Quantification of Adsorbates by X-ray Absorption Spectroscopy: Getting TGA-like Information for Free

Abstract

Hard X-ray absorption spectroscopy (XAS) is frequently applied in catalysis and gas sorption studies to monitor changes in oxidation states, coordination numbers, and interatomic distances of active sites under in situ and operando conditions. However, transmission XAS data can reveal also the change in the total amount of guest species adsorbed on the whole sample. Surprisingly, to the best of our knowledge, the latter property has never been exploited. Here, we present a simple method to quantify the amount of adsorbates from XAS data collected during the interaction of the sample with gases or liquids. The method relies on monitoring the change of the total absorption level below the measured absorption edge and does not require any additional instrumentation or modification of the XAS data collection procedure. Essentially, it is a way to obtain the information analogous to the one delivered by temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), or thermogravimetric analysis (TGA) directly from XAS at no extra cost.

Poisoning of Copper Chabazite Catalyst by Biodiesel Metal Contaminants: Effect of Alkali and Alkaline Earth Metals

“…The XANES region of PC1/6, presented in Figure a, is consistent with that previously observed for hydrated Cu zeolites. − Furthermore, the XANES of PC1/6 is similar to that of the Cu sulfate pentahydrate (Section S10). This compound contains Cu 2+ ions coordinated like fully hydrated Cu 2+ ions in an aqueous solution .…”

Light‐off Performance of Three‐Way Catalysts Before and After Accelerated Aging Test with an Engine‐Dynamometer

“…In addition, a decay in the total X‐ray absorption before the Pd K‐edge absorption edge in the low‐temperature range was observed (Figure S4), which could be interpreted as decrease in sample density but not specifically Pd species, thus release of oxide ions near the three‐phase interface, as previously discussed by Kimura et al [22] . and Lomachenko et al [23] . However, there was no apparent correlation between the decrease in the X‐ray absorption and the reduction behavior of Ce in our study.…”

“…In contrast, in the mid-to hightemperature range, a portion of the PdO x species was reduced to Pd metal, and NO reduction proceeded over Pd metal (Figure 3). In addition, a decay in the total X-ray absorption before the Pd K-edge absorption edge in the low-temperature range was observed (Figure S4), which could be interpreted as decrease in sample density but not specifically Pd species, thus release of oxide ions near the three-phase interface, as previously discussed by Kimura et al [22] and Lomachenko et al [23] However, there was no apparent correlation between the decrease in the X-ray absorption and the reduction behavior of Ce in our study. The catalytic performance of Pd/CZ (SLR900) under light-off conditions was significantly different from that of Pd/CZ (fresh), and the reaction behavior could be classified into three stages: low temperature (below 200 °C), medium temperature (200-300 °C), and high temperature (above 300 °C).…”

SO2 Poisoning of Cu-CHA deNOx Catalyst: The Most Vulnerable Cu Species Identified by X-ray Absorption Spectroscopy

“…The evolution of XANES spectra upon interaction with SO 2 shows that the most susceptible species are Cu II with mixed (NH 3 ) x O y ligation, whereas Cu I species or Cu II in the absence of NH 3 are much less affected. These findings are supported by X-ray adsorbate quantification (XAQ) data, 31 collected simultaneously with the XAS measurements during the exposure to SO 2 , and a TPD analysis of a parallel set of catalyst samples, exposed to the same pretreatments used in XANES experiments ( Figure 3 a). We find the highest sulfur content (S/Cu ratio) for the [Cu II 2 (NH 3 ) 4 O 2 ] 2+ and Cu II + NH 3 procedures.…”