Search

Abstract: Volume-doped CoTiO3 was synthesized via the polyol method. As volume dopants Gd, Ho, K, La, Li, Na, Pb, Sb, and Sm with a concentration of 2at.% were applied. By X-ray diffraction (XRD) materials structure was confirmed, while the materials morphology was imaged using scanning electron microscopy (SEM). Thick films of the nanocrystalline material were applied with a laboratory robotic system to a 8×8 multielectrode substrate. We show that the p-type semiconducting material doped with various metals is applicable for the fast detection of ethanol and propylene. The volume dopants affect the sensing and response behavior of the base material. [Copyright &y& Elsevier]

Abstract: Perovskite-type LnMO3 (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; M=Cr, Fe) oxides were prepared by the polyol mediated synthesis. Thick films of the prepared materials were electrically characterised using high throughput impedance spectroscopy (HT-IS). All samples showed p-type semiconductivity. Ethanol and propylene were used to test the gas sensing behaviour in a temperature range from 200 to 500°C. A correlation between the (Ln–O) binding energy and the sensing properties is observed. [Copyright &y& Elsevier]

Abstract: p-Type semiconducting nanocrystalline CoTiO3:La (2at.%) was synthesized via polyol method. X-ray diffraction (XRD) was used to confirm the materials structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to image the materials morphology. Thick films of the nanocrystalline material were applied with a laboratory roboting system to an 8×8 multielectrode substrate, developed for high-throughput impedance spectroscopy (HTIS). With this method it was shown that the base material doped with various metals (Au, Ce, Ir, Pd, Pt, Rh, Ru) in different concentrations (0.2–0.6at.%) is applicable for the fast detection of ethanol, propylene and NO2, depending on the surface doping and the operation temperature. [Copyright &y& Elsevier]

Zeolites are in use as catalyst materials in the selective catalytic reduction of NO x with NH 3 as reducing agent. An initial NH 3 -adsorption on the catalyst is essential for the reaction with NO and NO 2 to occur. Due to the adsorbed NH 3 , the proton conductivity of the zeolite increases markedly. This change of the electrical properties of the catalyst material can be monitored in a contactless way and in operando using a radio frequency-based method to determine the ammonia loading on the catalyst. In this work, the ammonia storage is examined on a copper exchanged Chabazite Cu-SSZ-13, a typical SCR catalyst as it is in use for serial applications, at different temperatures and various feed ratios. [ABSTRACT FROM AUTHOR]

Abstract: Spinel iron oxide nanoparticles of sizes from 12 to 60nm have been prepared via a hydrothermal synthesis. Thick films of the Fe3−x O4 nanoparticles deposited on interdigital electrodes were applied as resistive gas sensors. The electrical and gas sensing properties were characterized by impedance spectroscopy using multielectrode substrates. The reducing analytes CH4, NO, H2 and NH3 in N2 as a reference were applied in order to investigate the sensor response, the selectivity and the recovery behavior at temperature between 50°C and 300°C. The materials exhibit good sensor responses towards NH3 with low cross sensitivities towards H2 and NO at 250°C. A linearly increasing sensor response towards NH3 and H2 with decreasing particle size was found. [Copyright &y& Elsevier]

The development of more efficient zeolite catalysts for selective catalytic reduction of NO x by NH 3 (NH 3 -SCR) requires insights into both reaction mechanism and real-time state of the catalyst ( e.g. , the storage level of NH 3 ). Here, we show that impedance spectroscopy (IS) can be applied to sense electrically the uptake of NH 3 into proton-conducting, copper-promoted zeolite catalysts, i.e. , into Cu-ZSM-5 and Cu-SAPO-34. Comparative investigations indicate that Cu-SAPO-34, as compared to Cu-ZSM-5, showed high sensitivity to the change of NH 3 concentration at a broader temperature range. While both zeolites performed similarly for direct monitoring of the SCR conversion of stored NH 3 at temperatures above 350 °C, Cu-SAPO-34 showed a better performance than Cu-ZSM-5 at lower temperatures. A simultaneous IS and diffuse reflection infrared Fourier transform spectroscopy (IS-DRIFTS) study revealed that NH 4 + or NH 4 NO 3 intermediates form on the two zeolite catalysts under SCR-related conditions and affect the proton conductivity at low temperatures, thus influencing significantly the monitoring of SCR conversion of stored NH 3 . The correlation of integral electrical responses with molecular processes, achieved by our simultaneous IS-DRIFTS studies, not only clarifies the origin of the sensing mechanism of zeolite catalysts at a molecular level, but also provides a new perspective to understand the NH 3 -SCR mechanism over metal-promoted zeolites at low reaction temperatures. [ABSTRACT FROM AUTHOR]

In order to meet the legislative emission requirements for NO x -containing exhaust gases, SCR catalysts, in particular zeolites, are used. To improve catalysts and the catalytic processes, an in-depth understanding of the reaction mechanisms is required as well as an analysis of the physicochemical properties of the SCR catalysts, preferably in real-time. Here, we introduce a setup combining impedance spectroscopy and infrared spectroscopy in diffuse reflection mode for in situ measurements on zeolites under SCR-related conditions. This setup allows for the first time to simultaneously monitor both, the proton conductivity of zeolites and the vibration modes of the molecules involved in the catalytic conversion of NO by NH 3 . We studied both, pure and Fe-promoted H-form zeolites, as sensors and model catalysts at the same time, and found out that weakly bound NH 3 is dominating the proton conductivity of both zeolites in a temperature range below the desorption temperature of NH 3 . When a part of the weakly bound NH 3 is consumed by the SCR reaction, proton conductivity and thus the sensing effect gets dominated by strongly bound NH 3 . This allows applying impedance spectroscopy to assess the degree of NH 3 loading and the state of the SCR conversion process in zeolite catalyst. [ABSTRACT FROM AUTHOR]

Metal(IV) phosphates such as zirconium phosphate (ZrP) are well known proton conductors based on the mobility of protons localized at Brønsted-acid sites. By introduction of mesoporous silica into the interlayer region, these compact materials are transformed into Porous Phosphate Heterostructures (PPH). Here we studied the electrical properties of PPH and show that the proton conductivity is supported by ammonia, which does not occur neither in ZrP nor in the mesoporous silica. This demonstrates that transforming the layer structure of ZrP into a mesoporous hybrid material leads to a new ammonia gas sensing material. This concept might be promising for the development of new gas sensor materials in general. [ABSTRACT FROM AUTHOR]

Abstract: The dynamic C2H5OH sensitivity of ilmenite-type cobalt titanates volume-doped by 2at% Li, Na, K, Sb, La, Sm, Gd, Ho and Pb was systematically studied with respect to exhaust monitoring. Therefore, the p-type semiconducting CoTiO3 materials were characterized as resistive gas sensors via high-throughput impedance spectroscopy toward 5–200ppm C2H5OH at 300–500°C. The best performing materials were tested further by time-resolved and long-term measurements whereby the CoTiO3 volume-doped with K exhibited an outstanding overall performance. X-ray absorption spectroscopy on this particular material gave evidence that the local structure around Co and Ti remains unaffected by the doping despite of a slight increase in static disorder. Hence, the effect of K doping does not originate from alteration in the metal-to-oxygen interaction as expected from previous findings. [Copyright &y& Elsevier]

Abstract: We present a humidity sensor based on H-ZSM-5 type zeolite that is suitable to detect traces of humidity (∼10–110ppmV) under harsh conditions, e.g. reducing atmosphere (H2) and high temperature (up to 600°C). By means of complex impedance spectroscopy (IS) we show that the zeolite sensor responds linearly towards minimal changes in humidity. Therefore this result indicates that the zeolite sensor is capable to detect traces of humidity in processes where high temperatures in a hydrogen environment are required. [Copyright &y& Elsevier]