Changing active sites in Cu–CHA catalysts: deNOx selectivity as a function of the preparation method

A Consistent Reaction Scheme for the Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

“…However, only the Cu ions located in or close to the 6-rings seem to contribute to the SCR activity in Cu-CHA. 12,[45][46][47][48] Independent of the nature and structure of the catalyst, and the local environment of the active sites, the SCR reaction can be divided in a reduction part and an oxidation part, quite similar to the well known Mars-Van Krevelen scheme for oxidation reactions. The reduction part corresponds to the steps in which the ammonia reacts with the NO to nitrogen and the catalytic site is reduced.…”

Environmentally-benign catalysts for the selective catalytic reduction of NOxfrom diesel engines: structure–activity relationship and reaction mechanism aspects

“…The one-pot synthesis methods for Cu-based zeolite catalysts with small pore size using relatively cheap Cu-containing templates allow researchers to tune the Cu content, Cu distribution, and Si/Al ratio and thus the NH 3 -SCR activity efficiently, although this approach is restricted to those zeolitic systems that can be prepared using coordination complexes as templates. 156 For practical use of this approach in industry, we believe, there is still a long but exciting way to go.…”

Understanding the structure directing action of copper–polyamine complexes in the direct synthesis of Cu-SAPO-34 and Cu-SAPO-18 catalysts for the selective catalytic reduction of NO with NH3

“…In previous papers reporting the direct synthesis of Cu-SSZ-13, [7] Cu-SAPO-34 [9][10][11] and Cu-SAPO-18 [12] using Cu The main difference between the method of synthesis in this work from that of Corma and co-workers, [12] is that whereas a template, N,N-dimethyl-3,5-dimethylpiperidinium, is used in that work to direct the synthesis of the SAPO-18, entraining Cu 2+ and/or Cu 2+ complex at the same time, in our synthesis it is the Cu-232…”

“…We and others [9][10][11] have shown that the copper complexes of the linear polyamines triethylenetetramine and tetraethylenepentamine are suitable SDAs for SAPO-34, and that calcination gives active SCR catalysts. Linear polyamines are relatively affordable (compared to the azamacrocycle used in the synthesis of Cu-SAPO STA-7) so we set out to investigate the action of a range of copper complexes of the linear polyamines in the direct synthesis of Cu 2+ -containing SAPOs, and to understand the mechanism by which they direct crystallisation.…”

“…[6][7][8][9][10][11][12] Calcination then releases the Cu 2+ cations to extra-framework sites distributed throughout the crystals and removes the need for a cation-exchange step. This process was first demonstrated for SAPO STA-7, [6] and subsequently for SSZ-13, [7] SAPO-34, [9][10][11] and very recently for SAPO-18 [12] giving active, selective and hydrothermally stable catalysts. The details of the mechanism by which the calcination of the complex-bearing precursor to SAPO STA-7 gives a porous, acidic framework with dispersed copper cations has been followed by ex situ UV-visible spectroscopy and by in situ microcrystal IR spectroscopy.…”