Static volumetric apparatus

Essentially the static, volumetric gas adsorption equipment available commercially is for determining the amount of gas physically or chemically adsorbed on a powder surface. It is available for either single point or multipoint techniques and may be manual or automatic. Surface areas down to 1 m2 can be determined to 0.1 m2 using nitrogen adsorption provided care is taken. With coarser powders the dead space errors makes nitrogen unsuitable. Since the amount of gas in the dead space is proportional to the absolute pressure it is preferable to use gases with low saturation vapor pressures. Krypton with a 

Bel manufacture the Belsoip 28 for high precision, fully automated specific surface and pore size determination. This instrument has been used with a wide variety of adsorbates including hexane and carbon dioxide [192]. The Belsorp 18 is designed for measuring the adsorption of water, organic vapors and gases. 

The Cado Elba Sorpty 17S0 is a typical static, volumetric apparatus, the volume of adsorbed gas being calculated by measuring the pressure change resulting from adsorption of a known volume of gas by the powder sample. The adsorbate is introduced into a variable volume chamber until it reaches a preset pressure. The chamber is then coimected to a burette under vacuum containing the previously degassed sample. When the gas comes into contact with the adsorbent the gas molecules distribute themselves between the gas phase and the adsorbed phase until equilibrium is reached. From the final pressure the amount of adsorbed gas is calculated. Up to 14 routine surface area analyses can be carried out in a day. 

This instrument is a single point analyzer designed specifically for determining the surface area of carbon black. 

Having selected the sample adsoiption rate and number of experimental points, the analysis is automated using an automatic gas introduction 

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Platinum accessibility was obtained by the H2-O2 titration method at room temperature in a static volumetric apparatus. Isotherms were obtained in the 0-50 torr range. Extrapolation to the origin value was used to calculate the number of exposed atoms. 

BET surface area and microporous volume determination. Surface area measurements were performed by nitrogen physisorption at 77 K using the static volumetric apparatus (Micromeritics ASAP 2000 adsorption analyzer) with application of the BET method. All measurements were performed after treatment of solids under vacuum at 110 °C. 

Hydrogen chemisorption. The experiments were conducted at 35°C using a static volumetric apparatus Micromeritics ASAP 20IOC adsorption analyser. Samples (0.5 g) were in situ treated at 250°C for 1 h under a hydrogen flow then treated at 300°C for 2 h under a He flow. The volume of chemisorbed hydrogen obtained by extrapolation to a nominal value of the equilibrium pressure of 0 and a 1/1 stoechiometric ratio were used to evaluate the dispersion. 

Nitrogen adsorption measurements were performed at 77 K using a static volumetric apparatus (Micromeritics ASAP 2010 adsorption analyzer). The samples were degassed at 473 K for 24 hours and 10 Pa before analyses. 

Figure 5. Typical diagram of a static volumetric apparatus for gas adsorption.

The textural properties of all calcined samples were determined by nitrogen isotherms at liquid N2 temperature, using a Micromeritics ASAP 2010 apparatus (static volumetric technique). Before determination of adsorption-desorption isotherms the samples ( 0.2 g) were outgassed for 16 h at 350 °C under vacuum. 

The adsorption apparatus, shown in Figure 1, uses a static volumetric method to measure pure gas adsorption, and an open-flow adsorption/desorption method for mixture... 

The adsorption property was measured by a static method at 30 °C with a conventional volumetric apparatus as well as by the temperature programmed desorption (TPD) method. The details of the pretreatment and adsorption procedures were shown in Results and Discussion section. Metal-loaded zeolite samples were characterized by XRD, diffuse reflectance UV-Vis spectroscopy (DRS) and electron spin resonance (ESR). 

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]. 

The combination of the described techniques and the integration of the experimental results produce a detailed picture of the investigated catalyst, allowing a better comprehension of the reaction mechanisms in complicated processes and a detailed characterisation of catalyst activity and selectivity. Most of the experimental results shown in the present paper have been obtained in the application lab of CE Instruments (ThermoQuest S.p.A.), Milan - Italy. All the graphs related to static volumetric chemisorption have been obtained by the adsorption apparatus Sorptomatic 1990, while the graphs related to TPD, TPR/0 and pulse chemisorption analyses with the dynamic apparatus TPDRO 1100. 

In the direct calorimetric determination (-AH = f(njj), the amount adsorbed (nj is calculated either from the variations of the gas pressure in a known volume (volumetric determination) or from variations of the weight of the catalyst sample in a static or continuous-flow apparatus (gravimetric determination), or from variations of the intensity of a mass spectrometer signal [151]. 

Figure 2.18 I llustration of a static foam stability test apparatus in which foaming solution falls into a pool of the same solution in a volumetric receiver. Not drawn to scale.

For laboratory-scale modification, distinction has to be made between static and dynamic adsorption procedures. In a static procedure, the substrate is contacted with a known volume of gas at a well-defined pressure. The modifying gas may be stationary or circulating in a closed loop. Modification in a static gas adsorption apparatus allows the careful control of all reaction parameters. Temperature and pressure can be controlled and easily measured. Adsorption kinetics may be determined by following the pressure as a function of the reaction time. Figure 8.13 displays a volumetric adsorption apparatus, in which mercury is used, as a means to change the internal volume and for pressure measurement. 

Static hydrogen chemisorptions were performed using a standard volumetric glass adsorption apparatus. 

A prime requisite in all static methods, as has already been emphasized in the discussion of measurements in the low-pressure range, is that all air must be eliminated from the sample. With the apparatus just described, this is confirmed by checking the constancy of the vapour pressure measured over the full range from the dew volume to the bubble volume in the course of the volumetric measurements. 

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. 

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