Catalytic hydrogenation using zeolites

The paper deals with some new data concerning the state of the metal after reduction and the catalytic functions of zeolite catalysts containing nickel and platinum. By using the molecular sieve selectivity in the hydrogenation of mesitylene it has been proved that metal (platinum) is contained in the volume of the zeolite crystal. The temperature dependence of the formation of nickel crystals was investigated. The aluminosilicate structure and the zeolite composition influence mainly the formation of the metal surface which determines the catalytic activity. In the hydrocracking of cumene and disproportionation of toluene a bifunctional action of catalysts has been established. Hydrogen retarded the reaction. 

The catalytic addition of H2S to olefins follows the Markovnikov rule, with the -SH moeity attaching itself to the carbon atom connected to the least number of hydrogen atoms. With linear olefins, having terminal or internal double bonds, acid catalysis using zeolites, cation-exchange resins, and silica-alumina yields secondary mercaptans. The preferred route for secondary mercaptans is the H2S addition to olefinic compounds. 

The concept of zeolite membrane encapsulated catalyst (ZMEC) is an original way to use zeolite membranes in catalytic reactors [158,159]. The concept of coating catalyst particles with a selective zeolite layer can reveal useful for either increasing reactant selectivity (e.g. selective hydrogenation of linear molecules) or product selectivity (e.g. animation of methanol). It also protects the catalyst from poisoning. 

Table 8 shows the recent results from our laboratory [Lai and Song, 1996]. The catalytic reactions were mainly conducted at 200-250 °C for 0.15-8 h under an initial pressure of 0.79 h a N2 or H2 using six catalysts a hydrogen Y zeolite, a lanthanum ion-exchanged Y zeolite, a hydrogen mordenite, and three noble metal loaded mordenites. Selected results are given in Table 7. Pt- and Pd-loaded mordenites displayed the highest selectivity towards /rani-DeHN (nearly 100%), with a Zrani-DeHN/cw-DeHN ratio of about 13 under H2 at 2(X)°C however, they are less effective under N2. Pre-reduction of Pt/HM30A could improve its catalytic effectiveness in N2 atmosphere.

The continuous flow technique was used to measure the catalytic activity of zeolites in the reaction between methanol or ethanol and hydrogen sulphide (see ref.2). The catalysts were activated in helium at 674K for 4 hours. The reaction was carried out at 523K by using a reagent mixture containing... 

Bernardo P, Algieri C, Barbieri G, Drioli E. Hydrogen purification from carbon monoxide by means of selective oxidation using zeolite catalytic membranes. Sep Purif Technol 2009 62 629-635. 

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