Gf Froment

Selective conversion of decane into branched isomers: A comparison of platinum/ZSM-22, platinum/ZSM-5 and platinum/USY zeolite catalysts

Abstract Detailed product distributions from the bifunctional conversion of decane over Pt/ZSM-22, Pt/ZSM-5 and Pt/USY catalysts are compared. In contrast to other zeolites, the product selectivities from decane on Pt/ZSM-22 vary largely with the reaction conditions. Pt/ZSM-22 produces high yields of feed isomers under mild reaction conditions. Molecular graphics suggest that the isomerisation of decane cannot occur entirely inside the micropores of ZSM-22 crystals. It is suggested that isomerisation of decane on ZSM-22 is an example of zeolite pore-mouth catalysis. Type C hydrocracking of methylnonanes (involving β-scission of secondary into secondary alkylcarbenium ions) does not occur on Pt/ZSM-22, due to the limited access of these molecules in the zeolite pores. Hydrogenolysis on the platinum metal and type D hydrocracking of decane (involving β-scission of secondary into primary alkylcarbenium ions) account for the formation of cracked products.

Synergism of ZSM-22 and Y zeolites in the bifunctional conversion of n-alkanes

Abstract Intimate mixtures of bifunctional catalysts based on ZSM-22 and Y zeolites do not show merely the intermediate catalytic properties between those found for the individual zeolites. Such mixtures produce enhanced yields of multibranched isodecanes from n-decane. A mechanistic explanation for this synergetic effect is given. New experimental evidence is provided for the occurrence of free gas-phase olefinic intermediates in bifunctional catalysis with zeolites.

Selective key-lock catalysis in dimethylbranching of alkanes on ton type zeolites

The Pt/H-ZSM-22 catalyst exhibits peculiar dimethylbranching selectivities in the skeletal isomerization of C 8 -C 11 n-alkanes. Out of the large number of theoretically possible dibranched skeletal isomerization products, a few dimethylbranched isomers having methylbranchings at specific carbon atom positions are formed selectively. The observed selectivity is rationalized with stereospecific catalysis at the [001] crystallographic planes at the external crystal surface. Computer generated molecular models show that only the preferred dimethylbranched isomers can maximize their van der Waals interaction with specific sites on the zeolite external surface. Since these adsorption sites bridge two (or more) adjacent pore mouths, the ensemble allows the adsorption of only preferred isomers in a key-lock type of interaction.

ISOMERIZATION OF LONG-CHAIN N-ALKANES ON PT/H-ZSM-22 AND PT/H-Y ZEOLITE CATALYSTS AND ON THEIR INTIMATE MIXTURES.

Abstract Octane, decane and undecane are converted over bifunctional Pt/H-Y and Pt/H-ZSM-22 zeolites and on intimate 50–50 and 80–20 wt/wt mixtures of these zeolites. Compared to the individual zeolites, the zeolite mixtures exhibit an enhanced catalytic activity, and produce higher yields of feed isomers. The dependence of the synergetic effects on the chain length of the feed and on the relative catalytic activities of the two zeolites is discussed.