ASTM D4824-03(2008)

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:D4824–94 (Reapproved 1999) Designation: D 4824 – 03 (Reapproved 2008)
Standard Test Method for
Determination of Catalyst Acidity by Ammonia
Chemisorption
This standard is issued under the fixed designation D4824; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This test method involves the measurement of total catalyst acidity by chemisorption of ammonia
in a static volumetric system. Acidity is a very important parameter in determining catalyst activity
and selectivity in many commercial reactions. Zeolite based catalysts used in the petroleum industry
for catalytic cracking are a prime example. This test method describes a simple procedure employing
inexpensive equipment that could readily be assembled in most laboratories.
1. Scope
1.1 This test method covers the determination of acidity of catalysts and catalyst carriers by ammonia chemisorption. A
volumetric measuring system is used to obtain the amount of chemisorbed ammonia.
1.2
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D3766 Terminology Relating to Catalysts and Catalysis
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions—Consult—See Terminology D3766.
3.2 Symbols:
V = calibrated expansion volume, cm .
k
T = temperature of V at initial ammonia pressure, K.
1 k
T = temperature of V at final ammonia pressure, K.
2 k
P = initial ammonia pressure, torr.
P = final ammonia pressure, torr.
W = weightmass of sample, g.
s
W = tare weight of sample tube, g.
W = sample mass plus tare weight of tube, g.
P = initial ammonia pressure corrected to standard temperature, torr.
1T
P = final ammonia pressure corrected to standard temperature, torr.
2T
This test method is under the jurisdiction of ASTM Committee D-32 on Catalysts and is the direct responsibility of Subcommittee D32.01 on Physical-Chemical
Properties.
Current edition approved Jan. 15, 1994. Published March 1994. Originally published as D4824–88. Last previous edition D4824–93.
This test method is under the jurisdiction of ASTM Committee D32 on Catalysts and is the direct responsibility of Subcommittee D32.01 on Physical-Chemical
Properties.
Current edition approved April 1, 2008. Published April 2008. Originally approved in 1988. Last previous edition approved in 2003 as D4824–03.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
, Vol 05.03.volume information, refer to the standard’s Document Summary page on the ASTM website.
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D 4824 – 03 (2008)
4. Summary of Test Method
4.1 Asample is degassed by heating in a vacuum to remove adsorbed vapors from the surface. The sample is then exposed to
an excess of gaseous ammonia and the excess ammonia is removed by freezing it into a trap cooled with liquid nitrogen. The
chemisorbed ammonia is calculated as the difference between the volume of ammonia before exposure and the volume recovered
in the liquid nitrogen trap.
5. Significance and Use
5.1 This test method can be used to determine the acidity of catalysts and catalyst carriers by ammonia chemisorption for
materials specifications, manufacturing control, and research and development in the evaluation of catalysts.
6. Apparatus
6.1 Aschematic diagram of one type of apparatus is shown in Fig. 1. It may be constructed of glass or metal and may operate
manually or automatically. It has the following features:
−4
6.1.1 Vacuum System, capable of attaining and maintaining pressures below 10 torr (0.01 Pa) in the absence of catalyst.
3 3
6.1.2 Expansion Vessel, having a volume between 300 to 500 cm (V ) known to the nearest 0.01 cm (Note 1). This volume is
k
defined as the volume between stopcocks V and V and includes the pressure gage and ammonia bulb.
7 8
NOTE 1—An expansion vessel of smaller volume is recommended for materials of low surface area or smaller sample size.
−1
6.1.3 Constant Volume Gagecapable, capable of measuring 0 to 250 torr to the nearest 10 torr (10 Pa).
−3
6.1.4 Vacuum Gage, capable of measuring 0 to 1000 torr to the nearest 10 torr (0.1 Pa).
6.1.5 Valve, (Valve,(V ) from ammonia supply to the expansion volume.
6.1.6 Sample Tubes, with volume between 5 and 25 cm . The sample tube(s) may be connected to the apparatus with standard
taper joints, glass-to-glass seals, or compression fittings.
6.1.7 Dewar Flask(s), for immersion of ammonia (freeze-back bulb) in liquid nitrogen.
6.1.8 Thermometer or Thermocouple,formeasuringthetemperatureoftheexpansionvolume, V .Alternatively,theexpansion
k
volume may be thermostatted a few degrees above ambient to obviate the necessity of recording this temperature.
6.1.9 Heating Mantle or Small Furnace for, for each sample tube.
6.1.10 Balancewith 0.1-mg sensitivity. , with 0.1-mg sensitivity.
6.1.11 Thermometer or Thermocouple , for measuring the temperature of the samp
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