Mechanism for Solid-State Ion Exchange of Cu⁺ into Zeolites

Abstract

Density functional theory calculations are used to investigate solid-state ion exchange of copper into zeolites. In particular, the energetic conditions for functionalization of chabazite (CHA) with copper ions from Cu2O­(111) via formation of Cu­(NH3)2 + are explored. It is found that the diamine complexes form easily on Cu2O­(111) and diffuse with low barriers over the surface and in the CHA framework. The charge neutrality of the systems is maintained via counterdiffusion of H+ in the form of NH4 + from the zeolite to the Cu2O surface where water can be formed. The efficient solvation of Cu+ and H+ by ammonia renders the ion-exchange process exothermic. The present results highlight the dynamic character of the Cu ion sites and provide means to understand zeolite functionalization.

Effect of Al-distribution on oxygen activation over Cu–CHA

“…For non Cu-exchanged CHA, it has been shown that protons balancing Si-OIJ-)-Al preferably occupy a four-membered ring adjacent to the Al positions. 23 Here, we only consider such positions for H + .…”

“…[15][16][17]21,22 This complex is mobile and weakly bonded to the zeolite framework. 23 At higher temperatures, NH 3 desorbs and Cu is coordinated directly to the zeolite framework with lost mobility. 16,17,22 Density functional theory (DFT) calculations have shown that dissociation of O 2 on a pair of Cu-ions is considerably faster than on single Cu ions.…”

“…Si-OIJ-)-Al sites that are not balanced by CuIJNH 3 ) 2 + complexes have instead H + or NH 4 + as counter ions and ion-exchange-like processes may further facilitate the CuIJNH 3 ) 2 + mobility. 23 Oxygen activation and NH 3 -SCR activity could potentially be enhanced in Cu-CHA if the two CuIJNH 3 ) 2 + complexes are stabilized at distances that facilitate adsorption. For metallocomplexes this can be accomplished by ligand design choosing the second coordination shell appropriately.…”

Interpretation of NH3-TPD Profiles from Cu-CHA Using First-Principles Calculations

“…Experimental as well as computational studies have shown that Cu + is preferably solvated by two NH 3 ligands forming a linear [Cu(I)(NH 3 ) 2 ] + complex under low-temperature NH 3 -SCR conditions [18][19][20][21][22][23][24]. The [Cu(I)(NH 3 ) 2 ] + complex is mobile with low barriers for inter-cage diffusion and suggested to be important also for the solid-state ion-exchange reaction [25]. In addition to Cu + species, Cu-CHA also contain solvated Cu 2+ species in the form of [Cu(II)( [15,18,20].…”

Functionalization of SSZ-13 and Fe-Beta with Copper by NH3 and NO Facilitated Solid-State Ion-Exchange

“…It was suggested that copper becomes mobile at low temperature, in the presence of NH 3 , owing to the formation of [Cu(NH 3 ) 2 ] + complexes. By including NO during the exposure to NH 3 , the migration rate of Cu into the porous structure of the zeolite is enhanced and it was suggested that NO assists the reduction of Cu 2+ in CuO to Cu + , which with ammonia forms the mobile [Cu(NH 3 ) 2 ] + complexes [16,17]. The so-called [NO+NH 3 ]-SSIE method is simple as it only involves two operation steps (mixing the CuO and zeolite powders, and flushing ammonia and NO over the mixture), both in the absence of aqueous media, and can be performed at considerably lower temperatures compared to conventional solid-state ion-exchange in air.…”