ISSN:
1572-879X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract A study has been made of ZSM5 zeolite deacidification (dealumination) by high temperature treatment in SiCl4 vapour, monitoring total acidity by Na+-exchange, and external surface acidity by methylene blue adsorption (exchange), with comparative measurements of theN Si/NAl ratio (nominally external surface) by XPS. Using H-ZSM5, the highest specificity for external surface deacidification was found at the lowest usable values of treatment temperature, time andp Sicl4. Using Na-ZSM5 in place of H-ZSM5 did not offer a useful improvement. A steaming/HCl-leaching method was shown not to be suitable for selective external surface deacidification. Values ofN Si/NAl by XPS were dependent on the method of sample preparation, with mechanical stress (pelleting, pressing) tending to give abnormally low values due to crystal or aggregate fracture: this effect became more serious with increasing severity of SiCl4 treatment. Even after correcting for XPS emission from subsurface layers, agreement between surfaceN Si/NAl values from XPS and acidity measurements was poor for samples with a low degree of bulk deacidification (mild SiCl4 treatments), and is ascribed to non-acidic surface Al.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00770225
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