Discovering Surface Structure and the Mechanism of Graphene Oxide-Triggered CeO₂–WO₃/TiO₂ Catalysts for NO Abatement with NH₃

Abstract

Tricomponent cerium–tungsten–titanium catalysts have the potential for selective catalytic reduction of NO by NH3, while the accurate modulating of the surface structure and the understanding of the atomic-level mechanism remain extremely challenging. To resolve the conundrum, here, we investigate the modular ternary catalysts through advanced spectroscopic and computational studies. It reveals that the introduction of graphene oxide induces a high dispersion of W and Ce species, resulting in the generation of amorphous W–O–Ce- and Ce–O–Ti-bonding structures on the surface. More importantly, the high dispersion of CeO2 facilitates the formation of abundant oxygen vacancies, which are mobile active sites for adsorption and activation of NO and NH3. Temperature-programmed desorption of NO (NO-TPD) and temperature-programmed desorption of NH3 (NH3-TPD) validate the feasibility of adsorption of NO and NH3 at low temperatures. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of the transient reaction indicates that both NO2 and monodentate nitrate are active intermediates, which can react with the adsorbed NH3 to generate N2 and H2O during catalysis. X-ray absorption fine structure (XAFS), in situ Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) provide direct evidence for the presence of Ce, W, and Ti interactions. Theoretical simulations prove that the inherent interactions reliably accelerate the conversion efficiency of NO x to N2 by improving the electron transfer on the surface. Furthermore, the Langmuir–Hinshelwood mechanism is thermodynamically more feasible and predominant over the graphene oxide-triggered catalyst.

Endowing Porphyrinic Metal–Organic Frameworks with High Stability by a Linker Desymmetrization Strategy

“…Unexpectedly, the significant activity difference between USTC-9­(In) and USTC-9­(Fe) can be observed (Figure a, Table S2). The acidity strength is examined by NH 3 temperature-programmed desorption (TPD). , Broad desorption peaks can be observed in the range of 50–250 °C, which is ascribed to the adsorption of NH 3 on the Lewis acid sites. The Lewis acid strength of USTC-9­(Fe) is evaluated by the temperature of the maximum NH 3 desorption peak (126.2 °C), which is higher than that (105.7 °C) of USTC-9­(In) , accounting for the superior catalytic activity of USTC-9­(Fe) (Figure S21).…”

Water pretreatment promoting the removal of indoor formaldehyde over nano-CeO2 at ambient temperature

“…The DFT + U method was employed to eliminate the self-interaction error, and Hubbard U parameters were introduced to describe the Coulomb interactions of the Ce 4f electrons. 29 According to the literature, 29,30 the value of U is chosen as 5 eV to correctly represent the localization of the Ce 4f electrons. A periodic slab with exposed bridge oxygen was employed to model CeO 2 (111) and (220) surfaces, which were the two strongest XRD peaks.…”

“…Three possible adsorption sites of HCHO on the CeO 2 (111) and (220) surfaces could be the top Ce, bridged Ce–Ce and bridged Ce–O. The adsorption energy ( E ads ) per H 2 O or HCHO molecule was as follows: 30,31 E ads = E adsorbate/slab − ( E adsorbate + E slab )(adsorbate: HCHO or H 2 O),where E adsorbate/slab is the total energy of a slab model after adsorbate adsorption, and E slab and E adsorbate are the energies of the slab and a gaseous adsorbate molecule, respectively. A negative E ads value indicates exothermic adsorption.…”

Combined Experimental and Density Functional Theory Study on the Mechanism of the Selective Catalytic Reduction of NO with NH3 over Metal-Free Carbon-Based Catalysts

“…Nitrogen oxides (NO x ) are important contributors to air pollution, leading to acid rain, photochemical smog, and haze. NO x are mainly emitted from stationary sources and diesel engines. − Selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) has been the state-of-the-art technique for NO x abatement. − V-based catalyst is a widely used commercial SCR catalyst in coal-fired power plants that has been extensively studied by researchers, and the NH 3 -SCR reaction mechanism over V-based catalyst has been well elucidated. − However, V-based catalyst suffers from poor thermal stability, narrow and high-temperature window (300–400 °C), and toxicity concerns . Especially, the high-temperature window (300–400 °C) of conventional V-based catalysts is unsuitable for flue gas from non–electric industries, such as coking, steel metallurgy, cement, ceramics, and industrial boilers, characterized by low temperatures (120–300 °C). ,− As a result, developing V-free and even metal-free SCR catalysts with excellent low-temperature activity has become crucial for the economical and efficient NO x purification.…”