ASTM D4824-24

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: D4824 − 13 (Reapproved 2018) D4824 − 24
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) 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 property 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 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.
2. Referenced Documents
2.1 ASTM Standards:
D3766 Terminology Relating to Catalysts and Catalysis
E105 Guide for Probability Sampling of Materials
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
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 Nov. 1, 2018Feb. 1, 2024. Published December 2018February 2024. Originally approved in 1988. Last previous edition approved in 20132018
as D4824 – 13. DOI: 10.1520/D4824-13R18.– 13 (2018). DOI: 10.1520/D4824-24.
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
D4824 − 24
3. Terminology
3.1 Definitions—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 = mass of sample, g.
s
W = tare of sample tube, g.
W = sample mass plus tare of tube, g.
P = initial ammonia pressure corrected to standard temperature, torr.
1T
P = final ammonia pressure corrected to standard temperature, torr.
2T
4. Summary of Test Method
4.1 A sample is degassed by heating in a under 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 A schematic 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
FIG. 1 Apparatus
D4824 − 24
NOTE 1—An expansion vessel of smaller volume is recommended for materials of low surface area or smaller sample size.
−1
6.1.3 Pressure Sensing Device or Pressure Transducer, capable of measuring 0 to 250 torr to the nearest 10 torr (10 Pa).
−3
6.1.4 Pressure Sensing Device or Pressure Transducer, capable of measuring 0 to 1000 torr to the nearest 10 torr (0.1 Pa).
6.1.5 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, for measuring the temperature of the expansion volume, V . Alternatively, the expansion
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 each sample tube.
6.1.10 Balance, with 0.1-mg sensitivity.
6.1.11 Thermometer or Thermocouple, for measuring the temperature 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
...