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

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 N-2 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 NOx to N-2 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.

Automated summary

In this study, advanced spectroscopic and computational techniques were used to investigate the surface structure and reaction mechanism of tricomponent cerium-tungsten-titanium catalysts. The introduction of graphene oxide improved the dispersion of W and Ce species and resulted in specific bonding structures. The high dispersion of Ce facilitated the generation of oxygen vacancies, enhancing the adsorption and activation of NO and NH3. Experimental and theoretical evidence supported the feasibility of adsorption at low temperatures and revealed the reaction intermediates and interactions. The findings are important for understanding catalyst performance and developing new catalysts.