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Selective catalytic reduction (SCR) of NOxfrom the flue gas is still a grand challenge due to the easy deactivation of catalysts. The copoisoning mechanisms and multipoisoning-resistant strategies for SCR catalysts in the coexistence of heavy metals and phosphorus are barely explored. Herein, we unexpectedly found unique compensation effects of heavy metals and phosphorus copoisoning over NOxreduction catalysts and the introduction of heavy metals results in a dramatic recovery of NOxreduction activity for the P-poisoned CeO2/TiO2catalysts. P preferentially combines with Ce as a phosphate species to reduce the redox capacity and inhibit NO adsorption. Heavy metals preferentially reduced the Brønsted acid sites of the catalyst and inhibited NH3adsorption. It has been demonstrated that heavy metal phosphate species generated over the copoisoned catalyst, which boosted the activation of NH3and NO, subsequently bringing about more active nitrate species to relieve the severe impact by phosphorus and maintain the NOxreduction over CeO2/TiO2catalysts. The heavy metals and P copoisoned catalysts also possessed more acidic sites, redox sites, and surface adsorbed oxygen species, which thus contributed to the highly efficient NOxreduction. This work elaborates the unique compensation effects of heavy metals and phosphorus copoisoning over CeO2/TiO2catalysts for NOxreduction and provides a perspective for further designing multipoisoning-resistant CeO2-based catalysts to efficiently control NOxemissions in stationary sources.

The catalyst deactivation caused by the coexistence of alkali and heavy metals remains an obstacle for selective catalytic reduction of NOxwith NH3. Moreover, the copoisoning mechanism of alkali and heavy metals is still unclear. Herein, the copoisoning mechanism of K and Cd was revealed from the adsorption and variation of reaction intermediates at a molecular level through time-resolved in situspectroscopy combined with theoretical calculations. The alkali metal K mainly decreased the adsorption of NH3on Lewis acid sites and altered the reaction more depending on the formation of the NH4NO3intermediate, which is highly related to NOxadsorption and activation. However, Cd further inhibited the generation of active nitrate intermediates and thus decreased the NOxabatement about 60% on potassium-poisoned CeTiOxcatalysts. Physically mixing with acid additives for CeTiOxcatalysts could significantly liberate the active Lewis acid sites from the occupation of alkali metals and relieve the high dependence on NOxadsorption and activation, thus recovering the NOxremoval rate to the initial state. This work revealed the copoisoning mechanism of K and Cd on Ce-based de-NOxcatalysts and developed a facile anti-poisoning strategy, which paves a way for the development of durable catalysts among alkali and heavy metal copoisoning resistant catalytic reduction of NOx.

It is still a great challenge for the selective catalytic reduction (SCR) of NOxin the presence of SO2. Herein, active Cu species confined in TiO2nanotubes (TiO2NTs) as SCR catalysts were originally developed and proven to possess excellent SO2tolerance for NOxreduction. Most of the active Cu species were confined in TiO2NTs, which possessed a larger specific surface area, thus accelerating the redox cycle and increasing the Lewis acidity of the catalyst. Moreover, the special confinement effect of TiO2NTs on Cu species ensured more active Cu+sites emergence. Remarkably, the electron-rich state of active Cu+sites greatly weakened the SO2adsorption and oxidation process, and thus the active components were immunized from SO2poisoning. Therefore, the prominent SO2resistance of SCR catalysts was realized viathe special structure–activity relationship in that the surface electron cloud density of Cu was effectively adjusted by the confinement effect of TiO2NTs. This work provides a novel way for the development of highly efficient SCR catalysts with excellent SO2tolerance.

Reducing the poisoning effect of alkali and heavy metals over ammonia selective catalytic reduction (NH3-SCR) catalysts is still an intractable issue, as the presence of K and Pb in fly ash greatly hampers their catalytic activity by impairing the acidity and affecting the redox properties of the catalysts, leading to the reduction in the lifetime of SCR catalysts. To address this issue, we propose a novel self-protected antipoisoning mechanism by designing SO42–/TiO2superacid supported CeO2–SnO2catalysts. Owing to the synergistic effect between CeO2and SnO2and the strong acidity originating from the SO42–/TiO2superacid, the catalysts show superior catalytic activity over a wide temperature range (240–510 °C). Moreover, when K or/and Pb are deposited on SO42–/TiO2catalysts, the bond effect between SO42–and Ti–O would be broken so that the sulfate in the bulk of SO42–/TiO2superacid support would be induced to migrate to the surface to bond with K and Pb, thus prohibiting poisons from attacking the Ce–Sn active sites, and significantly boosting the resistance. Hopefully, this novel self-protection mechanism derived from the migration of sulfate in the SO42–/TiO2superacid to resist alkali and heavy metals provides a new avenue for designing novel catalysts with outstanding resistance to alkali and heavy metals.

It is challenging for selective catalytic reduction (SCR) of NOxby NH3due to the coexistence of heavy metal and SO2in the flue gas. A thorough probe into deactivation mechanisms is imperative but still lacking. This study unravels unexpected offset effects of Cd and SO2deactivation over CeO2-WO3/TiO2catalysts, potential candidates for commercial SCR catalysts. Cd- and SO2-copoisoned catalysts demonstrated higher activity for NOxreduction than a Cd-poisoned catalyst but lower than that for an SO2-poisoned catalyst. In comparison to SO2, Cd had more severe effects on acidic and redox properties, distinctly decreasing the SCR activity. After sulfation of Cd-poisoned catalysts, SO42–preferentially bonded with the surface CdO and released CeO2active sites poisoned by CdO, thus reserving the highly active CeO2-WO3sites and maintaining a high activity. The sulfation of Cd-poisoned catalysts also provided more strong acidic sites, and the synergistic effects between the formed cerium sulfate and CeO2contributed to the high-temperature SCR performance. This work sheds light on the deactivation mechanism of heavy metals and SO2over CeO2-WO3/TiO2catalysts and provides an innovative pathway for inventing high-performance SCR catalysts, which have great resistance to heavy metals and SO2simultaneously. This will be favorable to academic and practical applications in the future.

Crystal-to-glass transformation is a powerful approach to modulating the chemical and physical properties of crystals. Here we demonstrate that the glass transformation of cobalt hexacyanoferrate crystals, one of the Prussian blue analogues, increased the concentration of open metal sites and altered the electronic state while maintaining coordination geometries and short-range ordering in the structure. The compositional and structural changes were characterized by X-ray absorption fine structure, energy dispersive X-ray spectroscopy, and X-ray total scattering. The changes contribute to the flat band potential of the glass becoming closer to the redox potential of CO2reduction. The valence band energy of the glass also shifts, resulting in lower band gap energy. Both the increased open metal sites and the optimal electronic structure upon vitrification enhance photocatalytic activity toward CO2-to-CO conversions (9.9 μmol h–1CO production) and selectivity (72.4%) in comparison with the crystalline counterpart (3.9 μmol h–1and 42.8%).