Platinum Nanoparticle Based Dip-Catalyst for Facile Hydrogenation of Quinoline, Unfunctionalized Olefins, and Imines

Developing a bio-inspired catalyst with the efficiency of homogeneous catalysts and recyclability similar to heterogeneous catalysts is quite desirable but challenging. Incorporation of metal nanoparticles (<10 nm) on abundant, low-cost supports from agricultural waste can yield highly active and product-selective pseudo-homogeneous catalysts, with attributes such as ease of retrieval for next use, reusability, etc. In this work, the fabrication of an efficient and reusable ‘dip-catalyst’ by anchoring platinum nanoparticles on white jute plant (Corchorus capsularis) stems (JPS) and its use for the hydrogenation of N-heteroarenes, unfunctionalized olefins, and imines are described. The catalyst was characterized using XRD, SEM, EDS, TEM, HRTEM, FTIR, and XPS, and TEM shows spherical (average diameter 4–5 nm) non-agglomerated metal nanoparticles. Catalyst was used for the chemoselective (>99 % selectivity) hydrogenation of quinoline with a quantitative (>99 %) conversion to 1,2,3,4-tetrahydroquinoline (py-THQ) under hydrogen at a pressure <30 bar. Also, functional group tolerance is indicated by the quantitative hydrogenation of 6-chloroquinoline to 6-chloro-1,2,3,4-tetrahydroquinoline, which is a longstanding challenge owing to C−Cl bond cleavage. In the hydrogenation of structurally-challenging trisubstituted trans-2-methyl-3-phenyl-2-propen-1-ol olefins, 64 % conversion and >99 % selectivity was achieved. A series of imines with different chain lengths was also hydrogenated selectively in methanol with >99 % conversion. Density functional theory (DFT) calculations reveal the efficient adsorption of 6-chloroquinoline on the surface of Pt nanoparticles on Pt@JPS strips in a tilted orientation placing the C−Cl bond away from the metal and allowing facile desorption of 6-chloro-1,2,3,4-tetrahydroquinoline leading to higher chemoselectivity. The spent catalyst can be reused for 12 consecutive cycles without significant damage to the cellulosic surface.