Selective Reduction of NO into N2 Catalyzed by the RhM2O3- Clusters (M = Ta, V, and Al): Importance of the Triatomic Lewis Acid-Base-Acid Mδ+-Rhδ--Mδ+ Site

Catalytic NO reduction by CO into N2 and CO2 is imperative owing to the increasingly rigorous emission regulation. Identifying the nature of active sites that govern the reactivity and selectivity of NO reduction is pivotal to tailor catalysts, while it is extremely challenging because of the complexity of real-life systems. Guided by our newly discovered triatomic Lewis acid-base-acid (LABA, Ceδ+-Rhδ--Ceδ+) site that accounts for the selective reduction of NO into N2 catalyzed by the RhCe2O3- cluster in gas-phase experiments, the reactivity of the RhM2O3- (M = Ta, V, and Al) clusters in catalytic NO reduction by CO was explored. We determined theoretically that the LABA site still prevails to reduce NO to N2 mediated by RhTa2O3- and RhV2O3-, and the strong M-oxygen affinity was emphasized to construct the LABA site. An overall assessment highlights that RhV2O3- functions as a more promising catalyst because the well-fitting V-O bonding strength facilitates both elementary reactions of NO reduction and CO oxidation.

Cu/HZSM-5 Sorbent Treated by NH3 Plasma for Low-Temperature Simultaneous Adsorption-Oxidation of H2S and PH3

In this study, an NH₃ plasma-treated Cu/HZSM-5 sorbent was introduced to simultaneously remove H₂S and PH₃ in low-temperature and low-oxygen environments. The effects of the Cu loading amounts, modification methods, and plasma-treatment conditions on the adsorption-oxidation performance of the sorbents were investigated. From the performance test results, the sorbent treated by NH₃ plasma with the specific energy input (SEI, electrical input energy to the unit volume of gas) value of 1 J·mL^-1 (Cu/HZSM-5-[S1]) was identified as having the highest breakthrough capacities of 108.9 mg S·g^-1 and 150.9 mg P·g^-1 among all of the materials tested. After three times of regeneration, the sorbent can still maintain the ideal performance. The results of Fourier transform infrared (FT-IR) spectroscopy and CO₂ temperature-programmed desorption (CO₂-TPD) indicated that the NH₃ plasma treatment can introduce amino groups (functional groups) onto the sorbent surface, which greatly increases the number and strength of the basic sites on the sorbent surface. Results of N₂ adsorption/desorption isotherms and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) showed that the morphology of the sorbent changed after the plasma treatment, which exposed more active sites (copper species). In situ IR spectra showed that the amino groups are continuously consumed during the reaction process, indicating that these amino groups can help sorbents to capture gas molecules. Moreover, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses indicated that CuO is the main active species and the consumption of CuO and accumulation of the reaction products on the surface and inner pores of the sorbent are the primary reasons for the deactivation of the sorbent.

Meziane K, Kaddouri A, Nguyen HP, Taoufik M. Well-defined surface tungstenocarbyne complex through the reaction of [W(CtBu)(CH2tBu)3] with CeO2: a highly stable precatalyst for NOx reduction with NH3

A highly-efficient NH₃-SCR single site catalyst W(CtBu)(CH₂tBu)₃/CeO_2–200, was prepared by surface organometallic chemistry approach. This catalyst showed high catalytic activity and stability with a broad operational temperature window.

A novel regeneration method for deactivated commercial NH3-SCR catalysts with promoted low-temperature activities

A novel route is developed for regeneration of deactivated commercial NH₃-SCR catalysts, which includes an initial in situ construction of anatase TiO₂ porous film, followed by loading of MnO_x, CeO_x, and Mn-Ce mixed oxides as active components. The regenerated catalysts present largely improved low-temperature denitrification performance due to the synergetic effect of MnO_x and CeO_x. The denitrification efficiency could reach a high value of 97% at 200 °C and 100% at 250 °C when the Ce-Mn mixed oxides are loaded at the optimized molar quantity ratio of 10:9 (Ce:Mn). Properties and reaction mechanisms of the regenerated catalysts are investigated with characterizations of X-ray photoelectron spectroscopy (XPS), NH₃ temperature-programmed desorption (NH₃-TPD), H₂ temperature-programmed reduction (H₂-TPR), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Our results demonstrate that the adsorption and oxidation of NO plays a crucial role for these three catalysts even though a difference exists on the reaction pathways. Graphical abstract.