How can you experimentally confirmed that mno2 is a catalyst

Except for the stability, water resistance is another obstacle for the practical application of manganese-based catalysts in ozone decomposition 16 , Therefore, the ozone conversion is evaluated under high-humidity conditions.

However, for 7. This indicates that the graphene shells alleviate the effect of water vapour on the ozone conversion and make catalyst regeneration much easier. Those results indicate that the unique core—shell structure enables to significantly enhance the water resistance.

In order to compare the performance of the 7. S14 and S Those experimental results indicate that ultrathin graphene encapsulated 7. Although the obtained 7. Therefore, loading the catalyst on a suitable support is necessary for practical application. Herein, the prepared 7. It is generally accepted that water vapour affects the ozone conversion on manganese-based catalysts through competitive adsorption processes on the active sites 17 , 45 , However, a deep understanding on the water vapour competitive adsorption process still lacks.

However, the adsorbed water molecules would not affect further ozone conversion under low-humidity conditions, indicating that the active sites for water adsorption and ozone conversion are different. These results indicate that the hydrophobic graphene shells promote the initial water resistance of 7. Insets: surface electrostatic potential and molecular dipole of O 3 and H 2 O.

Mn 3s c and C 1s d spectra of 7. It has been reported that ozone molecules can reversibly adsorb on the graphene and further react with graphene to form epoxide groups 47 , A similar catalytic reaction mechanism has been reported on pure MnO 2 Interestingly, the peak intensity of 7. S18 but the decrease on the ozone conversion of 7. To explore the reason why the ozone conversion of 7. S19 , the AOS of Mn and contents of surface adsorbed oxygen species follow the same variation trend, suggesting the oxidation state of Mn is closely related to the surface oxygen species in 7.

Fortunately, the ozonation process only appears on the defective structure of the graphene shells and the surface oxygen concentration would not vary with the additional ozone exposure finally Fig. S20 49 , So, although the nongraphitic impurities possess an effect on the surface electronic structure, the ozone conversion of 7. Geunsik Lee et al. To further understand the nature of ozone-catalytic decomposition over MnO 2 GR, the density functional theory simulation is conducted.

The tetragonal MnO 2 with one MnO 2 -one-OV or ten MnO 2 -ten-OV oxygen vacancy is coated with graphene layer, respectively Table S2 to analyse the surface electronic structure since abundant oxygen vacancies exist on the surface of 7.

S22 and Bader charge analysis Fig. S24 - Notably, the number of transferred electrons from MnO 2 to graphene is 1. The average work function Fig. Second, charge-density differences Figs. For the Mn exposure site oxygen vacancy , the electrons are transferred from Mn atoms to the nearby graphene layer and correspondingly an electron-rich site is formed, while the electrons are transferred from the graphene layer to oxygen atoms at the oxygen exposure site.

The interfacial electron transfer is originated from the differences in the local work function In other words, the exposed oxygen atoms would increase the local work function of the nearby graphene layer, while the exposed Mn atoms would decrease the local work function of the nearby graphene layer.

In ozone-catalytic decomposition, a lower work function is beneficial for the ozone molecule to capture electrons for further decomposition. Therefore, the electron transfer from graphite carbon to oxygen atoms reduces the surface electron density and is not beneficial for ozone-catalytic decomposition, while the electron transfer from the unsaturated Mn atoms to graphite carbon enables to increase the surface electron density and benefit the ozone-catalytic decomposition.

The yellow and cyan regions refer to the increased and decreased charge distributions, respectively. The isosurface value of the colour region is 0.

The purple, red and grey ball in the models corresponds to the Mn, oxygen and carbon atoms, respectively. Since pure graphitic carbon is inert for ozone decomposition and the ozone molecule entering the interlayer of graphene sheets to react with the surface Mn species is excluded see details in Fig.

S27 , we propose that the graphitic carbon close to Mn atoms oxygen vacancy is the active site for ozone decomposition in MnO 2 GR. The local work function of the carbon sites around oxygen vacancy is lower than that of the graphene layer and higher than that of oxygen vacancy, which compromises the reaction barriers in the initial step of ozone adsorption and the desorption of the intermediate oxygen species, consequently accelerating the desorption of peroxide species.

Here, based on the above results and the ozone-conversion mechanism proposed in the literatures 15 , the ozone decomposition mechanism on the core—shell structure of MnO 2 GR is proposed as shown in Fig.

The surface carbon site is activated by the electron penetration from inner unsaturated Mn atoms oxygen vacancy. Finally, the peroxide species transfer one electron to the activated carbon and desorb from the active site.

On the surface of MnO 2 GR, the moderate local work function compromises the reaction barriers in initial ozone adsorption and the desorption of the intermediate oxygen species, which significantly enhances the stability. The hydrophobic graphene shells inhibit the chemical adsorption of water vapour and avoid the enrichment of H 2 O molecule on the catalyst surface. As a result, the 7.

In this scheme, the possible reaction processes of ozone-catalytic decomposition on the graphite carbon near unsaturated Mn atoms are proposed. The electron transfer from the unsaturated Mn atoms to the graphene shell turns the graphite carbon close to the unsaturated Mn atoms to be active site. In the unique core—shell structure, the electron penetration from the oxygen vacancy of MnO 2 to nearby graphene shells drives ozone-catalytic decomposition. Due to the interfacial charge transfer, a suitable local work function tuned by the graphene shell results in rapid decomposition of the intermediated oxygen species.

Thus, 7. In addition, hydrophobic graphene shells inhibit the chemical adsorption of water vapour and avoid the enrichment of H 2 O molecule on the catalyst surface. So, the ozone conversion of 7. These findings offer us a new perspective for the development of high-performance, stable and inexpensive catalyst and would promote manganese-based catalysts for practical application in ozone decomposition. Firstly, 1. After it cooled to room temperature, the products were washed with deionized DI water to remove the impurity.

Finally, the obtained samples were directly dehydrated via a freeze-drying process. For comparison, 1. GR was obtained by a hydrothermal process. In all, 0. CHID electrochemical system was used to examine the electrochemical measurements. Electrochemical impedance spectroscopy EIS was measured in three-electrode quartz cells using 0.

SCE served as a reference electrode; Platinum wire served as a counter electrode, and sample film electrodes on glassy-carbon electrode served as a working electrode. Then, the generated ozone mixed adequately with clear air in a mixing drum and then transported into the reactor. The inlet and outlet ozone concentration was recorded model , 2B Technologies and the ozone conversion was calculated through the following equation:.

All data presented in this study are included in the article and Supplementary Information. The data are available from the corresponding authors upon request.

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Abbass, O. Effectiveness of indoor plants for passive removal of indoor ozone. Article Google Scholar. Yang, S. Gong, S. The C 1s peaks eV of the catalyst XPS spectra were used for calibrating the binding energy values. All of the maximum intensities of the Mn 2p spectra were adjusted to 1. The partial electron yield detection mode was used for the NEXAFS spectra by recording the sample current normalized to a signal current measured simultaneously using a gold mesh in an ultrahigh vacuum UHV.

The pressure of the chamber was increased from 2. Their surface structures and energies were then determined using the generalized gradient approximation functional of PBESol with a plane wave cutoff of eV. Hence, a projector-augmented wave reconstruction is used in the CASTEP process to reduce the pseudopotential error, although little deviation from the spectra generated using an all-electron code was observed. Supporting Information.

Author Information. The authors declare no competing financial interest. High surface area chromia aerogel efficient catalyst and catalyst support for ethylacetate combustion Appl. Elsevier Science B. The effect of dispersion and the ensembling mode of chromium oxide nanocrystals in bulk xerogels and aerogels on their performance, as well as the efficiency of high-surface-area chromia aerogel as catalyst support, were investigated in complete Et acetate EA oxidn.

Oxidative treatment O2 at elevated temps. In both reduced and oxidized states, a high concn. Promotion with Ce and Mn additives improved the efficiency of the redox cycle in Cr aerogel and increased the concn. The catalytic oxidation of aromatic hydrocarbons over supported metal oxide J. X-ray diffraction, Brunauer Emmett Teller method, electron probe x-ray microanal.

Increasing the calcination temp. The smaller particle size of Cu, due to its high dispersion on support, had a pos. The activity of 5 wt. Increasing the reactant concn. Elsevier B. MnOx-CeO2 catalysts were prepd.

In ceria-rich materials, cryst. In Mn-rich materials, segregation of a Mn3O4 phase takes place. The mixed oxides get reduced by H2 at lower temps. The surface area of MnOx-CeO2 catalysts is larger than the one of single oxides prepd. The larger surface area of MnOx-CeO2 catalysts counterbalances their smaller specific activity allowing complete conversion of the examd. VOCs at lower temps.

Structure anal. The promoting effect of Pt was ascribed to enhance the effective activation of oxygen mol. Impact of synthesis method on catalytic performance of MnO x -SnO 2 for controlling formaldehyde emission Catal. MnOx-SnO2 synthesized by a redox co-pptn. Performance and kinetics of catalytic oxidation of formaldehyde over copper manganese oxide catalyst Build.

The present paper deals with the impact of the addn. With this aim, a series of cobalt catalysts supported on zirconia 5 wt. After the impregnation step, the cobalt supported materials are characterized at different stages of the prepn. Characterization results suggest that the carbohydrate ligand bound to the cobalt species retards the decompn.

Finally, these cobalt oxide catalysts prepd. The results are explained in terms of cobalt oxide dispersion and cobalt-support interactions.

Indeed, the cobalt oxide particles generated by the thermal decompn. The formation of a 3D ordered mesoporous structure was confirmed by low-angle XRD, nitrogen adsorption-desorption data, and TEM micrographs. The excellent catalytic performance of CoMn-HT was assocd. Oxides of copper, ceria promoted copper, manganese and copper manganese on Al 2 O 3 for the combustion of CO, ethyl acetate and ethanol Appl. Modification of the alumina with ceria before subsequent copper oxide deposition increases the activity for combustion of CO substantially, but the effect of ceria was small on the combustion of Et acetate and ethanol.

The activity increases with the CuOx loading until cryst. CuO particles are formed, which contribute little to the total active surface. In addn. At high loading, bulk CuO crystallites are present as well. Modification of the alumina with ceria before the copper oxide deposition gives well dispersed copper oxide species and bulk CuO crystallites assocd.

The distribution of copper species depends on the ceria and copper oxide loading. The alumina supported copper manganese oxide and manganese oxide catalysts consist mainly of cryst. CuMn2O4 and Mn2O3, resp. The removal of carbon monoxide from air J. Evaluation and characterization of Mn-Cu mixed oxide catalysts for ethanol total oxidation: influence of copper content Fuel , 87 , — DOI: Elsevier Ltd. The co-pptn. A small amt. This poor cryst. When the copper content increases, an extent of solid state reaction between Cu and Mn is favored and the partial oxidn.

The incorporation of manganese into incomplete spinel structure diminishes CO2 yield. Total oxidation of CO at ambient temperature using copper manganese oxide catalysts prepared by a redox method Appl.

Njagi, Eric C. Binary copper manganese oxides were prepd. The catalytic activity was found to be high, and compared favorably with a com. Hopcalite catalyst. The most active catalyst was able to completely oxidize CO at ambient temp. Catalytic activity decay, most likely due to carbon dioxide retention was obsd. The catalysts were deactivated by moisture but expelling water at moderate temps. The optimum copper loading was detd.

The effect of gold addition on the catalytic performance of copper manganese oxide catalysts for the total oxidation of propane Appl. Mixed copper manganese oxide catalysts Hopcalite were studied for the total oxidn. Catalysts were prepd. Calcination temp.

Characterization showed that the catalysts had a nanowire-type morphol. The incorporation of gold into the catalyst enhanced the activity for propane conversion, but the presence of gold did not noticeably enhance the light-off activity. Although the addn. Significantly the Hopcalite-based catalysts, particularly those contg. The improved activity on the incorporation of gold into Hopcalite is related to the reducibility of the catalysts, which is increased by gold addn.

The gold-contg. Gas-phase total oxidation of benzene, toluene, ethylbenzene, and xylenes using shape-selective manganese oxide and copper manganese oxide catalysts J.

C , , — DOI: Genuino, Homer C. American Chemical Society. Volatile org. VOC continue to be a major source of direct and indirect air pollution. This work synthesized cryptomelane-type, octahedral mol. MnO2, were characterized by various techniques. These catalysts were assessed for the gas-phase total oxidn. Differences in reactivity among VOC were rationalized in terms of degree of substrate adsorption and structural effects.

For example, xylene reactivity was dictated by the shape-selectivity of stable OMS MnO2 was attributed to a combination of factors, including structure, morphol. The mobility and reactivity of active O species were strongly correlated with catalytic activity. Lattice O was involved in VOC oxidn. The catalyst was then tested for the oxidn. This performance was attributed to the formation Mn1. Thus, after inhibition of the reactivity of imine, acac modified MnO x catalyst exhibited only specific types of sites required for aerobic dehydrogenation-coupling of benzylamine 1a to form imine.

One of the central issues challenging the continued development and refinement of this surface modification technique concerns the stability of the organic modification under demanding reaction conditions.

In order to examine the catalytic performance over extended periods of time, we attempted to recycle the catalyst without regeneration. This should be ascribed to the ability of acac to form stable coordination complexes on the surface of MnO x. Figure 4 shows data for aerobic oxidation of various substituted benzylamines see Supplementary Table 2 and Supplementary Figs. The MnO x catalyst is generally active and selective for the nitriles, while the acac-MnO x catalyst is highly selective for the imines.

In the presence of MnO x catalyst, benzylamine derivatives bearing electron-donating groups gave the corresponding nitriles in relative higher yields in comparison with those bearing electron-withdrawing groups, due to the facile hydrolysis reaction of electron-withdrawing groups substituted nitriles to amides.

For acac-MnO x catalyst, benzylamine derivatives bearing both electron-donating and electron-withdrawing groups reacted to produce the corresponding imines in good to excellent conversions and yields. Synthesis of nitriles and imines using benzylamine derivatives over unmodified and acac-modified MnO x.

In summary, we have demonstrated a method of using organic modifiers to tune the reaction pathway of redox-acid catalysis on the surface of metal oxide catalysts. Upon modification with enolic acetylacetones, the selectivity for manganese oxide catalyzed primary amines oxidation reaction switched from nitriles to imines.

The acetylacetone modification is stable under the reaction conditions and demonstrated good recyclability. The current study opens the door to the development of a class of highly stable and selectivity-switchable metal oxide catalysts via using the versatility of organic ligands to tune the surface properties of metal oxide catalysts.

MnO x was prepared according to the literature procedure After addition complete, adjust the pH to 8 with aq. Surface organic modified catalysts were prepared by immersing the catalyst in an acetonitrile solution of modifiers. The reactor was connected to an oxygen cylinder for reaction pressure. In a typical experiment, benzylamine After sealing and charging with O 2 0.

After reaction, the autoclave was cooled. The solution was separated by centrifugation and analyzed by GC using the internal standard method. The error bars standard deviation were calculated from repeat measurements.

The conversion of benzylamine and yield of corresponding products were evaluated using naphthalene as the internal standard. The conversion of other substrates and yield of corresponding products were determined based on area normalization without any purification.

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