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161.
本文采用CCSD(T)-F12a/cc-p VDZ-F12//M06-2X/6-311+G(2df,2p)方法并结合过渡态理论对HONO+OH→H_2O+NO_2抽氢反应以及H_2O参与该反应的微观机理和速率常数进行了理论研究.结果表明,由于复合物HONO…H_2O的高浓度和稳定性,我们预测HONO…H_2O+OH反应的大气相关性将比H_2O…HONO+OH和H_2O…OH+cis-HONO明显得多.进一步的速率常数计算结果表明,cisHONO…H_2O+OH反应的速率常数比H_2O…cis-HONO+OH和H_2O…OH+cis-HONO反应大了8~4个数量级.然而,cis-HONO…H_2O+OH反应的有效速率常数比无催化剂主反应cis-HONO+OH低了7~3个数量级.表明在实际大气环境中,H_2O对HONO+OH反应的催化效果并不明显. 相似文献
162.
E. -R. KENAWY 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(4):657-672
ABSTRACT Molecules with dendrimeric structure (cascade molecules) were attached to a polymer-montmorillonite system. The supported dendrimeric molecules were modified to produce ammonium and phosphonium salts. The catalytic phase-transfer activities of these systems have been investigated. The results from the catalytic activity studies showed that the dendrimeric system is highly activating the selected organic reactions. This was attributed to the dendrimeric structure of the system which consequently increase the weight efficiency. It is worth mentioning that this is the first report in the literature describing the formation of dendrimers on polymer-montmorillonite system and their use as phase-transfer catalysts. 相似文献
163.
Amide C?N bonds are thermodynamically stable and their fission, such as by hydrolysis and alcoholysis, is considered a long‐challenging organic reaction. In general, stoichiometric chemical transformations of amides into the corresponding esters and acids require harsh conditions, such as strong acids/bases at a high reaction temperature. Accordingly, the development of catalytic reactions that cleave not only primary and secondary amides, but also tertiary amides in mild conditions, is in high demand. Herein, we surveyed typical stoichiometric transformations of amides, and highlight our recent achievements in the catalytic esterification of amides using scandium, manganese, and zinc catalysts, together with some recent catalyst systems using late‐transition metal reported by other groups. 相似文献
164.
165.
Ir/Al2O3 catalysts with high metallic contents are applied on satellite thruster to decompose hydrazine. The present work has as principal aim the study of the morphologic evolution of Ir/Al2O3 catalysts with metallic contents from 12 to 30 wt.%. The catalysts were prepared through consecutive impregnations from the H2IrCl6 precursor, using three different types of aluminas. The specific surface area, volume and distribution of pore size, specific metallic area and metallic particles average diameter, as well as the mechanical resistance were determined. Results show that the Ir addition leads to a decrease of the specific surface area and the pores volumes, while increases the mechanical resistance. Values for average diameter of metallic particles are comprised between 1.4 and 2.4 nm when the metallic content increases from 12 to 30 wt.%. Catalysts containing 30 wt.% of Ir presents specific metallic areas around 30 m2/g, although pores volumes and distributions of pore size were considerably different for the three supports. Their metallic particles dispersion and size values are very close to those of a commercial catalyst Shell 405, even though the preparation methods were different. These results show that there is a strong interaction between the alumina and the iridium precursor. 相似文献
166.
167.
Michael R. Buchmeiser 《Monatshefte für Chemie / Chemical Monthly》2006,137(7):825-833
Summary. Selected trends and scientific achievements in the surface modification of polymers are reported. In this context, both UV-light
triggered free radical polymerization-based techniques relevant to industrial processes and ring-opening metathesis polymerization-based
chemistry, relevant for the manufacture of specialty materials, are addressed. 相似文献
168.
John G. Verkade 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1621-1631
A rationale for the unusually strong Lewis basicity and catalytic activity of the title pro-azaphosphatranes is presented. Four stoichiometric and four catalytic uses of such pro-azaphosphatranes are described, as well as some unexpected reactions in which these bases take part. Mechanistic pathways are put forth for several of the transformations outlined. 相似文献
169.
Yiqin Wan Paul Chen Bo Zhang Changyang Yang Yuhuan Liu Xiangyang Lin Roger Ruan 《Journal of Analytical and Applied Pyrolysis》2009,86(1):161-167
This study was intended to evaluate the effects of catalysts on product selectivity of microwave-assisted pyrolysis of corn stover and aspen wood. Metal oxides, salts, and acids including K2Cr2O7, Al2O3, KAc, H3BO3, Na2HPO4, MgCl2, AlCl3, CoCl2, and ZnCl2 were pre-mixed with corn stover or aspen wood pellets prior to pyrolysis using microwave heating. The thermal process produced three product fractions, namely bio-oil, gas, and charcoal. The effects of the catalysts on the fractional yields were studied. KAc, Al2O3, MgCl2, H3BO3, and Na2HPO4 were found to increase the bio-oil yield by either suppressing charcoal yield or gas yield or both. These catalysts may function as a microwave absorbent to speed up heating or participate in so-called “in situ upgrading” of pyrolytic vapors during the microwave-assisted pyrolysis of biomass. GC–MS analysis of the bio-oils found that chloride salts promoted a few reactions while suppressing most of the other reactions observed for the control samples. At 8 g MgCl2/100 biomass level, the GC–MS total ion chromatograms of the bio-oils from the treated corn stover or aspen show only one major furfural peak accounting for about 80% of the area under the spectrum. We conclude that some catalysts improve bio-oil yields, and chloride salts in particular simplify the chemical compositions of the resultant bio-oils and therefore improve the product selectivity of the pyrolysis process. 相似文献
170.
Satoshi Horikoshi Nick Serpone 《Journal of Photochemistry and Photobiology, C: Photochemistry Reviews》2009,10(2):96-110
Microwave radiation has recently become an active source of thermal energy in numerous chemical reactions. As such, the microwave energy is not ordinarily and is not likely to be used to drive photochemical reactions. Accordingly, is the role of microwaves then relegated solely to be a source of heat? They do not have to be since photochemical reactions can be activated indirectly by microwaves using the UV light emitted from certain gas-fills excited by microwave radiation. This article examines the microwave radiation not only as a dielectric heat source but also a source of vacuum-UV radiation and UV light through microwave discharge electrodeless lamp devices, which in some cases (depending on design) can also serve as photoreactors. 相似文献