This standard specifies the determination of the surface area of ​​catalysts and adsorbents by the static nitrogen adsorption capacity method. This standard is applicable to catalysts and adsorbents with type II or IV adsorption isotherms and a surface area greater than 1m2/g. GB/T 5816-1995 Method for determination of surface area of ​​catalysts and adsorbents GB/T5816-1995 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Determination of surface area of ​​catalysts and adsorbents
Catalysts and adsorbents-Determination of surface area1 Subject content and scope of application
This standard specifies the determination of the surface area of ​​catalysts and adsorbents by the static nitrogen adsorption capacity method. GB/T5816--1995
Replaces GB/T5816-86
This standard applies to catalysts and adsorbents with type II or type V adsorption isotherms and a surface area greater than 1m\/g. 2 Terminology
2.1 Surface area of ​​catalyst and adsorbent: the total surface area of ​​catalyst and adsorbent, m/g. 2.2 Dead space: the void volume of the sample tube (including the sample valve) when the sample tube containing the sample is immersed in liquid nitrogen at an appropriate depth (see 6.2.5), cm.
3 Method Summary
The static nitrogen adsorption capacity method is used to measure the volume of nitrogen adsorbed by the sample at different low pressures. At least four test points that meet the BET linear relationship must be measured, and the surface area is calculated using the BET two-parameter equation. 4 Instruments
4.1 Any test device that meets the basic principle of the static nitrogen adsorption capacity method, whether it is a classic glass vacuum adsorption device or a commercial automatic adsorption instrument, can be used as a measuring instrument for this standard, but the vacuum degree is required to be better than 1.3Pa, the constant temperature control of the volumetric tube is not greater than ±0.1C, the volume measurement accuracy is 0.05cm°, and the pressure measurement range is 0~133.3kPa, accurate to 13Pa. For glass vacuum adsorption devices, a nitrogen or oxygen vapor thermometer should be used to measure the liquid nitrogen temperature and give the liquid nitrogen saturated vapor pressure. If a height gauge is used, the minimum scale is 0.02cm. Note: ltorr =-133.3 Pa
4.2 Analytical balance: The sensitivity is 0.1mg.
4.3 Oven.
5 Materials
5.1 Nitrogen: in steel cylinders, purity not less than 99.9%. 5.2 Hydrogen: in steel cylinders, purity not less than 99.9%. 5.3 Liquid nitrogen: vapor pressure not higher than the atmospheric pressure of the day, 5.3 kPa. 6 Test steps
6.1 Sample pretreatment and degassing:
6.1.1 Place a clean empty sample tube in the instrument degassing system. After vacuuming, fill with ammonia to reach normal pressure. 6.1.2 Remove the sample tube from the degassing port, add a stopper and weigh to an accuracy of 0.1 mg. This mass is recorded as m1.6.1.3 Take an appropriate amount of sample and add it to the sample tube so that the estimated total surface area of ​​the sample is preferably between 20 and 100 m2. Connect the sample tube to each degassing port. Set the heating temperature to 300°C, put on the heating jacket, and start heating and evacuating the sample. When the heating temperature reaches 300°C and the system vacuum reaches 1.3 Pa, continue degassing for at least 4 hours. Allow the sample to degas overnight. Note: \1) For some materials that may decompose or sinter after heating at 300°C, degassing at a lower temperature is allowed, but this should be noted when reporting the results. 2) If the water content in the sample exceeds 5% (m/m), in order to avoid the powder sample "boiling" and "self-water vapor treatment" loss of surface area, the heating rate should be controlled: it is recommended that the heating rate should not exceed 100)/h. 6.1.4 Remove the heating jacket, wait for the sample tube to cool to room temperature, and fill the sample tube with ammonia to reach normal pressure. 6.1.5 Remove the stripped sample tube from the stripper, add a stopper and weigh it to an accuracy of 0.1 mg. This mass is recorded as mz, and the net weight of the sample is obtained from the difference between m2 and m1.
6.2 Dead space determination:
6.2.1 Add liquid nitrogen to each sample dewar. 6.2.2 Place the sample tube containing the sample on the sample interface of the analysis system. 6.2.3 Adjust the pressure sensor.
6.2.4 Vent the sample tube to be tested to remove the hydrogen gas, so that the system pressure is lower than 1.3Pa. 6.2.5 Immerse the sample tube in the liquid nitrogen dewar, control the distance between the sample and the liquid nitrogen surface to be no less than 50mm, and keep the liquid nitrogen surface constant during the entire measurement process.
6.2.6 Fill the manifold of the analysis system with ammonia to 79.9~119.9kPa, and record this pressure and manifold temperature. Then open the valve of the sample to be tested to allow ammonia to fill the sample tube.
6.2.7 After balancing for about 5 minutes, record the equilibrium pressure and manifold temperature. According to the recorded pressure and manifold temperature and the known manifold volume, accurately calculate the dead space.
6.2.8 Evacuate and remove the ammonia in the analysis system and sample tube to make the system pressure lower than 1.3Pa. 6.3 Adsorption measurement: Www.bzxZ.net
6.3.1 Fill the system with nitrogen according to the analysis requirements, and measure more than four adsorption test points between the relative pressure P/P of 0.04 and 0.20 or 0.25. Record the corresponding equilibrium pressure P and calculate the adsorption amount Va. 6.3.2 During the adsorption measurement, if the pressure change does not exceed 13Pa within 5 minutes, it can be regarded as reaching adsorption equilibrium. 6.3.3 Measure and record the saturated vapor pressure Po of liquid nitrogen. 6.3.4 After completing the adsorption measurement, evacuate and remove the nitrogen in the system and sample tube, remove the liquid nitrogen Dewar flask, wait for the sample tube temperature to return to room temperature, and fill the sample tube with nitrogen or ammonia vapor to normal pressure. 6.4 It is recommended to use an automatic physical adsorption instrument and input the analysis information of the sample to be tested through the computer keyboard. The analysis process of 6.2.4 to 6.3.4 above is automatically completed under computer control.
7 Calculation
7.1 According to the BFT parameter equation (1):
V(P/p,) --
Where: Vm··monolayer adsorption, cm\STP/g; nitrogen adsorption, cmSTP/g;
P; P relative pressure;
saturated gas F, kPa;
. Equilibrium pressure ka
constant related to the net heat of adsorption of red gas. C-
Use P/, V7/%m, and make a BET straight line graph. The intercept 1535
V..Ci slope S of the BET straight line graph can be directly obtained by graphical method or least square method, that is,
GB/T58161995
requires that within the selected BET straight line range, the deviation of each test point from the straight line is not greater than 0.6% of the ordinate value. 7.2 The monolayer adsorption capacity Vm (cm2STP/g) is calculated according to formula (2): 1
Vm=3+1
7.3 The surface area SsEr (m2/g) of the sample is calculated according to formula (3) (the cross-sectional area of ​​nitrogen molecules is taken as 0.162nm2): SBET4.353XVm
8 Precision
The reliability of the test results (95% confidence level) shall be judged according to the following provisions. ·(2)
8.1 Repeatability: The absolute value of the difference between two test results of the same sample determined by the same laboratory shall not be greater than the value specified in the following table. 8.2 Reproducibility: The absolute value of the difference between two test results of the same sample provided by different laboratories shall not be greater than the value specified in the following table. Surface area
9 Report
Repeatability
9.1 Take the arithmetic mean of the two repeated test results as the test result, and round it to three significant figures. 9.2 The report should include sample pretreatment and degassing temperature, additional notes:
This standard is under the technical jurisdiction of the Petrochemical Research Institute. This standard was drafted by the Petrochemical Research Institute. The main drafters of this standard are Zhang Heping and Li Guoying. Reproducibility
This standard is not equivalent to the American Society for Testing and Materials standard ASTMD3663--92 "Standard Test Method for Surface Area of ​​Catalysts". 536
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