Oxidation into CO2 is a major solution to CO abatement in air depollution treatments. The development of catalytic converters led to an extraordinary high number of publications on metal catalysts during the last fifty years. Due to the increasing price of noble metals and to remarkable progresses in oxide syntheses, catalytic oxidation of carbon monoxide over oxide catalysts has recently gained in interest, even if some oxides are known to present remarkable activity since the beginning of the 20th century. In this Review, the kinetics and mechanism of CO oxidation on single and mixed oxides are examined, alongside the catalyst structures

Catalytic Oxidation of Carbon Monoxide over Transition Metal Oxides

http://biostevera.com/wp-content/uploads/2014/11/02-Comprehensive-review.pdf

Stevia rebaudiana Bertoni, source of a high-potency natural sweetener: A comprehensive review on the biochemical, nutritional and functional aspects

The catalytic oxidation of CO on Fe-embedded graphene was investigated by means of first-principles computations. Fe atom can be constrained at a vacancy site of graphene with a high diffusion barrier (6.78 eV), and effectively activate the adsorbed O2 molecule. The reactions between the adsorbed O2 with CO via both Langmuir−Hinshelwood (LH) and Eley−Rideal (ER) mechanisms were comparably studied. The Fe-embedded graphene shows good catalytic activity for the CO oxidation via the more favorable ER mechanism with a two-step route.

CO Catalytic Oxidation on Iron-Embedded Graphene: Computational Quest for Low-Cost Nanocatalysts

Various iron(III) oxide catalysts were prepared by controlled decomposition of a narrow layer (ca. 1 mm) of iron(II) oxalate dihydrate, FeC2O4·2H2O, in air at the minimum conversion temperature of 175 °C. This thermally induced solid-state process allows for simple synthesis of amorphous Fe2O3 nanoparticles and their controlled one-step crystallization to hematite (α-Fe2O3). Thus, nanopowders differing in surface area and particle crystallinity can be produced depending on the reaction time. The phase composition of iron(III) oxides was monitored by XRD and 57Fe Mossbauer spectroscopy including in-field measurements, providing information on the relative contents of amorphous and crystalline phases. The gradual changes in particle size and surface area accompanying crystallization were evaluated by HRTEM and BET analysis, respectively. The catalytic efficiency of the synthesized nanoparticles was tested by tracking the decomposition of hydrogen peroxide. The obtained kinetic data gave an unconventional no...

Catalytic efficiency of iron(III) oxides in decomposition of hydrogen peroxide: competition between the surface area and crystallinity of nanoparticles.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/srin.201900108

Reduction of Iron Oxides with Hydrogen—A Review

Experiments were conducted on pure Fe2O3 fines (–250 mesh) which were mixed with 1, 2.5, 5 and 10% by weight of pure NiO of the same size. The powder mixtures were pressed into compacts and fired at 1473 K for 20 h. The fired compacts were isothermally reduced at 1173-1473 K with hydrogen. The reduction course was followed up by means of weight loss technique. Porosity measurements, reflected light microscope and X-ray diffraction analysis were used to elucidate the reduction kinetics. NiO was found to have a significant effect on the reduction of iron oxide. The rate of reduction at both the initial and final stages increased with the increases of dopant content at all reduction temperatures and this was attributed to the formation of mickel ferrite (NiFe2O4) phase and the consequent increase in the total porosity of compacts. Nix, Fey solid solution (ferronickel alloy) was produced during reduction at all tempetatures studied. The values of apparent activation energy calculated from the experimental results, the structure of partially reduced compacts and the application of gas-solid reaction model were used to elucidate the reduction mechanism.

https://www.jstage.jst.go.jp/article/isijinternational1989/35/9/35_9_1043/_pdf

Effect of Nickel Oxide Doping on the Kinetics and Mechanism of Iron Oxide Reduction

Nanocrystallite iron oxide powders were prepared by co-precipitation method using highly purified FeCl 3 and NH 4 OH solution. The prepared powders were tested for the catalytic oxidation of CO to CO 2 . The effect of oxidation temperature on the catalytic reaction was isothermally investigated using advanced quadrpole mass gas analyzer system. The mechanism of the catalytic oxidation reaction was estimated from the experimental data. Fe 2 O 3 nanocrystallite of 78 nm shows a good response towards catalytic CO oxidation at the temperature range 200–500 °C. The catalytic oxidation efficiency reached 98% at 400–500 °C. The reaction was found to be first order with respect to CO. The average activation energy of the reaction was found to be 26.3 kJ/mol which is smaller than the values reported in the literatures. The mechanism of CO catalytic oxidation was investigated by comparing the CO catalytic oxidation data in the absence and presence of oxygen. It was found that the catalytic oxidation of CO over Fe 2 O 3 nanocrystallite proceeded by adsorption mechanism. Based on the experimental results, Fe 2 O 3 nanocrystallite powders can be recommended as a promising catalyst for CO oxidation.

Effect of temperature on the catalytic oxidation of CO over nano-sized iron oxide

In order to maximize efficiency of plant propagation via direct organogenesis, the influence of plant growth regulators on the growth and development of Stevia rebaudiana grown in vitro was studied. Results indicated that benzyl adenine increased multiplication rate, vitrification and somaclonal variation. However, the best results were recorded with MS nutrient medium without plant growth regulators during in vitro growth and development of Stevia rebaudiana. MS basal medium supplemented with 2 mg/l BA recorded the highest number of shoots, but these shoots were very thin and vitrified and not suitable for multiplication through several subcultures. The nutrient medium (MS basal medium) supplemented with 10 mg/l kinetin recorded 45 shoots / explant as compared to MS nutrient medium which recorded 6.63 shoots / explant but growth parameters for Stevia rebaudiana plantlets grown in MS medium without kinetic is better than MS medium containing kinetin at high concentrations. Nutrient medium (MS basal medium) supplemented with IBA at low concentrations (0.01mg/l) or without auxins achieved the best in vitro growth of Stevia rebaudiana plantlets (100 % root formation). IBA was better than NAA and IAA for shoot and root formation. Increasing NAA concentrations decreased gradually number of shoots. Regarding the effect of NAA on root formation, data indicated that the per cent of shoots formed roots was 87% on MS basal medium without plant growth regulators as compared to MS basal medium supplemented with NAA at low concentrations 0.001, 0.01 and 0.1 mg/l NAA where root per cent was 80%, 73 % and 53 % respectively. On the other hand, NAA at 1.0 and 1.5 mg/l did not help shoots to form roots. Statistical analysis of variance showed no significant differences amongst IAA treatments for in vitro growth of plantlets. Stevia rebaudiana plants were adapted and grown well in planting media containing peat moss, sand and vermiculite at equal volume.

Plant growth regulators affecting in vitro cultivation of Stevia rebaudiana

Iron oxide compacts fired at 1373 K for one hour were reduced at 973-1373 K using different reducing gases; namely CO, H2, 50%H2-CO and simulated reformed natural gas. The reduction course has been followed up by means of recording weight-loss changes as a function of time. The structure of the compacts was examined by reflected light microscope whereas the volume change was measured by displacement method. It has been found that both temperature and reducing gas composition have a significant effect on the volume change behaviour during reduction. The volume change values of the completely reduced compacts were not well representing the volume change behaviour during reduction. The greater swelling was observed for compacts reduced with pure CO giving a maximum value of 24% for compacts reduced up to 90% reduction at 1173 K. Reduction with pure H2 showed a maximum contraction of 24% for compacts completely reduced at 1123 K. The volume change behaviour for compacts reduced with gas mixtures was mainly dependant on the relative contents of CO and H2 in the reducing gas. Mechanisms have been proposed for the volume change trends for compacts reduced with the different gases and correlated with the microstructure of the reduced compacts.

Effect of Reducing Gas on the Volume Change during Reduction of Iron Oxide Compacts

Pure Fe2O3 compacts were fired at 1373K for one hour then reduced with CO at 973-1373K. Reduction was followed up by means of weight-loss technique whereas volume change was measured by displacement method. The structure of the fired and reduced compacts was examined by reflected light microscope while the different phases were identified by X-ray diffraction technique. These measurements together with kinetic data were correlated for better understanding the gas-solid reaction mechanisms and the accompanying swelling phenomenon. A highest swelling value of 176% was obtained for compacts completely reduced at 1173K whereas a maximum swelling of 224% was obtained for compacts 90% reduced at the same temperature. At all reduction temperatures swelling increased with the increase in reduction extent up to 90% where a maximum swelling value was obtained followed by a small decrease in swelling when compacts were completely reduced. Excessive swelling was attributed to the carbon in metallic iron and/or iron carbide formed and their reactions with oxygen forming CO and/or CO2. A mechanism of disintegration of iron grains and swelling of the compacts has been proposed and correlated with reduction conditions.

Mahmoud Nasr

Papers

Effect of Nickel Oxide Doping on the Kinetics and Mechanism of Iron Oxide Reduction

Effect of temperature on the catalytic oxidation of CO over nano-sized iron oxide

Plant growth regulators affecting in vitro cultivation of Stevia rebaudiana

Effect of Reducing Gas on the Volume Change during Reduction of Iron Oxide Compacts

Carbon Monoxide Reduction and Accompanying Swelling of Iron Oxide Compacts