Chemisorption static method

Hydrogen chemisorption Static H2 chemisorption at 100°C on the reduced cobalt catalysts was used to determine the number of reduced surface cobalt metal atoms. This is related to the overall activity of the catalysts during CO hydrogenation. Gas volumetric chemisorption at 100°C was performed using the method described by Reuel and Bartholomew [6]. The experiment was performed in a Micromeritics ASAP 2010 using ASAP 2010C V3.00 software. 

There are various ways in which the monolayer volume can be measured. In the static method, successive small doses of the adsorbate are admitted, and the number of adsorbed molecules after equilibrium has been reached are deduced either gravimetrically (possible with carbon monoxide, difficult with hydrogen) or volumetrically from the residual pressure or by some other technique such as NMR or XANES. " The procedure is repeated until no further uptake occurs, when the monolayer capacity will be known. If chemisorption on the metal is strong and... 

Dynamic methods are very fast and relatively easy to handle, even by inexperienced users. The analytical results, especially for pulse chemisorption, can be compared to the static methods ones only taking into consideration the basic differences between the two systems. In fact, in pulse chemisorption, the weak chemisorbed species are removed as they forms and it is not possible to state that there is a real equilibrium between the probe gas phases (gaseous and bound). 

Carbon monoxide chemisorption was used to estimate the surface area of metallic iron after reduction. The quantity of CO chemisorbed was determined [6J by taking the difference between the volumes adsorbed in two isotherms at 195 K where there had been an intervening evacuation for at least 30 min to remove the physical adsorption. Whilst aware of its arbitrariness, we have followed earlier workers [6,10,11] in assuming a stoichiometry of Fe CO = 2.1 to estimate and compare the surface areas of metallic iron in our catalysts. As a second index for this comparison we used reactive N2O adsorption, N20(g) N2(g) + O(ads), the method widely applied for supported copper [12]. However, in view of the greater reactivity of iron, measurements were made at ambient temperature and p = 20 Torr, using a static system. 

In a similar approach Riihe et al. [279] reported the preparation ofpoly(2-oxazoline) brushes by the grafting onto as well as grafting from method. For LCSIP of 2-ethyl-2-oxazolines silane functionalized undecane tosylate was first prepared and then immobilized on the substrate surface. SIP resulted in PEOx layers with thickness close to 30 nm. PEOx brushes were prepared by chemisorption of PEOx disulfides onto gold substrates. Preliminary static and dynamic swelling experiments are reported for these brushes. However, later observations [243] contradicted these findings. 

The problem with sulfide catalysts (hydrotreatment) is to determine the active centres, which represent only part of their total surface area. Chemisorption of O2, CO and NO is used, and some attempts concern NIL, pyridine and thiophene. Static volumetric methods or dynamic methods (pulse or frontal mode) may be used, but the techniques do not seem yet reliable, due to the possible modification (oxidation) of the surface or subsurface regions by O2 or NO probe molecules or the kinetics of adsorption. CO might be more promising. Infrared spectroscopy, especially FTIR seems necessary to characterise co-ordinativcly unsaturated sites, which are essential for catalytic activity. CO and NO can also be used to identify the chemical nature of sites (sulfided, partially reduced or reduced sites). For such... 

The in sim characterization of catalysts was earned out in an apparatus which included a quadiupole mass-spectrometer and a gas chromatograph for TPO and H2 chemisorption measurements. In situ coking was performed by injecting a mixture of He and n-hexane vapor over the reduced catalysts at 500 C, In TPO experiments, ihe coked sample was heated at a rate of 8 C/min in a stream of 2 voL% O2 + 98% He. The amount of CO2 produced was recorded. The chemisorption of H2 was carried out in the same appanitus by a flow method after reduction or caking. The flow rate of carrier gas (Ar) was maintained at 25 ml/min and the volume of H2 injected was 0.062 ml/pulse. Since the partial piessiire of H2 was very low in this system, the hydrogenation of coke was never observed. Isobaric H2 chemisorption measurements with fresh catalysts were carried out in a static adsorption apparatus. Dehydrogenation of n-butane was carried out in a flow micro-rcactor in H2 atmosphere at LHSV = 3 h-l and H2/HC=1. Reaction products were... 

To determine nickel surface areas of fresh catalysts, hydrogen chemisorption measurements were performed with the atmospheric TPH apparatus described above. Nickel surface areas of the catalysts were also measured by static volumetric hydrogen chemisorption (Coulter Omnisorp 100 cx). Before these measurements, samples were reduced in situ in a pure hydrogen atmosphere by raising the temperature up to 900°C (20°C/min). The samples were then cooled in a helium flow and the measurements were performed at 30°C. The catalyst materials and the analytical methods are described in [4,6,7]. 

In this paper, I review the recent advances and developments of first-principle quantum chemical methods and discuss their application to modelling chemisorption, surface reactivity of reactants/intermediates, and the catalytic behavior for a series of relevant commercial chemistries. We focus primarily on the static representation of the surface. 

The quantity of molecules selectively chemisorbed by the metallic component of the catalyst may be determined by what are commonly described as static (volumetric) or dynamic (flow) methods. The former is performed at reduced pressure and involves allowing the system to reach equilibrium between the adsorbed and gaseous states. The later group of methods, which involves pulsed chemisorption, are generally performed at atmospheric pressure and the equilibrium between adsorbed and gas states is not achieved (or maintained). 

As described above, the main purpose of the chemisorption methods is to evaluate the number of active sites that can be reached or that can interact with a fluid phase. These techniques are based on a chemical reaction between a suitable reactive gas and the surface reactive site. There are different methods to perform the above operation, the static volumetric, the static gravimetric or the flow methods. In the volumetric method, the sample is kept under high vacuum before the analysis. The analytical instrument then introduces known doses of reactive gas into the sample holder, measuring afterwards the equilibrium... 

The choice of the most suitable method should take into consideration the main task of the method itself. Static volumetric chemisorption provides the most reliable data from the scientific point of view. In fact, this is the only technique assuring the correct equilibrium time between the gaseous and adsorbed phases,... 

A review of the applications of the pseudopotential method and total energy techniques to the electronic and structural properties of solids is presented. With this approach, it has recently become possible to determine with accuracy crystal structures, lattice constants, bulk moduli, shear moduli, cohesive energies, phonon spectra, solid-solid phase transformations, and other static and dynamical properties of solids. The only inputs to these calculations, which are performed either with plane wave or LCAO bases, are the atomic numbers and masses of the constituent atoms. Calculations have also been carried out to study the atomic and electronic structure of surfaces, chemisorption systems, and interfaces. Results for several selected systems including the covalent semiconductors and insulators and the transition metals are discussed. The review is not exhaustive but focuses on specific prototype systems to illustrate recent progress. 

Adsorption capacity on solid sm-face is a basic data, and accurate measmement of adsorption capacity is the basic skill for the study of adsorption. The methods used for the measurement of adsorption capacity include the capacity method, the weight method and the chromatography. The capacity method is often used in the research of chemisorption for most gases, that is, a certain amount of gas is introduced into an adsorption container with a certain volume in a static device, then according to the changes of gas pressure to detect the adsorption capacity on the sm-face of the sohd adsorbent. Such a device is generally composed by the vacurnn pmnp system, adsorbate container, measurement systems for pressure and volume. 

The chemisorption of carbon monoxide is an established method for determining the surface area of dispersal metals, particularly in supported catalysts. The average area occupied by each molecule depends on whether attachment is on one or two sites, a state that can vary from metal to metal and with surface coverage [85]. The quantity of chemisorbed gases is commonly measured by volumetric methods with apparatus similar to that used for static BET gas adsorption measurements. 

Example 4 Experimental Measurements by N2 Adsorption (BET) and H2 Chemisorption (Metallic Area) The adsorption measurements are essential for the determination of total and metal areas, volumes, and dispersions. Of course, experimental methods can be classified into static and dynamic. There are commercial devices (ASAP) that measure the isotherms allowing to calculate all parameters mentioned above. We intend here to illustrate an experiment. 

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