Interfacial Cu+ promoted surface reactivity: Carbon monoxide oxidation reaction over polycrystalline copper–titania catalysts

Abstract

We have studied the catalytic carbon monoxide (CO) oxidation (CO+0.5O 2 → CO 2) reaction using a powder catalyst composed of both copper (5wt% loading) and titania (CuO x-TiO 2). Our study was focused on revealing the role of Cu, and the interaction between Cu and TiO 2 , by systematic comparison between two nanocatalysts, CuO x-TiO 2 and pure CuO x. We interrogated these catal ysts under in situ conditions using X-ray Diffraction (XRD), X-ray Absorption Fine Structure (XAFS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) to probe the structure and electronic properties of the catalyst at all stages of the reaction and simultaneously probe the surface states or intermediates of this reaction. With the aid of several ex situ characterization techniques including Transmission Electron Microscopy (TEM), the local catalyst morphology and structure was also studied. Our results show that a CuO x-TiO 2 system is more active than bulk CuO x for the CO oxidation reaction due to its lower onset temperature and better stability at higher temperatures. Our results also suggests that a surface Cu + species observed in the CuO x-TiO 2 interface are likely to be a key player in the CO oxidation mechanism, while implicating that the stabilization of this species is probably associated with the oxide-oxide interface. Both in situ DRIFTS and XAFS measurements reveal that there is likely to be a Cu(Ti)-O mixed oxide at this interface. We discuss the nature of this Cu(Ti)-O interface and interpret its role on the CO oxidation reaction.

Low-Temperature Selective Catalytic Reduction of NO by CO in the Presence of O2 over Cu:Ce Catalysts Supported by Multiwalled Carbon Nanotubes

“…Low NO x conversion of Cu1:Ce3/CNT catalyst was observed at low temperature (140 °C), whereas enhancement was observed at temperature exceeding 180 °C. The effect may be due to the reduction of the catalyst by CO at increased temperature, which led to the formation of increased surface oxygen vacancies; moreover, increased temperature provided sufficient energy for dissociation of NO on SOV. , In addition, during CO oxidation in the CuO–CeO 2 catalyst, CO molecules can be efficiently adsorbed by Cu + , resulting in enhanced reaction. , The chemisorption of CO on Cu + sites and increased oxygen vacancies on the surface of the catalyst led to an increase in the catalyst reactivity.…”

“…35,38 In addition, during CO oxidation in the CuO−CeO 2 catalyst, CO molecules can be efficiently adsorbed by Cu + , resulting in enhanced reaction. 49,50 The chemisorption of CO on Cu + sites and increased oxygen vacancies on the surface of the catalyst led to an increase in the catalyst reactivity.…”

Elucidating the Nature of the Cu(I) Active Site in CuO/TiO2 for Excellent Low-Temperature CO Oxidation

“…The employment of metal oxide support such as CeO 2 , − TiO 2 , , and MnO x to form composite materials has been proved effective for the stabilization Cu + species. Among the above-mentioned metal oxide supports, TiO 2 attracts special attention owing to its outstanding physical/chemical stability, low cost, and ability to stabilize Cu + species. − Stable Cu + was found to exist in the model CuTiO x mixed oxide film prepared via a vacuum-assisted sputter deposition method. The formation of the O–TiCu–O trilayer increases the distance between the neighboring surface active Cu + sites, thereby inhibiting the O 2 dissociation and preventing the oxidation of Cu + to Cu 2+ .…”

The influence of support composition on the activity of Cu:Ce catalysts for selective catalytic reduction of NO by CO in the presence of excess oxygen

“…47,49 Besides, the higher Cu + content leads to a higher tendency for CO adsorption, which increases the number of oxygen vacancies on the surface of the catalyst. 50,51 Fig . 7 shows the Ce 3d spectra of the catalysts supported on different solid carriers.…”