Metal–organic framework MOF-199-catalyzed direct and one-pot synthesis of thiols,sulfides and disulfides from aryl halides in wet polyethylene glycols (PEG 400)

A highly porous metal–organic frame work Cu₃ BTC₂ (copper(II)-benzene-1,3,5-tricarboxylate) that is known as MOF-199 was synthesized from the reaction of 1,3,5-benzenetricarboxylic acid and Cu(OAc)₂·H₂O by a solvothermal method and characterized by several techniques including FT-IR, XRD, EDX and scanning electron microscopy. The MOF-199 used as an efficient catalyst for one-pot synthesis of thiols by domino reactions of aryl halides and thiourea, and subsequently conversion to aryl alkyl sulfides and diaryl disulfides in polyethylene glycols (PEGs). A variety of aryl alkyl sulfides can be obtained in good to excellent yields in a relatively short reaction time and in the presence of the trace amount of catalyst. Also, the catalyst can be separated from the reaction mixture by decanting, and be reused without significant degradation in catalytic activity.     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

ZnO/Cr2O3 catalyst for reverse-water-gas-shift reaction of CAMERE process

The stability and the activity of Fe₂O₃/Cr₂O₃ and ZnO/Cr₂O₃ catalysts were examined for a reverse-watergas-shift reaction (RWReaction). The initial activities of those catalysts were quite high so that the conversion reached close to equilibrium. The activity of Fe₂O₃/Cr₂O₃ catalyst decreased from 33.5 to 29.8% during the RWReaction for 75 h at 873 K with GHSV (ml/gcat · h) of 100,000. Moreover, the coke formation on the Fe₂O₃/Cr₂O₃ catalyst caused clogging in the RWReactor of the CAMERE process. On the other hand, the ZnO/Cr₂O₃ catalyst showed no coke formation and no deactivation for the RWReaction at 873 K with GHSV (ml/gcat · h) of 150,000. The ZnO/Cr₂O₃ was a good catalyst for the RWReaction of the CAMERE process.     

Effect of manganese on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

The effect of the addition of manganese to Cu/SiO₂ catalysts for cyclohexanol dehydrogenation reaction was investigated. At reaction temperature of 250 °C, the conversion and the selectivity to cyclohexanone were both increased with the addition of manganese to Cu/SiO₂ catalyst. However, as the reaction temperature was further increased, higher loading of manganese in Cu/SiO₂ catalyst led to a decrease in the conversion of cyclohexanol. Manganese in Cu/ SiO₂ catalyst decreased the reduction temperature of copper oxide, increased the dispersion of copper metal, and decreased the selectivity to cyclohexene. It was found that the dehydration of cyclohexanol to cyclohexene occurred on the intermediate acid sites of catalyst. At high Mn loading, catalyst surface was more enriched with manganese in used catalyst compared to that in freshly calcined or reduced catalyst, which may account for the sharp decrease of the conversion at high temperature of 390 °C. Upon reduction, copper manganate on silica was decomposed into fine particles of copper metal and manganese oxide (Mn₃O₄).     

Selective synthesis of mixed alcohols from syngas over catalyst Fe2O3/Al2O3 in slurry reactor

The Fe₂O₃/Al₂O₃ catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C₂₊ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H₂/CO = 2 and space velocity = 360 ml/g_cat h. The hydrogen temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system.     

Influence of homogeneous decane oxidation on the catalytic performance of lean NO x catalysts

Extensive homogeneous gasphase reactions were observed when decane was used as the hydrocarbon reductant for the selective reduction of NO _x . The catalytic performance of a SnO₂/CoO _x /Al₂O₃ catalyst was found to be strongly dependent on the extent of the homogeneous reaction in the precatalytic volume. The effect of the homogeneous reaction on the catalytic performance also depended on whether SO₂ was present in the feed. By filling the precatalytic volume with 25–35 mesh irregularly shaped quartz chips, gasphase reaction was suppressed significantly. This methodology was used to evaluate the inherent catalytic performance of SnO₂/CoO _x /Al₂O₃ and SnO₂/Al₂O₃ catalysts with decane as a reductant. It was found that in the absence of SO₂, SnO₂/Al₂O₃ was a better catalyst than SnO₂/CoO _x /Al₂O₃, but in the presence of 30 ppm of SO₂ the latter was a far better catalyst.     

Activity and stability of Cu/ZnO/Al2O3 catalyst promoted with B2O3 for methanol synthesis

The addition of B₂O₃ to a Cu/ZnO/Al₂O₃ catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The stability of the B₂O₃-containing Cu/ZnO/Al₂O₃ catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> xerogel support on hydrogen production by steam reforming of LNG over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> catalyst

An Al₂O₃-ZrO₂ xerogel (AZ-SG) was prepared by a sol-gel method for use as a support for a nickel catalyst. The Ni/AZ-SG catalyst was then prepared by an impregnation method, and was applied to hydrogen production by steam reforming of LNG. A nickel catalyst supported on commercial alumina (A-C) was also prepared (Ni/A-C) for comparison. The hydroxyl-rich surface of the AZ-SG support increased the dispersion of nickel species on the support during the calcination step. The formation of a surface nickel aluminate-like phase in the Ni/AZ-SG catalyst greatly enhanced the reducibility of the Ni/AZ-SG catalyst. The ZrO₂ in the AZ-SG support increased the adsorption of steam onto the support and the subsequent spillover of steam from the support to the active nickel sites in the Ni/AZ-SG catalyst. Both the high surface area and the well-developed mesoporosity of the Ni/AZ-SG catalyst improved the gasification of adsorbed surface hydrocarbons in the reaction. In the steam reforming of LNG, the Ni/AZ-SG catalyst showed a better catalytic performance than the Ni/A-C catalyst. Moreover, the Ni/AZ-SG catalyst showed strong resistance toward catalyst deactivation.     

Partial oxidation of ethanol over Pd/CeO2 and Pd/Y2O3 catalysts

The effect of the support nature on the performance of Pd catalysts during partial oxidation of ethanol was studied. H₂, CO₂ and acetaldehyde formation was favored on Pd/CeO₂, whereas CO production was facilitated over Pd/Y₂O₃ catalyst. According to the reaction mechanism, determined by DRIFTS analyses, some reaction pathways are favored depending on the support nature, which can explain the differences observed on products distribution. On Pd/Y₂O₃ catalyst, the production of acetate species was promoted, which explain the higher CO formation, since acetate species can be decomposed to CH₄ and CO at high temperatures. On Pd/CeO₂ catalyst, the acetaldehyde preferentially desorbs and/or decomposes to H₂, CH₄ and CO. The CO formed is further oxidized to CO₂, which seems to be promoted on Pd/CeO₂ catalyst.     

Effect of Ba Addition on Catalytic Activity of Pt and Rh Catalysts Loaded on γ-Alumina

The catalytic activity of Pt catalyst loaded on -alumina was improved by Ba addition in simulated automotive exhaust gases. On the other hand, the result of Rh catalyst was the opposite. From the results of the partial reaction orders in C₃H₆–O₂ reaction and TPR, it was concluded that the Ba addition to Pt catalyst suppressed the hydrocarbon chemisorption on the Pt catalyst and therefore allowed the catalytic reaction to proceed smoothly. On the other hand, Ba addition to Rh catalyst caused such a strong oxygen adsorption on Rh that rejected the hydrocarbon adsorption and suppressed the reaction.     

Synthesis of magnetic Pb/Fe3O4/SiO2 and its catalytic activity for propylene carbonate synthesis via urea and 1,2-propylene glycol

To facilitate the recovery of Pb/SiO₂ catalyst, magnetic Pb/Fe₃O₄/SiO₂ samples were prepared separately by emulsification, sol-gel and incipient impregnation methods. The catalyst samples were characterized by means of X-ray diffraction and N₂ adsorption-desorption, and their catalytic activity was investigated in the reaction for synthesizing propylene carbonate from urea and 1,2-propylene glycol. When the gelatin was applied in the preparation of Fe₃O₄ at 60°C and the pH value was controlled at 4 in the preparation of Fe₃O₄/SiO₂, the Pb/Fe₃O₄/SiO₂ sample shows good catalytic activity and magnetism. Under the reaction conditions of a reaction temperature of 180°C, reaction time of 2 h, catalyst percentage of 1.7 wt-% and a molar ratio of urea to PG of 1:4, the yield of propylene carbonate attained was 87.7%.     

Low-temperature Oxidation of Carbon Monoxide on Co/ZrO2

A 10%Co/ZrO₂ catalyst prepared by impregnation was tested for its activity for the oxidation of CO to CO₂ in excess oxygen. Activity tests showed that conversion could be obtained at temperatures as low as 20 °C. Time-on-stream studies showed no loss of activity in these experiments, indicating that this catalyst is stable in the experimental oxidizing conditions. The activation energy for the CO to CO₂ oxidation reaction was calculated as E_a = 54 kJ/mol over this catalyst. Characterization of the material by thermogravimetric analysis, temperature-programmed techniques, X-ray photoelectron spectroscopy, and laser Raman spectroscopy indicate that Co₃O₄ is present on monoclinic ZrO₂ after the calcination of the catalyst.     

Partial oxidation of methane over ruthenium catalysts

The catalytic partial oxidation of methane with oxygen to produce synthesis gas was studied under a wide range of conditions over supported ruthenium catalysts. The microreador results demonstrated the high activity of ruthenium catalysts for this reaction. A catalyst having as little as 0.015% (w/w) Ru on Al₂O₃ gave a higher synthesis gas selectivity than a catalyst having 5% Ni on SiO₂. XANES measurements for fresh and used catalyst samples confirmed that ruthenium is reduced from ruthenium dioxide to ruthenium metal early during the experiments. Ruthenium metal is thus the active element for the methane partial oxidation reaction.     

A Highly Flexible Green Synthesis of 3,4,5-Substituted Furan-2(5H)-ones Using Nano-CdZr4(PO4)6 as Catalyst under Microwave Irradiation

A concise and efficient method for the synthesis of 3,4,5-substituted furan-2 (5H)-ones was achieved through a three-component reaction of amines, dialkyl acetylene dicarboxylate, and aromatic aldehydes using nano-CdZr₄(PO₄)₆ as catalyst under microwave irradiation. This method has several advantages such as, high efficiency, short reaction times, simple workup, and recyclability of the catalyst up to seven runs without considerable loss of activity.     

Improvement of Pt/ZrO2 by CeO2 for high pressure CH4/CO2 reforming

CH₄/CO₂ reforming over Pt/ZrO₂, Pt/CeO₂ and Pt/ZrO₂ with CeO₂ was investigated at 2 MPa. Pt/ZrO₂, which shows stable activity under 0.1 MPa, and Pt/CeO₂ showed gradual deactivation with time at the high pressure. The deactivation was suppressed drastically on Pt/ZrO₂ with CeO₂ prepared by different impregnation order (co-impregnation of Pt and CeO₂ on ZrO₂, and consecutive impregnation of Pt and CeO₂ on ZrO₂). The amount of coke deposition was found insignificant and similar among all the catalysts (including Pt/ZrO₂ and Pt/CeO₂). Catalytic activity after the reaction for 24 h was in agreement with Pt particle size after the reaction for same period, indicating that the difference of the catalytic stability is mainly dependent on the extent of Pt aggregation through catalyst preparation, H₂ reduction, and the CH₄/CO₂ reforming. Pt aggregation and the amount of coke deposition were least pronounced on (Pt–Ce)/ZrO₂ prepared by impregnation of CeO₂ on Pt/ZrO₂ and the catalyst showed highest stability.     

Role of the surface state of Ni/Al2O3 in partial oxidation of CH4

The effect of gas phase O₂ and reversibly adsorbed oxygen on the decomposition of CH₄ and the surface state of a Ni/Al₂O₃ catalyst during partial oxidation of CH₄ were studied using the transient response technique at atmospheric pressure and 700°C. The results show that, when the catalyst surface is completely oxidized under experimental conditions, only a small amount of CO and H₂ can be produced from non‐selective oxidation of CH₄ by reversibly adsorbed oxygen which is more active in oxidizing CH₄ completely than NiO via the Rideal–Eley mechanism and both the conversions of CH₄ and O₂ and the selectivities to CO and H₂ are very low. Therefore, keeping the catalyst surface in the reduced state is the precondition of high conversion of CH₄ and high selectivities to CO and H₂. The surface state of the catalyst decides the reaction mechanism and plays a very important role in the conversions and selectivities of partial oxidation of CH₄. During partial oxidation of CH₄, no oxygen species but a small amount of carbon exists on the catalyst surface, which is favorable for maintaining the catalyst in the reduced state and the selectivity of CO. The results also indicate that direct oxidation is the main route for partial oxidation of CH₄, and the indirect oxidation mechanism is not able to gain dominance in the reaction under the experimental conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

SSITKA studies of the catalytic flameless combustion of methane

This paper presents results which were obtained for the flameless combustion of methane over the Pd(PdO)/Al₂O₃ catalyst by using the steady state isotopic transient kinetic analysis method. During the reaction switches between ¹⁶O₂/Ar/CH₄/He and ¹⁸O₂/CH₄/He were carried out. The obtained results indicate the presence of large amounts of oxygen as well as of intermediates leading to the formation of carbon dioxide on the surface of the palladium catalyst. Additionally, information was obtained proving that the complete oxidation of methane over Pd/Al₂O₃ catalyst proceeds according to the Mars and van Krevelen redox mechanism. With the increase of the reaction temperature there is an increase in the number of active centres on the Pd(PdO)/Al₂O₃ catalyst surface—a larger amount of oxygen from the lattice of the catalyst is accessible for the reaction of methane oxidation.     

Nano-CdZr4(PO4)6 as a reusable and robust catalyst for the synthesis of bis-thiazolidinones by a multicomponent reaction of aldehydes,ethylenediamine and thioglycolic acid

Nano-CdZr₄(PO₄)₆ has been used as an efficient catalyst for the preparation of bis-thiazolidinones by pseudo-five-component reaction of aldehydes, ethylenediamine and thioglycolic acid under reflux conditions in toluene. The present synthetic protocol has several advantages, such as simplicity, excellent yields, short reaction times, reusability of the catalyst and low catalyst loading.     

Activation of a Au/TiO2 Catalyst by Loading a Large Amount of Fe–Oxide: Oxidation of CO Enhanced by H2 and H2O

Catalytic activity of a 1 wt% Au/TiO₂ catalyst is markedly improved by loading a large amount of FeO_x, on which the oxidation of CO in excess H₂ is selectively promoted at temperature lower than 60 °C. Oxidation of CO with O₂ on the FeO_x/Au/TiO₂ catalyst is markedly enhanced by H₂, and H₂O moisture also enhances the oxidation of CO but its effect is not so large as the promotion by H₂. We deduced that activation of Au/TiO₂ catalyst by loading FeO_x is not caused by the size effect of Au particles but a new reaction path via hydroxyl carbonyl intermediate is responsible for the superior activity of the FeO_x/Au/TiO₂ catalyst.     

A study of the oxidative coupling of methane over SrO-La2O3/CaO catalysts by using CO2 as a probe

20%SrO-20%La₂O₃/CaO catalyst (SLC-2), prepared by impregnation, has shown 18% CH₄ conversion and 80% C₂-selectivity for the oxidative coupling of methane (OCM) at 1073–1103 K with CH₄O₂ molar ratio=91 and total flow rate of 100 ml/min. Addition of SrO onto La₂O₃/CaO (LC) catalyst strengthens the surface basicity and leads to an increase in CH₄ conversion and C₂-selectivity. Meanwhile, the reaction temperature required to obtain the highest C₂-yield increases with increasing SrO content. The formation of carbonate on the catalyst surface is the main reason for the deactivation of LC and SLC catalysts. If the amount of CO₂ added into the feed is appropriate and the reaction temperature is high enough, there is no deactivation at all. In such case, the added CO₂ will suppress the formation of CO₂ produced via the OCM reaction, therefore, improves the C₂-selectivity. The FT-IR spectra of CO₂ adspecies recorded at different temperatures show that CO₂ interacts easily with the catalyst surface to form different carbonate adspecies. Unidentate carbonate is the main CO₂ adspecies formed on the catalyst surface. On the LC catalyst surface, the unidentate carbonate was first formed on Ca²⁺ cations at room temperature. If the temperature is higher than 473 K, it will form on La³⁺ cations. On the SLC catalyst surface, if the temperature is lower than 573 K, only the unidentate carbonate formed on Ca²⁺ cations could be observed. When the temperature is higher than 673 K, it will then form on Sr²⁺ cations. This suggests that the unidentate carbonate can migrate on the LC and SLC catalyst surface on one hand, and on the other hand, that the surface composition of SLC catalysts is dynamic in nature. On the basis of both the decomposition temperatures of the carbonate species, and the temperature dependence of the value which is the difference of symmetric and asymmetric stretching frequencies of surface carbonates, the in situ FT-IR technique offered two approaches to measure the surface basicity of the SLC catalyst. The results thus obtained are in good agreement with that of CO₂-TPD. The role of the surface basicity of the SLC catalyst is also discussed.