The catalytic activity of alumina-supported platinum catalysts modified with rare earth metal (samarium, europium, gadolinium, ytterbium, yttrium) complexes in C 6 hydrocarbon reforming was studied.Production of aromatic hydrocarbons, in particular, benzene, which is a raw material for chemical industry, is an important direction of the catalytic reforming, since the production of polyamide, polyester, and other fibers and, in addition, some types of plastics and specialty rubbers is based on conversion of benzene and its nearest homologs.Alumina-supported platinum catalysts, which were for many years the main catalysts of hydrocarbon aromatization, now give place to the catalytic systems with a low platinum content, containing other metals (iridium, rhenium, germanium, tin) as modifiers [1].Modifying additives introduced into the platinum catalyst can affect the properties of both active metal itself and a support. With regard to bifunctionality of the alumina-supported platinum catalyst, whose platinum catalyzes hydrogenation and dehydrogenation, while alumina catalyzes paraffin isomerization and hydrocracking, we took rare-earth metals (REMs) differing in the dehydrogenation and dehydrocyclization power as modifying additives [2]. It was interesting to find how the initial REM compound affects the catalyst activity.
EXPERIMENTALThe catalyst properties were studied with a flowtype laboratory device within 440 3540oC in a hydrogen atmosphere. n-Hexane was used as a feed in reforming.To study the influence of REMs on the aluminasupported platinum catalyst and to develop a highperformance catalyst with a low platinum content, a series of catalysts containing 0.25 wt % platinum and 0.13 0.4 wt % samarium, europium, gadolinium, ytterbium, or yttrium were considered. The activity of the catalysts was evaluated by the content of benzene (aromatization) and C 1 3C 5 hydrocarbons (hydrocracking) in the catalyzate. We found that the catalytic activity of the modified catalysts decreases in the order Gd > Y > Eu > Sm > Yb (Table 1).The catalysts that were more active in aromatization also showed the elevated selectivity. Taking this into account, we studied the properties of the gadolinium-containing catalyst in the n-hexane conversion in more detail and found that, in the presence of the catalyst with gadolinium additives (0.13 0.4 wt %), the yield of benzene is higher than in the case of the REM3free alumina-supported platinum catalyst (Figs. 1, 2). Although the Gd-modified alumina-supported platinum catalyst is characterized by the elevated activity in hydrocracking, the ratio of the benzene concentration to the total concentration of C 1 3C 5 hydrocarbons [C 6 H 6 ]/S (C 1 3C 5 ) on the gadoliniummodified alumina-supported platinum catalyst is also higher than on the unmodified alumina-supported platinum catalyst, which indicates higher selectivity of the former in the aromatization. Table 1. Influence of REMs on catalytic properties of the alumina-supported platinum catalyst at 500oC ÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ...
