Design of Metallic Catalysts with Molecular Recognizing Function and Their Catalytic Activity for Highly Selective Challenging Reduction Reaction

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Hydrogenation of γ-butyrolactone as a model compound of esters has been studied over supported Pt-Sn bimetallic catalysts. Effect of Sn/Pt ratio was also investigated. The Pt-Sn/SiO_2, which Sn/Pt ratio was less than unity, indicated a low activity for the hydrogenation of γ-butyrolactone. The Sn/Pt ratio between 1 and 2 showed the marked enhancement of the activity by the addition of Sn to Pt/SiO_2. X-ray diffraction powder patterns of the catalysts suggested that co-existence of Pt metal and an alloy of Pt-Sn brought about the enhancement of the activity. The catalysts, which Sn/Pt ratio was less than unity, indicated only Pt crystals, whereas the catalysts which Sn/Pt ratio was higher than 2, showed only PtSn alloy phase. The higher activity was observed on the catalysts of which Sn/Pt ratio was in the range between 1 and 2. Other additives in the Pt/SiO_2 catalysts were also investigated for the hydrogenation of γ-butyrolactone. Aluminium, Ge, In, Pb and Ti were tested for the additives of Pt/SiO_2. The addition of Al, Ge, and In indicated no alloy formation with Pt on SiO_2 was observed. The addition of Pb brought about the formation of PtPb alloy on the SiO_2 support. Although Pb addition was expected to enhance the hydrogenation reaction of γ-butyrolactone, only decrease of activity was observed on Pt-Pb/SiO_2 catalysts. The addition of Al, Ge, In and Pb would only decrease the surface area of active Pt The titanium-added Pt catalysts, Pt-Ti/SiO_2 indicated enhancement of the activity. Titanium would modified the Pt surfaces and selectively activate carbonyl, group in γ-butyrolactone. The similar modification of Pt surfaces by Ti element was well known as SMSI of Pt/TiO_2