IDENTIFICATION OF THE VOLATILE PRODUCTS RESULTING FROM THE THERMAL-DECOMPOSITION OF TETRA-PROPYLAMMONIUM, TRI-PROPYLAMMONIUM, DI-PROPYLAMMONIUM, AND MONO-N-PROPYLAMMONIUM CATIONS OCCLUDED IN MFI-TYPE ZEOLITES

The volatile thermal decomposition products of Pr4N+, Pr3NH+, Pr2NH2+, and PrNH3+ (Pr = n-propyl), occurring as templates in MFI-type zeolites prepared in various media (presence of F- or OH- anions and T(III) substituents for Si), were analyzed by using differential thermal analysis (d.t.a.)-coupled mass spectrometry. In a second type of experiment, the products released during the d.t.a. were separated in a preliminary stage, using gas chromatography. The data from these combined techniques prompted a main decomposition scheme involving a Hofmann elimination, followed by beta-eliminations. In addition to propene and its oligomers, a variety of other molecules are evolved. Their nature and proportions depend on the type of PrxNHy+ template, on the kind of anion (OH- or F-) accompanying the organic cation in the ion pairs, and on the acidity of the zeolite, which is related to the substitution of Si by a T(III) element. The thermal decomposition products of a common template Pr4N+ were compared when T = Al, B, Fe, and Ga. A marked difference was observed when the in situ conversion of propene to aromatic or aliphatic hydrocarbons takes place. The extent of the catalytic side reactions in the thermal decomposition increases in the following sequence: mono- < di- < tri- < tetrapropylammonium.