Liang Dongbai

An in situ combined temperature-programmed reduction-Mössbauer spectroscopy of alumina-supported iron catalysts

Two 10% FeAl2O3 catalysts with supports of different surface areas were studied by means of an in situ combined temperature-programmed reduction (TPR)-Mossbauer spectroscopy technique, which enabled a Mossbauer measurement to be obtained in situ after temperature-programmed reduction to any temperature. Various reactions occurring during the TPR process of the catalysts were revealed. It was found that, although the iron concentration was high, considerably strong metal (oxide)-support interactions occurred in the catalyst with higher surface area, and the TPR of the sample consisted of three consecutive stages, namely, at around 460 °C, 790 °C, and above 850 °C. In the first stage from 300 to 600 °C mainly the reduction of Fe(III) to Fe3O4 and then Fe3O4 to Fe(II) aluminate took place. It was amazing to find that over the temperature range of 470–600 °C Fe3O4 was converted into Fe(II) and Fe(III) aluminates without the consumption of hydrogen, and thereby an increase in the amount of Fe(III) was observed when increasing the TPR temperature from 470 to 600 °C. In the meantime, the Fe(III) species which remained unreduced were also transformed to Fe(III) aluminate at these temperatures. In the second stage from 600 to 850 °C, Fe(III) aluminate was reduced, giving rise to the formation of Fe(II) aluminate and Fe(0). In the final stage, above 850 °C, Fe(II) aluminate was reduced to Fe(0). It was found that the reduction of Fe(II) aluminate was accompanied by a migration of the Fe(II) ions from the octahedral sites to the less stable tetrahedral ones, and thus facilitated the reduction. Chemical control of the reduction was present during the TPR over the temperature range of 470–700 °C. The catalyst with lower surface area gave a similar pattern of reduction, but with some varied features due to different extent of metal-support interactions.

An in situ Mössbauer investigation of the influence of metal–support and metal–metal interactions on the activity and selectivity of iron–ruthenium catalysts

The hydrogen reduction of a series of alumina- and silica-supported iron–ruthenium catalysts has been studied in situ by iron-57 Mossbauer spectroscopy. The data, complemented by results from temperature-programmed reduction experiments, show that ruthenium enhances the reducibility of iron and that the metal–support interaction in the silica-supported samples is weaker than in those supported on alumina.The performance of the iron–ruthenium catalysts for carbon monoxide hydrogenation has been evaluated in a fixed-bed microreactor, and the activity of the alumina-supported catalysts was found to be higher than those supported on silica. However, alumina-supported catalysts in which the iron content exceeded ca. 27 atom % showed a gradual decrease in activity. At ca. 65 atom % this began to approach the activities of the silica-supported materials, which were generally less dependent on the iron content of the bimetallic phase. Catalysts with low metal loadings were more active than their counterparts with high metal loadings. These variations in catalytic activity have been interpreted in terms of the stronger interactions between the metallic phase and alumina, as compared with silica, supports and the smaller metallic particle sizes which are obtained on alumina.Metal–support interactions and particle dispersions have also been found to influence selectivity. Hence ruthenium, which interacts strongly with alumina, showed high activity and tended to form higher-molecular-weight hydrocarbons, whilst silica-supported ruthenium was less active and favoured the formation of lower hydrocarbons. The addition of iron to alumina-supported ruthenium shifted the product distribution towards lower hydrocarbons but had little influence on the selectivity of catalysts supported on silica.The variations in metal–support interaction which result from changes in the iron concentration and which are reflected in the catalytic properties of the solids have been correlated with the Mossbauer data, which showed the capacity of iron to donate electrons to ruthenium.

Characterization of supported ruthenium catalysts by thermal analysis

Abstract The reduction-oxidation behaviour of unsupported and supported ruthenium components has been examined and the extent of metal-support interaction characterized. The sintering stability of the ruthenium crystallites on alumina and silica supports has been studied through reduction-oxidation cycles by DTA and the influence of the chloride impurities on the reduction-oxidation behaviour has also been examined. Finally, reduction kinetic parameters have been determined by the Freeman-Carroll procedure.

An investigation of metal-support interactions in some iron, ruthenium and iron-ruthenium catalysts by in situ iron-57 Mössbauer spectroscopy

Abstract The reduction by hydrogen of alumina- and silica-supported iron catalysts has been studied in situ by iron-57 Mo˝ssbauer spectroscopy. The results from catalysts with loadings of 5% iron show that the stronger metal support interaction between iron and alumina gives rise to small particle iron oxide which is partially reduced in hydrogen to iron(II) whilst silica-supported iron, in which the metal-support interaction is weaker, forms large particle magnetically ordered α-Fe 2 O 3 which is reduced to metallic iron and iron(II). Treatment of these and some alumina- and silica-supported iron—ruthenium catalysts of similar total metal loading in atmospheres of carbon monoxide and hydrogen give Mo˝ssbauer spectra which show that the reducibility of iron depends on both the ruthenium content of the bimetallic catalyst and the character of the support. Such treatment gives rise to the formation of an iron carbide phase in the silica-supported iron catalysts. Alumina- and silica-supported catalysts containing 10% iron, or 5% ruthenium, or 5% iron-5% ruthenium are more active towards carbon monoxide hydrogenation than those with lower iron loadings. The different catalytic properties of these materials, together with the changes induced in the activity and selectivity of alumina- and silica-supported ruthenium by the incorporation of iron, reflect the variation in metal-support interaction as the nature of the metallic phase is altered.

CO2 Hydrogenation for the Production of Light Alkenes over K-Fe-Mn/silicalite-2 catalyst

MnO and K 2 O are two kinds of promoters to Fe/Silicalite-2 (denoted as Fe/Si-2) catalyst for light olefin formation from CO 2 hydrogenation. It has been revealed that CO 2 adsorption capacity was enhanced by the addition of MnO, and that K 2 O could further increase both the adsorption capacity and bonding strength of the Fe-Mn/Si-2 catalyst to CO 2 and CO species. Based on a two step reaction mechanism in which a reversible water gas shift reaction and a Fischer-Tropsch reaction are involved, the promotional effects of these two kinds of promoters for the formation of C 2 H 4 and C 3 H 6 can be explained.

Oxidation of iron in titania-supported iron–ruthenium under reducing conditions: in situ evidence from 57Fe Mössbauer spectroscopy

In situ studies of ruthenium-rich iron-ruthenium clusters supported on titania of differing surface areas by 57Fe Mossbauer spectroscopy show that the pre-reduced bimetallic phase undergoes partial oxidation when treated in atmospheres of hydrogen or hydrogen and carbon monoxide.

In Situ Preparation of Ir/ZSM-5/Cordierite Honeycombs and their Application for NOx Abatement

ZSM-5 zeolites were synthesized in situ onto cordierite honeycombs by vapor phase transport (VPT) for the first time. The as-synthesized ZSM-5/cordierite honeycombs were impregnated with IrCl3 and tested for NOx reduction with a simulated exhaust gas as the reducing agent. Under the conditions of excess oxygen, the Ir/ZSM-5/cordierite monolith catalyst exhibited NO reduction of 73% at a temperature of 573 K and a space velocity of 20,000 h−1.

Titania Supported Iron-Ruthenium Catalysts for Fischer-Tropsch Synthesis

Iron-ruthenium catalysts supported on titania of differing surface areas have been prepared and characterised by in-situ 57 Fe Mossbauer spectroscopy and temperature programmed reduction techniques (TPR). The results have shown that interactions between iron and titania supports are strongest when high surface area titania is used. However, such interactions are weaker than those between iron and silica and between iron and aluminia. The catalytic properties of these materials for Fischer-Tropsch synthesis have been evaluated in a microreactor system at 235°C and at 25 Kg/cm 2 pressure. The incorporation of iron into titania-supported ruthenium catalysts has a significant influence on selectivity. In contrast, the selectivities of less active silica-svpported catalysts are insensitive to the iron concentration.

An In Situ mossbauer study on the metal -support Interaction of supported Iron Catalysts for CO Hydrogenation

Iron supported catalysts were investigated by in situ Mössbauer spectroscopy. Results showed that MSI can be vell Interpreted as a combination of the dispersion effect and the chemical interaction effect.