Effect Of Transition Metal Doping Research Articles

Research progress of low-temperature SCR denitration catalysts

Nitrogen oxide NOx (NO, NO_2, and N_2O) is one of the major pollutants in the air pollution, it can cause environmental problems such as photochemical smog, acid rain, and ozone layer destruction, which has posed threat to people's living environment and quality of life, and attracted great attention from the world. Countries made stricter emission standards for burning emissions from both fixed and mobile sources. The major denitrification technologies include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), oxidative denitrification, and activated carbon adsorption and denitrification at present. The SNCR has higher conditions in industrial applications, the main factors affecting successful operation are temperature, ammonia-nitrogen ratio, distribution of ammonia gas in the flue gas and residence time, so there were certain limitations in industrial application of SNCR. Compared with other denitrification technologies, SCR denitration technology is more widely used in industrial application, in which denitration is mostly arranged after dust removal and desulfurization, at this time, the temperature is mostly between 100~250℃. The performance of SCR denitrification in low-temperature must be improved, which is one of the most promising flue gas DeNOx technology. In this paper, the recent works on low-temperature SCR catalysts were reviewed on manganese-based catalysts, vanadium-based catalysts and carbon-based catalysts. Single-component Mn-based catalysts, supported Mn-based catalysts and composite Mn-based catalysts were reviewed, the effects of preparation of V-based catalysts on the de-dumping and denitrification mechanisms were described. The effect of transition metal doping on C-based catalysts was reviewed. The influence of H_2O and SO_2 resistance on low-temperature NH_3-SCR catalytic activity and reaction mechanism were also discussed. Finally, the virtues advantages and defects of low temperature SCR catalysts were summarized, and the future development direction was also given out. Key learning points: (1) Catalysts for different systems were reviewed. The problems of manganese-based catalysts, vanadium-based catalysts and carbon-based catalysts were analyzed. The preparation methods were used to improve the water and sulfur resistance and catalytic activity of the catalysts. (2) Denitrification mechanism. From the currently reported denitration mechanism to analyze the activity of the catalyst, it is expected that the mechanism rsearches will improve the low temperature performance of the catalyst. (3) Water and sulfur resistance of low temperature catalyst. The presence of SO_2 at low temperatures tends to result in ABS deposition.

Effects of Transition Metal Doping in Pt/M-TiO 2 (M= V, Cr, and Nb) on Oxygen Reduction Reaction Activity

High cost and low durability are unresolved issues that impede the commercialization of proton exchange membrane fuel cells (PEMFCs). To overcome these limitations, Pt/TiO2 is reported as an alternative electrocatalyst for enhancing the oxygen reduction reaction (ORR) activity and/or durability of the system. However, the low electrical conductivity of TiO2 is a drawback that may be addressed by doping. To date, most reports related to Pt/doped-TiO2 focus on changes in the catalyst activity caused by the Pt-TiO2 interaction (metal-support interaction), instead of the effect of doping itself; doping is merely considered to enhance the electrical conductivity of TiO2. In this study, we discuss the variation in the electronic fine structure of Pt caused by the dopant, and its correlation with the ORR activity. More extensive contraction of the Pt lattice in Pt/M-TiO2 (M = V, Cr, and Nb) relative to Pt/TiO2 and Pt/C leads to outstanding ORR specific activity of Pt/M-TiO2. Notably, a fourfold increase of the specific activity is achieved with Pt/V-TiO2 relative to Pt/C. Furthermore, an accelerated durability test (ADT) of Pt/V-TiO2 demonstrates that this system is three times more durable than conventional Pt/C due to the metal-support interaction.

Behavior of Manganese-Rich Layered Sodium Oxides in Aqueous Electrolytes

Aqueous sodium-ion batteries operating in neutral pH electrolytes offer the potential for low cost, low toxicity, high safety, and high power density energy storage for large-scale applications, such as those needed to store electricity from renewable energy sources. However, the mechanisms of ion intercalation into solid-state electrodes operating in neutral pH aqueous electrolytes are not well understood. Layered, Mn-rich sodium oxides are promising electrode materials because of the abundance and safety of manganese. Initial studies of the moisture-stable, layered P2-type oxide, NaxNi0.22Mn0.66Co0.11O2 (NaNMC) show an irreversible phase transition to a hydrated birnessite-like structure during electrochemical cycling in aqueous electrolytes with approximately 25 mAh/g reversible capacity. This work investigates the transformation mechanism of the NaNMC through ex situ X-ray diffraction, in situ Raman spectroscopy, and ex situ transmission electron microscopy. A systematic investigation is then conducted on the effect of transition metal doping in NaNMC to reduce the amount of Ni and Co, and to tune the redox potential and capacity for electrochemical cycling in aqueous electrolytes. In addition, aqueous solutions with both high and low salt concentrations are investigated to determine the effect of the electrolyte on the electrochemical behavior of layered sodium oxides

Promotional effect of transition metal doping on the properties of KF/CaO catalyst for biodiesel synthesis

ABSTRACTA series of heterogeneous KF/CaO catalysts modified with transition metals (lanthanum, cerium, and zirconium) were prepared via wet impregnation method and applied to the trsansesterification process of waste cooking oil (WCO) as feedstock with methanol to biodiesel production. The structure, performance of the solid catalysts was characterized by X-ray diffraction (XRD), temperature programmed desorption of CO2 (CO2-TPD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The effect of methanol/oil molar ratio, 1reaction time, reaction temperature, catalyst amount, and stability was investigated. The results showed that 10 wt% of lanthanum, cerium, and zirconium improved the catalytic activity of KF/CaO catalyst. The maximum catalytic activity using the lanthanum doping of 10wt% on KF/CaO catalyst was reached 98.7% under the optimal reaction condition of methanol/oil molar ratio of 12:1, reaction for 1 h at reaction temperature of 65°C, and 4% (wt/wt oil) catalyst amount. In addition, the FAME yield of KF/CaO/La catalyst remained higher than 95% after 10 cycles. The promotional effect of lanthanum doping could be attributed to the enhancement of the basicity strength of KF/CaO catalyst and block the leach of Ca2+ in the transesterification reaction.

Effect of transition metal doping on the catalytic performance of Au–Pd/3DOM Mn2O3 for the oxidation of methane and o-xylene

Palladium-based catalysts are highly active for eliminating volatile organic compounds. Reducing the use of noble metals and enhancing performance of a catalyst are always desirable. The three-dimensionally ordered macroporous (3DOM) Mn2O3-supported transition metal M (M=Mn, Cr, Fe, and Co)-doped Au–Pd nanoparticles (NPs) with an Au–Pd–xM loading of 1.86–1.97wt% were prepared using the modified polyvinyl alcohol-protected reduction method. It is found that the Au–Pd–xM NPs with a size of 3.6–4.4nm were highly dispersed on the surface of 3DOM Mn2O3. The 1.94wt% Au–Pd–0.21Co/3DOM Mn2O3 and 1.94wt% Au–Pd–0.22Fe/3DOM Mn2O3 samples performed the best for the oxidation of methane and o-xylene, respectively. The methane oxidation rate at 340°C (339.0×10−6mol/(gPds)) over 1.94wt% Au–Pd–0.21Co/3DOM Mn2O3 was three times higher than that (93.8×10−6mol/(gPds)) over 1.97wt% Au–Pd/3DOM Mn2O3, and the o-xylene reaction rate at 140°C (2.59μmol/(gNs) over 1.94wt% Au–Pd–0.22Fe/3DOM Mn2O3 was two times higher than that (0.93μmol/(gNs) over 1.97wt% Au–Pd/3DOM Mn2O3. It is concluded that doping a certain amount of the transition metal to Au–Pd/3DOM Mn2O3 could modify the microstructure of the alloy NPs, thus improving the oxygen activation and methane adsorption ability. We are sure that the M-doped Au–Pd/3DOM Mn2O3 materials are promising catalysts for the efficient removal of volatile organic compounds.

Corrigendum to “Effects of transition metal doping in Pt/M-TiO2 (M = V, Cr, and Nb) on oxygen reduction reaction activity” [J. Power Sources 320 (2016) 188–195

Corrigendum to “Effects of transition metal doping in Pt/M-TiO2 (M = V, Cr, and Nb) on oxygen reduction reaction activity” [J. Power Sources 320 (2016) 188–195

The effects of transition-metal doping and chromophore anchoring on the photocurrent response of titanium-oxo-clusters.

Titanium-oxo-clusters (TOCs), [Ti6O4(OiPr)10(Cat)2(BA)2] (1) and [Ti12M2O10(OEt)22(Cat)2(BA)4] (M = Co, Mn, Ni, 2-4; H2Cat = catechol, HBA = benzoic acid) are prepared in one step in an in situ solvothermal synthesis. Cluster structures of 2-4 can be considered as two 1 moieties merged together by two transition metal atoms. Unlike most TOCs with sphere-like structures, clusters 2-4 feature a unique single layered structure. They are not only transition metal doped TOCs but also charge transfer (CT) TOCs, CT from Cat to the TiO cluster core. Photoelectrodes were prepared by dipping the solution of clusters on a porous TiO2 substrate. Photocurrent response properties of the electrodes were studied in comparison with those of the electrodes of non-metal doped 1 and the non-Cat coordinated Ti6 cluster. The results showed that the photocurrent densities of metal doped clusters are higher than that of non-doped clusters and the highest photocurrent density was found for the redox active Co(ii) doped cluster. Charge transfer also plays an effective role in photocurrent conversion under visible light irradiation.

Effect of transition metal-doped Ni(211) for CO dissociation: Insights from DFT calculations

Density functional theory slab calculations were performed to investigate the adsorption and dissociation of CO over pure and M-doped Ni(211) (M=Fe, Co, Ru and Rh) with the aim to elucidate the effect of transition metal doping for CO activation. Doping the step edge of Ni(211) with Fe, Co and Ru is found to enhance the binding of CO in the initial state (IS) (in the sequence by the improvement degree: Fe>Ru>Co) as well as the co-adsorption of C and O in the final state (FS) (Ru>Fe>Co). In contrast, Rh doping is unfavorable both in the IS and in the FS. Analysis of the overall potential energy surfaces (PES) suggests CO dissociation is facilitated by Fe, Ru and Co doping both kinetically and thermodynamically, wherein Fe and Ru behave extraordinary. Interestingly, Fe substitute is slightly superior to Ru in kinetics whereas the contrary is the case in thermodynamics. Rh doping elevates the energy height from 0.97eV on Ni(211) to 1.32eV and releases 0.39eV less heat relative to Ni(211), again manifesting a negative effect. Besides the classical Brønsted–Evans–Polanyi relationship, we put forward another two neat linear relations, which can well describe the feature of CO dissociation. The differences of CO adsorption and activation in the IS over pure and doped Ni(211) surfaces are rationalized via electronic structure analysis. The findings presented herein are expected to provide theoretical guidance for catalyst design and optimization in relevant processes.

Effect of transition metal doping on the photocatalytic properties of FeVO4 nanoparticles

Abstract Undoped FeVO4 and FeVO4:M(2%) (where M = Mn2+, Ti4+ and Zn2+) nanostructures have been synthesized using a simple sonochemical method. The transition metal ions have been chosen as dopants to modify the electronic band structure which can lead to better exploitation of FeVO4 as a photocatalyst material. The samples have been characterized using powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and energy dispersion X-ray spectroscopy (EDS). Morphology and surface area of the samples has been elucidated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) method. Diffuse reflectance UV visible measurements confirm that the materials have their band gaps in the visible region. The photocatalytic activity of all the samples has been studied under UV and visible irradiation using model dye pollutants like methylene blue (MB) and malachite green (MG) solutions. Attempt has been made to discuss the photocatalytic degradation mechanism by performing trapping experiments using various scavengers. Moreover, the reusability of the material has also been tested and it has been found to have a good recycling potential.

Effects of Transition Metal Doping in Pt/M-TiO2 (M = V, Cr, and Nb) on the Oxygen Reduction Reaction

High cost and low durability are unresolved issues that impede the commercialization of proton exchange membrane fuel cells (PEMFCs). To overcome these limitations, Pt/TiO2 is reported as an alternative electrocatalyst for enhancing the oxygen reduction reaction (ORR) activity and/or durability of the system. However, the low electrical conductivity of TiO2 is a drawback that may be addressed by doping. To date, most reports related to Pt/doped-TiO2 focus on changes in the catalyst activity caused by the Pt-TiO2 interaction (metal-support interaction), instead of the effect of doping itself; doping is merely considered to enhance the electrical conductivity of TiO2. In this study, we discuss the variation in the electronic fine structure of Pt caused by the dopant, and its correlation with the ORR activity. More extensive contraction of the Pt lattice in Pt/M-TiO2 (M = V, Cr, and Nb) relative to Pt/TiO2 and Pt/C leads to outstanding ORR specific activity of Pt/M-TiO2. Notably, a fourfold increase of the specific activity is achieved with Pt/V-TiO2 relative to Pt/C. Furthermore, an accelerated durability test (ADT) of Pt/V-TiO2 demonstrates that this system is three times more durable than conventional Pt/C due to the metal-support interaction.

Effects of transition metal doping in Pt/M-TiO2 (M = V, Cr, and Nb) on oxygen reduction reaction activity

High cost and low durability are unresolved issues that impede the commercialization of proton exchange membrane fuel cells (PEMFCs). To overcome these limitations, Pt/TiO2 is reported as an alternative electrocatalyst for enhancing the oxygen reduction reaction (ORR) activity and/or durability of the system. However, the low electrical conductivity of TiO2 is a drawback that may be addressed by doping. To date, most reports related to Pt/doped-TiO2 focus on changes in the catalyst activity caused by the Pt-TiO2 interaction (metal-support interaction), instead of the effect of doping itself; doping is merely considered to enhance the electrical conductivity of TiO2. In this study, we discuss the variation in the electronic fine structure of Pt caused by the dopant, and its correlation with the ORR activity. More extensive contraction of the Pt lattice in Pt/M-TiO2 (M = V, Cr, and Nb) relative to Pt/TiO2 and Pt/C leads to outstanding ORR specific activity of Pt/M-TiO2. Notably, a fourfold increase of the specific activity is achieved with Pt/V-TiO2 relative to Pt/C. Furthermore, an accelerated durability test (ADT) of Pt/V-TiO2 demonstrates that this system is three times more durable than conventional Pt/C due to the metal-support interaction.

Influence of transition metal atoms doping on structural, electronic and nonlinear optical properties of Mg12O12 nanoclusters: A DFT study

Using density functional theory, we investigated the effect of transition metal doping on structural, electronic, energetic, linear and nonlinear optical properties of Mg12O12 nanocluster. The result revealed that transition metal atoms doping lead to reduce the Eg and increase the dipole moment. The doping of transition metal atom on Mg12O12 nanocluster enhances its polarizability value. Also polarizability values for doped nanoclusters decrease as the atomic number of transition metal increase. The first hyperpolarizability value dramatically increases as substitute a magnesium atom with a transition metal atom. Among the transition metal atom doped nanocage, scandium has the largest first hyperpolarizability value (β◦≈47,872au). The stability and remarkable values of β◦ (for Sc, Ti and V doped of nanocage) suggest that these compounds may be applicable as NLO material in industrial.

Effect of Transition Bi-metal Doping on ZnO Thin Films

Simple and economic sol-gel method is used to synthesize transition metal doped ZnO thin films in order to study the effects of transition metal doping of Mn and Fe. Fe/Mn with 1, 3 and 5wt% concentration are doped in pre-synthesized ZnO sol. Mn and Fe doped ZnO thin films are deposited on copper substrates by using spin coating technique. As-deposited thin films are annealed in magnetic field at 300˚C for 60mintues. Structural and magnetic properties of samples are investigated by X-ray powder diffractometer (XRD) and vibrating sample magnetometer (VSM). XRD results show the presence of hexagonal wurtzite ZnO lattices. VSM results indicate the room temperature ferromagnetism. Hence, transition metal doping improves magnetic properties of ZnO.

Promotional effect of transition metal doping on the basicity and activity of calcined hydrotalcite catalysts for glycerol carbonate synthesis

A series of transition metal doped hydrotalcites (HT-M) were prepared by using the “memory effect” of hydrotalcites (HT). Further calcination yields mixed oxides with more open structure and tunable basicity. The basicity of the calcined hydrotalcites (HTC-M) strongly depends on the type of transition metal and calcination temperature. The resulting HTC-M materials were used as solid base catalysts and evaluated in the transesterification between glycerol and dimethyl carbonate without using organic solvent. The correlation between the basic properties of the solid catalysts and the catalytic performance was investigated. The activity of HTC-M catalysts was demonstrated to be proportional to the surface density of basic sites. The HTC-Ni calcined at 500°C exhibited maximum activity, which is about 10 times higher than uncalcined HT precursor for the transesterification reaction. The promotional effect of Ni2+ doping could be attributed to the enhancement of the base strength of all three types of basic sites of the calcined hydrotalcite. The HTC-Ni catalyst can be readily recycled while maintaining high catalytic activity and selectivity of glycerol carbonate.

Effect of transition metal doping under reducing calcination atmosphere on photocatalytic property of TiO2 immobilized on SiO2 beads

TiO2 immobilized on SiO2 (TiO2/SiO2) have been prepared by sol-gel method and various ions of transition metals (Cr3+, Co2+, Ni2+, Cu2+, and Zn2+) were doped on the photocatalyst using wet impregnation method under reducing calcination atmosphere. The photocatalytic activity of metal doped TiO2/SiO2 towards phenol degradation under black light irradiation were investigated and compared with undoped TiO2/SiO2. The results showed that the photoresponse of Cu2+ and Zn2+ doped TiO2/SiO2 were larger than undoped TiO2/SiO2, indicating that the photogenerated carriers were separated more efficiently in Cu2+ and Zn2+ doped TiO2/SiO2. The reactivity was in the order of Cu2+ > Zn2+ > Ni2+ > Cr3+ > Co2+. The different photoreactivity was ascribed to combine effect of the different ionic radii and photocorrison tendency of the dopants. The sample was also characterized by surface analytical methods such as X-ray diffraction, scanning electron micrograph/electron dispersive X-ray analyzer and UV-Vis absorption spectrum.

Effects of transition metal doping and surface treatment to improve the electrochemical performance of Li2MnO3

A novel strategy to improve the electrochemical performance of Li2MnO3 using transition metal doping by the mechanochemical process is proposed. Li2MnO3 precursors are treated with transition metal containing chemicals in the mechanochemical process, followed by heat treatment. Cr containing Li2MnO3, with only 1 mol% Cr doping, exhibits unique electrochemical properties with a large initial discharge capacity of 234.9 mAh g−1, which is superior to the 205.0 mAh g−1 of pristine Li2MnO3, and all other transition-metal containing oxides. The structures of Li2MnO3 and Li2MnO3 with the transition metal element doping (TM-Li2MnO3) are studied by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and the electrochemical characteristics are further investigated using electrochemical impedance spectroscopy (EIS) measurements.

Enhanced properties of magnetron sputtered photocatalytic coatings via transition metal doping

To investigate the effect of transition metal doping on photocatalytic activity, thin films of titania doped with W, Mo, Nb or Ta were deposited onto soda-lime glass by pulsed DC reactive magnetron sputtering. As-deposited coatings and coatings annealed at both 400°C and 600°C were characterised by X-ray diffraction (XRD), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX). The band gap values were determined from optical data for all samples. The photocatalytic properties of the coatings were studied by the degradation of methylene blue dye under both ultra-violet and fluorescent light sources. The results of the study showed that annealed TiO2 coatings doped with Mo and Nb had high photocatalytic activity in terms of methylene blue degradation, due to the presence of the anatase crystalline phase, whereas W and Ta-doped samples were predominantly of the rutile phase, and exhibited a lower photocatalytic activity. Doping of the titania coatings with Mo and W caused a band gap shift towards the visible range and improved the photocatalytic activity under visible light, compared to undoped titania. Excessive doping in all cases reduced the photocatalytic activity.

Effect of defect complex on magnetic properties of (Fe, Mn)-doped ZnO thin films

We have observed room temperature ferromagnetism in Mn-doped and (Fe, Mn)-codoped ZnO thin films grown under different oxygen partial pressures by pulsed laser deposition. The X-ray diffraction and optical transmission spectra studies demonstrate the natural incorporation of Fe and Mn cations into wurtzite ZnO lattices. The effects of transition metal doping and defects on the magnetic properties was investigated. It is found that room temperature ferromagnetism is sensitive to oxygen vacancy and Zn vacancy. The absence of ferromagnetism in pure ZnO films grown under different oxygen partial pressures reveals that the transition metal ions should also play an important role in inducing the ferromagnetism.

Reduction of the photocatalytic activity of ZnO nanoparticles for UV protection applications

The detrimental effects of UV radiation are having a significant impact on our life and environment. The development of effective UV shielding agents is therefore of great importance to our society. ZnO nanoparticles are considered to be one of the most effective UV blocking agents. However, the development of ZnO–based UV shielding products is currently hindered due to the adverse effects of the inherent photocatalytic activity exhibited by ZnO. This paper reports our recent study on the possibility of reducing the photoactivity of ZnO nanoparticles via surface modification and impurity doping. It was found that the photoactivity was drastically reduced by SiO2–coatings that were applied to ZnO quantum dots using the Stöber method and a microemulsion technique. The effect of transition metal doping on the photoactivity was also studied using mechanochemical processing and a co–precipitation method. Cobalt doping reduced the photoactivity, while manganese doping led to mixed results, possibly due to the difference in the location of dopant ions derived from the difference in the synthesis methods.

Microwave-assisted hydrothermal synthesis of transition-metal doped ZnIn 2S 4 and its photocatalytic activity for hydrogen evolution under visible light

Aiming at the enhancement of photocatalytic activity for hydrogen evolution over ZnIn 2S 4, different transition metals (Cr, Mn, Fe, Co) are doped into the lattices of ZnIn 2S 4 to narrow the band gap. The doped ZnIn 2S 4 is characterized by XRD, Raman, UV–vis spectra, photoluminescence spectra, SEM and XPS techniques. The photocatalytic evaluation shows that Mn-doped ZnIn 2S 4 performs photocatalytic activity 20% higher than undoped ZnIn 2S 4, while Cr-, Fe-, and Co-doped ZnIn 2S 4 perform poorer activities in an order of Cr > Fe > Co. Based on the combined characterization results, the band structures of doped ZnIn 2S 4 are schematically depicted, which illustrates the different effects of transition-metal doping on the photocatalytic activity for hydrogen evolution. For Mn-doped ZnIn 2S 4, the enhancement of photocatalytic activity could be due to narrowed band gap induced by Mn doping. However, for Cr-, Fe-, and Co-doped ZnIn 2S 4, the suppressed photocatalytic activities should be attributed to the dopant-related impurity energy levels localizing the charge carriers or acting as non-radiative recombination centers for photoexcited electrons and holes. Hence, this study indicates that it is of great importance to make the in-depth investigation on the effects of band structures on the photocatalytic activity, especially for the doped semiconducting photocatalysts.