Catalytic reduction of NO on copper/MCM-41 studied by in situ EXAFS and XANES

Huang, Yu Chun; Wang, H.Paul; Lee, Jyh‐Fu

doi:10.1016/s0045-6535(02)00645-8

Cited by 26 publications

(10 citation statements)

References 21 publications

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“…This uncertainty is associated with the use of not completely transferable reference compounds for this analysis. Additional contributions to the EXAFS signal that are not strictly due to the EXAFS signal of CuO, as the corresponding Cu−(O−Cu)−Si and/or Cu−(O)−Cu species, are presented in these type of samples. , However, under the measurement conditions ( RT at atmospheric pressure) these species could not be observed. Continuing with the EXAFS analysis, all the distances (equatorial and axial ones) could be resolved because of their relatively small Debye−Waller factors.…”

Section: Resultsmentioning

confidence: 92%

Speciation of Copper in Spherical Mesoporous Silicates: From the Microscale to Angstrom

et al. 2010

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MCM-41 type mesoporous silicate particles with spherical morphology containing copper nanospecies were synthesized by conventional hydrothermal synthesis. A narrow distribution of silicate particle sizes between 2 and 3 µm and a well-defined mesoporosity were evidenced by electronic microscopy, even for loadings of copper of about 10 wt %. Moreover, CuO nanoparticles ∼30 nm in diameter occluded in the amorphous silica, possibly filling some secondary mesoporosity, were also detected. By Fourier transform infrared spectroscopy with pyridine adsorption and UV-vis diffuse reflectance spectroscopy measurements together with reduction experiments under H 2 flow, a detailed study about the relationship between copper loading degree and the acid properties with the local isolated Cu δ+ species surroundings was performed. The incorporation of copper into the silica framework generated surface Lewis acid sites which increase with copper content. The origin of these acid sites could be attributed to the presence of isolated Cu δ+ species possibly coordinated with the framework oxygen atoms. It is noteworthy that Brønsted acid sites were not detected in our materials. By X-ray absorption near edge structure spectroscopy, we determine the coexistence of copper +1 and +2 states. The average coordination numbers calculated from extended X-ray absorption fine structure experiments are consistent with a mixture of nanosized species of copper: CuO nanoparticles, besides isolated Cu δ+ cations located in framework positions with oligonuclear clusters like [Cu δ+ • • • O δ-• • • Cu δ+ ] n in its surroundings, confined within the pores.

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Section: Resultsmentioning

confidence: 92%

Speciation of Copper in Spherical Mesoporous Silicates: From the Microscale to Angstrom

et al. 2010

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“…These spectra illustrate three features at 8977, 8987, and 8998 eV, all of which are characteristic of Cu(II). 71,72 The preedge feature with low intensity at 8977 eV (see the inset of Figure S4) has been assigned to a dipole-forbidden 1s-to-3d transition found only in Cu(II) complexes, while the shoulder at 8987 eV and the intense feature at 8998 eV arises from 1s-to-4p transition in Cu(II). 71−73 Apart from the feature at 8977 eV, the absence of other pre-edge features below 8985 eV confirms the presence of copper only in a complete oxidation state (Cu(II)).…”

Section: Industrial and Engineering Chemistry Researchmentioning

confidence: 99%

Characterization of Cu–Zn/Core–Shell Al-MCM-41 as a Catalyst for Reduction of NO: Effect of Zn Promoter

Imyen

Yigit

Dittanet

et al. 2016

Ind. Eng. Chem. Res.

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A combination of three methodssubstitution, ionexchange, and impregnationwas used to prepare the Cu−Zn/core− shell Al-MCM-41 catalyst with various copper species. The roles of each preparation method and of Zn promoter in the nature of copper were studied by means of in situ Fourier transform infrared spectroscopy of CO and NO adsorption, diffuse reflectance ultraviolet−visible−nearinfrared spectroscopy, X-ray photoelectron spectroscopy, and H 2 temperature-programmed reduction. The results suggested that the different preparation methods strongly affected the nature of copper species. The amount of Cu(I) species in reduced catalysts was promoted by the stabilization effect of Zn. In addition, Zn species also provide additional sites for the formation of nitrate and enhance the acidity of the catalysts.

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“…2, the pre-edge XANES spectra of the fly ashes exhibited a very weak 1s-to-3d transition (8975-8980 eV), which is forbidden by the selection rule in the case of perfect octahedral symmetry [14]. A shoulder at 8984-8988 eV and an intense feature at 8995-9002 eV may be attributed to the 1s-to-4p z and 1s-to-4p x,y transitions, respectively that also indicate the existence of Cu(II).…”

Section: Resultsmentioning

confidence: 94%