Search

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 [...]

The ZnIn/HZSM-5 catalyst was prepared by the wetness impregnation method, and the structure of catalyst was characterized by XRD, SEM, TEM, [H.sub.2]-TPR, N[H.sub.3]-TPD, XPS, TG, and [N.sub.2] adsorption-desorption and then investigated in the coupling of propane with C[O.sub.2] to propylene. It is found that the addition of Zn species is beneficial to the dispersion of [In.sub.2][O.sub.3] over HZSM-5, which plays an important role in propene formation, and adjusts the acidity distribution of In/HZSM-5 catalyst, aswell assignificantly improves the activity of In/HZSM-5 catalyst. The selectivity of propylene is 68.21% in the coupling of propane with C[O.sub.2] over ZnIn/HZSM-5 catalyst when the time on stream (TOS) is 2 h, reaction temperature is 580 [degrees]C, reaction pressure is 0.3 MPa, [C.sub.3][H.sub.6]:C[O.sub.2]:[N.sub.2] = 1:4:5, catalyst mass is 0.2 g, and space velocity is 6000 mL [g.sub.cat.sup.-1] [h.sup.-1]. However, the selectivity of propylene is only 63.33% and 0.25% in the propane dehydrogenation or C[O.sub.2] hydrogenation reaction, respectively. The ZnIn/HZSM-5 catalyst showed a higher stability with only 0.80% conversion drop after three cycles. Key words: ZnIn/HZSM-5, coupling reaction, propane, C[O.sub.2], propylene. Nous avons prepare le catalyseur ZnIn/HZSM5 par la methode d'impregnation a l'humidite naissante, et nous en avons caracterise la structure par diffraction des rayons X (DRX), microscopie electronique a balayage (MEB), microscopie electronique en transmission (MET), reduction en temperature programmee sous hydrogene ([H.sub.2]TPR), desorption thermo-programmee de l'ammoniac (N[H.sub.3]TPD), spectroscopie de photoelectrons X (XPS), thermogravimetrie (TG) et analyse d'adsorption-desorption d'azote. Nous avons ensuite etudie ce catalyseur dans la reaction de couplage du propane avec le C[O.sub.2] pour former le propylene. Nous avons observe que l'ajout d'especes de Zn favorise d'une part la dispersion de l'In2O3 dans la zeolithe HZSM5--un facteur important dans la formation du propene--et d'autre part la distribution de l'acidite dans le catalyseur In/HZSM5, ce qui ameliore de facon significative de l'activite catalytique de ce dernier. Le couplage du propane avec le C[O.sub.2] sur le catalyseur ZnIn/HZSM5 offre une selectivite pour le propylene de 68,21% lorsque le temps de reaction est de 2 h, la temperature de reaction de 580 [degrees]C, la pression de reaction de 0,3 MPa, le rapport des reactifs [C.sub.3][H.sub.6]:C[O.sub.2]:[N.sub.2] de 1:4:5, le poids du catalyseur de 0,2 g et la vitesse spatiale de 6000 mL [g.sub.cat-1] [h.sup.-1]. Toutefois, la selectivite pour le propylene n'est que de 63,33% pour la reaction de deshydrogenation du propane et de 0,25% pour la reaction d'hydrogenation du C[O.sub.2]. Le catalyseur ZnIn/HZSM5 a montre une stabilite superieure, la baisse de conversion etant de seulement 0,80% apres trois cycles. [Traduit par la Redaction] Mots-cles: ZnIn/HZSM-5, reaction de couplage, propane, C[O.sub.2], propylene., 1. Introduction Emissions of carbon dioxide have continuously increased over the past few decades, mainly from the combustion of natural gas, coal, and petroleum. (1) The increased concentration of C[O.sub.2] [...]

Copyright of Canadian Journal of Chemistry is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)