Rational Design of a Novel Catalyst Cu-SAPO-42 for NH3 -SCR Reaction

Abstract

Cu-exchanged LTA-type aluminosilicate catalyst has been considered as an efficient catalyst for the selective catalytic reduction of NO_x with ammonia (NH₃ -SCR). However, expensive organic structure-directing agents (OSDAs) and the corrosive fluoride medium are inevitably used to synthesize LTA-type molecular sieve (high-silica LTA-type aluminosilicate and its analogue LTA-type silicoaluminophosphate SAPO-42). Herein, a series of cheap and commercialized OSDAs, which are successfully applied for the targeted synthesis of SAPO-42 in the fluoride-free system, are identified by a novel RSS (refine, summarize, and search) approach. Furthermore, Cu-SAPO-42 catalysts are utilized for NH₃ -SCR. Among these catalysts, Cu-SAPO-42 prepared with 2-(butylamino)ethanol (BAEA) as OSDA demonstrates the excellent activity even after hydrothermal aging at 800 °C for 16 h, which shows much better hydrothermal stability than the commercialized Cu-SAPO-34 catalyst with comparable Si and Cu contents. Electron paramagnetic resonance (EPR) spectroscopy and Rietveld refinement are performed to identify the locations of active Cu²⁺ ions. It turns out that the active Cu²⁺ ions are distributed near the center of single 6-rings of the lta cage.

Keywords: NH 3-SCR; SAPO-LTA; molecular sieves; porous materials; targeted synthesis.