Enhanced Activity of Ti-Modified V₂O₅/CeO₂ Catalyst for the Selective Catalytic Reduction of NO_<i>x</i> with NH₃

A novel V₂O₅/CeTiO_<i>x</i> catalyst showed excellent catalytic performance in the selective catalytic reduction (SCR) of NO_<i>x</i> with NH₃. The addition of Ti into V₂O₅/CeO₂ enhanced catalytic activity, N₂ selectivity, and resistance against SO₂ and H₂O. These catalysts were also characterized by N₂ adsorption, XRD, XPS, and H₂-TPR. The lower crystallinity, more reduced species, better dispersion of surface vanadium species, and more acid sites due to the modification of V₂O₅/CeO₂ with TiO₂ all improved the NH₃–SCR activity significantly. Based on <i>in situ</i> DRIFTS, it was concluded that the NH₃–SCR reaction over V₂O₅/CeTiO_<i>x</i> and V₂O₅/CeO₂ mainly followed the Eley–Rideal mechanism

Respective Role of Fe and Mn Oxide Contents for Arsenic Sorption in Iron and Manganese Binary Oxide: An X‑ray Absorption Spectroscopy Investigation

In our previous studies, a synthesized Fe–Mn binary oxide was found to be very effective for both As­(V) and As­(III) removal in aqueous phase, because As­(III) could be easily oxidized to As­(V). As­(III) oxidation and As­(V) sorption by the Fe–Mn binary oxide may also play an important role in the natural cycling of As, because of its common occurrence in the environment. In the present study, the respective role of Fe and Mn contents present in the Fe–Mn binary oxide on As­(III) removal was investigated via a direct <i>in situ</i> determination of arsenic speciation using X-ray absorption spectroscopy. X-ray absorption near edge structure results indicate that Mn atoms exist in a mixed valence state of +3 and +4 and further confirm that MnO_<i>x</i> (1.5 < <i>x</i> < 2) content is mainly responsible for oxidizing As­(III) to As­(V) through a two-step pathway [reduction of Mn­(IV) to Mn­(III) and subsequent Mn­(III) to Mn­(II)] and FeOOH content is dominant for adsorbing the formed As­(V). No significant As­(III) oxidation by pure FeOOH had been observed during its sorption, when the system was exposed to air. The extended X-ray absorption fine structure results reveal that the As surface complex on both the As­(V)- and As­(III)-treated sample surfaces is an inner-sphere bidentate binuclear corner-sharing complex with an As–M (M = Fe or Mn) interatomic distance of 3.22–3.24 Å. In addition, the MnO_<i>x</i> and FeOOH contents exist only as a mixture, and no solid solution is formed. Because of its high effectiveness, low cost, and environmental friendliness, the Fe–Mn binary oxide would play a beneficial role as both an efficient oxidant of As­(III) and a sorbent for As­(V) in drinking water treatment and environmental remediation

Supplementary_Material - Inflammatory Responses are Sex Specific in Chronic Hypoxic–Ischemic Encephalopathy

<p>Supplementary_Material for Inflammatory Responses are Sex Specific in Chronic Hypoxic–Ischemic Encephalopathy by Abdullah Al Mamun, Haifu Yu, Sharmeen Romana, and Fudong Liu in Cell Transplantation</p

The Effects of Mn²⁺ Precursors on the Structure and Ozone Decomposition Activity of Cryptomelane-Type Manganese Oxide (OMS-2) Catalysts

The effects of Mn²⁺ precursors on the structure and ozone decomposition activity of cryptomelane-type manganese oxide (OMS-2) catalysts were investigated under high-humidity conditions. The OMS-2 catalysts were synthesized using a hydrothermal approach. Characterization of OMS-2 was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ physical adsorption, Raman spectroscopy, X-ray absorption fine structure (XAFS), H₂ temperature-programmed reduction (H₂-TPR), and inductively coupled plasma (ICP) spectroscopy. The OMS-2-Ac synthesized using MnAc₂ as a Mn²⁺ precursor showed the best catalytic activity for ozone decomposition (∼80%) under RH = 90% and space velocity of 600000 h^–1 and is a promising catalyst for purifying waste gases containing ozone under high-humidity conditions. Acetate groups could prevent the aggregation of manganese oxide particles, which may introduce more crystalline defects. On the basis of the characterization results, it is supposed that the greater surface area and higher amount of Mn³⁺ are the main factors that contribute to the excellent performance of OMS-2-Ac. This study can improve our understanding of ozone decomposition on OMS-2 catalysts and serve as a guide in using OMS-2 for ozone removal

NH₃‑SCR Performance of Fresh and Hydrothermally Aged Fe-ZSM‑5 in Standard and Fast Selective Catalytic Reduction Reactions

Hydrothermal stability is one of the challenges for the practical application of Fe-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with NH₃ (NH₃-SCR) for diesel engines. The presence of NO₂ in the exhaust gases can enhance the deNOx activity because of the fast SCR reaction. In this work, a Fe-ZSM-5 catalyst was prepared by a solid-state ion-exchange method and was hydrothermally deactivated at 800 °C in the presence of 10% H₂O. The activity of fresh and hydrothermal aged Fe-ZSM-5 catalysts was investigated in standard SCR (NO₂/NO<i>x</i> = 0) and in fast SCR with NO₂/NO<i>x</i> = 0.3 and 0.5. In standard SCR, hydrothermal aging of Fe-ZSM-5 resulted in a significant decrease of low-temperature activity and a slight increase in high-temperature activity. In fast SCR, NO<i>x</i> conversion over aged Fe-ZSM-5 was significantly increased but was still lower than that over fresh catalyst. Additionally, production of N₂O in fast SCR was much more apparent over aged Fe-ZSM-5 than over fresh catalyst. We propose that, in fast SCR, the rate of key reactions related to NO is slower over aged Fe-ZSM-5 than over fresh catalyst, thus increasing the probabilities of side reactions involving the formation of N₂O

Engineering a PtCu Alloy to Improve N₂ Selectivity of NH₃–SCO over the Pt/SSZ-13 Catalyst

Improving the N2 selectivity is always a great challenge for the selective catalytic oxidation of ammonia (NH3–SCO) over noble-metal-based (especially Pt) catalysts. In this work, Cu as an efficient promoter was introduced into the Pt/SSZ-13 catalyst to significantly improve the N2 selectivity of the NH3–SCO reaction. A PtCu alloy was formed in the PtCu/SSZ-13 catalyst, as confirmed by X-ray diffraction, transmission electron microscopy, energy dispersive spectrometry mapping, and X-ray absorption spectroscopy results. As indicated by the X-ray photoelectron spectroscopy analysis, the Pt species in the alloyed PtCu nanoparticle was mainly present in the electron-rich state on PtCu/SSZ-13, while the electron-deficient Cu and isolated Cu2+ species were both present on the surface of PtCu/SSZ-13. Due to such a unique alloyed structure with an altered oxidation state, the N2 selectivity of NH3–SCO on the PtCu/SSZ-13 catalyst was remarkably improved, while the NH3–SCO activity was kept comparable to that on Pt/SSZ-13. The reaction path was changed from the NH mechanism on Pt/SSZ-13 to both NH and internal selective catalytic reduction mechanisms on the PtCu/SSZ-13 catalyst, which was considered the main reason for the enhanced N2 selectivity. This work provides a new route to synthesize efficient alloy catalysts for optimizing the N2 selectivity of NH3–SCO for NH3 slip control in diesel exhaust purification

Nature of Ag Species on Ag/γ-Al₂O₃: A Combined Experimental and Theoretical Study

The nature of silver species on Ag/Al₂O₃ catalysts with different silver loadings was studied by photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS) combined with theoretical calculation (DFT). On the basis of selective catalytic reduction of NO_<i>x</i> by ethanol experiments, it was found that the optimum silver content varies from 1 wt % to 2 wt %. The supported silver species are predominated by +1 oxidation state ions attached to surface oxygen atoms (Ag–O) under low silver loading of 2 wt %, which play a crucial role during the HC-SCR process. An Ag–Ag shell emerged clearly in analysis of EXAFS data when silver loading was increased to 2 wt %, which was beneficial for low-temperature activity. The theoretical models for Ag_n^δ+ species (1 ≤ <i>n</i> ≤ 4, both ions and oxidized silver clusters) on alumina were consistent with the coordination structure analysis by EXAFS. The predominant silver ions are most likely stabilized at isolated tetrahedral Al sites (Ag–O–Al_IVb) on the γ-Al₂O₃ (110) surface. However, the most reactive silver ion seems to be anchored on a tricoordinate Al_III site (Ag–O–Al_III). Density of states analysis revealed that the Ag–O–Al_III entity might be a very active silver species in terms of the hybridization of Ag, O, and Al orbitals to promote its catalytic activity

Significant Promotion Effect of Mo Additive on a Novel Ce–Zr Mixed Oxide Catalyst for the Selective Catalytic Reduction of NO_<i>x</i> with NH₃

A novel Mo-promoted Ce–Zr mixed oxide catalyst prepared by a homogeneous precipitation method was used for the selective catalytic reduction (SCR) of NO_<i>x</i> with NH₃. The optimal catalyst showed high NH₃-SCR activity, SO₂/H₂O durability, and thermal stability under test conditions. The addition of Mo inhibited growth of the CeO₂ particle size, improved the redox ability, and increased the amount of surface acidity, especially the Lewis acidity, all of which were favorable for the excellent NH₃-SCR performance. It is believed that the catalyst is promising for the removal of NO_<i>x</i> from diesel engine exhaust

Excellent Performance of One-Pot Synthesized Cu-SSZ-13 Catalyst for the Selective Catalytic Reduction of NO_<i>x</i> with NH₃

Cu-SSZ-13 samples prepared by a novel one-pot synthesis method achieved excellent NH₃–SCR performance and high N₂ selectivity from 150 to 550 °C after ion exchange treatments. The selected Cu_3.8-SSZ-13 catalyst was highly resistant to large space velocity (800 000 h^–1) and also maintained high NO_<i>x</i> conversion in the presence of CO₂, H₂O, and C₃H₆ in the simulated diesel exhaust. Isolated Cu²⁺ ions located in three different sites were responsible for its excellent NH₃–SCR activity. Primary results suggest that the one-pot synthesized Cu-SSZ-13 catalyst is a promising candidate as an NH₃–SCR catalyst for the NO_<i>x</i> abatement from diesel vehicles