F.R. van Buren

Potassium promotion of iron oxide dehydrogenation catalysts supported on magnesium oxide: 1. Preparation and characterization

Catalysts of iron oxide supported on magnesium oxide and promoted with potassium were prepared by incipient wetness impregnation of preshaped magnesium oxide support pellets with a solution of an iron complex, either ammonium iron (III) citrate or ammonium iron (III) EDTA and potassium carbonate. Iron and potassium were applied wither simultaneously or consecutively. As determined using X-ray diffraction, thermogravimetric analysis, and magnetic measurements, calcination above 923 K results in the formation of a mixed oxide of iron and potassium, viz., KFeO[sub 2]. After calcination at 973 K the average crystallite size of the KFeO[sub 2] phase is about 300 [angstrom]. The formation of KFeO[sub 2] appeared to have a strong retarding effect on the reduction of the iron oxide phase to metallic iron. It was found that the KFeO[sub 2] phase is unstable in atomspheric air due to reaction with carbon dioxide and moisture to form potassium (hydrogen) carbonate and (hydrated) iron oxide.

Properties of La1−xSrxBO3−y (B=Co or Fe) compounds as oxygen electrodes in alkaline solution: General aspects

Abstract La 0.50 Sr 0.50 BO 3−y (B=Co or Fe) were tentatively tested as oxygen electrodes in alkaline solution. Earlier reported reversible behaviour of La 0.50 Sr 0.50 CoO 3−y could be explained by non-equilibrium phenomena. Supported by measurements of electrical conductivity and thermogravimetry evidence exists that very slow oxygen ion diffusion inside the electrode material is involved in the equilibration process. Observable oxygen evolution starts at comparatively low potentials (≈1400 mV vs. a Pt/H 2 (1 atm) electrode in the same solution).

The electrochemical determination of oxygen ion diffusion coefficients in La0.50Sr0.50CoO3−y: Experimental results and related properties

Abstract Results of an electrochemical method for the determination of oxygen ion diffusion coefficients D O 2− in porous pellets of La 0.50 Sr 0.50 CoO 3−y are presented. Log D O 2− can be expressed as log D O 2− =−(2.3±0.2) 10 3 / T −(6.6±0.6) cm 2 s −1 . The activation energy E a for the diffusion process equals 44 kJ mol −1 . Further the related electrochemical measurement and the adjustment of the oxygen deficiency y are described. At 75°C the following empirical Nernst relation between the electrode potential E (vs. a Pt/H 2 (1 atm) electrode in the same solution) and Δ y is found: E =627–108 ln (Δ y + 0.0054) mV. (Δ y = y−y 0 ; y 0 =mole fraction of vacancies at the reversible O 2 potential of 1190 mV). The use of La 0.50 Sr 0.50 CoO 3−y as a solid solution electrode in practical storage cells seems to be excluded for thermodynamic and kinetic reasons.

An electrochemical method for the determination of oxygen ion diffusion coefficients in La1−xSrxCoO3−y compounds: Theoretical aspects

Abstract Theoretical aspects of a novel electrochemical method for the determination of O 2− diffusion coefficients in porous pellets of La 1− x Sr x CoO 3− y are discussed. This method is based on a bounded 3-dimensional diffusion model.

Potassium promotion of iron oxide dehydrogenation catalysts supported on magnesium oxide: 2. 1-Butene dehydrogenation activity

Abstract Potassium promotion of iron oxide catalysts supported on magnesium oxide results in considerably more active and selective 1-butene dehydrogenation catalysts. Upon promotion the activation energy was found to decrease from 194 to 156 kJ/mol. KFeO 2 appeared to be the active phase under dehydrogenation conditions. No reduction of KFeO 2 was observed. KFeO 2 shows high 1-butene dehydrogenation activity, yet it is not sufficiently effective to suppress coking entirely. For that purpose the presence of highly dispersed potassium carbonate at the catalyst surface is a prerequisite. Under identical dehydrogenation conditions, a commercial unsupported catalyst, S-105, which contains the more easily reducible KFe 11 O 17 , is reduced to Fe 3 O 4 . Compared with this unsupported S-105 catalyst, the supported catalysts show significantly higher 1,3-butadiene selectivities at comparable conversion levels, which is to be attributed to the different natures of their respective active phases.

The influence of the particle size distribution on the measurement of oxygen ion diffusion coefficients in La0.50Sr0.50CoO3−y

Abstract The influence of the particle size distribution on an earlier electrochemical measurement of the oxygen ion diffusion coefficient at 76°C in La0.50Sr0.50CoO3−y was examined. A value of 1.55×10−13 cm2 s−1 was found which compares favorably with the earlier value of 1.23×10−13 cm2 s−1 determined on the basis of a single characteristic particle size. The measured current differs only by a factor 1.3 from the calculated one, which factor can be attributed to the use of an idealized model with spherical particles.

Characterization of pre-shaped zirconia bodies for catalytic applications

Literature indicates that application of zirconia in a supported dehydrogenation catalyst is viable. Textural and structural properties of commercial pre-shaped zirconia supports from various suppliers were characterized using electron microscopy, element analysis, nitrogen physisorption, mercury intrusion porosimetry and X-ray diffraction. Most zirconias are sufficiently pure (>97 %) and thermostable to be applied in supported catalysts. Specific surface areas as large as 10 m2g−1 are stable at temperatures of about 850 °C. Specific surface areas up to about 30 m2g−1 can be established by a thermal treatment in air at temperatures up to the operating temperatures of the dehydrogenation process. Steam treatment affects the texture differently from treatment in dry air: sintering proceeds more rapidly in the presence of steam. The preshaped supports show a porosity (about 50%) which is higher than that reported for zirconia powders with the same pore-size distribution (5%). This is advantageous, both in the catalyst preparation step and in the catalytic reaction. However, the pre-shaped supports exhibit some microporosity.

Supported Dehydrogenation Catalysts Based on Iron Oxide

Abstract A magnesia-supported iron oxide catalyst promoted with potassium was prepared for the dehydrogenation of hydrocarbons, such as, e.g. ethylbenzene or 1-butene. With high-field magnetic measurements it was established that potassium ferrite, KFeO 2 , is the active phase of the catalyst under dehydrogenation conditions.

Assessment of the free surface area of magnesia-supported magnesium ferrite particles using selective oxygen chemisorption

The free surface area of iron oxide catalysts supported on magnesium oxide has been determined using selective oxygen chemisorption at room temperature. The oxygen chemisorption experiments were performed on reduced catalysts. It has appeared to be essential that the iron oxide phase, which is present as MgFe2O4 in the fresh calcined catalysts, is reduced uniquely to FeO, prior to the chemisorption experiment. Crystallite sizes typically in the range of 20–23 nm have been found independent of the catalyst loading and the type of precursors. A higher iron loading does not lead to larger crystallites, but rather to more crystallites of about the same average size. Results are in very good agreement with those obtained by X-ray line broadening and electron microscopy.

A new supported dehydrogenation catalysts: Influence of the support and preparation variables

The preparation of titania- and zirconia-supported dehydrogenation catalysts using pre-shaped supportbodies was investigated. Catalysts containing only iron and catalysts containing a potassium additive were prepared using simple salt and chelating agent precursors. The effect of the drying time on the were prepared using simple salt and chelating agent precursors. The effect of the drying time on the distribution of the active components was studied. Catalysts were characterized using microscopic techniques, XRD, TPR, magnetic analysis, DRIFTS, XPS, Mossbauer Spectroscopy, and by the catalytic dehydrogenation of 1-butene. It was possible to prepare catalysts showing a good interaction of the active components with the supportwith a uniform distribution over the support pellets. This interaction proved detrimental with titania-supported catalysts, which deactivate rapidly due to the formation of mixed compounds of iron and/or potassium with the support. Zirconia-supported catalysts, however proved to be very stable in the dehydrogenation reaction, which was attributed to the formation of a finely divided supported phase.