Adsorption-Catalytic Properties of Ag-modified ZSM-23

摘要

In the present research, the adsorption-desorption properties of the ZSM-23 zeolite (SiO_2/Al_2O_3 ratio of 100) with respect to toluene used as a model adsorbate were examined. Both the pristine and Ag-modified samples were studied using specially designed installation and technique allowing quantitative determination of the weakly and strongly bounded toluene species, which desorb within the ranges of 100-200 and 200-400 °C, respectively. Thermal stability of the samples along with the catalytic activity in oxidation of CO and hydrocarbons was investigated in a prompt thermal aging regime. It was found that toluene adsorbs predominantly on the outer surface of the zeolite, and the contribution of its inner porous structure into the adsorption process is negligible. Modification of the zeolite with silver was shown to improve the adsorption properties noticeably. Thus, the amount of strongly bounded toluene is increased by 1.8 times. At the same time, introduction of silver has a drawback connected with destruction of the zeolite structure. Moreover, after the prompt thermal aging the silver particles were mainly found to be agglomerated and coated by silica released from the zeolite lattice. Additionally, the part of silver species was found on alumina used a binder, thus testifying towards silver migration from one oxide support to another.