Kinetic insights into structure sensitivity of Ru catalyzed l-alanine hydrogenation to alaninol†

Abstract

Hydrogenation achieved on supported metal catalysts is normally structure sensitive, and comprehensive understanding of such sensitivity is pivotal for gaining insights into the active sites as well as the design of catalysts. Herein, a series of differently sized Ru nanoparticles supported on carbon nanotube (CNT) were prepared and employed as catalysts for L-alanine hydrogenation to examine the structure sensitivity of amino acid hydrogenation. The reaction rates for L-alanine conversion and the formation of alaninol are demonstrated to be strongly dependent on the sizes of Ru nanoparticles, highlighting the structure sensitivity of the L-alanine hydrogenation. The activation energies extracted from kinetic studies are insensitive to the sizes of Ru nanoparticles on the Ru catalysts sized ≥1.3 nm with similar electronic properties, pointing to a predominant type of active site for L-alanine hydrogenation. By further combining model calculations with the shape of Ru nanoparticles determined by transmission electron microscopy, the Ru(101) sites are identified as the dominant active sites for L-alanine conversion and alaninol formation, which is further rationalized by density functional theory calculations. The kinetic insights into such structure sensitivity are believed to be important for the design and optimization of catalysts for the reaction.