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

Abstract

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.

Roles of ZnO in Cu/Core–Shell Al–MCM-41 for NO Reduction by Selective Catalytic Reduction with NH3: The Effects of Metal Loading and Cu/ZnO Ratio

“…18 The presence of both external surface CuO and nanosized CuO crystals in the Cu-containing catalysts was also found in the previous works. 18,19…”

“…20 During the catalyst preparation, some part of the copper precursor (i.e., Cu(NO 3 ) 2 ) was confined by the capillary effect inside the channels of the catalyst, resulting in the formation of small crystalline CuO species in pores. 18 The presence of both external surface CuO and nanosized CuO crystals in the Cu-containing catalysts was also found in the previous works. 18,19 Generally, Cu 2+ ions at the exchange sites are reduced to Cu 0 via a two-step reduction process.…”

“…18 The presence of both external surface CuO and nanosized CuO crystals in the Cu-containing catalysts was also found in the previous works. 18,19 Generally, Cu 2+ ions at the exchange sites are reduced to Cu 0 via a two-step reduction process. 19 Hence, the reduction peaks at around 380−480 °C are attributed to the reduction of Cu 2+ to Cu + ions whereas the reduction peaks at around 570− 640 °C correspond to the reduction of Cu + to Cu 0 .…”

“…It should be noted that in this work, the Cu loading of the catalysts was increased by using the impregnation method, in which copper predominately exists as CuO species. 5,18 In addition, with higher metal loading, it is more difficult for a copper precursor to infiltrate deeper in the channels of the catalysts and occupy the exchange sites, leading to the formation of more CuO species on the surface of the catalyst.…”

Ketone Hydrogenation by Using ZnO−Cu(OH)Cl/MCM‐41 with a Splash of Water: An Environmentally Benign Approach

“…The survey spectrum and high‐resolution XPS of ZnO−Cu(OH)Cl/MCM‐41 showed the existence of Zn, Cu and O (Figure ). The high‐resolution XPS spectra of Zn 2p reveals the binding energies of Zn 2p 3/2 at about 1020.5 eV and Zn 2p 1/2 center at 1043.7 eV, peak shape and peak separation which is ∼23 eV revealed that presence of Zn +2 in ZnO as shown in Figure A. XPS spectra of Cu 2p showed the two peaks centered at 933 eV and 953 eV were assign to Cu 2p 3/2 and Cu 2p 1/2 present in Cu(OH)Cl in where Cu is in +2 oxidation state shown in Figure B .…”