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81.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
82.
ABSTRACT: The absorbance of 2,2-diphenyl-1-picrylhydrazyl (DPPH) at 517 nm in methanol and acetone decreased by 20 and 35% for 120 min at 25 °C under light, respectively; in the dark it did not change significantly for 150 min. Decomposition of DPPH under 21% oxygen after 90 min under light was significantly higher than that under 1% oxygen. Absorbance of DPPH in pH 4 buffer solution in methanol, and in pH 10 buffer solution in acetone, decreased by 55 and 80%, respectively, under light for 120 min. The evaluation of antioxidant activity by the changes of DPPH absorbance should be carefully interpreted since the absorbance of DPPH at 517 nm is decreased by light, oxygen, pH, and type of solvent in addition to the antioxidant. 相似文献
83.
Safron Adam; Barch Bennett; Bailey J. Michael; Gitelman Darren R.; Parrish Todd B.; Reber Paul J. 《Canadian Metallurgical Quarterly》2007,121(2):237
Men exhibit much higher levels of genital and subjective arousal to sexual stimuli containing their preferred sex than they do to stimuli containing only the nonpreferred sex. This study used event-related functional magnetic resonance imaging to investigate how this category-specific pattern would be reflected in the brains of homosexual (n = 11) and heterosexual (n = 11) men. Comparisons of activation to preferred sexual stimuli, nonpreferred sexual stimuli, and sports stimuli revealed large networks correlated with sexual arousal, spanning multiple cortical and subcortical areas. Both homosexual and heterosexual men exhibited category-specific arousal in brain activity. Within the amygdala, greater preference-related activity was observed in homosexual men, but it is unclear whether this is a cause or a consequence of their sexuality. In a subsequent analysis of regions hypothesized to support arousal, both participant groups demonstrated widespread increases in evoked activity for preferred stimuli. Aggregate data from these regions produced significant differences between stimulus types in 16 out of 22 participants. Significant activational differences matched reported sexual orientation in 15 of these 16 participants, representing an advance in psychophysiological measures of arousal. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
85.
EPDM/PP热塑性弹性体相态研究 总被引:3,自引:1,他引:2
采用透射电镜(TEM)研究动态硫化EPDM/PP热塑性弹性体制备工艺及增容改性对形态结构的影响,研究发现通过添加增容剂可使EPDM相呈颗粒分布于连续相中。 相似文献
86.
模拟计算表明:采用活性趋于表层的分布,可以较明显地提高国产中温变换催化剂的内表面利用率,有效地节省催化剂用量,而对“热点”温度没有多大影响。 相似文献
87.
88.
本文在气相色谱仪联用微反应器装置上,研究了LaBO_3型催化剂中的B位元素对催化氧化活性的影响规律,并进行了程序升温脱附实验。另外,还对LaBO_3型载体催化剂进行了活性筛选,并在柴油机台架上与贵金属Pt/Al_2O_3进行了有害气体净化效果的对比实验。实验结果表明,LaBO_3氧化物中LaMnO_3对CO、CH_4的催化氧化活性最高,且CO、CH_4活性中心并不一致。LaMnO_3/γ-Al_2O_3浸渍微量助化剂后,能使CO在130℃完全氧化,CH_4的氧化温度在300~500℃范围内,LaMnO_3载体催化剂对柴油机有害排放物的净化率很低,浸渍微量助化剂后,净化率提高一倍以上,特别是LaMnO_3/堇青石蜂窝陶瓷,浸渍后的净化效果同贵金属Pt/Al_2O_3接近。 相似文献
89.
Post-harvest loss of resources to microbial competitors affects a number of species of animals, and many of them have evolved behaviors that reduce the likelihood of such loss. We previously described the inhibition ofBacillus psychrophilus by dogwood fruits (Cornus drummondii), which can comprise a significant portion of the winter food cache of the eastern woodrat (Neotoma floridana). The present study is a further investigation of the ability of dogwood fruits to inhibit growth ofB. psychrophilus. Additionally, we tested the antimicrobial activity of dogwood fruits onEscherichia coli andStaphlococcus aureus. Results of our study indicate that fresh fruits inhibit the growth ofB. psychrophilus andS. aureus but notE. coli. However, fruits taken from woodrat dens after four and six months storage inhibited growth of all three species of bacteria. Further, the strength of inhibition increased over the test period. We suggest the presence of an inhibitor allows woodrats to compete effectively for a valuable and limited food resource. 相似文献
90.
《西安建筑科技大学学报(自然科学版)》1994,(4)
论述复合脱氧剂的一般化学特性,并以碳化硅和硅铝铁两种复合脱氧剂为例,讨论其对改善钢的质量,进行纯净钢生产的影响。 相似文献