The reaction of ethanol with propylene oxide over calcined layered double hydroxides(CLDH) was investigated. The results show that CLDH has a good activity and a good selectivity, but the activity and the selectivity ...The reaction of ethanol with propylene oxide over calcined layered double hydroxides(CLDH) was investigated. The results show that CLDH has a good activity and a good selectivity, but the activity and the selectivity of CLDH decrease when CLDH reforms LDH- the so called 'memory effect'. The influence of the 'memory effect' on the CLDH returning to LDH was studied by the hydration reaction. It is shown that the 'memory effect' is not complete, and the decreases of the Mg/Al molar ratio of LDH and the crystallite size due to the increase of the hydration reaction time result in the drop of the activity and the selectivity.展开更多
This paper discusses oasis stability at regional scale with a case study in the northern slope areas of the Tianshan Mountains (NSTM). The results showed certain significant aspects. (1) As long as water resources in ...This paper discusses oasis stability at regional scale with a case study in the northern slope areas of the Tianshan Mountains (NSTM). The results showed certain significant aspects. (1) As long as water resources in the oasis keep stable and their utilization efficiency can be maintained or gradually increased, the primary productivity could be continuously increased and the natural primary productivity keeped relatively stable. In this case, it is considered that the oasis is stable and its sustainable development can be achieved at regional scale. (2) Considering the availability of water resources in the oases, the oases on the alluvial-diluvial fans are highly stable. In the alluvial plain downstream of the groundwater overflowing zones the oases are moderately stable and in the lacustrine deltas or dry lacustrine deltas the oases are lowly stable. (3) Enlargement of oases and the increase of water resources and vegetation coverage in the oasis will certainly enhance the 'cold-island effect' of the oasis and increase the stability of oases.展开更多
Analysis of observed ozone data in 2006 from five monitoring sites(Xujiahui,Chongming,Baoshan,Pudong,Jinshan)in Shanghai reveals that ozone(O_3)concentrations in Xujiahui are higher at week-ends than those on weekdays...Analysis of observed ozone data in 2006 from five monitoring sites(Xujiahui,Chongming,Baoshan,Pudong,Jinshan)in Shanghai reveals that ozone(O_3)concentrations in Xujiahui are higher at week-ends than those on weekdays,despite the fact that emissions of ozone precursor substances,such as oxides of nitrogen(NOx),carbon monoxide(CO)and volatile organic compounds(VOCs)are lower at weekends than those on weekdays.The possible chemical cause of ozone"weekend effect"is that NO_2/NO ratio increases at weekends by 25.61%compared with those on weekdays.In addition,because of an average 12.13%reduction in NOx(NO+NO_2)in the early morning(05:00-09:00)at weekends compared with that on weekdays,the ozone inhibition period ends 0.5 h earlier at weekends resulting in the longer duration of ozone accumulation and the higher ozone production rate.The rate of ozone production is a function of VOCs and NOx in the atmosphere.VOCs/NOx ratio in Xujiahui is 4.55 at weekends,and 4.37 on weekdays,belonging to the"NOx-limited".The increasing VOCs/NOx ratio at weekends leads to ozone enhancement from 73 ppbv to 80 ppbv,which are consistent with ozone"weekend effect"in Xujiahui.Furthermore,combining with MICAPS cloud amount data,the fact that ozone"weekend effect"in Xujiahui weakens gradually along with the increasing of cloud amount indicates that ozone photochemical production leads to ozone"weekend effect"in Xujiahui of Shanghai.展开更多
文摘The reaction of ethanol with propylene oxide over calcined layered double hydroxides(CLDH) was investigated. The results show that CLDH has a good activity and a good selectivity, but the activity and the selectivity of CLDH decrease when CLDH reforms LDH- the so called 'memory effect'. The influence of the 'memory effect' on the CLDH returning to LDH was studied by the hydration reaction. It is shown that the 'memory effect' is not complete, and the decreases of the Mg/Al molar ratio of LDH and the crystallite size due to the increase of the hydration reaction time result in the drop of the activity and the selectivity.
基金funded by one of National Basic Research Program of China (Grant No.2009CB825105)the National Natural Science Foundation of China (Grant No.40671015)
文摘This paper discusses oasis stability at regional scale with a case study in the northern slope areas of the Tianshan Mountains (NSTM). The results showed certain significant aspects. (1) As long as water resources in the oasis keep stable and their utilization efficiency can be maintained or gradually increased, the primary productivity could be continuously increased and the natural primary productivity keeped relatively stable. In this case, it is considered that the oasis is stable and its sustainable development can be achieved at regional scale. (2) Considering the availability of water resources in the oases, the oases on the alluvial-diluvial fans are highly stable. In the alluvial plain downstream of the groundwater overflowing zones the oases are moderately stable and in the lacustrine deltas or dry lacustrine deltas the oases are lowly stable. (3) Enlargement of oases and the increase of water resources and vegetation coverage in the oasis will certainly enhance the 'cold-island effect' of the oasis and increase the stability of oases.
基金the National Natural Science Foundation of China(Grant Nos.40575060 and 40705046)the Special Research Project of China Meteorological Bureau
文摘Analysis of observed ozone data in 2006 from five monitoring sites(Xujiahui,Chongming,Baoshan,Pudong,Jinshan)in Shanghai reveals that ozone(O_3)concentrations in Xujiahui are higher at week-ends than those on weekdays,despite the fact that emissions of ozone precursor substances,such as oxides of nitrogen(NOx),carbon monoxide(CO)and volatile organic compounds(VOCs)are lower at weekends than those on weekdays.The possible chemical cause of ozone"weekend effect"is that NO_2/NO ratio increases at weekends by 25.61%compared with those on weekdays.In addition,because of an average 12.13%reduction in NOx(NO+NO_2)in the early morning(05:00-09:00)at weekends compared with that on weekdays,the ozone inhibition period ends 0.5 h earlier at weekends resulting in the longer duration of ozone accumulation and the higher ozone production rate.The rate of ozone production is a function of VOCs and NOx in the atmosphere.VOCs/NOx ratio in Xujiahui is 4.55 at weekends,and 4.37 on weekdays,belonging to the"NOx-limited".The increasing VOCs/NOx ratio at weekends leads to ozone enhancement from 73 ppbv to 80 ppbv,which are consistent with ozone"weekend effect"in Xujiahui.Furthermore,combining with MICAPS cloud amount data,the fact that ozone"weekend effect"in Xujiahui weakens gradually along with the increasing of cloud amount indicates that ozone photochemical production leads to ozone"weekend effect"in Xujiahui of Shanghai.
