Realization of rapid synthesis of H-ZSM-5 zeolite by seed-assisted method for aromatization reactions of methanol or methane

H-ZSM-5 zeolites are successfully synthesized within 1 h with an organic template free system by the seed-assisted method. The synthetic method not only reduces the production cost of H-ZSM-5 zeolite, but also decreases the environmental pollution produced compared with that of the conventional synthesis process. Characterization by SEM, XRD, [N.sub.2] adsorption-desorption, N[H.sub.3]-TPD, and Py-IR confirms that the H-ZSM-5 product has a high crystallinity and reveals that the rapid synthesis process is in accordance with the seed surface crystallization mechanism. To improve the aromatic selectivity on the H-ZSM-5 zeolite, different concentrations of Mo and Zn catalysts were prepared by incipient wetness impregnation and the ion-exchange method. Mo-Zn/H-ZSM-5-SAS-1 h have similar catalytic lifetimes and higher selectivity of paraxylene in aromatic products compared with Mo-Zn/H-ZSM-5-seed in the reaction of methanol to aromatic. However, the catalytic lifetime of 6%Mo/H-ZSM-5-SAS-1 h is shorter than that of the 6%Mo/H-ZSM-5-seed catalyst in methane to benzene reaction under the same reaction conditions. Key words: rapid synthesis, H-ZSM-5, organic template free, seed-assisted, aromatization. Nous avons reussi a synthetiser des zeolithes H-ZSM-5 en 1 h dans un systeme sans agent structurant organique par la methode assistee par ensemencement. La methode de synthese que nous avons employee permet non seulement de reduire le cout de production de la zeolithe HZSM5, mais egalement de prevenir la pollution environnementale comparativement au procede de synthese classique. La caracterisation par microscopie electronique a balayage (MEB), diffraction des rayons X (DRX), adsorption-desorption de [N.sub.2], desorption thermoprogrammee d'ammoniac (N[H.sub.3]DTP) et pyrolyse couplee a la spectroscopie infrarouge (PylR) revele que le processus de synthese rapide est en accord avec le mecanisme de cristallisation par ensemencement de la surface. Afin d'ameliorer la selectivite aromatique de la zeolithe HZSM5, nous avons prepare des catalyseurs a differentes concentrations de Mo et de Zn par impregnation a humidite naissante et echange d'ions. Le catalyseur Mo-Zn/HZSM5SAS1 h a une duree de vie catalytique similaire et une selectivite parmi les produits aromatiques plus elevee pour le paraxylene que le catalyseur MoZn/HZSM5seed dans la reaction d'aromatisation du methanol. Cependant, la duree de vie catalytique du catalyseur 6%Mo/HZSM5SAS1 h est plus courte que celle du catalyseur 6%Mo/HZSM5seed dans la reaction d'aromatisation du methane en benzene dans les memes conditions de reaction. [Traduit par la Redaction] Mots-cles: synthese rapide, H-ZSM-5, sans agent structurant organique, assistee par ensemencement, aromatization.
1. Introduction Aromatic hydrocarbons are important chemical intermediates in the fine chemical industry and have huge industrial demand. (1) In recent decades, the methanol to aromatics (MTA) and methane to [...]