Enzymatic scavenging of oxygen dissolved in water: Application of response surface methodology in optimization of conditions

In this work, removal of dissolved oxygen in water through reduction by glucose, which was catalyzed by glucose oxidase – catalase enzyme, was studied. Central composite design (CCD) technique was applied to achieve optimum conditions for dissolved oxygen scavenging. Linear, square and interactions between effective parameters were obtained to develop a second order polynomial equation. The adequacy of the obtained model was evaluated by the residual plots, probability-value, coefficient of determination, and Fisher’s variance ratio test. Optimum conditions for activity of two enzymes in water deoxygenation were obtained as follows: pH=5.6, T=40°C, initial substrate concentration [S] = 65.5 mmol/L and glucose oxidase activity [E] = 252 U/Lat excess amount of catalase. The deoxygenation process during 30 seconds, in the optimal conditions, was predicted 98.2%. Practical deoxygenation in the predicted conditions was achieved to be 95.20% which was close to the model prediction

LaBO3 (B = Mn, Fe, Co, Ni, Cu, and Zn) Catalysts for CO + NO Reaction

A series of transition-metal LaBO3 perovskites (B = Mn, Fe, Co, Ni, Cu, and Zn) have been synthesized and tested as catalysts for the simultaneous removal of CO and NO in a fixed-bed reactor. To improve the catalytic activity, LaFeO3, the most active formulation, was modified by partially substituting other active metals (Mn, Co, and Cu) for Fe in the perovskite formulation (LaFe0.7M0.3O3). The results revealed that Mn substitution significantly improved the catalytic activity because it increased the Mn(IV)-to-Mn(III) ratio, leading to the generation of a large amount of structural defects, and also because it increased the amount of reducible active sites.Financial support from the Iran National Science Foundation (INSF) is gratefully acknowledged

NO + CO reaction over LaCu0.7B0.3O3 (B = Mn, Fe, Co) and La0.8A0.2Cu0.7Mn0.3O3 (A = Rb, Sr, Cs, Ba) perovskite-type catalysts

In this paper, catalytic reduction of NO by CO over perovskite-type oxides LaCu0.7B0.3O3 (B = Mn, Fe, Co) synthesized by sol–gel method was investigated. LaCu0.7Mn0.3O3 showed the highest activity among LaCu0.7B0.3O3 perovskite catalysts (88% CO conversion and 93% NO conversion at 350 °C). The effect of alkali and alkaline earth metals (Rb, Sr, Cs and Ba) on the structure and catalytic activity of LaCu0.7Mn0.3O3 perovskite catalysts was also investigated. The results showed that catalytic activity was improved by partial substitution of La by alkali and alkaline earth metals. The superior activity of La0.8Sr0.2Cu0.7Mn0.3O3 with respect to other catalysts (93% CO conversion and 96% NO conversion at 350 °C) was associated with a higher reducibility at low temperature, more oxygen vacancies and synergistic effect between Cu and Mn. The catalysts were characterized by XRD, BET, H2-TPR, XPS and SEM

Catalytic Reduction of NO by CO over LaMn1−xFexO3 and La0.8A0.2Mn0.3Fe0.7O3 (A = Sr, Cs, Ba, Ce) Perovskite Catalysts

In this study, LaMn1−xFexO3 (x = 0, 0.3, 0.5, 0.7, 1) and La0.8A0.2Fe0.7Mn0.3O3 (A = Sr, Cs, Ba, Ce) perovskite oxides were synthesized by sol–gel method and their activities were evaluated in catalytic reduction of NO by CO. Perovskite catalysts were characterized by XRD, BET, H2-TPR, XPS and SEM. Synthesized perovskites present a high activity for the catalytic reduction of NO by CO, LaMn0.3Fe0.7O3 Show the highest activity among LaMn1−xFexO3 perovskite catalysts (71 % CO conversion and 82 % NO conversion at 350 °C). The effect of partial substitution of Sr, Cs, Ba and Ce in A-site was also examined on the structure and catalytic activity of LaMn0.3Fe0.7O3 perovskite catalyst. La0.8Sr0.2Fe0.7Mn0.3O3 and La0.8Ce0.2Fe0.7Mn0.3O3 present the highest activities among La0.8A0.2Fe0.7Mn0.3O3 perovskites. The introduction of Sr2+ and Ce4+ in A-site of perovskite change the reducibility of B-site cations and Fe4+/Fe3+ and Mn4+/Mn3+ ratios, and increase Oads/Olatt ratio and these factors create structural defects in perovskite which lead to higher catalytic activities.Financial supports from the Iran National Science Foundation (INSF) are gratefully acknowledged

Mineralogical Composition of Urinary Stones and Their Frequency in Patients: Relationship to Gender and Age

This investigation reports the mineralogy and possible pathological significance of urinary stones removed from patients in Fars province, Iran. X-ray diffraction (XRD), scanning electron microscopy (SEM) and polarizing microscope (PM) techniques were used to investigate the mineralogical compositions of urinary stones. The identified mineral components include whewellite, weddellite, hydroxyapatite, uricite and cystine. These techniques revealed that the whewellite and uricite were the most common mineral phases. Platy-like/monoclinic whewellite, prismatic/monoclinic uric acid and hexagonal cystine crystals were revealed by SEM. Biominerals (calcium carbonate) and quartz were also identified in PM images. Of the variables determining the type of precipitated minerals, the effects of pH on depositional conditions proved to be the most apparent parameter, as shown by occurrences and relationships among the studied minerals. Our results revealed the importance of detailed knowledge of mineralogical composition in assessing the effects of age and sex. The highest incidence of urinary stones was observed in the 40–60 age group. Calcium oxalate and uric acid stones are more frequent in men than women. Finally, the study concluded that knowledge of the mineralogical composition of urinary stones is important as it helps the scientific community to explain the chemistry and the etiology of the calculi in the urinary system

Characterization and activity of alkaline earth metals loaded CeO2–MOx (M = Mn, Fe) mixed oxides in catalytic reduction of NO

Nanocrystalline CeO2–MOx mixed oxides (M = Mn, Fe) with different M/(M + Ce) molar ratio are prepared by sol–gel combustion method. X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Temperature Programmed Reduction with H2 (H2-TPR) and N2-adsorption (BET) analyses are conducted to characterize the physical–chemical properties of the catalysts. The activity of catalysts for reduction of NOx with ammonia has been evaluated. The CeO2–MnOx catalysts showed better low temperature activity than CeO2–FeOx. The superior activity of CeO2–MnOx with Mn/(Mn + Ce) molar ratio of 0.25 respect to other catalysts (with 83% NO conversion and 68% N2 yield at 200 °C) is associated to nanocrystalline structure, reducibility at low temperature and synergistic effect between Ce and Mn that are observed by XRD, TEM and H2-TPR. The CeO2–FeOx catalysts were found to be active at high temperature, being Ce–Fe the best catalyst yielded 82% NO conversion at 300 °C. The effect of alkaline earth metals (Ca, Mg, Sr and Ba) loading on the structure and catalytic activity of cerium mixed oxides are also investigated. Loading of Ba enhanced the NO reduction activity of mixed oxides due to the increase of number of basic sites. Highest performance with 91% NO conversion and 80% N2 yield attained over CeO2–MnOx (0.25)-Ba (7%) catalyst at 200 °C.Iranian Nanotechnology Initiative and University of Tabriz, Iran

Modeling Preparation Condition and Composition–Activity Relationship of Perovskite-Type La_<i>x</i>Sr_1–<i>x</i>Fe_<i>y</i>Co_1–<i>y</i>O₃ Nano Catalyst

In this paper, an artificial neural network (ANN) is first applied to perovskite catalyst design. A series of perovskite-type oxides with the La_<i>x</i>Sr_1–<i>x</i>Fe_<i>y</i>Co_1–<i>y</i>O₃ general formula were prepared with a sol–gel autocombustion method under different preparation conditions. A three-layer perceptron neural network was used for modeling and optimization of the catalytic combustion of toluene. A high <i>R</i>² value was obtained for training and test sets of data: 0.99 and 0.976, respectively. Due to the presence of full active catalysts, there was no necessity to use an optimizer algorithm. The optimum catalysts were La_0.9Sr_0.1Fe_0.5Co_0.5O₃ (<i>T</i>_c = 700 and 800 °C and [citric acid/nitrate] = 0.750), La_0.9Sr_0.1Fe_0.82Co_0.18O₃ (<i>T</i>_c = 700 °C, [citric acid/nitrate] = 0.750), and La_0.8Sr_0.2Fe_0.66Co_0.34O₃ (<i>T</i>_c = 650 °C, [citric acid/nitrate] = 0.525) exhibiting 100% conversion for toluene. More evaluation of the obtained model revealed the relative importance and criticality of preparation parameters of optimum catalysts. The structure, morphology, reducibility, and specific surface area of catalysts were investigated with XRD, SEM, TPR, and BET, respectively