Abundant Surface Oxygen Species Research Articles

Easy-regeneration Mn-doped ZIF-67 derivate adsorbent with ultra-high adsorption capacity for tetracycline hydrochloride in wastewater

Adsorption capacity and reusability are critical to the practical applications of metal–organic framework (MOF)-based adsorbents. In this work, an easy-regeneration ZIF-67 derivate adsorbent (Mn-ZIF-400) was synthesized by calcining the manganese-modified MOF ZIF-67 (Mn-ZIF-67) precursor at 400 °C in air for the first time. Mn-ZIF-400 reveals an ultra-high adsorption capacity for tetracycline hydrochloride (TCH) (qmax = 1191.5 mg⋅g−1 at 308 K at pH = 4) in a wide pH range (pH = 3–10) owing to its great surface area (816.2 m2⋅g−1), surface polyvalent metal ions (Co2+/Co3+, Mn2+/ Mn 3+/ Mn4+), abundant surface oxygen species (including –COOH, –OH etc.) and π-electrons from benzene-ring. The adsorption mechanism of TCH on Mn-ZIF-400 belongs to the monolayer chemisorption mainly by π-π conjugation/π-cation interactions, hydrogen/coordination bonding, and pore filling. It also can maintain high adsorption performance in an actual aqueous environment. More importantly, Mn-ZIF-400 showed enhanced water stability and reusability after modification and no obvious loss in adsorption capacity in four recycles via simple water washing, being a promising adsorbent for antibiotic elimination.

Ozone catalytic oxidation of toluene over triple perovskite-type catalysts modified with KMnO4.

A unique triple perovskite-type catalyst was successfully synthesized using the simple sol-gel approach, and surface acid modification was added to improve the ozone catalytic oxidation (OZCO) process ability to remove toluene more effectively. Our study indicates that La3MnCuNiO9 catalyst treated with KMnO4 shows the best toluene oxidation activity. At 250 °C, the rates of conversion and mineralization were 100% and 83%, respectively, under thermal catalytic system when C7H8 concentration = 500 ppm. During the OZCO system ([C7H8] = 20 ppm, O3/C7H8=8; room temperature), for 6 h, the conversion rate remained at 100%. The high ratios of Mn4+/(Mn4++Mn3+), Cu2+, and abundant surface oxygen species, high specific surface area, and pore volume lead to remarkable catalytic performance of this catalyst. Meanwhile, the catalyst contributes to superior stability and water resistance. The catalytic mechanism of La3MnCuNiO9 after KMnO4 treatment in the context of OZCO was further discussed. Overall, after KMnO4 treatment, the La3MnCuNiO9 catalyst reveals extraordinary catalytic activity and excellent stability combination of this catalyst with ozone exhibits high toluene removal efficiency in the OZCO system and has a good potential for industrial applications.

Synergically regulated silver species and surface oxygen on manganese oxide for promoted activity of formaldehyde oxidation

Formaldehyde (HCHO) is a common indoor pollutant that is detrimental to human health. Its efficient removal has become an urgent demand to reduce the public health risk. In this work, Ag-MnOx-based catalysts were prepared and activated under different atmosphere (i.e., air, hydrogen (H2) and carbon monoxide (CO)) for efficient oxidation of HCHO. The catalyst activated with CO (Ag/Mn-CO) displayed the highest activity among the tested samples with 90% conversion at 100°C under a gas space velocity of 75,000 mL/(gcat·hr). Complementary characterizations demonstrate that CO reduction treatment resulted in synergically regulated content of surface oxygen on support to adsorb/activate HCHO and size of Ag particle to dissociate oxygen to oxidize the adsorbed HCHO. In contrast, other catalysts lack for either abundant surface oxygen species or metallic silver with the appropriate particle size, so that the integrate activity is limited by one specific reaction step. This study contributes to elucidating the mechanisms regulating the oxidation activity of Ag-based catalysts.

Improved catalytic oxidation of propane over phosphate-modified Pd/Al2O3-TiO2 catalyst

Al-Ti oxides supported noble-metal catalysts were prepared by combining the mechanical ball-milling method and incipient wetness impregnation method, in which the Al-Ti mixed oxides were etched by various concentrations of phosphoric acid for improving the performance of propane oxidation. Phosphate-modified Pd/Al2O3-TiO2 catalyst with Al/P ratios of 3:1 showed high catalytic activity that more than 90 % C3H8 was converted completely at 380 °C and GHSV of 100000 h−1, with 5 vol% H2O and 10 vol% CO2. Characterization results revealed that the mixing of Al2O3 and TiO2 provided a high specific surface area and excellent pore structure, while the modification of phosphate supplied a stronger interaction between Pd species and supporter which is favorable to their dispersion and enhancing the catalytic stability in the tough conditions. The H2-TPR and O2-TPD results suggested that marked brilliant redox ability and abundant surface oxygen species of phosphate-modified Pd/Al2O3-TiO2 catalysts are beneficial to the activation of O2 and the increase of catalytic activity. Moreover, the XPS spectra indicated that phosphate induced some electromigration and made the content of Pd0 and Pd2+ in an appropriate ratio which enable the Pd species to display brilliant ability in supplying active oxygen species and breaking the C-H bond, which improved the C3H8 catalytic activity of noble-metal catalyst greatly.

Mechanistic assessment of NO oxidative activation on tungsten-promoted ceria catalysts and its consequence for low-temperature NH3-SCR

Ceria has absorbed extensive interests in functioning as catalysts for low-temperature (LT) selective catalytic reduction (SCR) of NOx due to its abundant surface oxygen species and salient redox property. The mechanistic interpretations of how such redox property contributes to its LT-SCR activity, however, still remain debated. Here, we use a model tungsten-promoted ceria catalyst (WO3/CeO2), known as preeminent in LT-SCR reactions, and combine steady-state kinetic, structural characteristic and in situ spectroscopic experiments with theoretical treatments to reveal the mechanistic connections between NO oxidative activation and LT-SCR turnovers. We show that, compared with NO oxidation to NO2, NO oxidative activation to nitrite intermediates is both kinetically and thermodynamically more favorable; surface nitrate species are not detected in the present case, indicating their more difficult formation than nitrites. All these results thus suggest the prevalence of NO activation to nitrites over NO to nitrates or oxidation to NO2 and subsequent occurrence of fast SCR in the WO3/CeO2-catalyzed LT-SCR reaction. These findings progress the understanding of LT-SCR reaction mechanism on CeO2-based catalysts and convey a detailed perspective of different reaction intermediates and their consequences for LT-SCR turnovers, which may contribute to the rational design of catalysts towards further improved LT-SCR activity.

Highly ordered mesoporous MnOx catalyst for the NH3-SCR of NOx at low temperatures

MnOx catalysts with 3D structure (Mn-HT) were prepared by the hard-template method using KIT-6 as a template, and the catalytic performance for the selective catalytic reduction of NOx by NH3 (NH3-SCR) at low temperatures was investigated. The template KIT-6 prepared by the different hydrothermal temperatures can exert significant effect on the catalytic performance of Mn-HT catalysts. Among the Mn-HT catalyst, the catalyst prepared using the template obtained at the hydrothermal temperature of 140 °C (Mn-140) exhibited the highest catalytic performance. Characterizations showed that Mn-140 catalyst possesses high reducibility with abundant surface oxygen species and Mn4+ species. NH3-TPD and in situ DRIFTS demonstrated that there are more Lewis acid sites and Brønsted acid sites on the surface of Mn-140 catalyst, both of which would promote the adsorption and activation of NH3, leading to the reduction of NOx efficiently to proceed mainly by the Eley-Rideal(E-R) mechanism, accompanied by the Langmuir-Hinshelwood (L-H) mechanism.

Novel synthesis of reed flower-like SmMnOx catalyst with enhanced low-temperature activity and SO2 resistance for NH3-SCR

In this work, a novel co-precipitation coupled solvothermal procedure is proposed to prepare a SmMnOx catalyst (SmMnOx-CP + ST) with a reed flower-like structure for the selective catalytic reduction of NOx by NH3 (NH3-SCR). Over 90% NOx conversion and N2 selectivity was achieved at a low temperature range (25–200 °C), and 96% NOx conversion was achieved in the presence of 100 ppm SO2 at 75 °C. While the NH3-SCR of the SmMnOx catalysts prepared by co-precipitation (SmMnOx-CP) and solvothermal (SmMnOx-ST) methods performed much poorer than the SmMnOx-CP + ST catalyst. All catalysts were characterized by XRD, BET, SEM, XPS, H2-TPR, NH3-TPD, NOx-TPD, and FT-IR. The results revealed that the superior performance of the SmMnOx-CP + ST is due to the unique reed flower-like structure morphology, which endows the SmMnOx-CP + ST with the largest surface area, the strongest synergistic reaction of Sm and Mn, abundant surface oxygen species and surface active sites, and significantly enhances the redox ability. Furthermore, the amorphous reed flower-like structure showed strong short-range ordered interaction between the active components and weaken the formation of sulfates species. In addition, the highest content of Mn4+ and Mn3++Mn4+ greatly promotes the redox cycles of Sm2+↔Mn4+ and Sm2+↔Mn3+, and suppresses the production of sulfate species in the presence of SO2.

Exposed crystal facet tuning of CeO2 for boosting catalytic soot combustion: The effect of La dopant

The exposed crystal facets are crucial to heterogeneous catalysis. Herein, the facet controlled Ce1−xLaxOδ (0 ≤ x ≤ 0.30) nanocomposites have been constructed elaborately via a hydrothermal route and used for soot abatement. The catalysts were characterized by XRD, TEM, Raman, FT-IR, XPS, H2-TPR, and so forth. With the increasing content of La3+, part of CeO2 crystals transformed from nanocubes to nanorods, inducing distinct effects on the catalytic activity. When the concentration of La3+ was lower than 10 %, the exposed facet in the catalyst was (200). After La3+ were further introduced, the facet degraded to (111). La3+ at low concentration would enhance activity by facilitating lattice oxygen delivery and inducing abundant surface oxygen species, especially O-, which were vital to surface sensitive soot oxidation. Nevertheless, excessive La3+ ions would inhibit CO2 desorption due to the generation of La2O2CO3, a strong alkali as a result of phase separation. Among all the catalysts, Ce0.95La0.05Oδ showed the best catalytic performances for soot combustion, with T50 of 375 °C.

Modification of manganese oxides for enhancing ozone catalytic decomposition under moist conditions

Mn-based catalysts modified by copper, alumina and/or rGOs were synthesized by a simple coprecipitation method to decompose ozone under high humidity conditions, and their intrinsic mechanisms of ozone decomposition were investigated deeply. Hereinto, Mn-based catalysts doped by Cu-Al and Cu-Al-rGOs exhibited excellent activity and durability, maintaining above 94% and 98% ozone conversion for nearly 40 h under 85% RH and GHSV of 300 L·g−1·h−1 at 25 °C. The characterization results showed that the Cu dopants enhance the reducibility and regeneration speed owing to the formation of CuMn2O4 solid solutions, and the additions of Al and rGO significantly increase the amount of surface and sub-surface lattice oxygen, promoting effectually catalytic performances. XPS results revealed that the abundant surface oxygen species with high reactivity and stability were generated from the sites associated with Cu–O, Al–O bonds, and large amounts of Mn2+/Mn3+ in Mn-based catalysts modified by Cu, Al and GOs.

Catalytic ozonation of dichloromethane at low temperature and even room temperature on Mn-loaded catalysts.

Five Mn-loaded catalysts were synthesized on γ-Al2O3, TiO2, ZrO2, nano γ-Al2O3 and nanoZrO2 supports. The catalytic ozonation of DCM (dichloromethane) was evaluated under industrial conditions (i.e., temperature, O3 input, H2O and SO2 content). According to results, >90% DCM conversion without O3 residue was achieved for all samples at 120 °C and an O3/DCM ratio of 6. At 20-120 °C, the highest Mn3+ content, abundant surface oxygen species and more weak acid sites led to the best performance of Mn/nanoAl2O3 (M/A-II). At 20 °C and 120 °C, 80% and 95% DCM can be degraded respectively on M/A-II at 20 °C with matched surface oxygen species and acidity. An O3/DCM ratio of 6 was optimal for performance and economy. For the effects of complex exhaust, both H2O and SO2 deactivated M/A-II. The H2O-induced deactivation was recoverable and also removed surface-deposited chlorine-containing species, enhancing the HCl selectivity. Finally, the Cl equilibrium of the reaction was comprehensively analyzed.

Small-sized biomass-derived hydrothermal carbon with enriched oxygen groups quickens benzene hydroxylation to phenol with dioxygen

Metal-free carbon materials have attracted growing attention in terms of green and sustainable catalysis processes that could avoid potential metal leaching but usually suffered from inferior activity to metal-loaded counterparts. In this work, we constructed an efficient carbon catalyst via hydrothermal carbonization of biomass-derived feedstock glucose under relatively low temperature (180 °C). The resultant carbon material possessing abundant surface oxygen species effectively catalyzed the benzene hydroxylation with dioxygen (O2), a desirable but very difficult alternative process for producing the important bulk chemical phenol. A considerably high phenol yield of 13.1% was achieved within 4 h, a reaction time much shorter than all the previous metal-free catalysts and even shorter than most efficient metal-based catalysts. The fast reaction is determined by the formation of small-sized primary carbon particles with the abundant surface oxygen species, for which the adsorption enhancing effect in the media of this heterogeneous process was experimentally evidenced.

Surface Lattice Oxygen Activation by Nitrogen-Doped Manganese Dioxide as an Effective and Longevous Catalyst for Indoor HCHO Decomposition.

Oxygen vacancy plays an important role in catalytic oxidation of formaldehyde (HCHO), but the inherent drawback of its thermodynamic instability causes the deactivation of catalysts. Hence, improving the thermodynamic stability of oxygen vacancy is a crux during HCHO oxidation. Here, a novel and simple nitrogen doping of MnO2/C catalyst is designed for HCHO oxidation at room temperature. The surface lattice oxygen of MnO2 will be activated by nitrogen-doping, which acts as active sites for HCHO oxidation and solves the thermodynamic instability issue of oxygen vacancy. Furthermore, carbon is doped with nitrogen to promote electron transfer and accelerate the HCHO oxidation process. Therefore, the catalytic activity and stability of the catalyst can be significantly promoted, which can completely remove ∼1 ppm HCHO in the tank within 3 h, and remains highly active after 5 cycles at room temperature (RH = 55%). In addition, the excellent removal performance over the prepared catalyst is also attributed to abundant surface oxygen species, amorphous crystallinity, and low reduction temperature. In situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) and density functional theory (DFT) calculations reveal the reaction mechanism of HCHO. This strategy provides crucial enlightenment for designing novel Mn-based catalysts for application in the HCHO oxidation field.

In-situ atmosphere thermal pyrolysis of spindle-like Ce(OH)CO3 to fabricate Pt/CeO2 catalysts: Enhancing Pt–O–Ce bond intensity and boosting toluene degradation

In this work, a series of spindle-like CeO2 supports with different contents of surface oxygen vacancies were fabricated by an in-situ atmosphere thermal pyrolysis method. Due to the unique surface physicochemical properties of the modified CeO2 supports, the interaction between Pt and CeO2 can be regulated during the synthesis of the Pt/CeO2 catalyst. The abundant oxygen vacancies on the CeO2 support could preferentially trap Pt2+ ions in solution during the Pt impregnation process and enhance the Pt–CeO2 interaction in the subsequent reduction process, which results in the strongest Pt–O–Ce bonds formed on the PCH catalysts successfully (0.6% Pt loading on the CH support, which generated by thermal pyrolysis of Ce(OH)CO3 under H2 atmosphere). The strong Pt–O–Ce bond would trigger abundant surface oxygen species generated and enhanced the lattice oxygen species transfer from CeO2 supports to Pt nanoparticles. It was crucial to boosting the toluene catalytic activity. Therefore, the PCH catalyst exhibits the highest activity for toluene oxidation (T10 = 120 °C, T50 = 138 °C, and T90 = 150 °C with WHSV = 60,000 mL g−1 h−1) and remarkable durability and water resistance among all catalysts. We also conclude that the Pt–O–Ce bond may be the active site for toluene oxidation by calculating the turnover frequencies (TOFPt-O-Ce) value for all Pt/CeO2 catalysts. Moreover, the DFT calculation indicates that the Pt/CeO2 catalyst with a strong Pt–O–Ce bond possesses the lowest oxygen absorption energy and higher CO tolerance ability, which leads to excellent catalytic performance for toluene and CO catalytic oxidation.

Catalytic Combustion of Propane over MnNbOx Composite Oxides: The Promotional Role of Niobium

Metal-doping is an efficient strategy to develop high-activity composite metal oxides catalysts for VOCs abatement. Herein, MnNbOₓ composite oxides were prepared using niobium element as a modification additive, finding that niobium addition presented a promotional effect on boosting the catalytic activity of MnOₓ for propane combustion. It was demonstrated that niobium insertion into manganese oxides was in favor of the formation of Mn₃O₄ crystalline phase and concurrently caused higher redox ability, more abundant surface oxygen species, and acid sites. All these properties were considered to be crucial parameters for catalytic activity enhancement. Among all, the catalyst of Mn₀.₈₅Nb₀.₁₅Oₓ (simply designated as M₀.₈₅N₀.₁₅) showed the highest propane conversion efficiency and relatively good catalytic durability under CO₂-containing atmospheres. Moreover, the in situ DRIFTs analysis highlighted the important role of surface acidity in the surface catalytic pathways of propane adsorption, activation, and oxidation.

Simultaneous removal of NO and dichloromethane (CH2Cl2) over Nb-loaded cerium nanotubes catalyst

Herein, a series of niobium oxide supported cerium nanotubes (CeNTs) catalysts with different loading amount of Nb2O5 (0–10 wt.%) were prepared and used for selective catalytic reduction of NOx with NH3 (NH3-SCR) in the presence of CH2Cl2. Commercial V2O5-WO3-TiO2 catalyst was also prepared for comparison. The physcial properties and chemical properties of the Nb2O5 loaded cerium nanotubes catalysts were investigated by X-ray diffractometer, Transmission electron microscope, Brunauer-Emmett-Teller specific surface area, H2-temperature programmed reduction, NH3-temperature programmed desorption and X-ray photoelectron spectroscopy. The experiment results showed that the loading amount of Nb2O5 had a significant effect on the catalytic performance of the catalysts. 10 wt.% Nb-CeNTs catalyst presented the best NH3-SCR performance and degradation efficiency of CH2Cl2 among the prepared catalysts, due to its superior redox capability, abundant surface oxygen species and acid sites, the interaction between Nb and Ce, higher ratio of Nb4+/(Nb5++ Nb4+) and Ce3+/(Ce3+ + Ce4+), as well as the special tubular structure of cerium nanotube. This study may provide a practical approach for the design and synthesis of SCR catalysts for the simultaneously removal NOx and chlorinated volatile organic compounds (CVOCs) emitted from the stationary industrial sources.

Synthesis of manganese ore/Co3O4 composites by sol–gel method for the catalytic oxidation of gaseous chlorobenzene

Manganese ore/cobalt oxide composites were synthesized by using natural manganese ore and Co(NO3)2·6H2O via oxalic acid-assisted sol–gel method and applied in the catalytic oxidation degradation of gaseous chlorobenzene. The catalytic properties of the manganese ore/Co3O4 composites were investigated by X-ray diffraction (XRD), the electron microscopy technique (FE-SEM), N2 adsorption–desorption (BET), X-ray photoelectron spectroscopy (XPS) and H2-temperature programmed reduction (H2-TPR), respectively. The results showed that the composite catalyst with the mass ratio of manganese ore/cobalt oxide was 0.4 and calcined at 450 °C had the optimal catalytic performance. It could achieve 94% conversion of chlorobenzene, 83% selectivity of CO2 and over 36 h sustainability at 300 °C for the gaseous chlorobenzene with the initial concentration of 1200 mg m−3. The composite catalyst had the abundant surface oxygen species, good anti-chlorine poisoning performance and strong redox properties of composites, which were due to the interaction between manganese ore and Co3O4, and played a key role in degradation of chlorobenzene.

Facile homogeneous precipitation method to prepare MnO2 with high performance in catalytic oxidation of ethyl acetate

Altering the urea decomposition rate in the homogeneous precipitation progress enabled the formation of various morphologies of α-MnO 2 . The decrease in crystalline size led to an increase in the surface area and dominance of the (2 1 1) crystal plane. The abundant surface oxygen species and high reducibility related to unsaturated manganese played critical roles in the decomposition of ethyl acetate. • A facile method driven by a synchronous reaction of urea hydrolysis and potassium permanganate reduction was proposed. • Pure α-MnO 2 with various morphologies was obtained by tuning reaction parameters. • Oxygen species on the (2 1 1) crystal plane were found to be most active in oxidation. • The optimal α-MnO 2 catalyst exhibited high and stable catalytic performance. A facile homogeneous precipitation method driven by synchronous reactions of urea hydrolysis and potassium permanganate reduction is proposed for preparation of MnO 2 catalysts. Pure α-MnO 2 nanostructures with different morphologies, including nanowires, nanorods and nanoparticles, were obtained by simply tuning the precipitation conditions. The evolution of materials derived from different preparation conditions was investigated via X-ray diffraction, transmission electron microscopy, N 2 adsorption, X-ray photoelectron spectroscopy, chemisorption and DFT calculations. The precipitation temperature and time significantly influenced the physiochemical properties of as-prepared catalysts. With increasing precipitation temperature and time, the degree of crystallinity, BET surface area and amount of surface-adsorbed oxygen of α-MnO 2 exhibited a substantial increase. The main exposed surface facets varied from (2 0 0), (3 1 0) to (2 1 1) as temperature and time increased. The best precipitation temperature and time were 90 °C and 24 h respectively. The optimal α-MnO 2 catalyst demonstrated 100% conversion of 1000 ppm ethyl acetate under the high space velocity of 78,000 h −1 during a 113-h test at 190 °C, outperforming other manganese oxide catalysts and many typical noble metal catalysts in terms of activity and stability. Experimental results and DFT calculations were consistent and indicated that surface oxygen species originating from the (2 1 1) surface of α-MnO 2 were most active. This study provides important insights for manipulating the morphology of MnO 2 by a facile method and remarkably promoting the performance for ethyl acetate VOC elimination.

Enhanced Catalytic Oxidation of Toluene over Manganese Oxide Modified by Lanthanum with a Coral-Like Hierarchical Structure Nanosphere.

Coral-like lanthanum manganese oxides (LayMnOx) with a hierarchical structure nanosphere were successfully prepared using a simple method, which presented a high-efficiency catalytic performance for toluene combustion. Among them, La0.08MnOx with the Mn3O4 phase exhibits superior catalytic activity, such as a lower T95 value (218 °C), excellent H2O resistance, and catalytic stability. The effects of La addition on the bulk and surface physicochemical properties of LayMnOx were investigated by sorts of characterization including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, temperature-programmed reduction with H2, temperature-programmed desorption of O2, X-ray photoelectron spectroscopy, and so forth. The results demonstrate that the doping of La can induce the variation of physicochemical properties and the formation of more surface oxygen species and high valence state amorphous manganese oxides, improving low-temperature reducibility, which facilitates good catalytic activity for La0.08MnOx. A series of in situ diffuse reflectance infrared Fourier transform spectroscopy experiments for toluene adsorption were performed on the La0.08MnOx catalyst pretreated under different atmosphere conditions to investigate the role of oxygen species and the reaction processes. The results indicate that the abundant surface oxygen species over La0.08MnOx can make the rapid formation of benzoic acid species, further transfer into CO2 and H2O, which is considered as the key factor in the activation and oxidation of toluene.

Self-standing 3D nanoporous Ag2Al with abundant surface oxygen species facilitating oxygen electroreduction for efficient hybrid Zn battery

The hybrid battery integrating a typical Zn redox battery and a Zn-air battery is a promising green technology for energy storage, and the cathode integrating the redox reaction and electrocatalytic oxygen reduction is a key point for efficient electrochemical energy conversion. Herein, we report a scalable strategy to fabricate nanoporous Ag2Al intermetallic compound as a self-standing cathode for the hybrid Zn battery. The abundant surface oxygen species, the Ag-Al intermetallic interaction and the np-Ag2[email protected]x interface cooperatively contributed to the catalytic ORR activity. The electrode endows efficient catalytic oxygen reduction (a Tafel slope of 38.0 mV/dec and an onset potential of 0.998 V) and regulated redox activity as compared with Ag. The nanoporous channels allow efficient ion transport, interface charge exchange and gas molecular diffusion. Significantly, the assembled hybrid Zn-Ag2Al/air battery delivers a high capacity of 3.23 mAh/cm2 as compared with recent reports. As far as we know, this is the first exploration for the electrochemical property of Ag2Al, and it would inspire more exploration in developing multifunctional materials and robust hybrid batteries for practical applications.

Cobalt oxide with flake-like morphology as efficient passive NOx adsorber

A series of Co-based oxides were synthesized and investigated as passive NOx adsorbers (PNAs). The morphology variation of Co3O4 oxide from nanoparticle to flake shape enhanced the NOx storage efficiency (NSE) and improved the NOx desorption capability. The enhanced NSE of the flake-like sample is related to its abundant surface oxygen species and large surface area. DRIFTS and CO2-TPD experimental results indicated that Co3O4-flake and Co7Ni3Ox-flake samples with moderate basicity could store NOx as nitrite species, which facilitated NOx desorption at lower temperatures.