Effect Of Different Supports Research Articles

Characterization of iron-cobalt oxide catalysts: Effect of different supports and promoters upon the structure and morphology of precursors and catalysts

The effect of a range of preparation variables such as the precipitate ageing time and [Fe]/[Co] molar ratio of precipitation solution on the composition and morphology of iron-cobalt oxide catalysts prepared using a co-precipitation method is described and the optimum preparation conditions were identified with respect to the catalyst activity for the Fisher–Tropsch reaction. The effect of different promoters along with loadings of optimum support and promoter on the activity and selectivity of the 40%Fe/60%Co as an optimum molar ratio are studied and it was found that the catalyst containing 40%Fe/60%Co/15 wt%SiO 2/1.5 wt%K which aged for 2 h, is an optimum modified catalyst for the conversion of synthesis gas to ethylene and propylene. The results are interpreted in terms of the structure of the active catalyst. Characterization of both precursors and calcined catalysts were carried out using XRD, SEM, BET specific surface area and thermal analysis methods such as TGA and DSC. It was shown that all the different preparation variables influenced the catalyst precursor structure and morphology.

The preparation of chromium, nickel and chromium–nickel alloy nanoparticles on supports

Chromium, nickel and chromium–nickel alloy nanoparticles have been synthesised via the addition of a metal salt solution to a support, followed by drying and reduction with hydrogen at elevated temperatures. Chromium and chromium–nickel alloy particles were prepared using ethylene glycol solutions and were found to be stable on silica and baddeleyite (ZrO2) supports. The crystal structures adopted were investigated using high resolution electron microscopy (HRTEM) and found to be similar in both cases to the bulk metal and alloy. The particle morphology, also from HRTEM observations, was found to be pseudo-spherical. Nickel nanoparticles could be formed using an aqueous solution on a variety of supports and were found from powder X-ray diffraction (PXRD) and HRTEM data to adopt the face-centred cubic structure of the bulk metal. The effect of different supports on the average particle size was investigated with PXRD and the particle morphology with HRTEM. The supports were found to have little effect on the average particle size, but had a noticeable influence on morphology, with particles on alumina being found to be flat and angular in contrast to those on graphitised carbon and ceria, which had pseudo-spherical morphologies.

Attrition resistance of cobalt F–T catalysts for slurry bubble column reactor use

There exists much current interest in the use of supported Co catalysts and slurry bubble column reactors (SBCR) for the conversion of natural gas to higher hydrocarbons via the Fischer–Tropsch (F–T) synthesis. Catalyst attrition resistance is extremely important in the operation of slurry-phase reactor systems because of potential problems with plugging of system filters and/or contamination of the liquid products. This paper addresses the effects of different supports, promoters, and preparation methods on the attrition resistance of Co F–T catalysts for SBCR use. The calcined supports had attrition resistances (inversely related to % fines <11 μm generated during attrition testing) as follows: − Al 2 O 3> TiO 2( rutile)⪢ SiO 2 Loading of Co onto the supports improved the attrition resistances of both alumina and silica significantly. It has essentially no effect on titania. The resulting catalysts had attrition resistances in the order Co/ Al 2 O 3> Co/ SiO 2> Co/ TiO 2( rutile)>⪢ Co/ TiO 2( anatase) The addition of small amounts of metal (Ru, Cu) and oxide (La, Zr, K, Cr) promoters had mainly small effects on the attrition resistance of the supported Co catalysts. However, it would appear that the addition of Zr to Co/alumina had a negative impact on its attrition resistance. The different preparation methods used in this study (aqueous impregnation, non-aqueous impregnation, and kneading) did not appear to have a significant effect on catalyst attrition resistance.

Structure–Activity Correlations on Rh/Al2O3 and Rh/TiO2 Thin Film Model Catalysts after Oxidation and Reduction

A study of the effect of different supports on the stability and catalytic activity of Rh nanoparticles is only meaningful if the metal particles are perfectly identical in the catalysts to be compared. We have applied epitaxial thin film deposition to produce homogeneous distributions of well-faceted Rh nanocrystals, divided the sample in two, and subsequently supported the metal particles by Al2O3 and TiO2. Three corresponding pairs of Rh/Al2O3 and Rh/TiO2 model catalysts with mean particle sizes of 7.8, 13.3, and 16.7 nm were prepared and activated by different oxidation–reduction treatments at temperatures up to 723 K. The size, morphology, and structure of the metal particles and of the support and the changes upon activation were determined by transmission electron microscopy. Wetting of the support and coalescence of Rh particles were observed to occur upon high-temperature reduction of large (>10 nm) and closely-spaced Rh particles, around 623 K on titania and around 723 K on alumina. Catalysts with smaller Rh particles did not show such pronounced changes. The rate of ring opening of methylcyclobutane at 373 K was measured on the three pairs of Rh/Al2O3 and Rh/TiO2 model catalysts as a function of the reduction temperature after preoxidation at 723 K. Rh/alumina catalysts exhibited maximum activity after reduction at 523 K due to the formation of low-coordinated sites as shown by electron microscopy. The activity of Rh/titania peaked after reduction at 373 K and decreased almost exponentially with Tred up to 673 K. In the case of Rh/titania, the changes in particle size and microstructure as observed in the electron microscope can only account for part of the kinetic results. The rapid activity decrease in titania-supported Rh particles with increasing Tred is paralleled to an increase in the number of oxygen vacancies and in low-valent Ti cations, on the titania surface. The latter may affect the electric field at the metal–support boundary and thereby reduce the catalytic activity for hydrocarbon reactions. In addition, the decoration of Rh particles by migrating Ti suboxide will account for the diminished activity after reduction at higher temperature.

Rh/C catalysts in ethene hydroformylation: the effect of different supports and pretreatments

The activity, selectivity and stability of Rh/C catalysts prepared from nitrate precursor on three different active carbon supports was determined in ethene hydroformylation. The different active carbon supports yielded catalysts, which had different extents of reduction (62–94%) and dispersion (4–27%) after hydrogen reduction. The best activity and selectivity in the formation of propanal was obtained with the coconut shell based Rh/C(C) catalyst, presumably due to the better metal dispersion and the presence of unreduced Rh sites. Furthermore, without any pretreatment, the Rh/C(C) catalyst exhibited even higher activity and better propanal yields than its hydrogen treated counterpart. Most likely, the active sites remained better dispersed in the absence of pretreatment than after hydrogen reduction, and it was the well-dispersed sites that were active in the formation of propanal. High temperature CO pretreatment partially blocked the catalyst surface with carbonaceous residues, which improved propanal selectivity, but suppressed the overall activity. Thus, the right choice of pretreatment appears to be a key factor in providing an active and selective catalyst for heterogeneous hydroformylation. It should also be noted that the catalysts lost 10–30% of the metal deposited on the support during 24 h on stream.

Effect of Different Supports on the Reaction Rate of Rhizomucor Miehei Lipase in Organic Media

Five different aluminas, a silica and a zirconia support were used to adsorb lipase (E.C. 3.1.1.3) from Rhizomucor miehei. The activity of the immobilised lipase was measured by esterification of dodecanol and decanoic acid in hexane. The immobilised lipase and the organic phase were pre-equilibrated separately to known water activities before mixing them to commence the reactions. The aluminas, which varied in pore sizes and surface areas, adsorbed similar amounts of enzyme. However, the esterification activities varied about 10-fold, increasing with increasing surface area. The silica and zirconia supports adsorbed about half as much lipase as the aluminas. The esterification reaction rates per unit quantity of enzyme adsorbed were compared with those for aluminas with similar surface areas; this specific rate was about 2 times higher for the zirconia, but the difference with silica was only small. There was no clear correlation between the esterification rates at fixed water activity and the amount of ...

Activation of CH 4 and Its Reaction with CO 2 over Supported Rh Catalysts

The dissociation of CH 4 and CO 2, as well as the reaction between CH 4 and CO 2, has been investigated over supported Rh in a fixed-bed continuous-flow reactor. The decomposition of methane on rhodium occurred above 423 K, when transient evolution of hydrogen and ethane were observed. The deposition of different kinds of carbon species was established, which led to the termination of the decomposition. The reactivity of surface carbon towards hydrogen exhibited a great variance, and sensitively depended on the conditions of its formation. The dissociation of CO 2 was detected by infrared spectroscopy only above 523 K, and it was promoted by the presence of CH 4. The reaction between CO 2 and CH 4 proceeded rapidly above 673 K to give CO and H 2 with different ratios. No decay in the activity of Rh catalysts was experienced, and only very little, if any, carbon deposition was observed. The effects of different supports on all of the above processes have been examined.

Catalytic behaviour of rhodium supported on palygorskite, silica and titania in oil hydrogenation

Rhodium catalysts, prepared by reduction of a cationic organometallic rhodium compound anchored to various treated clays, silica and titania, were tested in the hydrogenation of a sunflower oil in acetone solution. The reaction was carried out at atmospheric pressure and room temperature. Preliminary results on the effect of different supports on the activity, selectivity and trans-isomer content are presented. Results show that rhodium supported on palygorskite, pretreated at 423 K in vacuum, gave rise to the highest activity of all the catalysts at an iodine value of more than 55, and the lowest trans-isomer formation among the catalysts supported on palygorskite for an iodine value of more than 65. The rate of hydrogenation is of the same order or less than that found for 1-hexene hydrogenation.

Effects of immobilization and environmental stress on growth and production of non-polar metabolites of Tagetes minuta cells

Tagetes minuta (marigold) cells were entrapped under sterile conditions in agarose, κ-carrageenan, agar and alginate. The effects of different supports on the growth rate of the entrapped cells during incubation for one week under standard conditions [ I] were studied. In the second part (weeks 2 and 3) of the experiment the effects of low temperature (10° C) [II], intermittent N 2 gassing [III], and omission of carbohydrates from the medium [IV]—superimposed on that of entrapment—on growth rate and the production of non-polar secondary metabolites were investigated. Compared to free cells, the impact of agarose on growth during the first week was nil, while the inhibition of growth increased in the order κ-carrageenan, agar and alginate, probably as a result of increasing rigidity of the support. In the second period the plant cells clearly had reached the stationary phase of the growth cycle in all cases. Again the pattern of growth on agarose closely followed that of free cells, i.e. a small increase in cases I and III, and a small decrease under the other two conditions. Low temperature [II] had the greatest effect on cell growth and cell release, probably as a result of gel structure at this temperature. Similarly to the effects on growth, the impact on secondary metabolite production was most pronounced in the case of alginate combined with low temperature. Both the omission of carbohydrates, and Nin2 gassing resulted in low concentrations of non-polar compounds in the media. The major trend observed was a shift away from mainly intracellular compounds in the case of free cells to mainly extracellular compounds in the case of entrapped cells at 10°C.

The Effects of Different Supports on the Formation and Reactivity of Surface Isocyanate on Pd, Ir, Ru and Rh

The Effects of Different Supports on the Formation and Reactivity of Surface Isocyanate on Pd, Ir, Ru and Rh

Catalytic reactions of ethane and n‐Butane as a tool for characterization metallic surfaces

AbstractIn the present paper the final goal is to use the hydrogenolysis of hydrocarbons as a diagnostic tool for characterizing the metallic surface, i.e. to give a technique for drawing conclusions about the character of a metallic surface itself from the observed kinetic parameters. The main features are as follows:Surface properties of a transition metal are essentially determined by the electron structure and geometry of the bulk, members of the group VIII metals possess, therefore, apriori activity in the hydrogenolysis of a given hydrocarbon. Vulcano shaped curves observed in the hydrogenolysis of ethane, n‐pentane, may, therefore, be an indication that neither too strong, nor too weak interaction between the catalyst surface and the substrate is good for the optimum catalyst performance.In addition to the ability of a metal in the “weak” to “strong” type of interconvension conceptualized earlier, the kinetic parameters may be influenced by some additional factors e.g. temperature, hydrogen pressure and the aging of the catalyst. A systematic change in the catalyst structure of platinum and ruthenium results in a characteristic variation in the activity of ethane and n‐butane hydrogenolysis as well as in selectivity. By carefully analysing the limiting factors mentioned the effect of different supports, metallic dispersion, impregnating substrate, alloying with iron and rhenium and adsorbed sulphide on the activity and selectivity was determined.