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Nanocrystalline powders of WO 3 , pure and with catalytic additives such as copper and vanadium, for ammonia gas detection are analyzed in detail. Material was annealed at two different temperatures ͑400 and 700°C͒ and catalytic additives were introduced in two different concentrations ͑0.2 and 2%͒ in order to study the gas sensor performances of these WO 3 -based materials. Crystalline structure characterization shows that a mixture of triclinic and monoclinic structure was present in the materials analyzed. Additive characterization reveals that catalytic metals were located as cations in the matrix lattice. Thick-film gas sensors based on pure WO 3 show an abnormal sensor response, which is attributed to a complex process originated by the oxidation of ammonia to NO. On the other hand, catalyzed WO 3 -based gas sensors show a more direct and simple sensor response. Interaction of ammonia with WO 3 was studied by diffuse reflectance infrared spectroscopy. Only pure WO 3 presented a WvO overtone band decrease and some nitrosil bands. In this case, NH 3 would react with the surface oxygen of terminal WvO bonds and would lead to the formation of NO. Catalyzed WO 3 avoided this reaction and so the unselective catalytic oxidation of NH 3 , improving sensor response. Influence of introduced additives on ammonia oxidation and thus on sensor response is discussed.Nowadays ammonia-gas detection is a very important target for different industrial processes and human comfort. 1,2 Current NH 3 measurement techniques, such as chromatography or infrared absorption, are too expensive or not fast enough to be used in a real time control system. 3 It is also very difficult to adapt these techniques to in situ measurements. On the other hand, detection of ammonia by gas sensors has been reported as problematic and not satisfactorily covered by present commercial products. 4 Gas sensors based on metal oxides are able to monitor gas concentrations by a change of electrical conductance of the sensitive layer. Although many materials have been proposed for NH 3 detection (SnO 2 ,TiO 2 ,Nb 2 O 5 ,MoO 3 ), 5-8 WO 3 is nowadays considered as one of the most promising materials for this purpose, according to recent literature. Sensor responses to this gas, 9 interference from NO x , 1 and influence of noble metals and metal oxides added to pure WO 3 10,11 have been considered. However, mechanisms of interaction between NH 3 and WO 3 are not well understood yet, and the role played by catalytic additives needs further explanation.The aim of this work is to contribute to the study of the interaction between NH 3 gas molecules and WO 3 nanopowders and to understand the role played by copper and vanadium as catalytic additives. Cu and V were chosen because they have been successfully used in catalysis involving NH 3 . 12,13 X-ray diffraction ͑XRD͒ and Raman spectroscopy were applied to structurally characterize the obtained material. X-ray photoelectron spectroscopy ͑XPS͒ and electron paramagnetic resonance ͑EPR͒ were employed to investigat...

The influence of carbonic anhydrase (CA) on the CO2 absorption rate and CO2 load in aqueous blends of the amino acid ionic liquid pentaethylenehexamine prolinate (PEHAp) and methyl diethanolamine (MDEA) was investigated and compared to aqueous monoethanolamine (MEA) solutions. The aim was to identify blends with good enzyme compatibility, several fold higher absorption rates than MDEA and superior desorption potential compared to MEA. The blend of 5% PEHAp and 20% MDEA gave a solvent with approximately 5-fold higher initial absorption rate than MDEA and a 2-fold higher regeneration compared to MEA. Experiments in a small pilot absorption rig resulted in a mass transfer coefficient (KGa) of 0.48, 4.6 and 15 mol (m 3 s mol fraction)-1 for 25% MDEA, 5% PEHAp 20% MDEA and 25% MEA, respectively. CA could maintain approximately 70% of its initial activity after 2 h incubation in PEHAp MDEA blends. Integration of CA with amine-based absorption resulted in a 31.7% increase in mass of absorbed CO2 compared to the respective non-enzymatic reaction at the optimal solvent: CA ratio and CA load. Combining novel blends and CA can offer a good compromise between capital and operating costs for conventional amine scrubbers, which could outperform MEA-based systems.

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