Search

The predictability of pyrolysis yields and product composition of mixed plastics has been studied. To do so, pyrolysis of virgin polymers (HDPE, LDPE, PP, PS and PET) and eight individual sorting categories from a real waste DKR-350 stream (PE rigid/film, PP rigid/film, PET, PS, multilayer flexibles, and clogged materials) was performed in a batch reactor at 500 °C at laboratory scale. The obtained oil/wax, gas, and solid yields and the composition of oil/wax of those individual feedstocks were used as input of a superposition model to predict the corresponding pyrolysis yields and oil/wax composition of mixed feeds, which were later compared with the experimentally measured product yields from the pyrolysis of those mixed streams. This linear model predicts the oil/wax yield of the mixed streams to a reasonable extent, with a maximum yield deviation (overestimation) of 8 percentage points. However, the presence of significant amounts of PET (above 33 wt%) in the mixed plastic streams negatively impacts the production of the condensable product and promotes the formation of solid products beyond the expected predicted values. Quantification of the type of carbon (aliphatic, aromatic and carbonyl) present in all the oil/wax products was done using 13C NMR spectroscopy. A linear model could also predict the aliphatic carbon yield in the condensable product from plastic waste streams with high accuracy (maximum yield difference of 6 percentage points). However, the aromatic carbon yield could not be predicted, probably due to the observed behavior of PET, which interacts with other polymers to promote solid product formation.

Oxidation is an excellent way to improve the properties of native starches. After oxidation, products are easier to handle due to a lowered paste viscosity in water, an improved stability and enhanced adhesive properties. Currently, oxidation by sodium hypochlorite (NaOCl) is the dominant commercial process for oxidized starches, which allows for oxidation of hydroxyl groups into carboxylic acids. Here, we show that by using a commercial homogeneous binuclear manganese catalyst ([MnIV2(μ-O)3(tmtacn)2][(CH3COO)2] (Mncat), with tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), and H2O2 as oxidant, starch can be oxidised without the cogeneration of ecotoxic chlorinated waste products. Although oxidation with H2O2 and other catalysts (mainly iron-based) has been done, high loadings were needed and the starch pasting properties were not yet on par with NaOCl oxidised starches. Starch granules suspended in water can be oxidized at room temperature with 0.0021 mol% Mncat and 1 wt% H2O2 yielding starch with similar properties (DSCOOH, yield, pasting properties) as those achieved by NaOCl oxidation. This catalytic oxidation of starch with an earth-abundant metal catalyst at ppm loadings, which is widely applied in detergents, highlights the potential for the development of a more sustainable process to produce oxidized starches.

Depolymerization of lignin by pyrolysis has been identified as a viable route to produce renewable fuels and biobased platform chemicals. Herein we report the pyrolysis of LignoBoost lignin in a molten salt consisting of ZnCl2-KCl-NaCl (60:20:20 mol ratio) in a g-scale reactor set-up with a focus on the liquid phase yields and composition. The effects of relevant process parameters such as temperature (250–450 °C), reaction time (10–50 min), and N2 flow rate (10–30 mL min−1) on the product yields were elucidated using design of experiments. The highest bio-oil yield was 47.1 wt% (450 °C, 10 min) and the yield of organics in the bio-oil at this condition was 24 wt% (on lignin intake), the remainder being water. The latter is considerably higher than found for an experiment at similar conditions without salt (16 wt%). Temperature and reaction time were shown to have the largest effects on bio-oil yield. Prolonged reaction times resulted in higher amounts of gas phase components (H2, CO2) and water, and a reduced amount of solid products. Statistical analyses and validation experiments showed that the experimental product yields are in good agreement with the predicted values from the model. The properties and molecular composition of the liquid products were determined using various analytical techniques and reveal that the presence of a molten salt during pyrolysis has a positive influence on the composition of the liquid phase like a higher level of depolymerization and higher selectivity to aromatic and phenolic monomers compared to thermal pyrolysis.

Oxidized starch can be efficiently prepared using H2O2 as an oxidant and iron(III) tetrasulfophthalocyanine (FePcS) as a catalyst, with properties in the same range as those for commercial oxidized starches prepared using NaOCl. Herein, we performed an in-depth study on the oxidation of potato starch focusing on the mode of operation of this green catalytic system and its fate as the reaction progresses. At optimum batch reaction conditions (H2O2/FePcS molar ratio of 6000, 50 °C, and pH 10), a high product yield (91 wt %) was obtained with substantial degrees of substitution (DSCOOH of 1.4 and DSCO of 4.1 per 100 AGU) and significantly reduced viscosity (197 mPa·s) by dosing H2O2. Model compound studies showed limited activity of the catalyst for C6 oxidation, indicating that carboxylic acid incorporation likely results from C-C bond cleavage events. The influence of the process conditions on the stability of the FePcS catalyst was studied using UV-vis and Raman spectroscopic techniques, revealing that both increased H2O2 concentration and temperature promote the irreversible degradation of the FePcS catalyst at high pH. The rate and extent of FePcS degradation were found to strongly depend on the initial H2O2 concentration where also the rapid decomposition of H2O2 by FePcS occurs. These results explain why the slow addition of H2O2 in combination with low FePcS catalyst concentration is beneficial for the efficient application in starch oxidation.

Pyrolysis of a post-consumer plastic waste stream (DKR-350) has been performed at a laboratory scale in a fixed-bed reactor at 500 °C. DKR-350 is a complex mixture of post-consumer plastics comprising polyethylene, polypropylene, polystyrene, polyethylene terephthalate, clogged materials, multilayer flexibles, together with considerable amounts of biogenic and inorganic residues and halogens. The influence of different washing procedures on feedstock composition and pyrolysis product yields was investigated. Washing effectively lowers the biogenic, inorganic and halogen contents in DKR-350, though does not affect the yield of the desired oil/wax (66 to 69 wt%). 27% of the oil/wax lies in the boiling point range of naphtha and gasoline (< 200 °C). During pyrolysis, the oxygen content of the oil/wax is reduced to 8–14 wt%, compared to 10–16 wt% in the feed. Chlorine analysis revealed that most of the chlorine present in the feed is removed by washing. Nevertheless, the concentration of chlorine in the oil/wax is still high (>150 ppm), showing the presence of recalcitrant organochlorides in the feed. Thus, post-treatment is still required to upgrade it to feedstock for the production of fuels and/or chemicals.

Pyrolysis is an important technology to convert lignocellulosic biomass to a renewable liquid energy carrier known as pyrolysis oil or bio-oil. Herein we report the pyrolysis of pigeon pea wood, a widely available biomass in the Philippines, in a semi-continuous reactor at gram scale. The effects of process conditions such as temperature (400-600 ◦C), nitrogen flow rate (7-15 mL min−1) and particle size of the biomass feed (0.5-1.3 mm) on the product yields were determined. A Box-Behnken three-level, three-factor fractional factorial design was carried out to establish process-product yield relations. Of particular interest is the liquid product (bio-oil), of which the yield was shown to depend on all independent variables in a complex manner. The optimal conditions for highest bio-oil yield (54 wt.% on dry feed intake) were a temperature of 466 ◦C, a nitrogen flow rate of 14 mL min−1 and a particle size of 1.3 mm. Validation of the optimized conditions proved that the average (n = 3) experimental bio-oil yield (52 wt.%) is in good agreement with the predicted value from the model. The properties of product oils were determined using various analytical techniques including gas chromatography-mass spectrometry (GC-MS), gel-permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (13C- and HSQC-NMR) and elemental and proximate analyses. The bio-oils were shown to have low ash content (0.2%), high heating value (29 MJ kg−1) and contain high value-added phenolics compounds (41%, GC peak area) as well as low molecular weight aldehydes and carboxylic acids. GPC analysis indicated the presence of a considerable amount of higher molecular weight compounds. NMR measurements showed that a large proportion of bio-oil contains aliphatic carbons (~60%), likely formed from the decomposition of (hemi)cellulose components, which are abundantly present in the starting pigeon pea wood. Subsequent preliminary scale-up pyrolysis experiments in a fluidized bed reactor (~100 gfeed h−1, 475 ◦C and N2 flow rate of 1.5 L min−1) gave a non-optimized bio-oil yield of 44 wt.%. Further fractionation and/or processing are required to upgrade these bio-oils to biofuels and biobased chemicals.

Catalytic pyrolysis of crude glycerol over a shaped H-ZSM-5 zeolite catalyst with (partial) recycling of the product oil was studied with the incentive to improve benzene, toluene, and xylene (BTX) yields. Recycling of the polycyclic aromatic hydrocarbon (PAH) fraction, after separation from BTX by distillation and co-feeding with the crude glycerol feed, was shown to have a positive effect on the BTX yield. Further improvements were achieved by hydrogenation of the PAH fraction using a Ru/C catalyst and hydrogen gas prior to co-pyrolysis, and BTX yields up to 16 wt% on feed were obtained. The concept was also shown to be beneficial to other biomass feeds such as e.g., Kraft lignin, cellulose, and Jatropha oil.

Hexavalent molybdenum ions substituted into the mixed-valent framework of octahedral molecular sieve manganese oxides (1-10 mol% Mo-K-OMS-2) were systematically prepared via a single-step refluxing method. The structure, composition, morphology, thermal stability, and textural and redox properties of the Mo-K-OMS-2 materials were characterized by various experimental techniques. Density functional theory (DFT) calculations were performed to study the electronic properties of K-OMS-2 materials, including the influence of molybdenum on such properties. The catalytic activity of K-OMS-2 towards CO oxidation dramatically increased with Mo dopant concentration, until an optimum incorporation of 5 mol% was reached, giving full CO conversion at 120 degrees C (1 vol% CO, 1 vol% O-2). More importantly, the activity of the 5% Mo-K-OMS-2 catalyst was (reversibly) inhibited by water vapour (3%) in the feed only at low temperatures and exhibited better tolerance and stability during long-run experiments (28 h) as compared to undoped K-OMS-2. The superior performance of Mo-K-OMS-2 catalyst for CO oxidation can be attributed to the following factors: (1) morphological evolution from nanofibers to nanospheres, as well as the slightly distorted structure, generated a sharp increase in the specific surface area up to 258 m(2) g(-1), hence, increased the number of surface active sites; (2) improved mobility of reactive oxygen species at the surface and enhanced redox properties; and (3) tailored electronic properties promoted more active sites for oxidation reactions, which is supported by DFT calculations.

Mesoporous sulfated-metal oxides and mixed-metal oxides prepared by a facile coprecipitation method employing titanium oxysulfate–sulfuric acid complex as a precursor of both titanium and sulfate are highly active and selective for direct methanolysis of carbohydrates to methyl levulinate. The most active sulfated TiO 2 –ZrO 2 catalyst selectively converted fructose to methyl levulinate with a remarkably high yield (71%) after 1 h at 200 °C. Significant amounts of methyl levulinate were also obtained from sucrose (54%) and glucose (23%) after 1 h at 200 °C. The used catalyst was easily recovered and recycled without any loss of selectivity although activity decreased due to humin deposition on the surface. The spent catalysts were easily rejuvenated through calcination in air. The formation of ethers during dehydration was negligible suggesting that methanol can be recycled after distillation.

Silicatein α, an enzyme found at the center of silica spicules in marine sponges, is known to play a role in silica condensation from seawater. It has also been shown to catalyze the formation of silica from various silica precursors such as tetraethyl orthosilicate (TEOS). Inspired by the finding that the serine-26 and histidine-165 amino acids in the enzyme are required for silica formation from TEOS, we synthesized poly(hydroxylated isoprene-b-2-vinylpyridine) block copolymers to mimic these amino acid residues. Here, we present the results of our investigation utilizing this biomimetic polymer to condense titania from titanium iso-propoxide (TiP). Our silicatein α mimic is shown to condense titania at neutral pH and room temperature and is compared to material produced by standard sol–gel methods. Heats of crystallization are observed to be 72% lower for the titania made from the mimic polymer, and indistinct X-ray diffraction peaks, even after heating well above the crystallization temperature, sugge...

High-valent vanadium ions were substituted into the synthetic cryptomelane manganese oxide (K-OMS-2) framework through a simple and low-cost reflux method and investigated for total and preferential catalytic oxidation of carbon monoxide. Substitutional doping of V5+ resulted in materials with modified composition, morphology, thermal stability; and textural, redox, and catalytic properties. The catalytic activity increased with V concentration until an optimum amount (≈10 % V incorporated) was reached, beyond that a structural “crash point” was observed, resulting in a material with low crystallinity, nanosphere morphology, and reduced catalytic activity. An increase in O2 concentration in the feed gas resulted in an increase in conversion over 10% V K-OMS-2. This most active catalyst was deactivated by moisture only at low temperatures and showed better tolerance than undoped K-OMS-2. This catalyst also preferentially oxidized CO to CO2 from 25 °C to 120 °C in large amounts of H2 under dry conditions, without significantly affecting CO conversion. The doped catalyst also showed stable activity and selectivity in long-run experiments. The mobility and lability of surface oxygen, formation of hydroxyl groups, and enhanced surface redox properties promoted by V doping were strongly correlated with the enhancement of catalytic activities of K-OMS-2 nanomaterials.

A bimodification synthesis method—“in situ oxidation at the interface (IOI) coupled with an ion exchange”—has been developed for the internal surface modification of mesoporous silicon oxide (MPS) templates. First, manganese oxide was formed at the internal surface of the MPS template through IOI. In the IOI method, high-valent oxo-anions of manganese (MnO4 � ) were used for the selective oxidation of poly(ethylene oxide) (PEO) groups of the Pluronic P123 (PEO20PPO70PEO20; PPO = poly(propylene oxide)) surfactant and they formed manganese oxide at the organic–inorganic (corona) interface. The oxide formation was restricted at the corona interface by a positively charged CTA + (cetyltrimethylammonium) head group of the cationic surfactant CTABr. Then, the second modification of the MPS template was also performed by introducing promoter cations (Cs + ,K + ,o r H + ) through an ion exchange reaction

Hydrofluoric acid (HF) is a common ingredient in car wash cleaning solutions mainly because it is highly effective and relatively inexpensive. Particulate matter from brake pads and discs, tire wear, and abrasion of road surface accumulated on the exterior of automobiles are aggressively removed with the use of car wash cleaning solutions containing HF. The unique properties of HF to dissolve silica, concrete, most metals, and metallic oxides cause effective breakdown of rust, road dust, and grime on automobiles. However, HF is a very caustic and a highly toxic substance. Due to hazards associated with the storage, use, and exposure of HF to humans and the environment, there is a need to find safe, yet equally effective alternatives to HF as a cleaning agent. Improvements in cleaning processes, development of available technologies, and utilization of cleaning products containing natural and various benign polymers and surfactants are healthy and environmentally sound alternatives to HF for car wash applications. However, these alternatives may not be as effective as HF. Efforts geared towards finding a replacement for HF remain a challenge, but the outcome would render several benefits to the car wash industry, including abating pollution and providing a safer working environment for everyone.

A novel continuous-flow reactor was developed to investigate the synergetic effects of ultraviolet (UV) and microwave (MW) radiation on TiO2 nanoparticles for the enhancement of photodegradation of Direct Red-81 (DR-81) and Bromothymol Blue (BTB) dyes. The efficiency of the combined UV and MW radiation was higher than the sum of the isolated and corresponding thermal effects and directly proportional to the MW power. The % photodegradation of DR-81 after 105 min irradiation at ambient conditions was 40%, 68%, 72%, and 100% using UV/MW100W, UV/MW300W, UV/MW500W, and UV/MW700W methods, respectively. The % photodegradation of BTB under the same conditions was 58%, 78%, 82%, and 88%, respectively. High dissolved oxygen concentration increased DR-81 photodegradation, whereas ambient air conditions were optimum for BTB. The extent of photomineralization of both dyes was dependent on MW power. Degradation products showed that both dyes were successfully oxidized through different intermediate species. The proper...

Volatile organic compounds (VOCs) continue to be the major source of direct and indirect air pollution. Here, cryptomelane-type octahedral molecular sieve (OMS-2) manganese oxide, amorphous manganese oxide (AMO), and mixed copper manganese oxide (CuO/Mn2O3) nanomaterials were synthesized and, together with commercial MnO2, characterized by various techniques. These catalysts were investigated for gas-phase total oxidation of six VOCs under air atmosphere. Using OMS-2 at 250 °C, the average conversions for toluene, benzene, ethylbenzene, p-xylene, m-xylene, and o-xylene were 75%, 61%, 45%, 23%, 13%, and 8%, respectively, whereas using CuO/Mn2O3, 72%, 44%, 37%, 29%, 27%, and 26%, respectively, were obtained. Generally, the conversion of VOCs to CO2 using the synthesized catalysts increased in the order: o-xylene ≈ m-xylene < p-xylene < ethylbenzene < benzene < toluene. However, using commercial MnO2, benzene (44% conversion) was more reactive than toluene (37%), and the xylenes showed similar reactivities (...

The effects of visible and UV light on the characteristics and properties of Prudhoe Bay (PB) and South Louisiana (SL) emulsions were investigated to better understand the role of sunlight on the fate of spilled crude oils that form emulsions with a dispersant in the aquatic environment. Before irradiation, crude oil emulsions showed the presence of dispersed crude oil micelles in a continuous water phase and crude oil components floating on the surface. The crude oil micelles decreased in size with irradiation, but emulsions retained their high degree of polydispersity. UV irradiation reduced the stability of emulsions more effectively than visible light. The reduction of micelles size caused the viscosity of emulsions to increase and melting point to decrease. Further, irradiation increased acid concentrations and induced ion formation which lowered the pH and increased the conductivity of emulsions, respectively. Ni and Fe in PB emulsions were extracted from crude oil with UV irradiation, which may provide an efficient process for metal removal. The emulsions were stable toward freeze/thaw cycles and their melting temperatures generally decreased with irradiation. Evidence of ˙OH production existed when emulsions were exposed to UV but not to visible light. The presence of H(2)O(2) enhanced the photodegradation of crude oil. Overall, the changes in emulsion properties were attributed to direct photodegradation and photooxidation of crude oil components.

Continuous-flow synthesis of one-dimensional (1D) metal oxide nanostructures and/or their integration into hierarchical structures under nonthermal conditions is still a challenge. In this work, a nonthermal, continuous-flow approach for the preparation of γ-manganese oxide (γ-MnO2) and cerium oxide (CeO2) microspheres has been developed. By this technique, γ-MnO2 materials with surface areas of 240, 98, and 87 m2/g and CeO2 microspheres with a surface area of 1 m2/g have been fabricated successfully. Characterization of the materials was carried out using powder X-ray diffraction, infrared and inductively coupled plasma optical emission spectrometer (ICP/OES), nitrogen sorption, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. The synthesized materials showed good catalytic activity in the oxidation of α-methyl styrene.

Vanadium pentoxide nanomaterials were prepared by a facile microwave-assisted refluxing reaction of VOSO4 and (NH4)2S2O8 solutions under atmospheric pressure at 100 °C for 1 h. The synthesized products were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and Brunauer–Emmett–Teller surface area measurements. The catalytic oxidation and photocatalytic activities of the synthesized V2O5 were evaluated by oxidative cyanation of N,N-dimethylaniline in methanol and photodegradation of N-nitrosodimethylamine (NDMA) in aqueous solution, respectively. V2O5·xH2O nanofibers were formed when VOSO4 and (NH4)2S2O8 solutions were irradiated with microwaves under reflux conditions at 100 °C within 1 h. Nanostructured V2O5 was synthesized by calcining V2O5·xH2O at 280 °C for 12 h. The conversion of N,N-dimethylaniline to N-methyl-N-phenylcyanamide increased with an increase in the amount of V2O5 catalyst. As the amount of synthesized V2...

Nanosized α-Fe2O3 powder was synthesized by a microwave-assisted hydrothermal reaction of Fe(NO3)3 and urea at 120 °C for 30 min. The products were characterized by X-ray diffraction, transmission electron microscopy, BET measurements, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The catalytic performance of α-Fe2O3 was studied for the oxidation of CO and 2-propanol to CO2, and the adsorption properties were investigated for the removal of As(III) in water treatment. Uniform α-Fe2O3 particles about 5.0 nm in diameter were formed with a surface area of around 173.0 m2 g–1. When 0.1 g of α-Fe2O3 powder worked as a catalyst, CO was oxidized to CO2 over 120 °C and completely transformed to CO2 at 170 °C, and 2-propanol was fully oxidized to CO2 at 350 °C. The adsorption capacity for As(III) reached 51.8 mg g–1 at room temperature. This work facilitates the preparation of nanosized α-Fe2O3 materials with excellent catalytic and adsorption performance.

Significant levels of potentially carcinogenic bromate were measured in chlorinated tap drinking water in Metropolitan Manila, Philippines, using an optimized ion-chromatographic method. This method can quantify bromate in water down to 4.5 μg l⁻¹ by employing a postcolumn reaction with acidic fuchsin and subsequent spectrophotometric detection. The concentration of bromate in tap drinking water samples collected from 21 locations in cities and municipalities within the 9-month study period ranged from 7 to 138 μg l⁻¹. The average bromate concentration of all tap drinking water samples was 66 μg l⁻¹ (n = 567), almost seven times greater than the current regulatory limit in the country. The levels of bromate in other water types were also determined to identify the sources of bromate found in the distribution lines and to further uncover contaminated sites. The concentration of bromate in water sourced from two rivers and two water treatment plants ranged from 15 to 80 and 12 to 101 μg l⁻¹, respectively. Rainwater did not contribute bromate in rivers but decreased bromate level by dilution. Groundwater and wastewater samples showed bromate concentrations as high as 246 and 342 μg l⁻¹, respectively. Bromate presence in tap drinking water can be linked to pollution in natural water bodies and the practice of using hypochlorite chemicals in addition to gaseous chlorine for water disinfection. This study established the levels, occurrence, and possible sources of bromate in local drinking water supplies.

Mesoporous copper manganese oxides with high surface areas (>268 m 2 /g) were prepared using the redox method and tested in the preferential oxidation of CO. These materials were highly active and selective under typical operating conditions of a proton-exchange membrane fuel cell. The synthesized catalysts preferentially oxidized CO with a stoichiometric amount of oxygen in the feed gas. The presence of CO 2 and H 2 O in the feed gas retarded catalytic activity significantly at low ( 2 oxidation.

Short reaction times and morphology control in the synthesis of inorganic materials under nonthermal conditions remain a challenge. Herein we report a rapid, self-templating, and nonthermal method based on ultraviolet light to prepare metal oxide hierarchical structures. With this method, the morphology of the metal oxides was controlled readily without using templates.

The enhancement of the photodegradation of toxic N -nitrosodimethylamine (NDMA) in water using amorphous manganese oxide (AMO) and platinum manganese oxide (Pt/Mn 3 O 4 ) catalysts was investigated. Characterization of the catalysts was carried out using XRD, FESEM, TEM, EDXS, BET, XPS, and AOS. Pt/Mn 3 O 4 and its precursor AMO, synthesized by a redox reaction of Mn 2+ and Mn 7+ , showed similar morphologies. High surface area AMO was confirmed to be amorphous, whereas Pt/Mn 3 O 4 was a mixture of two crystalline structures. The optimum catalyst loading was 25 mg per 100 mL NDMA solution for which the photocatalytic activity was maximized. The average hydrodynamic particle size of a given amount of catalyst increased due to aggregation as a result of an increase in temperature during UV illumination ( λ = 254 nm). Photocatalytic studies showed that NDMA degraded according to zero-order kinetics under air saturation at pH 7.0. AMO and Pt/Mn 3 O 4 showed photostability and comparable activities with pure TiO 2 and platinized TiO 2 . Mixed valencies of Mn and the presence of O 2 on the surface of the catalysts, which reacts with photogenerated electrons to form reactive oxygen species (hydroxyl and superoxide anion radicals), played significant roles in the enhancement of the photodegradation of NDMA in water.

Iron and silver nanoparticles were synthesized using a rapid, single step, and completely green biosynthetic method employing aqueous sorghum extracts as both the reducing and capping agent. Silver ions were rapidly reduced by the aqueous sorghum bran extracts, leading to the formation of highly crystalline silver nanoparticles with an average diameter of 10 nm. The diffraction peaks were indexed to the face-centered cubic (fcc) phase of silver. The absorption spectra of colloidal silver nanoparticles showed a surface plasmon resonance (SPR) peak centered at a wavelength of 390 nm. Amorphous iron nanoparticles with an average diameter of 50 nm were formed instantaneously under ambient conditions. The reactivity of iron nanoparticles was tested by the H(2)O(2)-catalyzed degradation of bromothymol blue as a model organic contaminant.

Binary copper manganese oxides were prepared by a novel redox method and their catalytic activity for CO oxidation at ambient temperature evaluated. The catalytic activity was found to be high, and compared favorably with a commercial Hopcalite catalyst. The most active catalyst was able to completely oxidize CO at ambient temperature. Catalytic activity decay, most likely due to carbon dioxide retention was observed. The catalysts were deactivated by moisture but expelling water at moderate temperatures easily restored their catalytic activity. The catalysts were characterized by means of BET, FE-SEM, TEM, EDAX, XPS, TPD and X-ray powder diffraction. The optimum copper loading was determined to be ∼9% of the manganese content.

The first example of a highly water-tolerant, hydrophobic polymer coated metal oxide catalyst systems is reported for CO oxidation. Studies show that protected catalysts have 5.3 times longer lifetimes than unprotected catalysts under highly humid conditions. This idea is simple and general for many different metal oxide catalyst systems.

Manganese-containing MFI-type Mn-ZSM-5 zeolite was synthesized by a facile one-step hydrothermal method using tetrapropylammonium hydroxide (TPAOH) and manganese(III)-acetylacetonate as organic template and manganese salts, respectively. A highly crystalline MFI zeolite structure was formed under pH = 11 in 2 days, without the need for additional alkali metal cations. Direct evidence of the incorporation of Mn in the zeolite framework sites was observed by performing structure parameter refinements, supported by data collected from other characterization techniques such as IR, Raman, UV-vis, TGA, N2-adsorption, SEM, TEM, EDAX, and XPS. UV-vis spectra from the unique optical properties of Mn-ZSM-5 show two absorption peaks at 250 and 500 nm. The absorption varies in different atmospheres accompanied by a color change of the materials due to oxygen evolution. Raman spectra show a significant and gradual red shift from 383 cm(-1) to 372 cm(-1) when the doping amount of Mn is increased from 0 to 2 wt %. This suggests a weakened zeolite structural unit induced by the Mn substitution. The catalytic activity was studied in both gas-phase benzyl alcohol oxidation and toluene oxidation reactions with remarkable oxidative activity presented for the first time. These reactions result in a 55% yield of benzaldehyde, and 65% total conversion of toluene to carbon dioxide for the 2% Mn-ZSM-5. Temperature programmed reduction (TPR) using CO in He demonstrates two reduction peaks: one between 300 and 500 °C and the other between 500 and 800 °C. The first reduction peak, due to manganese-activated oxidation sites shifted from higher temperature to lower temperature, and the peak intensity of CO2 rises when the dopant amount increases. For the first time, calculated photophysical properties of a model Mn(O-SiH3)4(-) compound, an Mn-embedded zeolite cluster, and model Mn oxides help to explain and interpret the diffuse reflectance spectroscopy of Mn-ZSM-5 zeolites.

Manganese oxide octahedral molecular sieves (OMS) are important materials in environmental chemistry, electrochemistry, and heterogeneous catalysis. Cryptomelane and Ag-hollandite type manganese oxides (OMS-2) were synthesized by microwave-reflux and hydrothermal methods, respectively. In this current study, silver doping of cryptomelane and Ag-hollandite was performed using both UV irradiation and KBH4 reduction methods. The formation process, particle size, crystallite size, crystal structure, and properties of these nanomaterials were characterized by powder X-ray diffraction, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and nitrogen sorption. Studies by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) showed that the produced OMS-2 have a nanofiber structure. The produced catalysts showed high activity, as high as 100% in the low-temperature CO oxidation at 140 degrees C. The catalysts doped with silver by KBH4 reduction method showed higher activities than other doping methods and template catalysts. In longtime stability tests, 80% CO conversion can be maintained for 26 h at 120 degrees C. The high activities, and stabilities of the Ag/K-OMS-2-KBH and Ag/Ag-OMS-2-KBH were attributed to the stable presence of Ag-0 and Ag+ species and the unique morphologies of the cryptomelane and Ag-hollandite nanofibers. CO oxidation is believed to follow the Mars-van Krevelen mechanism via the Ag+ - O2- - Mn4+ Ag-0 - Mn3+ + O-2 redox reaction. (C) 2013 Elsevier B.V. All rights reserved.

A facile single-step method was developed for synthesizing todorokite-type manganese oxide octahedral molecular seieves (OMS-1) and 2 × 4 tunnel structured manganese oxide (OMS-5) materials. Selection of starting materials and initial pH conditions in the syntheses are crucial.