Influence of aluminium distribution on the diffusion mechanisms and pairing of Cu(NH3)2+ complexes in Cu-CHA

JD Bjerregaard and M Votsmeier and H Grönbeck, NATURE COMMUNICATIONS, 16, 603 (2025).

DOI: 10.1038/s41467-025-55859-1

The performance of Cu-exchanged chabazite (Cu-CHA) for the ammonia- assisted selective catalytic reduction of NOx (NH3-SCR) depends critically on the presence of paired Cu(NH3)2+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$$\rmCu( \rmNH_3)_2<^>+$$\enddocument complexes. Here, a machine-learning force field augmented with long-range Coulomb interactions is developed to investigate the effect of Al-distribution and Cu-loading on the mobility and pairing of Cu(NH3)2+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$$\rmCu( \rmNH_3)_2<^>+$$\enddocument complexes. Performing unbiased and constrained molecular dynamics simulations, we obtain unique information inaccessible to first-principle calculations and experiments. The free energy barrier for Cu(NH3)2+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$$\rmCu( \rmNH_3)_2<^>+$$\enddocument diffusion between CHA- cages depends sensitively on both the local and distant Al-distribution. Importantly, certain Al-distributions and arrangements of neighboring Cu(NH3)2+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$$\rmCu( \rmNH_3)_2<^>+$$\enddocument and NH4+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$$\rmNH_4<^>+$$\enddocument cations make paired Cu(NH3)2+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$ $\rmCu(\rmNH_3)_2<^>+$$\enddocument complexes exothermic with respect to separated configurations. Our results suggest that the NH3-SCR activity can be enhanced by increasing the Cu-loading and Al-content. The dynamic interplay between Cu(NH3)2+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$$\rmCu( \rmNH_3)_2<^>+$$\enddocument and NH4+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$$\rmNH_4<^>+$$\enddocument diffusion is crucial for the Cu(NH3)2+\documentclass12ptminimal \usepackageamsmath \usepackagewasysym \usepackageamsfonts \usepackageamssymb \usepackageamsbsy \usepackagemathrsfs \usepackageupgreek \setlength\oddsidemargin-69pt \begindocument$ $\rmCu(\rmNH_3)_2<^>+$$\enddocument mobility and stresses the need to explore large systems including long- range Coulomb interactions when studying diffusion of charged species in zeolites.

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