ASTM D3908-20

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.
Designation: D3908 − 03 (Reapproved 2015) D3908 − 20
Standard Test Method for
Hydrogen Chemisorption on Supported Platinum Catalysts
by Volumetric Vacuum Method
This standard is issued under the fixed designation D3908; 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.
1. Scope
1.1 This test method covers the determination of the chemisorption of hydrogen at 298 K (25°C)(25 °C) on supported platinum
catalysts that have been reduced in flowing hydrogen at 723 K (450°C).(450 °C). It incorporates a static volumetric vacuum
technique at constant volume.
1.2 The test method is intended for use on unused supported platinum on alumina catalysts of loadings greater than 0.3 weight
%. Data on other supports and lower platinum loadings were not tested.
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:
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.
3.2 Quality and Statistics—See Terminology E456.
3.3 Precision and Bias—See Practice E177.
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 June 2015November 2020. Originally approved in 1980. Last previous edition approved in 20082015 as
D3908 – 03 (2008).(2015). DOI: 10.1520/D3908-03R15.10.1520/D3908-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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
D3908 − 20
FIG. 1 Schematic: Static Vacuum System
3.4 Symbols—The following symbols are used:
P = pressure of gas in calibrated bulb, torr
c
P = pressure of gas in calibrated bulb and manifold, torr
mc
P = pressure in manifold, torr
m
P = pressure in manifold and dead space, torr
md
P = pressure in manifold prior to expansion into sample tube for X equilibration point, torr
m
x
P = equilibrium pressure after expansion for generating X equilibrium point, torr
e
x
V = volume of calibrated bulb, cm
c
V = volume of manifold between stopcocks 12 and 2 with only 4 and 1 open, cm
m
V = volume of dead space in sample cell containing catalyst (volume between 2 and 3), cm
d
V (STP) = volume of gas adsorbed at STP, cm
ads x
V (STP) = cumulative volume of gas adsorbed through X, cm
ads cx
V = monolayer volume of gas adsorbed at STP, cm
S
T = temperature representative of the manifold prior to expansion into the sample cell, K
m
Ax
T = temperature representative of the entire system after equilibrium pressure (P ) has been established, K
m e
Bx x
T = temperature of manifold prior to expansion into sample cell for dead space determination, K
m
T = temperature of entire system after equilibrium pressure has been established for dead space determination, K
m
D
T = average manifold temperature for a given dose, K
= (T + T )/2
m m
Ax Bx
W = mass of catalyst, g
cat
X = weight percent of platinum
%D = percent platinum atoms on the surface
4. Significance and Use
4.1 This test method sets forth a procedure by which duplicate catalyst samples can be compared either on an interlaboratory or
intralaboratory basis. It is anticipated that catalyst producers and users will find this test method of value.
4.2 Discrimination of the samples for which this procedure is recommended must be exercised when considering carrier (support)
materials that sorb appreciable quantities of hydrogen or could cause an alteration of the state of the catalyst during pretreatment,
or both, (that is, sintering or metal occlusion). These materials must be identified by the user and experimented with to determine
the most significant conditions of measurement.
4.3 This test method provides a measure of the total hydrogen uptake (volume of hydrogen at STP, cm /g of catalyst) without
specifying the nature of the hydrogen-platinum interaction. Persons interested in using hydrogen uptake data to calculate percent
platinum dispersion in a specific catalyst should be aware of carrier (support) interactions, spillover effects, and other phenomena
related to the hydrogen uptake capabilities of the catalyst in question.
5. Apparatus
5.1 Gas-Handling System, System—as A suitable instrument configuration is shown in Fig. 1. The components may be either glass
D3908 − 20
FIG. 2 Suitable Sample Cell
or metal. Commercial metal instruments are available. The following components are to be included in the glass system:
−5
5.1.1 Vacuum System, capable of attaining pressures below 1 mPa (1 × 10 torr). The vacuum can be monitored with any suitable
vacuum gauge. A diffusion pump backed by a mechanical pump mustshould be isolated from the system by a trap held at liquid
nitrogen temperature. High-vacuum stopcocks using a low-vapor pressure grease can be employed.
5.1.2 Pressure-Measuring Device, that operates at constant volume and that is capable of reading in the range from 0 to 66.7 kPa
(0 to 500 torr) to the nearest 0.01 kPa (0.1 torr).
5.1.3 Calibration Bulb, whose volume has been carefully determined to within 0.1 % prior to attachment to the main manifold.
Typically one fills the bulb and stopcock bore with mercury, weighs it, and calculates the volume of the bulb from the density of
mercury at the temperature of the measurement. Following careful cleaning, the bulb is attached to the main manifold. One should
make sure that the glass blowing is sufficiently far removed from the calibrated volume to avoid distortion.
5.1.4 Flow-Through Cell, that can be evacuated and that can be detached from the main manifold as, manifold; for example, see
Fig. 2. This is accomplished by including a removable joint, if glass, a male cone joint, on the manifold end of the tube. (Other
types of joints, that is, Swagelok with TFE-fluorocarbon fittings, and so forth, are suitable.) Its mate is attached to the main
manifold by a glass vacuum stopcock. A stopcock is also included on the vent side of the cell to allow for vacuum and flow-through
procedures.
5.1.5 Catalyst Sample, secured by a quartz wool plug upstream of the catalyst and another quartz wool plug downstream (Fig. 2).
The sample should be in the form of an extrudate, pellets, or powder greater than 20 mesh.
D3908 − 20
5.1.6 Furnace, capable of maintaining a heating rate of 5 K ⁄min and a temperature-control mechanism capable of maintaining the
furnace at temperatures in the range from 673 to 773 6 10 K (400 to 500°C).500 °C).
5.1.7 Thermometer or Thermocouple, to monitor the furnace temperature to within 65 K and two thermometers to register the
temperature of the manifold system and sample cell during uptake determination to the nearest 60.1 K.
5.1.8 Balance, measuring to the nearest 1 mg (60.001 g).
5.1.9 Flowmeter, for hydrogen capable of measuring a flow rate of between 10 and 25 6 3 cm (STP) gas per minute.
5.2 Gas Purification Facilities , for helium and hydrogen.
6. Reagents
6.1 High-Purity Helium, Helium Gas—A cylinder of gas at least 99.999 % pure. Lower grade helium can be purified by passing
through a trap containing activated (Note 1) molecular sieve of the A type or 13X type, maintained at liquid nitrogen temperature.
NOTE 1—Activation as suggested by manufacturer.
6.2 High-Purity Hydrogen, Hydrogen Gas—A cylinder of gas at least 99.999 % pure. Lower grade hydrogen can be purified by
passing first through an oxygen removal catalyst or palladium thimble and then through a trap containing activated molecular sieve
of the A type or 13X type maintained at liquid nitrogen temperature.
6.3 High-Purity Cylinder Air, purified by passing through a trap containing activated molecular sieve of the A series.
7. Safety Hazards
7.1 Follow the usual precautions associated with handling hydrogen gas. Keep any gas cylinders separated from any oxidizing
reagents. Adequately vent the hydrogen flow at the roughing pump discharge and vent the sample (stopcock 3). A flash arresting
check valve and pressure relief valves or safety manometers should be incorporated into the design of the apparatus.
7.2 Adequately tape or otherwise shield glass reservoirs to avoid unrestricted explosion in the event of an over-fill and to avoid
flying glass in the event of an implosion during evacuation.
7.3 Eye protection is essential when operating the vacuum system.
7.4 Avoid accidental formation of mixtures of hydrogen and air at all times.
8. Volume Calibrations
8.1 The reliability of any gas adsorption measurement is naturally dependent on the accuracy with which the system volume is
known. It is therefore essential that the manifold volume be frequently determined very car
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