Studies on the calcium poisoning and regeneration of commercial De-NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> SCR catalyst

The poisoning effect of calcium on a commercial De-NO _x SCR catalyst (V₂O₅–WO₃/TiO₂) and the regeneration process of deactivated catalysts via water or H₂SO₄ washing were investigated under simulated condition in laboratory. The physicochemical properties of the catalysts were characterized by SEM–EDX, XRD, BET, TPD and FT-IR measurements, and the deactivation mechanism was discussed. The poisoning of calcium was attributed to the coverage of active sites and the reduction of acid sites on the surface of catalyst. The change of V=O bonds on catalyst surface was an important reason, which plays a significant role in the catalytic cycle of SCR. Due to the suction deliquescence of CaO to Ca(OH)₂, the catalytic activity of deactivated catalyst can be finitely recovered by water washing. Besides, as the result of the re-exposure of active sites by washing CaO off and the promotional effect of surface sulfation, the process of regeneration via sulfuric acid washing has a favorable effect in the experiment.     

Properties of anodic RuNiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(OH)<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> catalysts synthesized on carbon supports with various dispersion degree

A number of catalysts of the (Ru-Ni)/C system is synthesized and studied for application in anodes of alkaline ethanol-air fuel cells. The carbon supports used are carbon blacks with different specific surface area and graphite powders. The X-ray photoelectron spectroscopy technique allowed detecting on the catalyst surface metallic ruthenium and nickel in the form of Ni(OH)2 hydroxide and possibly oxyhydroxide NiOOH. It is shown that the catalyst activity in the reaction of ethanol electrochemical oxidation grows at an increase in the specific surface area of the carbon support. The method of carbon monoxide oxidative desorption was used to determine the values of the specific surface area of the catalyst metallic phase. It is shown that at an increase in the relative ruthenium content from (1Ru3Ni)/C to Ru/C, the specific catalytic activity in the catalysts of the (Ru-Ni)/C system reaches the maximum value near the composition of (2Ru1Ni)/C. It is shown that the found optimum catalyst composition is independent of the carbon support dispersion degree. Activity in ethanol electrooxidation of the (2Ru1Ni)/C catalyst supported on the Ketjenblack EC-600 carbon black is 18 ± 3 A/g of the catalyst (>120 A/g of Ru) at 40°C and potential E = 0.5 V in the 2MKOH + 1 M C₂H₅OH electrolyte.     

Low-temperature NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Selective Reduction by Hydrocarbons on H-Mordenite Catalysts in Dielectric Barrier Discharge Plasma

Toward achieving selective catalytic reduction of NO _x by hydrocarbons at low temperatures (especially lower than 200 °C), C₂H₂ selective reduction of NO _x was explored on H-mordenite (H-MOR) catalysts in dielectric barrier discharge (DBD) plasma. This work reported significant synergistic effects of DBD plasmas and H-MOR catalysts for C₂H₂ selective reduction of NO _x at low temperatures (100–200 °C ) and across a wide range of O₂ content (0–15%). At 100 °C, NO _x conversions were 3.3, 11.6 and 66.7% for the plasma alone, catalyst alone and in-plasma catalysis (IPC) cases (with a reactant gas mixture of 500 ppm NO, 500 ppm C₂H₂, 10% O₂ in N₂, GHSV = 12,000 h⁻¹ and input energy density of 125 J L ⁻¹), respectively. At 200 °C, NO _x conversions were 3.8, 54.0 and 91.4% for the above three cases, respectively. Also, strong signals of hydrogen cyanide (HCN) byproduct were observed in the catalyst alone system by an on-line mass spectrometer. By contrast, almost no HCN was detected in the IPC system.     

Mechanistic study of Ce-modified MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/TiO<Subscript>2</Subscript> catalysts with high NH<Subscript>3</Subscript>-SCR performance and SO<Subscript>2</Subscript> resistance at low temperatures

A series of Ce–MnO _x /TiO₂ catalysts were prepared using a novel sol–gel template method and investigated for low-temperature selective catalytic reduction (SCR) of NO with NH₃ at temperatures ranging from 353 to 473 K. The 0.07Ce–MnO _x /TiO₂ catalyst showed the highest activity and best resistance to SO₂ poisoning. The structure and properties of the catalysts were characterized using X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), thermogravimetry (TG)–differential scanning calorimetry (DSC)–mass spectroscopy (MS), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) measurements, H₂-temperature-programmed reduction (TPR), and NH₃-temperature-programmed desorption (TPD). The superior catalytic activity of the 0.07Ce–MnO _x /TiO₂ catalyst was probably due to a change in the active components, an increase in surface active oxygen and surface acid sites, and lower crystallinity and larger surface area with Ce doping. Furthermore, the reduction ability also became stronger. The SO₂ poisoning resistance of the 0.07Ce–MnO _x /TiO₂ catalyst improved because doping with Ce can effectively decrease the formation of ammonium salt on the catalyst surface and the sulfation of MnO _x . In situ diffuse-reflectance infrared Fourier-transform (DRIFT) spectroscopy experiments indicated that addition of Ce could promote adsorption of NH₃ and inhibit generation of some nitryl species. The SCR reactions over the catalysts mainly followed the Eley–Rideal mechanism accompanied with a partial Langmuir–Hinshelwood mechanism.     

Continuous synthesis of <Emphasis Type="Italic">N</Emphasis>-ethylethylenediamine over supported Cu-Zn-La catalysts

A series of Cu-based catalysts were prepared and employed in the N-ethylation of ethylenediamine with ethanol in a fixed-bed reactor. Satisfying results were obtained using Cu-Zn-La/Al₂O₃ as a catalyst. In addition, Cu-Zn-La/SiO₂, Cu-Zn-La/Al₂O₃ and Cu-Zn-La/HZSM-5 were characterized by the Brunauer-Emmett-Teller method (BET), H₂- temperature program reduction (H₂-TPR), X-ray diffraction (XRD), transmission electron microscopic measurements (TEM) and NH₃-temperature programmed desorption (NH₃-TPD) in order to investigate the influence of supports on their catalytic performance. It was found that both the BET surface area and the acidity of the support are key factors in the catalytic performance. Moreover, reaction parameters including temperature, hydrogen pressure and liquid hourly space velocity were optimized. Under optimal conditions, a 73.3 % conversion of ethylenediamine and a 71.2 % selectivity of N-ethylethylenediamine were achieved. Finally, the lifetime of the catalysts was evaluated and the reaction proceeded con-tinuously for over 200 h.     

Promotional effect of Ce on the SCR of NO with NH<Subscript>3</Subscript> at low temperature over MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> supported by nitric acid-modified activated carbon

Different amounts of Mn and Ce oxides were loaded onto nitric acid-modified activated carbon (ACN) by wet impregnation. The series of catalysts were employed for the selective catalytic reduction of NO _x by NH₃ at temperatures between 100 and 250 °C. Cerium-modified catalysts exhibited higher de-NO _x performance than those modified with Mn/ACN, even with the same total loadings. The precursor solution with a molar ratio for Ce/(Mn + Ce) of 0.4 exhibited the highest catalytic activity. Enhanced resistance to SO₂ and H₂O and better stability were observed for 10%Mn–Ce(0.4)/ACN relative to 10%Mn/ACN. The catalysts were further characterized by N₂ physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The N₂ physisorption and XRD results suggested that co-doping Ce with Mn increased the surface area and promoted the dispersion of Mn–Ce binary metal oxides. H₂-TPR the NH₃-TPD results demonstrated that the interaction between manganese oxide and cerium oxide species enhanced the redox and surface acidity of 10%Mn–Ce(0.4)/ACN.     

Synthesis,characterization and olefin hydroformylation reactions of <Emphasis Type="Italic">mer</Emphasis>-[Mo(CO)<Subscript>3</Subscript>(p-C<Subscript>5</Subscript>H<Subscript>4</Subscript>N-CN)<Subscript>3</Subscript>]

Mer-[Mo(CO)₃(p-C₅H₄N-CN)₃] was prepared by UV-irradiation of a THF solution of Mo(CO)₆ and para-cyanopyridine under heating. The complex was characterized by FT-IR, MS, ¹H and ¹³C NMR and showed catalytic activity for olefin hydroformylation (1-hexene, cyclohexene and 2,3-dimethyl-2-butene as model olefins; 600 psi synthesis gas (pCO/pH₂ = 1); 100 °C; 24 h; toluene). An examination of the complex catalyzed hydroformylation of a real naphtha cut (El Palito refinery, Venezuela), under the same conditions, also showed activity in the conversion to oxygenated products.     

Molecular mechanism of propane oxidative dehydrogenation on surface oxygen radical sites of VO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/TiO<Subscript>2</Subscript> catalysts

Minimum energy pathways of propane oxidative dehydrogenation to propene and propanol on supported vanadium oxide catalyst VO _x /TiO₂ were studied by periodic discrete Fourier transform (DFT) using a surface oxygen radical as the active site. The propene formation pathway was shown to consist of two consecutive hydrogen abstraction steps. The first step includes C_β–H bond activation of propane followed by the formation of a surface hydroxyl group V–O _t H and a propyl radical n-C₃H₇. This step with the activation energy E* = 0.56 eV (54.1 kJ/mol) appears to be rate-determining. The second step involves the reaction of the bridging O _b oxygen atom with the methylene C–H bond of propyl radical n-C₃H₇ followed by the formation of a hydroxylated surface site HO _t –V⁴⁺–O _b H and propene. The initial steps of the C–H bond activation during propane conversion to propanol and propene by ODH on V⁵⁺–(O _t O _b )^? active sites are identical. The obtained results demonstrate that participation of surface oxygen radicals as the active sites of propane ODH makes it possible to explain relatively low activation energies observed for this reaction on the most active catalysts. The presence of very active radical species in low concentration seems to be the key factor for obtaining high selectivity.     

Highly efficient mesoporous WO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/KIT-6 catalysts for oxidative desulfurization of dibenzothiophene with hydrogen peroxide

Oxidative desulfurization (ODS) of organic compounds containing sulfur element from a model oil was performed using tungsten oxide catalysts supported on mesoporous silica with cubic Ia3d mesostructure, well-defined mesopores (7.2 nm), high surface area (719 m²/g), and three-dimensional pore network (WO _x /KIT-6). The prepared WO _x /KIT-6 catalysts (5–20 wt% WO _x ) were characterized by X-ray diffraction analysis, N₂ sorption measurements, electron microscopy, H₂-temperature programmed reduction, Raman spectroscopy, and thermogravimetric analysis. Among the mesoporous catalysts, 10 wt% WO _x /KIT-6 exhibited the best catalytic performance. Sulfur-containing organic compounds, such as dibenzothiophene, 4,6-dimethyldibenzothiophene, and benzothiophene, were completely (100 %) removed from the model oil over 10 wt% WO _x /KIT-6 catalyst in 2 h. In addition, the catalyst could be reused several times with only slight decrease in catalytic activity.     

<Emphasis Type="Italic">N</Emphasis>-doped carbon supported Pd catalysts for <Emphasis Type="Italic">N</Emphasis>-formylation of amines with CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>

Using mesoporous N-doped carbons (NCs) derived from glucose and melamine as the supports, a series of Pd/NC catalysts were prepared, in which Pd nanoparticles with average size<2.0 nm were uniformly distributed on the supports. It was indicated that the resultant Pd/NC catalysts were effective for N-formylation of amines with CO₂ and H₂ in ethanol without any additives. Especially, the catalyst Pd/NC-800-6.9% containing quaternary N showed the best performance, affording a series of formylamides in good or even excellent yields. Further investigation reveals that the interaction between the Pd nanoparticles and quaternary nitrogen in the NC support was responsible for the good performance of the catalyst.     

The physicochemical and catalytic properties of the Pt-CeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> system

The properties of the Pt-CeO _x system prepared by the oxidation of the Pt₂Ce intermetallic compound were studied. The sample was characterized by X-ray diffraction in situ, thermogravimetry, scanning electron microscopy (with an accessory for energy dispersion analysis), transmission electron microscopy, and temperature-programmed reduction with hydrogen. The catalytic properties of the sample were studied in the model reaction of toluene hydrogenation. The oxidation of the intermetallic compound caused the appearance of metallic platinum and cerium oxide phases and high-dispersity platinum particles encapsulated in cerium oxide. Metallic platinum on the surface of the catalyst experienced rapid deactivation in the presence of hydrogen sulfide; high-dispersity platinum particles encapsulated in cerium oxide exhibited enhanced stability toward sulfur compounds.     

Catalytic cracking of C<Subscript>5</Subscript> raffinate to light olefins over NaOH-treated ZSM-5

A series of ZSM-5 catalysts (ZSM-5 (X)) treated with different NaOH concentration (X = 0, 0.05, 0.1, and 0.2 M) were prepared for use in the production of light olefins (ethylene and propylene) through catalytic cracking of C₅ raffinate. The effect of NaOH concentration on their physicochemical properties and catalytic activity was investigated. It was found that textural and physicochemical properties of ZSM-5 (X) catalysts were strongly influenced by the NaOH concentration. Mesopore volume of ZSM-5 (X) catalysts increased with increasing NaOH concentration, while acidity of the catalysts decreased with increasing NaOH concentration. Conversion of C₅ raffinate and yield for light olefins (ethylene and propylene) showed the volcano-shaped curves with respect to NaOH concentration (X). This implies that NaOH treatment of ZSM-5 was an efficient method to produce light olefins through catalytic cracking C₅ raffinate, and that optimal NaOH concentration was required for maximum production of light olefins. Among the catalysts tested, ZSM-5 (0.05) catalyst showed the best catalytic performance due to its favorable porosity and acidity.     

Study of <Emphasis Type="Italic">n</Emphasis>-hexane isomerization on Pt/SO<Subscript>4</Subscript>/ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts: Effect of the state of platinum on catalytic and adsorption properties

The state of surface Pt atoms in the Pt/SO₄/ZrO₂/Al₂O₃ catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al₂O₃ alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO₄/ZrO₂/Al₂O₃ superacid catalyst were used in this study. With the use of IR spectroscopy (CO_ads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.     

The application of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylhydroxylamine as reductant for the separation of plutonium from uranium

Both single stage and multi-stages experiments on stripping plutonium with N,N-dimethylhydroxylamine (DMHAN) as reductant with methylhydrozine (MMH) as supporting reductant were carried out. The effect of contact time, temperature, acidity, concentration of DMHAN on back-extraction rate of plutonium was investigated in the single stage experiment. The results demonstrated that the reaction of stripping Pu(IV) in the organic phase (30% TBP–kerosene) 1BF solutions by DMHAN exhibits excellent stripping efficiency. Under the given conditions, the back-extraction rate of plutonium reaches 90% within 2 min. Higher temperature, lower acidity and the increased concentration of DMHAN benifit the stripping reaction. The concentration profile of HNO₃, uranium and plutonium were determined in a multi-stages mixer-settler after the steady state of the back-extraction, and the multi-stages results show that the plutonium can be separated effectively from uranium. The recovery of plutonium and uranium reach 99.995% or over 99.99% respectively. The separation factor of U from Pu (SF_Pu/U) is about 2 × 10⁴.     

Comparative extraction efficiencies of tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate and <Emphasis Type="Italic">N,N</Emphasis>-dihexyloctanamide for uranium recovery using supercritical CO<Subscript>2</Subscript>

Extraction of uranium from tissue paper, synthetic soil, and from its oxides (UO₂, UO₃ and U₃O₈) was carried out using supercritical carbon dioxide modified with methanol solutions of extractants such as tri-n-butyl phosphate (TBP) or N,N-dihexyl octanamide (DHOA). The effects of temperature, pressure, extractant/nitric acid (nitrate) concentration, and of hydrogen peroxide on uranium extraction were investigated. The dissolution and extraction of uranium in supercritical CO₂ modified with TBP, from oxide samples followed the order: UO₃ ≫ UO₂ > U₃O₈. Addition of hydrogen peroxide in the modifier solution enhanced the dissolution/extraction of uranium in dynamic mode. DHOA appeared better than TBP for recovery of uranium from different oxide samples. Similar enhancement in uranium extraction was observed in static mode experiments in the presence of hydrogen peroxide. Uranium estimation in the extracted fraction was carried out by spectrophotometry employing 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) as the chromophore.     

Oxidative dehydrogenation of propane on the VO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CeZrO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> supported catalyst

The oxidative dehydrogenation of propane on a supported vanadium catalyst was studied (the support was a complex oxide system consisting of a ceria–zirconia solid solution deposited on γ-Al₂O₃ (CeZrO/γ-Al₂O₃)). A comparative analysis of the properties of the support and the catalyst prepared on its basis was performed. The support and catalyst were characterized by the BET method, scanning electron microscopy, X-ray diffraction analysis, and Raman spectroscopy. The catalytic properties of the catalyst and support were studied in propane oxidation at 450 and 500°C with pulse feeding of the reagent. The effect of propane on the support was found to improve the oxidative properties of the latter. This behavior of the support is related to the preparation procedure, which leads to the formation on its surface of the crystalline phase of the ceria–zirconia solid solution and amorphous ZrO₂ and Al₂O₃ phases and/or their solid solution. Similar processes occur with the catalyst support during the oxidative dehydrogenation, giving rise to additional active centers (CeVO₄).     

Oxidative Dehydrogenation of <Emphasis Type="Italic">n</Emphasis>-Butenes to 1,3-Butadiene over Bismuth Molybdate and Ferrite Catalysts: A Review

1,3-Butadiene, an important raw material for a variety of chemical products, can be produced via the oxidative dehydrogenation (ODH) of n-butenes over multicomponent oxide catalysts based on bismuth molybdates and ferrites. In this review, the basic concept, reaction mechanism, and catalysts typically used in an ODH reaction are discussed.     

Fibrinolytic Serine Protease Isolation from <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis> An6 Grown on <Emphasis Type="Italic">Mirabilis jalapa</Emphasis> Tuber Powders

In this study, Mirabilis jalapa tuber powder (MJTP) was used as a new complex organic substrate for the growth and production of fibrinolytic enzymes by a newly isolated Bacillus amyloliquefaciens An6. Maximum protease activity (1,057 U/ml) with casein as a substrate was obtained when the strain was grown in medium containing (grams per liter) MJTP 30, yeast extract 6, CaCl₂ 1, K₂HPO₄ 0.1, and K₂HPO₄ 0.1. The strain was also found to grow and produce extracellular proteases in a medium containing only MJTP, indicating that it can obtain its carbon, nitrogen, and salts requirements directly from MJTP. The B. amyloliquefaciens An6 fibrinase (BAF1) was partially purified, and fibrinolytic activity was assayed in a test tube with an artificial fibrin clot. The molecular weight of the partially purified BAF1 fibrinolytic protease was estimated to be 30 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel filtration. The optimum temperature and pH for the caseinolytic activity were 60 °C and 9.0, respectively. The enzyme was highly stable from pH 6.0 to 11.0 and retained 62% of its initial activity after 1 h incubation at 50 °C. However, the enzyme was inactivated at higher temperatures. The activity of the enzyme was totally lost in the presence of phenylmethylsulfonyl fluoride, suggesting that BAF1 is a serine protease.     

Simultaneous removal of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and SO<Subscript>2</Subscript> by low-temperature selective catalytic reduction over modified activated carbon catalysts

A series of modified porous activated carbon (AC) catalysts prepared by impregnation were investigated for the low-temperature (≤250°C) selective catalytic reduction (SCR) of NO _x with NH₃ with simultaneous removal of SO₂. The effects of various preparation conditions and reaction conditions on NO and SO₂ conversions were observed, such as support type, active components, copper loading, calcination temperature and presence of H₂O and O₂. The modified AC catalysts were characterized by BET, XRD, TG and TPX methods. The activity test results showed that the optimal catalyst is 15% Cu/WCSAC which can provide 52% NO conversion and 68% SO₂ conversion simultaneously at 175°C with a space velocity of 30000 h^?1, and the optimal calcination temperature was 500°C. The presence of H₂O could inhibit NO conversion and promote the SO₂ conversion. The effect of O₂ (0–5%) was evaluated, and the NO and SO₂ conversions were best when the concentration of O₂ was 3%. Research demonstrated that Cu/WCSAC catalyst was a kind of potential catalysts due to the amorphous phase, high specific areas and high active ability.     

Toxic effects of protoberberine alkaloids from <Emphasis Type="Italic">Rhizoma Coptidis</Emphasis> on <Emphasis Type="Italic">Tetrahymena thermophila</Emphasis> BF<Subscript>5</Subscript> growth based on microcalorimetry

Rhizoma Coptidis consists mainly of protoberberine alkaloids (PAs), and has been used for many years as a traditional medicine. Recent research revealed the toxicity of Rhizoma Coptidis, but studies focusing on the relationships between the structures of PAs and their toxicities are lacking. The toxic effects of four PAs from Rhizoma Coptidis on the growth of Tetrahymena thermophila BF₅ were investigated by microcalorimetry. The power-time curves of T. thermophila BF₅ with and without PAs were obtained; the extent and duration of toxic effects on the metabolism of this organism were evaluated by studying thermokinetic parameters and the half-inhibitory ratio (IC ₅₀). All the thermokinetic parameters showed regular variations with alteration of PA concentrations. The magnitude of the toxic effects of PAs was ascertained from IC ₅₀ values: palmatine > jateorhizine > berberine ≈ coptisine. The structure–function relationship of PAs indicated that the C2 and C3 positions contributed more to the toxic effect of PAs. That is, when substituted with methoxyl groups, the toxic effect would be increased.