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The effect of 1-(3-phenoxypropyl) pyridazin-1-ium bromide, a new pyridazinium derivative, on steel corrosion in a HCl (1 M) solution was analyzed using electrochemical impedance and ...XPS spectroscopy. Experimental results indicated that the inhibition efficiency increased with an increase in an inhibitor concentration. Electrochemical impedance spectroscopy measurements revealed that an increase in the immersion time of steel in an acidic medium from 1 to 12 h and further to 24 h decreased the charge transfer resistance (Rct) and thus decreased the inhibition efficiency. The SEM and XPS analyses linked the inhibition effect to the adsorption of the inhibitor (1-(3-phenoxypropyl) pyridazin-1-ium bromide) on the steel surface.
Ni
2P catalysts supported on mesoporous silica (MCM-41) were prepared by temperature programmed reduction through a novel method using nickel(II) dihydrogenphosphite, Ni(HPO
3H)
2, as a precursor ...salt, and preparing three catalysts with nickel loadings of 5, 10 and 15 wt% denoted as Ni
2P-
x, where
x is the percentage in weight of nickel. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N
2 adsorption–desorption isotherms were used to study the formation of the phase. The dibenzothiophene (DBT) hydrodesulfurization (HDS) activity was measured for Ni
2P-
x catalysts and they showed good TOF values at 400 °C. The conversion hardly changes with the metallic loading, and increases with temperature in all cases. On the other hand, Ni
2P-5 catalyst shows a better intrinsic activity of Ni
2P phase. Further, an improvement in the activity is found with time on stream, where an increase in both stability and activity are observed, reaching conversions of close to 95%. XRD and XPS analysis of spent catalysts show that the formation of a more active Ni
2P phase takes place under the reaction conditions. The support impregnated with nickel(II) dihydrogenphosphite, without prior reduction, was also active in this reaction, increasing in activity with time on stream as a consequence of the formation of the corresponding Ni
2P or other mixed NiP
x
S
y
phases under the experimental conditions.
Ni
2P/MCM-41 catalysts were prepared by H
2-TPR through a novel method using nickel(II) dihydrogenphosphite, Ni(HPO
3H)
2, as a precursor salt. The formation of more Ni
2P phase takes place with time on stream.
•High surface area Fe2O3 (208m2g−1) prepared using a hard template method.•Fe2O3 formed by aggregation of nanocrystals prepared by soft chemistry.•Mesoporous Fe2O3 are very active for the combustion ...of VOCs (propane and toluene).•Soft chemistry higher reducibility than hard template method.•The type of VOC influences the nature of the most active catalysts.
The total oxidation of two representative VOCs, propane and toluene, has been studied using mesoporous α-Fe2O3 catalysts. Different preparation methods have been followed leading to mesoporous materials with different characteristics. Whilst a mesoporous catalyst formed by aggregation of nanocrystals has been produced by soft chemistry using oxalic acid as precipitating agent, a mesoporous material with crystalline walls have been prepared by a nanocasting route using a hard template. These catalysts have been characterized by several physicochemical techniques: XRD, N2 adsorption, TPR, XPS, TEM, HR-TEM, SAED and EDX. Among the different α-Fe2O3 catalysts synthesized differences not only in the surface area and morphology have been observed but also in the lattice parameter, in the concentration of oxygen defects for VOCs adsorption and in the reducibility. In the case of the toluene oxidation it has been observed that the catalytic activity is highest for the catalysts prepared by a nanocasting route, which presents a very high surface area of 208m2g−1. Conversely, for propane oxidation the most active catalyst resulted to be the mesoporous nanocrystalline catalyst formed by aggregation. In this case, a direct relationship between reducibility and catalytic activity normalized per surface area has been observed. The differences between toluene and propane oxidation can be tentatively ascribed to different reaction mechanisms to be accounted for.
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•Bimetallic PdNb catalysts show promising results in the dry reforming of methane.•A synergic effect between Pd and Nb is observed.•The addition of Nb improved the catalytic activity ...minimizing carbon deposits formation.•The catalytic stability depended on the reoxidation degree of active sites.
This work describes the use of Pd-Nb catalysts supported on commercial silica in the dry reforming of methane. The effect of Pd/Nb ratio was evaluated and it determined the catalytic response of the prepared catalysts. Thus, it was observed that the catalytic activity increased with the Pd/Nb ratio and bimetallic samples were more active than the monometallic ones. The sample with the highest Pd/Nb ratio was the best in terms of conversion, selectivity and stability. Nb presence decreased the amount of carbon deposited on the catalysts since the decomposition of CH4 is minimised in the operating conditions.
The deactivation behaviors of MeMo/La2O3-Al2O3- and MeMo/Nb2O5 supported catalysts were investigated in the tri-reforming of methane (TRM). Characterizations by XRD, SEM-EDS, HRTEM, XPS, FTIR, and ...Raman spectroscopies were performed, after testing the catalysts in distinct TRM reaction conditions. The effects the transition metal components had on the causes of the deactivations of the solids were evaluated. The reaction conditions favored PtO x species residing in close contact with Mo sites to form a PtMo alloy. This enhanced the CH4 activation avoiding carbon accumulation in PtMo/Nb2O5. In contrast, LaPtO x Pton surface oxygen species formation neither avoided sintering of the Pto particles on Mo/La2O3-Al2O3 nor oxidized the deposited carbon. The incorporation of Co in Mo/La2O-Al2O3 and Mo/Nb2O5 caused the continuous reoxidation of Co species because of the presence of O2, CO2, and steam reactants during the TRM reaction. Significant coke depositions on the Nio sites of NiMo/La2O3-Al2O3 and NiMo/Nb2O5 by the contribution of Boudouard and methane cracking reactions were observed, in short-term stability runs.
•Zeolite type A was synthesized from natural resources under mild conditions.•Textural properties and crystallinity can be controlled through synthesis conditions.•Microporosity plays a key role on ...CO2/N2 and CO2/H2O selectivies.•Under dry conditions, CO2 is readily desorbed at moderate temperatures.•The presence of water hinders the desorption of the physisorbed species.
In light of the urgent need of reducing the atmospheric CO2 emissions, the use of low-cost adsorbents, that exhibit a high affinity and CO2 adsorption capacity, is a promising method from the economic and environmental point of view to separate CO2 from the flue gas emitted from large sources of emissions like power-fueled plants. Clay minerals are low-cost raw materials with high availability all over planet and great versatility in the fields of adsorption and catalysis processes. The present study pretends to elucidate the link between the reaction conditions during the synthesis of the zeolite from kaolinite and its CO2 adsorption capacity. For that purpose, the type A zeolite was synthesized via hydrothermal process in alkaline solution using metakaolinite as a starting material. The metakaolinite was obtained by calcination of kaolinite at 600 °C and some parameters such as temperature and synthesis time were modified to optimize the synthesis aiming for a high CO2 adsorption capacity adsorbent. Synthesized materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), N2 adsorption–desorption at −196 °C and CO2 adsorption at 0 °C (up to 10 bars) isotherms and Nuclear Magnetic Resonance of solids (NMR). In addition, the adsorption capacity of CO2 was evaluated by means of CO2 adsorption–desorption isotherms at 25 °C up to atmospheric pressure. The obtained results indicated that synthesized zeolite 4A can be successfully prepared from natural kaolinite (via metakaolinization) at 100 °C for 48 h under alkaline conditions, showing chemical and physical properties similar to that of the commercial 4A zeolite.
A glassy carbon electrode (GCE) was surface-modified with carbon quantum dots (CQDs) and applied for the effective enhancement of the electrochemical signal for dopamine and uric acid determination. ...CQDs were prepared from graphite by a green modification of the Hummers method. They were characterized by FTIR-ATR, XPS, solid-state NMR, fluorescence and Raman spectroscopies. TPD-MS analysis was applied to characterize the functionalization of the surface. The CQDs were assembled on the glassy carbon electrode by adsorption because of the large number of carboxy groups on their surface warrants effective adsorption. The modified GCE exhibits a sensitivity that is almost 10 times better than of the bare GCE. The lower limits of detection are 1.3μM for uric acid and 2.7μM for dopamine.
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•Carbon quantum dots (CQDs) were obtained by a green variant of Hummers’ method.•CQDs were characterized by FTIR-ATR, XPS, solid-state NMR, fluorescence and Raman.•TPD-MS analysis was applied to characterize functionalization of the surface.•The glassy carbon electrode was easily modified by adsorption of CQDs.•The CQDs modified electrode was used to quantify dopamine and uric acid.
Highly photoluminescent carbon dots have been prepared in a one step procedure by hydrothermal treatment of formaldehyde at 180 °C. They show green fluorescence under UV light exposure and emission ...spectra are centered at 440 nm. Fluorescence lifetimes comprise between 0.7 and 2.70 ns, when the synthesis process lasted for 1-7 days. TEM images of nanoparticles showed a homogeneous size/shape distribution. When the thermal treatment process was carried out for a long time (30 days) formation of aggregates occurred. Carbon dots were further analyzed using (1)H and (13)C-NMR, Raman and FTIR spectroscopy techniques and XPS. Cell imaging of nanoparticles was carried out by using mouse MC3T3-E1 pre-osteoblasts as a model. The nanoparticles were selectively localized in the cytoplasm without further functionalization and could be realized by cellular phagocytosis, so that the fluorescence of these can be used for live cell imaging in vitro.
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•Potential biolubricants were synthesized from soybean fatty methyl esters.•Water, 2-ethylhexanol and their mixtures were studied as nucleophilic agent.•Bio-based lubricants were ...obtained with viscosities at 40 °C ranging from 26.6 to 99.6 cSt.•Process integration between a biodiesel plant and biolubricant production was evaluated.•An industrial process was proposed to obtain both biodiesel and biolubricants.
The competitiveness of the biodiesel industry may be improved by adding value through co-products and integration with the oleochemical industry, especially for novel products such as biolubricants, a product of increasing world demand. In this study the synthesis of biolubricants from soybean oil was evaluated using transesterification, epoxidation and oxirane ring opening reactions. Water, 2-ethylhexanol and their mixtures were used to obtain hydroxyl-rich and/or ether-type branched molecules. All chemical modifications were monitored by Nuclear Magnetic Resonance (1H NMR) and evaluated through the physicochemical properties of the products. Several potential biolubricant samples were synthesized with viscosities at 40 °C ranging from 26.6 to 99.6 cSt, viscosity index from 26 to 139, densities at 20 °C from 0.925 to 0.964 g/cm3, and pour points from −3 to −12 °C. From these results, a proposal of a feasible industrial process for the production of biolubricants from soybean oil is presented, consisting of 16 units, of which 15 may be integrated with an existing biodiesel plant.
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Fluorescent carbon dots (CDs) and its nitrogen doped (N-CDs) nanoparticles have been synthesized from lactose as precursor using a bottom-up hydrothermal methodology. The synthesized ...nanoparticles have been characterized by elemental analysis, FTIR, Raman, TEM, DLS, XPS, and steady-state and life-time fluorescence. The synthesized carbon nanoparticles, CDs and N-CDs, have a size at about 7.7±2.4 and 50±15nm, respectively, and quantum yields of 8% (CDs) and 11% (N-CDs). These techniques demonstrated the effectiveness of the synthesis procedure and the functionalization of the CDs surface with amine and amide groups in the presence of NH3 in aqueous media. The effect of excitation wavelength and pH on the luminescent properties was studied. Under the optimal conditions, the nitrogen doped nanoparticles can be used as pyridine sensor in aqueous media because they show an enhancement of its fluorescence with a good linear relationship. The analytical method is simple, reproducible and very sensitive for pyridine determination.
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