1、Designation: D 4567 03Standard Test Method forSingle-Point Determination of Specific Surface Area ofCatalysts and Catalyst Carriers Using Nitrogen Adsorptionby Continuous Flow Method1This standard is issued under the fixed designation D 4567; the number immediately following the designation indicate
2、s the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the single-point dete
3、rminationof the surface area of catalysts and catalyst carriers that exhibitType II or Type IV nitrogen adsorption isotherms using anitrogen-helium flowing gas mixture. This test method isapplicable for the determination of total surface areas from 0.1to 300 m2, where rapid surface area determinatio
4、ns are desired.1.2 Because the single-point method uses an approximationof the BET equation, the multipoint BET method (Test MethodD 3663) is preferred to the single-point method.NOTE 1This is particularly true when testing microporous materials.1.3 The values stated in SI units are to be regarded a
5、s thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of whoever uses this standard to consult andestablish appropriate safety and health practices and d
6、eter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 3663 Test Method for Surface Area of CatalystsD 3766 Terminology Relating to Catalysts and CatalysisE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminol
7、ogy Relating to Quality and StatisticsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsSee Terminology D 3766.3.2 Symbols:Acs= cross-sectional area of nitrogen, 16.2 3 1020m2.CI= integrator counts.CITa = integrator counts c
8、orrected for ambient tempera-ture.CIPa = integrator counts corrected for ambient pressure.N = Avogadros number, 6.02 3 1023, molecules/mole.P = partial pressure of nitrogen, torr.Pa= ambient pressure, torr.Po= saturated equilibrium vapor pressure of liquid ni-trogen, torr.R = gas constant, 82.1 cm3a
9、tm/K mole.Ta= ambient temperature, K.V = volume of nitrogen adsorbed at ambient tempera-ture and pressure, cm3.W1= tare of sample cell, g.W2= sample mass + tare of sample cell after analysis, g.Ws= mass of sample, g.4. Summary of Test Method4.1 The sample is degassed by heating in a flow of inert ga
10、sto remove adsorbed vapors from the surface. The sample isthen immersed in a liquid nitrogen bath causing adsorption ofnitrogen from a flowing mixture of a fixed concentration ofnitrogen in helium. When adsorption is complete, the sample isallowed to warm to room temperature causing desorption,which
11、 results in an increase in the nitrogen concentration in theflowing mixture. The quantity of nitrogen gas desorbed isdetermined by sensing the change in thermal conductivity.4.2 Calculation of the surface area is based on a modifiedform of the BET equation.1This test method is under the jurisdiction
12、 of Committee D32 on Catalysts andis the direct responsibility of Subcommittee D32.01 on Physical-Chemical Proper-ties.Current edition approved Oct. 1, 2003. Published October 2003. Originallyapproved in 1986. Last previous edition approved in 1999 as D 456799.2For referenced ASTM standards, visit t
13、he ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,
14、 United States.5. Significance and Use5.1 This test method is useful for determining the specificsurface area of catalysts and catalyst carriers for materialspecifications, manufacturing control, and research and devel-opment in the evaluation of catalysts.6. Apparatus6.1 A schematic diagram of the
15、apparatus is shown in Fig. 1.The apparatus may be constructed of glass or metal tubing. Ithas the following features:6.1.1 Differential Flow Controller from the gas inlet valveto a flow control valve to eliminate fluctuations in the gas flow.6.1.2 Two Thermal Conductivity DetectorsA referencedetecto
16、r (A) to sense the nitrogen-helium gas mixture and asecond detector (B) to sense changes in the gas mixture afterflowing through the sample cell. The two detectors are initiallybalanced to allow the detection of changes in the nitrogenconcentration.6.1.3 Flow-Through Sample Cells, of various volumes
17、 andshapes depending on the application.6.1.4 Two Equilibration Tubes selected by a selector valve,between the sample cell and detector (B). The small volumetube has a volume of approximately 20 cm3and the largevolume tube has a 100 cm3capacity to allow for temperatureand pressure equilibration of a
18、 wide range of volumes of gases.6.1.5 Flow Meter, to monitor the flow rate of the nitrogen-helium mixture maintained at approximately 20 cm3/min.6.1.6 Diffusion Baffle, to prevent air from diffusing back intothe system during cooling of the sample.6.1.7 Bridge Balance Meter, to display balance or im
19、bal-ance between detectors A and B.6.1.8 Digital Integrator, to measure the imbalance betweendetectors A and B and display the surface area of the sample.6.1.9 Septum or Fixed Loop, for injection of calibration gas.6.1.10 Degassing Station, for removal of adsorbed vaporsfrom the sample.6.1.11 Cold T
20、rap, for removal of impurities in the gasmixture.6.1.12 Thermal Equilibration Tube, to allow the flowing gasmixture to reach temperature and pressure equilibration beforereaching detector (A).6.2 Heating Mantle.6.3 Dewar Flasks.6.4 Laboratory Balance with 0.1 mg (107kg) sensitivity.6.5 Gas-Tight Syr
21、inge or Gas Sampling Loop, 1.00 cm3.7. Reagents7.1 Liquid Nitrogen, of such purity that the saturated equi-librium vapor pressure is not more than 20 torr above ambientpressure.7.2 Cylinder, with pressure regulator, of high purity 30mole % nitrogen in helium equivalent to a relative pressure ofappro
22、ximately 0.3, where the nitrogen concentration is knownto within 0.1 mole %. Concentrations lower than 30 mole %should be used for materials containing micropores, for ex-ample, zeolites.8. Calibration of the Apparatus8.1 If the gas mixture contains impurities, place a Dewarflask containing liquid n
23、itrogen around the cold trap.8.2 Using a gas-tight syringe inject 1.00 cm3(or some otherknown volume) of air or nitrogen into the calibration septum.The digital integrator should display 2.84 6 0.03 counts (see11.3) for a 1.00-cm3injection (or a proportional number ofcounts for a different volume).
24、If the counts are greater than2.84, increase the gas flow through the flow control valve. Ifthe counts are less than 2.84, decrease the gas flow and retest.9. Preparation of Sample9.1 Weigh to 0.0001 g a clean, dry empty sample cell.Record the mass, W1.FIG. 1 ApparatusD45670329.2 Place the catalyst
25、sample into the sample cell. Choosethe sample size to provide an estimated surface area of 0.1 to300 m2.9.3 Attach the sample cell to the degassing station.9.4 Attach an empty cell to the sample station.9.5 Open the gas inlet valve and adjust the flow controlvalve to allow a gas flow of approximatel
26、y 20 cm3/min.Observe the reading on the flow meter.9.6 Install a heating mantle around the sample cell and raisethe temperature to 300C (573 K).NOTE 2Certain materials will decompose at 300C (for example,alumina hydrates) or will sinter (for example, platinum black). Lowerdegassing temperatures are
27、permitted for such materials. However, thedegassing temperature should be specified when reporting the results.9.7 Continue degassing at about 300C (573 K) for aminimum of 1 h. Overnight degassing is permissible. If lowertemperatures are used for degassing, longer times may berequired.9.8 Remove the
28、 heating mantle and allow the sample tocool.9.9 Remove the sample cell from the degassing station,protecting the sample from exposure to atmospheric contami-nants.9.10 Remove the empty cell from the sample station.10. Surface Area Determination10.1 Attach the sample cell to the sample station.10.2 A
29、llow any air to be purged from the system by theflowing gas mixture. This condition can be ascertained byobserving that the bridge balance meter indicates a balance.10.3 To initiate adsorption, place a Dewar flask of liquidnitrogen around the sample cell so that the liquid level isapproximately 2 to
30、 3 cm from the top of the cell.10.4 When adsorption is complete, as indicated by thebridge balance meter and digital integrator, remove the Dewarflask.10.5 Clear the digital integrator.10.6 Immerse the sample cell in a beaker of room tempera-ture water until the gas flow returns to its original rate
31、 asindicated by the flow meter.NOTE 3If the flow meter does not return to its original value, obtainedbefore the digital integrator starts to count, either remove some of thesample or use the large volume equilibration tube (see Fig. 1) and repeatsteps 10.2-10.6.10.7 When the counter stops counting,
32、 record the counterreading.10.8 Remove the sample cell from the sample station, drythoroughly and weigh. Record the mass, W2.11. Calculations11.1 Calculate the total surface area of the sample from amodified form of the BET equation as follows:Total surface area 5 PaVNAcs!/RTa!1 2 P/Po! (1)11.2 Usin
33、g 30 mole % nitrogen as the adsorbate in helium atan ambient temperature of 22C (295 K) and a pressure of 1.0atm (760 torr) and assuming that Pois 775 torr,Total surface area 5 2.84 V (2)11.3 Thus, 2.84 m2of surface area corresponds to 1.00cm3of nitrogen adsorbed.11.4 Calculate the mass of sample as
34、 follows:WS5 W22 W1(3)11.5 For ambient temperatures other than 295 K, multiplythe integrator counts (CI) by 295/Ta.CiTa 5 CI3 295/Ta (4)11.6 For ambient pressures other than 760 torr, multiply theintegrator counts (CI)byPa/760.CIPa 5 CI3 Pa/760 (5)11.7 For gas concentrations other than 30 mole %, mu
35、ltiplythe integrator counts by (1 P/Po)/0.706. The partial pressureP of the gas is the product of the mole fraction and ambientpressure. Pois assumed to be ambient pressure plus 15 torr.11.8 Calculate the specific surface area as follows:Specific surface area 5 CI/WS(6)or if the corrections in 11.5,
36、 11.6, or 11.7, or combinationthereof, have been used:Specific surface area 5CIWS3295Ta3Pa76031 2 P/Po0.706(7)12. Presentation of Data12.1 Report the specific surface area in square metres pergram to three significant figures.13. Precision and Bias313.1 Test ProgramAn interlaboratory study was con-d
37、ucted in which the named property was measured in threeseparate test materials in 22 separate laboratories. PracticeE 691, modified for nonuniform data sets, was followed for thedata reduction. Analysis details are in the research report.13.2 PrecisionPairs of test results obtained by a proce-dure s
38、imilar to that described in the study are expected to differin absolute value by less than 2.772 S, where 2.772 S is the95 % probability limit on the difference between two testresults see Table 1, and S is the appropriate estimate ofstandard deviation. Definitions and usage are given in Termi-nolog
39、y E 456 and Practice E 177, respectively.13.3 BiasThe test method described is without knownbias. Results from this single-point method are statisticallycomparable to those of the multipoint method based on threesamples ranging in specific surface areas from 10 to 280 m2/g.3Supporting data have been
40、 filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: D32-1019.TABLE 1 Repeatability and ReproducibilityTest Result(Consensus),m2/g95% Repeatability Limit(Within Laboratory),m2/g, (%)95% Reproducibility Limit(Between Laboratories),m2/g, (%)10.33 0.17 (1.7) 1.
41、82 (17.6)153.2 2.66 (1.7) 22.24 (14.5)277.6 4.49 (1.6) 46.61 (16.8)D4567033NOTE 4No microporous materials were tested in the interlaboratorystudy supporting this method. Microporous materials may produce differ-ent results.14. Keywords14.1 adsorption; catalyst carriers; catalysts; continuousflow; su
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45、TM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D4567034
