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