(77d) Promotion of Platinum for Alkane Dehydrogenation: Intermetallic Alloys with Two Catalytically Active Metals

Metal nano-particle alkane dehydrogenation catalysts utilize Pt and are generally promoted by Sn, Zn, Ga or In. While Pt bimetallic nano-particles are highly selective, their exact structure is not generally known, especially in very small nano-particles. Recently, it was shown that intermetallic alloys were are present on PtIn dehydrogenation catalysts and other bimetallic compositions. The increased olefin selectivity was suggested to be due to isolation of the active Pt atoms by inactive promoter atoms. Changes in the turnover rate (TOR) and activation energy also suggested electronic effects.

Several intermetallic alloy structures can also be formed with Pt and a second catalytically active atom. In this study we show that two catalytic metals can be selective for alkane dehydrogenation. The intermetallic structure is dependent on the metal loading. The catalytic performance suggests that the Pt atoms dominate the alkane conversion. At high promoter loading, excess monometallic promoter forms, which has low selectivity and deactivates rapidly. The catalysts have been characterized by in situ synchrotron X-ray absorption and X-ray diffraction to identify the nano-structures formed with different compositions.