In Situ XAS Study on Growth of PVP‐Stabilized Cu Nanoparticles

Abstract

Cu nanoparticles have been synthesized from copper acetate using NaBH4 as a reducing agent and poly(N‐vinyl‐2‐pyrrolidone) (PVP) as a stabilizing agent under an inert ambience. In‐situ time‐resolved X‐ray absorption spectroscopy (XAS) measurement, which include both X‐ray near edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS) techniques, have been carried out in a specially designed measurement cell during the formation of Cu nanoparticles using a specialized computer controlled flow setup. Principal Component Analysis (PCA) and Multivariate Curve Resolution with Alternating Least Squares (MCR‐ALS) analysis have been successfully applied to the time‐resolved Cu K‐edge XANES data recorded during the growth of Cu nanoparticles. PCA of the XANES spectra predicted three chemical species present in the reaction solution including an intermediate species apart from the initial and the product species. From MCR‐ALS analysis of the Cu K‐edge XANES spectra, the oxidation state of the reaction intermediate species and the concentration profile of the constituents during the reactions have been determined. Finally the EXAFS spectra of the intermediate species has been extracted and analyzed to predict the local structure of Cu cations in this species.

Elucidation of the Structure of a Thiol Functionalized Cu-tmpa Complex Anchored to Gold via a Self-Assembled Monolayer

“…The absence of the rising edge feature in the XANES spectrum measured for EDTA Au|mixed SAM|Cu might be the result of broadness of the XANES data caused by heterogeneity of the sample. Further comparison of the XANES spectrum of EDTA Au|mixed SAM|Cu with XANES data obtained from the literature for metallic copper and Cu 0 nanoparticles shows a significant negative shift of the onset energy of the absorption edge for both Cu 0 references (Figure green line and dashed green line). , This shift supports an assignment of the +I oxidation state for the anchored copper species and rules out the +0 oxidation state. The relatively low onset energy of the absorption edge observed for modified electrode EDTA Au|mixed SAM|Cu might, however, be the result of the presence of a minor Cu 0 species besides the major Cu I species.…”

“…XANES region of the Cu K-edge XAS spectra measured for EDTA Au|mixed SAM|Cu (bold blue line) and [Cu­(tmpa)­(MeCN)]­(OTf) 2 (red line). Reference spectra from the literature of a distorted trigonal bipyramidal Cu II complex (red dashed line, complex 1 in Figure S8), 13 Cu I complexes − (thin blue lines, complexes 2–14 in Figure S8), metallic copper (green line), and Cu 0 nanoparticles (dashed green line) are depicted as well. The spectral data of the red dashed line was reprinted and adapted with permission from ref .…”

“Inverting” X-ray Absorption Spectra of Catalysts by Machine Learning in Search for Activity Descriptors

“…A good example of application of MCR-ALS technique for studies of zeolites-based catalysts is also the recent study by Pappas et al, where MCR-ALS was used for the interpretation of HERFD XANES data for Cu-based catalyst for methane-to-methanol conversion. Applications of MCR-ALS methods to zeolites were also recently reviewed by Guda et al Among other recent examples of MCR-ALS method applications, one can mention speciation of Co-based Fischer–Tropsch catalysts from time-resolved QXAFS data, ,, study of Cr oxidation state changes in Phillips catalyst during ethylene polymerization, in situ study of formation of Ni–Mo catalysts for hydrodesulfurization reaction and Fe–Ni catalyst for furfural hydrogenation, as well as in situ studies of Cu NPs growth. , …”

“…For the interpretation of obtained spectra, one can compare them with the spectra of reference materials either as well as in situ studies of Cu NPs growth. 173,174 Overall, the PCA and BSS methods provide the biggest advantage for speciation over conventional LCA method, when the structure of the investigated material differs significantly from the structure of well-defined bulk reference materials. Examples of such (catalytically relevant) systems are small NPs, 36 , 1 74 , 1 7 5 bimetallic alloys 15 5 , 16 0 1 72 and zeolites.…”

CO2 Methanation on Cu-Cluster Decorated Zirconia Supports with Different Morphology: A Combined Experimental In Situ GIXANES/GISAXS, Ex Situ XPS and Theoretical DFT Study

“…In the MCR-ALS approach, in turn, the spectra corresponding to pure compounds (which are not known a priori for nanosized materials) are determined automatically from the series of experimental data for mixtures. The MCR-ALS method and its application to XANES data analysis are discussed in refs and − . In particular, ref is a good example of application of the MCR-ALS method for identification of different species in copper-based nanocatalysts from temperature-dependent Cu K-edge XANES data and demonstrates clearly the limitations of the LCF technique.…”