Butadiene–Styrene Rubber Hydrogenation over Palladium Catalysts Synthesized In Situ from Emulsion

Abstract

Unsupported palladium catalysts are synthesized by the ex-situ and in-situ reduction from emulsions of a precursor solution in cyclohexane. It is shown that the presence of the polymer—nitrile–butadiene rubber and butadiene–styrene rubber—in cyclohexane affects the morphology of catalyst particles. When synthesized in the presence of the polymer, the catalyst has a grapelike structure formed by ball-shaped agglomerates of palladium particles with a diameter of about 20 nm. Introduction of the polymer contributes to the integration and retention of palladium particles in the polymer network, hampers the agglomeration of particles, and facilitates their reduction. The catalytic properties of the obtained systems in the butadiene–styrene rubber hydrogenation are studied. The optimum catalyst concentration is 1 wt % Pd per polymer, and the optimum weight ratio palladium : nitrile–butadiene rubber in the synthesis stage is 1 : 10. It is advisable to perform the synthesis in situ. The catalytic activity persists during two cycles of use, after which regeneration is required. For comparison, the activity of the commercial palladium catalyst 2% palladium on activated carbon (PC) is estimated under the same conditions. It is demonstrated that in terms of activity the synthesized unsupported catalysts surpass PC. The thermal stability of the original and hydrogenated rubbers is studied by differential scanning calorimetry.