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221.
222.
In situ UV-vis and EPR study on the formation of hydroperoxide species during direct gas phase propylene epoxidation over Au/Ti-SiO(2) catalyst 总被引:1,自引:0,他引:1
Chowdhury B Bravo-Suarez JJ Mimura N Lu J Bando KK Tsubota S Haruta M 《The journal of physical chemistry. B》2006,110(46):22995-22999
In recent years, there have been great experimental and theoretical advances in the understanding of the epoxidation of propylene by O(2) and H(2) over Au supported on titanium-containing oxidic supports; however, thus far spectroscopic evidence of reacting species for proposed mechanisms has been lacking. Hydroperoxide species have been postulated as an intermediate responsible for the epoxidation of propylene with O(2) and H(2). In order to obtain direct evidence for the different type of active oxygen species, in situ UV-vis and EPR measurements were carried out during the epoxidation of propylene with O(2) and H(2) over a Au/Ti-SiO(2) (Ti/Si = 3:100) catalyst. It was determined that the adsorbed species of oxygen (O(2)(-)) resided on Au, more likely at a perimeter site, and it led to the formation of titanium hydroperoxo species. These results support the possible mechanism of formation of these hydroperoxo species via H(2)O(2) produced from O(2) and H(2) adsorbed on the Au surfaces. 相似文献
223.
Biswanath Das Nikhil Chowdhury Kongara Damodar Bommena Ravikanth 《Helvetica chimica acta》2007,90(10):2037-2040
A new and convenient stereoselective synthesis of (Z)‐2‐(chloromethyl)alk‐2‐enoates has been achieved from Baylis–Hillman adducts by treatment with PPh3/Cl3CCONH2 at room temperature. The synthesis can proceed under mild and acid‐free conditions to form the products in high yields. 相似文献
224.
Our aim in this paper is mainly to prove some existence results for solutions of generalized variational-like inequalities
with (η,h)-pseudo-monotone type III operators defined on non-compact sets in topological vector spaces. 相似文献
225.
Let
and
be Hausdorff topological vector spaces over the field
, let
be a bilinear functional, and let
be a non-empty subset of
. Given a set-valued map
and two set-valued maps
, the generalized bi-quasi-variational inequality (GBQVI) problem is to find a point
and a point
such that
and
for all
and for all
or to find a point
a point
and a point
such that
and
for all
. The generalized bi-quasi-variational inequality was introduced first by Shih and Tan [8] in 1989. In this paper we shall obtain some existence theorems of generalized bi-quasi-variational inequalities as application of upper hemi-continuous operators [4] in locally convex topological vector spaces on compact sets. 相似文献
226.
P. Ghosh A. Sarkar M. Ghosh A.K. Meikap S.K. Chattopadhyay S.K. Chatterjee P. Chowdhury B. Saha 《Czechoslovak Journal of Physics》2003,53(12):1219-1227
We report the electrical resistivity of HCl doped polyaniline in the temperature range 77 T 300 K. A maximum is obtained in the conductivity versus concentration of HCl curve at 3(N) HCl. The resistivity of the sample has been observed to show a decreasing trend with increase in temperature. The resistivity obeys the Mott variable range hopping theory. The Mott characteristic temperature (T
Mott) is very low in this sample compared to other studies. The Hall voltages have been found to be negative. The Hall coefficient, carrier concentration, and density of states have been determined from Hall measurement. From the conductivity versus temperature plot, different physical quantities such as localisation length and molecular vibrational frequency have been determined. 相似文献
227.
228.
Biswanath Das Anjoy Majhi Joydeep Banerjee Nikhil Chowdhury 《Journal of molecular catalysis. A, Chemical》2006,260(1-2):32-34
The Baylis–Hillman adducts have efficiently been converted into the corresponding allyl amides in stereoselective manner by heating in acetonitrile under reflux in the presence of Amberlyst-15 as a catalyst. The catalyst works under heterogeneous conditions and can be recycled. 相似文献
229.
Chowdhury D Sarkar SP Kalita D Sarma TK Paul A Chattopadhyay A 《Langmuir : the ACS journal of surfaces and colloids》2004,20(4):1251-1257
In this paper we report the experimental observation of spreading and recoil of surfactant-containing water drops on various alcohol films supported on glass slides. The time evolution of spreading and recoil behavior was recorded by placing a web camera above the drop. We observed that the drop spread the fastest on CH3OH, followed by C2H5OH, and the slowest on i-PrOH. On the other hand, the recoil behavior was just the opposite. The drop recoiled the slowest on CH3OH and fastest on i-PrOH, while it recoiled in an intermediate time on C2H5OH. In addition, concentration of surfactant in the drop played a prominent role in the spreading and recoil time of the drop, with higher surfactant concentration making the drop spread and recoil faster. The time evolution of spreading velocity of the drop on different alcohol films at various surfactant concentrations occurred with a Gaussian distribution and the peak velocity was reached earliest on CH3OH followed by C2H5OH, while on i-PrOH it took the longest time. The recoil behavior was similar. The variation of velocity as a function of radius exhibited oscillatory behavior, indicating the existence of an interfacial phenomenon. We also report the observation that spreading of the drop occurred without observable fingering instability. Further, we observed by Fourier transform infrared (FTIR) spectroscopic measurements that the drop had mixed with the alcohol films as it spread. Miscibility of the alcohol in the film with the drop, alcohol evaporation cooling-induced temperature gradient, and Marangoni effect probably play important roles in the spreading and recoil behavior of the drop. 相似文献
230.
A highly sensitive and virtually specific method has been developed for the trace and ultra trace 5 ng ml−1-1 μg ml−1 fluorimetric analysis of nitrite. The method is based on the quenching action of nitrite on the native fluorescence of murexide (ammonium purpurate) [λex=349.0 nm, λem=444.5 nm] in the acid range of 0.045-0.315 (M) H2SO4. The method is very precise and accurate (S.D.=±0.4877 and R.S.D.=0.4878% for the determination of 0.1 μg ml−1 of nitrite in 11 replicates). Relatively large excesses of over 35 cations and anions do not interfere. The proposed technique has been successfully applied for the determination of nitrite and nitrate in ground water, surface water and sea water, nitrite in soil and nitrate in forensic samples. The method has also been extended for the analysis of NOx in air. 相似文献