Elucidating the reaction mechanism of SO with Cu-CHA catalysts for NH-SCR by X-ray absorption spectroscopy.

The application of Cu-CHA catalysts for the selective catalytic reduction of NO by ammonia (NH-SCR) in exhaust systems of diesel vehicles requires the use of fuel with low sulfur content, because the Cu-CHA catalysts are poisoned by higher concentrations of SO. Understanding the mechanism of the interaction between the Cu-CHA catalyst and SO is crucial for elucidating the SO poisoning and development of efficient catalysts for SCR reactions. Earlier we have shown that SO reacts with the [Cu(NH)O] complex that is formed in the pores of Cu-CHA upon activation of O in the NH-SCR cycle.

Assessing the Influence of Zeolite Composition on Oxygen-Bridged Diamino Dicopper(II) Complexes in Cu-CHA DeNO Catalysts by Machine Learning-Assisted X-ray Absorption Spectroscopy.

Cu-exchanged chabazite is the catalyst of choice for NO abatement in diesel vehicles aftertreatment systems via ammonia-assisted selective catalytic reduction (NH-SCR). Herein, we exploit X-ray absorption spectroscopy powered by wavelet transform analysis and machine learning-assisted fitting to assess the impact of the zeolite composition on NH-mobilized Cu-complexes formed during the reduction and oxidation half-cycles in NH-SCR at 200 °C. Comparatively analyzing well-characterized Cu-CHA catalysts, we show that the Si/Al ratio of the zeolite host affects the structure of mobile dicopper(II) complexes formed during the oxidation of the [Cu(NH)] complexes by O.

SO Poisoning of Cu-CHA deNO Catalyst: The Most Vulnerable Cu Species Identified by X-ray Absorption Spectroscopy.

Cu-exchanged chabazite zeolites (Cu-CHA) are effective catalysts for the NH-assisted selective catalytic reduction of NO (NH-SCR) for the abatement of NO emission from diesel vehicles. However, the presence of a small amount of SO in diesel exhaust gases leads to a severe reduction in the low-temperature activity of these catalysts. To shed light on the nature of such deactivation, we characterized a Cu-CHA catalyst under well-defined exposures to SO using X-ray absorption spectroscopy.

Investigating the role of Cu-oxo species in Cu-nitrate formation over Cu-CHA catalysts.

The speciation of framework-interacting Cu sites in Cu-chabazite zeolite catalysts active in the selective catalytic reduction of NO with NH is studied, to investigate the influence of the Al content on the copper structure and their reactivity towards a NO/O mixture. To this aim, three samples with similar Cu densities and different Si/Al ratios (5, 15 and 29) were studied using in situ X-ray absorption spectroscopy (XAS), FTIR and diffuse reflectance UV-Vis during pretreatment in O followed by the reaction. XAS and UV-Vis data clearly show the main presence of ZCu sites (with Z representing a framework negative charge) at a low Si/Al ratio, as predicted.

Structure and Reactivity of Oxygen-Bridged Diamino Dicopper(II) Complexes in Cu-Ion-Exchanged Chabazite Catalyst for NH-Mediated Selective Catalytic Reduction.

The NH-mediated selective catalytic reduction (NH-SCR) of NOx over Cu-ion-exchanged chabazite (Cu-CHA) catalysts is the basis of the technology for abatement of NOx from diesel vehicles. A crucial step in this reaction is the activation of oxygen. Under conditions for low-temperature NH-SCR, oxygen only reacts with Cu ions, which are present as mobile Cu diamine complexes [Cu(NH)].

A comparative test of different density functionals for calculations of NH-SCR over Cu-Chabazite.

A general challenge in density functional theory calculations is to simultaneously account for different types of bonds. One such example is reactions in zeolites where both van der Waals and chemical bonds should be described accurately. Here, we use different exchange-correlation functionals to explore O dissociation over pairs of Cu(NH) complexes in Cu-Chabazite.

Investigating the Low Temperature Formation of Cu -(N,O) Species on Cu-CHA Zeolites for the Selective Catalytic Reduction of NO.

In this work, we show the potentiality of operando FTIR spectroscopy to follow the formation of Cu -(N,O) species on Cu exchanged chabazite zeolites (Cu-CHA), active for the selective catalytic reduction of NO with NH (NH -SCR). In particular, we investigated the reaction of NO and O at low temperature (200 and 50 °C) on a series of Cu-CHA zeolites with different composition (Si/Al and Cu/Al ratios), to investigate the nature of the formed copper nitrates, which have been proposed to be key intermediates in the oxidation part of the SCR cycle. Our results show that chelating bidentate nitrates are the main structures formed at 200 °C.

Conversion of methanol to hydrocarbons: how zeolite cavity and pore size controls product selectivity.

Liquid hydrocarbon fuels play an essential part in the global energy chain, owing to their high energy density and easy transportability. Olefins play a similar role in the production of consumer goods. In a post-oil society, fuel and olefin production will rely on alternative carbon sources, such as biomass, coal, natural gas, and CO(2).

New method for analysis of nanoparticle geometry in supported fcc metal catalysts with scanning transmission electron microscopy.

To apply the knowledge of reaction mechanisms of heterogeneously catalyzed reactions on the atomic scale to supported catalyst systems, a detailed description of the structure of active particles on the atomic scale is required. In this article, a method is developed to construct atomic-scale geometric models for supported active fcc metal nanoparticles, based on a measurement of particle sizes and particle volumes by Scanning Transmission Electron Microscopy (STEM) and the M-M coordination number determined from EXAFS. The method is applied to supported Au/TiO(2), Au/MgAl(2)O(4)(-), and Au/Al(2)O(3) catalysts.