Impregnation Of Γ-alumina Research Articles

Surface active holmia/ γ-alumina nanocatalyst: Preparation and characterization

Holmia supported γ-alumina nanocatalyst was prepared by impregnation of γ-alumina with aqueous solution of holmium acetate hydrate Ho(CH3COO)3.3.5 H2O. The physicochemical characteristics of the nanocatalyst calcined at 600°C were established by different techniques, using surface adsorption–desorption of N2 (SBET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (DRS). The recorded optical reflectance of the sample showed that the new self-assembled nanocatalyst is excellent as host material for advanced optical applications. Moreover, the catalyst showed enhanced catalytic activity toward Isopropyl alcohol decomposition.

Comparative study of propane oxidative dehydrogenation in fluidized and fixed bed reactor

ABSTRACTSupported vanadia catalyst was successfully synthesized using wet impregnation of γ-alumina to study propane oxidative dehydrogenation (POD). The prepared catalysts were characterized with X-ray diffraction and BET tests. To investigate performance of fluidized bed reactor in comparison to fixed bed micro-reactor, propane conversion and propylene selectivity were measured in temperatures of 480 to 550°C and GHSV of 48000, 60000, and 78000 cc/gr.hr at equimolar feed ratio of propane to oxygen. The results indicated that at constant temperature propane conversion obtained in the fixed bed reactor was higher. But fluidized bed is superior to fixed bed reactor in terms of propylene selectivity leading to considerably higher propylene yields over the fixed bed. It is suggested that pre-filtering effect induced by hydrodynamics of fluidized bed reactor has major effect in the enhancement of propylene selectivity beyond that of fixed bed micro-reactor.

Characterisation and performance of three promising heterogeneous catalysts in transesterification of palm oil

AbstractIn this work, the performance of three heterogeneous catalysts, namely potassium hydroxide/γ-alumina, bulk calcium oxide, and nano-calcium oxide, in comparison with the homogeneous potassium hydroxide was studied in the transesterification of palm oil to produce methyl esters and glycerol. The physical and chemical properties of the heterogeneous catalysts were thoroughly characterised and determined using a number of analytical methods to assess their catalytic activities prior to transesterification. The reaction products were analysed using liquid chromatography and their properties were quantified based on the American Society of Testing and Materials and United State Pharmacopoeia standard methods. At the 65°C reaction temperature, the oil-to-methanol mole ratio of 1: 15, 2.5 h of the reaction time, and catalyst (φ r = 1: 40), potassium hydroxide, potassium hydroxide/γ-alumina, nano-calcium oxide, and bulk calcium oxide gave methyl ester yields of 97 %, 96 %, 94 %, and 90 %, respectively. The impregnation of γ-alumina with potassium hydroxide displayed a catalytic performance comparable with the performance of potassium hydroxide where the former could be physically separated via filtration resulting in a relatively greater purity of products. Other advantages included the longer reusability of the catalyst and more active sites with lower by-product formation.

Mn/Al2O3 Systems: Structure and Activity

α-Mn2O3 and KMn8O16 were detected on catalysts prepared by pore volume impregnation of γ-alumina using manganous nitrate and ammonium permanganate, respectively. While the surface texture was not remarkably affected: decomposition activities towards H2O2 and 2-propanol were higher for the later.

Hydrotreatment Catalysts Prepared with Heteropolycompound: Characterisation of the Oxidic Precursors

Molybdenum-based catalysts were prepared by impregnation of γ-alumina with heteropolycompound (HPC) solutions: two salts were used, a nonreduced compound (Co3/2PMo12O40) and a reduced one (Co7/2PMo12O40). The dried and calcined solids were characterised with laser raman and diffuse reflectance spectroscopies. Extraction of the surface entities of the oxidic precursors was performed by washing them with various electrolytic solutions and the filtrates analysed by polarography. On the basis of these characterisations, a detailed description of the evolution of the entities during the preparation as well as the nature of the surface oxomolybdate species of the oxidic precursor have been deduced. It has been shown that the nonreduced HPCs were decomposed upon impregnation, whereas the reduced HPCs were preserved on the support after impregnation and drying. After calcination for 4 h at 673 K (in air for the nonreduced and in air or N2 for the reduced compounds), the HPCs were decomposed. However, it appears that the nature of the surface oxomolybdenum phase of the calcined solids strongly depends on the nature of the starting material. This difference should explain the variation in the thiophene conversion.

Characterization of lanthanum-modified γ-alumina by X-ray photoelectron spectroscopy and carbon dioxide absorption

The chemical interaction of dispersed lanthanum with γ-alumina was investigated by combining X-ray photoelectron spectroscopy (XPS) and carbon dioxide absorption. In order to establish the saturation concentration of lanthanum dispersed in the alumina surface layer, a series of materials was formulated at lanthanum concentrations corresponding to La/Al atomic ratios in the range from 0.05 to 2.0. The samples were prepared by impregnation of γ-alumina with aqueous lanthanum nitrate solutions, followed by calcination in air at 925 °C. Upon exposure to carbon dioxide, particles of La 2O 3 reacted to form bulk La 2 (CO 3) 3, while lanthanum interacting with alumina did not. The reacted carbon dioxide was quantified by observing the carbonate in the C 1s spectra. The La/Al atomic ratio observed by XPS at low loadings from 0.05 to 0.15 was in good agreement with the bulk ratios. The carbon dioxide uptake remained constant at these loadings, while the La 3d 5/2 spectral envelope appeared approximately 1.8 eV higher than that expected for La 2O 3. This shift to higher binding energy and the agreement of theoretical and XPS measurements is consistent with a monolayer dispersion previously reported. As the La loading increased above La/Al =0.15, the ratio measured by XPS increased first slightly, and then substantially over the bulk La/Al ratio, while the amount of carbon dioxide absorbed increased at the same time. In addition, the O 1s, Al 2p and La 3d 5/2 spectral envelopes gradually shifted to lower binding energies. As the La/Al bulk ratio approached 2.0, the La 3d 5/2 and O 1s spectral envelopes were shifted to what is expected for La 2O 3, while the Al 2p peak shifted to a binding energy observed for LaAlO 3. The differences observed spectrally and quantitatively at low and high loadings imply a change in the coordination of lanthanum.

A study of supported molybdenum cluster complexes as catalyst precursors: Part II. Evaluation of the catalytic activity of clusters supported on γ-alumina and fluorided γ-alumina

The supported molybdenum clusters previously described [1] were tested for their potential activity in the catalysis of cumene hydrocracking, thiophene hydrogenolysis, propene hydrogenation and, in some instances, gas oil hydrocracking. The effect of modifying the alumina support by the addition of fluoride ion was also investigated for those materials which showed promising catalytic activity, and the molybdenum loading was varied over the calculated range 4 – 10%. The effect of cobalt and nickel promoters was then examined. The results were compared with those obtained from conventional catalysts, prepared by impregnation of γ-alumina with molybdate with and without fluoride, cobalt and nickel additives. The most active catalysts tested were those prepared from the hexanuclear cluster, (H 3O +) 2[Mo 6Cl 14] 2−·6H 2O. These catalysts gave surprisingly high conversions in cumene hydrocracking, and had substantial activity in HDS studies. As hydrocracking catalysts for application to commercial feedstocks they showed considerable promise, especially when the Mo loading factor was taken into account. XPS studies of one of this series of catalysts suggested that in the hydrocracking of cumene and in the hydrodesulfurization of thiophene, the integrity of the cluster is destroyed during use, and hence the clusters should be regarded as precursors of the active catalytic species rather than being the active species themselves.

Modelling of impregnation of γ-alumina with cobalt and molybdenum salts. Co(NO3)2-(NH4)2MoO4-γ-alumina (chloride type) system

The kinetics of one-component and two-component impregnation of γ-alumina (prepared from aluminium trichloride) with aqueous solutions of cobalt nitrate and ammonium molybdate were studied and treated in terms of a mathematical model accounting for the simultaneous diffusion and adsorption of the active components. The time-dependent radial concentration profiles of the components across the cylindrical support particle were obtained. The profiles of the cobalt-to-molybdenum atomic ratio were derived from the results. The conclusions are applicable to the development of procedures for the preparation of hydrodesulphuration catalysts for the working of crude oil fractions.

Modelling of impregnation of γ-alumina with cobalt and molybdenum salts. CoCl2-(NH4)2MoO4-γ-Al2O3 (aluminate type) system

Adsorption data for the impregnation of alumina with an aqueous solution of cobalt dichloride and ammonium molybdate were treated in terms of the Langmuir adsorption isotherm and compared with a mathematical model set up to describe the kinetics of simultaneous impregnation of a support by two components. The effective diffusion coefficients of the two components at 25 °C in a cylindrical particle of alumina were obtained. The validity of the model used was verified qualitatively by comparing the numerical results with the experimental time dependent concentration profiles of the active components in a catalyst particle, measured by electron microanalysis technique.