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Synergistic control of nitrogen oxides (NOx) and nitrogen-containing volatile organic compounds (NVOCs) from industrial furnaces is necessary. Generally, the elimination of n-butylamine (n-B), a typical pollutant of NVOCs, requires a catalyst with sufficient redox ability. This process induces the production of nitrogen-containing byproducts (NO, NO2, N2O), leading to lower N2selectivity of NH3selective catalytic reduction of NOx(NH3-SCR). Here, synergistic catalytic removal of NOxand n-B via spatially separated cooperative sites was originally demonstrated. Specifically, titania nanotubes supported CuOx–CeO2(CuCe–TiO2NTs) catalysts with spatially separated cooperative sites were creatively developed, which showed a broader active temperature window from 180 to 340 °C, with over 90% NOxconversion, 85% n-B conversion, and 90% N2selectivity. A synergistic effect of the Cu and Ce sites was found. The catalytic oxidation of n-B mainly occurred at the Cu sites inside the tube, which ensured the regular occurrence of the NH3-SCR reaction on the outer Ce sites under the matching temperature window. In addition, the n-B oxidation would produce abundant intermediate NH2*, which could act as an extra reductant to promote NH3-SCR. Meanwhile, NH3-SCR could simultaneously remove the possible NOxbyproducts of n-B decomposition. This novel strategy of constructing cooperative sites provides a distinct pathway for promoting the synergistic removal of n-B and NOx.

NOxand CH3SH as two typical air pollutants widely coexist in various energy and industrial processes; hence, it is urgent to develop highly efficient catalysts to synergistically eliminate NOxand CH3SH. However, the catalytic system for synergistically eliminating NOxand CH3SH is seldom investigated to date. Meanwhile, the deactivation effects of CH3SH on catalysts and the formation mechanism of toxic byproducts emitted from the synergistic catalytic elimination reaction are still vague. Herein, selective synergistic catalytic elimination (SSCE) of NOxand CH3SH via engineering deep oxidation sites over Cu-modified Nb–Fe composite oxides supported on TiO2catalyst against toxic CO and HCN byproducts formation has been originally demonstrated. Various spectroscopic and microscopic characterizations demonstrate that the sufficient chemisorbed oxygen species induced by the persistent electron transfer from Nb–Fe composite oxides to copper oxides can deeply oxidize HCOOH to CO2for avoiding highly toxic byproducts formation. This work is of significance in designing superior catalysts employed in more complex working conditions and sheds light on the progress in the SSCE of NOxand sulfur-containing volatile organic compounds.

Catalyst deactivation caused by alkali metal poisoning has long been a key bottleneck in the application of selective catalytic reduction of NOxwith NH3(NH3–SCR), limiting the service life of the catalyst and increasing the cost of environmental protection. Despite great efforts, continuous accumulation of alkali metal deposition makes the resistance capacity of 2 wt % K2O difficult to enhance via merely loading acid sites on the surface, resulting in rapid deactivation and frequent replacement of the NH3–SCR catalyst. To further improve the resistance of alkali metals, encapsulating alkali metals into the bulk phase could be a promising strategy. The bottleneck of 2 wt % K2O tolerance has been solved by virtue of ultrahigh potassium storage capacity in the amorphous FePO4bulk phase. Amorphous FePO4as a support of the NH3–SCR catalyst exhibited a self-adaptive alkali-tolerance mechanism, where potassium ions spontaneously migrated into the bulk phase of amorphous FePO4and were anchored by PO43–with the generation of Fe2O3at the NH3–SCR reaction temperature. This ingenious potassium storage mechanism could boost the K2O resistance capacity to 6 wt % while maintaining approximately 81% NOxconversion. Besides, amorphous FePO4also exhibited excellent resistance to individual and coexistence of alkali (K2O and Na2O), alkali earth (CaO), and heavy metals (PbO and CdO), providing long durability for CePO4/FePO4catalysts in flue gas with multipollutants. The cheap and accessible amorphous FePO4paves the way for the development and implementation of poisoning-resistant NOxabatement.

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.

SO2-resistant selective catalytic reduction (SCR) of NOxremains a grand challenge for eliminating NOxgenerated from stationary combustion processes. Herein, SO2-resistant NOxreduction has been boosted by modulating electronic interaction of short-range Fe–O coordination over Fe2O3/TiO2catalysts. We report a remarkable SO2-tolerant Fe2O3/TiO2catalyst using sulfur-doped TiO2as the support. Via an array of spectroscopic and microscopic characterizations and DFT theoretical calculations, the active form of the dopant is demonstrated as SO42–residing at subsurface TiO6locations. Sulfur doping exerts strong electronic perturbation to TiO2, causing a net charge transfer from Fe2O3to TiO2via increased short-range Fe–O coordination. This electronic effect simultaneously weakens charge transfer from Fe2O3to SO2and enhances that from NO/NH3to Fe2O3, resulting in a remarkable “killing two birds with one stone” scenario, that is, improving NO/NH3adsorption that benefits SCR reaction and inhibiting SO2poisoning that benefits catalyst long-term stability.

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.

Selective catalytic reduction (SCR) of NOxover V2O5-based oxide catalysts has been widely used, but it is still a challenge to efficiently reduce NOxat low temperatures under SO2and H2O co-existence. Herein, SO2- and H2O-tolerant catalytic reduction of NOxat a low temperature has been originally demonstrated via engineering polymeric VOxspecies by CeO2. The polymeric VOxspecies were tactfully engineered on Ce–V2O5composite active sites via the surface occupation effect of Ce, and the obtained catalysts exhibited remarkable low-temperature activity and strong SO2and H2O tolerance at 250 °C. The strong interaction between Ce and V species induced the electron transfer from V to Ce and tuned the SCR reaction via the E–R pathway between the NH4+/NH3species and gaseous NO. In the presence of SO2and H2O, the polymeric VOxspecies had not been hardly influenced, while the formation of sulfate species on Ce sites not only promoted the adsorption of NH4+species and the reaction between gaseous NO and NH4+but also facilitated the decomposition of ammonium bisulfate through weakening the strong bond between HSO4–and NH4+. This work provided a new strategy for SO2- and H2O-tolerant catalytic reduction of NOxat a low temperature.

Releasing the poisoning effect of alkali metals over catalysts is still an intractable issue for selective catalytic reduction (SCR) of NOxwith ammonia. The presence of K in fly ash always dramatically suppressed catalytic activity by impairing acidity and redox properties, leading to severe reduction of lifetime for SCR catalysts. Herein, alkali-resistant NOxreduction over TiO2-supported Fe2(SO4)3catalysts was originally demonstrated via naturally coupling active and poisoning sites. Notably, TiO2-supported Fe2(SO4)3catalysts expressed admirable NOxconversion and K resistance within a quite broad temperature window of 200–500 °C. The catalysts with more conserved sulfate species revealed that sulfate groups preferred to migrate from the bulk phase to surface, thus effectively binding with K poisons to release the damage on iron active sites. Because of protection effects of migrated sulfates and closely coupling effects with Fe active sites, NH3and NO adsorption amounts and rates were well maintained. In this way, Fe metal sites and sulfate species closely coupled together on a self-preserved TiO2-supported Fe2(SO4)3catalyst played essential roles as highly active sites and unique poisoning sites. This work paves a new way to design SCR catalysts with superior alkali resistance that are more reliable in practical deNOxapplication.

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.