the partial oxidation of methane

Zirconia-supported nickel catalysts with different amounts of aluminum (Al/Zr = 0.2, 1 and 2) were studied in this work in order to find alternative supports for nickel-based catalysts for the partial oxidation of methane. This reaction is a promising route for producing hydrogen and syngas for different applications. Samples were prepared by precipitation and impregnation techniques, characterized by several techniques and evaluated in the partial oxidation of methane in the range of 450–750 °C and 1 atm. It was found that aluminum affects the textural and catalytic properties of zirconia-supported nickel catalysts. The tetragonal phase of zirconia was stabilized by aluminum and gamma-alumina was also found in the aluminum-richest samples. Aluminum increased the porosity and the specific surface area of the solids. The catalytic activity also increased with the amount of aluminum in solids probably due to the stronger interaction of nickel with the support, which slowly generates active sites during the reduction step. The methane conversion and hydrogen selectivity increased with temperature, indicating no deactivation. The hydrogen to carbon monoxide molar ratio decreased due to aluminum but was not significantly affected by temperature. The coke produced was not harmful to the catalysts and aluminum affected its amount, although no simple relationship was found between these parameters. The most promising catalyst was the sample with aluminum to zirconium molar ratio of 2, which showed high activity and hydrogen selectivity and was stable under the reaction condition.     

Evaluation and characterization of Mn-Cu mixed oxide catalysts for ethanol total oxidation: Influence of copper content

Mixed oxides of manganese and copper with different wt% of copper have been prepared and evaluated in ethanol combustion. The co-precipitation method used for the synthesis of MnxCuy mixed oxides is adequate to obtain catalysts with excellent catalytic performance in combustion reactions. Catalysts were characterized by means of XRD, FT-IR, TPR and O₂-TPD. A small amount of copper prevents manganese oxide reaching a crystalline structure. This poor crystalline structure of manganese oxide may improve the existence of oxygen vacancies giving a best performance in ethanol combustion to CO₂. When the copper content increases, an extent of solid state reaction between Cu and Mn is favored and the partial oxidation of ethanol becomes more important. The incorporation of manganese into incomplete spinel structure diminishes CO₂ yield.     

Study of Y zeolite catalysts for coal tar hydro-cracking in supercritical gasoline

For coal tar hydrocracking process in supercritical gasoline, it requires a new catalyst with high activity under low temperature conditions to improve the light oil yield. The effects of Mo–Co–Y and Mo–Ni–Y series catalyst on the light oil yield were investigated in this paper, and the coke deposition on catalyst and catalyst stability were also investigated. Experimental results show that the Mo–Co–Pd–Y zeolite catalyst with a suitable Co/(Co+Mo) atom ratio and calcination temperature could maximize the light oil yield, and the acid amount of the catalyst is closely related to its activity. Coke deposition on the Mo–Co–Pd–Y zeolite catalyst is very little and the catalyst remains high activity within used time of 8 h.     

Novel efficient catalysts based on Ru or Pd oxide for selective liquid-phase oxidation of alcohols with nitrous oxide

Ru^IV–M and Pd^II–M (MCo^III, Fe^III and Mn^III) binary oxides supported on γ-alumina are demonstrated to be novel, active catalysts for selective liquid-phase oxidation of primary and secondary alcohols to, respectively, aldehydes and ketones with nitrous oxide under 10 bar N₂O pressure and 100 °C. The Ru and Pd catalysts have comparable activities but Ru ones are more selective, the Ru–Co system (Ru/Co=1:1) showing the best performance. Activated primary alcohols (benzyl and cinnamyl alcohol) and secondary alcohols give aldehydes or ketones with 100% selectivity at 95–100% conversion. Non-activated primary alcohols (e.g. 1-dodecanol) give aldehydes with some over-oxidation to acids; the latter is completely inhibited by adding a radical scavenger. The Ru–Co catalyst can be reused without loss of selectivity, although with a gradual decrease in its activity. Compared to the Ru–Co catalysed oxidation of alcohols with O₂ studied earlier, the oxidation with N₂O has the advantage of considerably higher selectivity, albeit occurring under higher pressures.     

Ceria-based oxides as supports for LaCoO3 perovskite; catalysts for total oxidation of VOC

Supported LaCoO₃ perovskites with 10 and 20 wt.% loading were obtained by wet impregnation of different Ce_1−xZr_xO₂ (x = 0–0.3) supports with a solution prepared from La and Co nitrates, and citric acid. Supports were also prepared using the “citrate method”. All materials were calcined at 700 °C for 6 h and investigated by N₂ adsorption at −196 °C, XRD and XPS. XRD patterns and XPS measurements evidenced the formation of a pure perovskite phase, preferentially accumulated at the outer surface. These materials were comparatively tested in benzene and toluene total oxidation in the temperature range 100–500 °C. All catalysts showed a lower T₅₀ than the corresponding Ce_1−xZr_xO₂ supports. Twenty weight percent LaCoO₃ catalysts presented lower T₅₀ than bulk LaCoO₃. In terms of reaction rates per mass unit of perovskite calculated at 300 °C, two facts should be noted (i) the activity order is more than 10 times higher for toluene and (ii) the reverse variation with the loading as a function of the reactant, a better activity being observed for low loadings in the case of benzene. For the same loading, the support composition influences drastically the oxidative abilities of LaCoO₃ by the surface area and the oxygen mobility.     

Cobalt molybdenum oxide catalysts for selective oxidation of cyclohexane

Oxidation of cyclohexane has been carried out using molecular oxygen over cobalt molybdenum oxide (CoMoO₄) catalysts in solvent free conditions. The catalysts were prepared using citrate method with three different molar ratios of Co:Mo, 1:1, 1:2, and 2:1 along with individual oxides for comparative studies. While all the catalysts showed significant activity and selectivity, CoMoO₄ with 1:1 ratio showed the best performance compared to the others with a conversion of 7.38%, with selectivity to cyclohexanol and cyclohexanone (KA oil) of 94.3%, in 1 h. The performance of the catalyst, has been studied as a function of oxygen pressure, reaction temperature, and catalyst loading. It was observed that the catalyst deactivates during the course of the reaction. The reasons for deactivation and methods for restoring the activity have been studied. A kinetic model is presented that captures the complex kinetics and matches well with the experimental data. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4384–4402, 2016     

Immobilized iron Schiff base histidine complexes on Al-MCM-41 and zeolite Y as catalyst for oxidation of cycloalkanes

Iron complexes of N-salicylidene-l-histidine with or without bipyridine ligand immobilized on Al-MCM-41 and zeolite Y designated as Fe(sal-l-his)(bipy)complex/Al-MCM-41 or Fe(sal-l-his)complex/Al-MCM-41 and Fe(sal-l-his)(bpy)complex/Y or Fe(sal-l-his)complex/Y respectively, were prepared and characterized by X-ray powder diffraction (XRD), FT-IR, N₂ adsorption/desorption and chemical analysis techniques. Fe(sal-l-his)/Al-MCM-41 and Fe(sal-l-his)(bipy)complex/Al-MCM-41 were found to successfully catalyze the oxidation of cyclohexane, methyl cyclohexane, cyclooctane and adamantane with H₂O₂. The oxidation results and promising catalytic behavior of Fe(sal-l-his)(bipy)complex/Al-MCM-41 for oxidation of cyclooctane with 90 % conversion and excellent selectivity toward the formation of cyclooctanone will be discussed in this presentation.     

Mixtures of room temperature ionic liquid/ethanol solutions as electrolytic media for cerium oxide thin layer electrodeposition

A cerium oxide thin layer was electrodeposited onto stainless steel, using mixed room temperature ionic liquid (the 1-methyl-3-butylimidazolium bis(trifluoromethyl sulfonyl)imide)/ethanol solutions, as electrolytic medium. The hydrophobic ionic liquid content is one of the main parameters in the morphology control influencing the ceria growth rate and crystallinity. Micro-nano structural properties and electrical behaviour are presented, using XRD, SEM/EDS and impedance spectroscopy, as a function of electrodeposition conditions.     

Novel utilization of mesoporous molecular sieves as supports of cobalt catalysts in Fischer–Tropsch synthesis

Mesoporous molecular sieves (MCM-41 and SBA-15) with different pore diameters have been studied as supports of high loading of Co catalysts, and the performances in FT synthesis have been examined with a fixed bed stainless steel reactor at 2.0 MPa for the purpose of efficient production of C₁₀–C₂₀ fraction as the main component of diesel fuel. The method of exchanging template ions in uncalcined MCM-41 with Co²⁺ ions is effective for holding 10–20% Co within the mesopores while keeping the structure regularity of MCM-41 to some extent, compared with the conventional impregnation method using calcined MCM-41. At 523 K, CO conversion and selectivity to C₁₀–C₂₀ hydrocarbons are both higher at larger loading of 20% Co for the exchanged catalysts with pore diameters of 2.7–2.9 nm. When four kinds of 20% Co/SBA-15 with the diameters of 3.5–13 nm, prepared by the impregnation method using an ethanol solution of Co acetate, are used in FT synthesis at 523 K, the catalyst with the diameter of 8.3 nm shows the largest CO conversion, which is higher than those over MCM-41 supported Co catalysts. At a lower temperature of 503 K, however, the acetate-derived Co is almost inactive. In contrast, the use of Co nitrate alone or an equimolar mixture of the acetate and nitrate as Co precursor drastically enhances the reaction rate and consequently provides high space–time yield (260–270 g C/kg_cat h) of C₁₀–C₂₀ hydrocarbons. The X-ray diffraction and temperature-programmed reduction measurements show that the dependency of the catalytic performance of 20% Co/SBA-15 on its precursor originates probably from the differences in not only the reducibility of the calcined catalyst but also the dispersion of metallic Co. Catalyst characterization after FT synthesis strongly suggests the high stability of the most effective Co/SBA-15 in the dispersion and reducibility of the oxide species and in the mesoporous structure.