Understanding the Distinct Effects of Ag Nanoparticles and Highly Dispersed Ag Species on N<sub>2</sub> Selectivity in NH<sub>3</sub>–SCO Reaction

Selective catalytic oxidation of NH3 is the most promising method for removing low-concentration NH3. However, achieving high activity and N2 selectivity remains a great challenge. A Ag/CeSnO x tandem catalyst with dual active centers was designed and synthesized, which couples the NH3 over-oxidation on the noble metal active sites with NO x reduction on the support. The tandem catalyst exhibited excellent NH3 selective catalytic oxidation (NH3–SCO) performance at 200–400 °C. Based on various characterization techniques and DFT calculations, it was identified that the silver species on the Ag/CeSnO x catalysts existed as AgO nanoparticles (AgO NPs), and the electrons on the support were more easily transferred to AgO NPs, which promoted the oxidation activity of AgO and the reduction performance of the CeSnO x support. The coupling between the AgO NPs and CeSnO x helped balance the NH3 oxidation rate and the NO x reduction rate. In addition, the uniform adsorption of gaseous NH3 on the oxidation and reduction sites was also demonstrated by theoretical calculations, which is a prerequisite for tandem catalysis. By in situ DRIFTS, we revealed that the NH3–SCO reaction over Ag/CeSnO x catalysts mainly follows the internal selective catalytic reduction mechanism. It was characterized by excessive oxidation of NH3 to NO x on AgO NPs. At a temperature lower than 200 °C, NO x was reduced to N2 by the adsorbed NH3 on the AgO. When the temperature was higher than 200 °C, NO x was reduced to N2 by NH3 or NH4 + adsorbed on the CeSnO x support. Therefore, the charge transfer at the Ag/CeSnO x catalyst interface and the coordination of atomic scale catalytic sites have realized the conversion of NH3 to N2 through NO x in a tandem catalytic mode.

show abstract

“…Hence, CeSnO x and 1.75Ag/CeSnO x catalysts offer different NH 3 reaction pathways. 23,26 3.2. Structure of Catalysts.…”

Section: Resultsmentioning

confidence: 99%

“…The apparent activation energy ( E a ) on the CeSnO x is 82.8 KJ/mol, which is significantly higher than that on the 1.75Ag/CeSnO x catalyst ( E a = 47.9 KJ/mol). Hence, CeSnO x and 1.75Ag/CeSnO x catalysts offer different NH 3 reaction pathways. , …”

Section: Resultsmentioning

confidence: 99%

Elimination of NH₃ by Interfacial Charge Transfer over the Ag/CeSnO_x Tandem Catalyst

Zhang

Zang

et al. 2023

ACS Catal.

View full text Add to dashboard Cite

show abstract

“…Noble metals have been widely used in heterogeneous catalysis. To maximize their efficiency, the noble metal catalysts are often dispersed on a support with a high surface area, and the size typically falls in the range of nanometers or even single atoms. , As an inexpensive noble metal catalyst, Ag presents remarkable performance in various chemical reactions. − Typically, a strong size effect often exhibits in Ag-catalyzed reactions, and many studies have shown that smaller metal clusters present higher activities. Lei et al reported that Ag 3 clusters showed much higher catalytic activity than 3.5 nm Ag nanoparticles (NPs) on γ-Al 2 O 3 in selective oxidation of propylene .…”

Section: Introductionmentioning

confidence: 99%

Surface Hydroxyl-Determined Migration and Anchoring of Silver on Alumina in Oxidative Redispersion

Fan

Wang

et al. 2023

ACS Catal.

View full text Add to dashboard Cite

Hydroxyl (OH) groups are widely present on an oxide surface, which have been recognized as a key factor affecting surface properties of the oxide and interaction of the metal overlayer with the oxide. Here, γ-alumina (γ-Al2O3) supports with different OH contents are prepared by calcinating pseudo-boehmite (AlOOH) at different temperatures. The surface OH effect on oxidative redispersion of supported Ag nanoparticles including surface migration and anchoring of Ag species has been explored using in situ X-ray diffraction and UV–visible spectroscopy, as well as ex situ X-ray photoelectron spectroscopy and transmission electron microscopy. We reveal that the dispersion capacity, i.e., the amount of anchored Ag species associated with the steady dispersion state is thermodynamically determined by the surface OH contents, while the dispersion rate related to the surface migration process is kinetically limited by surface OH densities at low Ag loading. The higher dispersion ability is observed on the support with higher OH contents, and the quicker dispersion occurs on the support with higher OH densities. The results reveal that both OH contents and OH densities are critical in the redispersion of metal particles on oxide surfaces, which can be used to manipulate the Ag-catalyzed CO oxidation reaction.

show abstract

“…Various types of catalysts, including noble-metal-based materials − and transition-metal-based materials, − have been reported for NH 3 -SCO over the past few years. The low cost and high N 2 selectivity of Cu-based materials are proven to be a promising catalyst for the NH 3 -SCO reaction.…”

Section: Introductionmentioning

confidence: 99%

Construction of CuO/CeO₂ Catalysts via the Ceria Shape Effect for Selective Catalytic Oxidation of Ammonia

Sun

Wang

2023

ACS Catal.

View full text Add to dashboard Cite

Tuning the interaction between the loaded metal oxide and the support material is an efficient strategy to boost catalytic purification of ammonia (NH 3 ) as an important factor in the formation of haze. Herein, CuO/CeO 2 catalysts based on the ceria shape effect (Ce-NR and Ce-NC) are prepared and tested for the selective catalytic oxidation of ammonia (NH 3 -SCO). The interaction between CuO and CeO 2 with different shapes is crucial to regulate the interface structure and the content of oxygen vacancies. The Cu/Ce-NR possesses more Cu + -O v -Ce 3+ interfacial sites and more oxygen vacancies and achieves a higher catalytic activity (T 100 = 240 °C) and a lower apparent activation energy (37.18 kJ mol −1 ) for NH 3 -SCO compared with Cu/Ce-NC (T 100 = 270 °C, 86.57 kJ mol −1 ). In situ diffuse reflectance infrared Fourier transform spectra and density functional theory calculation results prove that the Cu + -O v -Ce 3+ interfacial site is the main adsorption site for NH 3 . The further reaction of in situ generated nitrate with NH 3 is the rate-determining step over the CuO/CeO 2 catalysts, and it is revealed that NH 3 much more easily reacts with the monodentate nitrate species formed on the Cu/Ce-NR catalyst than the bidentate nitrate formed on the Cu/Ce-NC catalyst at 240 °C. This study enriches the understanding of designing efficient catalysts by support shape to modulate their interfacial structure and thus improve the activity of NH 3 -SCO.

show abstract

Understanding the Distinct Effects of Ag Nanoparticles and Highly Dispersed Ag Species on N₂ Selectivity in NH₃–SCO Reaction

Cited by 19 publications

References 45 publications

Elimination of NH₃ by Interfacial Charge Transfer over the Ag/CeSnO_x Tandem Catalyst

Elimination of NH₃ by Interfacial Charge Transfer over the Ag/CeSnO_x Tandem Catalyst

Surface Hydroxyl-Determined Migration and Anchoring of Silver on Alumina in Oxidative Redispersion

Construction of CuO/CeO₂ Catalysts via the Ceria Shape Effect for Selective Catalytic Oxidation of Ammonia

Contact Info

Product

Resources

About

Understanding the Distinct Effects of Ag Nanoparticles and Highly Dispersed Ag Species on N2 Selectivity in NH3–SCO Reaction

Cited by 19 publications

References 45 publications

Elimination of NH3 by Interfacial Charge Transfer over the Ag/CeSnOx Tandem Catalyst

Elimination of NH3 by Interfacial Charge Transfer over the Ag/CeSnOx Tandem Catalyst

Surface Hydroxyl-Determined Migration and Anchoring of Silver on Alumina in Oxidative Redispersion

Construction of CuO/CeO2 Catalysts via the Ceria Shape Effect for Selective Catalytic Oxidation of Ammonia

Contact Info

Product

Resources

About

Understanding the Distinct Effects of Ag Nanoparticles and Highly Dispersed Ag Species on N₂ Selectivity in NH₃–SCO Reaction

Elimination of NH₃ by Interfacial Charge Transfer over the Ag/CeSnO_x Tandem Catalyst

Elimination of NH₃ by Interfacial Charge Transfer over the Ag/CeSnO_x Tandem Catalyst

Construction of CuO/CeO₂ Catalysts via the Ceria Shape Effect for Selective Catalytic Oxidation of Ammonia