Application Prospect of K Used for Catalytic Removal of NOx, COx, and VOCs from Industrial Flue Gas: A Review

Highly Enhanced Photocatalytic NO Removal and Inhibited Peroxyacetyl Nitrate Formation in Synergistic Acetaldehyde Degradation

The coexistence of NO and CH3CHO in the air is considered to produce secondary peroxyacetyl nitrate (PAN) under sunlight irradiation, threatening the ecological environment and public health. Herein, we provide a simple strategy for the photocatalytic removal of NO and acetaldehyde (CH3CHO) on Sr2Sb2O7. In comparison with the single removal, the nearly complete removal of NO is reached by deep oxidation to NO3- with the assistance of CH3CHO. The underlying mechanism is revealed by GC-MS, in situ DRIFTS, and density functional theory calculations. The intermediates •CH3 from CH3CHO and NO2- from NO tend to bond and further oxidize to CH3ONO2, thus promoting NO removal. CH3NO2 and CH3ONO2 are the key products instead of PAN on Sr2Sb2O7 from the synergistic degradation of NO and CH3CHO. This work brings new insights into reaction pathway regulation for promoting performance and suppressing byproducts during synergistic air pollutant removal.

Effect of Hydroxyl Groups on Metal Anchoring and Formaldehyde Oxidation Performance of Pt/Al2O3

Pt/Al₂O₃ catalysts showing excellent activity and stability have been used in various reactions, including HCHO oxidation. Herein, we prepared Pt-Na/Al₂O₃ catalysts with a Pt content of 0.05 wt % to reveal the key factors determining the anchoring of Pt as well as the catalytic activity and mechanism of HCHO oxidation. Pt-Na/nano-Al₂O₃ (denoted as Pt-Na/nAl₂O₃) catalysts with 0.05 wt % Pt content could completely oxidize HCHO to CO₂ at room temperature, which is the lowest Pt content used in HCHO catalytic oxidation to our knowledge. After Na addition, terminal hydroxyl groups (denoted as HO-μ_ter) on nano-Al₂O₃ were transformed to doubly bridging hydroxyl groups between Na and Al (denoted as HO-μ_bri(Na-Al)), which atomically dispersed Pt species. Pt anchoring further promoted the regeneration of HO-μ_bri(Na-Al) by activating O₂ and H₂O, oxidizing HCHO to CO₂ directly by the fast reaction step ([HCOO^-] + [OH]_a → CO₂ + H₂O). Our study revealed that the HO-μ_bri(Na-Al) synergistically generated by HO-μ_ter and Na species provided anchoring sites for Pt species.

Achieving acetone efficient deep decomposition by strengthening reactants adsorption and activation over difunctional Au(OH)Kx/hierarchical MFI catalyst

Realizing the simultaneous adsorption and activation of O₂ and reactants over supported noble metal catalysts is crucial for the oxidation of organic hydrocarbons. Herein, we report a facile one-step ethylene glycol reduction method to synthesize difunctional Au(OH)K_x sites, which were anchored on a hierarchical hollow MFI support and adopted for acetone decomposition. The alkali ion-associated adjacent surface hydroxyl groups were coordinated with Au nanoparticles, resulting in partially oxidized Au¹⁺ sites with improved dispersion. The results obtained from exclusive ex situ and in situ experiments illustrated that the proper content of K and hydroxyl groups significantly enhanced the adsorption of surface O₂ and acetone molecules around the Au sites simultaneously, whereas the excess K species inhibited the catalytic performance by blocking the pore structure and decreasing the acidity of catalysts. The Au(OH)K_0.7/h-MFI catalyst exhibited the highest efficiency for acetone oxidation, over which 1500 ppm acetone can be completely oxidized at just 280 °C with an extremely low activation energy of 32.5 kJ mol^-1. The carbonate species were detected as the main intermediates during acetone decomposition over the difunctional Au(OH)K_x sites through a Langmuir - Hinshelwood (L - H) mechanism. This finding paves the way for designing and constructing efficient functional active sites for the complete oxidation of hydrocarbons.

Enhanced activity and sulfur resistance of Cu- and Fe-modified activated carbon for the reduction of NO by CO from regeneration gas

The reduction of NO by CO was proposed to be applied for regeneration gas to remove NOx from industrial flue gas with activated carbon purification technology.

The mechanism of alkali promoting water splitting on g-C3N4

Alkali promotes H+ to obtain electrons and turn into H2.

Activity of Ag/CeZrO2, Ag+K/CeZrO2, and Ag-Au+K/CeZrO2 Systems for Lean Burn Exhaust Clean-Up

Herein, the activity of Ag and bimetallic Au-Ag catalysts, supported over Ce0.85Zr0.15O2 (CZ), was investigated in a complex stream, whose components included CO, C3H8, NO, O2, and, optionally, an injection of water vapor. In such a stream, three of the possible reactions that can occur are CO oxidation, propane combustion, and NO oxidation. The aim of these studies was to explore whether silver, due to its strong affinity to oxygen, will counteract the stabilization of oxygen by potassium. The effect of the presence of potassium ions on the activity of the monometallic silver catalysts is beneficial in the complex stream without water vapor in all three studied reactions, although it is negligible in the model CO stream. It has been shown that water vapor strongly suppresses the activity of the Ag+K/CZ catalyst, much more so than that of the Ag/CZ catalyst. The second purpose of the work was to determine whether the negative effect of potassium ions on the activity of nanogold catalyst can be countered by the addition of silver. Studies in a model stream for CO oxidation have shown that, for a catalyst preloaded with gold, the effect of potassium is nulled by silver, and the activity of AuAg + 0.15 at%K/CZ and AuAg + 0.30 at%K/CZ is the same as that of the monometallic Au catalyst. Conversely, when the reaction is carried out in a complex stream, containing CO, C3H8, NO, O2, and water vapor, the presence of water vapor leads to higher CO conversion as well as increased NO2 formation and slightly suppresses the C3H8 combustion.

A highly active Ca/Cu/YCeO2–TiO2 catalyst for the transient reduction of NO with CO and naphthalene under oxidizing conditions

The transient combustion of biomass leads to the evolution of a variety of pollutants (NO, CO, organic compounds, and many others) that can react with each other on a suitable catalyst to generate compounds of lower toxicity. Here, the transient reduction of NO with CO and naphthalene in the presence of oxygen was studied on a Ca/Cu/YCeO₂–TiO₂ catalyst. Response surface methodology was used to identify the optimum amounts of calcium, copper, and cerium. The optimized Ca/Cu/YCeO₂–TiO₂ catalyst was then extensively studied and characterized. The coupling of yttrium-stabilized ceria with TiO₂ provided an active support that effectively activated naphthalene. When calcium and copper were added to the support, the obtained Ca/Cu/YCeO₂–TiO₂ catalyst achieved the full conversion of CO and naphthalene and 72% conversion of NO. The Ca/Cu/YCeO₂–TiO₂ catalyst possessed labile oxygen species, which might be related to the high catalytic activity.

A highly-active Ca/Cu/YCeO₂–TiO₂ catalyst shows full conversion of CO and naphthalene and 72% conversion of NO under oxygen.