Synthesis of Mesoporous Copper Aluminosilicate Hollow Spheres for Oxidation Reactions

Abstract

Hollow functional metal silicate materials have received the most interest due to their large inner space, permeable and functional shell, lighter density, and better use of material compared to their solid counterparts. While tremendous success has been made in the synthesis of individual metal silicates with uniform morphology, the synthesis of multiphase hollow silicates has not been explored yet, although their direct applications could be promising. In this study, mesoporous aluminosilicate spheres (MASS) are transformed to submicrometer copper aluminosilicate hollow spheres (CASHS) via a one-pot hydrothermal process. CASHS has a hollow interior with Cu−Al−Si thorn-like moieties in a lamellar structure on its outer shell. The structure and morphology of CASHS are unique and different from the previously reported tubular copper silicates that are emanated from Stober silica spheres. Herein, we also demonstrate that the extent of hollowing in CASHS can be attained by controlling the aluminum content of pristine MASS, highlighting the existence of parameters for in situ controlling the shell thickness of hollow materials. The application of CASHS as a potential heterogeneous catalyst has been directed to important oxidation processes such as olefin oxidation and the advanced oxidation process (AOP). In cyclohexene oxidation, for instance, high selectivity to cyclohex-2-en-1-one is achieved under moderate conditions using tert-butyl hydroperoxide as the oxidant. CASHS is a robust heterogeneous catalyst and recyclable for this reaction. CASHS-derived catalysts also favor AOP and enhance the removal of cationic dyes together with H 2 O 2 through an adsorption−degradation process.

Revamping SiO2 Spheres by Core–Shell Porosity Endowment to Construct a Mazelike Nanoreactor for Enhanced Catalysis in CO2 Hydrogenation to Methanol

“…Figure S12e, Supporting Information, also shows that the Cu K-edge shoulder of both calcined samples are almost vanished compared to that of CuO reference sample, demonstrating the deviation of CuO 4 cell structure from the square-planar one. [28] In the spent catalysts, a mixture of Cu and CuO was found in both samples with CZZ/ MVmSiO 2 featuring a higher amount of metallic copper and showing a significant metallic Cu-Cu band at R-space value of 2.1 Å (Figure S12f, Supporting Information). Linear combination (LC) of metallic and oxidized copper (CuO) XANES spectra also helps in evaluating the amount of Cu 0 /Cu 2+ in the samples (Figure S13a, Supporting Information).…”

“…Worthwhile to mention is that XANES and EXAFS spectra are influenced by two parameters including structural disorder arising from material nature and temperature disorder arising from temperature changes at which XANES and EXAFS measurement was performed. [28,31] Due to the limited X-ray energy range of our XAFCA beamline, we were unable to collect XAS data for zirconium element. Nevertheless, chemical features of Zr in these samples had been investigated by XPS and are reported in Figure S12c, Supporting Information.…”

Single Solid Precursor-Derived Three-Dimensional Nanowire Networks of CuZn-Silicate for CO2 Hydrogenation to Methanol

“…XANES spectra suggest that Cu takes a distorted four-bond planar structure with a valence state of 2+, similar to its precursor (Figure S15a). The partially reduced Cu + state was affirmed by the pronounced shoulder peak at 8983 eV (following the Cu 2 O XANES spectrum) …”

Hierarchy Concepts in Design and Synthesis of Nanocatalysts

“…In the former one, similar to the sculpturing process from a single block of raw marble, an overall nanostructure or microstructure is “carved” from a dimensionally defined solid precursor or crystallite aggregate through various chemical and/or physical means [27,35,36,37] . In particular, pyrolysis, [35] chemical etching, [38,39] modified Kirkendall diffusion, [38,40] Ostwald ripening, [41] core removal, [33] galvanic replacement, [42] chemical transformation, [43,44,45,46] and antisolvent strategy etc [47] . are effective methods to obtain a conceivable end product.…”