Engineering Spatial and Electrostatic Confinement in Zeolites for Enhanced Low-Temperature NO Oxidation

Abstract

Low-temperature catalytic oxidation of nitric oxide (NO) has drawn significant attention, underscoring the need for catalysts with enhanced activity in the low-temperature regime. Zeolites possess intrinsic advantages for NO oxidation, as their confined microporous frameworks can stabilize the transition state (TS) through enthalpic interactions while mitigating entropy loss, thereby enabling efficient catalysis at reduced temperatures. To achieve stronger confinement of the NO oxidation TS and consequently improve catalytic performance, a three-step zeolite optimization strategy was developed to simultaneously regulate spatial and electrostatic environments within the framework. First, a zeolite with appropriate void spaces was selected; second, its Si/Al ratio (SAR) was adjusted to fine-tune the framework properties; and third, ion exchange was conducted to further modulate spatial and electrostatic effects. The results indicate that both pore size and extra-framework cations play critical roles in governing the catalytic activity of zeolites for NO oxidation. Among the synthesized materials, potassium-exchanged SSZ-13 with an SAR of 8 (K-SSZ-13-8) exhibited the highest low-temperature NO oxidation activity, achieving 87.2% of NO conversion at 25°C, along with relatively good tolerance to sulfur dioxide. This study provides a rational design strategy for developing high-performance zeolite catalysts for low-temperature NO oxidation.