ASTM D4780-95

Standard Test Method for Determination of Low Surface Area of Catalysts by Multipoint Krypton Adsorption

SCOPE
1.1 This test method covers the determination of the specific surface area of catalysts and catalyst carriers in the range from 0.05 to 10 m/g. A volumetric measuring system is used to obtain at least three data points which fall within the linear BET region.
1.2 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.

General Information

• Status: Historical
• Publication Date: 14-Aug-1995
• Technical Committee: D32 - Catalysts
• Drafting Committee: D32.01 - Physical-Chemical Properties

Relations

• Replaced By: ASTM D4780-95(2001) - Standard Test Method for Determination of Low Surface Area of Catalysts by Multipoint Krypton Adsorption
• Effective Date: 15-Aug-1995

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 4780 – 95
Standard Test Method for
Determination of Low Surface Area of Catalysts by
Multipoint Krypton Adsorption
This standard is issued under the fixed designation D 4780; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
P = initial Kr pressure, torr.
T8 = manifold temperature at initial Kr pressure,
1.1 This test method covers the determination of the specific
K.
surface area of catalysts and catalyst carriers in the range from
T = manifold temperature at initial Kr pressure,
0.05 to 10 m /g. A volumetric measuring system is used to 1
°C.
obtain at least three data points which fall within the linear
P = Kr pressure after equilibration, torr.
BET region.
T8 = manifold temperature at P ,K.
2 2
1.2 This standard does not purport to address all of the
T = manifold temperature at P , °C.
2 2
safety concerns, if any, associated with its use. It is the
P = liquid nitrogen vapor pressure, torr.
o,N
responsibility of the user of this standard to establish appro-
P = calculated krypton vapor pressure, torr.
o,krypton
priate safety and health practices and determine the applica-
T8 = liquid nitrogen temperature, K.
s
bility of regulatory limitations prior to use.
X = relative pressure, P /P .
2 o,krypton
V = volume of manifold, cm .
d
2. Referenced Documents
V = the apparent dead-space volume, cm .
s
2.1 ASTM Standards:
W = weight of sample, g.
s
D 3663 Test Method for Surface Area of Catalysts
W = tare weight of sample tube, g.
D 3766 Terminology Relating to Catalysts and Catalysis
W = weight of sample plus tare weight of tube, g.
V = volume of krypton in the dead-space, cm.
E 177 Practice for Use of the Terms Precision and Bias in
ds
V = See 11.3.5.
ASTM Test Methods
V = See 11.3.6.
E 456 Terminology Relating to Quality and Statistics 2
V = See 11.3.7.
E 691 Practice for Conducting an Interlaboratory Study to t
3 V = See 11.3.9.
a
Determine the Precision of a Test Method
V = See 11.6.
m
3. Terminology
4. Summary of Test Method
3.1 Definitions:
4.1 A catalyst sample is degassed by heating in vacuum to
3.1.1 Consult Terminology D 3766.
remove absorbed vapors from the surface. The quantity of
3.2 Symbols:
krypton adsorbed at various low pressure levels is determined
by measuring pressure differentials after introduction of a fixed
P = initial helium pressure, torr. volume of krypton to the sample at liquid nitrogen temperature.
H1
P = helium pressure after equilibration, torr.
The specific surface area is then calculated from the sample
H2
T = temperature of manifold at initial helium
H1 weight and adsorption data using the BET equation.
pressure,° C.
T = temperature of manifold after equilibration, 5. Significance and Use
H2
°C.
5.1 This test method has been found useful for the determi-
nation of the specific surface area of catalysts and catalyst
carriers in the range from 0.05 to 10 m /g for materials
specification, manufacturing control, and research and devel-
This test method is under the jurisdiction of ASTM Committee D-32 on
opment in the evaluation of catalysts. The determination of
Catalysts and is the direct responsibility of Subcommittee D32.01 on Physical-
Chemical Properties.
surface area of catalysts and catalyst carriers above 10 m /g is
Current edition approved Aug. 15, 1995. Published October 1995. Originally
addressed in Test Method D 3663.
published as D 4780 – 88. Last previous edition D 4780 – 94.
Annual Book of ASTM Standards, Vol 05.03.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4780
6. Apparatus and has greater precision, or a resistance thermometer from
which P values may be derived.
6.1 A schematic diagram of the apparatus is shown in Fig. 1. o,N
It may be constructed of glass or of metal and may operate
7. Reagents
manually or automatically. It has the following features:
7.1 Purity of Reagents—Reagent grade chemicals shall be
6.1.1 Vacuum System, capable of attaining pressures below
-4 used in all tests. Unless otherwise indicated, it is intended that
10 torr (1 torr = 133.3 Pa). This will include a vacuum gage
all reagents shall conform to the specifications of the Commit-
(not shown in Fig. 1). Access to the distribution manifold is
tee on Analytical Reagents of the American Chemical Society,
through the valve V.
where such specifications are available. Other grades may be
6.1.2 Distribution Manifold, having a volume between 5
3 3 used, provided it is first ascertained that the reagent is of
and 40 cm (V ) known to the nearest 0.01 cm . This volume is
d
sufficiently high purity to permit its use without lessening the
defined as the volume between the stopcocks or valves and it
accuracy of the determination.
includes the volume within the pressure gage.
7.2 Helium Gas, at least 99.9 % pure.
6.1.3 Constant Volume Gages, capable of measuring 1 to 10
7.3 Krypton Gas, at least 99.9 % pure.
torr to the nearest 0.001 torr and 0 to 1000 torr to the nearest
7.4 Liquid Nitrogen, of such purity that the saturation vapor
torr (1 torr = 133.3 Pa).
pressure P is not more than 20 torr above barometric
o,N
6.1.4 Valve (H), from the helium supply to the distribution
pressure. A fresh daily supply is recommended.
manifold.
6.1.5 Valve (K), from the krypton supply to the distribution
8. Procedure—Sample Preparation and Degassing
manifold.
8.1 Select a sample tube of the desired size. A 5 cm tube is
6.1.6 Sample Tube(s), with volume between 5 cm and 25
preferred for small samples to minimize dead space. However,
cm , depending on the application. The sample tube(s) may be
larger tubes may be required for larger samples or for finely
connected to the distribution manifold with standard taper
powdered samples, to avoid boiling when degassing is started.
joints, glass-to-glass seals, or compression fittings.
8.2 Evacuate the sample tube and then fill to atmospheric
NOTE 1—Modern commercial instruments may employ simple tubes
pressure with helium. This may be done on the surface area
with volumes outside of this range, and may be capable of testing multiple
unit, or on a separate piece of equipment.
samples simultaneously rather than separately as stated in 9.1.
8.3 Remove the sample tube, cap, and weigh. Record the
weight as W .
6.1.7 Dewar Flask(s) for immersion of the sample tube(s)
8.4 Place the sample, whose weight is known approxi-
in liquid nitrogen. The nitrogen level should be fixed at a
mately, into the sample tube. If possible, choose the sample
constant height by means of an automatic level controller or
size to provide an estimated total surface area of 1 to 5 m .
manually refilled to a predetermined mark on the sample
tube(s) about 30 to 50 mm below the distribution manifold 8.5 Attach the sample tube to the apparatus. If other samples
are to be run, attach them at this time to the other ports.
connectors.
6.1.8 Thermometer for measuring the temperature of the 8.6 Open the S valves where there are samples.
8.7 Slowly open the V valve, monitoring the rate of pressure
distribution manifold (T (i)or T (i)) in degrees Celsius. (Al-
1 2
ternatively, the distribution manifold may be thermostatted a decrease to avoid too high a rate, which might lead to excessive
fluidization of powdered samples.
few degrees above ambient to obviate the necessity of record-
ing this temperature.) 8.7.1 If a diffusion pump is used, it may be necessary to
close the V valve system periodically to protect the diffusion
6.1.9 Heating Mantle(s) or Small Furnace(s) for each
sample tube to allow outgassing samples at elevated tempera- pump fluid from exposure to pressures above 0.1 torr for
periods of more than 30 s. Close the valve off for 2 min.
tures.
−7
6.1.10 Laboratory Balance with 0.1 mg (10 kg) sensitiv- 8.8 Install a heating mantle or furnace around each sample
and raise the temperature to about 300°C (573 K).
ity.
6.1.11 Thermometer for measuring the temperature of the
NOTE 2—Caution: Take special precautions if the moisture content
liquid nitrogen bath (T8 (i)) in kelvins. This will preferably be
s
exceeds approximately 5 % to avoid “bumping’’ of powdered catalyst,
a nitrogen vapor-pressure-thermometer that gives P directly
o,N and to avoid surface area loss by self-steaming. It is recommended that the
heating rate not exceed 100 K/h under these circumstances.
8.9 Continue degassing at about 300°C (573 K) for a
−3
minimum of 3 h, at a pressure not to exceed 10 torr.
Overnight degassing is permissible.
NOTE 3—Certain materials decompose or sinter at 300°C. Lower
degassing temperatures are permissible for such materials; however, the
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
listed by the American Chemical Society, see Analar Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,
FIG. 1 Schematic Diagram of Surface Area Apparatus MD.
D 4780
degassing temperature should be specified when reporting the results.
10.8 Repeat 10.2-10.7 until there are at least three points in
the linear BET region (P /P = 0.05 to 0.30). Designate
8.10 Remove the heating mantles, and allow the samples to 2 o,krypton
the pressures, manifold temperatures, liquid nitrogen bath
cool.
temperatures or nitrogen vapor pressures as P (i), P (i), T (i),
8.11 Close the S valves. 1 2 1
T (i), T8 (i), and P (i) respectively for each i8th iteration (i
8.12 It is permissible to exercise the option of preliminary 2 s o,N
=2 to n, where n is the total number of points).
degassing on an external unit. In such a case, follow the
procedures of 8.5-8.11 and then repeat on the adsorption unit,
NOTE 4—The quantity of krypton gas admitted at each adsorption point
except that the degassing on the adsorption unit can be at room
in step 10.2 depends on the manifold volume, possible dosing s
...