Selective catalytic oxidation of ammonia into nitrogen and water vapor (NH3-SCO) is considered to be an efficient technique to eliminate the hazardous and pungent gaseous phase NH3, which mainly emitted...

The selective catalytic oxidation of ammonia (NH3-SCO) into N2 and H2O is a recognized effective protocol to eliminate excessive NH3 emission. Nevertheless, it is a great challenge for NH3-SCO catalysts to balance the NH3 oxidation activity with N2 selectivity. Herein, promotion effects of the dynamically constructed CuO x -OH interfacial sites for NH3 oxidation activity without the scarification of N2 selectivity were unraveled. The enrichment of coordination unsaturated Cu sites and Cu-OH acid sites in CuO x -OH interfacial sites optimized the adsorption and activation for NH3 and O2, leading to the over 9-fold increase in NH3 oxidation rate and the 40 kJ/mol decrease in apparent activation energy compared with the conventional CuO sites. Unexpectedly, the fast internal-selective catalytic reduction (i-SCR) mechanism was identified on CuO x -OH interfacial sites, which is characterized by the presence of consumable NO2 adsorbed species. This work paves an innovative way for the development of effective NH3-SCO catalysts and contributes to the deeper understanding of the reaction mechanism.

Currently, SO2-induced catalyst deactivation from the sulfation of active sites turns to be an intractable issue for selective catalytic reduction (SCR) of NO x with NH3 at low temperatures. Herein, SO2-tolerant NO x reduction has been originally demonstrated via tailoring the electron transfer between surface iron sulfate and subsurface ceria. Engineered from the atomic layer deposition followed by the pre-sulfation method, the structure of surface iron sulfate and subsurface ceria was successfully constructed on CeO2/TiO2 catalysts, which delivered improved SO2 resistance for NO x reduction at 250 °C. It was demonstrated that the surface iron sulfate inhibited the sulfation of subsurface Ce species, while the electron transfer from the surface Fe species to the subsurface Ce species was well retained. Such an innovative structure of surface iron sulfate and subsurface ceria notably improved the reactivity of NH x species, thus endowing the catalysts with a high NO x reaction efficiency in the presence of SO2. This work unraveled the specific structure effect of surface iron sulfate and subsurface ceria on SO2-toleant NO x reduction and supplied a new point to design SO2-tolerant catalysts by modulating the unique electron transfer between surface sulfate species and subsurface oxides.

The development of highly efficient catalysts for low-temperature NO x abatement still existed as a scabrous issue. An acid-etched mullite-type SmMn2O5 catalyst (SM-E) was developed and applied in ultralow-temperature selective catalytic reduction of NO x with NH3 (NH3-SCR) to meet the increasingly rigorous demands of emission control in the nonelectric industry, which can convert more than 90% NO x in a wide operating window (90–200 °C). It has been demonstrated that NO can be preferably adsorbed and activated on the unique Mn–Mn dimer sites and further react with the adsorbed NH3 on adjacent Mn–O sites over the SM-E catalyst. The synergistic effects of these abundant exposed dual-functional active sites on the SM-E catalyst contributed to the extraordinary NH3-SCR performance compared to the pristine SmMn2O5 catalyst exposing deficient active sites as well as the Sm–Mn composite oxides containing sole Mn–O sites. This work sheds light on a novel strategy to deeply study the structure–performance relationship and provides deep insights into the rational design of NH3-SCR catalysts for ultralow-temperature NO x abatement.

Severe catalyst deactivation caused by multiple poisons, including heavy metals and SO2, remains an obstinate issue for the selective catalytic reduction (SCR) of NO x by NH3. The copoisoning effects of heavy metals and SO2 are still unclear and irreconcilable. Herein, the unanticipated differential compensated or aggravated Pb and SO2 copoisoning effects over ceria-based catalysts for NO x reduction was originally unraveled. It was demonstrated that Pb and SO2 exhibited a compensated copoisoning effect over the CeO2/TiO2 (CT) catalyst with sole active CeO2 sites but an aggravated copoisoning effect over the CeO2–WO3/TiO2 (CWT) catalyst with dual active CeO2 sites and acidic WO3 sites. Furthermore, it was uniquely revealed that Pb preferred bonding with CeO2 among CT while further being combined with SO2 to form PbSO4 after copoisoning, which released the poisoned active CeO2 sites and rendered the copoisoned CT catalyst a recovered reactivity. In comparison, Pb and SO2 would poison acidic WO3 sites and active CeO2 sites, respectively, resulting in a seriously degraded reactivity of the copoisoned CWT catalyst. Therefore, this work thoroughly illustrates the internal mechanism of differential compensated or aggravated deactivation effects for Pb and SO2 copoisoning over CT and CWT catalysts and provides effective solutions to design ceria-based SCR catalysts with remarkable copoisoning resistance for the coexistence of heavy metals and SO2.

Methane dry reforming (MDR) attracts great attention due to the comprehensive conversion and utilization of CO2 and CH4 into an equimolar ratio of H2/CO. Boron nitride-supported Ni-based catalysts show great promise for the efficient coking resistance but exhibit weak interactions with active sites and poor gas adsorption capacity. Herein, carbon-doped boron nitride (BCN) was originally developed to anchor Ni nanoparticles on the boundary or near the boundary between layers with strong interactions, which exhibited excellent MDR activity and high coking resistance. It has been demonstrated that the modification of the electronic structure of BN surfaces by doping carbon strengthens the interactions between Ni and BCN as well as the CO2 activation capacity. The stable I D/I G ratio observed during the MDR process implies that carbon doping effectively inhibits the formation of graphitic carbon by weakening the occurrence of side reaction and makes the catalysts possess excellent coking resistance. Abundant active intermediates, such as −OH groups and formate species as well as CO, were observed over Ni/BCN catalysts signifying the strong activation of CO2 and CH4 cleavage capacity, which can facilitate the MDR process. This discovery presents in-depth insights into the relationship of surface electronic structure and gas activation over Ni/BCN catalysts and also paves the way for the development of highly efficient coking- and sintering-resistant Ni-based catalysts.

Selective catalytic reduction (SCR) of NO x from 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 NO x reduction catalysts and the introduction of heavy metals results in a dramatic recovery of NO x reduction activity for the P-poisoned CeO2/TiO2 catalysts. 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 NH3 adsorption. It has been demonstrated that heavy metal phosphate species generated over the copoisoned catalyst, which boosted the activation of NH3 and NO, subsequently bringing about more active nitrate species to relieve the severe impact by phosphorus and maintain the NO x reduction over CeO2/TiO2 catalysts. 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 NO x reduction. This work elaborates the unique compensation effects of heavy metals and phosphorus copoisoning over CeO2/TiO2 catalysts for NO x reduction and provides a perspective for further designing multipoisoning-resistant CeO2-based catalysts to efficiently control NO x emissions in stationary sources.

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