Hydrothermal and sulfur aging of CeTi/CeWTi catalysts for selective catalytic reduction of NO with NH3

Engineering Co3O4@3DOM LaCoO3 multistage-pore nanoreactor with superior SO2 resistance for toluene catalytic combustion

Sulfur dioxide poisoning is a significant factor in catalyst deactivation during the catalytic combustion of volatile organic compounds. In this study, we prepared the LaCoO3 and Co3O4 composite catalysts using both the Ship-in-Bottle and Building-Bottle-Around-Ship approaches. Three-dimensionally ordered macropores (3DOM LaCoO3) were utilized as nanoreactors to protect the active sites during the catalytic combustion of toluene, preventing SO2 poisoning. Additionally, we grew ZIF-67 confined in the nanoreactor to create a multistage-pore structure. The Co3O4@3DOM LaCoO3 catalysts exhibited excellent activity in the complete catalytic oxidation of toluene. Various characterization studies confirmed the presence of a significant number of Co3+ species and an abundance of surface weak acid sites in the Co3O4@3DOM LaCoO3 catalysts, which synergistically enhanced the conversion of VOCs at low temperatures. Notably, the multistage pore structure provided a favorable reaction environment, accelerating the adsorption and diffusion of toluene and intermediates, resulting in excellent sulfur resistance of the catalysts. Moreover, XPS analysis confirmed a strong interaction between Co3O4 and LaCoO3, promoting rapid electron transfer and increasing the activation of O2-. In situ DRIFTS experiments verified that toluene mainly follows the MvK mechanism over Co3O4@3DOM LaCoO3 catalysts, indicating the following reaction pathway: toluene adsorption → benzyl alcohol → benzaldehyde → benzoate → anhydride → CO2 and H2O.

Low-Dose Element-Doped CeCrM/TiO2 (M = La, Cu, Fe, LaCu, LaFe) Catalyst for Low-Temperature NH3-SCR Process: Synergistic Effect of LaCu/LaFe

A series of CeCrM/TiO₂ (M = La, Cu, Fe, LaCu, LaFe) catalysts were prepared via impregnation method and are employed as low-temperature NH₃-SCR catalysts. The present study investigates the low-dose element doping on the TiO₂-supported catalyst to improve the NH₃-SCR performance. And CeCrLaCu/TiO₂ exhibited the best catalytic performance (NO conversion approaching 100% at 260-420 °C). The characterization results show that the synergistic effect of LaCu and LaFe on the catalytic performance was more obvious than that of Cu, Fe, and La alone. The doping of LaCu/LaFe decreased the specific surface area of the catalyst but increased the dispersion, surface acidity, and reducibility of the catalyst. Moreover, LaCu/LaFe promoted the formation of valence state distribution and oxygen vacancy content on the surface of the catalyst. There were more Ce³⁺, Cr⁶⁺, Cu⁺, and oxygen adsorbed on the surface of the CeCrLaCu/TiO₂ catalyst. H₂-TPR analysis showed that the synergistic effect of LaCu was more likely to promote the reduction of Cr and Cu and increase the reduction degree of metal oxides. However, Fe is easier to coordinate with La, thus improving the redox performance of the catalyst. Compared with CeCrLaFe/TiO₂, the ammonia adsorption capacity of CeCrLaCu/TiO₂ is better. Therefore, the synergistic effect of LaCu can promote the reaction performance of NH₃-SCR better.

Flame synthesized nanoscale catalyst (CuCeWTi) with excellent Hg0 oxidation activity and hydrothermal resistance

In view of poor hydrothermal resistance of impregnation prepared catalysts (Cu5Ce5W9Ti-I), this paper aims to enhance thermal and hydrothermal resistance of Cu/Ce based catalysts for Hg⁰ oxidation via flame synthesis technology. The result found that the flame synthesis method could form nanoscale Cu10Ce10W9Ti-F particles with smaller lattice size (8-25 nm), more stable carrier structure and more oxygen vacancies. The inter-doping and inter-substitution of Ce, Cu and Ti oxides created more oxygen vacancies (Ce³⁺) and L-sites (O^2-). Furthermore, the carrier TiO₂ of Cu10Ce10W9Ti-F existed in form of highly thermostable rutile rather than anatase. High Hg⁰ oxidation efficiency (MOE) of 83.9-99.7% at 100-450 °C proved excellent oxidation activity of Cu10Ce10W9Ti-F catalyst. Moreover, the thermal and hydrothermal treatment (700 °C) only decreased MOE by less than 5% since L-sites kept fine thermostability of Cu10Ce10W9Ti-F. The flame synthesis was proven to be a promising catalyst preparation method to enhance thermal and hydrothermal resistance.

Effect of mass ratio on micro-mesoporous Cu-SSZ-13/CeWTi composite catalysts for the selective catalytic reduction of NO with ammonia

A series of micro-mesoporous SSZ-13/CexWyTiz composites with different zeolite/oxide ratios were synthesized using a one-step crystallization method. The effects of the mass ratio on the crystal form, specific surface area, pore structure, surface element properties, redox properties, surface acidity and deNO_x performance of the Cu-SSZ-13/CeWTi composite catalysts were investigated using X-ray diffractometry (XRD), Brunauer–Emmett–Teller analysis (BET), X-ray photoelectron spectroscopy (XPS), H₂ temperature programmed reduction (H₂-TPR) and NH₃ temperature programmed desorption (NH₃-TPD). The results reveal that the Cu-SSZ-13/CeWTi composite catalysts formed a micro-mesoporous structure. The increase in the mass ratio leads to the increased microporous ratio of the composite catalysts, the improved crystal structure of SSZ-13 and a higher specific surface area and pore volume, which is conducive to enhancing the low-temperature deNO_x activity, but its high-temperature performance (450 °C and above) decreases. The introduction of micropores into mesoporous materials can result in the production of more Ce⁴⁺, surface chemisorption oxygen species O_α and acid sites. The Cu-SSZ-13/CeWTi composite catalyst with a mass ratio of 1 : 4 demonstrated the best micro-mesoporous ratio, low-temperature selective catalytic reduction (SCR) performance and hydrothermal stability.

A series of micro-mesoporous SSZ-13/CexWyTiz composites with different zeolite/oxide ratios were synthesized using a one-step crystallization method.