Role of the Various Surface Sites and Species in CO Hydrogenation Over Alumina-supported Co-Pd Catalysts

The paper is focused on evaluation of active centres and impact of adsorbed species on (10%Co+0.5%Pd)/Al2O3 catalyst system performance aiming selectivity optimization. Application of different sets of precursor pretreatment and reduction resulted in catalysts exhibiting high CO conversion or high methane selectivity. A sample of high selectivity was prepared by pretreatment in hydrogen and the performance was determined by lower amount of strongly adsorbed CO, strongly adsorbed carbonate species, and higher amount of reduced metal and bimetallic particles. A more active system was formed by pretreatment in air leading to larger amount of unreduced metal and CO-bridged species on the surface, stable coverage of hydroxyl groups on the support, and medium-strength sites for adsorption of carbonates. Ratios of hydrogen to carbon monoxide adsorption (H/СО) and of strongly to weakly adsorbed СО species appeared as important criteria for catalyst efficiency together with supported metal state, amount of unreduced ions, bimetallic particle formation, and alumina’s ability to adsorb CO and CO2. This work is licensed under a Creative Commons Attribution 4.0 International License

Treatment of Biogenic Iron-Containing Materials

Biogenic iron oxides could find application in catalysis but their structure and composition should be well characterized. The content of organic rests due to their origin should also be controlled. Samples of natural biomass and biomass obtained after cultivation in Adler’s medium of the Sphaerotilus-Leptothrix group of bacteria were treated by different techniques to reduce or totally remove the organic residues. The aim of the study was to find procedures, which prevent changes in the oxidation state of the iron and of the type of iron-containing compound(s) during treatment. Mössbauer spectroscopy, IRS, DTA, and SEM were used in the study. Chemical treatment with H2O2 or NaOH at room temperature did not significantly change the samples. Thermal treatment in oxidative flow mixture conducted up to 250 °C resulted in a transformation of the iron-containing phases only. The organic matter, which is included in the structure of the particles, cannot easily be affected. DTA revealed that removal of organic rests occurred in the interval of 250–600 °C. However, the transformation of the initial compounds could not be prevented using such a treatment

Comparative analysis of the catalytic behaviour in CO oxidation of iron containing materials obtained by abiotic and biotic methods and after thermal treatment

This work concerns synthesis of iron oxide containing materials by biotic and abiotic methods and comparison of their properties aimed at finding a common point of intersection that may determine a possible replacement of abiotic materials. Biosynthesis comprised Leptothrix genus of bacteria cultivation in growth medium of Adler. Thermal treatment of biomass samples was used in order to approximate synthesis conditions of the biogenic iron oxide material to those of abiotically obtained hematite. The catalytic activity of the samples was measured in the reaction of CO oxidation by two ways: in situ infrared spectroscopy using a diffuse-reflectance measuring chamber of Nicolet 6700 spectrometer high-temperature vacuum accessory and a flow-type glass reactor. Biomass showed low CO conversions up to 200°C but an increase at 250°C was registered by both used methods. This increase was accompanied by phase transformation. Initial catalytic activity was a result of predominant work of lepidocrocite, whereas a higher activity at 250°C was due to formed maghemite. Abiotic hematite was a bit more active below 240°C than a thermally treated biomass sample in flow-type glass reactor experiments. At higher temperatures, both materials demonstrated the same CO conversion. Spent samples did not show any changes of composition. Although the studied samples were synthesized by different methods, which resulted in different original iron oxide phases, their catalytic performance was very close. Thermally treated biomass samples (obtained by cultivation in Adler's medium) could replace chemically obtained iron oxide as a catalyst in the studied reaction

A study of the dispersity of iron oxide and iron oxide-noble metal (Me=Pd, Pt) supported systems

Samples of one-(Fe) and two-component (Fe-Pd and Fe-Pt) catalysts were prepared by incipient wetness impregnation of four different supports: TiO2 (anatase), gamma-Al2O3, activated carbon, and diatomite. The chosen synthesis conditions resulted in the formation of nanosized supported phases - iron oxide (in the onecomponent samples), or iron oxide - noble metal (in the two-component ones). Different agglomeration degrees of these phases were obtained as a result of thermal treatment. Ultradisperse size of the supported phase was maintained in some samples, while a process of partial agglomeration occurred in others, giving rise to nearly bidisperse (ultra- and highdisperse) supported particles. The different texture of the used supports and their chemical composition are the reasons for the different stability of the nanosized supported phases. The samples were tested as heterogeneous catalysts in total benzene oxidation reaction

A model of slow wave propagation and entrainment along the stomach

10.1007/s10439-010-0051-1Annals of Biomedical Engineering3893022-3030ABME