间二甲苯的离解光电离的实验与理论研究

本文利用同步辐射真空紫外和超声分子束反射式飞行时间质谱系统研究间二甲苯的光电离和离解光电离.通过测定母体离子C_(8)H_(10)^(+)和主要碎片离子(C_(8)H_(9)^(+)和C_(7)H_(7)^(+))的光电离效率谱,确定了母体分子的电离能和主要碎片离子(C_(8)H_(8)^(+)和C_(7)H_(7)^(+))的出现势分别为8.60±0.03 eV,11.76±0.04 eV和11.85±0.05 eV eV.在B3LYP/6-311++G(d,p)水平上优化了两个主要解离通道的反应物、过渡态、中间体和产物的结构,并在G3水平上计算了它们的能量,以及两个主要的离解光电离通道产物C_(7)H_(7)^(+)+CH_(3)和C_(8)H_(9)^(+)+H的能量.结合理论和实验结果,间二甲苯的离解光电离机理主要过程是C-H键或C-C键的离解和氢迁移.

Co3O4-CeO2氧化物对丙烷完全氧化的催化性能（英文）

挥发性有机化合物(VOCs)是全球大气污染物的主要来源,近年来已造成严重的环境问题.催化氧化是一种有效的、经济可行的VOCs去除技术,其研究的关键在于开发高效、稳定的催化剂.在本文中,我们采用柠檬酸法合成了一系列具有不同Co/(Ce+Co)摩尔比的Co3O4-CeO2二元氧化物催化剂,研究了其对丙烷(低碳VOCs)的催化氧化性能.在催化活性测试中,反应气的组成为0.2 vol.%C3H8和5 vol.%O2,Ar为平衡气,气体总流速为200 mL min^-1.实验结果表明,Ce的掺入能够明显提高Co3O4的丙烷催化氧化性能,Co3O4-CeO2催化剂的丙烷催化氧化活性顺序为CoCeOx-70>CoCeOx-90>Co3O4>CoCeOx-50>CoCeOx-20>CeO2.当Co/(Ce+Co)摩尔比为70%时,CoCeOx-70催化剂的丙烷催化氧化性能最好.在丙烷转化率达到90%时,CoCeOx-70催化剂的反应温度为310℃(GHSV=120000mL h^-1 g^-1),相比于单一的Co3O4催化剂的反应温度降低了25℃.XRD和TEM表征结果显示,在Co3O4-CeO2二元氧化物催化剂中存在Co3O4和CeO2两种晶型,同时随着Ce的掺入,催化剂的粒径明显降低.Raman光谱图显示,Ce的掺入使催化剂的晶格发生畸变,促进催化剂表面氧空位的产生,为催化剂中氧的迁移提供晶格位点.H2-TPR和C3H8-TPSR结果表明,Co3O4与CeO2间存在相互作用,能够提高催化剂的低温还原性能,以促进催化剂的丙烷催化氧化.O2-TPD和O 1s XPS结果表明,Ce的掺入能够增加催化剂表面活性氧物种的产生,提高催化剂中氧的移动性,从而提高了催化剂对丙烷的催化氧化活性.在对Co3O4和CoCeOx-70催化剂进行in-situ DRIFTS表征和简单的动力学研究,我们发现Ce的掺入不改变催化剂的丙烷催化氧化反应路径,其存在能够促进丙烷在催化剂表面的吸附和活化,以提高催化剂的丙烷催化氧化活性.同时,丙酮和酯作为中间物参与到丙烷的催化氧化反应过程中.此外,我们考察了反应气氛中水蒸气和CO2的存在对催化剂催化性能的影响.结果表明,CO2和水蒸气的存在都抑制了催化剂的丙烷催化氧化活性,催化性能随着CO2和水蒸气浓度的增加而降低.在相同条件下,水蒸气对催化剂催化性能的抑制作用明显大于CO2的抑制作用,但这种抑制作用会随着反应气中水蒸气和CO2的消失而消失.在稳定性测试中,CoCeOx-70催化剂表现出优异的抗水蒸气和CO2性能.在反应气中存在5 vol.%水蒸气和5 vol.%CO2的条件下,CoCeOx-70催化剂在50 h的稳定性测试中均未出现明显的失活现象.同时,经过10次加热和降温循环测试后,催化剂的催化活性也没有发生明显变化,这为CoCeOx-70催化剂的未来工业化的应用提供了可能.

East Asian Winter Monsoon record from the environmental sensitive grain size component of QF Old Red Sand, Haitan Island, China

The ＂Old Red Sand＂ is widely distributed along the coast of Fujian Province, China. Most studies have been carried out from as- pects of the origin, age and laterization of the ＂Old Red Sand＂, but this paper focused on reconstructing the history of the Asian Winter Monsoon change. On the basis of granulometric analysis of high-resohition samples, we have obtained environmental sen- sitive grain size component （ESGSC） from the Qingfeng （QF） profile by using the grain size-standard deviation method, which proves that the selected ESGSC is an important climate proxy. The mean grain size of this ESGSC could be used to reconstruct the East Asian Winter Monsoon （EAWM） intensity. As such, the history of the EAWM change since 44.0 ka reconstructed here reveals three main phases based on chronology dates of previous researches： （1） 44.0-25.5 ka B.P., the EAWM is relatively weak but increases gradually with fluctuations; （2） 25.5-15.5 ka B.P., relatively strong with high frequency fluctuations; （3） 15.5-7.1 ka B.P., with a weaker winter monsoon, but during 11-10 ka B.P. is remarkably enhanced. The EAWM recorded by mean grain size of the two neighboring sections have a better repeatability, so the millennial scales oscillation should be a reliable signal of the EAWM intensity. The climate recorded by ESGSC of the QF ＂Old Red Sand＂ compared to 6-80 of Huhi Cave stalagmites and Greenland GISP2 ice cores shows a good consistency, especially in detail, the YD event and four Heinrich events are all recorded, but the signal of D-O cycles was relatively weak.

Microfossil evidence of rice cultivation on the Southeast China Coast 7500 years ago

Located on the southeast coast of China,Fujian is an important junction for the spread and migration of agriculture and populations from mainland Asia to Taiwan and the Island Southeast Asia.Research on the emergence of agriculture and its relationship with the regional environmental context is key to understanding the evolution of ancient human-land interactions in the coastal zone of China.This paper presents a detailed microfossil analysis of the Dapingding site,which is located in the lower reaches of the Min River on the southeast coast of China.We found a large number of phytoliths produced in rice stems and leaves from the cultural layers of this site,dated to 7,500 cal.a BP.In addition,we found rice husk impressions and rice phytoliths in the pottery sherds of these cultural layers.Among these phytoliths,rice bulliform phytoliths with≥9 fish-scale patterns indicating the degree of rice domestication,accounted for 44%.This percentage is much higher than the established standard for wild rice bulliform phytoliths with fish-scale patterns,suggesting that rice cultivation had already occurred on the southeast coast of China approximately 7,500 years ago.Subsequently,the starting time of agricultural activity on the southeast coast of China was pushed from 5,000 to 7,500 years ago.Comparing the regional history of sea level and coastline changes in the early to mid-Holocene,we suggest that the emergence of early rice cultivation in Southeast China was associated with high sea levels in the midHolocene and the last transgression in the Fuzhou Basin.The’Fuzhou Bay’,formed by the retreating coastline and transgression driven by high sea levels,may have provided a sea channel for the southward movement of northern rice farmers.