Brunauer-Emmett-Teller surface area, characterization

Surface physics is an old and well-established science but when ultrahigh vacuum equipment became available it was apparent that the previous results were inconsistent with the new data and everything had to be measured over again. The analytical techniques developed in surface physics were a great help for surface chemistry as the surface reactions in catalysis were analyzed with them. One of those techniques is the BET (Brunauer-Emmett-Teller) technique to characterize surfaces Figure 6.2 shows the adsorption isotherms that are used to measure specific surface areas of heterogeneous catalysts and characterize their pores. 

TPRS = temperature-programmed reaction spectroscopy XRD = X-ray diffraction BET = Brunauer-Emmett-Teller method (specific BET surface area) and BJH = Barrett-Joyner-Halenda method (determination of pore volume and diameter), both determined by nitrogen physisorption NMR= characterization by solid-state NMR. 

Determination of surface areas by Brunauer-Emmett-Teller (BET) isotherms is also an important method for the characterization of amorphous catalysts. For example, the effects of different pretreatments have been followed by measuring BET surface areas (37, 38, 43). BET measurements revealed a dramatic increase in surface areas concomitant with a substantial increase in catalytic activities for Zr-containing amorphous alloys (48, 53-56) during the early period of hydrogenation of CO. 

The distinguished career of Professor Paul H. Emmett has spanned six decades, beginning with his Ph.D. research under A.F. Benton at the California Institute of Technology in 1922. His pioneering contributions to the field of catalysis have provided the foundation for much of the present-day work in the field. Among his most notable contributions is the BET method for determining the surface area of solids, done in collaboration with Stephen Brunauer and Edward Teller. Surface area measurement by the BET method is probably the most widely used characterization method in catalysis today. 

There are special characterization requirements for mechanochemistry performed on particles in the solid state. Since reaction here depends on surfaces and fracture planes, surface area measurements are an important parameter [46]. Common methods for surface area measurements involve dye or gas adsorption as by the Brunauer-Emmett-Teller (BET) method [47, 48]. 

Lipid Crystals. Tripalmitin (>99% pure) (PPP obtained from Sigma Chemical Co., Stockholm, Sweden) was used. Crystals were recrystallized in hexane to give well-characterized 3-crystals. Hieir surface area was measured by Brunauer, Emmett, and Teller analysis to be 2.077 mVg. 

Methods for micro-measurement of surface areas include the Brunauer, Emmett, and Teller (BET) method (2), which relies on the adsorption of monolayers of gas, commonly nitrogen or argon, the adsorption of organic molecules such as ethylene glycol and ethylene glycol monoethyl ether (EGME) (10). and the use of infrared internal reflectance spectroscopy (11) which characterizes bonding of sorbed water. These last two techniques have been confined principally to surface areas of clay minerals. 

Important methods for the determination of the specific surface area and of the pore size distribution are based on the measurement of the gas adsorption isotherm [1,2]. The gas adsorption method and the evaluation according to Brunauer, Emmett and Teller using the two-parameter BET equation has been standardized in several countries for a number of years and an ISO standard just appeared. To establish the pore size distribution the method of Barrett, Joyner and Halenda (BJH) is generally accepted. Other methods for this purpose make use of the flow resistance of air through the compressed sample. The Blaine test and other flow tests used to characterize building materials are standardized world-wide. 

Nitrogen adsorption at low temperature is a routine characterization technique of nanoporous materials. For instance, the specific surface of porous materials is usually assessed from adsorption experiments (prior to capillary condensation of the fluid) on the basis of the Brunauer, Emmett, and Teller (BET) method. The BET model corresponding to the N2 adsorption isotherm at 77 K in the atomistic model of MCM-41 materials fits very well the simulated data with a correlation coefficient = 0.999 (see [39] for the comparison). We found Sbet 1000 m /g (the latter value is obtained by considering as the surface area occupied by an adsorbed N2 molecule, A 2 = 0.162 nm ) and C = 100. The value obtained for C... 

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