Electronic Structure Evolution of Pd@Co Nanocatalysts Under Oxidation and Reduction Conditions and Preferential CO Oxidation

Abstract

Herein, we present the surface electronic structure and morphological evolution under reduction and oxidation conditions for Pd@Co (PC) core‐shell nanoparticles with different Pd : Co ratio (PC=2 : 1, 1 : 1 and 1 : 2). Extensive measurements have been made with NAPXPS (near ambient pressure x‐ray photoelectron spectroscopy) under oxidising and reducing conditions, and ex‐situ HRTEM. It has been demonstrated that PC catalysts are thermally stable towards morphological changes, at least up to 575 K. Nonetheless, it shows a significant surface electronic structure changes under reaction environments, which are highly relevant to heterogeneous catalysis. As expected, high (low) population of metallic (oxidised) Co was observed, while retaining core shell structure under reduction (H2 and vacuum annealing) environment. Interestingly, the Pd−Co metallic interface helps to overcome the pyrophoric nature of cobalt and stabilised a significant amount of metallic Co at Pd−Co interface even in the presence of 0.1 mbar O2 up to 575 K. The presence of Pd−Co and Pd−Co@Co3O4 interfaces in reaction environment makes the catalyst dual functional. The proof of concept has been explored in terms of oxidation of CO in the presence of H2 or O2.

Sustainable CO2 Reduction on In2O3 with Exclusive CO Selectivity: Catalysis and In Situ Valence Band Photoelectron Spectral Investigations

“…Indeed, compared to the FWHM of 50–60 meV for gas-phase CO 2 and H 2 vibration features, the maximum broadening observed with 1:0.67 CO 2 :H 2 (306 meV) suggests that the catalyst surface is, in fact, highly heterogeneous. This is amply demonstrated earlier on different systems. ,, Indeed, reactant molecules sense the heterogeneity of the surface precisely, even for minor changes. To understand further, core-level NAP-XPS was also carried out to explore the possible reaction intermediate species present under the reaction conditions.…”

“…This underscores the possible dynamic changes, especially O v creation and utilization that occur under reaction conditions. The present work is part of the on-going efforts of our group to address bridging the pressure and material gap aspects of heterogeneous catalysis. − …”

“…This is amply demonstrated earlier on different systems. 24,25,46 Indeed, reactant molecules sense the heterogeneity of the surface precisely, even for minor changes. To understand further, corelevel NAP-XPS was also carried out to explore the possible reaction intermediate species present under the reaction conditions.…”

Aqueous Methanol to Formaldehyde and Hydrogen on Pd/TiO2 by Photocatalysis in Direct Sunlight: Structure Dependent Activity of Nano-Pd and Atomic Pt-Coated Counterparts

“…36 Reports are also available on the core−shell catalysts for different applications such as catalytic, electrocatalytic, and photocatalytic reactions. 32,37,38 For instance, Bai et al, reported the tuning of Pt shell thickness over a Pd core, and it is possible to produce highly active and stable cocatalysts with titania for photocatalytic hydrogen generation due to enhanced charge separation features. 39 In fact, it is well established in the literature that the synergetic effects of various components has been demonstrated for improved performance of various catalytic reactions.…”

“…Luo et al reported on the morphology effects of Pt–Pd alloy nanoparticles over a CdS host for solar hydrogen production from the aqueous (NH 4 ) 2 SO 3 solution under visible light; they found that Pt–Pd-nanocubes loaded CdS exhibited better activity compared to Pt–Pd nanooctahedrans . Reports are also available on the core–shell catalysts for different applications such as catalytic, electrocatalytic, and photocatalytic reactions. ,, For instance, Bai et al, reported the tuning of Pt shell thickness over a Pd core, and it is possible to produce highly active and stable cocatalysts with titania for photocatalytic hydrogen generation due to enhanced charge separation features . In fact, it is well established in the literature that the synergetic effects of various components has been demonstrated for improved performance of various catalytic reactions. − Particular attention is paid to understand the changes in surface properties and its correlation to the photocatalytic results observed in the present work.…”