ASTM D4222-20

Standard Test Method for Determination of Nitrogen Adsorption and Desorption Isotherms of Catalysts and Catalyst Carriers by Static Volumetric Measurements

SIGNIFICANCE AND USE
5.1 The test method has two main functions: first, it provides data useful for establishing the pore size distribution of catalyst materials, which in turn may influence their performance; and second, it serves as a laboratory test which may be used to study porosity changes that may occur during the manufacture and evaluation of catalysts.
SCOPE
1.1 This test method covers the determination of nitrogen adsorption and desorption isotherms of catalysts and catalyst carriers at the boiling point of liquid nitrogen.2 A static volumetric measuring system is used to obtain sufficient equilibrium adsorption points on each branch of the isotherm to adequately define the adsorption and desorption branches of the isotherm. Thirty points evenly spread over the isotherm is considered to be the minimum number of points that will adequately define the isotherm.  
1.2 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• ICS: 17.060 - Measurement of volume, mass, density, viscosity
• ICS: 71.040.30 - Chemical reagents
• Technical Committee: D32 - Catalysts
• Drafting Committee: D32.01 - Physical-Chemical Properties

Relations

• Refers: ASTM D3766-24a - Standard Terminology Relating to Catalysts and Catalysis
• Effective Date: 01-Feb-2024
• Refers: ASTM D3766-24 - Standard Terminology Relating to Catalysts and Catalysis
• Effective Date: 01-Jan-2024
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM D3766-08(2018) - Standard Terminology Relating to Catalysts and Catalysis
• Effective Date: 01-Nov-2018
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E456-13a - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13ae1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13ae2 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13ae3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Aug-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM D3766-08(2013) - Standard Terminology Relating to Catalysts and Catalysis
• Effective Date: 01-Mar-2013

Overview

ASTM D4222-20, published by ASTM International, defines the standard test method for determining nitrogen adsorption and desorption isotherms of catalysts and catalyst carriers using static volumetric measurements. This test method is designed to characterize the pore structure and surface properties by measuring the amount of nitrogen gas adsorbed and desorbed at the boiling point of liquid nitrogen. Understanding the pore size distribution and porosity is critical, as these properties can significantly influence catalyst performance during industrial processes.

Key Topics

• Nitrogen Adsorption and Desorption: The method determines isotherms by gradually introducing nitrogen gas to the catalyst sample at liquid nitrogen temperature and recording the amounts adsorbed and desorbed at different equilibrium points.
• Static Volumetric System: Utilizes an apparatus capable of precise pressure, temperature, and volume measurements to ensure accurate and repeatable results.
• Data Collection: At least thirty data points are required, evenly spanning the isotherm, to accurately define both adsorption and desorption curves.
• Porosity and Pore Size Distribution: The isotherm data provide insights into total pore volume and pore size distribution, essential for optimizing catalyst properties.
• Sample Preparation: Includes degassing and pretreatment protocols to remove contaminants that might skew nitrogen adsorption measurements.
• Reporting: All key experimental parameters, including sample identification, pretreatment conditions, adsorption/desorption data, and calculated pore volumes, are essential for reproducibility.

Applications

• Catalyst Characterization: Used extensively in research, quality control, and production environments to determine the surface area, pore volume, and pore size distribution of catalyst materials and carriers.
• Process Optimization: Enables manufacturers and researchers to monitor porosity changes during catalyst synthesis, activation, or after reaction cycles, facilitating improved catalyst design and performance.
• Material Evaluation: Suitable for a wide range of porous solids, enabling comparison and benchmarking of commercial and developmental catalyst materials.
• Compliance and Quality Assurance: Assists manufacturers in adhering to industry standards and verifying that product specifications meet desired criteria.

Related Standards

The following ASTM standards and terminology documents are frequently used in conjunction with ASTM D4222-20:

• ASTM D3663: Standard Test Method for Surface Area of Catalysts and Catalyst Carriers.
• ASTM D3766: Terminology Relating to Catalysts and Catalysis.
• ASTM E177: Practice for Use of the Terms Precision and Bias in ASTM Test Methods.
• ASTM E456: Terminology Relating to Quality and Statistics.
• ASTM E691: Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method.

Practical Value

Implementing ASTM D4222-20 provides a robust, internationally recognized approach for measuring nitrogen adsorption and desorption isotherms-crucial parameters for catalyst evaluation and quality assurance. Laboratories and manufacturers utilize this standard to ensure consistent, repeatable results that drive process improvements and support regulatory compliance. By providing detailed instructions for apparatus, method, sample preparation, and data reporting, this standard streamlines catalyst assessment and supports innovations in catalysis for the chemical, petrochemical, and environmental sectors.

Keywords: nitrogen adsorption, desorption isotherms, catalysts, catalyst carriers, static volumetric measurements, pore size distribution, porosity, ASTM D4222-20, catalyst characterization

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D4222 − 20
Standard Test Method for
Determination of Nitrogen Adsorption and Desorption
Isotherms of Catalysts and Catalyst Carriers by Static
Volumetric Measurements
This standard is issued under the fixed designation D4222; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope D3766Terminology Relating to Catalysts and Catalysis
E177Practice for Use of the Terms Precision and Bias in
1.1 This test method covers the determination of nitrogen
ASTM Test Methods
adsorption and desorption isotherms of catalysts and catalyst
2 E456Terminology Relating to Quality and Statistics
carriers at the boiling point of liquid nitrogen. A static
E691Practice for Conducting an Interlaboratory Study to
volumetric measuring system is used to obtain sufficient
Determine the Precision of a Test Method
equilibriumadsorptionpointsoneachbranchoftheisothermto
adequately define the adsorption and desorption branches of
3. Terminology
the isotherm. Thirty points evenly spread over the isotherm is
3.1 Definitions—See Terminology D3766.
considered to be the minimum number of points that will
adequately define the isotherm. 3.2 Symbols:
1.2 Units—The values stated in SI units are to be regarded
as standard. The values given in parentheses after SI units are
PH = initial helium pressure, torr.
providedforinformationonlyandarenotconsideredstandard.
PH = helium pressure after equilibration, torr.
TH = temperature of manifold at initial helium pressure,
1.3 This standard does not purport to address all of the
°C.
safety concerns, if any, associated with its use. It is the
TH = temperature of manifold after equilibration, °C.
responsibility of the user of this standard to establish appro-
P = initial N pressure, torr.
1 2
priate safety, health, and environmental practices and deter-
T = manifold temperature at initial N pressure, K.
1 2
mine the applicability of regulatory limitations prior to use.
T' = manifold temperature at initial N pressure, °C.
1 2
1.4 This international standard was developed in accor-
P = pressure after equilibration, torr.
dance with internationally recognized principles on standard-
T = manifold temperature after equilibrrium, K.
ization established in the Decision on Principles for the
T' = manifold temperature after equilibrium, °C.
Development of International Standards, Guides and Recom-
P = initial N pressure during desorption, torr.
3 2
mendations issued by the World Trade Organization Technical
T = manifold temperature at initial N pressure, K.
3 2
Barriers to Trade (TBT) Committee.
T' = manifold temperature at initial N pressure, °C.
3 2
P = pressure after equilibration during desorption, torr.
2. Referenced Documents
T = manifold temperature after equilibration, K.
T' = manifold temperature after equilibration, °C.
2.1 ASTM Standards:
P = liquid nitrogen vapor pressure, torr.
D3663Test Method for Surface Area of Catalysts and 0
T = liquid nitrogen temperature, K.
Catalyst Carriers s
X = relative pressure, P /P .
2(4) 0
V = volume of manifold, cm .
d
1 V = the dead-space volume factor, cm (STP)/torr.
This test method is under the jurisdiction of ASTM Committee D32 on s
W = mass of sample, g.
Catalysts and is the direct responsibility of Subcommittee D32.01 on Physical-
s
Chemical Properties.
W = tare of sample tube, g.
Current edition approved Oct. 1, 2020. Published November 2020. Originally
W' = sample mass + tare of tube after degassing, g.
ε1
approved in 1983. Last previous edition approved in 2015 as D4222–03(2015) .
W = sample mass + tare of tube after adsorption, g.
DOI: 10.1520/D4222-20.
V = volume of nitrogen in the dead-space, cm (STP).
Adamson,A. W., Physical Chemistry of Surfaces, 3rd ed., John Wiley & Sons, ds
V = see 12.4.3.
New York, NY, 1976, p. 532.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
V = see 12.4.4.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
V = see 12.4.5.
t
Standards volume information, refer to the standard’s Document Summary page on
V = see 12.4.7.
ad
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4222 − 20
6.1.1 Distribution Manifold, having a (V ), known to the
d
nearest 0.05 cm . This volume is defined as the volume
between the stopcocks or valves and includes the pressure
gauge.
6.1.2 Vacuum System, capable of attaining pressures below
-4
10 torr (1 torr = 133.3 Pa). This will include a vacuum gauge
(not shown in Fig. 1). Access to the distribution manifold is
through the valve V.
6.1.3 Pressure Sensing Devices or Pressure Transducers,
capable of measurements with a sensitivity of at least 0.1 torr,
FIG. 1 Schematic Diagram of Adsorption Apparatus
in the range from 0 to 1000 torr (1 torr = 133.3 Pa).
6.1.4 Value (H), from the helium supply to the distribution
manifold.
V = see 12.5.
de
6.1.5 Valve (N), from the nitrogen supply to the distribution
manifold.
4. Summary of Test Method
6.1.6 The connection between the sample tube and the S
4.1 Thesampleisheatedandevacuatedtoremoveadsorbed
valve can be a standard-taper glass joint, a glass-to-glass seal,
vapors from the surface.The nitrogen adsorption branch of the
or a compression fitting.
isotherm is determined by evacuating the sample, cooling the
3 3
6.2 Sample Tubes, with volumes from 5 cm to 100 cm
sample to the boiling point of liquid nitrogen (;77.3 K), and
depending on the application.
subsequently adding stepwise, known amounts of nitrogen gas
to the sample in such amounts that the form of the adsorption
6.3 Heating Mantles or Small Furnaces.
isotherm is adequately defined and the saturation pressure of
6.4 Dewar Flasks.
nitrogen is reached. Each additional dose of nitrogen is
10−7
6.5 Laboratory Balance, with 0.1-mg ( kg) sensitivity.
introduced to the sample only after the foregoing dose of
nitrogen has reached adsorption equilibrium with the sample.
6.6 Thermometer or Thermocouple, for measuring the tem-
By definition, equilibrium is reached if the change in gas
perature of the distribution manifold [T' (i)or T' (i)] in °C.
1 2
pressure is no greater than 0.1 torr over a 5 min interval. The
6.6.1 The manifold may be thermostated at a particular
desorption isotherm is determined by desorbing nitrogen from
temperature, a few degrees above ambient, to obviate the
the saturated sample in a stepwise mode with the same
necessity of recording this temperature at each reading.
precautions taken to ensure desorption equilibration as applied
6.7 Thermometer, for measuring the temperature of the
under adsorption conditions. It is essential that the experimen-
liquidnitrogenbath(T (i))inKelvin.Preferably,thisthermom-
s
tal points be distributed over the isotherm in such a manner as
eter will be a nitrogen vapor-pressure-thermometer, often
tocorrectlyidentifyanddefinetheisotherm.Iftheadditionsor
referred to in a commercial instrument as a pressure saturation
withdrawals of nitrogen are too large, the temporarily too-high
tube, that gives P directly and has greater precision, or a
nitrogengaspressureduringadsorptionortoo-lowgaspressure
resistance thermometer from which P values may be derived.
during desorption, may result in so-called scanning effects
NOTE1—Apressuretransducermaybeplacedbetweenthesampletube
within the hysteresis loop of the adsorption-desorption
and the manifold to monitor equilibrium pressure, but this is not a
branches of the isotherm. The occurrence of scanning may
requirement of the system.
result in too-high equilibrium values for the adsorption iso-
therm and too-low values for the desorption isotherm.
7. Reagents
7.1 Helium Gas—Acylinderofheliumgasatleast99.999%
5. Significance and Use
pure.
5.1 The test method has two main functions: first, it pro-
7.2 Liquid Nitrogen, of such purity that P is not more than
vides data useful for establishing the pore size distribution of
20 torr above barometric pressure. A fresh daily supply is
catalyst materials, which in turn may influence their perfor-
recommended.
mance; and second, it serves as a laboratory test which may be
used to study porosity changes that may occur during the
7.3 Nitrogen Gas—A cylinder of nitrogen gas at least
manufacture and evaluation of catalysts.
99.999% pure.
6. Apparatus 8. Procedure-Sample Preparation and Degassing
6.1 Ageneric schematic diagram of the minimum apparatus 8.1 Selectasampletubeofthedesiredsize.Tominimizethe
requirement is shown in Fig. 1.Acommercial instrument may dead-space, a 5cm sample tube is preferred for samples not
be used and may be constructed of glass or of metal. The exceeding about 1 g. However, to avoid boiling when degas-
specific commercial apparatus chosen may have a different sing is started, a 25cm sample tube may be preferred for
configuration than that shown in Fig. 1 and may require finely powdered catalysts. A small glass-wool plug or fritted
modification of the sequence of valve operation and of the disk placed in the neck of the sample tube above the liquid
calculations and equations used. It should have the following nitrogen level, will eliminate the possibility of any small
features as a minimum: catalyst particles entering the vacuum system.
D4222 − 20
8.2 Fill the sample tube with nitrogen or helium at atmo- 9. Procedure-Dead-Space Determination
sphericpressure,afterremovingairbyevacuation.Thismaybe
9.1 From this point on, each sample being tested for
done on the adsorption unit or on a separate piece of equip-
nitrogen adsorption must be run on an individual basis. Thus,
ment.
9.2through11.4mustbecarriedoutseparatelyforeachtubein
test.
8.3 Remove the sample tube from the system, cap, and
weigh. Record the mass as W .
9.2 Thedead-spaceisthequantityofgaswithinthecharged
sample tube, including the S valve, when the tube is immersed
8.4 Place the catalyst sample, whose approximate mass is
in liquid nitrogen to the proper depth.
known,intothesampletube.Choosethesamplesizetoprovide
NOTE 5—The dead-space may be determined after the nitrogen adsorp-
an estimated total sample surface area of approximately 20m
tion and desorption, if more convenient, as long as adequate degassing
or greater.
precedesit.Inthatcase,replacetheliquidnitrogenbathafter10.14before
proceeding with 9.3 – 9.9. Then, remove the Dewar flask before carrying
NOTE 2—Follow instrument manufacturer’s recommendations for
out 10.15 and 10.16.
sample amounts when using commercial instruments.
NOTE 6—Some commercial equipment allows for helium-free determi-
nation of the dead-space by calibration of a blank cell and accounting for
8.5 Attachthesampletubetotheapparatus.Ifothersamples
the skeletal volume of the sample when the cell is charged. This can be
are to be run, attach them at this time to the other ports.
consideredequivalenttodeterminationofdeadspacebyheliumandcanbe
used if helium is not available. Follow the recommendations of the
8.6 Open the S valve.
instrument manufacturer for these measurements.
8.7 Slowlyopenthe Vvalve,monitoringtherateofpressure
9.3 PlaceaDewarflaskofliquidnitrogenaroundthesample
decreasetoavoidtoohigharate,whichmightleadtoexcessive
and adjust the liquid level to a fixed point on the sample tube.
fluidization of powdered samples.
Maintain this level throughout the test.
8.8 Install a heating mantle or furnace around each sample
NOTE 7—Some modern commercial instruments do not require manual
maintenance or readjusting of the level of liquid nitrogen during the
and raise the temperature to about 300°C (573K).
analysis. Follow the manufacturer’s recommendations for operating the
particular instrument used.
NOTE 3—Take special precautions if the moisture content exceeds
approximately 5% to avoid bumping of powdered catalyst and to avoid
9.4 Zero the pressure gauge.
surface area loss by self-steaming. A stepped or pressure-controlled
heating routine is recommended under these circumstances. 9.5 Admit the helium gas into the system to a pressure of
NOTE 4—Not all catalysts or their supports are stable to 300°C. This 600 to 900 torr by carefully opening the H valve. Record this
should be noted and the appropriate temperature should be used based on
pressure as P , and the manifold temperature as T .
H1 H1
thermal properties of the material.
9.6 Open the S valve to admit helium to the sample.
8.9 Continue degassing at about 300°C (573 K) for a
9.7 After about 5 min of equilibration, readjust the liquid
-3
minimum of 3h, at a pressure not to exceed 10 torr.
nitrogenlevel,andrecordthepressureas P andthemanifold
H2
Overnight degassing is permissible. It is recommended that a
temperature as T .
H2
rateofrisetestbeperformedtodeterminethecurrentreadiness
9.8 Repeat 9.5 – 9.7 for each sample on the manifold.
of the sample. For such tests, isolate the sample from vacuum
and monitor the cell for pressure change associated with a
9.9 Open the S valve; then slowly open the V valve to
vapor pressure from the sample. If the pressure is nearly
remove the helium gas.
constant over a prolonged period (15 to 30min), degassing is
−3
9.10 Close the S va
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
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.
´1
Designation: D4222 − 03 (Reapproved 2015) D4222 − 20
Standard Test Method for
Determination of Nitrogen Adsorption and Desorption
Isotherms of Catalysts and Catalyst Carriers by Static
Volumetric Measurements
This standard is issued under the fixed designation D4222; 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 (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Eq 10 in subsection 12.4.7 was corrected editorially in August 2015.
1. Scope
1.1 This test method covers the determination of nitrogen adsorption and desorption isotherms of catalysts and catalyst carriers
at the boiling point of liquid nitrogen. A static volumetric measuring system is used to obtain sufficient equilibrium adsorption
points on each branch of the isotherm to adequately define the adsorption and desorption branches of the isotherm. Thirty points
evenly spread over the isotherm is considered to be the minimum number of points that will adequately define the isotherm.
1.2 Units—The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information
only.after SI units are provided for information only and are not considered standard.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D3663 Test Method for Surface Area of Catalysts and Catalyst Carriers
D3766 Terminology Relating to Catalysts and Catalysis
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions—See Terminology D3766.
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, 2015Oct. 1, 2020. Published August 2015November 2020. Originally approved in 1983. Last previous edition approved in 20082015
ε1
as D4222 – 03 (2008).(2015) . DOI: 10.1520/D4222-03R15.10.1520/D4222-20.
Adamson, A. W., Physical Chemistry of Surfaces, 3rd ed., John Wiley & Sons, New York, NY, 1976, p. 532.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4222 − 20
3.2 Symbols:
PH = initial helium pressure, torr.
PH = helium pressure after equilibration, torr.
TH = temperature of manifold at initial helium pressure, °C.
TH = temperature of manifold after equilibration, °C.
P = initial N pressure, torr.
1 2
T = manifold temperature at initial N pressure, K.
1 2
T' = manifold temperature at initial N pressure, °C.
1 2
P = pressure after equilibration, torr.
T = manifold temperature after equilibrrium, K.
T' = manifold temperature after equilibrium, °C.
P = initial N pressure during desorption, torr.
3 2
T = manifold temperature at initial N pressure, K.
3 2
T' = manifold temperature at initial N pressure, °C.
3 2
P = pressure after equilibration during desorption, torr.
T = manifold temperature after equilibration, K.
T' = manifold temperature after equilibration, °C.
P = liquid nitrogen vapor pressure, torr.
T = liquid nitrogen temperature, K.
s
X = relative pressure, P /P .
2(4) 0
V = volume of manifold, cm .
d
V = the dead-space volume factor, cm (STP)/torr.
s
W = mass of sample, g.
s
W = tare of sample tube, g.
W' = sample mass + tare of tube after degassing, g.
W = sample mass + tare of tube after adsorption, g.
V = volume of nitrogen in the dead-space, cm (STP).
ds
V = see 12.4.3.
V = see 12.4.4.
V = see 12.4.5.
t
V = see 12.4.7.
ad
V = see 12.5.
de
4. Summary of Test Method
4.1 The sample is heated and evacuated to remove adsorbed vapors from the surface. The nitrogen adsorption branch of the
isotherm is determined by evacuating the sample, cooling the sample to the boiling point of liquid nitrogen (;77.3 K), and
subsequently adding stepwise, known amounts of nitrogen gas to the sample in such amounts that the form of the adsorption
isotherm is adequately defined and the saturation pressure of nitrogen is reached. Each additional dose of nitrogen is introduced
to the sample only after the foregoing dose of nitrogen has reached adsorption equilibrium with the sample. By definition,
equilibrium is reached if the change in gas pressure is no greater than 0.1 torr/5 torr over a 5 min interval. The desorption isotherm
is determined by desorbing nitrogen from the saturated sample in a stepwise mode with the same precautions taken to ensure
desorption equilibration as applied under adsorption conditions. It is essential that the experimental points be distributed over the
isotherm in such a manner as to correctly identify and define the isotherm. If the additions or withdrawals of nitrogen are too large,
the temporarily too-high nitrogen gas pressure during adsorption or too-low gas pressure during desorption, may result in so-called
scanning effects within the hysteresis loop of the adsorption-desorption branches of the isotherm. The occurrence of scanning may
result in too-high equilibrium values for the adsorption isotherm and too-low values for the desorption isotherm.
5. Significance and Use
5.1 The test method has two main functions: first, it provides data useful for establishing the pore size distribution of catalyst
materials, which in turn may influence their performance; and second, it serves as a laboratory test which may be used to study
porosity changes that may occur during the manufacture and evaluation of catalysts.
6. Apparatus
6.1 A generic schematic diagram of the minimum apparatus requirement is shown in Fig. 1. A commercial instrument may be used
D4222 − 20
FIG. 1 Schematic Diagram of Adsorption Apparatus
and may be constructed of glass or of metal. The specific commercial apparatus chosen may have a different configuration than
that shown in Fig. 1 and may require modification of the sequence of valve operation and of the calculations and equations used.
It should have the following features as a minimum:
6.1.1 Distribution Manifold, having a (V ), known to the nearest 0.05 cm . This volume is defined as the volume between the
d
stopcocks or valves and includes the pressure gauge.
-4
6.1.2 Vacuum System, capable of attaining pressures below 10 torr (1 torr = 133.3 Pa). This will include a vacuum gauge (not
shown in Fig. 1). Access to the distribution manifold is through the valve V.
6.1.3 Pressure Sensing Devices or Pressure Transducers, capable of measurements with a sensitivity of at least 0.1 torr, in the
range from 0 to 1000 torr (1 torr = 133.3 Pa).
6.1.4 Value (H), from the helium supply to the distribution manifold.
6.1.5 Valve (N), from the nitrogen supply to the distribution manifold.
6.1.6 The connection between the sample tube and the S valve can be a standard-taper glass joint, a glass-to-glass seal, or a
compression fitting.
3 3
6.2 Sample Tubes, with volumes from 5 cm to 100 cm depending on the application.
6.3 Heating Mantles or Small Furnaces.
6.4 Dewar Flasks.
10−7
6.5 Laboratory Balance, with 0.1-mg ( kg) sensitivity.
6.6 Thermometer or Thermocouple, for measuring the temperature of the distribution manifold [T' (i) or T' (i)] in °C.
1 2
6.6.1 The manifold may be thermostated at a particular temperature, a few degrees above ambient, to obviate the necessity of
recording this temperature at each reading.
6.7 Thermometer, for measuring the temperature of the liquid nitrogen bath (T (i)) in Kelvin. Preferably, this thermometer will be
s
a nitrogen vapor-pressure-thermometer, often referred to in a commercial instrument as a pressure saturation tube, that gives P
directly and has greater precision, or a resistance thermometer from which P values may be derived.
NOTE 1—A pressure transducer may be placed between the sample tube and the manifold to monitor equilibrium pressure, but this is not a requirement
of the system.
7. Reagents
7.1 Helium Gas—A cylinder of helium gas at least 99 % 99.999 % pure.
D4222 − 20
7.2 Liquid Nitrogen, , of such purity that P is not more than 20 torr above barometric pressure. A fresh daily supply is
recommended.
7.3 Nitrogen Gas—A cylinder of nitrogen gas at least 99.999 % 99.999 % pure.
8. Procedure-Sample Preparation and Degassing
8.1 Select a sample tube of the desired size. To minimize the dead-space, a 5-cm5 cm sample tube is preferred for samples not
exceeding about 1 g. However, to avoid boiling when degassing is started, a 25-cm25 cm sample tube may be preferred for finely
powdered catalysts. A small glass-wool plug or fritted disk placed in the neck of the sample tube above the liquid nitrogen level,
will eliminate the possibility of any small catalyst particles entering the vacuum system.
8.2 Fill the sample tube with nitrogen or helium at atmospheric pressure, after removing air by evacuation. This may be done on
the adsorption unit or on a separate piece of equipment.
8.3 Remove the sample tube from the system, cap, and weigh. Record the mass as W .
8.4 Place the catalyst sample, whose approximate mass is known, into the sample tube. Choose the sample size to provide an
estimated total sample surface area of approximately 20 m20 m or greater.
NOTE 2—Follow instrument manufacturer’s recommendations for sample amounts when using commercial instruments.
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.
8.6 Open the S valve.
8.7 Slowly open the V valve, monitoring the rate of pressure decrease to avoid too high a rate, which might lead to excessive
fluidization of powdered samples.
8.8 Install a heating mantle or furnace around each sample and raise the temperature to about 300°C (573 K).300 °C (573 K).
NOTE 3—Take special precautions if the moisture content exceeds approximately 5 % 5 % to avoid bumping of powdered catalyst and to avoid surface
area loss by self-steaming. It is recommended that the heating rate not exceed 100 K/h A stepped or pressure-controlled heating routine is recommended
under these circumstances.
NOTE 4—Not all catalysts or their supports are stable to 300 °C. This should be noted and the appropriate temperature should be used based on thermal
properties of the material.
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8.9 Continue degassing at about 300°C300 °C (573 K) for a minimum of 3 h, 3 h, at a pressure not to exceed 10 torr. Overnight
degassing is permissible. It is recommended that a rate of rise test be performed to determine the current readiness of the sample.
For such tests, isolate the sample from vacuum and monitor the cell for pressure change associated with a vapor pressure from the
sample. If the pressure is nearly constant over a prolonged period (15 to 30 min), degassing is complete.
NOTE 3—Certain materials will decompose at 300°C (for example, alumina hydrates) or will sinter (for example, platinum black). Lower degassing
temperatures are permissible for such materials; however, the degassing temperature should be specified when reporting the results.
8.10 Remove the heating mantle, and allow the sample to cool.
8.11 Close the S valve.
8.12 It is permissible to exercise the option of preliminary degassing on an external unit. In such a case, follow the procedures
of 8.4 – 8.10 and then repeat on the adsorption unit, except that the degassing time in 8.9 should not exceed 1 h.
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8.13 If it is desired to weigh the sample after preliminary degassing on an external unit, back-fill with the same gas used in 8.2
to above atmospheric pressure. Close the S valve.
8.14 Detach the sample tube from the apparatus, recap with the stopper used previously, and weigh. Record the mass as W' .
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8.15 Remove the backfilled gas by evacuation to less than 10 torr at room temperature.
9. Procedure-Dead-Space Determination
9.1 From this point on, each sample being tested for nitrogen adsorption must be run on an individual basis. Thus, 9.2 through
11.4 must be carried out separately for each tube in test.
9.2 The dead-space is the quantity of gas within the charged sample tube, including the S valve, when the tube is immersed in
liquid nitrogen to the proper depth.
NOTE 5—The dead-space may be determined after the nitrogen adsorption and desorption, if more convenient, as long as adequate degassing precedes
it. In that case, replace the liquid nitrogen bath after 10.14 before proceeding with 9.3 – 9.9. Then, remove the Dewar flask before carrying out 10.15
and 10.16.
NOTE 6—Some commercial equipment allows for helium-free determination of the dead-space by calibration of a blank cell and accounting for the skeletal
volume of the sample when the cell is charged. This can be considered equivalent to determination of deadspace by helium and can be used if helium
is not available. Follow the recommendations of the instrument manufacturer for these measurements.
9.3 Place a Dewar flask of liquid nitrogen around the sample and adjust t
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