1、Designation: D4824 13Standard Test Method forDetermination of Catalyst Acidity by AmmoniaChemisorption1This standard is issued under the fixed designation D4824; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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.Ac
3、idity is a very important property in determining catalyst activity andselectivity in many commercial reactions. Zeolite based catalysts used in the petroleum industry forcatalytic cracking are a prime example. This test method describes a simple procedure employinginexpensive equipment that could r
4、eadily 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 regarded a
5、s 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 determine th
6、e applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D3766 Terminology Relating to Catalysts and CatalysisE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsSee Terminology D3766.3
7、.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 of tube
8、, g.P1T= initial ammonia pressure corrected to standardtemperature, torr.P2T= final ammonia pressure corrected to standardtemperature, torr.4. Summary of Test Method4.1 Asample is degassed by heating in a vacuum to removeadsorbed vapors from the surface. The sample is then exposedto an excess of gas
9、eous 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 test method ca
10、n 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 may be const
11、ructed 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 approved April 1, 20
12、13. Published August 2013. Originallyapproved in 1988. Last previous edition approved in 2008 as D4824 03(2008).DOI: 10.1520/D4824-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume info
13、rmation, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.1.1 Vacuum System, capable of attaining and maintainingpressures below 104torr (0.01 Pa) in the absence of cata
14、lyst.6.1.2 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 s
15、urface area or smaller sample size.6.1.3 Pressure Sensing Device or Pressure Transducer,capable of measuring 0 to 250 torr to the nearest 101torr (10Pa).6.1.4 Pressure Sensing Device or Pressure Transducer,capable of measuring 0 to 1000 torr to the nearest 103torr (0.1Pa).6.1.5 Valve, (V8) from ammo
16、nia supply to the expansionvolume.6.1.6 Sample Tubes, with volume between 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
17、.8 Thermometer or Thermocouple, for measuring thetemperature of the 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 Balanc
18、e, with 0.1-mg sensitivity.6.1.11 Thermometer or Thermocouple, for 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
19、 Liquid Nitrogen.7.3 Nitrogen Gas, at least 99.9 % pure, passed throughdrying 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 ope
20、n the valve to the vacuum system (V4),monitoring the rate of pressure 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 moist
21、ure content exceedsapproximately 5 % to avoid “bumping” of powdered 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
22、3Certain materials will decompose at 673 K or will sinter.Lower degassing temperatures are permissible for such materials;however, the degassing temperature should be specified when reportingthe results.8.7 After outgassing, lower the sample temperature to448 K.8.8 Close stopcock V7to isolate the sa
23、mples from theexpansion volume, Vk, and admit ammonia to Vkthrough 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
24、bulb by immersing the bulb in liquidnitrogen.FIG. 1 ApparatusD4824 1328.10 After the ammonia 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 V
25、7to the vacuum source and remove the liquid nitrogenfrom the ammonia bulb so the ammonia may expand into Vk.Measure the pressure, P1and temperature T1.8.12 Close valve V4to the vacuum source and open samplevalves V7, then V5or V6, exposing the sample(s) to excessammonia for 30 min. Sample temperatur
26、e should be 448 K.8.13 After 30-min exposure, freeze ammonia back 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 f
27、reeze-backperiod, then the system leaks and the test should be repeated.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 coo
28、l to ambient temperature. Backfill the sampletube(s) with nitrogen 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.
29、 Calculation9.1 Calculate the mass of sample, Ws, as follows:Ws5 W22 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 centime
30、tres per gram asfollows:A 5 Vads/Ws(5)10. Report10.1 The report shall include pretreatment, outgassingtemperatures, and the temperature of the samples duringexposure.10.2 Report the result as cubic centimetres per gram to threesignificant figures or the nearest 0.01 cm3/g, whichever isgreater.11. Pr
31、ecision and Bias311.1 Test ProgramAn interlaboratory study was con-ducted in which the named property was measured in fourseparate test materials in nine separate laboratories. PracticeE691, modified for nonuniform data sets, was followed for thedata reduction. Analysis details are in the research r
32、eport. The95 % repeatability interval is about 10 % and the 95 % 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 p
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35、mments will receive careful consideration at a meeting of theresponsible 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 copyrigh
36、ted 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
37、-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).3Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D32-1023.D4824 133
