Comparison of the Catalytic Performance and Carbon Monoxide Sensing Behavior of Pd‐SnO₂ Core@Shell Nanocomposites

Abstract

The catalytic activity of Pd‐SnO2 core@shell nanocomposites in the oxidation of CO and their CO‐sensing behavior were compared. For this purpose, Pd particles were placed on the inside and the outside of SnO2 hollow spheres, as demonstrated by electron tomography, X‐ray photoelectron spectroscopy, and X‐ray absorption spectroscopy. Both the sensing and catalytic effect were studied in a systematic manner on such nanocomposites, and striking differences in the catalytic performance of the nanocomposites in CO oxidation and CO and H2 sensing were found. At low temperatures, SnO2@Pd was found to be a good sensor, and the light‐off temperature was significantly lower than that of Pd@SnO2. Above the ignition temperature, CO was probably rapidly removed from the gas so that the sensing effect disappeared. This demonstrated that understanding of the sensing and catalytic behavior can help in unraveling the functional properties of core@shell and Pd‐SnO2 nanocomposites in more detail.

Exploiting Synergies in Catalysis and Gas Sensing using Noble Metal‐Loaded Oxide Composites

“…Pd‐ or bimetallic Pd‐Pt‐based materials are applied, for example, for the oxidation of CH 4 or unburned hydrocarbons in the exhaust of natural gas vehicles. Furthermore, systems consisting of Pt/Pd‐SnO 2 or Pt/Pd‐CeO 2 are well known for their good catalytic oxidation properties, for example, in low‐temperature CO oxidation …”

“…Similar to CH 4 sensing, the optimal operation temperature for sensing of CO is decreased by the addition of noble metals . Here, recent operando studies revealed that, similar to the improvement of the catalytic activity in CH 4 combustion, not the noble metal but mostly oxidized Pd species led to the improved sensing properties . This leads to a pronounced structure sensitivity reflected by influence of size, morphology, support and gas atmosphere.…”

“…One of the main challenges of sensor and catalyst design is long‐term stability, that is, immobilization of Pd/Pt particles to prevent sintering, poisoning and oxidation. Apart from so‐called “intelligent catalyst systems” exploiting the migration of active species into the supporting oxide with subsequent segregation, core–shell‐structures gained a lot of interest . This novel kind of nanocomposite has lately proven to be a very attractive catalyst,, and sensing material.…”

“…This novel kind of nanocomposite has lately proven to be a very attractive catalyst,, and sensing material. A first set of complementary studies on the sensing behavior and catalytic performance of Pd@SnO 2 and SnO 2 @Pd core@shell nanocomposite systems has just been reported …”

“…Advanced characterization techniques led to a very complex picture of an inter‐ and counterplay of catalysis and sensing which is depicted in Figure , also depending on the sensor temperature, the porosity of the SMOX shell and the positioning of the active noble metal phase . If the active Pd phase was positioned inside of the porous SnO 2 hollow sphere the sensor was exceptionally stable towards humidity and showed very high sensor signals at temperatures below 200 °C …”