Zeolites are groups of compounds which produce water when they are heated. They have a three-dimensional crystalline structure which contains oxygen, aluminium and silicon. Zeolites are commonly used to purify water and extra nitrogen from air hence increasing the amount of oxygen content there is in the atmosphere
Zeolites contain small pores or cavities in its structure which enable them to act as good host molecules. This allows it to exchange cations such as Na+, K+, Ca2+ in its pores. This unique property allows many applications of Zeolites some of which are; removing ammonium ions from waste streams, treatment of sewages, controlling bad odour, use as catalysts and use in agriculture.
There are channels within the molecule which screen molecules which are of a certain size. Any molecule which is too large to pass through the channel at the given parameters are excluded, hence this forms a 'molecular sieve'.
Aim: The aim of this experiment was to analyse and indentify the structures of Zeolites using Xray powder diffraction [2]
Experimental
The x-ray powder diffraction pattern for Zeolites X and Y were collected using the same procedure.
Sample preparation
The Zeolite sample was crushed to powder in a pestal and mortar. The resulting mixture was then sieved to make sure the powder was of regular grain size. The sample holder was cleaned and dried using water followed by methanol. The powdered zeolite was poured into the sample holder (covering the indentation). A microscope slide was drawn across the surface of the powder so that it formed a smooth surface.
Data collection
The sample holder was placed in the sample changer of the Brucka D8 diffractometer and then locked into place (push and then hold). The door is then closed. The PC is used to control the diffractometer. The XRD wizard is opened on the computer and this sets the parameters for data. The range was set between 5-40 (this is normal).The step size = 0.04 (the smaller the step size the more accurate the data).Time per step = 2 seconds. This showed it is going to take 29 minutes to complete the cycle. The file was then saved and closed.
Now the XRD commander was opened and then Clicked on 'jobs' > 'create jobs'. The Zeolite X was placed in position 1. And Zeolite Y was placed in position 2. The parameter file was opened again and a raw file was generated (this must be called the same name as the sample ID). The instrument was started and began to collect data.
Data Analysis
Even though the sample was powder it is still a crystalline sample as it has order to it, it is not amorphous. The powder pattern gave peaks. Once the data had been collected the data evaluation programme EVA was used to process the data. The peak list was obtained and imported to Excel. Plots of the two experimental patterns were also obtained.
Results & discussion
2-Theta °
Theta °
Theta 2
Sin2 Theta °
Ratio
Common Multiplier
Miller Index
a
6.276
3.138
0.002999581
0.002999577
1
3
1
1
1
24.37971879
10.122
5.061
0.007802386
0.007802306
2.601135887
8
2
2
0
24.37971879
11.89
5.945
0.010766101
0.010765893
3.589137536
11
3
1
1
24.37971879
13.555
6.7775
0.013992451
0.013991994
4.664656341
14
3
2
1
24.37971879
15.599
7.7995
0.018530548
0.018529487
6.177367552
19
3
3
1
24.37971879
18.568
9.284
0.026255784
0.026252768
8.752157757
26
5
1
0
24.37971879
20.245
10.1225
0.031212626
0.031207558
10.40398756
31
4
3
2
24.37971879
22.664
11.332
0.03911721
0.039107234
13.03758469
39
6
1
1
24.37971879
23.521
11.7605
0.04213144
0.042118977
14.04164066
42
5
4
1
24.37971879
26.863
13.4315
0.054954564
0.054926908
18.31155343
55
6
4
2
24.37971879
29.426
14.713
0.065941255
0.065893477
21.96759232
66
8
1
1
24.37971879
30.49
15.245
0.070796142
0.070737017
23.58233378
71
8
2
2
24.37971879
31.148
15.574
0.073884796
0.073817592
24.60933672
74
7
5
0
24.37971879
32.201
16.1005
0.078964786
0.078882748
26.29796054
79
8
3
2
24.37971879
33.823
16.9115
0.082653663
0.082559585
27.52374578
83
9
1
1
24.37971879
Zeolite X
2-Theta °
Theta °
Theta2
Sin2 Theta °
Ratio
Common Ratio
Miller Index
a
6.209
3.1045
0.002935878
0.002935874
1
3
1
1
1
24.64279438
10.155
5.0775
0.007853344
0.007853263
2.674931688
8
2
2
0
24.64279438
11.874
5.937
0.010737145
0.010736939
3.657152317
11
3
1
1
24.64279438
15.642
7.821
0.018632851
0.018631773
6.34624358
19
3
3
1
24.64279438
18.706
9.353
0.026647508
0.026644355
9.075441569
27
5
1
1
24.64279438
20.375
10.1875
0.031614767
0.0316095
10.76663997
32
5
2
2
24.64279438
22.786
11.393
0.039539478
0.039529176
13.46419286
40
6
2
0
24.64279438
23.643
11.8215
0.042569633
0.042556777
14.49543628
43
5
3
3
24.64279438
25.015
12.5075
0.047653605
0.047635571
16.22534483
49
7
0
0
24.64279438
25.769
12.8845
0.050569642
0.050548091
17.21738999
52
6
4
0
24.64279438
27.062
13.531
0.055771782
0.055742874
18.98680611
57
7
2
2
24.64279438
27.78
13.89
0.058770478
0.058736652
20.00652917
59
7
3
1
24.43258711
29.624
14.812
0.066831644
0.066781904
22.74685506
68
8
2
0
24.64279438
30.72
15.36
0.071868266
0.071806415
24.45827388
73
8
3
0
24.64279438
31.412
15.706
0.075142549
0.075071854
25.57052852
77
8
3
2
24.64279438
Zeolite Y
Looking at the data generated, the structure of Zeolites X and Y are both Faujasites (FAU). This can be confirmed by comparing the experimental cell dimensions for zeolite X and zeolite Y which are 24.379 and 24.643 Amstrongs respectively, with the literature value of 24.3 [3]
Faujasites contain large cavities which are perpendicular to one another. The cavities contain cages which are connected through hexagonal prisms. Faujasites are used for catalytic cracking which are convert petroleum crude fractions (with high boiling points) to more valuable products such as gasoline and diesel.
Because there is no 7 present as a value in the common multiplier column, this verifies that both Zeolites X and Y are face centred molecules.
Conclusion
In order for the structure of the unknown compounds to be determined accurately, the unit cell dimensions must also be determined accurately and hence finely ground powder must be used.
In this experiment we have established that the values calculated signify that both molecules are face centred and are both Faujasites. However the experimental values differ slightly from the literature values and this can be because of a number of reasons. The sample may not have been ground into fine particles, it may not have been mixed thoroughly or it can also be because there are experimental errors from the machinery or other apparatus. Also there may be some reading errors which cause the results to be inaccurate. In future it is important to ensure that all apparatus is cleaned thoroughly before use and that attention to the smallest detail is paid to ensure better results are obtained.
