Effects of Precursor Composition on the Local Structure of Cu Dispersed on Mesoporous Silica:  A Detailed X-ray Absorption Spectroscopy Study

Abstract

A low-temperature grafting approach using two CuI molecular precursors ([CuOSi(O t Bu)3]4 and [CuO t Bu]4) and a high-temperature exchange reaction using CuCl were utilized with a mesoporous silica support (SBA-15) to investigate the effects of catalyst preparation on the nature of copper−support interactions and site speciation. Detailed X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure studies (EXAFS) studies were performed to characterize the nature of the Cu sites and the Cu−support interactions. The freshly prepared materials from the nonaqueous grafting of [CuOSi(O t Bu)3]4 (CuOSi/SBA (x.x), where x.x refers to the Cu weight %) exhibit CuI site isolation (by EXAFS and XANES). In contrast, EXAFS and XANES studies of the freshly prepared materials from the nonaqueous grafting of [CuO t Bu]4 (CuO t Bu/SBA (x.x)) suggest that the Cu−O−Cu linkages of the molecular precursor remain intact upon interacting with the support. Isolated CuI sites are observed as the major species in the freshly prepared material from the high-temperature exchange reaction using CuCl (CuCl/SBA (3.0)) (by XANES and EXAFS). Treatment of the materials under He at 573 K leads to loss of the organic species from the grafted materials (by 1H NMR spectroscopy, thermogravimetric analysis, EA, and IR spectroscopy). EXAFS and XANES studies revealed that CuCl/SBA (3.0) and the CuOSi/SBA (x.x) materials still exhibit up to 95% isolated CuI sites, whereas the CuO t Bu/SBA (x.x) materials only exhibit Cu as Cu0 nanoparticles of ca. 7 Å in diameter. After calcination under O2 at 573 K, residual chloride from the high-temperature preparation of CuCl/SBA (3.0) leads to formation of crystalline CuO particles, whereas the CuOSi/SBA (x.x) and CuO t Bu/SBA (x.x) materials exhibit more amorphous CuO character after an identical oxidative treatment.

Photocatalytic hydrogen production from methanol aqueous solution under visible-light using Cu/S–TiO2 prepared by electroless plating method

“…The peaks at 0.225, 0.33, 0.405 and 0.47 nm (weak) are attributable to the first four coordination shells of Cu in Cu metal. In addition, the spectra also showed a peak at 0.15 nm assigned to Cu-O backscattering, suggesting the existence of Cu 1+ [25]. In contrast, the profile of EP is very different from the CR sample.…”

“…However, the prominent peaks at 0.15 and 0.25 were observed, which could be assigned to CuO. In addition, the peak at 0.2 nm combined with the one at 0.15 nm showed the existence of Cu 2 O [25].…”

“…4. The spectra for CR have characteristic peaks similar to Cu foil [25]. The peaks at 0.225, 0.33, 0.405 and 0.47 nm (weak) are attributable to the first four coordination shells of Cu in Cu metal.…”

Planting of bis(1,5-cyclooctadiene) nickel upon silica to harvest NiO (<5 nm) nanoparticles in a silica matrix

“…2 Chemical vapour deposition and grafting methods have been found to be efficient in improving the dispersion through the reaction between the precursor and the support surface hydroxyl groups. Atomically dispersed isolated Ti, 3 V, 4 Fe, 5 Cu, 6 Ta, 7 Cr and W centres 8 have been synthesized through grafting of either organometallics or metal-containing silsequioxane species in organic solvents and, as a result, catalytic activity *Correspondence to: Ryan M. Richards, School of Engineering and Science, International University of Bremen, 28759 Bremen, Germany. E-mail: r.richards@iu-bremen.de Contract/grant sponsor: International University of Bremen.…”

AgOC(CF3)3 and AgOSiiPr3—Synthesis and Characterization of a Donor‐Free Silver(I) Alkoxide and Silyl Oxide

“…[2][3][4][5][6][7][8] Several of these homoleptic Cu I alkoxides and silyl oxides were successfully tested for chemical vapor deposition (CVD) processes. [6,9] Of the Cu I alkoxides and silyl oxides, only CuOCR 3 and CuOSiR 3 (R = CH 3 and C 6 H 5 ) have been structurally characterized. [4][5][6][7][8] In all cases, the compounds are tetranuclear species and form approximately square-planar eight-membered rings in the solid state.…”