Revealing the Chemical State of Palladium in Operating In₂O₃ Gas Sensors: Metallic Pd Enhances Sensing Response and Intermetallic In_xPd_y Compound Blocks It

Abstract

The sensing response of metal oxides activated with noble metal nanoparticles is significantly influenced by changes to the chemical state of corresponding elements under operating conditions. Here, a PdO/rh-In 2 O 3 consisting of PdO nanoparticles loaded onto rhombohedral In 2 O 3 was studied as a gas sensor for H 2 gas (100-40000 ppm in an oxygen-free atmosphere) in the temperature range of 25-450 °C. The phase composition and chemical state of elements were examined by resistance measurements combined with synchrotron-based in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy. As found, PdO/rh-In 2 O 3 undergoes a series of structural and chemical transformations during operation: from PdO to Pd/PdH x and finally to the intermetallic In x Pd y phase. The maximal sensing response (R N2 /R H2 ) of ~5 • 10 7 towards 40000 ppm (4 vol %) H 2 at 70 °C is correlated with the formation of PdH 0.706 /Pd. The In x Pd y intermetallic compounds formed around 250 °C significantly decrease the sensing response.

In situ/operando plug-flow fixed-bed cell for synchrotron PXRD and XAFS investigations at high temperature, pressure, controlled gas atmosphere and ultra-fast heating

“…The data generated with both techniques can be combined to obtain a more thorough description of a catalyst in situ. This RMSI results in the formation of irreversible intermetallic compounds (IMCs) in the PdO/rh-In 2 O 3 system, influencing its catalytic and gassensing properties (Ovsianytskyi et al, 2023). Our previous in situ synchrotron PXRD studies showed that 5 wt% PdOloaded rh-In 2 O 3 undergoes a sequence of phase transformations upon heating under a pure H 2 atmosphere at 1 bar and up to 500 C (Ovsianytskyi et al, 2023;Schlicker et al, 2018b).…”

“…This RMSI results in the formation of irreversible intermetallic compounds (IMCs) in the PdO/rh-In 2 O 3 system, influencing its catalytic and gassensing properties (Ovsianytskyi et al, 2023). Our previous in situ synchrotron PXRD studies showed that 5 wt% PdOloaded rh-In 2 O 3 undergoes a sequence of phase transformations upon heating under a pure H 2 atmosphere at 1 bar and up to 500 C (Ovsianytskyi et al, 2023;Schlicker et al, 2018b). In this experiment we studied the influence of H 2 on the sequence of these phase transformations.…”