Mechanistic insights into NH3-assisted selective reduction of NO on CeO2: a first-principles microkinetic study on selectivity and activity.

To understand the activity- and selectivity-limiting factors of selective catalytic reduction of NO with NH3 (NH3-SCR) catalyzed by CeO2-based oxides, a molecular-level mechanistic exploration was performed on CeO2(110) using a first-principles microkinetic study. Herein, the favored reaction pathway for N2 formation on CeO2(110) is unveiled, which includes three key subprocesses. (i) NH3 adsorbs on the Cecus site and dissociates into *NH2 assisted by Olat; (ii) *NH2 preferentially couples with NO adsorbed on Olat (ONO#), forming *NH2NO on the Cecus site; (iii) *NH2NO undergoes dehydrogenation into *NHNO, which can be easily anchored by Ovac and can then decompose into N2. The quantitative microkinetic results show that the transfer of NHNO from Cecus to Ovac, rather than the further conversion of N2O to N2 on Ovac, emerges as the N2 selectivity-determining step on CeO2, in which Ovac plays a key role. The number of Ovac is an important factor determining the N2 selectivity of CeO2-based catalysts. The sensitivity analysis reveals that NH2NO formation, i.e., *NH2 + ONO# → *NH2NO + O#, is the rate-determining step for NH3-SCR on the CeO2 catalyst; accordingly, enhancing NH3 adsorption could be an effective strategy to boost the catalytic activity of CeO2 for NH3-SCR. In general, creating Ovac on CeO2 and introducing components (e.g., WO3) with strong NH3 adsorption would be efficient for designing CeO2-based catalysts with superior N2 selectivity and activity. These results could provide a consolidated theoretical basis for understanding and optimizing CeO2-based catalysts for NH3-SCR.

Water-Induced Micro-Hydrophobic Effect Regulates Benzene Methylation in Zeolite.

Water is a ubiquitous component in heterogeneous catalysis over zeolites and can significantly influence the catalyst performance. However, the detailed mechanism insights into zeolite-catalyzed reactions under microscale aqueous environment remain elusive. Here, using multiple dimensional solid-state NMR experiments coupled with ultrahigh magic angle spinning technique and theoretical simulations, we establish a fundamental understanding of the role of water in benzene methylation over ZSM-5 zeolite under water vapor conditions. We show that water competes with benzene for the active sites of zeolite and facilitates the bimolecular reaction mechanism. The growth of water clusters induces a micro-hydrophobic effect in zeolite pores, which reorients benzene molecules and drives their interactions with surface methoxy species (SMS) on zeolite. We identify the formation and evolution of active SMS-Benzene complexes in a microscale aqueous environment and demonstrate that their accumulation in zeolite pores boosts benzene conversion and methylation.