Sven Järås

Catalytic Materials for High-Temperature Combustion

Abstract Catalytic combustion, as an alternative to conventional thermal combustion, has received considerable attention during the past decade. Research efforts have been promoted by the need to meet governmental demands concerning pollution and the wish to use energy sources more efficiently. The two main advantages offered by catalytic combustors over flame combustors apply to these goals: Catalytic combustion can be carried out over a wide range of fuel concentrations in air and at low temperatures. These low temperatures result in attaining NO, emission levels substantially lower than possible with conventional combustors.

Mixed manganese oxide/platinum catalysts for total oxidation of model gas from wood boilers

Abstract Mixed manganese oxide/platinum catalysts in the form of monoliths have been prepared by the deposition-precipitation method. The influence of the platinum content and the calcination temperature has been investigated by activity measurements for total oxidation of methane, naphthalene and carbon monoxide in the presence of steam and carbon dioxide, and by the temperature programmed reduction (TPR) technique. Manganese oxide behavior is influenced by the presence of even very small amounts of platinum especially when the catalyst is calcined at a higher temperature due to favorable synergetic effects.

Total oxidation catalysts based on manganese or copper oxides and platinum or palladium I: Characterisation

Abstract Temperature-programmed reduction (TPR), oxidation (TPO), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to characterise catalysts based on manganese oxides, copper oxides or one of them mixed with platinum or palladium-supported on γ-alumina. The catalysts were characterised before and after they had been exposed either to high temperature in the presence of steam or to sulphur dioxide. Raman spectroscopy, XRD, XPS and TPR performed on the fresh samples of MnO x , mixed MnO x –Pt and MnO x –Pd revealed the presence of a mixture of manganese oxides, particularly Mn 2 O 3 . In the fresh mixed MnO x –Pd and CuO x –Pd samples, Pd catalysed the reduction of both MnO x and CuO x , whereas Pt only catalysed the reduction of MnO x . After hydrothermal treatment at 900°C of the MnO x , mixed MnO x –Pt and MnO x –Pd samples, there was a formation of new manganese oxide phase, Mn 3 O 4 detected by Raman spectroscopy. TPR revealed increasing interaction between the metal oxides and the noble metals in the hydrothermally treated mixed MnO x –Pd and CuO x –Pd samples, and also the appearance of interaction in the treated mixed CuO x –Pt sample. The sulphur adsorbed in all the MnO x samples formed sulphate, which was more difficult to reduce than the oxides. Also, the reduction temperature of sulphates was lowered when noble metals are present.

Production of hydrogen by partial oxidation of methanol over Cu/ZnO catalysts prepared by microemulsion technique

Production of hydrogen by partial oxidation of methanol, using air as oxidant. has been studied over a series of Cu/ZnO catalysts prepared by microemulsion technique. The catalytic activity was com ...

A review of the use of plasma techniques in catalyst preparation and catalytic reactions

Abstract The application of plasma techniques in the preparation of catalysts and in catalytic reactions published during the last fifteen years is briefly reviewed. Two different types of plasma are used in this field: low temperature plasma (low pressure plasma) and high temperature plasma. The first type of plasma technique is widely used for the modification of surface oxides, and for the preparation and regeneration of catalysts as well as for catalytic synthesis and decomposition. The second type is applied for the preparation of ceramic-based supports, recovery of precious metals from used catalysts, and catalytic reactions. Both oxides and supported metal catalysts have been prepared by this method. The catalytic reactions involving the plasma technique essentially involve NO, methane or ammonia as reactants. An interesting potential for this technique is its application in the recovery of the precious metals from car exhaust catalysts.

Catalytic combustion of methane over cerium-doped palladium catalysts

Various Pd-supported catalysts have been prepared using three different types of alumina as support material: (a) gamma-alumina, (b) Ba-stabilized alumina, and

Production of hydrogen by partial oxidation of methanol over ZnO-supported palladium catalysts prepared by microemulsion technique

Selective production of hydrogen by partial oxidation of methanol, using air as oxidant, was studied over a series of ZnO-supported Pd catalysts. Microemulsion-assisted synthesis and conventional impregnation techniques were used for preparation of catalysts containing Pd particles of different sizes. Catalyst characterisation included BET, XRD and TEM analyses. The influence of Pd particle size on catalytic activity and product distribution was studied by carrying out activity measurements at temperatures between 230 and 300 ◦ C using a stoichiometric feed composition. All catalysts performed well with respect to methanol conversion and hydrogen yield. Both methanol conversion and hydrogen selectivity increased with increasing reaction temperature, the latter at the expense of water formation. Oxygen conversion was complete throughout the examined temperature range. These selectivity trends, with a strong dependence of hydrogen and carbon monoxide selectivities on methanol conversion and reaction temperature, support a reaction scheme consisting of consecutive methanol combustion, steam reforming and decomposition. More importantly, a correlation between Pd particle size and carbon monoxide selectivity was found. When the microemulsion catalysts are compared, carbon monoxide formation increases with increasing particle size. This was not observed over the impregnated reference catalysts, which exhibited high carbon monoxide-levels throughout the examined temperature range. Bimetallic PdZn particles were detected in spent catalysts by means of XRD and it is suggested that the catalytic activity is dependent on the formation of PdZn, the catalytic function being different from that of Pd 0 .

Comparison and Functionalization Study of Microemulsion-Prepared Magnetic Iron Oxide Nanoparticles

Magnetic iron oxide nanoparticles (MION) for protein binding and separation were obtained from water-in-oil (w/o) and oil-in-water (o/w) microemulsions. Characterization of the prepared nanoparticles have been performed by TEM, XRD, SQUID magnetometry, and BET. Microemulsion-prepared magnetic iron oxide nanoparticles (ME-MION) with sizes ranging from 2 to 10 nm were obtained. Study on the magnetic properties at 300 K shows a large increase of the magnetization ~35 emu/g for w/o-ME-MION with superparamagnetic behavior and nanoscale dimensions in comparison with o/w-ME-MION (10 emu/g) due to larger particle size and anisotropic property. Moringa oleifera coagulation protein (MOCP) bound w/o- and o/w-ME-MION showed an enhanced performance in terms of coagulation activity. A significant interaction between the magnetic nanoparticles and the protein can be described by changes in fluorescence emission spectra. Adsorbed protein from MOCP is still retaining its functionality even after binding to the nanoparticles, thus implying the extension of this technique for various applications.

Catalytic abatement of emissions from small-scale combustion of wood : A comparison of the catalytic effect in model and real flue gases

The aim of this study was to evaluate a laboratory technique for testing catalysts, as well as to investigate two commercial catalysts, for total oxidation of unburnt hydrocarbons and CO in flue gases from wood combustion. The catalyst activities for oxidation of methane, naphthalene and CO in the presence of steam and carbon dioxide were measured in a laboratory flow reactor and the activity for oxidation of methane, C2 hydrocarbons, benzene and CO in real flue gases was analysed in a 15 kW wood-fired heater. The results from the two investigations were compared to verify whether the laboratory method is a useful tool to simulate catalytic oxidation of the flue gases. The noble metal catalyst had a higher activity for naphthalene and CO than the metal oxide catalyst, and deactivation was also less pronounced for the noble metal catalyst. The emissions from the wood-fired heater were also evaluated and related to data in the literature.

Catalytic combustion of methane over bimetallic catalysts a comparison between a novel annular reactor and a high-pressure reactor

Abstract The effects of adding a co-metal, Pt or Rh, to Pd/γ-Al2O3 catalysts were studied with respect to the catalytic activity for methane combustion and compared to a Pd/γ-Al2O3 catalyst, using both a pressurized pilot-scale and a lab-scale annular reactor. Temperature programmed oxidation (TPO) experiments were also carried out to investigate the oxygen release/uptake of the catalyst materials. Palladium showed an unstable behavior both in the pilot and lab-scale experiments at temperatures well below the PdO to Pd transformation. An addition of Pt to Pd stabilized, and in some cases increased, the catalytic activity for methane combustion. The TPO experiments showed that the oxygen release peak was shifted to lower temperatures even for low additions of Pt, i.e. Pd:Pt=2:1. For additions of rhodium only small beneficial effects were seen. The steady-state behavior of the lab-scale annular reactor correspond well to the pressurized pilot-scale tests.