Catalytic ring opening of decalin on Ir- and Pt-containing zeolite Y – Influence of the nature of the charge-compensating alkali cations

The catalytic hydroconversion of cis-decalin was studied at a hydrogen pressure of 5.2 MPa and temperatures ranging from 240 to 380 °C in a continuously operated fixed-bed reactor. Two series of catalysts were used based on zeolite Y in which the alkali cations from lithium to cesium were introduced by ion exchange. One catalyst series contained 3 wt.% of iridium, the other the same amount of platinum. Both metals were introduced by ion exchange. Upon the reduction of the metals with hydrogen, Brønsted acid sites were formed, the strength of which decreased from the lithium to the cesium forms of zeolite Y, according to the Sanderson electronegativity concept.By far the fastest reaction was the stereoisomerization of cis- to trans-decalin. Other reactions of decalin were skeletal isomerization, ring opening to C10 hydrocarbons with one remaining naphthenic ring, double ring opening to open-chain decanes and degradation of the carbon number to C9- hydrocarbons. Spiro[4.5]decane was found to be a primary product of decalin isomerization, both via a bifunctional pathway and on platinum. Ring opening on the catalysts used in this study seems to occur mainly on the respective metal. On Ir/Na,H-Y and Pt/Na,H-Y yields of open-chain decanes close to 40% could be achieved. On the iridium-containing catalysts the C9- hydrocarbons followed a hitherto unknown carbon number distribution with relatively large amounts of C1 + C9 and C2 + C8, for which the term “hammock-type curve” was coined.

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► We studied the ring opening of decalin on bifunctional Y zeolites at pH2 = 5.2 MPa.
► The nature of the alkali cation influenced the strength of the Brønsted acid sites.
► Ring opening appeared to occur mainly via hydrogenolysis on iridium or platinum.
► Yields of open-chain decanes (OCDs) close to 40% can be achieved.
► OCDs formed on platinum instead of iridium tend to be less strongly branched.