Catalytic Hydrogenation with Amorphous and Crystalline Pd 80 Si 20
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CATALYTIC HYDROGENATION WITH AMORPHOUS AND CRYSTALLINE Pd 8 0Si 2 0 BILL C. GIESSEN, SABRI S. MAHMOUD, DAVID A. FORSYTH AND MARKUS HEDIGER Materials Science Division, Institute of Chemical Analysis* and Department of Chemistry, Northeastern University, Boston, Massachusetts 02115, U.S.A. ABSTRACT Several metallic glasses in the form of ribbons were screened for activity as hydrogenation catalysts. Pd 8 0Si 20 and (NisoFe5 o)gOB2o showed activity in reducing cyclohexene. Pd 8 0 Si 2 0 was further examined for differences between the glassy and crystalline phases in the selectivity shown during hydrogenation reactions of n-hexenes, phenylethyne, c-pinene, and cyclododecene. No significant differences were found for catalytic selectivity in regard to cis-trans isomerization, double bond migration, and stereochemistry of addition under the reaction conditions used. Minor differences were observed in hydrogen-deuterium exchange. INTRODUCTION We report here on the behavior of amorphous and crystalline Pd 8 0Si 2 0 in the catalysis of hydrogenation reactions studied as part of an ongoing research program to explore the catalytic properties of amorphous metals. In particular, we seek to discover whether amorphous metal alloys differ in their catalytic properties from the corresponding crystalline alloys. This initial study uses hydrogenation of alkenes and alkynes as a probe of catalytic behavior because the variety of competing reactions affords the opportunity to observe selectivity differences between catalysts. Selectivity differences can manifest themselves through differences in cis-trans isomerization, double bond migration, hydrogen-deuterium exchange, or stereochemistry of product formation. Such selectivity differences could be of considerable practical value in organic synthesis. There are as yet only very few studies of the catalytic properties of glassy metals reported in the literature; [1,2] some of the reported work deals with Fischer Tropsch gas phase reactions and some also refers to hydrogeneation of unsaturated hydrocarbons. Specifically, we report here on preliminary screening of metallic glasses for catalytic activity and review results on hexenes, phenylethyne, pinene, and cyclododecene obtained with a Pd-Si alloy catalyst. RESULTS AND DISCUSSION Five alloys, as both the glassy and crystalline phases, were surveyed for activity in catalyzing the hydrogenation of cyclohexene. The alloys were Pd 8 0Si 2 0 , (Nis0Fes0)g0B 2 0, Ni6 0 Zr 4 0 , Cuz 0Zr 6 0 , and (Fe 5 oNis5) 6 0(C5 0Ps0)20. The amorphous alloys were in the form of ribbons prepared by melt-spinning [3]. Crystalline ribbons were produced by heating the amorphous ribbons in quartz tubes under vacuum. Reaction conditions were 0.30 g alloy and 2.0 mL cyclo0 hexene in 10 mL 1,4-dioxane at 50 C under 1.3 atm H2 pressure for 24 hours. *Communication No. 116 from the Institute of Chemical Analysis.
256 Hydrogenation was observed only with Pde 0 Si 2 0 and (Ni 5 OFe 5 o) 8 0B2 0 . The activity (extent of cyclohexene reduction) was similar for
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