Highly oxidized Pt species stabilized inside carbon nanotubes for asymmetric hydrogenation

Abstract

The chemical state and its influence on Pt species in or outside of the channels of CNTs and the effect on the asymmetric hydrogenation of α-ketoester were investigated. XPS analysis showed that 13% Pt species in a highly oxidized state (Pt 4+ ) were stabilized inside the channels in the presence of Na + . There were more highly oxidized Pt species inside the CNTs than outside. The highly oxidized Pt species promoted the interaction between the nanoparticle and chiral modifier, which is crucial for high enantioselectivity. Hydrogen temperature programmed desorption showed that Pt nanoparticles confined in the channels can better activate hydrogen, which contributed to their high activity even at low hydrogen pressure.

Hydrogenation of Phenol over Pt/CNTs: The Effects of Pt Loading and Reaction Solvents

“…Compared with the outer spaces, the internal nanospaces of CNTs act as a nanoreactor for phenol hydrogenation. Guan et al [38] reported that the CNTs as a nanoreactor function not only to enrich the molecules inside the channels, but also to stabilize the higher oxidative state of Pt. Since the reuse performance of the supported noble metal catalysts is one major factor in practical application, we also examined the catalytic performances of the recycled catalysts (Table 3).…”

Recent developments in the control of selectivity in hydrogenation reactions by confined metal functionalities

“…Metallic species confined in carbon nanotubes (CNTs) are prepared by several methods. Dispersed metallic species in the channels of CNTs can be achieved by loading metallic precursors using classical impregnation methods [129][130][131][132] or chemical vapor deposition approaches. 133 Other more complexes synthesis involve the thermal annealing of MOFs bearing the desired metal.…”

“…13). 129,131 Additionally, CNTs possess electron-deficient internal walls due to charge transfer from the…”

“…142 Taking benefit of the capillarity forces of CNTs, several reports described the use of CNTs as micro-reactors for asymmetric hydrogenation reactions. 129,131,143,144 Pt NPs confined in multi-walled (MW) CNTs with open channels were chirally modified by cinchonidine (CD), which was present in the internal cavities with a 2700 times higher concentration than in the bulk solution. 131 This modification allowed for the asymmetric hydrogenation of ethyl pyruvate (α-ketoester) with a high TOF (10 5 h −1 ) and 96% ee.…”

“…Finally, generating cationic Pt n+ in the form of Pt(ONa) x was found to further increase the electronegativity of the Pt NPs and consequently strengthen the interaction of NPs with chiral modifier/reactant. 129 This resulted in a better chiral environment on the surface of the Pt nanoparticles giving rise to high enantioselectivity.…”