1、Designation: D 3908 03 (Reapproved 2008)Standard Test Method forHydrogen Chemisorption on Supported Platinum Catalystsby Volumetric Vacuum Method1This standard is issued under the fixed designation D 3908; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 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 determination of the chemi-sorption of hydrogen at 298
3、 K (25C) on supported platinumcatalysts that have been reduced in flowing hydrogen at 723 K(450C). It incorporates a static volumetric vacuum techniqueat constant volume.1.2 The test method is intended for use on unused supportedplatinum on alumina catalysts of loadings greater than 0.3weight %. Dat
4、a on other supports and lower platinum loadingswere not tested.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applic
5、a-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 3766 Terminology Relating to Catalysts and CatalysisE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and StatisticsE 691 Practice for Conducting
6、 an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsSee Terminology D 3766.3.2 Quality and StatisticsSee Terminology E 456.3.3 Precision and BiasSee Practice E 177.3.4 SymbolsThe following symbols are used:Pc= pressure of gas in calibrated bulb, torrPmc=
7、pressure of gas in calibrated bulb andmanifold, torrPm= pressure in manifold, torrPmd= pressure in manifold and dead space, torrPmx= pressure in manifold prior to expansion intosample tube for X equilibration point, torrPex= equilibrium pressure after expansion forgenerating X equilibrium point, tor
8、rVc= volume of calibrated bulb, cm3Vm= volume of manifold between stopcocks 12and 2 with only 4 and 1 open, cm3Vd= volume of dead space in sample cell con-taining catalyst (volume between 2 and 3),cm3Vads(STP)x= volume of gas adsorbed at STP, cm3Vads(STP)cx= cumulative volume of gas adsorbedthrough
9、X,cm3VS= monolayer volume of gas adsorbed at STP,cm3TmAx= temperature representative of the manifoldprior to expansion into the sample cell, KTmBx= temperature representative of the entire sys-tem after equilibrium pressure (Pex) hasbeen established, KTm= temperature of manifold prior to expansionin
10、to sample cell for dead space determina-tion, KTmD= temperature of entire system after equilib-rium pressure has been established for deadspace determination, KT = average manifold temperature for a givendose, K=(TmAx+ TmBx)/21This test method is under the jurisdiction of ASTM Committee D32 onCataly
11、sts and is the direct responsibility of Subcommittee D32.01 on Physical-Chemical Properties.Current edition approved April 1, 2008. Published May 2008. Originallyapproved in 1980. Last previous edition approved in 2003 as D 390803.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
12、 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, United States.Wcat= mass of c
13、atalyst, gX = weight percent of platinum%D = percent platinum atoms on the surface4. Significance and Use4.1 This test method sets forth a procedure by whichduplicate catalyst samples can be compared either on aninterlaboratory or intralaboratory basis. It is anticipated thatcatalyst producers and u
14、sers will find this test method of value.4.2 Discrimination of the samples for which this procedureis recommended must be exercised when considering carrier(support) materials that sorb appreciable quantities of hydrogenor could cause an alteration of the state of the catalyst duringpretreatment, or
15、 both, (that is, sintering or metal occlusion).These materials must be identified by the user and experi-mented with to determine the most significant conditions ofmeasurement.4.3 This test method provides a measure of the totalhydrogen uptake (volume of hydrogen at STP, cm3/g ofcatalyst) without sp
16、ecifying the nature of the hydrogen-platinum interaction. Persons interested in using hydrogenuptake data to calculate percent platinum dispersion in aspecific catalyst should be aware of carrier (support) interac-tions, spillover effects, and other phenomena related to thehydrogen uptake capabiliti
17、es of the catalyst in question.5. Apparatus5.1 Gas-Handling System, as shown in Fig. 1. The compo-nents may be either glass or metal. Commercial metal instru-ments are available. The following components are to beincluded in the glass system:5.1.1 Vacuum System, capable of attaining pressures below1
18、 mPa (1 3 105torr). The vacuum can be monitored with anysuitable vacuum gage.Adiffusion pump backed by a mechani-cal pump must be isolated from the system by a trap held atliquid nitrogen temperature. High-vacuum stopcocks using alow-vapor pressure grease can be employed.5.1.2 Pressure-Measuring Dev
19、ice, that operates at constantvolume and that is capable of reading in the range from 0 to66.7 kPa (0 to 500 torr) to the nearest 0.01 kPa (0.1 torr).5.1.3 Calibration Bulb, whose volume has been carefullydetermined to within 0.1 % prior to attachment to the mainmanifold. Typically one fills the bul
20、b and stopcock bore withmercury, weighs it, and calculates the volume of the bulb fromthe density of mercury at the temperature of the measurement.Following careful cleaning, the bulb is attached to the mainmanifold. One should make sure that the glass blowing issufficiently far removed from the cal
21、ibrated volume to avoiddistortion.5.1.4 Flow-Through Cell, that can be evacuated and that canbe detached from the main manifold as, for example, see Fig.2. This is accomplished by including a removable joint, ifglass, a male cone joint, on the manifold end of the tube. (Othertypes of joints, that is
22、, Swagelok with TFE-fluorocarbonfittings, and so forth, are suitable.) Its mate is attached to themain manifold by a glass vacuum stopcock. A stopcock is alsoincluded on the vent side of the cell to allow for vacuum andflow-through procedures.5.1.5 Catalyst Sample, secured by a quartz wool plugupstr
23、eam of the catalyst and another quartz wool plug down-stream (Fig. 2). The sample should be in the form of anextrudate, pellets, or powder greater than 20 mesh.5.1.6 Furnace, capable of maintaining a heating rate of5 K/min and a temperature-control mechanism capable ofmaintaining the furnace at temp
24、eratures in the range from 673to 773 6 10 K (400 to 500C).5.1.7 Thermometer or Thermocouple, to monitor the fur-nace temperature to within 65 K and two thermometers toregister the temperature of the manifold system and sample cellduring uptake determination to the nearest 60.1 K.5.1.8 Balance, measu
25、ring to the nearest 1 mg (60.001 g).5.1.9 Flowmeter, for hydrogen capable of measuring a flowrate of between 10 and 25 6 3cm3(STP) gas per minute.5.2 Gas Purification Facilities , for helium and hydrogen.6. Reagents6.1 High-Purity Helium, purified by passing through a trapcontaining activated (Note
26、1) molecular sieve of the A type or13X type, maintained at liquid nitrogen temperature.NOTE 1Activation as suggested by manufacturer.6.2 High-Purity Hydrogen, purified by passing first throughan oxygen removal catalyst or palladium thimble and thenthrough a trap containing activated molecular sieve
27、of the Atype or 13X type maintained at liquid nitrogen temperature.6.3 High-Purity Cylinder Air, purified by passing through atrap containing activated molecular sieve of the A series.7. Safety Hazards7.1 Follow the usual precautions associated with handlinghydrogen gas. Adequately vent the hydrogen
28、 flow at theroughing pump discharge and vent the sample (stopcock 3). Aflash arresting check valve and pressure relief valves or safetymanometers should be incorporated into the design of theapparatus.7.2 Adequately tape or otherwise shield glass reservoirs toavoid unrestricted explosion in the even
29、t of an over-fill and toavoid flying glass in the event of an implosion during evacu-ation.7.3 Eye protection is essential when operating the vacuumsystem.7.4 Avoid accidental formation of mixtures of hydrogen andair at all times.8. Volume Calibrations8.1 The reliability of any gas adsorption measur
30、ement isnaturally dependent on the accuracy with which the systemvolume is known. It is therefore essential that the manifoldvolume be frequently determined very carefully to ensureaccurate hydrogen uptake data. Recalibrate the system if anychanges are made to the system. The volume of the standardb
31、ulb shown in the diagram was previously measured (see5.1.3). Expansion of a known pressure of gas into the evacu-ated system will allow a determination of system volume. Thefollowing steps are recommended for system calibration. Referto Fig. 1 for location of numbered stopcocks.D 3908 03 (2008)28.1.
32、1 Evacuate main manifold by opening stopcocks 1, 4, 5,8, and 12 with all others closed.8.1.2 Close stopcocks 12 and 8 and introduce helium to thesystem by opening 6. After establishment of a pressure of lessthan one atmosphere, close 6. Record the pressure (Pc).8.1.3 Close stopcock 5, open 12, and e
33、vacuate.8.1.4 Close stopcock 12 and expand gas in the calibrationbulb by opening 5. Record final pressure (Pmc).8.1.5 Repeat Steps 8.1.2-8.1.4 ten times and average toobtain the final pressure (Pmc).9. Charging Sample9.1 The amount of sample to be charged is determined bythe expected hydrogen uptake
34、 and the maximum capacity ofthe sample cell. Experience and the platinum loading willdictate the optimum amount, but a minimum of1gisconsidered essential. This mass need not be precisely knownsince a final weighing will be made after determination of thehydrogen uptake. It may, however, be useful fo
35、r the determi-nation of volatile or combustible matter present, or both, on theunused catalyst.9.1.1 Plugs of quartz wool are to be charged to the cell asshown in Fig. 2. Weigh the cell and wool plug(s).9.1.2 Charge at least1gofcatalyst to the cell.9.1.3 Connect the cell to the main manifold at stop
36、cock 2and vent.9.1.4 Secure the thermocouple to the glass along the outsideof the center of the catalyst bed (Fig. 2).10. Air Calcination10.1 To ensure removal of adsorbed hydrocarbons from thecatalyst surface due to ambient contamination a calcination inpurified air is recommended.10.1.1 Close all
37、stopcocks except 3, 2, and 1. Establish aflow of air between 10 and 25 cm3/g of catalyst per minute byopening stopcocks 13 and 9.10.1.2 Commence heating of the catalyst to 723 K (450C)at a rate not to exceed 10C/min. Hold at 723 K (450C) for 1h.10.1.3 Cool to 673 to 698 K (400 to 425C).10.1.4 Close
38、stopcocks 3 and 13. Evacuate by opening 12cautiously to avoid disturbance of the sample. Open 8. Con-tinue to evacuate until a vacuum of about 1 mPa (105torr) isestablished. Close 8.10.1.5 Remove furnace and cool cell to room temperature.Close stopcock 12.11. Sample Reduction11.1 Open stopcocks 11,
39、9, 4, 2, and 1 and allow thehydrogen pressure to reach atmospheric. Open 3 and adjust thehydrogen flow to between 10 and 25 cm3/g of catalyst perminute. Continue purge for 15 to 30 min or until reasonablyconfident that the system is essentially free of air.11.1.1 Replace the furnace and commence hea
40、ting thesample cell at a rate not exceeding 10C/min.11.1.2 Hold at 723 K (450C) for 1 to 2 h.11.1.3 Cool to between 673 and 698 K (400 and 425C).FIG. 1 Schematic: Static Vacuum SystemFIG. 2 Suitable Sample CellD 3908 03 (2008)311.1.4 Close stopcock 3 and then immediately 9, then 2.Open 12 and 8 and
41、evacuate. After a good vacuum (about 1mPa (105torr) is reached, open 2 slowly to avoid disturbanceof the sample.11.1.5 Continue evacuation until the vacuum gage readsabout 5 mPa (5 3 105torr) or less. If this requires more than1 h, a vacuum leak may be suspected. Repair it and repeat from11.1. Remov
42、e the furnace, cool the sample rapidly to roomtemperature, and then close stopcock 2.11.1.6 After the sample cell is at room temperature closestopcocks 8 and 12.12. Procedure: Hydrogen Up-Take12.1 Gradually open stopcock 7 and expand hydrogen intothe manifold up to stopcock 2. Experience will dictat
43、e asuitable pressure; about 6.67 kPa (50 torr) is usually accept-able. Close 7. Record Pm1. Record TmA1, the temperaturerepresentative of the manifold prior to expansion into thesample cell.12.1.1 After thermostating the sample to a desired tempera-ture ;295 to 298 K (;20 to 25 C) water in a Dewar f
44、lask issuitable), open stopcock 2 and expand hydrogen into thesample cell. Note the temperature of the sample, T.12.1.2 Follow an approach to equilibrium by noting thechange in pressure with time. Record the equilibration pressure(Pe1). Typical equilibration times will be 30 to 60 min. RecordTmB1, t
45、he temperature representative of the entire system afterpressure equilibrium has been established.12.1.3 After equilibration, close stopcock 2 and add addi-tional hydrogen to the manifold by carefully opening 7. Recordthe pressure (Pm2). Record TmA2.12.1.4 Repeat procedure 11.1-11.1.4 through a mini
46、mum ofthree times approximately evenly spaced between 13.3 kPa(100 torr) and 40 kPa (300 torr). Record equilibration pressuresto Pe3or to Pexwhere x3.Record TmAxand TmBxfor eachdosing.13. Dead Space13.1 Open stopcocks 12 and 8 and evacuate cell andmanifold to 1.3 3 103Pa (105torr).13.1.1 Close stopc
47、ocks 2, 8, and 12 and gradually bleedhelium to a pressure of about 53.2 to 66.5 kPa (400 to 500 torr)into manifold by gently opening 6. Close 6. Record thepressure (Pm). Record the temperature Tm.13.1.2 Open stopcock 2 and expand the gas from manifoldinto the sample cell. Record the pressure (Pmd).
48、Record theTmD.13.1.3 Repeat 13.1-13.1.2 at least three times.13.1.4 Close stopcock 2 and gradually open 3.13.1.5 Remove the sample cell from the system.13.1.6 Weigh the catalyst sample and cell. Subtract the taremass from 9.1.1 to obtain the sample mass, Wcat.14. Calculation for Manifold Calibration
49、Vm5 VcFPcPmc2 1G(1)NOTE 2It is assumed that this measurement is taken in a time elementshort enough that the temperature of the system is constant.15. Calculation for Dead Space VolumeVd5 VmFPmPmd2 1G(2)NOTE 3It is assumed that this measurement is taken in a time elementshort enough that the temperature of the system is constant.16. Calculation for Hydrogen Chemisorption (AdsorptionMethod)DOSE 1VadsSTP!15FVmSPm1/TmA1Pe1/TmB12 1D2 VdGS273TDSPe1760D(3)DOSE 2VadsSTP!25FVmSPm2/TmA2Pe2/TmB22 1D1 Vd SPe1/TmB1Pe2/TmB22 1DGS273TDSPe2760D(4)DOSE 3VadsSTP!35FVmSPm3/
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