1、Designation: D 4824 03Standard Test Method forDetermination of Catalyst Acidity by AmmoniaChemisorption1This standard is issued under the fixed designation D 4824; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis test method involves the measurement of total catalyst acidity by chemisorption of ammoniain a static volumetric system
3、. Acidity is a very important parameter in determining catalyst activityand selectivity in many commercial reactions. Zeolite based catalysts used in the petroleum industryfor catalytic cracking are a prime example. This test method describes a simple procedure employinginexpensive equipment that co
4、uld readily be assembled in most laboratories.1. Scope1.1 This test method covers the determination of acidity ofcatalysts and catalyst carriers by ammonia chemisorption. Avolumetric measuring system is used to obtain the amount ofchemisorbed ammonia.1.2 The values stated in SI units are to be regar
5、ded as thestandard. The values given in parentheses are for informationonly.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 determi
6、ne the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 3766 Terminology Relating to Catalysts and CatalysisE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsSee Terminology
7、D 3766.3.2 Symbols:Vk= calibrated expansion volume, cm3.T1= temperature of Vkat initial ammonia pressure, K.T2= temperature of Vkat final ammonia pressure, K.P1= initial ammonia pressure, torr.P2= final ammonia pressure, torr.Ws= mass of sample, g.W1= tare of sample tube, g.W2= sample mass plus tare
8、 of tube, g.P1T= initial ammonia pressure corrected to standard tem-perature, torr.P2T= final ammonia pressure corrected to standard tem-perature, torr.4. Summary of Test Method4.1 A sample is degassed by heating in a vacuum to removeadsorbed vapors from the surface. The sample is then exposedto an
9、excess of gaseous ammonia and the excess ammonia isremoved by freezing it into a trap cooled with liquid nitrogen.The chemisorbed ammonia is calculated as the differencebetween the volume of ammonia before exposure and thevolume recovered in the liquid nitrogen trap.5. Significance and Use5.1 This t
10、est method can be used to determine the acidity ofcatalysts and catalyst carriers by ammonia chemisorption formaterials specifications, manufacturing control, and researchand development in the evaluation of catalysts.6. Apparatus6.1 A schematic diagram of one type of apparatus is shownin Fig. 1. It
11、 may be constructed of glass or metal and mayoperate manually or automatically. It has the following fea-tures:1This test method is under the jurisdiction of ASTM Committee D32 onCatalysts and is the direct responsibility of Subcommittee D32.01 on Physical-Chemical Properties.Current edition approve
12、d Oct. 1, 2003. Published October 2003. Originallyapproved in 1988. Last previous edition approved in 1999 as D 482494 (1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information,
13、 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.6.1.1 Vacuum System, capable of attaining and maintainingpressures below 104torr (0.01 Pa) in the absence of catalyst.6.
14、1.2 Expansion Vessel, having a volume between 300 to500 cm3(Vk) known to the nearest 0.01 cm3(Note 1). Thisvolume is defined as the volume between stopcocks V7and V8and includes the pressure gage and ammonia bulb.NOTE 1An expansion vessel of smaller volume is recommended formaterials of low surface
15、area or smaller sample size.6.1.3 Constant Volume Gage, capable of measuring 0 to 250torr to the nearest 101torr (10 Pa).6.1.4 Vacuum Gage, capable of measuring 0 to 1000 torr tothe nearest 103torr (0.1 Pa).6.1.5 Valve,(V8) from ammonia supply to the expansionvolume.6.1.6 Sample Tubes, with volume b
16、etween 5 and 25 cm3.The sample tube(s) may be connected to the apparatus withstandard taper joints, glass-to-glass seals, or compressionfittings.6.1.7 Dewar Flask(s), for immersion of ammonia (freeze-back bulb) in liquid nitrogen.6.1.8 Thermometer or Thermocouple, for measuring thetemperature of the
17、 expansion volume, Vk. Alternatively, theexpansion volume may be thermostatted a few degrees aboveambient to obviate the necessity of recording this temperature.6.1.9 Heating Mantle or Small Furnace, for each sampletube.6.1.10 Balance, with 0.1-mg sensitivity.6.1.11 Thermometer or Thermocouple, for
18、measuring thetemperature of the sample tube.6.1.12 Liquid Nitrogen Cold Trap, for vacuum system.6.1.13 Drying Tube, for drying ammonia gas (for example,a 3A molecular sieve or BaO).7. Reagents7.1 Ammonia Gas, at least 99.9 % pure.7.2 Liquid Nitrogen.7.3 Nitrogen Gas, at least 99.9 % pure, passed thr
19、oughdrying tube.8. Procedure8.1 Weigh sample tubes to 0.1 mg and record as W1. Placeapproximately2gofsample into the sample tube.8.2 Attach the sample tube to the apparatus.8.3 Open the sample valves (V5or V6, or both).8.4 Slowly open the valve to the vacuum system (V4),monitoring the rate of pressu
20、re decrease to avoid too high arate, which might lead to excessive fluidization of powderedsamples.8.5 Place a heating mantle or furnace around each sampleand raise the temperature to 673 K.NOTE 2Take special precautions if the moisture content exceedsapproximately 5 % to avoid “bumping” of powdered
21、 sample. It isrecommended that the heating rate not exceed 100 K/h under thesecircumstances.8.6 Continue degassing at 673 K for a minimum of 3 h, ata pressure not to exceed 103torr (0.1 Pa) Pa. Overnightdegassing is permissible.NOTE 3Certain materials will decompose at 673 K or will sinter.Lower deg
22、assing temperatures are permissible for such materials; how-ever, the degassing temperature should be specified when reporting theresults.8.7 After outgassing, lower the sample temperature to448 K.8.8 Close stopcock V7to isolate the samples from theexpansion volume, Vk, and admit ammonia to Vkthroug
23、h valveV8. Assume a chemisorption of approximately 5 cm3/g andadmit sufficient ammonia to give an excess pressure of 100 to150 torr (13 to 20 KPa) during exposure.8.9 Close the ammonia valve, V8, and freeze the ammoniainto the ammonia bulb by immersing the bulb in liquidnitrogen.8.10 After the ammon
24、ia is frozen, close the sample valvesV5and V6, open valve V7, and pump out noncondensibleimpurities. (Two minutes is normally sufficient pump time.)8.11 After pumping out noncondensible impurities, closevalve V7to the vacuum source and remove the liquid nitrogenfrom the ammonia bulb so the ammonia m
25、ay expand into Vk.Measure the pressure, P1and temperature T1.FIG. 1 ApparatusD48240328.12 Close valve V4to the vacuum source and open samplevalves V7, then V5or V6, exposing the sample(s) to excessammonia for 30 min. Sample temperature should be 448 K.8.13 After 30-min exposure, freeze ammonia back
26、into theammonia bulb for a period of2hbyimmersion in liquidnitrogen.8.14 After freeze-back period, close valve V7to separatesample tube(s) from expansion volume, Vk. If the pressure isnot less than 0.1 torr (10 Pa) at the end of the freeze-backperiod, then the system leaks and the test should be rep
27、eated.Remove liquid nitrogen and allow ammonia to expand into Vk.If system does not leak there should be no condensibles.Measure pressure, P2, and temperature, T2.8.15 Remove the mantle or furnace from around the sampletube(s) and cool to ambient temperature. Backfill the sampletube(s) with nitrogen
28、 to atmospheric pressure or slightly above.Close the sample valve.8.16 Detach the sample tube(s) from the apparatus andweigh. Record as W2to 0.1 mg. (If standard tapered joints areused, take care to remove grease prior to weighing.)9. Calculation9.1 Calculate the mass of sample, Ws, as follows:Ws5 W
29、22 W1(1)9.2 Calculate the pressures at standard temperature, P1TandP2T, as follows:P1T5 P13273T1(2)P2T5 P23273T2(3)9.3 Calculate the volume adsorbed, Vadsas follows:Vads5SP1T2 P2T760DVk(4)9.4 Calculate the acidity, A, in cubic centimetres per gram asfollows:A 5 Vads/Ws(5)10. Report10.1 The report sh
30、all include pretreatment, outgassing tem-peratures, and the temperature of the samples during exposure.10.2 Report the result as cubic centimetres per gram to threesignificant figures or the nearest 0.01 cm3/g, whichever isgreater.11. Precision and Bias311.1 Test ProgramAn interlaboratory study was
31、con-ducted in which the named property was measured in fourseparate test materials in nine separate laboratories. PracticeE 691, modified for nonuniform data sets, was followed for thedata reduction. Analysis details are in the research report. The95 % repeatability interval is about 10 % and the 95
32、 % repro-ducibility interval is about 30 %.11.2 BiasThe procedure described is without known bias.12. Keywords12.1 catalysts; nitrogen adsorption; pore size distributionASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin
33、this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must
34、 be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of ther
35、esponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700,
36、 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).3Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: D32-1023.D4824033
