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

Improvement of Nb Doping on SO₂ Resistance of VO_<i>x</i>/CeO₂ Catalyst for the Selective Catalytic Reduction of NO_<i>x</i> with NH₃

The influence of sulfation treatment on Nb–VO_<i>x</i>/CeO₂ and VO_<i>x</i>/CeO₂ catalysts for the selective catalytic reduction (SCR) of NO_<i>x</i> with NH₃ was fully investigated. The Nb–VO_<i>x</i>/CeO₂ catalyst showed higher catalytic activity and stronger resistance to SO₂ than VO_<i>x</i>/CeO₂. The formation of sulfates, small specific surface area, and reduction in the number of active sites were all responsible for the low catalytic activity over VO_<i>x</i>/CeO₂ after sulfation under SCR conditions. On the contrary, Nb–VO_<i>x</i>/CeO₂ adsorbed much more nitrate than sulfate when sulfated under SCR conditions and showed much higher NH₃-SCR activity than VO_<i>x</i>/CeO₂ after the same treatment. After sulfation by SO₂ + O₂ only, instead of sulfation under SCR conditions, both of the samples exhibited decreased NH₃-SCR activity, mainly due to the formation of sulfates and the blockage of the Langmuir–Hinshelwood reaction pathway

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

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

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

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

Accelerating Catalytic Oxyanion Reduction with Inert Metal Hydroxides

Adding CrIII or AlIII salts into the water suspension of platinum group metal (PGM) catalysts accelerated oxyanion pollutant reduction by up to 600%. Our initial attempts of adding K2CrVIO4, K2CrVI2O7, or KCrIII(SO4)2 into Pd/C enhanced BrO3– reduction with 1 atm H2 by 6-fold. Instrument characterizations and kinetic explorations collectively confirmed the immobilization of reduced CrVI as CrIII(OH)3 on the catalyst surface. This process altered the ζ-potentials from negative to positive, thus substantially enhancing the Langmuir–Hinshelwood adsorption equilibrium constant for BrO3– onto Pd/C by 37-fold. Adding AlIII(OH)3 from alum at pH 7 achieved similar enhancements. The Cr–Pd/C and Al–Pd/C showed top-tier efficiency of catalytic performance (normalized with Pd dosage) among all the reported Pd catalysts on conventional and nanostructured support materials. The strategy of adding inert metal hydroxides works for diverse PGMs (palladium and rhodium), substrates (BrO3– and ClO3–), and support materials (carbon, alumina, and silica). This work shows a simple, inexpensive, and effective example of enhancing catalyst activity and saving PGMs for environmental applications