Precipitated K-promoted Co-Mn-Al mixed oxides for direct NO decomposition: Preparation and properties

Direct decomposition of nitric oxide (NO) proceeds over Co-Mn-Al mixed oxides promoted by potassium. In this study, answers to the following questions have been searched: Do the properties of the K-promoted Co-Mn-Al catalysts prepared by different methods differ from each other? The K-precipitated Co-Mn-Al oxide catalysts were prepared by the precipitation of metal nitrates with a solution of K2CO3/KOH, followed by the washing of the precipitate to different degrees of residual K amounts, and by cthe alcination of the precursors at 500 degrees C. The properties of the prepared catalysts were compared with those of the best catalyst prepared by the K-impregnation of a wet cake of Co-Mn-Al oxide precursors. The solids were characterized by chemical analysis, DTG, XRD, N-2 physisorption, FTIR, temperature programmed reduction (H-2-TPR), temperature programmed CO2 desorption (CO2-TPD), X-ray photoelectron spectrometry (XPS), and the species-resolved thermal alkali desorption method (SR-TAD). The washing of the K-precipitated cake resulted in decreasing the K amount in the solid, which affected the basicity, reducibility, and non-linearly catalytic activity in NO decomposition. The highest activity was found at ca 8 wt.% of K, while that of the best K-impregnated wet cake catalyst was at about 2 wt.% of K. The optimization of the cake washing conditions led to a higher catalytic activity.Web of Science97art. no. 59

Anodic TiO2 nanotube layers for wastewater and air treatments: Assessment of performance using sulfamethoxazole degradation and N2O reduction

The preparation of anodic TiO2 nanotube layers has been performed using electrochemical anodization of Ti foil for 4 h at different voltages (from 0 V to 80 V). In addition, a TiO2 thin layer has been also prepared using the sol-gel method. All the photocatalysts have been characterized by XRD, SEM, and DRS to investigate the crystalline phase composition, the surface morphology, and the optical properties, respectively. The performance of the photocatalyst has been assessed in versatile photocatalytic reactions including the reduction of N2O gas and the oxidation of aqueous sulfamethoxazole. Due to their high specific surface area and excellent charge carriers transport, anodic TiO2 nanotube layers have exhibited the highest N2O conversion rate (up to 10% after 22 h) and the highest degradation extent of sulfamethoxazole (about 65% after 4 h) under UVA light. The degradation mechanism of sulfamethoxazole has been investigated by analyzing its transformation products by LC-MS and the predominant role of hydroxyl radicals has been confirmed. Finally, the efficiency of the anodic TiO2 nanotube layer has been tested in real wastewater reaching up to 45% of sulfamethoxazole degradation after 4 h.Web of Science2724art. no. 895

The role of the g-C3N4 precursor on the P doping using HCCP as a source of phosphorus

This work describes the doping of graphitic carbon nitride (g-C3N4) with phosphorus performed by 2-h heat treatment of a mechanical mixture of g-C3N4 precursor (urea, dicyandiamide, and guanidine hydrochloride) with hexachlorocyclotriphosphazene at 525 degrees C. The amount of fixed phosphorus in the resulting g-C3N4 structure reached approximately 10 wt% in the case of the urea precursor. For the other two precursors, the fixed phosphorus content in the final products was less than 5 wt%. Several experimental techniques (SEM, XRFS, TG, XRD, FTIR, physisorption of nitrogen, UV-VIS DRS, PL spectroscopy, and electrochemical analysis) were used to characterize the prepared samples. The photodegradation activity of the samples was determined by degradation of Rhodamine B under irradiation with visible light (420 nm). In general, the photodegradation activity of the samples was dependent on the phosphorus content. The highest photodegradation activity was obtained for urea-based g-C3N4 doped with the lowest phosphorus content, with a threefold increase in calcination product yield. The mechanism of incorporation of phosphorus into the final g-C3N4 structure was explained as a two-phase process.Web of Science183335331

Hydrogen production from microwave catalytic pyrolysis of spruce sawdust

The production of energy from wood biomass is as old as humanity itself. In the last 20 years there has been enormous progress in research of torrefaction, pyrolysis and mainly gasification of biomass. Products from conventional pyrolysis of biomass are gas known as pyrolysis gas, a liquid condensate known as bio-oil and char named bio-char. Most of the articles dealing with convectional pyrolysis of biomass are focused on the production of bio-oil. Only some works deal with the possibility of producing high-quality syngas (H-2 + CO) or hydrogen itself. For this purpose, the technology of microwave pyrolysis could be suitable. Microwaves can generate microplasma and hot spots, which promote heterogeneous catalytic reactions and produce a greater concentration of hydrogen in the resulting gas than convectional pyrolysis. In this work, an experimental study of spruce sawdust microwave pyrolysis was performed in the presence of catalysts to maximize the yield of hydrogen or syngas. Experiments were carried out in a microwave reactor with a power of 400 W. As catalysts char from sawdust, or sawdust char-doped with metal ions (Ni, Co, Fe) were used. Ions of metals were used to increase the yield of hydrogen (e.g. Nickel is widely used in the catalytic cracking of methane). The influence of the catalyst on the quantity of products (gas, liquid and solid) was studied, as well as the amount of hydrogen generated in the pyrolysis gas, or the amount of waste water in the liquid condensate.Web of Science12417917

La–Ni based alloy modification by Ce and Fe for the next hydrogen storage in low-temperature metal hydrides

La-Ni based alloys have been established as suitable materials for reversible hydrogen storage. Low-temperature metal hydrides (LT MH) facilitate hydrogen storage at ambient temperatures and pressure of 1-1.5 MPa. Nevertheless, further research and modifications of these alloys are needed. In this paper, the parent LaNi5 alloy was modified by partially replacing La with Ce and Ni with Fe. The alloys were prepared in two different ways: conventional melting of pure powder metals, and thermochemical reaction using corresponding metal chlorides. Steps were taken to optimize the time-temperature parameters of alloy synthesis. A comparative analysis of the obtained alloy samples followed. Hydrogen sorption isotherms were obtained for the unmodified LaNi5 and modified (La0.5Ce0.5)Ni-5 samples made from pure powder metals. Due to strong oxidation of the alloys prepared from metal chlorides, sorption isotherms for these alloys were not obtained.Web of Science60549849

La–Ni based alloy modification by Ce and Fe for the next hydrogen storage in low-temperature metal hydrides

La-Ni based alloys have been established as suitable materials for reversible hydrogen storage. Low-temperature metal hydrides (LT MH) facilitate hydrogen storage at ambient temperatures and pressure of 1-1.5 MPa. Nevertheless, further research and modifications of these alloys are needed. In this paper, the parent LaNi5 alloy was modified by partially replacing La with Ce and Ni with Fe. The alloys were prepared in two different ways: conventional melting of pure powder metals, and thermochemical reaction using corresponding metal chlorides. Steps were taken to optimize the time-temperature parameters of alloy synthesis. A comparative analysis of the obtained alloy samples followed. Hydrogen sorption isotherms were obtained for the unmodified LaNi5 and modified (La0.5Ce0.5)Ni-5 samples made from pure powder metals. Due to strong oxidation of the alloys prepared from metal chlorides, sorption isotherms for these alloys were not obtained.Web of Science60549849

Catalytic activity of advanced titanosilicate zeolites in hydrogen peroxide S-oxidation of methyl(phenyl)sulfide

Titanium-containing zeolite-based catalysts have been synthesized and investigated as catalysts in methyl (phenyl)sulfide oxidation with hydrogen peroxide. A hierarchical TS-1 prepared by the secondary templating and a layered TS-1 without and with silica and silica-titania pillars have been studied. Conventional TS-1 was a benchmarking material. The study focuses on observation of the different catalytic performance with regard to textural properties; presence and volume of mesopores and different diffusion characteristics. Thus, a deficiency and excess of the oxidizing agent were used in the catalysed reactions and the progress of reaction and selectivity to products were studied. All tested catalysts have shown after 240 min almost total conversion of methyl (phenyl)sulfide with different selectivity (substrate/catalyst mass ratio 10). It was observed that the reactants ratio hydrogen peroxide/ methyl(phenyl)sulfide influences the selectivity to sulfoxide or sulfone over a particular catalyst. In the case of hydrogen peroxide deficiency experiments (H2O2/sulfide = 0.5 mol/mol) the catalysts exhibited different distributions of products. Lamellar catalyst provided 100% selectivity to sulfoxide, the others in range of 90-65% selectivity to sulfoxide; however, the selectivity was independent on the reaction time and substrate conversion. In the case of the excess of the oxidant, except for Ti-pillared TS-1, all the catalysts showed stabile selectivity of 65% towards methyl(phenyl)sulfoxide being independent of the catalyst. The Ti-pillared TS-1 has shown, during the reaction progress, a decrease in the selectivity to sulfoxide from initial 60% to final 20% of sulfoxide at almost total conversion. The only case when higher selectivity to sulfone was achieved was gradual dosing of hydrogen peroxide.Web of Science32415314

Effect of talc in mixtures with fly ash on sintering crystalline phases and porosity of mullite-cordierite ceramics

The effect of talc in the two mixtures with the representative sample of fly ash (Class F) was investigated at sintering temperatures of 1000, 1100, and 1200 degrees C. X-ray diffraction, thermal DTA/TGA, and mercury intrusion porosimetry analyses were applied to characterize the mineral phase transformation of talc and fly ash in cordierite ceramic. The influence of iron oxide on talc transformation to Fe-enstatite was verified by the simulated molecular models and calculated XRD patterns and the assumption of Fe-cordierite crystallization was confirmed. The fly ash mixtures with 10 mass% of talc in comparison with 30 mass% of talc at 1000 degrees C and 1100 degrees C showed higher linear shrinkage and lower porosity. At a temperature of 1200 degrees C, sintering expansion and larger pores in mullite and cordierite ceramics also containing sapphirine and osumilite demonstrated that magnesium in FA and Tc structure did not react with the other constituents to form crystalline cordierite. The ceramics produced in the present work using fly ash and talc have similar properties to the commercial ceramics produced at sintering temperatures higher than 1250 degrees C.Web of Science112art. no. 15

Cement Substitution in High-Temperature Concrete

An alternative binder to calcium aluminate cement (CAC) was prepared by the sol-gel method. Chemically pure systems such as tetraethylorthosilicate (SiC8H20O4) and nonahydrate of alumina nitrate (Al(NO3)3·9H2O) were used as major raw materials. The manufacturing process of binder via solution is mentioned, and transitions in binder structure as a function of thermal treatment in the range between 85 and 1400 °C are described. Finally, binder efficiency was verified by its application in high-temperature concrete instead of calcium aluminate cement (CAC). Newly developed sol-gel binder was characterized by XRFS quantitative analyses, XRD diffraction, STA-DTA and TG analyses and the BET method. Samples of concrete which were based on natural bauxite raw material showed cold compressive strength of 42 MPa compared to the same material where a conventional CAC was applied, and samples reached cold compressive strength of 44 MPa

The effect of Zr loading in Zr/TiO2 prepared by pressurized hot water on its surface, morphological and photocatalytic properties

Zr/TiO2 anatase photocatalysts with 0.5, 1, 2, 5 and 7.5mol.% Zr were prepared using pressurized hot water crystallization and their photocatalytic activity was explored in acid orange 7 photodegradation. Parent TiO2 was also prepared and tested. From all tested photocatalysts, 2mol.% Zr/TiO2 showed the highest photoactivity, and 7.5mol.% Zr/TiO2 showed the lowest photoactivity. The poor photoactivity of 7.5mol.% Zr/TiO2 can be explained by the amorphous ZrO2 present in the surface layer (similar to 1-3m depth) of TiO2 anatase nanocrystallite agregates which changed the aggregate morphology and shielded the anatase nanocrystallite surface. The type and amount of defects (e.g., oxygen vacancies, lattice defects) did not effect the photoactivity of Zr/TiO2 in AO7 photodegradation. The addition of Zr to TiO2 significantly affects the photocatalyst morphology and the location where amorphous ZrO2 forms. The optimal Zr loading in TiO2 was determined to be 2mol.%.Web of Science90237936