Iron–cobalt mixed oxide nanocatalysts: Heterogeneous peroxymonosulfate activation, cobalt leaching, and ferromagnetic properties for environmental applications

Sulfate radical-based advanced oxidation technologies (SR-AOTs) are attracting considerable attention due to the high oxidizing ability of SRs to degrade organic pollutants in aqueous environments. This study was carried out to respond to current concerns and challenges in SR-AOTs, including (i) need of heterogeneous activation of sulfate salts using transition metal oxides, (ii) nanoscaling of the metal oxide catalysts for high catalytic activity and promising properties with respect to leaching, and (iii) easy removal and recovery of the catalytic materials after their applications for water and wastewater treatments. In this study, we report a novel approach of using Fe–Co mixed oxide nanocatalysts for the heterogeneous activation of peroxymonosulfate (PMS) to generate SRs targeting the decomposition of 2,4-dichlorophenol, and especially focus on some synthesis parameters such as calcination temperature, Fe/Co contents, and TiO₂ support. The physicochemical properties of the catalysts were investigated using porosimetry, XRD, HR-TEM, H₂-TPR, and XPS. Ferromagnetic CoFe₂O₄ composites formed by thermal oxidation of a mixed phase of Fe and Co exhibited significant implications for the efficient and environmentally friendly activation of PMS, including (i) the cobalt species in CoFe₂O₄ are of Co(II), unlike Co₃O₄ showing some detrimental effects of Co(III) on the PMS activation, (ii) CoFe₂O₄ possesses suppressed Co leaching properties due to strong Fe–Co interactions (i.e. Fe–Co linkages), and (iii) Fe–Co catalysts in form of CoFe₂O₄ are easier to recover due to the unique ferromagnetic nature of CoFe₂O₄. In addition, the presence of Fe was found to be beneficial for enriching hydroxyl group content on the Fe–Co catalyst surface, which is believed to facilitate the formation of Co(II)-OH complexes that are vital for heterogeneous PMS activation.     

Fischer–Tropsch synthesis over Re-promoted Co supported on Al2O3, SiO2 and TiO2: Effect of water

The activity and selectivity of rhenium promoted cobalt Fischer–Tropsch catalysts supported on Al₂O₃, TiO₂ and SiO₂ have been studied in a fixed-bed reactor at 483 K and 20 bar. Exposure of the catalysts to water added to the feed deactivates the Al₂O₃ supported catalyst, while the activity of the TiO₂ and SiO₂ supported catalysts increased. However, at high concentrations of water both the SiO₂ and TiO₂ supported catalyst deactivated. Common for all catalysts was an increase in C₅₊ selectivity and a decrease in the CH₄ selectivity by increasing the water partial pressure. The catalysts have been characterized by scanning transmission electron microscope (STEM), BET, H₂ chemisorption and X-ray diffraction (XRD).     

Catalytic activity of dispersed CuO phases towards nitrogen oxides (N2O, NO, and NO2)

A systematic reactivity study of N₂O, NO, and NO₂ on highly dispersed CuO phases over modified silica supports (SiO₂–Al₂O₃, SiO₂–TiO₂, and SiO₂–ZrO₂) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N₂O) to selective reductions by hydrocarbons (N₂O, NO, and NO₂) and oxidation (NO to NO₂). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO₂–Al₂O₃ and SiO₂–ZrO₂, led to a better activity and selectivity of CuO for the reactions of N₂O, NO, and NO₂ reductions and N₂O decomposition than SiO₂–TiO₂. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values.     

Catalytic removal of perchloroethylene (PCE) over supported chromium oxide catalysts

The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on SiO₂, SiO₂–Al₂O₃, activated carbon, mordenite type zeolites, MgO, TiO₂ and Al₂O₃. Supported chromium oxide catalysts were more active than any other metal oxide catalysts including noble metal examined in the present study. PCE removal activity of chromium oxide catalysts mainly depended on the type of supports and the content of metal loaded on the catalyst surface. TiO₂ and Al₂O₃ containing high surface areas were effective for the high performance of PCE removal, since the formation of well dispersed Cr(VI) active reaction sites for the present reaction system, was enhanced even for the high Cr loading on the catalyst surface. CrO_x catalysts supported on TiO₂ and Al₂O₃ also exhibited stable PCE removal activity at a low feed concentration of PCE of 30 ppm up to 100 h at 350°C. However, significant catalyst deactivation was observed at high PCE concentration of 10 000 ppm. CrO_x/TiO₂ revealed stronger water tolerance than CrO_x/Al₂O₃ due to the surface hydrophobicity.     

Co3O4对2,4-二氯苯酚的吸附性能影响

以硝酸钴(Co(NO₃)₂·6H₂O)为钴源,考察了不同沉淀剂(6 mol/L氨水、1 mol/L NaOH溶液、饱和碳酸铵溶液)对Co₃O₄吸附2,4-二氯苯酚(2,4-DCP)性能的影响。考察了焙烧温度、pH值、沉淀剂种类、吸附剂用量、2,4-DCP初始质量浓度对Co₃O₄吸附性能的影响,并进行了离子干扰实验。结果表明,焙烧温度为300℃、pH=9.0、沉淀剂为1 mol/L NaOH时,Co₃O₄对20 mg/L 2,4-DCP吸附性能最佳。Co₃O₄对2, 4-DCP的动力学吸附过程符合准二级动力学方程,等温吸附方程符合Langmuir方程,吸附过程以单分子层化学吸附为主。     

In situ XAFS analysis of catalytically active cobalt species in porous clays for deep hydrodesulfurization

Mesoporous smectite-type clays containing cobalt species in lattice (MST(Co)) were prepared by a hydrothermal method and examined for hydrodesulfurization (HDS). The MST(Co) catalysts showed higher HDS activities than a commercial alumina-supported cobalt–molybdenum catalyst (Co–Mo/Al₂O₃). The active structure of MST(Co) was studied by in situ X-ray absorption fine structure and nitrogen adsorption techniques.     

A model catalyst approach to the effects of the support on Co–Mo hydrodesulfurization catalysts

Co–Mo model sulfide catalysts, in which CoMoS phases are selectively formed, were prepared by means of a CVD technique using Co(CO)₃NO as a precursor of Co. It is shown by means of XPS, FTIR and NO adsorption that CoMoS phases form selectively when the Mo content exceeds monolayer loading. A single exposure of MoS₂/Al₂O₃ to a vapor of Co(CO)₃NO at room temperature fills the edge sites of the MoS₂ particles. It is suggested that the maximum potential HDS activity of MoS₂/Al₂O₃ and Co–Mo/Al₂O₃ catalysts can be predicted by means of Co(CO)₃NO as a “probe” molecule. An attempt was made to determine the fate of Co(CO)₃NO adsorbed on MoS₂/Al₂O₃. The effects of the support on Co–Mo sulfide catalysts in HDS and HYD were investigated by use of CVD-Co/MoS₂/support catalysts. XPS and NO adsorption showed that model catalysts can also be prepared for SiO₂-, TiO₂- and ZrO₂-supported catalysts by means of the CVD technique. The thiophene HDS activity of CVD-Co/MoS₂/Al₂O₃, CVD-Co/MoS₂/TiO₂ and CVD-Co/MoS₂/Al₂O₃ is proportional to the amount of Co species interacting with the edge sites of MoS₂ particles or CoMoS phases. It is concluded that the support does not influence the HDS reactivity of CoMoS phases supported on TiO₂, ZrO₂ and Al₂O₃. In contrast, CoMoS phases on SiO₂ show catalytic features characteristic of CoMoS Type II. With the hydrogenation of butadiene, on the other hand, the Co species on MoS₂/TiO₂, ZrO₂ and SiO₂ have the same activity, while the Co species on MoS₂/Al₂O₃ have a higher activity.     

TiO2与SiO2掺杂对Al2O3相转变的研究

通过球磨混合法,制备TiO2、SiO2和TiO2+SiO2掺杂的Al2 O3粉体,经不同温度煅烧后进行X射线衍射(XRD)测试,比较研究这三种掺杂对Al2 O3粉体相转变温度的影响.研究结果表明,TiO2、SiO2掺杂对γ-Al2 O3向α-Al2 O3的相转变均有促进作用.在掺杂质量分数为0.5％的情况下,二者可分别...     

Promoting effect of water vapor on catalytic oxidation of methane over cobalt/manganese mixed oxides

Methane oxidation was conducted in a fixed bed quartz tubular reactor on a series of mixed oxides of cobalt/manganese prepared by a sol–gel method. A unique promoting effect of water vapor on methane conversion was observed for the first time on these cobalt/manganese mixed oxides calcined at 450 or 600 °C. However, these mixed catalysts lost their catalytic activities after being calcined at 850 °C. The catalytic activity of methane oxidation was significantly improved by supporting the cobalt/manganese mixed species onto the high surface area SiO₂ or Al₂O₃–SiO₂ materials. It was noteworthy that the water enhancement effect was retained on these supported catalysts.     

Co改性活性炭吸附NO的实验研究

采用Co(NO_3)_2对活性炭进行改性,考察浸渍浓度和吸附温度等条件对活性炭吸附NO性能的影响,并对已吸附NO的0.3 mol·L~(-1)的Co(NO_3)_2改性活性炭进行再生。通过BET、SEM、吸附等温线和FT-IR表征样品的比表面积、颗粒形貌和表面官能团。结果表明,当浸渍溶液浓度为0.3 mol·L~(-1)时,吸附效果最佳,80 min时吸附效率达88.90%。活性炭的吸附效率随着温度升高而降低,用0.3 mol·L~(-1)Co(NO_3)_2改性的活性炭在200℃时的吸附效率大于90%,并可持续50 min。SEM和FT-IR表征结果表明,在Co(NO_3)_2改性的活性炭表面和孔隙生成了Co_3O_4,促进NO催化氧化为NO_2并进行吸附。加热再生后的0.3 mol·L~(-1)Co(NO_3)_2改性活性炭对NO的吸附效率在60 min内仍高于88.90%,再生效果较好,可持续再生利用。     

Attrition resistance of cobalt F–T catalysts for slurry bubble column reactor use

There exists much current interest in the use of supported Co catalysts and slurry bubble column reactors (SBCR) for the conversion of natural gas to higher hydrocarbons via the Fischer–Tropsch (F–T) synthesis. Catalyst attrition resistance is extremely important in the operation of slurry-phase reactor systems because of potential problems with plugging of system filters and/or contamination of the liquid products. This paper addresses the effects of different supports, promoters, and preparation methods on the attrition resistance of Co F–T catalysts for SBCR use.

The calcined supports had attrition resistances (inversely related to % fines <11 μm generated during attrition testing) as follows:

−Al₂O₃>TiO₂(rutile)SiO₂

Loading of Co onto the supports improved the attrition resistances of both alumina and silica significantly. It has essentially no effect on titania. The resulting catalysts had attrition resistances in the order

Co/Al₂O₃>Co/SiO₂>Co/TiO₂(rutile)>Co/TiO₂(anatase)

The addition of small amounts of metal (Ru, Cu) and oxide (La, Zr, K, Cr) promoters had mainly small effects on the attrition resistance of the supported Co catalysts. However, it would appear that the addition of Zr to Co/alumina had a negative impact on its attrition resistance. The different preparation methods used in this study (aqueous impregnation, non-aqueous impregnation, and kneading) did not appear to have a significant effect on catalyst attrition resistance.     

Liquid phase hydrodechlorination of chlorophenols over Pd/C and Pd/Al2O3: a consideration of HCl/catalyst interactions and solution pH effects

The liquid phase hydrodechlorination (HDC) of 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) has been studied over 1% (w/w) Pd/C and Pd/Al₂O₃ under conditions of minimal mass transport constraints. The HDC of 2,4-DCP generated HCl and 2-CP as the only intermediate partially dechlorinated product which reacts further to yield phenol; cyclohexanone was formed over Pd/Al₂O₃, but not over Pd/C, prior to complete dechlorination. Pd/Al₂O₃ is characterized (on the basis of TEM analysis) by a narrow distribution of smaller Pd particles to give a surface area weighted mean particle DIAMETER = 2.4 nm that is appreciably lower than the value of 13.2 nm established for Pd/C, where the latter is characterized by a broader distribution of larger (spherical) particles. The addition of NaOH served to increase fractional dechlorination by suppressing HDC inhibition due to the HCl that is generated. Reuse of the catalysts revealed an appreciable deactivation of Pd/C and a limited loss of activity in the case of Pd/Al₂O₃. Deactivation of Pd/C can be linked to a decrease (up to ca. 60%) in the initial BET surface area allied to appreciable leaching (up to ca. 40%) of the starting Pd content through the corrosive action of HCl and, while the average Pd diameter is essentially unaffected, there is evidence of a preferred leaching of larger Pd particles. The stronger metal/support interactions prevalent in Pd/Al₂O₃ results in limited Pd leaching and comparable initial HDC activities during catalyst reuse with/without NaOH addition. Inclusion of HCl in the reaction mixture (pH 5–1.5) resulted in a marked decline in the initial HDC rate associated with Pd/Al₂O₃ and a lesser drop in HDC activity for Pd/C. The difference in response to bulk solution pH variations are discussed in terms of the nature of the reactive species in solution and the amphoteric behavior of the Pd supports.     

Improvement of catalytic activity and sulfur-resistance of Ag/TiO2–Al2O3 for NO reduction with propene under lean burn conditions

Ag-based catalysts supported on various metal oxides, Al₂O₃, TiO₂, and TiO₂–Al₂O₃, were prepared by the sol–gel method. The effect of SO₂ on catalytic activity was investigated for NO reduction with propene under lean burn condition. The results showed the catalytic activities were greatly enhanced on Ag/TiO₂–Al₂O₃ in comparison to Ag/Al₂O₃ and Ag/TiO₂, especially in the low temperature region. Application of different characterization techniques revealed that the activity enhancement was correlated with the properties of the support material. Silver was highly dispersed over the amorphous system of TiO₂–Al₂O₃. NO₃⁻ rather than NO₂⁻ or NOx reacted with the carboxylate species to form CN or NCO. NO₂ was the predominant desorption species in the temperature programmed desorption (TPD) of NO on Ag/TiO₂–Al₂O₃. More amount of formate (HCOO⁻) and CN were generated on the Ag/TiO₂–Al₂O₃ catalyst than the Ag/Al₂O₃ catalyst, due to an increased number of Lewis acid sites. Sulfate species, resulted from SO₂ oxidation, played dual roles on catalytic activity. On aged samples, the slow decomposition of accumulated sulfate species on catalyst surface led to poor NO conversion due to the blockage of these species on active sites. On the other hand, catalytic activity was greatly enhanced in the low temperature region because of the enhanced intensity of Lewis acid site caused by the adsorbed sulfate species. The rate of sulfate accumulation on the Ag/TiO₂–Al₂O₃ system was relatively slow. As a consequence, the system showed superior capability for selective adsorption of NO and SO₂ toleration to the Ag/Al₂O₃ catalyst.     

载体对铁基整体式催化剂上丙烯催化还原NO的影响

以Al₂O₃、SiO₂和TiO₂为载体,采用凝胶-溶胶法和浸渍法制备铁基堇青石整体式催化剂,并对其丙烯选择性催化还原NO性能进行了研究。通过N₂物理吸附/脱附、XRD、SEM、H₂-TPR、Py-FTIR和原位DRIFTS技术对催化剂进行了表征。不同载体对催化剂的表面酸性、氧化还原性能、比表面积和表面形貌有显著影响,从而导致丙烯还原NO的催化活性明显差异。C₃H₆-SCR的催化活性按Fe/Al₂O₃/CM > Fe/SiO₂/CM > Fe/TiO₂/CM依次降低。在450℃的有氧条件下,在Fe/Al₂O₃/CM上催化C₃H₆还原NO效率可达到100%,这主要是因为较好的氧化还原性能和丰富的Lewis酸性位。基于原位的DRIFTS研究表明,Lewis酸性位的增加有助于促进形成NO₂/NO₃^-物种,从而提高了催化性能。     

Partial oxidation of methane to CO and H2 over nickel and/or cobalt containing ZrO2, ThO2, UO2, TiO2 and SiO2 catalysts

The influence of different metal oxide supports (i.e. ZrO₂, ThO₂, UO₂, TiO₂ and SiO₂) on the performance of Ni- and/or Co-containing catalysts [Ni and/or Co/MO₂ mole ratio (where M=Zr, Th, U, Ti or Si)=1.0] in the oxidative methane-to-syngas conversion at very low contact time (GHSV=5.2×10⁵ cm³ g⁻¹ h⁻¹ at STP) was investigated. The nickel-containing ZrO₂, ThO₂ and UO₂ catalysts (with or without pre-reduction by hydrogen at 500°C) showed good performance in the process; the order of their performance is NiO–ThO₂>NiO–UO₂>NiO–ZrO₂. The NiO–TiO₂ showed appreciable catalytic activity only after its reduction at 800°C. However, this catalyst and the NiO–SiO₂ catalyst showed poor performance in the process. These two catalysts are also deactivated very fast, mostly because of sintering of Ni and/or formation of catalytically inactive binary metal oxide phases by solid–solid reaction at the high catalyst calcination and/or catalytic reaction temperature. Although the Ni-containing ThO₂, UO₂ and ZrO₂ catalysts showed good performance, carbon deposition on them during the process is fast. However, because of the addition of cobalt to these catalysts (with Co/Ni=1.0), the rate of carbon deposition on them in the process is drastically reduced. This Co addition however resulted in a significant decrease in both the conversion and selectivity; the decrease in the selectivity was small.     

SiO2负载钴系催化剂的环己烯环氧化性能

采用沉积沉淀法制备不同负载量的SiO₂（硅胶）负载钴氧化物催化剂,采用X射线衍射（XRD）、X射线光电子能谱（XPS）、透射电镜（TEM）、N₂吸脱附等手段对催化剂进行表征,结果表明钴系氧化物为Co₃O₄,并且钴氧化物均匀地负载在SiO₂（硅胶）载体上,其活性组分的粒子大小集中分布在2～10nm。将制备的催化剂应用于环己烯环氧化反应,以环己烯、分子氧为原料,异丁醛为催化助剂,N,N-二甲基甲酰胺（DMF）为反应溶剂,在高压釜中进行。同时将SiO₂负载钴氧化物催化剂与不同载体上制备的钴系催化剂进行比较,发现催化剂用量0.20g、环己烯2.00g、异丁醛3.50g、反应温度50℃、反应时间5h、氧气压力4MPa时,环己烯的转化率和环氧环己烷的选择性分别可达到66.56%和71.03%。     

恒热流直管中纳米流体对流传热的实验研究(英文)

In this work, the laminar convective heat transfer performance and the pressure drop of water-based nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles flowing through a straight circular tube were experimen-tally investigated. The experimental results showed that addition of small amounts of nano-sized Al2O3 and TiO2 particles to de-ionized water increased heat transfer coefficients considerably, while the SiO2 nanofluids showed the opposite behavior attracting the authors’ interests. An average of 16%and 8.2%increase in heat transfer coefficient were observed with the average of 28%and 15%penalty in pressure drop for Al2O3 and TiO2 nanofluids.     

Photocatalytic oxidation of methanol using titania-based fluidized beds

Experiments determined methanol removal and catalyst elutriation rates during photocatalytic oxidation (PCO) of fluidized and packed beds of various titania-based catalysts. The study developed elutriation-resistant catalysts in which TiO₂ was precipitated from solution (p-TiO₂), or was coated on an Al₂O₃ support (TiO₂/Al₂O₃) and compared them to Degussa P-25 TiO₂. Although Degussa P-25 TiO₂ oxidized methanol effectively, it elutriated at a rate that was two orders of magnitude greater than those of p-TiO₂ and TiO₂/Al₂O₃. In addition, TiO₂/Al₂O₃ removed methanol at a significantly greater rate than did P-25, with p-TiO₂ being the least active. Fluidized beds produced greater PCO rates than did packed beds of P-25 and TiO₂/Al₂O₃. Fluidization enhancers, such as vibration and incorporation of a static mixer, improved the performance of the P-25 fluidized bed, but did not change the effectiveness of TiO₂/Al₂O₃ or p-TiO₂. The activity of TiO₂/Al₂O₃ decreased with increasing calcination temperature (over the temperature range 673–873 K). The optimum TiO₂ loading for TiO₂/Al₂O₃ was 30 wt.%.     

Low-pressure chemical and photochemical reactions of oxides of nitrogen on alumina taken as a model substance for mineral dust in relation to air pollution

The interaction of γ-Al₂O₃, taken as a model substance of tropospheric mineral dust, with N₂O, NO and NO₂ has been studied using kinetic and temperature-programmed desorption (TPD) mass-spectrometry in presence and absence of UV irradiation. At low surface coverages (<0.001 ML), adsorption of N₂O and NO₂ is accompanied by dissociation and chemiluminescence, whereas adsorption of NO does not lead to appreciable dissociation. Upon UV irradiation of Al₂O₃ in a flow of N₂O, photoinduced decomposition and desorption of N₂O take place, whereas in a flow of NO, only photoinduced desorption is observed. Dark dissociative adsorption of N₂O and NO and photoinduced N₂O dissociation apparently occur by a mechanism involving electron capture from surface F- and F⁺-centers. Photoinduced desorption of N₂O and NO may be associated with decomposition of complexes of these molecules with Lewis acid sites, V-centers or OH-groups. TPD of N₂O and NO proceeds predominantly without decomposition, while NO₂ partially decomposes to NO and O₂.