Physico-chemical and catalytic properties of ytterbium introduced into Y-zeolite

Abstract

Ytterbium was introduced into K+-exchanged Y-zeolite (Yb/K-Y) by impregnation from a liquid ammonia solution of the metal, and the change in the chemical state of the metal with evacuation temperature was investigated by infrared (IR), X-ray absorption fine structure (XAFS) and X-ray photoelectron (XPS) spectroscopies.When ammonia was removed by brief evacuation at room temperature followed by evacuation at 333 K, the IR spectrum showed the presence of Yb amides. The amide species were observed up to 423 K. The Yb L,-edge X-ray absorption near-edge structure (XANES) spectrum showed that the Yb species exist as 16.4% Yb(ii) and 83.6% Yb(iii) after evacuation at 333 K. The fraction of Yb2+ increased with increasing evacuation temperature and reached 44.2% at 573 K by the decomposition of Yb(ii, 111) amides to Yb(ii, 111) imides. The fraction of Yb(iit) species increased at an evacuation temperature >600 K, owing to the decomposition of Yb imides to Yb nitride with concomitant formation of hydrogen. The Yb(ii) imide species catalyses the isomerization of but-1-ene and the Michael reaction of cyclopent-2-enone with dimethylmalonate, while the Yb(iii) nitride species catalyses the hydrogenation of ethene.

A mini-review on solid superbase catalysts developed in the past two decades

“…22 In addition, much attention has been paid to generate strong basic materials from zeolites due to unique properties such as capability in recognizing, discriminating and organiz-ing molecules with excellent precision. 23,[58][59][60][61][62] Superbasic sites were created by dispersion and decomposition of potassium nitrate on basic KL zeolite. Upon calcination at 873 K in a conventional impregnation procedure, 23 basic strength higher than H 2 = 27 was obtained and the numbers of superbasic sites were 0.75, 0.94 and 1.03 mmol g 21 for the samples loaded with potassium nitrate of 10, 21 and 30 wt%, respectively.…”

Valence of Highly Dispersed Cerium Oxide Species on Silica Quantitatively Estimated by Ce L<SUB>III</SUB>-edge XANES

“…The similar shift due to valence has been observed for rare earth. [31][32][33][34] The relative height of B 2 to T 4 was determined to be 0.85 (Table 1) for CeO 2 .…”

“…29) The curve fitting analysis of XANES spectra was carried out by using arctangent TðxÞ and Lorentzian LðxÞ functions (eqs. 1-3): [30][31][32][33][34][35][36][37] …”

Local Structure and L1- and L3-Edge X-ray Absorption Near Edge Structures of Middle Lanthanoid Elements (Eu, Gd, Tb, and Dy) in Their Complex Oxides

“…8 However, XANES studies on the local configuration of the Ln elements are more scarce than those on 3d and 4d elements probably because the Ln L-edge XANES spectra of various Ln-containing compounds are featureless because of the large natural widths of the core level. 9 In the meanwhile, extended X-ray absorption fine structure (EXAFS) spectroscopy, the other part of X-ray absorption spectroscopy (XAS), is more widely used to analyze the local structure around an X-ray absorbing atom, based on the quantitative analysis of the EXAFS oscillations proposed by Sayers et al 10 EXAFS spectroscopy has been applied not only to 3d, 4d, and 5d transition metals but also to Ln elements in various materials such as catalysts, 11,12 semiconductors, 13,14 and optical devices. 15,16 For the EXAFS study of the lanthanoid elements, Ln L 3 -edge is usually employed because even La Kedge, which is the lowest absorption edge among the Ln Kedges, needs sufficient X-ray flux, higher than 38 keV.…”

“…In the meanwhile, extended X-ray absorption fine structure (EXAFS) spectroscopy, the other part of X-ray absorption spectroscopy (XAS), is more widely used to analyze the local structure around an X-ray absorbing atom, based on the quantitative analysis of the EXAFS oscillations proposed by Sayers et al EXAFS spectroscopy has been applied not only to 3d, 4d, and 5d transition metals but also to Ln elements in various materials such as catalysts, , semiconductors, , and optical devices. , For the EXAFS study of the lanthanoid elements, Ln L 3 -edge is usually employed because even La K-edge, which is the lowest absorption edge among the Ln K-edges, needs sufficient X-ray flux, higher than 38 keV. It is only available at the world’s largest synchrotron radiation facilities such as SPring-8 (Super Photon ring-8GeV, Japan), APS (Advanced Photon Source, USA), and ESRF (European Synchrotron Radiation Facility, France).…”