排序方式: 共有34条查询结果,搜索用时 15 毫秒
1.
Tanja Kolli Katariina Rahkamaa-Tolonen Ulla Lassi Auli Savimki Riitta L. Keiski 《Catalysis Today》2005,100(3-4):303-307
In this study, Pd/Al2O3 and Pd/BaO/Al2O3 metallic monoliths were used to investigate the effect of BaO in C2H4 and CO oxidation as well as in NO reduction. A FT-IR gas analyser was used to study the activity of the catalysts. Several activity experiments carried out with dissimilar feedstreams revealed that BaO enhances CO and C2H4 oxidation as well as NO reduction reactions in rich conditions. This effect is due to BaO, which causes a decrease in the ethene poisoning of palladium. In lean conditions BaO is present in the form of Ba(OH)2 which reacts with oxidised NO releasing water. Therefore, NO was stored during the lean reaction. 相似文献
2.
T. Kanerva V. Kröger K. Rahkamaa-Tolonen M. Vippola T. Lepistö R. L. Keiski 《Topics in Catalysis》2007,45(1-4):137-142
Laboratory-scale ageing and poisoning procedures were performed on selected diesel catalysts. The results showed that phosphorus
poisoning together with high temperature ageing has a strong effect on the catalytic activity and microstructure of platinum
containing catalysts. Phosphorus poisoning contaminated the catalysts resulting in phosphate formation, e.g. CePO4 and AlPO4. Poisoning and air ageing increased platinum particle-size and washcoat grain-size. 相似文献
3.
Kolli T. Rahkamaa-Tolonen K. Lassi U. Savimäki A. Keiski R. L. 《Topics in Catalysis》2004,30(1-4):341-346
Topics in Catalysis - The interaction of CO, C2H4, O2, and NO reaction gas compounds over the metallic Pd/Al2O3 and Pd/OSC/Al2O3 monoliths was investigated in order to understand the behaviour of... 相似文献
4.
Katariina Rahkamaa-Tolonen Teuvo Maunula Mari Lomma Mika Huuhtanen Riitta L. Keiski 《Catalysis Today》2005,100(3-4):217-222
The activity of fresh and hydrothermally aged zeolite-based catalysts in the NH3-selective catalytic reduction (SCR) reaction with excess of oxygen were studied. In addition, the effect of NO2 in the gas feed as well as the acidity of the catalysts for the SCR activity was investigated. The studied catalysts were hydrogen, copper, iron and silver ion exchanged ZSM-5, mordenite, beta, ferrierite, and Y-zeolites. The investigation verifies that the zeolite-based catalysts are very promising for the ammonia SCR reaction. Especially, the activity at low and high temperatures was higher than the activity of commercial vanadia-based catalysts. From the studied catalysts, Fe-beta was the most potential one. The presence of NO2 in the inlet flow enhanced significantly the catalytic activity of fresh and hydrothermally aged zeolite catalysts. This suggests that the oxidation of NO to NO2 is probably the rate-determining step for the SCR reaction. 相似文献
5.
Preliminary results on MS-325 versus ProHance enhanced magnetic resonance angiography (MRA) at low field strength in a rabbit
model are reported. MS-325-enhanced images were acquired in vivo and compared with pre-contrast as well as conventional contrast-enhanced
images. Visual image quality observations correlated with measurements of signal-to-noise ratio (SNR) and contrast-to-noise
ratio (CNR). While published in vitro data show 7-fold greater relaxivity for MS-325 compared with conventional contrast agents,
we observed an even greater effect here due, presumably, to better matching of the longer vascular lifetime with longer scan
time in this study. In addition, overall vessel clarity improved significantly throughout all the phases of the experiment
in MS-325-enhanced images when compared with conventional contrast-enhanced images. 相似文献
6.
Nurmi Jari-Erik; Pulliainen Harry; Salmela-Aro Katariina 《Canadian Metallurgical Quarterly》1992,7(2):194
Control beliefs play an important role in how people direct their own development during their life span. However, research into age differences in control beliefs has produced inconsistent results. In this study, 381 Ss (aged 19–71 yrs) completed a questionnaire in which they were asked to write down their goals and concerns. They were then asked to rate each on a 4-point bipolar rating scale measuring internality–externality. The results showed that Ss' control beliefs became more external with age. However, part of the increase in externality was found to be caused by increasing interest in domains that are generally considered uncontrollable. Ss' beliefs about health-, self-, offspring-, and property-related goals became more external with age, unlike goals concerning future education, occupation, family, and travel. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
Yrjö H. Roos Katariina Roininen Kirsi Jouppila Hely Tuorila 《International Journal of Food Properties》2013,16(2):163-180
Abstract A crispy snack model, composed of maltodextrin, wheat flour, salt, and water, with a clearly measurable glass transition was designed and produced by extrusion. The material was used to investigate effects of glass transition and water plasticization on mechanical properties and sensory crispness. Water sorption and the glass transition temperature range were determined gravimetrically and using differential scanning calorimetry (DSC) for samples stored at 0 to 85% relative humidity (RH), respectively. Mechanical properties were determined for extradates rehumidified at 0 to 76% RH. Three sensory panels evaluated crispness intensities of extrudates rehumidified at 33 to 76% RH by either breaking samples with fingers (Finger Task), biting using the incisor teeth (Bite Task), or biting and chewing (Bite‐and‐Chew Task). The extrudate was plasticized by water, as observed from a typical decrease of Tg with increasing water content. Changes in mechanical properties and loss of crispness occurred at an intermediate water activity level coinciding with the extent of plasticization depressing the Tg to below ambient temperature. The changes in mechanical properties and sensory crispness intensities with increasing water activity had sigmoid shapes following the Fermi's model. Loss of crispness as a result of water plasticization is likely to apply to a number of low‐moisture food materials, although various mechanical and sensory properties do not necessarily change in unison as the materials undergo a glass transition. 相似文献
8.
Katariina Penttilä Mikko Keskilammi Lauri Sydänheimo Markku Kivikoski 《The International Journal of Advanced Manufacturing Technology》2006,31(1-2):116-124
The trend in industrial automation is to move towards fast and real-time identification, further improving the high-level of accuracy that is needed to enable continuous identification and monitoring. The interest in adopting radio frequency identification (RFID) technology for use in automation systems with minimal manual involvement is increasing rapidly. RFID systems are capable of providing real-time object visibility with high accuracy enabling continuous identification and location of all items and thereby providing accurate real-time data management instead of simple snapshots. In this paper, the use of multiple reader antennas is examined against collision and interference avoidance. Also, antenna operation is studied in typical industrial environments containing metallic objects or other conducting surfaces. In addition, this paper reviews different tag antennas and their characteristics for particular item identification cases. These cases include items made of specific materials that obstruct or prevent radio wave propagation by either absorbing or reflecting them. The results given in this paper are fully applicable with practical RFID solutions. 相似文献
9.
Mika Huuhtanen Katariina Rahkamaa-Tolonen Teuvo Maunula Riitta L. Keiski 《Catalysis Today》2005,100(3-4):321-325
In this study, pure and platinum-loaded zeolites, ZSM-5, Beta, zeolite Y and Ferrierite, were examined for the reduction of NO with propene in lean conditions and at low temperatures. The studies were carried out by utilising the FT-IR technique both in determination of surface species as well as concentrations in the gas flow at reactor outlet. The maximum in the intermediate formation can be observed at the light-off temperatures over all studied catalyst materials. The maximum conversions of NO were reached with 1 wt% Pt-loaded Beta and Y zeolites in excess oxygen. The lowest light-off temperatures of NO as well as propene can be detected also with Beta and Y zeolite catalysts. 相似文献
10.
Kröger V. Kanerva T. Lassi U. Rahkamaa-Tolonen K. Lepistö T. Keiski R. L. 《Topics in Catalysis》2007,42(1-4):433-436
Powdered ZSM-5 and Pt/ZSM-5 catalysts were studied as fresh and after two treatments: hydrothermal ageing and phosphorus poisoning
in hydrothermal conditions. The results showed that the deactivating effect of phosphorus was stronger than the effect of
the hydrothermal treatment alone. Phosphorus had accumulated in the samples during the ageing. The decrease in specific surface
area and increase in Pt particle size indicated the possible reasons for deactivation. 相似文献