Superior co-catalytic activity of Pd(core)@Au(shell) nanocatalyst imparted to TiO2 for the selective hydrogenation under solar radiations

Abstract

The bimetallic core–shell nanostructures of galvanic metals have gained considerable scientific interest in improving the TiO2 photocatalysis under solar radiations over the monometallic analogues. In the present research work, Pd@Au core–shell supported TiO2 nanostructures were synthesized via galvanic replacement reaction and were examined for their catalytic/ photocatalytic hydrogenation. Three different types of bimetallic Pd@Au nanostructure were synthesized by varying Pd:Au weight ratio i.e. (1:1), (1:2) and (1:3). DLS measurements revealed that with increasing Au weight ratio, the hydrodynamic size increases from 126 to 157 nm. The optical studies showed a considerable blue shift in the absorption band of Au nanoparticles from 529 to 518 nm in the case of Pd@Au (1:1). The co-existence of absorption characteristic of Pd and Au suggests the successful synthesis of bimetallic nanostructure. STEM and EDS mapping further confirmed the formation of Pd@Au nanostructure with inner Pd core and outer Au shell. Bimetallic Pd@Au nanocatalyst displayed superior activity and selectivity towards hydrogenation of cinnamaldehyde in comparison to monometallic analogues. However, when Pd@Au nanostructures were impregnated on the surface of TiO2, a significant improvement in the hydrogenation reaction was observed under solar radiations relative to catalytic conditions. The photocatalytic performance of Pd@Au-TiO2 was found to be varied as a function of shell thickness and the optimized APT-2 (Pd1@Au2-TiO2) photocatalyst exhibited higher rate constant (2.3 × 10−1 h−1) for cinnamaldehyde hydrogenation. Hence, the plasmonic Pd@Au-TiO2 hetero-junction could be a promising greener photocatalyst for selective hydrogenation of unsaturated carbonyls for large scale industrial applications.