Halenda

The pore size distribution based on BJH (Barrett-Joyner-Halenda) calculations, the micropore fraction (t-plot analysis), and the BET (Brunauer-Enunett-Teller) surface area of the catalysts were acquired by physisorption measurements of nitrogen at 77 K (Micrometries Gemini 2360). Prior to BET analysis the samples were evacuated at 373 K for at least 12 h. 

Physical properties of calcined catalysts were investigated by N2 adsorption at 77 K with an AUTOSORB-l-C analyzer (Quantachrome Instruments). Before the measurements, the samples were degassed at 523 K for 5 h. Specific surface areas (,S BEX) of the samples were calculated by multiplot BET method. Total pore volume (Vtot) was calculated by the Barrett-Joyner-Halenda (BJH) method from the desorption isotherm. The average pore diameter (Dave) was then calculated by assuming cylindrical pore structure. Nonlocal density functional theory (NL-DFT) analysis was also carried out to evaluate the distribution of micro- and mesopores. 

BET and Barrett-Joyner-Halenda (BJH) measurements for the catalysts were conducted to determine the loss of surface area with loading of the metal and changes in pore size distributions. These measurements were conducted using a Micromeritics Tri-Star system. Prior to the measurement, samples were slowly ramped to 160°C and evacuated for 24 h to approximately 50 mTorr. 

The surface area was calculated using the BET equation,36 while the total pore volume and the average pore size were calculated from the nitrogen desorption branch applying the Barrett-Joyner-Halenda (BJH) method.37 BET and BJH adsorption measurements were carried out with a Micromeritics Tri-Star system on both the supports and the calcined catalysts. Prior to measurements, the samples were evacuated at 433 K to approximately 50 mTorr for 4 h. 

Barrett, E.P., Joyner, L.G., and Halenda, P.P. 1951. The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms. J. Am. Chem. Soc. 73 373-80. 

A number of models have been developed for the analysis of the adsorption data, including the most common Langmuir [49] and BET (Brunauer, Emmet, and Teller) [50] equations, and others such as t-plot [51], H-K (Horvath-Kawazoe) [52], and BJH (Barrett, Joyner, and Halenda) [53] methods. The BET model is often the method of choice, and is usually used for the measurement of total surface areas. In contrast, t-plots and the BJH method are best employed to calculate total micropore and mesopore volume, respectively [46], A combination of isothermal adsorption measurements can provide a fairly complete picture of the pore size distribution in sohd catalysts. Mary surface area analyzers and software based on this methodology are commercially available nowadays. 

Thus, either type I or type IV isotherms are obtained in sorption experiments on microporous or mesoporous materials. Of course, a material may contain both types of pores. In this case, a convolution of a type I and type IV isotherm is observed. From the amount of gas that is adsorbed in the micropores of a material, the micropore volume is directly accessible (e.g., from t plot of as plot [1]). The low-pressure part of the isotherm also contains information on the pore size distribution of a given material. Several methods have been proposed for this purpose (e.g., Horvath-Kawazoe method) but most of them give only rough estimates of the real pore sizes. Recently, nonlocal density functional theory (NLDFT) was employed to calculate model isotherms for specific materials with defined pore geometries. From such model isotherms, the calculation of more realistic pore size distributions seems to be feasible provided that appropriate model isotherms are available. The mesopore volume of a mesoporous material is also rather easy accessible. Barrett, Joyner, and Halenda (BJH) developed a method based on the Kelvin equation which allows the calculation of the mesopore size distribution and respective pore volume. Unfortunately, the BJH algorithm underestimates pore diameters, especially at... 

E. P. Barrett, L. G. Joyner, and P. P. Halenda, The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms, J. Am. Chem. Soc., 73, 373-380(1951)... 

The calculation method for the mesopore size distribution generally follows that described by Barret, Joyner and Halenda [79, 85]. With the so-called BJH method, the pore sizes using a certain pore geometry are calculated along the isotherm. This involves an imaginary emptying of condensed adsorptive in the pores in a... 

EA = elemental analysis IR = infrared spectroscopy PXRD = powder X-ray diffraction BET = Brunauer-Emmett-Teller method (specific BET surface area) and BJH = Barrett-)oyner-Halenda method (determination of pore volume and diameter), both determined by nitrogen physisorption ... 

Halenda SP, Volpi M, Zavoico GB, et al Effects of thrombin, phorbol myristate acetate, and prostaglandin D2 on 40-41 kDa protein that is ADP ribosylated by pertussis toxin in platelets. FEES Lett 204 341-346, 1986 Hall RC, Gardner ER, Popkin MK, et al Unrecognized physical illness prompting psychiatric admission a prospective study. Am J Psychiatry 138 629-635, 1981 Hallcher LM, Sherman WR The effects of lithium ion and other agents on the activity of myo-inositol-1-phosphatase from bovine brain. J Biol Chem 255 10896-10901, 1980... 

The nitrogen adsorption-desorption isotherms were obtained at 77K by AutoSorb-1 -C (Quantachrome). Prior to measurement, the samples were outgassed at 300°C for 3 h. The specific surface areas of the samples were determined from the linear portion of the BET plots. Pore size distribution was calculated from the desorption branch of N2 desorption isotherm using the conventional Barrett-Joyner-Halenda (BJH) method, as suggested by Tanev and Vlaev [15], because the desorption branch can provide more information about the degree of blocking than the adsorption branch. 

The N2 adsorption-desorption isotherm at -196°C and the micro- and mesopore size distributions are presented in figure 2. In the partial pressure range -0.02-0.3 the upward deviation indicates the presence of supermicropores (15-20A) or small mesopores (20-25A). From the De Boer t-plot the presence of an important microporosity can be deduced, so a unique combined micro- and mesoporosity is present for this type of material. Indeed, this combined pore system is confirmed when considering the micropore (Horvath-Kawazoe) and mesopore (Barrett-Joyner-Halenda) size distributions with maxima at respectively 6A and 17.5 A pore diameter (figure 5). An overview of the surface area, micro- and mesoporosity data of the unmodified PCH can be found in table 1. 

Figure 5. Micropore (Horvath-Kawazoe) and mesopore (Barrett-Joyner-Halenda) size distributions of A) the unmodified PCH B) Al-PCH-75% C) AI-PCH-200%...

The BET specific surface area [28] was calculated in the relative pressure range between 0.04 and 0.2. The total pore volume was determined from the amount adsorbed at a relative pressure of 0.99 [28], The primary mesopore volume and external surface area were evaluated using the as-plot method [24, 28, 29] with the reference adsorption isotherm for macroporous silica [29], The pore size distributions were determined using the Kruk-Jaroniec-Sayari (KJS) equation [30] and the calculation procedure proposed by Barrett, Joyner and Halenda (BJH) [31]. 

Olivopontocerebellar atrophy Quinolinate AMPA (Feinstein and Halenda, 1988)... 

Feinstein M. B. and Halenda S. P. (1988). Arachidonic acid mobilization in platelets The possible role of protein kinase C and G-proteins. Experientia 44 101-104. 

Figure 1. Plots of differential pore volume against pore diameter calculated from the N2 gas adsorption isotherms obtained from meso/macroporous carbon specimens I (-0-), II (- -), and III (-A-) using Barrett-Joyner-Halenda (BJH) method. Reprinted with permission from G. -J. Lee and S. -I. Pyun, Carbon, 43 (2005) 1804. Copyright 2005, with permission from Elsevier.

Based upon the Kelvin equation, the PSD of the meso/macropores has been generally determined by Barrett, Joyner, and Halenda (BJH) method.104 Furthermore, the density functional theory94 which is based upon a molecular-based statistical thermodynamic theory was recently introduced in order to analyze... 

---