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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.

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.

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.