Specific Surface Area Of Catalyst Research Articles

MnCeOx/diatomite catalyst for persulfate activation to degrade organic pollutants

Persulfate (PS)-based oxidation technologies are attracting increasing attentions in water treatment due to their high efficiency and stability. In this study, a novel diatomite supported MnCeOx composite (MnCeOx/diatomite) was prepared and characterized for activation of PS to degrade organic pollutants. Results indicated that diatomite not only dispersed MnCeOx and increased the specific surface area of catalyst, but also improved the low-valence metal site (Mn2+ and Ce3+) and reactive oxygen species site (–OH) of MnCeOx, thus enhancing the activities of MnCeOx. MnCeOx/diatomite/PS showed high efficiency for multiple dyes and pharmaceutical pollutants. Constant rate (k) of MnCeOx/diatomite (kMnCeOx/diatomite) was three times higher than the sum of constant rate of MnCeOx (kMnCeOx) and constant rate of diatomite (kdiatomite). In addition, MnCeOx/diatomite showed wide pH application (5–9). Cl− and NO32− had no effect while SO42− and humid acid had slightly negative effects on MnCeOx/diatomite/PS system. Moreover, MnCeOx/diatomite showed good reusability and stability. Mechanism analyses indicated that electron transfer of Mn and Ce attributed to the activation of PS and oxygen to produce free radicals. SO4−, OH and O2− on the surface of catalyst were the main active free radicals to attack pollutants.

Enhancement of the NH3-SCR property of Ce-Zr-Ti by surface and structure modification with P

The Px-Ce0.3-Zr-Ti catalysts were prepared by hydrothermal method and the effect of P modification on NH3-SCR property and structure was investigated. The P0.15-Ce0.3-Zr-Ti catalysts showed an excellent NH3-SCR activity in wide temperature range (Over 80% NOx conversion at 180–400 °C). Surprisingly, some nano-hollow spheres structures formed in P0.15-Ce0.3-Zr-Ti catalysts by introducing appropriate amount of H4P2O7, greatly increasing the specific surface area of catalysts and providing more reaction sites for active gases. And further characterizations indicated that there existed a new substance CePO4 in catalysts. With the increase of surface Ce3+, the redox ability of catalysts was greatly improved, resulting in a better catalytic activity at low temperature. Meanwhile, the catalysts modified by H4P2O7 produced more surface active oxygen species and other defects, as well as more surface acid sites, which played an important role in catalytic activity within a wide temperature window. DRIFTS results suggested that modification with P could promote the formation of NO2 and monodentate nitrates, thereby enhancing SCR reaction process (Langmuir-Hinshelwood reaction pathway). Besides, the presence of amide species (NH2) is an important marker for the catalyst to follow the E-R reaction mechanism.

Features of obtaining the catalyst for the synthesis of carbon nanotubes

In this paper, the features of obtaining a Co-Mo/Al2O3 catalyst to synthesize carbon nanotubes (CNTs) by thermal decomposition were studied. It was revealed that the duration of the pre-catalyst thermal decomposition stage in the process of developing a metal oxide system has a significant impact on its activity in the synthesis of carbon nanostructured materials by chemical vapor deposition (CVD). It was proved that an effective catalyst for CNTs synthesis can be obtained by through thermal decomposition of the pre – catalyst, without calcination of the metal oxide system. The use of the Co-Mo/Al2O3 catalyst, synthesized in such a way, in the CVD process makes it possible to reduce the cost of synthesized CNTs. Using scanning electron microscopy, it was shown that the size of the grains, and specific surface area of the formed Co-Mo/Al2O3 catalyst depend on the thermal treatment conditions of the pre-catalyst. Under the conditions for the implementation of the pre-catalyst thermal decomposition stage (temperature, volume, duration, etc.), it is possible to contro not only the characteristics of the resulting catalyst (specific surface area, efficiency), but also the characteristics of the CNTs (diameter, degree of defectiveness). In the course of experiments, the optimal modes of implementation of the method for obtaining the Co-Mo/Al2O3 catalyst allowed forming a system with a specific surface area of ~ 108 m2/g. The use of the resulting catalyst in the synthesis of nanostructured materials provides a high specific yield of multi-walled CNTs with a diameter of 8-20 nm and a degree of defectiveness of 0.97.

Influence of the specific surface area and silver crystallite size of mesoporous Ag/SrTiO3 on the selectivity enhancement of ethylene oxide production

ABSTRACTBackgroundEthylene oxide, which is industrially produced by ethylene epoxidation, is an important versatile chemical intermediate, thus its selectivity enhancement can bring substantial economic profits. In this work, the effects of two important, but still debatable, factors, i.e. catalyst specific surface area and active phase crystallite size, on the catalyst selectivity enhancement were investigated. Surfactant assisted sol–gel method with good control ability on the pores structure was selected to produce mesoporous strontium titanate (SrTiO3) nanocrystals with various specific surface area. The SrTiO3 nanocrystals were used as the supports of silver (Ag) for ethylene epoxidation.ResultsThe Ag/SrTiO3 catalysts with various surface areas were obtained by changing the surfactant‐alkoxide ratio and the calcination time. The ethylene oxide selectivity of the prepared catalysts was examined in a laboratory‐scale fixed bed reactor. The best performance was observed at the lowest surfactant–alkoxide ratio of 0.2 and calcination time of 4 h, with the surface area of 1.7 m2/g and Ag crystallite size of 15 nm.ConclusionThe best catalyst selectivity was observed at the lowest surface area and the highest average Ag crystallite size. In this condition, the selectivity of the Ag/SrTiO3 catalyst without any modifier was superior to a commercial Ag/Al2O3 catalyst with 3.7m2/g surface area and alkaline earth metal modifiers. © 2019 Society of Chemical Industry

Cooperative Effect of the Ce–Co‐Ox for the Catalytic Oxidation of Toluene

AbstractPure CeO2, Co3O4 and CeO2‐CoOx catalysts were successfully prepared by co‐precipitation method and investigated for toluene oxidation. The introduction of cobalt improved the porous texture and increased the specific surface area of catalysts. The cooperative effect of Co and Ce was characterized by several techniques. The characterization results indicated that CeO2‐CoOx showed the largest concentration of Ce3+, oxygen vacancy and surface adsorbed oxygen due to the generation of more structural defects, resulting in better redox properties. Hence, CeO2‐CoOx exhibited excellent catalytic activity and ideal CO2 selectivity than pure CeO2 and Co3O4.

Zirconium Doped Precipitated Fe-Based Catalyst for Fischer–Tropsch Synthesis to Light Olefins at Industrially Relevant Conditions

Direct conversion of synthesis gas to light olefins (ethylene, propylene, and butylenes) over Fe–Zr co-precipitated catalysts was investigated in a continuous-flow fixed-bed reactor at industrially relevant conditions. The effect of incorporation of zirconium on the textural properties, surface physicochemical properties, and reduction/carburization ability of Fe-based multi-component catalysts were examined by N2 adsorption–desorption, X-ray diffraction, transmission electron microscope, H2 temperature-programmed reduction (H2-TPR), CO temperature-programmed reduction, and X-ray photoelectron spectroscopy. The results indicated that the addition of less zirconium can promote the dispersion of iron oxide particles and increase the specific surface area of catalyst, leads to a higher Fischer–Tropsch synthesis activity. However, excessive addition of the zirconium promoter will cover the surface active sites and suppress the reduction and carburization of catalyst, which lead to lower activity. Meanwhile, the catalytic stability was destroyed by the addition of less Zr. The charge transfer between Fe and other promoter was redistributed by Zr, which disturbed the original Fe–Mg interaction. When the content of Zr further increased, the stability was improved again by a new formed Fe–Zr interaction. The zirconium promoter can effectively inhibit the chain growth probability and hydrogenation ability, resulting in the improvement of light olefins selectivity.

CuZn Catalysts Superior to Adkins Catalysts for Dimethyl Adipate Hydrogenolysis

AbstractIndustrial hydrogenolysis of esters to alcohols relies on the use of Adkins catalysts whose production and disposal is an environmental burden. This work is focused on CuZn catalysts that represent an ecological alternative to Adkins catalysts. Four CuZn catalysts with Cu/Zn atomic ratio ranging from 0.5 to 2.0 and single phase CuO and ZnO catalysts were prepared by co‐precipitation and their hydrogenolysis activity was compared with a commercial Adkins catalyst. Dimethyl adipate was used to test the catalyst performance in a flow reactor at temperatures ranging from 175 to 205 °C and hydrogen pressure of 16 MPa. The increase in ZnO content was directly responsible for the reduction in copper crystallite size and increase in the catalyst specific surface area. The CuZn catalysts exhibited higher conversion than the Adkins catalyst despite their specific surface area declined during the experiments more significantly than that of the Adkins catalyst. Nonetheless, the TOF of CuZn catalysts exceeded that of the commercial Adkins catalyst.

Effects of Aging Treatment on the Hydrotreating Performance of the Unsupported Catalyst

An unsupported Ni–Mo–W catalyst was synthesized by the hydrothermal method and treated by an aging treatment to improve its specific surface area and pore size. The effect of different aging conditions was studied by BET, XRD, SEM, and HRTEM techniques. The catalytic activity of the unsupported catalyst was evaluated with a simulated diesel feed. BET results showed that the catalyst specific surface area and pore volume increased significantly after aging treatment, and the hydrotreating results revealed that aging treatment resulted in higher catalytic activity than untreated catalyst, which is beneficial to the production of Ultra-Low-Sulfur Diesel (ULSD).

Catalytic gasification of refuse-derived fuel in a two-stage laboratory scale pyrolysis/gasification unit with catalyst based on clay minerals

Municipal solid waste (MSW) disposal is a serious environmental issue requiring immediate solution and good waste management strategy. Mechanical-biological treatment (MBT) plants offer the opportunity to reduce the amount of MSW that is, otherwise, disposed of in landfills. Up to 40% of MSW is converted to waste fuel, also called refuse-derived fuel (RDF). Gasification is a promising alternative of RDF processing. It can be defined as high temperature treatment of the feedstock with lower than stoichiometric amount of oxygen resulting mainly in a gaseous product (syngas). High hydrogen content, specific ratio of H2/CO, and low tar content are important parameters of syngas for its application in both energy production and chemical synthesis. Reduction of tar content in syngas can be achieved by catalytic tar cracking. In this work, a catalyst prepared from natural clay was characterised by thermogravimetric, specific surface area, X-ray diffraction, X-ray fluorescence and scanning electron microscopy (SEM) analyses. Catalyst activity was tested in two reactions, namely in decomposition of model tar constituent, p-xylene, and in cracking of tar produced in RDF gasification experiments. Influence of the reaction temperature and the amount of catalyst on the p-xylene conversion and products’ distribution was studied. The results proved high catalytic activity of the prepared catalyst in the decomposition of p-xylene. Coupled RDF pyrolysis and the produced volatiles gasification experiments were carried out in a two-stage laboratory scale reactor using a bed of tar cracking catalyst in the second stage. Tar decomposition experiments were carried out at the reactor temperatures of 700–850 °C applying different amounts of catalyst (0.75 g, 1 g, 1.25 g, 1.5 g, 2 g and 4 g) per 1 g of pyrolised RDF. Results indicate that the presence of catalyst had significant effect on both tar cracking efficiency and gas composition. Loss of the catalyst specific surface area was observed when the experiments were carried out at temperatures exceeding 800 °C.

Fabrication of manganese-based Zr-Fe polymeric pillared interlayered montmorillonite for low-temperature selective catalytic reduction of NOx by NH3 in the metallurgical sintering flue gas.

A series of Zr-Fe (Zr/Fe = 4:0, 3:1, 2:2, 1:3, 0:4) polymeric pillared interlayered montmorillonite loading 10wt.% MnOx (Mn/Zr-Fe-PILM) were investigated for the selective catalytic reduction of NOx by NH3 (NH3-SCR) in metallurgical sintering flue gas. The X-ray diffraction (XRD), N2 adsorption-desorption isotherm, scanning electron microscope (SEM), and ammonia temperature-programmed desorption (NH3-TPD) were used to analyze the physicochemical property. The Fe polymerized with Zr exchanged to montmorillonite can improve the Mn/Zr-Fe-PILM low-temperature NOx conversion and N2 selectivity. The Mn/Zr-Fe-PILM (1:3) shows the highest NOx conversion between 140 and 180°C. The XRD results suggest that the growth of crystalline ZrO2 phase is intensely restrained for the Fe2O3 migration into the ZrO2 lattice. The ZrO2 and MnOx have an excellent dispersion in montmorillonite. The N2 adsorption result illustrates that the increase of Fe molar content in the Zr-Fe-PILM support increases the catalyst-specific surface area. The NH3-TPD results elucidate that the Mn/Zr-Fe-PILM (1:3) has the most total acid sites. Therefore, the low-temperature catalytic activity of the Mn/Zr-Fe-PILM (1:3) has been assigned to the large specific surface area, abundant acid sites, and the dispersion of metallic oxides.

Analysis of Influence of Impurities in Hydrogen on PEFC Performance, Based on Measurement of Current Distribution Using Electrochemical Impedance Distribution Analyzer

Polymer electrolyte fuel cells (PEFC) systems have attracted considerable attention in that they can be powered by the hydrogen that is produced as a by-product of various industrial processes, such as caustic soda production and petrochemical processes. Most of the by-product hydrogen is discarded as a waste stream or used for heat production. Therefore, such plants could realize significant energy savings by installing PEFC systems, allowing them to generate power with a high level of efficiency by using the by-product hydrogen to fuel PEFC systems. However, the by-product hydrogen produced by these plants typically contains impurities. Although most of these impurities can be removed, a small amount inevitably remains in the hydrogen and can cause the performance of a PEFC system to degrade. Therefore, the influence of these impurities must be clarified before installing a PEFC system. Given the above, we have been developing a means of quickly evaluating the influence of impurities on a PEFC. The measurement of the current distribution is an important analysis approach that provides information on the local electrochemical reaction conditions in each of the cells of a PEFC. These cells are composed of an electrolytic membrane, a catalyst layer, a diffusion layer, and a flow channel. We have devised a means of measuring the current distribution using current distribution measurement sensors (S++ Simulation Services, Germany) which are inserted between the gas flow channel and current collector of either electrode. This method of measuring the current distribution allows us to quickly analyze the influence of impurities on the PEFC performance, relative to conventional voltage measurements, and can clarify which areas in a cell have degraded because the voltage change is the average of the values for every area in a cell, whereas the current change appears as an absolute value in a local area. Electrochemical impedance spectroscopy (EIS) is a valuable electrochemical analysis tool that can be applied to many kinds of electrochemical devices, including fuel cells. EIS can provide much useful information on the electrolyte membrane, the catalyst layer, and the reactant transfer in a PEFC cell. Although the measurement of the electrochemical impedance distribution in a cell provides a useful means of analyzing the influence of impurities on the PEFC performance, to the best of our knowledge, no previous studies have attempted a high-resolution analysis of the distribution. Therefore, we have developed a new measurement system that enables us to measure both the electrochemical impedance distribution and current distribution. The measurement system is an improved current distribution measurement sensor, intended for application to a JARI-standard cell, with an active area of 25 cm2 and which has 81 segmented internal current shunt resistances for measuring DC current and 81 segmented external connectors for measuring AC current signals. In the present study, to simulate impurities in the hydrogen, we added NH3 (25 ppm) and analyzed its influence on the PEFC performance. We used the measurement system to measure the change in the electrochemical impedance distribution and current distribution over time. The operating temperature, humidification temperatures of the anode and cathode, and current density of the cell were set to 65 ºC, 65 ºC, and 0.3 A/cm2 respectively. The AC current for measuring the electrochemical impedance was 1 Ap-p and the frequency range was 100 mHz–100 kHz. The current distribution measurement (Fig. 1) revealed that the influence of the NH3 was greatest at the inlet to the cell. Furthermore, from the results of the electrochemical impedance distribution measurement, it was found that the current distribution and some aspects of the resistance distribution, as determined from the electrochemical impedance, were correlated. Meanwhile, the most significant factor influencing the effect of NH3 on the PEFC performance is the increase in the activation overvoltage at the inlet of the cell. In addition, it was also thought that the cathode reaction resistance of the cell increases, which is caused by the catalyst-specific surface area decreasing at the inlet of the cell. In conclusion, our new measurement method provides an effective means of determining the largest degraded area and the largest degradation factor affecting PEFC performance, as a result of the presence of impurities in hydrogen. Therefore, relative to conventional measurements, we can quickly evaluate the influence of impurities on the PEFC performance by focusing on and analyzing these areas and factors. In the future, we will apply our new measurement method to the evaluation of the influence of impurities on the PEFC performance by acquiring information on the influence of such impurities on PEFC performance. Figure 1

Slurry methanol synthesis from CO2 hydrogenation over micro-spherical SiO2 support Cu/ZnO catalysts

The micro-spherical SiO2 support is prepared by the spray-drying method, and then a series of SiO2 supported Cu/ZnO-based catalysts with different percentage of Cu and ZnO are synthesized by ammonia-evaporation method. The Cu and ZnO loadings play a critical role on the physicochemical properties and catalytic performance of catalysts. The results show that Cu and Zn cations can be deposited into the pores of the micro-spherical SiO2 with well-distributed when the metal loadings are below 47.91 wt%. In addition, the specific surface area of catalysts increases with increasing loadings due to the formation of porous structure inside SiO2 support, while it decreases when the metal loading is above 47.91 wt%. According to XRD, XPS, XAES and CO adsorption in situ FTIR analysis, both Cu+ and Cu° species exist on the reduced surface of Cu/ZnO/SiO2 catalysts. The catalytic performance for slurry methanol synthesis from CO2 hydrogenation is examined. The Cu/ZnO/SiO2 catalyst exhibits an optimum catalytic activity when the metal loading reaches to 28.23 wt%. However, the CO2 conversion changes slightly with a further increase of metal loadings, because the pore of support is blocked and the reducibility of catalysts is decreased significantly with incorporation of excess metal compounds into SiO2. In addition, the methanol selectivity enhances with increasing metal loadings due to the decrease of the proportion of Cu+ species.

A study into syngas production from catalytic steam reforming of palm oil mill effluent (POME): A new treatment approach

This paper reports on the novel application of catalytic steam reforming process to convert palm oil mill effluent (POME) into syngas over a 20wt%Ni/80wt%Al2O3 catalyst. The catalyst possessed high degree of crystallinity and was impurity-free, judging from the obtained XRD pattern. Furthermore, the BET specific surface area of catalyst was low (2.09 m2 g−1), consistent with smooth surface captured by the FESEM images. CO2-desorption and NH3-desorption profiles showed a presence of both acid and basic sites on the surface of catalyst. In the absence of catalyst, about 7.0% reduction of chemical oxygen demand (COD) was achieved at 6.0 mL h−1 flow rate of POME, reforming temperature of 873 K and 20 mL min−1 of N2-flow. Significantly, the COD reduction shot up to 93.7% in the presence of catalyst and liquid-hourly-space-velocity (LHSV) of POME of 90 mL h−1 gcat−1 at 873 K. The corresponding biochemical oxygen demand (BOD) reduction recorded was 93.8%. However, normalized carbon loss indicates that a high LHSV would favour carbon deposition. In addition to high LHSV, the carbon deposition was also influenced by reaction temperature. High reaction temperature has reduced carbon deposition, as well as organics removal. COD reduction was 99.41% and BOD reduction was 99.52% at 1173 K when LHSV was 60 mL h−1 gcat−1. In the gas phase, four species were consistently detected, viz. H2, CO2, CO and CH4, with H2 as the major component. The H2 selectivity increased with both LHSV and reaction temperature.

Highly-efficient catalytic combustion performance of 1,2-dichlorobenzene over mesoporous TiO2–SiO2 supported CeMn oxides: The effect of acid sites and redox sites

High specific surface area CeMn/TiO2–SiO2 catalysts were synthesized and evaluated for the catalytic combustion of 1,2-dichlorobenzene (o-DCB). Mesoporous TiO2–SiO2 supports were prepared by evaporation-induced self-assembly (EISA) method to investigate the promotion of Si on the acid properties of TiO2. Pore structures of TiO2–SiO2 were modulated by controlling the amount of hydrochloric acid during the preparation process of mesoporous supports, and the influence of structures and physicochemical properties of CeMn/TiO2–SiO2 catalysts on the activity and stability of o-DCB catalytic combustion were thoroughly studied. The results showed that Mn cations incorporated into CeO2 fluorite structure caused the formation of more active oxygen species. The active oxygen species and high specific surface area of catalysts played significant roles in o-DCB oxidation reaction. The influence of water on o-DCB catalytic combustion was also studied, and two different observations were obtained at low or high content of water. Due to deposition of Cl species on the surface of catalyst, CeMn/TiO2–SiO2 loses partial activity during o-DCB catalytic combustion, and most of activity could be recovered through Deacon reaction.

Synthesis of Cr/Al<sub>2</sub>O<sub>3</sub>- Bentonite Nanocomposite as the Hydrocracking Catalyst of Castor Oil

Synthesis and characterization of Cr/Al2O3-bentonite nanocomposite as a hydrocracking catalyst of castor oil have been conducted. The catalyst was prepared according to the following method. At the first step, bentonite was activated using H2SO4 to obtain H-bentonite, after that the activated clay was pillarized by Al2O3, Next, a salt solution of Cr (NO3)3·9H2O was impregnated in the pillared bentonite sample, followed by calcination and reduction to obtain the final catalyst, i.e. Cr/Al2O3-bentonite. The catalysts including unpillared bentonite were characterized using infrared spectrometer (FT-IR), X-Ray diffractometer (XRD), X-ray Fluorescence spectrometer (XRF), Transmission Electron Microscope (TEM) and gas sorption analyzer. GC-MS analysis was conducted to characterize the hydrocracking product. The research results showed that pillarization of bentonite caused an increasing of the basal spacing of bentonite in an amount of 1.01 nm. Although Chrom was unevenly dispersed on the bentonite and it probably blocked the bentonite framework resulted in the decrease of catalyst specific surface area, Cr/Al2O3-bentonite catalyst gave the best conversion of 64.03%. The GC-MS analysis data showed that the hydrocracking products contained various kinds of organic compounds such as acetone, acetic acid, methyl benzene, octane, heptanal, 2-octene, 1-undecanoic acid, 9-octadecenal and 10-undecenoic acid.

Effect of Catalytic Ozonation Coupling with Activated Carbon Adsorption on Organic Compounds Removal Treating RO Concentrate from Coal Gasification Wastewater

ABSTRACTThis paper reports a novel system of catalytic ozonation coupling with activated carbon adsorption for removing the organic compounds treating in the RO concentrate from coal gasification wastewater. The effect of ozone dosage, catalyst dosage, reaction time, influence pH, and temperature on organic compounds removal were examined for the processes. In the catalytic ozonation process, increasing solution pH, dosages ozone, and catalyst were statistically significant for improving the performance. In addition, the high salinity with chloride concentration of 15 g/L could reduce the catalyst specific surface area by 18%. Thus, high salinity showed negative influence on the catalytic effect in TOC removal. Regarding activated carbon adsorption process, modified activated carbon by NaOH revealed advantages in adsorbing organic compounds treating catalytic ozonation effluent. With the ozone dosage of 120 mg/L, catalyst dosage of 2.0 g/L, catalytic ozonation reaction time of 1 h, and modified activated carbon adsorption time of 1 h, the average TOC removal efficiencies were maintained at the stable level of 58% with the TOC concentration of 26 mg/L.

Molybdenum anchoring effect in Fe–Mo/MgO catalyst for multiwalled carbon nanotube synthesis

Two Fe-based monometallic and four bimetallic catalysts based on Fe–Co and Fe–Mo, supported on commercial Al2O3 and MgO, were tested in carbon nanotube (CNT) synthesis by catalytic ethylene pyrolysis. The focus was to evaluate the influence of Mo addition to Fe, together with the particular role of support. Transmision electron microscopy revealed a synergetic effect of Mo and MgO: optimal metal-support interaction (MSI) resulted in small, well-defined and highly distributed Fe–Mo nanoparticles, enabling the best pyrolytic performance. It can be portrayed as the highest CNT yield presented per catalyst specific surface area, as well as the thinnest CNTs with the narrowest diameter distribution. Raman and X-ray diffraction examination of the CNTs obtained on the same catalyst revealed their highest quality in terms of lattice defects, as well as the degree of crystallinity.

Ultrasonic impregnation of MnO2/CeO2 and its application in catalytic sono-degradation of methyl orange

MnO2/CeO2 catalyst was prepared by ultrasonic impregnation method. The traditional and stirring impregnation methods were used as control. Results showed that ultrasonic impregnation was the best synthesis method. The impregnation time was shortened from 120 min (traditional method) to 20 min, the specific surface area of catalyst was three times larger, and the catalytic activity of catalyst was also the highest. Furthermore, MnO2 had crystalline structure and distributed uniformly on the support, CeO2. The preparing conditions were further examined and the optimal conditions were found to be: 20 min of ultrasonic impregnation, 4.3 mol/L of manganese nitrate concentration and 450 °C of calcination temperature. The so prepared catalyst removed 94% of methyl orange in 30 min with a dosage of 0.5 g/L. The efficiency was 77.7% and 85.9% for traditional and stirring impregnation method under the same experimental conditions. The reaction process involved two stages: adsorption-dominated and degradation-dominated stages. The reaction rate constant of adsorption-dominated stage had little difference. However, compared with traditional impregnation, the reaction rate constant of degradation-dominated stage improved from 0.01 to 0.14 min−1 by ultrasonic impregnation. Mechanism analysis showed that the activity of ultrasonic impregnation MnO2/CeO2 was improved by the effects of acoustic cavitation and ultrasound oscillation on solid–liquid transport and distribution status.

Effect of coating modification of cordierite carrier on catalytic performance of supported NiMnO3 catalysts for VOCs combustion

NiMnO3 perovskite catalysts supported on cordierite modified by CexZr1-xO2 coatings were prepared using impregnation and sol–gel methods for catalytic combustion of single/double component VOCs at different concentrations and GHSV of 15,000 h−1, which were characterized by BET, XRD, SEM, FT-IR, H2-TPR and O2-TPD. After coating modification, the specific surface area of catalysts is improved obviously. Among the catalysts, the Ce0.75Zr0.25O2 coating modified NiMnO3 catalyst exhibits the best catalytic activity for VOCs combustion with 95.6% conversion at 275 °C and has stable activity when catalyst is embalmed at 800 °C. In addition, the catalyst also presents the excellent water-resistant and conversion stability over time-on-stream condition. The reason is that Ce0.75Zr0.25O2 coating can promote more lattice distortion and defects and smaller crystal size, which improve oxygen transfer capability and dispersion of active component.

Porous MnO2/CNT catalysts with a large specific surface area for the decomposition of hydrogen peroxide

H2O2 vapor sterilization is an effective and safe method for removing various pathogens. To improve the efficiency of this technique, the time required for sterilization must be shortened. The aeration time constitutes a large portion of the total sterilization time; therefore, the development of a catalyst for H2O2 decomposition is necessary. Bulk MnO2 is typically used in H2O2 decomposition, but it has a low specific surface area. To increase H2O2 decomposition activity, specific surface area and electron transfer ability of catalyst need improvement. In this study, MnO2/CNT(x), where x denotes the weight ratio of CTAB to H2O in the catalyst preparation, was synthesized using a soft template method with varying amounts of the template. Overall, the catalyst specific surface area remarkably increased to 190–200 m2/g from 0.043 m2/g for bulk MnO2 and these increased surface areas resulted in superior H2O2 decomposition activity. Among the CNT-supported catalysts tested, MnO2/CNT (1.0) exhibited the highest activity, which was 570 times that of bulk MnO2. Aeration times were also calculated with some assumptions and the aeration can be finished within 1 hr (bulk MnO2 needs about 25 hr).