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排序方式: 共有960条查询结果,搜索用时 31 毫秒
101.
Ashok Kumar Singh N. Chaurasia Shahla Rahmani Jaya Srivastava Bharat Singh 《Catalysis Letters》2004,94(3-4):135-141
The NO/H2 reaction has been studied over a Ni loaded carbon film catalysts using in situ FTIR spectroscopy at the temperature range 25–350°C. On these catalysts, the differences in activity and selectivity were found depending on the nature of the surface functional groups. These differences were correlated with transient infrared spectral features which appeared during the reaction. It has been proved experimentally that the chemical character of the support is of vital importance during the process. The rise in NO conversion and N2 selectivity was observed when the surface of the catalysts was changed by the NH3 chemisorption. Amide and/or imide species formed due to the reduction of ammonium salts of carboxylic acids can play a significant role as active centers during the NO reduction. 相似文献
102.
Snehalkumar Parmar Kamal K. Pant Mathew John Kishore Kumar Shivanand M. Pai Shalini Gupta Bharat L. Newalkar 《Journal of Porous Materials》2014,21(5):849-857
Hydroisomerization of n-hexadecane is performed over ZSM-12 framework having tailored Brønsted acidity to investigate the effect in terms of product selectivity and yield. For this purpose, pure phase of ZSM-12 (bulk molar ratio Si/Al ~ 60) has been synthesized using TEABr as a structure directing agent. The framework Brønsted acidity is tailored with group II elements (M) viz. Ca, Ba and Mg, by means of ion-exchange method. The samples so prepared have been characterized for phase purity, textural parameters, morphology by employing powder X-ray diffraction, nitrogen adsorption–desorption isotherm measurement at 77 K, and scanning electron microscopy technique, respectively. Similarly, % metal exchange is estimated using inductively coupled plasma technique. The quantification of Brønsted acidity for H+–M++–ZSM-12 samples has been estimated by means of ammonia temperature programmed desorption (NH3-TPD) and Fourier transform infrared spectroscopy of ammonia (NH3-FTIR). The well characterized H+–M++–ZSM-12 samples were loaded with Platinum (Pt, 0.5 wt%) and subjected to hydroisomerization of n-hexadecane using an up-flow fixed bed reactor to verify the effect of process parameters like temperature and WHSV. Pt/H+–Ba2+–ZSM-12 with tailored Brønsted acidity in the range of about 25 % demonstrated the optimum performance among all the catalysts with an increased isomer selectivity and yield (89.2 and 80.3 %, respectively) by about 4 wt% at a conversion level of about 90 % compared to Pt/H+–ZSM-12 framework at 568 K. Such enhancement in isomer selectivity and yield is found to be significant from commercial application point of view. Based on the obtained trend, the potential benefits of implementation of Pt/H+–Ba2+–ZSM-12 (bulk molar ratio Si/Al ~ 60) framework for cold flow property improvement of ‘bio-ATF’ have been envisaged. 相似文献
103.
Bharat Ugale C. M. Nagaraja 《Journal of Inorganic and Organometallic Polymers and Materials》2014,24(6):1032-1037
A new metal–organic framework of Zn(II) ion, [Zn(muco)(bipy)·2H2O] (where, muco = trans, trans-muconate dianion, bipy = 4,4′-bipyridine) has been synthesized by solvothermal reaction of Zn(II) ion, muco ligand and bipy spacer. X-ray structure determination reveals that compound 1 has a 3D diamondoid (dia) framework with novel fivefold interpenetrating nets. Topological analysis shows the presence of 4-connected Zn(II) nodes with {66} topology. Thermal analysis reveals that the compound is stable up to 340 °C. Photoluminescence study shows the emission of 1 owing to the presence of muco ligand and the intensity of luminescence emission is higher than that of free muco ligand. 相似文献
104.
In the current study, we use Galerkin finite‐element simulation to analyze the concept of triple diffusive flow with magnetic field effect toward a power law stretching sheet. The fluid comprises dissolved solutal particles and nanoparticles in the base fluid. The three important mechanisms that are responsible for rise in phenomenon of convective transportation are diffusophoresis, thermophoresis along with Brownian motion have been considered. Recently, the proposed nanoparticles' mass flux and heat flux boundary conditions have been imposed. Nanoparticle mass transportation, solutal mass transportation with heat transportation for prominent physical parameters, such as stretching parameter, magnetic influence parameter, thermophoresis parameter, and Brownian motion parameter are calculated. To further verify and understand the strength of the relationship between heat transportation rate and controlling parameters, the multiple regression process is used. The finite difference approach was adopted to numerically solve the nonlinear governing equations and the linked boundary conditions. In the present study, we used MATLAB software for finding the final outcomes and relating the concluding results for with extant outcomes in the literature as a limiting case in the absence of the magnetic intensity parameter and an excellent agreement was noted. It was observed that the magnetic field has a positive effect on heat and mass transfer. This study also helps in understanding and thus controlling the velocity of the flow along with solutal depositions, which has a significant engineering application in the process of extrusion. The findings of the present study help to control the rate of heat and mass transfer, aiding manufacturing companies in obtaining the desired quality of product. 相似文献
105.
A novel electrochemical route is used to form highly {111}-oriented and size-controlled Au nanoprisms directly onto the electrodes of quartz crystal microbalances (QCMs) which are subsequently used as mercury vapor sensors. The Au nanoprism loaded QCM sensors exhibited excellent response-concentration linearity with a response enhancement of up to ~ 800% over a non-modified sensor at an operating temperature of 28?°C. The increased surface area and atomic-scale features (step/defect sites) introduced during the growth of nanoprisms are thought to play a significant role in enhancing the sensing properties of the Au nanoprisms toward Hg vapor. The sensors are shown to have excellent Hg sensing capabilities in the concentration range of 0.123-1.27 ppm(v) (1.02-10.55 mg m(-3)), with a detection limit of 2.4 ppb(v) (0.02 mg m(-3)) toward Hg vapor when operating at 28?°C, and 17 ppb(v) (0.15 mg m(-3)) at 89?°C, making them potentially useful for air monitoring applications or for monitoring the efficiency of Hg emission control systems in industries such as mining and waste incineration. The developed sensors exhibited excellent reversible behavior (sensor recovery) within 1 h periods, and crucially were also observed to have high selectivity toward Hg vapor in the presence of ethanol, ammonia and humidity, and excellent long-term stability over a 33 day operating period. 相似文献
106.
Infrared microspectroscopy is widely used for the chemical analysis of small samples. In particular, spectral properties of small cylindrical samples are important in forensic analysis, understanding relationships between microstructure and mechanical properties in fibers or fiber composites, and development of cosmetics and drugs for hair. The diameters of the constituent cylinders are typically of the order of the central wavelength of light used to probe the sample. Hence, structure and material spectral response are coupled and recorded spectra are usually distorted to the extent of becoming useless for molecular identification. In this paper, we apply rigorous optical theory to predict the spectral distortions observed in IR microspectroscopic data of fibers. The theory is used, first, to compute the changes that are observed for cylinders of various dimensions under different instrument configurations when compared to the bulk spectrum from the same material. We provide a method to recover intrinsic material spectral response from fibers by correcting for distortion introduced by the cylindrical structure. The theory reported here should enable the routine use of IR microspectroscopy and imaging for the molecular analysis of cylindrical domains in complex materials. 相似文献
107.
Sasi?Bhushan?Bhimavarapu Amit?Kumar?MaheshwariEmail author Deepti?Bhargava Shashi?Prakash?Narayan 《Journal of Materials Science》2011,46(9):3191-3199
The hot deformation behavior of Al 2024 was studied by isothermal hot compression tests in the temperature range of 250–500 °C
and strain rate range of 10−3 to 102 s−1 in a computer-controlled 50 kN servo-hydraulic universal testing machine (UTM). The results show that the flow stress of
Al 2024 alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization.
The processing map exhibits two domains of optimum efficiency for hot deformation at different strains, including the low
strain rate domain at 500 °C and between 10−2 and 10−1 s−1 and the high strain rate domain in 250 and 300 °C in the strain rate range of 101 to 102 s−1. An attempt has been made in this article to generate a new hybrid 4D process map which illustrates contours of power dissipation
and instability in the 3D space of strain rate, temperature, and strain. 相似文献
108.
S C Bhargava J L Dormann S Sayouri J Jove G Priftis H Pankowska O Gorochov R Suryanarayanan 《Bulletin of Materials Science》1991,14(3):687-690
We have studied the Mössbauer spectra of YBa2Cu3?x Fe x O7?d (11 compositions) and present here the results obtained from quantitative analyses of the paramagnetic and magnetic spectra. 相似文献
109.
110.
Gelcasting is a promising technique for shape forming of bulk dense or porous ceramic, metal structures. The process offers
a number of advantages over processes such as slip casting, injection molding in forming complex ceramic shapes. It is shown
here that the optimization of slurry rheology, choice of mold material, mold design and the drying conditions have a significant
role in the overall success of the process. In this process, components of simple or complex shapes can be produced to near
net shape by direct casting. If required complex shapes can also be produced by machining the green gelcast bodies. The process
of gelcasting also has a lot of potential in forming highly porous ceramic shapes. 相似文献