T-plot method

Vu is the total microporous volume known from nitrogen experiment data (t-plot method). 

Zeolite samples (NaY. Na-mordenite and Na-ZSM-5) were prepared in Research Institute for Petroleum and Hydrocarbon Gases in Bratislava. A mesoporous alumina, the carrier for reforming catalyst was used. Porosity of pure mesoporous alumina evaluated by t-plot method did not show the presence of micropores within the range of accuracy of 0.001 cm3/g. Mixtures of zeolites with mesoporous alumina were prepared on the base of dried samples in 5% steps. The prepared mixtures of alumina with zeolite were homogenized in vibration mill. 

Physical adsorption of nitrogen was carried out on an ASAP 2400 Micromeritics apparatus. Before measurements, samples were evacuated overnight at 350 °C at vacuum of 2 Pa. For all samples the same adsorption data table was used. Collected adsorption data were treated by BET-isotherm in the range 0.05 < P/micropore volume and mesopore + external surface, t-plot method, with master isotherm of nonporous alumina (Harkins-Jura) was used, t-plot was linearized in the range of 0.35 < t < 0.6 nm. 

An example involving the akaganeite hematite transformation is shown in Figure 14.8 where the average pore diameter increased from 1.1 nm at 150 °C to 3.7 nm at 350 °C and then to > 15 nm at 500 °C. The t-plot method using H2O as an adsorbate has also been used to investigate the location of H2O in the tunnel structure of akaganeite (Naono et al., 1993). 

The surface area of the catalyst as well as the pore size distribution can easily be measured, and the zeolite and matrix surface areas of the catalyst can be determined by the t-plot method. The different FCC yields can then be plotted as a function of the ZSA/MSA ratio, zeolite surface area or matrix surface area, and valuable information can be obtained [9], The original recommendation was that a residue catalyst should have a large active matrix surface area and a moderate zeolite surface area [10,11]. This recommendation should be compared with the corresponding recommendation for a VGO catalyst a VGO catalyst should have a low-matrix surface area in order to improve the coke selectivity and allow efficient stripping of the carbons from the catalyst [12], Besides precracking the large molecules in the feed, the matrix also must maintain the metal resistance of the catalyst. 

The catalysts were characterized by measuring the total surface area, BET area, and the pore size distribution by nitrogen adsorption in a Micromeritics ASAP 2010 unit. The zeolite and matrix surface areas were calculated by the t-plot method [16,17], For data see Table 4.2. 

Porosity of carbon blacks can be detected by the de Boer t-plot method [4.30]. The total surface area and the geometrical surface area outside the pores can be determined separately from the adsorption isotherm. Special attention must be paid to the selection of a suitable master t curve. Due to the small diameters of most carbon black primary particles, methods for the determination of mesopores are of no importance. 

The t-plot method of Lippens and de Boer [27] assumes that a multilayer of adsorbed nitrogen is formed freely on the solid surface, and the thickness of adsorbed nitrogen increases with, and depends essentially on, the equilibrium relative pressure by the equation... 

The parameters of the pore size distribution flmction given in Table I are related to the microporosity of the activated carbon. The total pore volume is 0.272 cm g. We compared these results to those provided by the classical characterization methods based on the treatment of a nitrogen isotherm at 77 K. (t-plot, D-R, H-K). The micropore volume provided by the t-plot method is 0.413 cm g. The macropore and mesopore surface area is 62 m g". The t-plot method shows that the main part of the microporosity is located in the very low pore diameter area (//<7.08 A). For such pore diameters, the t-plot method should be considered with care as it is valid for a layer thickness higher than 3.54 A. The H-K method as well as the D-R method provide a total micropore volume of 0.414 cm g. The maximum of the pore size distribution flmction provided by the H-K method is located at //=9.2 A. 

Textural characterization was performed by N2 adsorption-desorption at 77 K using a Micromeritics ASAP 2010 analyzer. The samples were preheated under vacuum in three steps of Ih at 423 K, Ih at 513 K, and finally 4 h at 623 K. BET specific surface area, Sbet, was calculated using adsorption data in the relative pressure range, P/Po, from 0.05 to 0.2. Total pore volume, Vp , was estimated by Gurvitsch rule on the basis of the amount adsorbed at P/Po of about 0.95. The primary mesopore diameter, Dp, was evaluated using the BJH method from the desorption data of the isotherm. The primary mesopore volume, Vp, and the external surface area, Sext were determined using the t-plot method with the statistical film thickness curve of a macroporous silica gel [5]. 

Textural Parameters. Adsorption-desorption isotherms of N2 at 77K were determined in a Micromeritics ASAP 2010 with a micropore system. Prior to measurement, the samples were outgassed at 140 C for at least 16 h. The specific surface area was determined by the BET method, assuming that the area of a nitrogen molecule is 0.162 nm [12]. Micropore volume was calculated by the t-plot method using the Harkins and Jura [13] thickness. We used model isotherms calculated from density functional theory (DFT) to determine the pore size distributions and cumulative pore volume of the pillared samples by taking the adsorption branch of the experimental nitrogen isotherm, assuming slit-like pores [14]. 

The BET surface areas of the zeolite samples were determined by N2 adsorption-desorption at -196 C in a Micromeritics ASAP 2010 equipment. Prior to the determination of the adsorption isotherm, the calcined sample (0.5 g) was outgassed at 400 C under a residual pressure of 1 Pa in order to remove moisture. The adsorption data were treated with the full BET equation. The t-plot method using the universal t-curve was applied in order to obtain an estimation of the micropore volume, microporous surface and external surface area [7]. 

In this study, activated carbon fibers (ACFs) deposited by copper metal were prepared by electroplating technique to remove nitric oxide (NO). The surface properties of ACFs were determined by FT-IR and XPS analyses. N2/77K adsorption isotherm characteristics, including the specific surface area, micropore volume were investigated by BET and t-plot methods respectively. And, NO removal efficiency was confirmed by gas chromatographic technique. From the experimental results, the copper metal supported on ACFs appeared to be an increase of the NO removal and a decrease of the NO adsorption efficiency reduction rate, in spite of decreasing the BET S specific surface area, micropore volume, and micro-porosity of the ACFs. Consequently, the Cu content in ACFs played an important role in improving the NO removal, which was probably due to the catalytic reactions of C-NO-Cu. 

Nitrogen isotherms were measured by using an ASAP (Micromeritics) at 77K. Prior to each analysis, the samples were outgassed at S73K for 10 - 12 h to obtain a residual pressure of less than 10 torr. The amount on nitrogen adsorbed was used to calculate specific surface area, and the micro pore volumes determined from the BET equation [14] and t-plot method [15], respectively. Also, the Horvath-Kawazoe model [16] was applied to the experimental nitrogen isotherms for pore size distribution. 

Table 1 shows the structural properties of the ACFs studied. As shown in Table 1, all samples have well-developed mictopore and microporosity of Cu plated ACFs are decreased as compared diat of as-received. Also, the volume fiaction of micropore is decreased with increasing of Cu contoit on ACFs. It can be seen that the copper plating shows pore-blocking phenomena owing to deposition of copper metal on ACFs [13]. Specific surfiice areas are decreased result fiom micropore volume fiom t-plot method was decrrased. 

Bulk Si/Al ratios were determined by AAS. Surface areas and pore volumes were determined by N2 absorption isotherms measured at liquid nitrogen temperature using a Micromeritics ASAP 2000M (Table 1). The zeolites were degassed under vacuum at 150°C for the as-s)mthesised and 450°C for the modified zeolites for at least 3 hours. The total surface area was derived using the BET equation [12], the micropore volume and the external surface area (ESA) were estimated by means of the t-plot method of Lippens et al [13] and the total and mesopore volumes were calculated by Barrett-Joyner-Halenda anaylsis of the desorption branch of the N2 isotherm [14]. 

Less favorable is the situation with analyses of obtained data, viz. the most common cases of solids containing both micro- and meso-pores. Here the Brunauer-Emmet-Teller (BET) isotherm is nearly always incorrectly applied. The t-plot method [1] is only of limited applicability because it requires knowledge of adsorption isotherms on non-porous solids of the same chemical nature as the measured sample (master isotherm). Only recently it was shown in this Laboratory [2] that an extension of BET isotherm together with non-linear parameter fitting could solve this problem. 

The adsorbent we considered is an activated carbon F30-470 type provided by CHEMVIRON CARBON (total micropore volume 0 394 10 m kg, total pore volume 0.497 10 m kg, mesopore and macropore surface area 56 lO" m kg determined by the t-plot method)... 

N2 adsorption is also used to estimate the micro pore volume and the pore size distribution (see e. g. Glasauer et al. 1999) whieh ean be derived from a plot of adsorbed N2 vs. the thiekness of a statistieal monolayer, t, whieh is a function of the relative gas pressure (t-plot method). Mereury porosimetiy serves the same purpose (Celis et al. 1998). N2 adsorption isotherms have also been used to determine the fractal dimensions of Fe oxide particles (c. f.. Celis et al. 1998 Weidler et al. 1998). 

Surface areas of catalysts were determined by N2 adsorption using an ASAP 2000 analyzer from Micromeritics. Matrix and zeolite surface areas were calculated by the t-plot method accordingly to the ASTM-D-4365 standard test [11]. Zeolite unit cell size (UCS) was determined by X-Ray diffraction using a SIEMENS D-500 automated analyzer according to the ASTM-D-3942-80 standard [11]. 

B.E.T. surface areas and micropore volumes were determined on a Quantachrome Autosorb 1-C apparatus at liquid nitrogen temperatures. B.E.T. surface areas were calculated in the range of P/Po between 0.05 and 0.10. Micropore volumes were as determined by the t-plot method. 

Sample Characterization. The BET nitrogen adsorption-desorption isotherms were performed in an ASAP 2000 instrument using N2 at -195 °C. The microporous area was estimated using the correlation of t-Harkings Jura (T-plot method). 

Micropore volume calculated by t-plot method from adsorption branch. 

The nitrogen adsorption-desorption isotherms for specific surface area and porosity assessment were recorded at -196 C in a Gemini instrument from Micromeritics. The specific surface areas were determined by the Brunauer-Emmett-Teller (BET) method. The pore size distributions were obtained from the desorption branch, and the micropore volume was determined by the t-plot method, using literature software [14]. 

For TGA, a Setaram TGA-DTA 92 apparatus was used. Alternatively, a home-built apparatus was employed for TPD-MS. GC analysis was on a Chrompack CP-Sil-5 column, eventually coupled to a Fisons mass spectrometer. ESR spectra were recorded with a Bruker ESP-300 and a TE104 cavity at temperatures between 130 and 300 K. N2 sorption experiments were performed with an Omnisorp-100 instrument. The t-plot method was applied for the analysis of the pore volume. Solid state NMR spectra were recorded using a Bruker MSL 400 spectrometer at a resonance frequency of 100.61 MHz. Cross polarization was optimized with glycine as a reference. For the measurement of liquid samples, a Bruker AMX 300 system was used, operating at 300.13 and 75.47 MHz for iH and C, respectively. 

Physical, structural, and morphological characteristics of the various supports have been reported previously [6]. The corresponding features of the Pt-containing catalysts were determined by the usual means (i) BET areas with a conventional all-glass gas-volumetric appartus, using N2 uptake at 77 K and the t-plot method [11] (ii) crystal phases with XRD... 

Measured by atomic absorption spectrometry. Reference untreated NaY. c).d) Low pressure argon adsorption. t-Plot method of Lippens-De Boer, Harkins-Jura equation. 

Micropore and mesopore volumes were deduced from the isotherms of adsorption of nitrogen at 77 K (T-plot method). 

The main drawback of BET characterization is that the surface area obtained includes micropores whose surface cannot be reached by elastomeric chains, which are much bigger than nitrogen (Bradley et al 1996). So, many are now using the t-plot method that allows the determination of the net surface excluding micropores (Wampler, 1997). 

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