techniques for soot reduction in diesel engines is the wall-flow filter, which involves the entrapment of the soot, after which the deposited soot is burned off as a result of the catalyst placed on the filter [ 5, 6 ]. This technology has proven to be
Authors:M. N. Ramsis, Ch. A. Philip, M. Abd El Khalik, and E. R. Souaya
CoO/Al2O3 catalysts containing amounts of cobalt ranging form 2 to 20% were prepared atpH 11 from neutral mesoporous alumina composed of γ-Al2O3 and poorly crystalline boehmite, and were then dried at 80‡C. X-ray diffraction, DTA and TG techniques were used to study the structural changes produced upon thermal treatment up to 700‡C.
Kaolinic and bentonitic-clays are selected to prepare transition metals, iron, cobalt and nickel catalysts. The metals are
incorporated into two supports through new impregnation technique. The original clays and the prepared catalysts were subjected
to different techniques. The crystallite size (X-ray diffraction analysis) increases from iron to cobalt then to nickel upon
heating and the increase for bentonitic-catalysts is higher than that for kaolinic-ones. Infrared spectra show the appearance
of bands signifying the presence of iron, cobalt and nickel bonded to OH group constituting the silica-silica tetrahedral
sheets inside the clay structure. The enthalpy (ΔH) andentropy (ΔS) values (differential scanning calorimetric) are lower for bentonitic-catalysts than for kaolinic-catalysts. Thus, the incorporation
of the metal hydroxide in the interlamella of the silicate-silicate bentonite clay structure facilitates the
interaction between the unpaired electrons on the adjacent atoms and the support which enables the prepared catalysts to be
more active for catalytic conversion.
Authors:R. Frost, A. Locke, M. Hales, and W. Martens
TG combined with MS has been used to study the thermal decomposition of a synthetic aurichalcite with varying copper-zinc
ratios from 0.1:0.9 to 0.5:0.5. In general, five decomposition steps are observed at 235, 280, 394, 428 and 805°C. The principal
mass loss step increases in temperature from 255°C (0.1/0.9) to 300°C (0.5/0.5). MS using ion current curves show that the
OH units and carbonate units decompose simultaneously and the two decomposition steps after the main decomposition are attributed
to the decomposition of ZnCO3 and CuCO3. A higher temperature decomposition at around 805°C, based upon the ion current curves is assigned to the decomposition of
CuO to Cu. The thermal decomposition of aurichalcite offers a method of preparing metal oxides mixed at the molecular level
making the thermally activated aurichalcites as suitable for use as catalysts.
Simultaneous DSC-TG and DTA-TG were used to investigate the calatytic effect of the metal on the thermal decomposition of
a cellulose matrix containing small copper particles. The techniques were also used to demonstrate the effect of the metal
particles on the subsequent activation of the carbon matrix, a process which develops the pore structure necessary to expose
the metal particles to the gas phase. Temperature programmed desorption was used to study the initial mass loss found on activation.
To quantify the catalytic effect of the copper particles on the activation process an estimate was made of the activation
energy of the catalysed and uncatalysed reactions. The work gives valuable information on the processes involved in the preparation
of a new range of metal-carbon catalysts.
A 5 wt% Pd/SiO2 catalyst was synthesized by heating PdCl2-impregnated SiO2 in H2 at 300°C for 2 h. It was found that the metal particle dispersion is improved when the reduction step is preceded by calcination
at 300°C for 2h. Thermogravimetry of the impregnated support in air, N2 and H2 atmospheres was used to monitor the interactions occurring during the various preparative steps (i.e. drying, calcination
and reduction) of the catalyst. The solid prduct of each preparative step was characterized by X-ray diffractometry and UV/Vis
diffuse reflectance spectroscopy. The results indicate that following the drying step (at 110°C in air) the palladium occurs
in two detectable forms: PdCl2 particles and Si−O−Pdn+ surface species. The calcination appears to transform the PdCl2 particles into the latter surface species. The H2-reduction eventually converts the surface species into finely-dispersed Pd° metal particles (average size=8–14 nm). No other
reduction products, such as PdySix, were detected.
Preparations were characterized by specific surface area, thermogravimetry, and X-ray diffractometry. Thermal effects observed were (a) sulfur loss, (b) sintering, (c) crystallization and transformation of the crystalline phase(s). Thermoanalytical curves indicate that decomposition of the sulfate occurs in two distinct steps. Decrease of surface area due to (b) and (c) is concomitant to decomposition of sulfate. Sulfate was found to hinder sintering, crystallization and phase transformations of ZrO2 and TiO2. In low-titania and -zirconia sulfated TiO2-ZrO2 the minor component enhances the effect of sulfate. In equimolar TiO2-ZrO2 sulfate decomposition is accompanied by rapid formation of crystalline TiZrO4.
Authors:K. V. Novikova, M. O. Kompanets, O. V. Kushch, S. P. Kobzev, M. M. Khliestov, and I. O. Opeida
calculated from the slope of the linear plots of the volume of oxygen uptake vs. time. All kinetic measurements were carried out by using freshly prepared samples.
The catalysts were characterized by comparison of their physical properties with those
Authors:Szabolcs Harnos, György Onyestyák, and Dénes Kalló
vegetable oil at moderate temperatures (300–420 °C) with hydrogen at elevated pressures (20–100 bar). Conventional hydrodesulfurization (HDS) catalysts, such as sulfided CoMo, NiMo, or NiW supported on alumina have achieved the complete conversion of