Citric Acid Method Research Articles

Promotion effect of niobium on ceria catalyst for selective catalytic reduction of NO with NH3

The CeO2, Ce–Nb–Ox and Nb2O5 catalysts were synthesized by citric acid method and the promotion effect of Nb on ceria for selective catalytic reduction (SCR) of NO with NH3 was investigated. The catalytic activity measurements indicate that the mixed oxide Ce–Nb–Ox presents a higher SCR activity than the single oxide CeO2 or Nb2O5 catalyst. In addition, the Ce–Nb–Ox catalyst shows high resistance towards H2O and SO2 at 280 °C. The Raman, X-ray photoelectron spectra and temperature programmed reduction with H2 results indicate that the incorporation of Nb provides abundant oxygen vacancies for capturing more surface adsorbed oxygen, which provides a superior redox capability and accelerates the renewal of active sites. Furthermore, the Fourier transform infrared spectra and temperature programmed desorption of NH3 results suggest that niobium pentoxide shows high surface acidity, which is partly retained in the Ce–Nb–Ox catalyst possessing a high content of Lewis and Brønsted acid sites. Therefore, the incorporation of Nb improves both the redox and acidic capacities of Ce–Nb–Ox catalyst for the SCR reaction. Here, the redox behavior is primarily taken on Ce and the acidity is well improved by Nb, so the synergistic effect should exist between Ce and Nb. In terms of the reaction mechanism, in situ DRIFT experiments suggest that both NH3 on Lewis acid sites and NH4+ on Brønsted acid sites can react with NO species, and adsorbed NO and NO2 species can both be reduced by NH3. In the SCR process, O2 primarily acts as the accelerant to improve the redox and acid cycles and plays an important role. This work proves that the combination of redox and acidic properties of different constituents can be feasible for catalyst design to obtain a superior SCR performance.

Effect of pH on synthesis, characterization and fluorescence behavior of WO3:Eu3 nano powders

WO3:Eu3+ nanoparticles with different pH values were prepared by citric acid method. The structure and morphology of nano-powders were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The luminescence properties of the nano-powders were tested by a fluorescence spectrometer. The results showed that the average particle size of the prepared WO3:Eu3+ nano powders were the smallest and reached 32 nm at pH = 1. Under different excitation wavelengths, the main emission peak of the sample was at 615 nm, corresponding to the 5D0 →7F2 electron transition of Eu3+. The emission intensity of WO3:Eu3+ nanoparticles prepared at pH = 5 was the highest at 615 nm.

Fabrication of Al2O3/CaO with anti-sintering for efficient removal of As2O3 in simulated flue gas: Experimental and DFT study

Calcium oxide (CaO), as a high temperature sorbent, has been widely applied in the field of heavy metal removal due to its low price and stable chemical properties, but CaO tends to sinter at high temperature, which affects the adsorption performance. In this work, Al2O3/CaO sorbent with resistance to sintering was synthesized via citric acid and calcine method, which was innovatively employed to the adsorption of As2O3 combining experiment and theoretical analysis. The experimental results demonstrate that the adsorption capacity of untreated CaO reduces immensely with the temperature rising from 1073 to 1273 K, and arsenic adsorption capacity reduces from 303 to 50 mg/kg. Whereas, arsenic adsorption capacity of Al2O3/CaO almost maintains at high level and reaches to 534 mg/kg at 1173 K, which proves that the addition of Al2O3 can improve the anti-sintering ability of CaO. Meanwhile, through density functional theory (DFT), the adsorption sites of Al2O3/CaO was further studied. Al site of Al2O3/CaO was found to be the main adsorption active site and electron transfer channel, which effectively facilitates the separation of lattice oxygen. Finally, the adsorption mechanism of As2O3 on Al2O3/CaO was proposed.

Effect of Acid Treatment on the Catalytic Activity and Mechanical Stability of SmMnO3/Cordierite Monolithic Catalysts

AbstractSmMnO3/cordierite monolithic catalysts were synthesized by a modified citric acid method and treated with dilute HNO3, which was used to explore the effect of acid treatment on the catalytic performance and mechanical stability of the monolithic catalysts. Firstly, acid treatment can significantly improve catalytic activity of catalyst in o‐xylene oxidation, which is attributed to the increase of the specific surface area of the catalyst and the change of surface oxygen species. A series of single factor experiments show that the SmMnO3/cordierite monolithic catalyst treated by 1.0 mol/L HNO3 for 6 h and calcined at 450 °C for 1 h has the best performance. Furthermore, the mechanical stability of the catalysts treated by dilute HNO3 was tested, which show that too long acid treatment time and too high acid concentration will reduce the mechanical stability of the catalyst and 1.0 mol/L HNO3 treatment for 1 h is the best. Different calcination temperature and calcination time will also affect the mechanical stability of the catalyst. Finally, the catalyst has good stability of catalytic performance and mechanical stability.

Barium Titanate as a Highly Stable Oxygen Permeable Membrane Reactor for Hydrogen Production from Thermal Water Splitting

Hydrogen production from water splitting by a mixed ionic-electronic conducting membrane is an efficient and promising technology; however, it is severely impeded by the poor reduction tolerance of the existing cobalt- or iron-containing membrane materials. In this work, a novel BaMg0.1Zr0.05Ti0.85O3−δ (BMZ-Ti) perovskite was synthesized by combining citric acid and ethylenediaminetetraacetic acid methods. The new membrane is characterized by its superior chemical stability in a wet H2 atmosphere as well as with environment-responsive mixed conductivity, generating from the mild reduction of Ti4+ at low oxygen partial pressure. Benefiting from these combined properties, the BMZ-Ti membrane showed an oxygen permeation flux larger than 0.3 mL min–1 cm–2 under a H2O/(CH4–CO2) gradient, more than 50 times larger than that under an air/He gradient, which was able to be used for coupling methane reforming with water dissociation to efficiently produce hydrogen with a production rate of 0.8 mL min–1 cm–2. Furthermore, no performance degradation was observed during an over 100 h test. These results highlight the potential of the BMZ-Ti membrane, with both environment-responsive mixed conductivity and excellent chemical stability, as a novel oxygen permeable membrane for hydrogen production from water.

A novel cobalt-free and CO2-stable LDC-LSCF membrane with high oxygen permeability

Cobalt (Co)-free and carbon dioxide (CO2)-stable Ce0.8La0.2O2−δ –La0.1Sr0.9Cu x Fe1−x O3−δ (LDC-LSCF) dual-phase oxygen-permeable membranes have been successfully developed through the one-pot ethylenediaminetetraacetic acid–citric acid method. The appropriate amount of copper (Cu) doping can increase the content of oxygen (O) vacancies and improve the oxygen (O2) permeability of the materials. At 900°C, the oxygen permeation flux of 60 wt.% Ce0.8La0.2O2−δ –La0.1Sr0.9Cu0.2Fe0.8O3−δ (60LDC-LSCF-0.2) membrane reaches 0.58 (ml/min)/cm2 with pure helium (He) as the sweep gas, which is the highest oxygen permeation flux among dual-phase membranes with different copper-doping contents. The effects of different LDC contents on the static stability, conductivity and oxygen permeability of the dual-phase membranes are studied. The oxygen permeation flux of the 60LDC-LSCF-0.2 membrane remains 0.37 (ml/min)/cm2 with pure carbon dioxide as the sweep gas during the long-term oxygen permeation test. The present results indicate that LDC-LSCF oxygen-permeable membranes are promising membranes for oxygen production and carbon dioxide capture.

Improved NH3-SCR deNOx activity and tolerance to H2O & SO2 at low temperature over the NbmCu0.1-mCe0.9Ox catalysts: Role of acidity by niobium doping

A series of NbmCu0.1-mCe0.9Ox catalysts were synthesized with the help of citric acid method, and used for the selective catalytic reduction of NOx with NH3 (NH3-SCR). The catalytic performance of the NbmCu0.1-mCe0.9Ox samples was greatly improved after the introducing of niobium. Among all catalysts, the Nb0.06Cu0.04Ce0.9Ox catalyst revealed the best low-temperature SCR activity, higher N2 selectivity and extraordinary SO2 and H2O durability with 100% NO conversion at 150–390 °C. The various characterization techniques were carried out to investigate the effect of niobium doping on the physical structures, surface properties and NH3-SCR activity of catalysts. Results reveal that the oxidation ability decrease but the acidity is enhanced with the Nb addition. The improved acidity by niobium doping is considered the primary cause for the superior deNOx performance of the Nb0.06Cu0.04Ce0.9Ox catalyst at low temperature, which can offset the negative effects of the reduced oxidation ability on activity. Furthermore, in situ DRIFTS results were applied for the investigation of the reaction process in detail.

Effect of Electron Doping on the Crystal Structure and Physical Properties of an n = 3 Ruddlesden–Popper Compound La4Ni3O10

The physical properties of La4Ni3O10 with a two-dimensional (2D)-like Ruddlesden–Popper-type crystal structure are extraordinarily dependent on temperature and chemical substitution. By introducing Al3+ atoms randomly at Ni sites, the average oxidation state for the two nonequivalent Ni cations is tuned and adopts values below the average of +2.67 in La4Ni3O10. La4Ni3–xAlxO10 is a solid solution for 0.00 ≤ x ≤ 1.00 and is prepared by the citric acid method, with attention paid to compositional control and homogeneity at low Al level (x) concentrations. The samples adopt a slightly distorted monoclinic structure [P21/a (Z = 4)], evidenced by peak broadening of the (117) reflection. We report a remarkable effect on the electronic properties induced by tiny amounts of homogeneously distributed Al cations, with clear correspondence between resistivity, magnetization, diffraction, and density functional theory (DFT) data. DFT shows that electronically, there is no significant difference between the nonequivalent Ni atoms and no tendency toward any Ni3+/Ni2+ charge ordering. The resistivity changes from metallic to semiconducting/insulating with increasing band gap at higher Al levels, consistent with results from DFT. The metal-to-metal (M-T-M) transition reported for La4Ni3O10, which is often interpreted as a charge density wave, is maintained until x = 0.15 Al level. However, the temperature characteristics of the resistivity change already at very low Al levels (x ≤ 0.03). A coupling of the M-T-M transition to the lattice is evidenced by an anomaly in the unit cell dimensions. Moreover, there is an excellent correlation between the resistivity and magnetization data shown by the metallic and Pauli paramagnetic regime for La4Ni3–xAlxO10 with x < 0.25. The introduction of the fixed +3 oxidation state of Al atoms randomly at the Ni sites reduces the overall oxidation state of Ni2.67+ by keeping the oxygen stoichiometry unchanged. In addition, the nonmagnetic Al3+ for Ni is likely to block Ni–O–Ni exchange pathways through −Ni–O–Al–O–Ni– fragments into the network of corner-shared octahedra with the emergence of possible short-range ferromagnetic ordering of the ferromagnetic domains/clusters that are formed due to Al substitutional disorder in a paramagnetic insulating matrix.

Effect of the Preparation Method of LaSrCoFeOx Perovskites on the Activity of N2O Decomposition

N2O remains a major greenhouse gas and contributor to global warming, therefore developing a catalyst that can decompose N2O at low temperatures is of global importance. We have investigated the use of LaSrCoFeOx perovskites for N2O decomposition and the effect of surface area, A and B site elements, Co–O bond strength, redox capabilities and oxygen mobility have been studied. It was found that by using a citric acid preparation method, perovskites with strong redox capabilities and weak Co–O bonds can be formed at relatively low calcination temperatures (550 °C) resulting in highly active catalysts. The enhanced activity is related to the presence of highly mobile oxygen species. Oxygen recombination on the catalyst surface is understood to be a prominent rate limiting step for N2O decomposition. Here the reduced strength of Co–O bonds and mobile lattice oxygen species suggest that the surface oxygen species have enhanced mobility, aiding recombination, and subsequent regeneration of the active sites. La0.75Sr0.25Co0.81Fe0.19Ox prepared by citric acid method converted 50% of the N2O in the feed (T50) at 448 °C.Graphic

Sb-Containing Metal Oxide Catalysts for the Selective Catalytic Reduction of NOx with NH3

Sb-containing catalysts (SbZrOx (SbZr), SbCeOx (SbCe), SbCeZrOx (SbCeZr)) were prepared by citric acid method and investigated for the selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR). SbCeZr outperformed SbZr and SbCe and exhibited the highest activity with 80% NO conversion in the temperature window of 202–422 °C. Meanwhile, it also had good thermal stability and resistance against H2O and SO2. Various characterization methods, such as XRD, XPS, H2-TPR, NH3-TPD, and in situ diffuse reflectance infrared Fourier transform (DRIFT), were applied to understand their different behavior in NOx removal. The presence of Sb in the metal oxides led to the difference in acid distribution and redox property, which closely related with the NH3 adsorption and NO oxidation. Brønsted acid and Lewis acid were evenly distributed on SbCe, while Brønsted acid dominated on SbCeZr. Compared with Brønsted acid, Lewis acid was slightly active in NH3-SCR. The competition between NH3 adsorption and NO oxidation was dependent on SbOx and metal oxides, which were found on SbCe while not on SbCeZr.

Preferred enhancement of fast-SCR by Mn/CeSiOx catalyst: Study on Ce/Si promotion and shape dependence

A series of Mn/CeSiOx catalysts were synthesized to investigate the Ce/Si ratios and morphology effect of Ce/SiOx support for the selective catalytic reduction (SCR) of NO with NH3 at low temperature. The characterization and catalytic test showed that the 0.3Mn/Ce8Si2Ox-R catalyst exhibits high NOx conversion at low temperature. The Ce/Si ratio was 8/2 over the 0.3Mn/Ce8Si2Ox-R catalyst, increasing the surface acidity and inhibiting the side reaction of NH3. The {110} and {100} facts of the nanorod structure are rich in Ce3+ species and oxygen vacancies for the SCR reaction. Moreover, the citric acid method was employed on 0.3Mn/Ce8Si2Ox-R-CA to improve the interaction between Mnn+ and Ce8Si2Ox-R and enhance the strength of surface acidity, leading to the highest NOx conversion and Fast-SCR process. During the suppression effect of SO2 or HCl on catalytic activity, the 0.3Mn/Ce8Si2Ox-R-CA catalyst shows higher poison resistance to HCl than SO2.

Physicochemical properties and antioxidant activity of pectin from hawthorn wine pomace: A comparison of different extraction methods

In the paper, to enhance the value and utilization rate of hawthorn wine pomace waste, four kinds of pectin were gained from hawthorn wine pomace by hydrochloric acid method (HA-HP), citric acid method (CA-HP), cellulase method (E-HP) and microwave-assisted chelating agent method (MH-HP). The physical and chemical properties of extracted hawthorn pectin were analyzed, however, different extraction methods lead to different characteristics of extracted pectin samples. We found that the extracted hawthorn pectin was all low-methoxy pectin, and the highest extraction yield of 72.89% with high ash (9.20%) was obtained by the MH-HP method, while the galacturonic acid (Gal A) content was up to 72.24% after dealing with the CA-HP method which was the highest among the four samples, besides, the quality of gel formed by E-HP method was the best. What's more, the four extracted samples all reveled degrees of antioxidant activity with dose-dependent in vitro antioxidant, and it was CA-HP method had the best antioxidant activity, making this the first comprehensive research describing the extracting pectin from hawthorn wine pomace. This research also provides a base for industrial production of high-value products from low-cost raw materials.

Insight into catalytic properties of Co3O4-CeO2 binary oxides for propane total oxidation

A series of Co3O4-CeO2 binary oxides with various Co/(Ce+Co) molar ratios were synthesized using a citric acid method, and their catalytic properties toward the total oxidation of propane were examined. The activities of the catalysts decrease in the order CoCeOx-70 > CoCeOx-90 > Co3O4 > CoCeOx-50 > CoCeOx-20 > CeO2. CoCeOx-70 (Co/(Ce+Co) = 70% molar ratio) exhibits the highest catalytic activity toward the total oxidation of propane, of which the T90 is 310 °C (GHSV = 120000 mL h−1 g−1), which is 25 °C lower than that of pure Co3O4. The enhancement of the catalytic performance of CoCeOx-70 is attributed to the strong interaction between CeO2 and Co3O4, the improvement of the low-temperature reducibility, and the increase in the number of active oxygen species. In-situ DRIFTS and reaction kinetics measurement reveal that Ce addition does not change the reaction mechanism, but promotes the adsorption and activation of propane on the catalyst surface. The addition of water vapor and CO2 in reactant gas has a negative effect on the propane conversion, and the catalyst is more sensitive to water vapor than to CO2. In addition, CoCeOx-70 exhibits excellent stability and reusability in water vapor and CO2 atmosphere.

Effect of extraction methods on geometric, gravimetric and colour aspects of tomato seeds

Tomato seeds, a major food industry waste, were separated from the skin using different extraction methods viz. normal water, fermentation, hydrochloric acid (HCl), and citric acid method. Physical, gravimetric, and colour properties of tomato seeds extracted using the above methods were studied and it was observed that the maximum percent yield of tomato seeds was obtained from the citric acid method (0.51%). The moisture content of tomato seeds was noted in the range of 7.68–8.09 percent. The maximum oil yield (21.39%) was obtained from tomato seeds extracted using the HCl method. Length, width, and thickness from all the four methods varied from 3.70–4.94 mm, 2.78–3.36 mm, and 0.73–1.14 mm, respectively. The highest surface area was found in HCl treated seeds (19.37 mm). Mean values for sphericity, aspect ratio, 1000 kernel weight, bulk density, and porosity were recorded as 56.86 percent, 74.93 percent, 3.09 g, 0.21 g/cc, and 78.40 percent, respectively. Colour values revealed a slightly dark and yellow appearance of seeds.

Microwave direct denitration for synthesis of Cu-Ce-Zr-O composite oxide and its characterization

A Cu-Ce-Zr-O composite oxide was synthesized by microwave direct denitration (MDD) and citric acid (CA) methods, with the latter used as an experimental control. X-ray diffraction analysis confirmed that MDD facilitated the formation of a highly homogeneous Cu-Ce-Zr-O composite oxide. The specific surface area and oxygen release rate of the MDD product were 2.2–2.4 and 1.4–1.7 times larger than those of the CA product, respectively, whereas the oxygen storage capacity of the former product was slightly lower than that of the latter. Consequently, it was concluded that MDD did not significantly improve catalytic performance, although it reduced synthesis time and simplified the synthesis process.

Efficient hydrogenation of CO2 to methanol over Pd/In2O3/SBA-15 catalysts

The catalytic hydrogenation of CO2 to methanol has been regarded as the one of the most economical and effective ways to reduce CO2 emissions. It can also provide a feasible idea for solving the energy crisis. In this paper, a series of Pd/In2O3/SBA-15 catalysts were prepared by the citric acid method. The DFT simulation and catalyst characterization including the N2 adsorption, XRD, H2-TPR, TEM, XPS and CO2-TPD were applied. The results showed that the as-prepared Pd/In2O3/SBA-15 catalysts exhibited superior catalytic activity with 83.9% methanol selectivity and 12.6% CO2 conversion, corresponding to a STY of 1.1 × 10-2 mol·h-1·gcat-1 under reaction conditions of 260 °C, 5 Mpa and 15,000 cm3 h-1·gcat-1. It is suggested that the synergetic effect of H2 dissociation on Pd species and CO2 activation on In2O3 promoted the high efficiency conversion of CO2 to methanol.

Influence of Interaction Components on the NOx Adsorption Properties of Cu-Ba-Ce Composite Catalysts.

For further investigating the role of components in copper-cerium-barium composite oxide catalysts, a series of noble metal-free catalysts with different barium contents were synthesized by citric acid method. The prepared catalysts were characterized by X-ray diffraction, Brunauer-Emmett- Teller method, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. Catalysts were evaluated by NO oxidation, NOx adsorption, and NOx temperature-programmed desorption. The results showed that barium content significantly affected the catalysts' properties. With barium addition, interactions among components considerably changed; hence, the microstructure and performance of catalysts were distinctly different. In general, the interactions of barium-copper and barium-cerium were not conducive to catalyst adsorption. Adsorption performance derived from barium carbonate was superior to those of the other two components.

Preparation of CaO-based sorbent from coal fly ash cenospheres for calcium looping process

With the aim to synthesize an inexpensive and high-stable sorbent for CO2 capture processes, an industrial waste-product derived from coal-fired power plant, the so-called coal fly ash (CFA) cenospheres, was employed as inert supporting material. The CaO-based sorbent derived from CFA cenospheres (mainly composed of mullite and quartz) was prepared via a solution-based citric acid method. The obtained slurry was decomposed at 500 °C in air for 2 h. From the XRD results the CaO-CFA500 sorbent was mainly composed of Ca12Al14O33 (mayenite) and Ca(OH)2 along with trace of γ-Al(OH)3 and CaCO3 and starting SiO2. A further air-heating at 900 °C was conducted because the CO2 sorbent is submitted at high temperature for regeneration. The CaO-CFA900 sorbent was made of free-CaO and two crystalline calcium-alumino-silicate phases, namely gehlenite (Ca2Al2SiO7) and anorthite (CaAl2Si2O8). The optimized mesopore size particles belonging to CaO-CFA900 was reflected in a high stability over multiple cycles of carbonation/calcination. The initial CO2 capture capacity of the sorbent was 0.33 g CO2 g−1 sorbent, which was about three times the value of pure CaO (0.11 g CO2 g−1 CaO), and reduced to 0.22 g CO2 g−1 sorbent after 20 cycles remaining then stable over 200th cycles. From the present results it can be argued that CaL process could be easily scalable by re-using a coal-fired plant waste-product.

Investigation of catalytic activity and mechanism for RhB degradation by LaMnO3perovskites preparedviathe citric acid method

LaMnO3exhibits an excellent degradation ability of RhB under highly acidic conditions without adding additional oxidants or light irradiation.

Sol‐Gel Preparation of Perovskite Oxides Using Ethylene Glycol and Alcohol Mixture as Complexant and Its Catalytic Performances for CO Oxidation

AbstractWe reported an updated sol‐gel method for the preparation of perovskite oxide using ethylene glycol and alcohol mixture as complexant. Relative to that prepared by sol‐gel method using citric acid as complexant, the sample prepared by this updated method showed porous structure, higher surface area, more oxygen vacancies and stronger reducibility, due to a two‐step combustion process. By comparing the phase transformation temperature of perovskite oxides using different transition metals, it was inferred that the electron distribution in the 3d orbit is a crucial factor influencing the formation of perovskite structure. The easier the electrons to be excited, the easier the perovskite structure to be formed. Catalytic results showed that the sample (e. g., LaCoO3‐EM) prepared by the updated method is more active for CO oxidation than that prepared by citric acid method, with full CO conversion obtained at 135 °C and no activity loss is observable either by long‐term (30 h) or by cycling (3 times) stability tests. Effect of the chain length of alcohols on the properties of LaCoO3 was also studied.