Hydrogen spillover on Ni–CsxH3−xPW12O40 (x = 0, 1, 2) double-function hydrocracking catalyst was studied by temperature-programmed desorption (H2-TPD and NH3/H2-TPD) and thermodynamic calculations. The results of H2-TPD show that the hydrogen adsorption amount on the two-component Ni–CsxH3−xPW12O40 (x = 0, 1, 2) catalysts is much greater than that on single-component catalysts, such as nickel, tungstophosphoric acid and its cesium salts. Moreover, the H+ content is related to the content of Ni–CsxH3−xPW12O40. The above phenomena can be explained by the spillover hydrogen H combining with H+ to form Hn+ (n = 2, 3). The results of NH3/H2-TPD can also indirectly prove the existence of Hn+. It is demonstrated by the theoretical calculation that the formation of Hn+ (n = 2, 3) from H and H+ is favorable in energy, and NH3 may combine with H3+ to form NH6+.
Authors:Zhiwei Wu, Fan Yang, Huabang Wang, Jianchao Ma, Ligong Chen, and Yang Li
A general process for the cyclization of aminoalcohols to the corresponding amines over Cu–Cr–La/γ-Al2O3 is established in a continuous fixed-bed reactor. The catalyst was characterized by XRD, XPS and NH3-TPD. The doped Cr is found to improve the copper particle dispersion. The addition of La neutralized the strong acid sites and decreased the amount of the acid sites, which facilitated the desorption of amino compounds on the surface of catalysts and inhibited the carbon deposition. Under the optimum conditions, the yields of pyrrolidine, piperidine and piperazine were 99.5, 99.5 and 98.6 %, in order, while the yields of hexahydro-1H-azepine and homopiperazine were 46.5 and 32.7 % due to the unstable seven-membered ring by the cyclization of the corresponding aminoalcohols over Cu–Cr–La/γ-Al2O3.
Authors:Mojtaba Nasr-Esfahani and Abolghasem Nourmohammadi
We have produced zinc oxide (ZnO) photocatalyst nanostructure films by the deposition of ZnO onto indium tin oxide (ITO) glass substrates. A polyethylene glycol (PEG) aided sol–gel route using zinc acetate, 2-methoxyethanol and monoethanolamine, followed by spin coating and heat treatment, was utilized to form these photocatalyst films. The obtained interface nanostructure films were characterized with X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The photocatalytic activity of the films were also investigated using Direct Sky Blue 5B (C. I. Direct Blue 15) as a model organic compound under UV light irradiation. The influence of operating parameters, including the pH of the solution and the number of ZnO layers on Direct Sky Blue 5B degradation, were examined. An interesting decolorization performance was observed in the ZnO/ITO thin films produced using 2 % PEG.
Authors:Hugo Rojas, José J. Martínez, Sonia Mancípe, Gloria Borda, and Patricio Reyes
The hydrogenation of citral over Au, Ir–Au and Ir catalysts prepared from colloids using as supports TiO2 and Nb2O5 has been studied. The samples were characterized by N2 adsorption at 77 K, transmission electron microscopy and temperature programmed reduction. The reactivity and selectivity differences between the prepared catalysts have been explained considering that the deposition of colloids prepared in basic media at high pressures of hydrogen occurs preferentially as iridium oxide or gold complexes, similarly to classical methods of preparation (wetness impregnation and deposition–precipitation). In this sense, the catalytic behavior of supported colloids is similar to these methods without the reduction process. This was corroborated when the solids were reduced at 773 K, which leads to catalysts active and highly selective to the hydrogenation of the carbonyl bond.
Authors:Heondo Jeong, Churl Hee Cho, and Tae Hwan Kim
Methanol synthesis by carbon dioxide hydrogenation was investigated over a series of Cu/ZnO catalysts prepared by various pH conditions. These catalysts were confirmed by XRD, BET, N2O chemisorption and TPR measurements before and after the reaction. It was revealed that pH conditions on catalyst preparation played an important role in active metal formation on the catalysts surface and catalytic performance in the hydrogenation of carbon dioxide. Zr added to Cu/ZnO catalysts favorably served in enhancing copper dispersion on the catalyst surface and improving carbon dioxide conversion. Among the catalysts tested, Cu/ZnO/ZrO2/Al2O3 catalyst exhibited the highest carbon dioxide conversion, methanol yield and CO concentration in the outlet gas.
The gas phase selective hydrogenation of a series of nitroarenes (nitrobenzene, p-chloronitrobenzene, p-bromonitrobenzene, p-nitroaniline, p-nitrotoluene, p-nitrophenol and p-nitroanisole) has been examined over Au/TiO2 (0.3 % w/w Au, mean Au particle size = 3.9 nm). Compensation behavior is demonstrated with an associated isokinetic temperature (Tiso) of 558 ± 32 K. We account for this response in terms of the selective energy transfer (SET) model where the occurrence of resonance between catalyst and reactant vibrations generates the activated complex. An analysis of the stepwise variation of the activation energies has identified a critical vibrational frequency of 853 cm−1, which is close (±2 cm−1) to the reference value for nitro-group (in-plane symmetric O–N–O bending and stretching) vibrations. Application of SET suggests activation of weakly adsorbed nitroarene (at the support or metal/support interface) by excitation of the nitro-group via IR radiation from a strongly adsorbed surface nitroarene component. The excited nitroarene is then attacked by reactive hydrogen supplied by the Au sites to generate the respective aromatic amine with 100 % selectivity. Agreement of the SET predicted Tiso with the experimental value requires the incorporation of a term due to C–N torsional entropy resulting from distortion of the O–N–O plane.
The influence of the activation conditions on the catalytic performance and microstructure of supported V–Mo oxides used for benzene oxidation to maleic anhydride has been investigated. To activate the catalysts, two sets of activation conditions were tested. In condition I, the catalysts were activated in an atmosphere of air and benzene, which was similar to the industrial practice. In condition II, the catalysts were pre-activated in an atmosphere consisting of the gas products produced by the decomposition of the freshly prepared catalysts during activation process. The activity and selectivity of the catalysts were evaluated on a bench scale reactor as well as on a pilot reactor. The catalysts activated by condition II at the appropriate temperature showed a better performance: the selectivity and yield of MA were nearly 80 and 100 wt%, respectively. They are 5 % higher than those of the catalyst activated by condition I. The catalysts were characterized in terms of several techniques including isotherm adsorption, TG-DTG, XRD, SEM, EDX and XPS. The characterization results indicated that the microstructures of the catalysts were significantly influenced by the activation conditions. Based on the above information, the better performance exhibited by the catalyst activated by condition II are analyzed.
Authors:O. Machalický, L. Lichý, M. Tomica, R. Hrdina, and O. Šolcová
The photocatalytic decomposition of indigo-5,5′-disulfonic acid (indigocarmine) and indigo-6,6′-dicarboxylic acid has been studied using TiO2 suspension and the polychromatic irradiation of a high-pressure Hg arc lamp. The dyestuffs were dissolved in aqueous medium at pH = 10 and photolyzed in a back-flow tubular photoreactor. The reaction products were determined by HPLC, NMR and MS spectroscopy. Two main photoproducts obtained from indigocarmine (2-amino-5-sulfobenzoic acid and isatine-5-sulfonic acid) were detected. The photocatalysis of indigo-6,6′-dicarboxylic acid gave aminoterephthalic acid and isatine-6-carboxylic acid as two main products. The quantitative analyses of reaction products were performed with UV/Vis and HPLC using chemical standards. A stoichiometric model and kinetic description of photocatalysis of sulfo and carboxy indigo dyes are suggested. The effect of hydroxide and carbonate anions on the rate of photocatalysis was also studied.
Nanosized Pd doped and supported on Mn2O3 catalysts were prepared and tested for CO oxidation. The introduction of Pd in Mn2O3 enhances the activity for CO oxidation due to a synergistic effect. The supported samples showed total CO conversion at lower temperature as compared to doped samples, whereas pristine Mn2O3 showed total CO conversion at a much higher temperature. The presence of Pd greatly improved the catalytic activity for CO oxidation. The presence of moisture in the feed gas does not deactivate the catalysts for CO oxidation. XRD pattern substantiates the formation of Mn2O3 phase, SEM images show that the particles are in the nanosized range and roughly spherical in appearance. From TEM images, the average particle size was found to be around 50 nm. Thermal analysis data indicates the phase change from Mn2O3 to Mn3O4 beyond 900 °C and also gives information regarding the thermal stability of Mn2O3 after the incorporation of Pd in the lattice.
Effects of KNO3, CeO2, Fe2O3, their mixture and their thermally treated mixture on the combustion reactivity of two coals, bituminous coal (BC) and high ash coal (HAC), were investigated by thermogravimetric analysis. The ignition performance, burnout performance and exothermic behavior were used to evaluate the catalytic effect. Moreover, the kinetic parameters were determined using the Coats–Redfern method. The results indicated that the activity sequence of the catalysts on BC relative to the ignition performance can be described as follows: the thermally treated mixture > the mixture > KNO3 > Fe2O3 > CeO2, and the activity sequence relative to the burnout performance is the same. The activity sequence of the catalysts on HAC relative to the ignition performance can be described as follows: the thermally treated mixture > the mixture > Fe2O3 > CeO2 > KNO3, and the activity sequence relative to the burnout performance is the same. The exothermic heats of catalyst-incorporating samples increased and the activation energies of the samples decreased.