Organic zeolite interpretation

Although TEM-HREM is a more useful technique as can reveal a picture of the atoms in the materials, however this picture is difficult to interpret. On the other hand, radiation damage from the electron beam is an issue (in HREM observations), as long periods of TEM observation (> 1 min) usually can alter/damage seriously the stmcture of many industrial applications materials like organic chemical compounds, zeolites, polymers, etc. 

The conversion of simple organic molecules (e.g. methanol, ethanol or ethylene) can also be monitored by the use of combined TG-DTA. For instance such an analysis, applied to ethylene conversion on the acid form of ZSM-5, enabled the transformation to be interpreted in terms of five different reaction steps [25]. Another example of thermal analysis application to the study of the development of a catalyzed reaction is the use of isothermal TG for investigating the kinetics of coke deposition in inner or external zeolitic sites and its subsequent removal by oxidation in air [25]. 

Another important parameter is the Si/Al ratio ( number of Si atoms over the number of A1 atoms). The magnitude of this ratio may vary in natural zeolites from 1 to 5. However by chemical processes ( alumination or dealumination ) or by synthetic means it is possible to obtain samples covering a much wider range of Si/Al ratios for a given zeolite. The Si/Al ratio can affect many properties tike thermal stability, acidity , etc. in ways which are as yet not clearly understood. To a large extent present interpretations rest mainly on the distribution of the AIO 4 tetrahedra inside the zeolite, which presumably are so organized as to rranain compatible wifri Loewenstein s rule. 

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