Redox Precipitation Method Research Articles

Synthesis of low-temperature NH3-SCR catalysts for MnOx with high SO2 resistance using redox-precipitation method with mixed manganese sources

It remains a big challenge to enhance the SO2 resistance of catalyst in low-temperature NH3-SCR reduction. In this work, a series of MnOx-a%Mn (a = 0, 1, 3, 5, 10) catalysts were prepared by introducing manganese acetylacetonate during the reaction between lactic acid and KMnO4, based on the molar ratio of manganese acetylacetonate to KMnO4. Notably, MnOx-5 %Mn exhibited more than 95 % NO conversion and 100 % N2 selectivity at 80–240 °C. Moreover, the catalyst demonstrated excellent sulfur resistance by sustaining over 90 % NO conversion at 140 °C at the presence of 100 ppm SO2 for more than 6 h. Furthermore, XPS characterization indicated that adding manganese acetylacetonate enhanced electron transfer efficiency and improved the reduction capacity of the catalyst due to the interconversion between Mn3+ and Mn4+, which improved electron transfer efficiency. The enhanced reduction capacity of the catalyst promoted the formation of oxygen vacancies and surface-adsorbed oxygen species (Oα), avoiding over-oxidation of NH3. The results elucidated that manganese acetylacetonate could optimize the overall performance by modulating the synergistic effect between the oxidizing ability and surface acidity of the catalyst. Therefore, the MnOx-5 %Mn catalyst possessed a broad operational temperature window (40–240 °C) and SO2 resistance in the NH3-SCR reaction, indicating its potential for practical application.

Fe-doping induced textural and morphological evolution of MnO2 and its enhanced performance for o-xylene complete oxidation

Fe-MnO2 nanocomposite was prepared via a redox–precipitation method combined with a subsequent aging treatment at low-temperature. Various characterizations showed that Fe was incorporated into MnO2 lattice that changed the relative intensity of MnO2 crystal planes. Thus, the structural defect was formed and the anisotropic growth of the MnO2 crystallite phase was suppressed. As a result, the morphology of MnO2 was transformed from nanowires to nanoparticles. In addition, the catalytic property of Fe-MnO2 was significantly enhanced than that of pristine MnO2 for the complete oxidation of o-xylene. This work provides a simple and effective strategy for regulating MnO2 texture and activity.

Insight into modified Ce[sbnd]Mn based catalysts for efficient degradation of toluene by in situ infrared

Trace activated carbon (AC) and diatomaceous earth (DE) were used as structural promoters to be incorporated into Ce-Mn-based solid-solution catalysts by the redox precipitation method. The modified catalysts exhibit superior reducibility, with abundant Ce3+, Mn3+and reactive oxygen species, which are facilitated to the migration of oxygen and the generation of oxygen vacancies. In particular, the catalytic combustion temperatures of 90 % toluene (3000 ppm) on Ce1Mn3Ox-AC/DE were 84 °C (dry) and 123 °C (10 vol% H2O), respectively. The role of lattice oxygen and adsorbed oxygen was revealed by in situ DRIFTS. Additionally, in situ DRIFTS was employed to verify that the degradation of toluene by Ce1Mn3Ox-AC/DE satisfied the Langmuir-Hinshelwood (L-H) mechanism and the Mars-Van Krevelen (MvK) mechanism. The possible reaction pathway was elucidated (toluene → benzyl alcohol → benzoic acid → maleic anhydride → CO2 + H2O). Furthermore, final products attributed to toluene oxidation were detected by in situ DRIFTS at 50 °C in the absence of oxygen, confirming that the catalyst possessed outstanding performance at low temperatures beyond mere adsorption.

Catalytic Ozonation of Ethyl Acetate with Assistance of MMn2O4 (M = Cu, Co, Ni and Mg) Catalysts through In Situ DRIFTS Experiments and Density Functional Theory Calculations

Catalytic ozonation, with enhanced efficiency and reduced byproduct formation at lower temperatures, proved to be efficient in ethyl acetate (EA) degradation. In this work, MMn2O4 (M = Cu, Co, Ni, Mg) catalysts were prepared via a redox-precipitation method to explore the catalytic ozonation mechanism of EA. Among all the catalysts, CuMn exhibited superior catalytic activity at 120 °C, achieving nearly 100% EA conversion and above 90% CO2 selectivity with an O3/EA molar ratio of 10. Many characterizations were conducted, such as SEM, BET and XPS, for revealing the properties of the catalysts. Plentiful active sites, abundant oxygen vacancies, more acid sites and higher reduction ability contributed to the excellent performance of CuMn. Moreover, the addition of NO induced a degree of inhibition to EA conversion due to its competition for ozone. H2O had little effect on the catalytic ozonation of CuMn, as the conversion of EA could reach a stable platform at ~89% even with 5.0 vol.% of H2O. The presence of SO2 usually caused catalyst deactivation. However, the conversion could gradually recover once SO2 was discontinued due to the reactivation of ozone. A detailed reaction mechanism for catalytic ozonation was proposed via in situ DRIFTS measurements and DFT calculations.

Efficient catalytic ozonation of ethyl acetate over Cu-Mn catalysts: Further insights into the reaction mechanism

A series of Cu-Mn oxides were synthesized by the redox-precipitation method with different precipitants to evaluate the catalytic ozonation of ethyl acetate (EA). It was found that CuMn-II (with H2C2O4 as precipitant) exhibited the best catalytic activity, which achieved an EA conversion of 99 % at 120 °C with an O3/EA molar ratio of 10. The reaction temperature, O3/EA molar ratio, ozone utilization rate, and COx selectivity were also discussed. Meanwhile, many characterizations were conducted to reveal the properties of catalysts, such as SEM, XRD, BET, XPS, H2-TPR and NH3-TPD. Abundant surface defects, plentiful oxygen vacancies, larger specific surface area, higher content of Mn3+ and more acid sites contributed to the superior performance of CuMn-II. Catalyst poisoning occurred when SO2 was added, however, the conversion of EA could gradually recover to 88 % once SO2 was stopped. In-situ DRIFTS measurement was carried out to reveal the formation of intermediate species during the reaction. Combined with DFT calculations, a reaction mechanism for the catalytic ozonation of EA over CuMn2O4 catalysts was proposed.

Low-temperature catalytic oxidation of PCDD/Fs over MnCeCoOx/PPS catalytic filter.

Catalytic destruction of nitrogen oxides (NOx) combined with dust removal technique has attracted much attention, yet the application in the solid waste incineration air pollution control process is still lacking due to the complex flue gas atmosphere. In this work, the Mn-Ce-Co-Ox catalyst-coated polyphenylene sulfide (PPS) filter fiber with efficient dust removal and low-temperature polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) destruction has been prepared with a redox-precipitation method. The catalyst was uniformly grown around the PPS fiber with appropriate catalyst loading. The effects of several key operating parameters (e.g., reaction temperature, catalyst loading amount, and filtration velocity) on the catalytic efficiency were comprehensively investigated. The results show that the Mn-Ce-Co-Ox/PPS has a decomposition yield of 78.0% in PCDD/Fs and 96% in nitric oxide (NO) conversion at 200 °C. The poisoned catalytic filter exhibits a removal efficiency of 88.6% for PCDD/Fs. In addition, the catalytic filter can completely reject particles smaller than 1.0 μm with a low filtration resistance. Therefore, this efficient and energy-conserving catalytic filter shows promising applications in flue gas pollution treatments.

Tetracycline removal via three-way synergy between pistachio shell powder, zerovalent copper or iron, and peroxymonosulfate activation

Pistachio shell powder (PS) immobilized zerovalent iron and zerovalent copper (ZVI@PS and ZVC@PS) were investigated for the tetracycline (TCH) removal via sulfate radical based advanced oxidation process (S-AOP's). Eco-efficient ZVI@PS and ZVC@PS nanocomposite prepared by one-pot redox precipitation method were characterized by using FTIR, XRD, SEM, BET, TGA/DTA, and XPS techniques. The EDX, TGA, and AAS analysis techniques confirmed the loading of 44 % Fe and 40 % Cu (w/w %) onto the pistachio shell biomass in ZVI@PS and ZVC@PS nanocomposites, respectively. This report comprehensively discusses the effect of various contributing factors for the TCH removal via advanced oxidation processes such as catalytic dosage, initial pH, PMS dosage and initial TCH concentrations, etc. Besides that, the role of reactive oxygen species (SO4−,.OH, O2−, and 1O2) in the TCH degradation process was investigated using radical scavenging experiments. A three-way synergistic approach was established between adsorption efficiencies of pistachio shell powder, heterogeneous ZVI or ZVC mediated Fenton-process and enhanced PMS activation process, for the observed enhanced TCH degradations. The observed rate constant (kobs.) values of ZVI@PS-PMS (0.34 min−1) and ZVC@PS-PMS (0.16 min−1) processes for TCH removal suggests that the ZVI@PS was more efficient in TCH removal compared to ZVC@PS.

Epsilon-MnO2 simply prepared by redox precipitation as an efficient catalyst for ciprofloxacin degradation by activating peroxymonosulfate.

Four kinds of manganese oxides were successfully prepared by hydrothermal and redox precipitation methods, and the obtained oxides were used for CIP removal from water by activating PMS. The microstructure and surface properties of four oxides were systematically characterized. The results showed that ε-MnO2 prepared by the redox precipitation method had large surface area, low crystallinity, high surface Mn(III)/Mn(Ⅳ) ratio and the highest activation efficiency for PMS, that is, when the concentration of PMS was 0.6 g/L, 0.2 g/L ε-MnO2 could degrade 93% of CIP within 30 min. Multiple active oxygen species, such as sulfate radical, hydroxyl radical and singlet oxygen, were found in CIP degradation, among which sulfate radical was the most important one. The degradation reaction mainly occurred on the surface of the catalyst, and the surface hydroxyl group played an important role in the degradation. The catalyst could be regenerated in situ through the redox reaction between Mn4+ and Mn3+. The ε-MnO2 had the advantages of simple preparation, good stability and excellent performance, which provided the potential for developing new green antibiotic removal technology.

The treatment of As(III)-contaminated water by using granular Fe-Mn-Cu composite oxide: Removing As(III) via the oxidation-adsorption process and handling the release of manganese ions

It is a challenge to obtain an outstanding removal performance for the treatment of As(III)-contaminated water without the risk of secondary pollution. In this study, a novel granular adsorbent of Fe-Mn-Cu composite oxide (GFMCO) was fabricated by the redox-precipitation method. Batch adsorption experiments were conducted to investigate the adsorption behavior of As(III) onto GFMCO, including adsorption isotherms, adsorption kinetics, the influences of pH and competing anions, and reuse performance. The adsorption equilibrium of As by GFMCO could be achieved within 12 h. As(III) can be effectively oxidized to As(V) and adsorbed by GFMCO with a theoretical maximum As adsorption capacity of 72.88 mg/g. The As removal performance remained stable within a wide pH range of 3–9. Phosphate and silicate anions inhibited As removal, whereas chloride ions, sulfate anions, calcium ions, and magnesium ions had little effect. In addition, GFMCO could be successfully regenerated and reused with almost no loss in adsorption capacity during four consecutive cycles. Moreover, the GFMCO-packed column used as an adsorption reactor could produce approximately 969 bed volumes of treated water with the effluent arsenic concentration below 10 μg/l. Although divalent manganese ions (Mn(II)) were released from the GFMCO-packed column, efficient Mn(II) removal could be achieved with the combination of sodium hypochlorite dosing and the manganese sand filtration. Overall, this work provides a promising adsorbent for As(III) removal with satisfactory efficiency and good security.

Evaluation of synergistic adsorption approach for terbinafine removal by cotton shell powder immobilized zerovalent copper: Adsorption kinetics and DFT simulation

Cotton shell powder (CS), nano zerovalent copper (nZVC) and cotton shell powder immobilized zerovalent copper (ZVC@CS) were evaluated for their adsorption efficiencies towards terbinafine hydrochloride (TBH), an antifungal drug. The nZVC and ZVC@CS synthesized via one pot redox precipitation method were characterized by FTIR, XRD, BET, FESEM and TGA analysis. The TGA and AAS analysis confirmed the loading of nearly 10% of nZVC on cotton shell powder in ZVC@CS. The effect of operational parameters (pH, adsorbent dose, initial drug concentration, time, etc.) determining the extent of terbinafine hydrochloride adsorption on ZVC@CS were investigated to ascertain the optimal experimental conditions to achieve maximum adsorption efficiencies. To investigate the adsorption behavior of TBH on ZVC@CS, the experimental data were fitted for five different adsorption models viz. Langmuir, Freundlich, Temkin, Redlich-Peterson and Hill isotherms. The TBH adsorption data was best fit with Hill isotherm model indicating cooperative sorption of TBH molecules on ZVC@CS surface. Among the five kinetic equations namely the pseudo-first-order (PFO), the pseudo-second-order (PSO), Elovich model, the intraparticle diffusion model, and Boyd kinetic model used to estimate the adsorption mechanism, the PFO kinetic model give best fit with a good correlation for the physisorption of TBH on ZVC@CS composite. The mechanism of the adsorption process was observed to be complex, consisting of both surface adsorption and pore diffusion. However, the Boyd plot confirms external mass transport as the rate limiting step for the adsorption of TBH on ZVC@CS. The synergistic adsorption of TBH on ZVC@CS was hypothesized, and the idea was supported by structure optimization results from DFT studies. The ZVC@CS exhibits equilibrium TBH adsorption efficiency (qmax) of 285.3 mg.g−1, significantly higher than adsorbents used in literature for the TBH removal.It is suggested that ZVC@CS may serve as sustainable adsorbents for the removal of cationic contaminants from acidic medium.

Synthesis of xCe-MnO2 with three-dimensional ultra-thin nanosheet structure and its excellent low-temperature reducibility for toluene catalysis.

A series of xCe-MnO2 (x = 0-1) catalysts were synthesized using ammonium oxalate as a precipitator via the redox precipitation method and hydrothermal synthesis method. The results indicate that 0.25Ce-MnO2 exhibited the highest catalytic activity for toluene oxidation, with the T99 of 240°C. Characterization results from XRD, Raman, SEM, TEM, EDS-mapping, BET, and other techniques reveal that the 0.25Ce-MnO2 catalyst exhibited a three-dimensional multistage ultrathin nanosheet structure by adjusting the introduction amount of Ce, with abundant active sites, and effectively formed Ce-Mn homogeneous dispersion. The larger pore size and volume of 0.25Ce-MnO2 catalyst lead to it excellent toluene transfer ability. Furthermore, compared with MnO2, the crystal pattern of 0.25Ce-MnO2 shifted to the tetragonal cryptomelane type α-MnO2 phase and exposed more crystal planes which are beneficial to catalyze toluene. H2-TPR, O2-TPD, and XPS characterization further confirmed the strong interaction between Ce and Mn oxides, which exhibited better low-temperature reducibility and oxygen migration, along with abundant Ce3+ and Mn3+ species, where lattice oxygen played a major role. Moreover, in situ DRIFTS revealed that the 0.25Ce-MnO2 catalyst showed higher adsorption and desorption capacity for toluene than the MnO2 catalyst, and benzoate species were the key intermediates for catalytic oxidation. Additionally, benzoate and surface phenolic species were the key intermediates for catalytic oxidation of MnO2. Because 0.25Ce-MnO2 possesses better ability of converting toluene to benzoate species, it exhibits better activity.

Tailoring Oxygen Vacancies and Active Surface Oxygen Species in Copper-Doped MnO2 Catalysts for Total Catalytic Oxidation of VOCs

Catalytic oxidation has been considered an essential route to tackle volatile organic compounds (VOCs)-driven pollution. To this point, surface engineering has emerged as a robust pathway to promote the efficiency of MnO2-based materials toward VOC oxidation. However, regulating such surface properties has been a critical challenge. This investigation attempts to tailor surface oxygen vacancies and active surface oxygen for the total catalytic oxidation of various VOCs (e.g., formaldehyde, isopropanol, and toluene) via doping copper into cryptomelane and birnessite-type MnO2 catalysts. The catalysts are synthesized by a novel facile successive redox precipitation method between KMnO4 and an ethanol solution containing copper nitrate precursors, followed by annealing. It turns out that the low amount of Cu dopants, corresponding to the copper-to-manganese ratio of 0.17 (RCu/Mn = 0.17), generates a tunnel-structured cryptomelane-type MnO2 with strong bulk oxygen mobility. Such a crystalline structure exhibits the best catalytic performance for the total catalytic oxidation of toluene. The higher copper loading (RCu/Mn = 0.27–0.34) drives the formation of Cu-doped layered birnessite-type MnO2 materials containing rich oxygen vacancies and high active surface oxygen species. Those catalysts promote the oxidation of isopropanol and formaldehyde, respectively. To this end, oxygen vacancies and surface oxygen species crucially steer the molecular oxygen activation and interactions toward adsorbed oxygen species, significantly promoting the total oxidation of isopropanol and formaldehyde, respectively. The explored finding could disclose an outstanding platform toward highly selective and efficient oxidation of VOCs.

Construction of surface oxygen vacancy active sites upon MnOx/AC composite catalysts for efficient coupling adsorption and oxidation of toluene

Activated carbon (AC) has been widely used as adsorbent and support of noble metal catalysts for the elimination of VOCs, owing to its high specific surface area and effective regulation of interfacial properties of catalysts via metal-support interaction. Herein, a series of MnOx/AC composite catalysts are prepared by in-situ redox precipitation method using KMnO4 as manganese source, ethylene glycol (EG) as reducing agent and coconut shell-based AC as active carrier. The obtained MnOx/AC catalysts have been fully characterized by XRD, SEM, TEM, N2 adsorption-desorption, FT-IR, XPS, EPR, H2-TPR, TPD-MS and toluene-TPSR-Ms (with and without O2) and their catalytic properties are evaluated for low temperature oxidation of toluene. It is found that the introduction of AC support significantly enhanced the adsorption capacity of toluene upon the MnOx/AC composite catalysts. Amongst, the MnOx/AC-0.3 shows excellent low-temperature catalytic activity (T90 = 193 °C), which can be related to highly efficient synergy of AC and MnOx species in toluene combustion. Especially, the construction of efficient MnOx/AC interfaces with more oxygen vacancy active sites, better lattice oxygen mobility, and stronger molecular oxygen activation ability, makes MnOx/AC-0.3 composite catalyst possess the best coupling adsorption oxidation capacity of toluene, and thus resulting in significant improvement in catalytic performance. Additionally, the obtained MnOx/AC-0.3 catalyst has also exhibited good catalytic stability and water resistance (5 vol%). This work deepens the understanding of the metal-support interaction in MnOx/AC composite catalysts and provides new ideas for the design of environmentally friendly catalysts.

Tuning the Surface Mn/Al Ratio and Crystal Crystallinity of Mn–Al Oxides by Calcination Temperature for Excellent Acetone Low-Temperature Mineralization

Here, Mn–Al oxides with the strengthened synergistic effect of Mn and Al species were fabricated by facilely adjusting the calcination temperature with the hydrolysis-driven redox-precipitation method. Results demonstrated that the surface Mn/Al ratio and KMn8O16 phase can be effectively tamed under different calcination temperatures, which obviously alter the CO2 selectivity, reaction rate, and stability of Mn–Al oxides for catalytic oxidation of acetone, among which the Mn5Al-350 catalyst exhibits the best catalytic performance (90% of acetone converted at 159 °C) with CO2 selectivity higher than 99.5%, mainly owing to its higher surface Mn/Al ratio and weaker Mn–O bond with more Mn3+ as compared to Mn5Al-250, Mn5Al-450, and Mn5Al-550. Although a decrease in the consumption rate of acetic acid in the presence of 3.0 vol % H2O leads to the slight reduction of acetone conversion and CO2 yield, Mn5Al-350 still exhibits a superior catalytic stability. The reaction intermediates including acetaldehyde, ethanol, acetic acid, and formic acid species before total mineralization are determined by proton transfer reaction–mass spectrometry, theoretical calculations, and in situ DRIFTS. Theoretical calculations also reveal that the p-orbital interaction of C with a certain anisotropy leads to a weak catalytic effect in the process of acetic acid decomposition as the rate-limiting step.

Highly efficient acetone oxidation over homogeneous Mn-Al oxides with enhanced OMS-2 active phase

The homogeneous dispersed material with enhanced active species plays a dominant role in the catalytic activity. The Mn-Al oxides are facilely synthesized by the hydrolysis-driven redox-precipitation method. The OMS-2 active phase and surface properties can be effectively adjusted by Al/Mn molar ratio, which alters the acetone conversion and CO2 selectivity of prepared catalysts. Among them, MnAl0.15 exhibits the best catalytic performance (90% of acetone converted at 168 °C) with CO2 selectivity higher than 95%, mainly owing to its abundant Olatt and Mn3+with weaker Mn-O bond. Although the presence of H2O results in the slow consumption rate of acetic acid that leads to the slightly reduction of acetone conversion and CO2 yield, the MnAl0.15 still exhibits superior catalytic stability. The PTR-MS and in situ DRIFTS demonstrate that the acetone can firstly be oxidized to acetaldehyde and ethanol, and then further decomposed to acetic acid and formic acid before total mineralization.

Generation of abundant oxygen vacancies in Fe doped δ-MnO2 by a facile interfacial synthesis strategy for highly efficient catalysis of VOCs oxidation

A series of homogenous Fe-Mn oxides with superior catalytic oxidation activity was developed via interfacial redox-precipitation method for eliminating VOCs from industrial waste gas. Among them, Fe1Mn5 oxide achieved the optimum catalytic performance for toluene oxidation with a T90 of 209 ℃. In addition, the catalyst demonstrated superior stability for long-time operation and great water resistance. By combining an array of analytical techniques with DFT calculations, the results revealed that Fe doping and interfacial redox-precipitation method synergistically resulted in high concentration of oxygen vacancy defect over Fe1Mn5 oxide, which improved lattice oxygen mobility and oxygen species activity, thus enhancing its low temperature reducibility. Meanwhile, in situ DRIFTS analysis revealed that both the adsorbed oxygen species and lattice oxygen with improved mobility could interact with adsorbed toluene, thus facilitating rapid dehydrogenation of methyl and demethylation of toluene and promoting the breakage of CC bond in the aromatic ring.

Leaching inhibition of K species over 3DOM La0.8Sr0.2MnO3 perovskite through CuO embedding: Enhanced stability induced by phase transition for soot elimination

Catalytic combustion is one of the most effective soot elimination technologies, whereby the development of catalyst with high performance and stability becomes the emphasis. Herein, we elaborately fabricated an innovative catalyst of K-Cu decorated 3DOM La0.8Sr0.2MnO3 perovskite called 5KxCLSM for soot combustion, in which Cu species were introduced via redox precipitation method and K species were loaded by impregnation method. The dispersion and interaction between CuO and perovskite were enhanced by this redox precipitation method. CuO could facilitate the phase transition to form K2−xMn8O16, thereby, the free K species were stabilized. However, excessive CuO would cover the active sites and even destroy 3DOM structure. Among all as-prepared catalysts, 5K2CLSM exhibited the best activity with T50 of 357 ℃ and TOF of 2.97 × 10−3 s−1 (320 ℃) and possessed admirable water-resistance and hydrothermal stability. This work rationalizes an approach to develop an active and stable catalyst for soot combustion or other systems.

Engineering oxygen vacancies in metal-doped MnO2 nanospheres for boosting the low-temperature toluene oxidation

Promoting the catalytic activity by engineering oxygen vacancies is a fascinating strategy in heterogeneous catalysis. Herein, a series of metal oxide catalysts with different metal doping were prepared through a redox precipitation method to regulate oxygen vacancies in MnO2 and tested in toluene catalytic oxidation at low temperature. To accurately elaborate the structure–activity relationship of different catalysts, the prepared catalysts were systematically characterized by various techniques. Results showed that the doped metals entered the MnO2 skeleton as expected and resulted in the lattice distortion, as well as oxygen vacancies. The catalyst Cu-MnO2, which was obtained by doping Cu into MnO2, had the most oxygen vacancy contents and increased oxygen migration mobility, thus showing the best catalytic toluene oxidation activity at low temperature (T90 = 219 °C). Meanwhile, in-situ DRIFTs demonstrated the intermediates like benzene methanol, benzaldehyde, benzoic acid, maleic acid generated at different environments and revealed that the rate-controlling step probably be the deep oxidation of benzoate species. In addition, the supplement of gas phase oxygen played an important role in the complete transformation of the intermediate benzoic acid. This work open up an attractive method for acquiring metal-doped MnO2 nanospheres catalysts for toluene oxidation.

Manganese oxide nanorod catalysts for low-temperature selective catalytic reduction of NO with NH3.

MnOx nanorod catalysts were successfully synthesized by two different preparation methods using porous SiO2 nanorods as the template and investigated for the low-temperature selective catalytic reduction (SCR) of NO with NH3. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, and NH3 temperature-programmed desorption. The results show that the obtained MnOx-P nanorod catalyst prepared by redox precipitation method exhibits higher NO removal activity than that prepared by the solvent evaporation method in the low temperature range of 100–180 °C, where about 98% NO conversion is achieved over MnOx(0.36)-P nanorods. The reason is mainly attributed to MnOx(0.36)-P nanorods possessing unique flower-like morphology and mesoporous structures with high pore volume, which facilitates the exposure of more active sites of MnOx and the adsorption of reactant gas molecules. Furthermore, there is a lower crystallinity of MnOx, higher percentage of Mn4+ species and a large amount of strong acid sites on the surface. These factors contribute to the excellent low-temperature SCR activity of MnOx(0.36)-P nanorods.

Low-temperature catalytic combustion of benzene over Zr–Mn mixed oxides synthesized by redox-precipitation method

Zr-Mn mixed oxides with various Zr/Mn molar ratios were synthesized by redox-precipitation method and applied to benzene catalytic combustion. The results showed that the addition of Zr to MnO2 could improve the benzene combustion activity, among which Zr/MnO2-0.2 catalyst performed the best catalytic activity with T50 and T90 of 171 °C and 195 °C (1000 ppm benzene, GHSV = 60,000 ml · g−1 · h−1, 0% RH (relative humidity), 20 vol% O2/N2), respectively. A series of characterizations were used to investigate the structure–activity relationship of Zr–Mn mixed oxides, which demonstrated that the larger specific surface area, more surface reactive oxygen species, higher low-temperature reduction and acidity contributed to the enhanced catalytic activity of Zr–Mn mixed oxides. Finally, the possible pathways of benzene combustion over Zr–Mn mixed oxides were explored by in-situ DRIFTS spectra and the possible intermediates generated under different conditions were also revealed.