Low Temperature Hydrolysis of Carbonyl Sulfide Using γ-Alumina Catalysts

The hydrolysis of COS using alumina as catalyst in the temperature range 10–80°C is described in detail. The rate of COS hydrolysis is found to be approximately first order in [COS] but is significantly inhibited with increasing [H₂O]. Addition of CO₂ is also found to have an inhibiting effect on the rate of hydrolysis, but no marked effect is observed when additional H₂S is present in the feedstock. The reaction in this temperature range is contrasted with the previous studies at higher temperatures and it is suggested that the reaction proceeds via reaction of adsorbed COS with surface hydroxyl groups on the alumina. Supporting evidence for this is provided from experiments in which water was not co-fed with COS, or the flow of water vapour was interrupted. In both cases, an initial increase in the rate of COS hydrolysis is observed. The rate of COS hydrolysis can be significantly enhanced by the addition of Fe, Co, Ni, Cu and Zn to the alumina.     

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.     

Influence of pH on the preparation of monometallic rhodium and platinum,and bimetallic RhodiumPlatinum Catalysts supported on γ-Alumina

¹⁹⁵PtNMR and Raman experiments indicated that H₂PtCl₆ adsorbed monomolecularly on the surface of alumina up to a loading of 1 μmol m⁻² during pore volume impregnation. Above this limit crystalline H₂PtCl₆ was formed during the subsequent drying procedure. Adsorption experiments showed that RhCl₃ exhibited the same behaviour, with an even larger monomolecular coverage. The coverage of both metal complexes was dependent on the pH during adsorption and decreased with decreasing pH, due to a shift in the bonding equilibrium between the metal complexes in solution and the complexes adsorbed on the support surface. Because of the acidic properties of RhCl₃ and H₂PtCl₆, the amounts of rhodium and platinum adsorbed during co-adsorption were smaller than during adsorption of the separate metal complexes. The reduction of RhCl₃+H₂PtCl₆ supported on Al₂O₃ was governed by mobile rhodium atoms and small bimetallic clusters. Large metal salt crystals smothered the reduction process.     

Silica-Supported Cobalt Catalysts for Fischer–Tropsch Synthesis: Effects of Calcination Temperature and Support Surface Area on Cobalt Silicate Formation

Cobalt silicate formation reduces the activity of the catalyst in Fischer–Tropsch synthesis (FTS). In this article, the effects of calcination temperature and support surface area on the formation of cobalt silicate are explored. FTS catalysts were prepared by incipient wetness impregnation of cobalt nitrate precursor into various silica supports. Deionized water was used as preparation medium. The properties of catalysts were characterized at different stages using FTIR, XRD and BET techniques. FTIR-ATR analysis of the synthesized catalyst samples before and after 48 h reaction identified cobalt species formed during the impregnation/calcination stage and after the reduction/reaction stage. It was found that in the reduction/reaction stage, metal-support interaction (MSI) added to the formation of irreducible cobalt silicate phase. Co/silica catalysts with lower surface area (300 m²/g) exhibited higher C₅₊ selectivity which can be attributed to less MSI and higher reducibility and dispersion. The prepared catalysts with different drying and calcination temperatures were also compared. Catalysts dried and calcined at lower temperatures exhibited higher activity and lower cobalt silicate formation. The catalyst sample calcined at 573 K showed the highest CO conversion and the lowest CH₄ selectivity.     

Simultaneous Synthesis of Dimethyl Carbonate and Poly（ethylene terephthalate） Using Alkali Metals as Catalysts

Dimethyl carbonate （DMC） and poly（ethylene terephthalate） was simultaneously synthesized by the transesterification of ethylene carbonate （EC） with dimethyl terephthalate （DMT） in this paper. This reaction is an excellent green chemical process without poisonous substance. Various alkali metals were used as the catalysts. The results showed alkali metals had catalytic activity in a certain extent. The effect of reaction condition was also studied. When the reaction was carded out under the following conditions： the reaction temperature 250℃, molar ratio of EC to DMT 3 ： 1, reaction time 3h, and catalyst amount 0.004 （molar ratio to DMT）, the yield of DMC was 68.9%.     

Effect of Calcination Temperature on the Catalytic Performance of γ-Bi2MoO6 in the Oxidative Dehydrogenation of n-Butene to 1,3-Butadiene

γ-Bi₂MoO₆ catalysts prepared by a co-precipitation method were calcined at various temperatures (425–675 °C), and were applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene in a continuous flow fixed-bed reactor. Conversion of n-butene and yield for 1,3-butadiene were high at low calcination temperature (425–475 °C), but were decreased with increasing calcination temperature (525–675 °C). Temperature-programmed reoxidation (TPRO) measurements revealed that the catalytic performance of γ-Bi₂MoO₆ was well correlated with the oxygen mobility of the catalyst. Yield for 1,3-butadiene was increased with increasing oxygen mobility of γ-Bi₂MoO₆ catalyst. Among the catalysts tested, γ-Bi₂MoO₆ catalyst calcined at 475 °C showed the best catalytic performance due to its facile oxygen mobility.     

Hydroprocessing of Aromatics Using Sulfide Catalysts Supported on Ordered Mesoporous Phenol–Formaldehyde Polymers

Ni–W sulfide catalysts for the hydroprocessing of aromatic hydrocarbons were synthesized by the in situ decomposition of tetrabutylammonium nickel thiotungstate complex supported on ordered mesoporous phenol–formaldehyde polymer. Catalysts obtained with and without additional sulfidation with dimethyl disulfide were characterized by X-ray photoelectron spectroscopy and transmission electron microscopy. The catalytic activity has been studied using naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, and anthracene as examples. It is shown that the system used in this study proved to be active in hydrogenation and hydrocracking of polyaromatic hydrocarbons.     

The Interaction of γ-Glycidoxypropyltrimethoxysilane with Oxidised Aluminium Substrates: The Effect of Drying Temperature

The interaction of γ-glycidoxypropyltrimethoxysilane (GPS) with oxidised aluminium substrates has been investigated in terms of the effect of the drying, or curing, temperature. Samples treated with aqueous solutions of GPS at concentrations of 1,4 and 8% v/v were cured at 25, 50, 93 and 120°C. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to construct adsorption isotherms and determine the thicknesses of the various GPS coatings. A temperature effect induces subtle changes in the structure of the resulting films. The uptake of GPS is increasing with increasing concentration of GPS. The structure of the films changes at a threshold temperature between 50 to 93°C. XPS and ToF-SIMS data both indicate that the interaction of the GPS film on aluminium is different for low and high temperatures drying regimes. Using the Beer-Lambert equation, it was found that increasing the curing temperature leads to the variation of the thickness of silane films. This is interpreted in terms of changes in the crosslink density of the films and in their state of hydration and/or degradation.     

Low Temperature Water–Gas Shift: Alkali Doping to Facilitate Formate C–H Bond Cleaving over Pt/Ceria Catalysts—An Optimization Problem

Doping Pt/ceria catalysts with alkali metals was found to lead to an important weakening of the formate C–H bond, as demonstrated by a shift to lower wavenumbers of the ν(CH) vibrational mode. However, with high alkalinity (∼2.5%Na or equimolar amounts of K, Rb, or Cs), a tradeoff was observed such that while the formate became more reactive, the stability of the carbonate species, which arises from the formate decomposition, was found to increase. This was observed by TPD-MS measurements of the adsorbed CO₂ probe molecule. Increasing the amount of alkali to levels that were too high also led to lower catalyst BET surface area, the blocking of the Pt surface sites as observed in infrared measurements, and also a shift to higher temperature of the surface shell reduction step of ceria during TPR. When the alkalinity was too high, the CO conversion rate during water–gas shift decreased in comparison with the undoped Pt/ceria catalyst. However, at lower levels of alkali, the abovementioned inhibiting factors on the water–gas shift rate were alleviated such that the weakening of the formate C–H bond could be utilized to improve the overall turnover efficiency during the water–gas shift cycle. This was demonstrated at 0.5%Na (or equimolar equivalent levels of K) doping levels. Not only was the formate turnover rate found to increase significantly during both transient and steady state DRIFTS tests, but this effect was accompanied by a notable increase in the CO conversion rate during low temperature water–gas shift.     

Kinetics of Hydrolysis of Erythro-Guaiacylglycerol β-(2-Methoxyphenyl) Ether and Its Veratryl Analogue Using Hc1 and Aluminum Chloride As Catalysts

The rates of hydrolysis of the β-aryl ether bond were determined in the temperature range 130° to 155°C for guaiacylglycerol-P (2-methoxyphenyl) ether and its veratryl analogue using both HC1 and AICI₃ as catalysts in a mixed ethanol-water medium. The data, based on quantitative determinations of guaiacol liberated in the process, demonstrate the absence of competing intramolecular condensation processes. The rates of HCl-catalyzed hydrolyses are first-order with respect to both catalyst and substrate concentrations, higher in dioxane-water than in aqueous or ethanol-water media, and the activation energies were nearly identical for both model compounds, 36.1 and 35.5 kcal/mol, respectively. In general, the hydrolysis of the guaiacyl model was four times faster than that of the veratryl analogue. The catalytic effect of AICI3 appears to be based on HCI released at higher temperatures by gradual hydrolysis.     

Fullerene C60 Supported on Silica and γ-Alumina Catalyzed Photooxidations of Alkenes

Deposition of fullerene C₆₀ (2% w/w) on silica and -alumina provokes a two orders-of-magnitude increase of its activity for the liquid-phase photooxidation of 2-methyl-2-heptene. Kinetic studies concerning the above photooxidation showed a first-order dependence of the reaction rate on the alkene concentration. The corresponding reaction-rate constant was found to be higher in the case where -alumina was used as carrier. The nature of the carrier does not influence the mechanism and the selectivity of the reaction. High dispersion of the supported fullerene is achieved on the surface of the carriers, which increase the fullerene light absorbance especially in the visible range.     

N2O Abatement Over γ-Al2O3 Supported Catalysts: Effect of Reducing Agent and Active Phase Nature

A series of metal catalysts (Pd, Rh, Ru, Cu, Fe, In and Ni) supported on γ-Al₂O₃ carrier, were evaluated during N₂O catalytic conversion to N₂ in the absence and presence of excess oxygen and reducing agents (CH₄ or C₃H₈). Among all catalysts tested, Pd-, Ru- and Rh-based samples exhibited the best catalytic performance, in all reaction conditions examined. The reaction was inhibited by O₂, in particular at lower temperatures, while its effect was essentially negligible at higher ones. In the presence of reducing agents and under lean reaction conditions, N₂O conversion was comparably enhanced, with C₃H₈ being more efficient than CH₄; however even in the presence of hydrocarbons N₂O decomposition is the major pathway for N₂O abatement, since reducing agents mainly act as oxygen scavengers reducing and concurrently activating the metal sites. The influence of different co-existing gases (CO, H₂O and SO₂) on the performance of Pd supported catalysts was also investigated, whereas thermal stability tests in the presence of SO₂ indicate a gradual irreversible decrease in activity until a new steady state was established.