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Formaldehyde dehydrogenase (FaldDH) is used as a catalyst to reduce formate to formaldehyde in a cascade reaction to convert CO2 to methanol. This enzyme, however, has low activity and is sensitive to substrate/product concentration and pH. To improve the performance of FaldDH, it can be immobilized through physical adsorption in siliceous mesostructured cellular foams (MCF), which physical properties are suitable for the immobilization of large molecules as FaldDH (molecular size of 8.6 × 8.6 × 19 nm). In this work two MCF materials were synthesized: MCF1 with a pore size of 26.8 nm and window size of 10.5 nm; and MCF2 with a pore size of 32.9 nm and window size of 13.0 nm. The surfaces of the materials were functionalized with octyl, mercaptopropyl or chloromethyl groups. FaldDH was successfully immobilized inside all the materials, yielding enzyme loadings of about 300 mg g‐1 in MCF1 and more than 750 mg g−1 in MCF2. However, the enzyme was inactive upon immobilization on MCF1, whereas on MCF2 the enzyme retained its catalytic activity presumably owing to the larger pores of this material and the need for the enzyme to undergo configurational changes during the reaction. Using MCF2 functionalized with mercaptopropyl groups the activity of FaldDH was enhanced beyond that of the free enzyme. Additionally, low leakage of the enzyme from the MCF2 was observed during the reactions. Thus, tailored MCF is a highly attractive material for employment of the FaldDH enzyme.

Development of non-precious metal catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells with high activity and durability and with optimal water management properties is of outmost technological importance and highly challenging. Here we study the possibilities offered through judicious selection of small molecular precursors used for the formation of ordered mesoporous carbon-based non-precious metal ORR catalysts. By combining two complementary precursors, we present a one-pot synthesis that leads to a composite material consisting of transition metal ion-chelating ordered mesoporous carbon and multi-walled carbon nanotubes (TM-OMC/CNT). The resulting composite materials show high specific surface areas and a carbon structure that exhibits graphitic signatures. The synthesis procedure allows for tuning of the carbon structure, the surface area, the pore volume and the ratio of the two components of the composite. The TM-OMC/CNT composites were processed into membrane electrode assemblies and evaluated in single cell fuel cell measurements where they showed a combination of good ORR activity and very high durability.

We report on sulfur-functionalized ordered mesoporous carbons aimed for lithium-sulfur battery electrode applications with improved charge capacity retention. The carbons were obtained by a hard-template strategy using a mixture of furfuryl alcohol and furfuryl mercaptan. For the application as electrode material in lithium-sulfur batteries, the carbons were additionally loaded with sulfur following a traditional melt-diffusion approach. It was found that the sulfur interacts stronger with the sulfur-functionalized carbon matrix than with the non-functionalized material. Electrodes showed very high capacity in the second discharge-charge cycle amounting to approximately 1500, 1200 and 1400 mAh/g (sulfur) for carbon materials with no, medium and high degrees of sulfur functionalization, respectively. More importantly, the sulfur-functionalization of the carbon was found to increase the capacity retention after 50 discharge-charge cycles by 8 and 5% for the carbons with medium and high degrees of sulfur-functionalization, respectively, compared to carbon with no sulfur-functionalization. We attribute this significant improvement to the presence of covalently bound sulfur groups at the internal surface of the functionalized carbon providing efficient anchoring sites for catenation to the sulfur loaded into the pores of the carbons and provide experimental support for this in the form of results from cyclic voltammetry and X-ray photoelectron spectroscopy.

Hybrid energy storage systems aim to achieve both high power and energy densities by combining supercapacitor-type and battery-type electrodes in tandem. The challenge is to find sustainable materials as fast charging negative electrodes, which are characterized by high capacity retention. In this study, mesoporous anatase beads are synthetized with tailored morphology to exploit fast surface redox reactions. The TiO2-based electrodes are properly paired with a commercial activated carbon cathode to form a Li-ion capacitor. The titania electrode exhibits high capacity and rate performance. The device shows extremely stable performance with an energy density of 27 mWh g-1 at a specific current of 2.5 A g−1 for 10,000 cycles. The remarkable stability is associated with a gradual shift of the potential during cycling as result of the formation of cubic LiTiO2 on the surface of the beads. This phenomenon renews the interest in using TiO2 as negative electrode for Li-ion capacitors.

Alkaline sodium silicate solutions with SiO2:Na2O molar ratios in the range 4-10 are known to be colloidally unstable manifested in phase separation or gelation. The mechanistic understanding of this instability is generally poor. To improve this situation the microscopic structure of a series of solutions with ratios in the range 3.3-8.9 has been characterised using small-angle X-ray scattering, Dynamic light scattering, Fourier transformed infrared spectroscopy, and (29)Si Nuclear magnetic resonance spectroscopy to cover the relevant length scales related to silica clusters, aggregates, and particles present. In the starting solution, with ratio 3.3, there are silica present in three fractions. The main part is present as small silica clusters with a radius of 0.7 nm. There are also a significant portion of monomers/small oligomeric silica species as well as a minute amount of larger colloidal silica particles. At a higher SiO2:Na2O ratio, above approximately 4, smaller spherical colloidal particles are formed due to condensation reactions. However, as a result of a too high ionic strength the suspension is not stable and the particles aggregate to fractal structures with a size that depends on ratio and ageing time. At the highest SiO2:Na2O ratio, fractals are not formed because of the lower ionic strength and the smaller colloidal particles are stable in the solution. By carefully adding small amounts of NaCl to the high ratio solution it is possible to induce gelation of the solution confirming the hypothesis that the instability region is due to too high electrolyte concentration for the silica species present under those conditions.

Alumina-supported In2O3, Ga2O3 and B2O3 were investigated as catalysts for lean NOx reduction with DME as reducing agent and compared to pure Al2O3 and In2O3. The In2O3-promoted alumina catalysts showed the highest NOx conversion at low temperatures, although with a narrow temperature window. Pure In2O3, on the other hand, was inactive for NOx reduction with DME. The Ga2O3- and B2O3-promoted alumina catalysts gave the highest NOx conversion at higher temperatures, showed a temperature window similar to pure alumina, but were less sensitive to H2O inhibition. Possible reasons for these observations are discussed.

Bismuth telluride thin films have been synthesized by electrochemical deposition onto stainless steel substrates from acidic solutions. The influence of deposition variables on film composition, morphology and crystal orientation associated with the growth of the film was investigated by means of constant potential deposition and pulsed potential deposition. In-plane thermoelectric and transport properties of the electrodeposited films were measured. The carrier concentration of the electrodeposited films was found to be one order of magnitude larger than typically reported for optimized bulk bismuth telluride, which explains the unusually low Hall mobility and Seebeck coefficient values found for the electrodeposited films. Pulse deposited films showed slightly lower electrical resistivity and higher Seebeck coefficient due to the lower porosity and less preferred crystal orientation of the films compared to the continuously deposited films. Improvements of the film properties are necessary to make them viable for applications.

A range of ethers, alcohols and alkanes were compared as reducing agents for NOx over a Cu-ZSM-5 lean NOx catalyst. The nature of the reducing agent was found to determine the degree of NOx reduction. Methanol and DME were virtually inactive as reductants over this catalyst, while higher ethers and alcohols showed high NOx conversion. A detailed study was performed to investigate the differences. Among the studied variables, the chemical structure of the reductant was found to be especially important. Despite having a lower reducing capacity than DME, ethylene glycol was active for NOx reduction. It is concluded that a C-C bond in the reducing agent is required for lean NOx reduction over Cu-ZSM-5. The absence of this bond in DME and methanol explains their low activity for NOx reduction over this catalyst.

High catalytic activity for selective catalytic reduction of NOx with dimethyl ether and methanol (DME- and methanol-SCR) has been found over a γ-alumina catalyst. The surface species involved in the DME-SCR reaction were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in combination with mass spectrometry and compared to the corresponding species observed during methanol-SCR. Dimethyl ether adsorbs mainly as methoxy groups (OCH3) on the catalyst surface, while methanol adsorbs as methoxy groups and molecularly. With increasing temperature, DME desorbs in two steps, whereas methanol desorbs first as methanol and at higher temperatures as DME. At higher temperatures, the two reducing agents display similar DRIFTS spectra showing first formaldehyde-like species and then formates on the surface. In the presence of NO or NO2, reactions between NO x species and carbon-containing species occur. Formohydroxamic acid (CHON(H)OH) forms isocyanates (NCO), and both are observed at temperatures relevant for DME-SCR. Since these species are likely intermediates for hydrocarbon-SCR over Ag/Al2O3, a partly similar reaction mechanism may be operational for DME-SCR over γ-Al2O 3 despite the fact that Ag/Al2O3 does not catalyze DME-SCR efficiently. The difference is thus due to the reaction steps leading to the formation of formohydroxamic acid that with DME follow a more efficient route over γ-Al2O3 than over Ag/Al 2O3.© 2010 Elsevier Inc. All rights reserved.

The sorption capacity of the recently reported crystalline microporous semiconductor Rb-CTH-1 was investigated, revealing that the structure demonstrates heat-induced reversible sorption of 3 wt% water and hydrocarbons. The Rb-CTH-1 structure maintains its crystallinity and semiconducting properties when heated to 150 degrees C. The treatment causes desorption induced irreversible rearrangements of the remaining guest species with a response in the semiconductive properties of the material. (C) 2010 Elsevier Inc. All rights reserved.

Microporous semiconducting crystal structures are exceedingly rare and their usefulness for applications typical for microporous semiconductors is largely related to their sorption properties and to their semiconductor response to sorption. The sorption properties of the unique crystalline microporous semiconducting antimony(III) oxide telluride K-SBC-1 were evaluated by means of temperature-resolved diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermogravimetric analysis (TGA/DSC), and X-ray powder diffraction. K-SBC-1 was found to demonstrate heat-induced reversible sorption and desorption-induced rearrangements of guest water molecules. Upon heating to 300 degrees C 66% of the water content of K-SBC-1 desorbed. Desorption of water could be made more facile through activation of K-SBC-1 by heat treatment and then occurred at room temperature in a flow of nitrogen. These are unique properties compared to the few known related structures and thus represent a significant advancement in the field of microporous semiconductors. (C) 2010 Elsevier Inc. All rights reserved.

Miniaturization of Bi2Te3 compounds is of great interest in semiconductor industries due to their distinct anisotropic thermoelectric properties at room temperature. The aim of the present work was to investigate the mechanism of the electrodeposition of Bi2Te3 compounds on stainless steel substrates and relate the morphology and composition of the resulting deposits to experimental parameters. Cyclic voltammetry (CV) experiments in acidic solutions containing Bi3+ and/or HTeO2+ ions show that the deposition potential for the Bi2Te3 compound is more positive than either of the single elements alone. A detailed mechanism of the co-deposition was obtained by varying the concentrations of the two elements and evaluating the corresponding morphological and compositional changes of the deposits. The results show that the deposition of Te is kinetically hindered and that Bi deposition plays a major role during the co-deposition.

In the selective catalytic reduction (SCR) of NO by dimethyl ether (DME), the formation of unexpectedly high amounts of NO2 over 300 degrees C has previously been reported, In this study, we explain this phenomenon by radical reactions initiated by DME and O-2, during which DME is partly oxidized and NO2 is formed in the presence of NO. For the design criteria of a DME-SCR catalyst, these gas phase reactions have mainly three consequences: (i) another type of reducing agent than that fed into the reactor reaches the catalyst. (ii) no activation of the reducing agent such as partial oxidation is required, and (iii) several of the proposed intermediate species for HC-SCP, e.g. NO2, HONO, CH3-NO2, and CH3-NO form already in the gas phase. An efficient DME-SCR catalyst should thus have high selectivity for reduction of NO, predominately by partially oxidized Cl-compounds, and it should not have particularly strong oxidizing properties to avoid non-selective oxidation of these Cl-compounds. These two requirements appear to be reasonable well met by the acidic zeolite H-ZSM-5.

The reversible sorption of water molecules in the crystalline microporous semiconductor K-SBC-1 was investigated using temperature-resolved single-crystal XRD analysis. Three crystallographic sites of adsorbed water molecules, differing in adsorption strength, were discovered in the pores of K-SBC-1. The least tightly bound is located at the centre of the {Sb12O18} tube and begins to desorb around 50°C. Above 200°C the more strongly bound water molecules rearrange from their potassium-coordinating positions to the centre of the tube, thus obtaining the characteristics of the loosely bound water, and desorb thereafter. At 240°C approximately 10% of the water has desorbed, leaving the host framework of K-SBC-1 intact. Upon re-adsorption of water at room temperature the molecules preferentially adsorb at sites in the centre of the {Sb12O18} tube. This shows that a heat treatment of 240–300°C activates K-SBC-1 for sorption and explains the observed facile desorption of water from activated samples.

Seven samples within the series YMn 4+ x Al 8 − x (−2.0 ≤ x ≤ 2.5) were synthesized using direct reaction of the elements. The thermoelectric properties of the samples were characterized by measurements of resistivity, thermal conductivity and thermopower. According to transport measurements, slight Mn-deficiency influences the electronic conductivity of the YMn 4+ x Al 8 − x system, implying that the electronic structure is marginal to the metal-semiconductor boundary. Furthermore, the ZT values of the samples prepared in this study were low. Experimental results indicated that structurally ordered YMn 4 Al 8 shows metallic conductivity, whereas off-stoichiometric compounds displayed semiconductor-like behavior, at low temperatures.

Micrometre-sized aluminium particles are used as pigments in silver inks and for environmental reasons it is desirable to develop water-based formulations of such pigments. In waterborne coatings, however, aluminium is prone to react with water, with subsequent hydrogen gas evolution and loss of the silvery lustre. The protection against water of aluminium pigments by adsorption of either a nonionic or an anionic surfactant has been evaluated. Phosphate esters with different lengths of the hydrocarbon tail have been synthesised and tested, and were found to provide very effective protection of the pigments. Sodium dodecyl sulphate (SDS), on the other hand, was completely ineffective as inhibitor, even though the adsorption isotherm was about the same as for the structurally similar sodium dodecyl phosphate (SDP). This difference may be explained by formation of different types of complexes with the aluminium oxide surface. Outer-sphere complexes are suggested for SDS, whilst SDP can form more stable inner-sphere complexes. Tests with the non-surface active methyl phosphate as inhibiting agent gave insufficient protection, indicating that surface activity is crucial for the inhibition, and that the use of the phosphates as such is not enough to give proper protection. The work shows that amphiphilic compounds having phosphate as anchoring group are efficient in providing water resistance to aluminium pigments.

Anatase TiO 2 is evaluated as catalyst support material in authentic Pt-TiO 2 /C composite gas diffusion electrodes (GDEs), as a different approach in the context of improving the proton exchange membrane fuel cell (PEMFC) cathode stability. A thermal stability study shows high carbon stability as Pt nanoparticles are supported on TiO 2 instead of carbon in the Pt-TiO 2 /C composite material, presumably due to a reduced direct contact between Pt and C. The performance of Pt-TiO 2 /C cathodes is investigated electrochemically in assembled membrane-electrode assemblies (MEAs) considering the added carbon fraction and Pt concentration deposited on TiO 2 . The O 2 reduction current for the Pt-TiO 2 alone is expectedly low due to the low electronic conductivity in bulk TiO 2 . However, the Pt-TiO 2 /C composite cathodes show enhanced fuel cell cathode performance with growing carbon fraction and increasing Pt concentration deposited on TiO 2 . The proposed reasons for these observations are improved macroscopic and local electronic conductivity, respectively. Electron micrographs of fuel cell tested Pt-TiO 2 /C composite cathodes illustrate only a minor Pt migration in the Pt-TiO 2 /C structure, in which anatase TiO 2 is used as Pt support. On the whole, the study demonstrates a stable Pt-TiO 2 /C composite material possessing a performance comparable to conventional Pt-C materials when incorporated in a PEMFC cathode. © 2008 Elsevier B.V. All rights reserved.

Silver/alumina is one of the most promising catalyst materials for HC-SCR. The reaction mechanism remains incompletely understood, however. Isocyanate species (–NCO) and cyanide species (–CN), important intermediates in the reaction path in HC-SCR, were investigated by gas-phase FTIR and DRIFT spectroscopy in step-response experiments. In accordance with the literature, the corresponding gas-phase species, HNCO and HCN, were always detected at the same time at the different steps of the experiment; however, the accumulation and consumption of surface –NCO and –CN species did not show a similar correlation. Consequently, in conflict with the literature, we propose two parallel, independent reaction pathways for –NCO and –CN species. In one of these reaction pathways, surface nitrates react with C-containing surface species either directly to –NCO or via R–NO2 species. In the other pathway, C-containing surface species react with gas-phase NOx or short-lived N-containing surface species to R–NO species and subsequently to –CN species.

Hexagonal phase mesoporous (H-1-Pt) was recently reported to have different catalytic properties compared to conventional platinum catalysts. To further investigate this observation the catalytic activity of H-1-Pt/Al2O3 for CO oxidation was compared with the activity of a corresponding catalyst prepared from Pt-black (Pt-black/Al2O3). The H-1-Pt/Al2O3 catalyst showed ignition at lower temperatures but extinction at higher temperatures compared to Pt-black/Al2O3. These observations were further supported by oxygen step-response experiments at constant temperature, where the H-1-Pt/Al2O3 catalyst showed ignition at lower oxygen concentrations when starting from a CO poisoned surface and extinction at higher O-2 concentrations when starting from the high-reactive state. Furthermore, adsorption of CO on the catalysts was studied in situ using infrared spectroscopy in absence and presence of oxygen after pre-oxidation and pre-reduction, respectively. At 150 degrees C the H-1-Pt/Al2O3 sample showed activity for CO oxidation in the presence of oxygen regardless of pretreatment, whereas Pt-black/Al2O3 was inactive due to CO self-poisoning. The differences observed in the low reactive state are suggested to be due to structural differences of the platinum surface in the catalysts resulting in a lower sensitivity of the H-1-Pt/Al2O3 catalyst towards CO self-poisoning and a higher capacity to activate oxygen, and thus a higher activity for CO oxidation. During the high reactive state, the observed higher sensitivity to the concentration ratio between CO and oxygen, and to the temperature is likely due to less optimal ratio between the sticking coefficients of the reactants on the H-1-Pt catalyst and to higher mass-transport limitations in its narrower pores during the initial stage of the extinction.

Colloidal suspensions of almost spherical and crystalline Pt nanoparticles between 1.6 and 2.6 nm in diameter and with narrow size distribution were synthesized using the phase transfer method (P ...

Sr3NiPtO6 and Sr3CUPtO6 were evaluated as low-platinum alternative oxygen reduction catalysts in a solid polymer electrolyte fuel cell at 80 degrees C. The oxides were synthesised using a new method based on an organometallic precursor route. The electrochemical evaluation showed similar oxygen reduction performance for Sr3NiPtO6 and Sr3CUPtO6, with a slightly higher activity for Sr3NiPtO6. In comparison with the oxides, the oxygen reduction activity for a commercial Pt/C catalyst was approximately 10 times higher. XRD analysis of the used electrodes revealed that the oxides were not stable in the PEMFC environment, and converted into platinum during operation. Elemental analysis of the used electrodes also showed a difference in platinum formation, where the platinum content on the surface of the electrode facing the gas diffusion layer was several times higher for Sr3NiPtO6 than Sr3CUPtO6. This indicates that the Sr3NiPtO6 electrode may be more susceptible to platinum migration.

Platinum nanoparticles were incorporated within the pore system of ordered mesoporous carbon (OMC) by impregnating the carbon with a water-in-oil (w/o) microemulsion containing dissolved platinum salt followed by reduction of the platinum ions in situ inside the carbon pore system. The procedure provides preparation of metallic nanoparticles from hydrophilic precursors inside the hydrophobic carbon support structure with simultaneous control of the maximum metal particle size. Electron tomography was used to verify the presence of platinum nanoparticles inside the carbon material.

Nanosized, crystalline rutile TiO2 was synthesized at room temperature using a microemulsion-mediated system followed by hydrothermal treatment. The formed rutile had a specific surface area of about 40 m2 g-1 and the rutile crystals had dimensions of about 10 nm × 150 nm, which aggregated into 200-1000 nm sized bundles. The adsorption and photocatalytic degradation of diisopropyl fluorophosphate (DFP) and dimethyl methylphosphonate (DMMP) over these rutile TiO2 nanoparticles in dry and wet synthetic air was investigated by in situ diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy during simulated solar light illumination. The methyl and isopropyl groups do not dissociate upon adsorption on either dry or humidified rutile nanoparticles. The F atom in DFP is, however, easily hydrolyzed and is readily dissociated upon interaction with hydroxyls on the TiO2 surfaces and leads to a destabilization of the DFP molecule. The initial solar light induced photodegradation rate for DFP and DMMP is 5.9 × 10-4 and 1.0 × 10-4 s-1 in dry conditions and 8.1 × 10-4 and 0.7 × 10-4 s-1 in wet conditions (corresponding to 2-3 monolayers (ML) water coverage), respectively. The main intermediate partial oxidation surface products are found to be surface bound formate-carboxylate-carbonate (R-COO-) and phosphate (R-POO-) species. Among them η1-coordinated acetone and μ-formate, bicarbonate, and bidentate R-POO- moieties are detected. These surface species accumulate on the surface during the entire illumination period (60 min), and lead to a decreased total oxidation rate. Controlled humidification of the rutile surface leads to a reduction of the concentration of R-COO- intermediates, while at the same time maintaining approximately the same rate of DFP and DMMP photooxidation. The latter is due to blocking of Ti surface cation sites, which prevents the formation of strongly bonded surface compounds, in particular μ-coordinated R-COO- and R-POO- species. The findings show that, it is possible to optimize the sustained photocatalytic degradation of organic phosphorous compounds by controlled humidification of the reaction gas.

saturated hydrocarbons, propane and isobutane, has been investigated over acidic zeolite HZSM-5. The activity for NO2 reduction and the selectivity for N-2 formation correlate well with the intracrystalline acidity (Bronsted acid sites) of the zeolite. Isobutane is a more efficient reducing agent than propane due to its tertiary hydrogen being more readily activated than the secondary hydrogen in propane. In situ DRIFT step-response experiments with NO2 and isobutane show formation of surface bound NO+, isocyanate, unsaturated hydrocarbons and amine species. The NO+ species seems to play an important role in the reduction of NO2 probably by reacting with alkenes formed from carbenium ion adsorbates. These species likely form isocyanates, amine species and finally nitrogen.

Physical mixtures of CuFER and HZSM-5, CuFER and AgMOR, and CoFER and AgMOR zeolites were investigated as potential dual pore system catalysts for continuous lean NO x reduction with propene or isooctane as reducing agents. The effects of variations in temperature and oxygen concentrations were studied using steady-state experiments. Despite lower rates of external and internal mass transfer, the mixture of CuFER and HZSM-5 was found to have the highest NO x reduction activity with isooctane as the reducing agent. A maximum NO x reduction of about 40% was found for this catalyst at 350 °C and 12% oxygen. In this case, the CuFER extrudate acted as an NO oxidation catalyst, and the NO 2 formed was reduced by the isooctane in the HZSM-5 extrudate. The better performance of the CuFER and HZSM-5 mixture compared with the other mixtures was attributed to a higher selectivity for NO 2 to form nitrogen in the reduction reaction. When propene was used, the two mixtures containing CuFER showed similar reduction activity with a maximum conversion of about 65% at 370 °C and 2% oxygen. In contrast with the isooctane, the NO x reduction with propene occurred primarily in the extrudate containing ferrierite. Again, the selectivity of NO 2 to form nitrogen governed the overall NO x reduction.

Monolithic Pt/gamma-Al2O3 catalysts were prepd. by depositing of the platinum phase, either homogeneously or heterogeneously (i.e., local high platinum concn.), in the washcoat. The influence of the platinum distribution on the ignition and extinction processes for oxidn. of CO, propene, and propane, resp., was investigated by both temp.-programmed and oxygen step-response flow-reactor expts. In addn., in situ XANES spectroscopy was used to follow changes in the chem. state of platinum during propane oxidn. For samples with heterogeneous platinum distribution, the results show an improved low-temp. activity for CO oxidn., whereas no clear improvement is obsd. for oxidn. of propene or propane. Comparison of the results for CO and hydrocarbon oxidn. shows that the improved activity cannot be explained by thermal effects. Moreover, calcns. indicate that the enhanced activity for CO oxidn. can be due to mass-transfer phenomena. This could not be confirmed by our expts., however. Instead, the improved activity for CO oxidn. can be due to varying platinum particle size between the samples. Furthermore, the oxidn. of propane is shown to be highly influenced by the oxygen concn., showing an activity max. for gas compositions close to the stoichiometric. High oxygen levels result most probably in a predominantly oxygen-covered surface, which inhibits the reaction and, as supported by the in situ XANES experiments, passivates the surface by forming platinum oxide.

The photocatalytic decomposition of diisopropylfluorophosphate (DFP) over nanostructured anatase and rutile TiO2 powder was investigated by FTIR and XPS. Upon irradiation with artificial solar light DFP decomposed on both polymorphs as evidenced by FTIR. For both crystalline structures acetone and subsequently coordinated formate and carbonate were observed on the surface during the photocatalytic reaction as the isopropyl groups dissociated from DFP. XPS revealed that small amounts of phosphates and inorganic fluoride (TiF) gradually built up on both TiO2 surfaces, while organic F was present only on the rutile phase. From repeated cycles of intermittent DFP adsorption and irradiation measurements, the decomposition rates and formation of residuals on the surface were deduced. It was found that the overall oxidation yield is higher on anatase than rutile. The oxidation rate decreases with increasing irradiation time, an effect that is more pronounced on rutile. We find that both the difference between the polymorphs and the initial decrease of the oxidation yield can largely be explained by variations in surface area rather than poisoning by POx or F species. In particular, we observe a dramatic decrease of the specific area of rutile as a function of photocatalytic oxidation cycle.

This study focuses on the mechanism of lean NOx reduction by propane, over acidic zeolites (HZSM-5), and the influence of surface acidity. In situ FTIR measurements of ammonia adsorption indicate a higher number of Bronsted acid sites for a sample with a low SiO2/Al2O3 ratio. The activity for NOx reduction and the selectivity for N2 formation correlate well with the Bronsted acidity. Step-response experiments with NO2 and propane show the formation of surface-bound NO+, isocyanate, unsaturated hydrocarbons, and amine species. Formation of the latter two seems to be closely related to the Bronsted acidity. In the NO2 reaction with propane, the NO+ species seem to play a vital role, probably reacting with carbenium ions (from propane cracking) to form isocyanates, which may be hydrolysed to amine species. Step-response experiments with isopropylamine and NO2 indicate a fast reaction, where the amine and NO+ species react over Bronsted acid sites. Hence, amine species are possible reaction intermediates in the lean reduction of NO2 by saturated hydrocarbons, such as propane, over HZSM-5.

Mixed metal oxides with perovskite structure were prepared using microemulsions. The perovskite materials had the nominal composition La0.8Sr0.2M1-xRhxO3 (where M = Mn, Co, Fe and x = 0, 0.1). X-ray diffraction analysis showed that the perovskite phase was generally obtained at relatively low temperatures, ≤700C. When the calcination temperature was kept low, the surface areas were relatively high and the highest surface area (25m2/g) was observed for La0.8Sr0.2Mn0.9Rh0.1O3 after calcination at 500C. Microstructural analysis using TEM and SEM showed particles in the size range of microns consisting of smaller crystallites in the range of 30–50 nm. The materials were tested as catalysts for the selective reduction of NOx with NH3 (NH3-SCR) and the activity varied between samples with different transition metal. However, potassium, which originated from the technical surfactant used in the microemulsion, was detected by XRF analysis in various amounts in the samples and it was therefore not possible to conclude if the differences in catalytic performance were due to the different transition metals or to the potassium in the samples. Characterisation showed that it was possible to incorporate rhodium in the perovskite materials, which generally resulted in enhanced catalytic activities for the reduction of NOx with NH3.

In order to reduce CO2 emissions there is a trend towards an increased use of more fuel-efficient lean burn combustion engines and thus an increased need for deNOx catalysts for such engines. In this study a mechanical mixture of CoFER and HZSM-5 zeolites was studied as a dual pore system catalyst for the continuous lean reduction of NOx with isobutane as reducing agent. The degree of NOx conversion was found to be strongly dependent on the oxygen concentration in the gas mixture, and the highest degree of reduction was achieved with 10% O2. This optimum is explained by the need for NO2 as an intermediate for the catalyst to work efficiently, and that above a certain oxygen concentration O2 oxidises the hydrocarbon resulting in a lower reduction potential for NOx. At an operating temperature of 350 °C the conversion of NOx to N2 was 52% under steady-state conditions, but the efficiency can be improved further by optimisation of the oxidising zeolite and of the mixing ratio of the two zeolites.

Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance.

The effect of ammonia supply on the selective catalytic reduction of NOX over zeolite H-ZSM-5 was investigated using step response experiments between 200 and 500 degrees C. For inlet NO:NO2 ratios > 1, the activity for NOX reduction transiently increased when NH3 was removed from the feed. For NO:NO2 ratios less than or equal to 1, the NOX reduction however decreased. By pulsing NH3 to the feed, the activity for NO reduction was enhanced up to five times compared to continuous supply of ammonia. For NO:NO2 ratios exceeding one, also the selectivity towards N2O formation was lower with transient ammonia supply. Temperature programmed reaction experiments with preadsorbed NH3 showed highest initial NOX reduction activity when ammonia had been adsorbed at 300 or 250 degrees C compared to 200 degrees C. A minimum in NO reduction was observed at 130 degrees C independent of the ammonia adsorption temperature. For NO:NO2 ratios > 1, the results strongly indicate that NO oxidation is the rate determining step in the ammonia selective catalytic reduction (NH3-SCR) reaction over H-ZSM-5.

Platinum nanoparticles have been prepared by the reduction of metal ions with hydrazine in oil–water microemulsions consisting of sodium bis(2-ethylhexyl)sulphosuccinate (AOT)+cyclohexane+water of varying composition. The catalytic efficiency of the synthesized metal nanoclusters has been tested for oxidation of carbon monoxide. Effects of the nature of the platinum salt, [H 2 O]/[surfactant] ratio in the microemulsions and the addition of polymers on the catalytic efficiency of the synthesized metal nanoparticles have been investigated. Catalytic oxidation of CO gas was carried out in a vertical quartz tube connected to a quadrupole mass spectrometer. Whereas, using pure alumina as a catalyst, complete conversion of CO to CO 2 was observed at 325 °C, platinum nanoparticles adsorbed on alumina was found to carry out such conversion at 145 °C.

Formation of ordered mesoporous materials using surfactant templating proceeds via mechanisms relying on optimising interactions between the inorganic and organic components of the synthesis. For oxides, the rates of hydrolysis and condensation of the inorganic species relative the rate of assembly of the mesostructure is crucial. Synthetic strategies to control these factors have been reviewed and it appears that mesostructured silica can be prepared in most phases found in binary surfactant–water systems by optimising the volume fraction of the surfactant and the hydrolysed inorganic precursor.

Oxidation of CO over Co3O4 at ambient temperature was studied with flow reactor experiments, and in-situ spectroscopic and structural methods. The catalyst deactivates during the reaction. The rate of deactivation increased with increasing CO or CO2 gas-phase concentration but decreased with increased 02 concentration or increased temperature. Regeneration of the catalyst in 10% O-2/Ar was more efficient than regeneration in Ar alone. The presence of carbonates and surface carbon on the deactivated catalyst was concluded from TPO experiments. None of these species could, however, be correlated with the deactivation of the catalyst. In-situ FTIR showed the presence of surface carbonates, carbonyl, and oxygen species. The change in structure and oxidation state of the catalyst was studied by in-situ XRD, in-situ XANES, XPS, and flow reactor experiments. One possible explanation for the deactivation of the catalyst is a surface reconstruction hindering the redox cycle of the reaction.

A preparation method for making a high temperature stable monolith catalyst, using a cobalt-rich cobalt-aluminate spinel (Co1.66Al1.34O4) as the active material, is proposed. This catalyst, which is known for being active for CO oxidation at low temperatures, was prepared and characterised by BET, SEM, XRD, XPS and CO-TPD. The catalyst was tested for its capacity to oxidise carbon monoxide using oxygen only and oxygen in combination with other compounds typically present in cold start exhausts from Otto engines, i.e. CO2, C3H6. NO, H2, H2O or SO2. When the catalytic activity was tested with only CO and O-2 present in the feed gas, complete conversion was reached at room temperature. When other compounds were present in the gas mixture, they inhibited the CO oxidation to various degrees. The degree of inhibition for the compounds investigated was found to be: SO2 > H2O > NO = C3H6 > H2 > CO2. The main reason for the loss of activity is suggested to origin from the compounds adsorption and formation of different species on the cobalt oxide surface, which seems to inhibit the reduction and/or re-oxidation process of the metal oxide surface and/or the adsorption of CO.

Mean-square displacements (MSDs) and individual-ion square-displacements (ISDs) for the different constituents in Ca-doped CeO2(0 1 1) slabs at 300 K have been studied as a function of depth from t ...

Clathrates are periodic solids in which tetrahedrally coordinated atoms form cages that surround a metal atom. We examine Slack's suggestion that the metal atoms scatter phonons but not electrons, thus lowering the thermal but not the electric conductivity. If this is true, as transport measurements indicate, these compounds are promising thermoelectric materials.

Solid solutions of nanophase cerium oxides have been prepared and the relationship between their bulk crystal structure and surface characteristics has been studied at room temperature with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS

The catalytic activities of nanophase doped cerium oxides have been investigated. Markedly enhanced catalytic activities for the reaction 2 CO + SO2 → 2 CO2 + S0 were invoked by the dopants. A Ca-doped CeO2 sample had a light-off temperature at 430 °C, which was 70 °C lower than an undoped CeO2 sample. Neither of the samples were subject to phase changes during the reaction. Samples of Pb-doped and Co-doped CeO2 initially showed low catalytic activities for the reaction, but became, during the experiments, more active than the undoped CeO2 sample. These samples developed a PbS and a CoS2 phase during the respective experiments. All samples showed a hysteresis in the activity for the reaction. This hysteresis was larger for the doped samples than the undoped, giving fall-off temperatures in the range of 200–320 °C. The materials were further evaluated by temperature programmed reduction and oxidation (TPR/TPO) studies using CO and SO2 gases.