Titration of Cu(I) Sites in Cu-ZSM-5 by Volumetric CO Adsorption

Abstract

Cu-exchanged zeolites are widely studied materials because of their importance in industrial energetic and environmental processes. Cu redox speciation lies at the center of many of these processes but is experimentally difficult to investigate in a quantitative manner with regular laboratory equipment. This work presents a novel technique for this purpose that exploits the selective adsorption of CO over accessible Cu(I) sites to quantify them. In particular, isothermal volumetric adsorption measurements are performed at 50 °C on a series of opportunely prereduced Cu-ZSM-5 to assess the relative fraction of Cu(I); the setup is fairly simple and only requires a regular volumetric adsorption apparatus to perform the actual measurement. Repeatability tests are carried out on the measurement and activation protocols to assess the precision of the technique, and the relative standard deviation (RSD) obtained is less than 5%. Based on the results obtained for these materials, the same CO adsorption protocol is studied for the sample using infrared spectroscopy, and a good correlation is found between the results of the volumetric measurements and the absorbance of the peak assigned to the Cu(I)−CO adducts. A linear model is built for this correlation, and the molar attenuation coefficient is obtained, allowing for spectrophotometric quantification. The good sensitivity of the spectrophotometric approach and the precision and simplicity of the volumetric approach form a complementary set of tools to quantitatively study Cu redox speciation in these materials at the laboratory scale, allowing for a wide range of Cu compositions to be accurately investigated.

MOF-Derived CeO2 and CeZrOx Solid Solutions: Exploring Ce Reduction through FTIR and NEXAFS Spectroscopy

“…The slope of the scatter plot linear fit ( Figure S9 ) indicated that . This approach is conventionally used for determining ε of adsorbed species [ 62 , 63 , 64 , 65 ]. In contrast, this is so far the first attempt to evaluate the Ce 3+ molar extinction coefficient and it could potentially be used in the future to evaluate Ce 3+ concentration from FT-IR measurements.…”

Cu-loaded zeolites enable the selective activation of ethane to ethylene at low temperatures and pressure

“…All the samples have been well characterized with techniques like XRD, SEM, elemental analysis, and N 2 -physisorption, in previous publications. 9,10 The relevant elemental composition and the samples corresponding activity in the methane to methanol (MTM) conversion is reported in Table S1 in the ESI †. In this fundamental study, we report a new pathway for ethane conversion over Cu-zeolites, and we explore the structural and compositional requirements for an effective reaction.…”

Influence of ion mobility on the redox and catalytic properties of Cu ions in zeolites

“…35 Another fascinating example is the complexation of Cu + ions in Cu-ZSM-5 by CO, forming homogeneous-like structures where the metal ion is partially detached from the framework. 8,36,37 Keeping in mind this knowledge about metal ions in zeolite, this perspective deals with the recent ndings about mobilization of Cu ions in zeolites under reaction conditions, with particular attention to the role of reactants and ligands on the ions redox properties and reactivity in the two most studied reactions over Cu-zeolites in recent years: the Selective Catalytic Reduction of NO x mediated by NH 3 (NH 3 -SCR) and the direct conversion of methane to methanol (DMTM).…”

“…35 Another fascinating example is the complexation of Cu + ions in Cu-ZSM-5 by CO, forming homogeneous-like structures where the metal ion is partially detached from the framework. 8,36,37…”