Enhanced Redox Properties Research Articles

Carbon monoxide oxidation over copper and nitrogen modified titanium dioxide⋆

Copper-Titanium Dioxide (Cu-TiO2) catalysts have been widely used to catalyze small molecules through photo- and thermal-catalytic approaches. We report nitrogen doped titanium oxide (N-TiO2) improved catalytic performance of Cu-TiO2 in the carbon monoxide oxidation reaction. Anatase TiO2 and rutile TiO2 are chosen to investigate the effect of the TiO2 phase for nitrogen modification. XPS and DFT results showed both interstitial nitrogen and substitutional nitrogen exists over nitrogen doped anatase TiO2, N-TiO2 (A). Only substitutional nitrogen exists over nitrogen doped rutile TiO2, N-TiO2 (R). Compared with copper over titanium dioxide (Cu-TiO2) catalysts, copper over nitrogen doped titanium dioxide catalysts (Cu-N-TiO2) showed enhanced redox properties based on analysis of temperature programmed reactions including H2-TPR and CO-TPSR. IR studies using CO as a probe molecule as well as copper XPS results showed that surface copper concentration distributed differently with the addition of nitrogen. Therefore, correlation between the ratio of [Cu+]/[Osurf.] and the reaction rate is suggested, because this ratio represents contributions from both active and spectator species in the carbon monoxide oxidation reaction.

SO2-Tolerant NOx Reduction by Marvelously Suppressing SO2 Adsorption over FeδCe1-δVO4 Catalysts.

SO2-tolerant selective catalytic reduction (SCR) of NOx at low temperature is still challenging. Traditional metal oxide catalysts are prone to be sulfated and the as-formed sulfates are difficult to decompose. In this study, we discovered that SO2 adsorption could be largely restrained over FeδCe1-δVO4 catalysts, which effectively restrained the deposition of sulfate species and endowed catalysts with strong SO2 tolerance at an extremely low temperature of 240 °C. The increasing oxygen vacancies, enhanced redox properties, and improved acidity contributed to the SCR activity of the FeδCe1-δVO4 catalyst. The reaction pathway changed from the reaction between bidentate nitrate and the NH3 species over CeVO4 catalysts via the Langmuir-Hinshelwood mechanism to that between gaseous NOx and the NH4+/NH3 species over FeδCe1-δVO4 catalysts via the Eley-Rideal mechanism. The effective suppression of SO2 adsorption allowed FeδCe1-δVO4 catalysts to maintain the Eley-Rideal pathways on account of the reduced formation of sulfate species. This work demonstrated an effective route to improve SO2 tolerance via modulating SO2 adsorption on Ce-based vanadate catalysts, which presented a new point for the development of high-performance SO2-tolerant SCR catalysts.

Total catalytic oxidation of chlorinated aromatics over bimetallic Pt–Ru supported on hierarchical HZSM-5 zeolite

Combination of great redox-acidity and strong chlorine-resistant, are critical to constructing efficient catalyst for the total oxidation of chlorinated aromatics. Herein, bimetallic Pt–Ru supported on hierarchical HZSM-5 zeolites were prepared by an improved co-impregnation. The distinct catalytic properties of the well-characterized Pt–O–Ru structures were demonstrated for chlorobenzene (CB) oxidation. For CB streams containing 1000 ppm CB/dry air, GHSV = 40,000 mL/g h, T 50 of Pt 0 · 5 Ru 0.5 / m -HZ (234 °C) is significantly better than monometallic Pt 1 / m -HZ (294 °C) and Ru 1 / m -HZ (298 °C). Additionally, Pt 0 · 5 Ru 0.5 / m -HZ is stable during 50-h test with high selectivity for less toxic products (CO 2 and HCl) and scarce formation of chlorinated byproduct. In situ DRIFTS reveals that CB reacted with Brønsted acid sites to produce phenolates, which is sequentially converted into maleic anhydride, aldehyde and carboxylates under the synergetic effects of redox-acidity properties prompted by Pt–O–Ru structures. The partial oxidation products are finally oxidized into CO 2 , HCl and H 2 O by surface oxygen. • Pt x Ru y / m -HZ catalysts prepared by improved co-impregnation present Pt–O–Ru structure. • The interaction of SiAlOH with Pt–Ru precursors leads to the formation of Pt–O–Ru. • Pt–O–Ru shows the stronger acidity, enhanced redox property and surface oxygen. • Pt 0 · 5 Ru 0.5 / m -HZ catalyst presents high stable activity in both CB and toluene oxidation. • Adsorption and activation of CB occur under the synergism of Pt, Ru and HZSM-5.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.

Investigation of Co3O4–CeO2 Composite Oxide as Catalyst for the Decomposition of N2O

Co3O4–CeO2 composite oxides with various ratios of Ce/Co were fabricated by the hydrothermal method, and their activities in N2O decomposition have been studied. Co3O4–CeO2 catalyst is more active than pristine Co3O4 and CeO2 catalysts. Over Co3O4–CeO2 catalyst the strong interaction between Co3O4 and CeO2 existed, which suppressed the crystallization of Co3O4, resulting in the large surface area. Particularly, the synergetic effect between Co3O4 and CeO2 induces the formation of more active Co3+ and enhanced redox property of Co3O4–CeO2 catalyst. The desorption of adsorbed oxygen, which is the key step in N2O decomposition, can be promoted due to the existed redox cycle (Co2+ + Ce4+ ↔ Co3+ + Ce3+). Therefore, Co3O4–CeO2 composite oxide showed high activity for N2O decomposition.

An Efficient Pt/CeyCoOx Composite Metal Oxide for Catalytic Oxidation of Toluene

Using ZIF-67 as a precursor, a series of Pt/CeyCoOx composite metal oxide catalysts with different molar ratios were prepared by a co-precipitation method and further used for catalytic oxidation of toluene. The Pt/Ce0.2CoOx catalyst showed the highest activity for toluene oxidation (T90 = 173 °C), which was related to the presence of Co-Ce solid solution, the more abundant surface adsorbed oxygen species and the enhanced redox property.

A Route to Develop the Synergy Between CeO2 and CuO for Low Temperature CO Oxidation

Highly active nano-composite oxide of cerium-copper was synthesized via physical grinding of respective metal oxides using mortar and pestle for the oxidation of carbon monoxide. The prepared oxides were characterized using X-ray diffraction (XRD), Thermal-gravimetric studies (TG), Infrared spectroscopy (IR), Scanning electron microscopy (SEM) and BET surface area. In addition, CO adsorption and surface reduction–oxidation property was studied through CO pulse titration, H2-TPR and O2-TPO to understand their surface sensitivity towards it. Among the tested catalysts, synergy interaction produced between cerium and copper oxides after grinding them using mortar and pestle leads to an excellent CO to CO2 conversion. High CO chemisorption and an enhanced redox property are the evidence for the synergy exhibited by CeO2–CuO composite catalyst. The grinding route helped in improving the CO oxidation by decreasing the active temperature region for the reaction showed a good correlation with high CO adsorption and increased oxygen mobility at lower temperature gradient over CeO2–CuO composite. Further, good reaction stability was also seen with the addition of moisture in the reaction mixture.

N-doping activated defective Co3O4 as an efficient catalyst for low-temperature methane oxidation

Development of non-noble metal catalyst for low-temperature methane oxidation is extremely important yet is still a challenge. Here, we construct a defective N-doped Co3O4 by a facial N2 plasma engraving method. The obtained catalyst exhibits excellent catalytic activity with methane conversion rate of 6.5 μmol g−1 s-1 at reaction temperature of 342 °C and space velocity of 46,800 mL g−1 h−1, which is about 7.3 times that of pristine Co3O4, and is among the highest active non-noble metal catalyst. The catalyst also shows high stability under hydrothermal environment. By systematic characterization and theory calculations, the superior performance could be attributed to the defective structure, enhanced redox property and highly exposed active sites. Meanwhile, N doping plays significant role in activating Co3O4 by improving the electrophilicity of surface oxygen and lowering C–H bond activation energy. The study will bring significative insight into the design of advanced Co3O4 catalysts for methane oxidation.

Component synergistic catalysis of Ce-Sn-W-Ba-Ox/TiO2 in selective catalytic reduction of NO with ammonia

The component synergistic catalysis of the Ce-Sn-W-Ba-Ox/TiO2 in selective catalytic reduction of NO (in the presence/absence of H2O and SO2) was investigated. Results verified that CeO2 was an essential primary active component, and WO3, SnO2 and BaO were essential cocatalyst. TiO2 provided enough acid sites, CeO2 enhanced redox properties, weakened acid strength and increased chemisorbed oxygen concentration, which was beneficial to accelerate the activation and desorption of NH3. SnO2 increased chemisorbed oxygen concentration, enhanced redox properties and improved activation rate of NH3. WO3 increased acid amount and BaO enhanced the anti-influences to water vapor and SO2. Their synergistic effects made Ce-Sn-W-Ba-Ox/TiO2 exhibit excellent catalytic performance for NH3-SCR, reaching the highest value about 100% at 350 °C in presence of H2O and SO2. Moreover, in situ DRIFTS study showed that the reaction followed L-H mechanism at high temperature and tended to simultaneously follow E-R and L-H mechanisms at low temperature.

Structural effects on the charge transport properties of chemically and electrochemically doped dioxythiophene polymers

Dioxythiophene polymers incorporating linear side chains show higher solid-state conductivity and enhanced redox properties.

Improvement in alkali metal resistance of commercial V2O5–WO3/TiO2 SCR catalysts modified by Ce and Cu

Commercial V2O5–WO3/TiO2 (abbreviated to VWTi) SCR catalysts are modified with Ce and different contents of Cu in wet impregnation method to improve their alkali metals resistance, which is beneficial for prolonging their service life. After K poisoning, NOx conversion of VWCeCuTi sample modified with 0.30% Ce and 0.05% Cu is 89% at 350 °C, which is obviously higher than that of VWTi with a 50% NOx conversion. A series of characterization tests were conducted and verified that the ratio of V5+ and the surface-active oxygen on VWCeCuTi sample increases due to the interaction between V, Ce and Cu. Additionally, with the addition of Ce and Cu, surface acid sites are increased and their stability is strengthened. The enhanced redox property and surface acidity contribute together to the excellent K resistance of VWCeCuTi catalyst.

Anchoring Pt on surface/bulk of LaCoO3 nanotubes via one step of coaxial electrospinning for efficient total propane oxidation

The effect of location sites of platinum (Pt) nanoparticles on LaCoO3 support for complete catalytic oxidation of propane (C3H8) was investigated. Pt nanoparticles were anchored on the surface, bulk and surface/bulk of LaCoO3 by using three different loading methods: incipient-wetness impregnation, single-needle electrospinning and coaxial electrospinning, respectively, followed by a simple 300 °C H2 reduction process. The obtained catalysts were systematically characterized. It turns out that one step synthesis of coaxial electrospun Pt/LaCoO3 nanotubes with both surface and bulk Pt species exhibits a relatively more efficient catalytic activity, where surface Pt favors the reduction of Co3+ to Co2+ and bulk Pt accelerates that of Co2+ to Co0. Meanwhile, Co species are active sites for C3H8 oxidation despite Pt loading, but the enhanced redox property and oxygen mobility upon Pt loading are crucial for the Mars-van Krevelen mechanism obeyed total C3H8 oxidation. Additionally, good thermal stability is found over coaxial electrospun Pt/LaCoO3, removing propane at a temperature of 450 °C over 48 h without a significant decrease in propane conversion. The addition of water vapor has a little inhibition effect on the catalytic activity under the reaction condition. Such route of Pt anchoring will provide an effective means for designing highly efficient perovskite based catalysts with low precious loadings for total oxidation reaction.

Insights into the highly efficient Co modified MnSm/Ti catalyst for selective catalytic reduction of NOx with NH3 at low temperature

A novel cobalt-decorated MnSm/Ti catalyst was proposed for removal of NOx at low temperatures. Catalytic performance have been tested and the physicochemical properties were comprehensively characterized using X-ray diffraction, N2 adsorption, X-ray photoelectron spectroscopy, NH3-temperature programmed desorption, H2-temperature programmed reduction and in situ diffuse reflectance infrared Fourier transform spectroscopy. The best 5CoMnSm/Ti catalyst achieved above 90% NOx conversion at 100–200 °C with a gas hourly space velocity of 60,000 h−1. The 5CoMnSm/Ti catalyst possesses increased Lewis acid sites and enhanced redox property attributed to the synergistic interaction among Mn, Co and Sm, which are beneficial to the chemisorption and activation of NO and NH3. The facile electron transfer through the redox cycle of Mn3+ + Co3+ ↔ Mn4+ + Co2+ and the enhanced oxygen mobility can maintain the surface high valence metal ions and chemisorbed oxygen at high concentration. All these factors elevate the low-temperature catalytic activity of 5CoMnSm/Ti catalyst towards selective catalytic reduction of NOx with NH3. The bidentate nitrate is a reactive nitrate species after Co doping, which can participate in the NH3-SCR. The reaction over the 5CoMnSm/Ti catalyst can proceed through both Eley–Rideal and Langmuir–Hinshelwood mechanisms, in which the Eley–Rideal mechanism is predominant owing to its fast reaction rate.

A green road map for heterogeneous photocatalysis

Abstract In the new millennium the well-established paradigms of organic photochemistry have come alive as the basis for a wide range of synthetic methodologies that take advantage of the enhanced redox properties of excited states. While many strategies have been developed using rare, expensive and non-reusable catalysts, the road forward should include catalysts based on more abundant elements and reusable materials. This green road leads to the exploration of heterogeneous systems that can be eventually adapted for flow photocatalysis, and also adopted for the solution of environmental problems such as water treatment and fuel generation using solar radiation. If heterogeneous photocatalysis can play a role in supplying solutions to drug synthesis, energy and potable water supplies, then photochemistry will have an unprecedented societal impact.

Direct Decomposition of N2O over C-Type Cubic Yb2O3-Co3O4 Catalysts

Abstract (Yb1−xCox)2O3−δ catalysts with cubic (C-type) rare-earth sesquioxide structure were synthesized by a co-precipitation method. The introduction of Co2+/3+ ions into the Yb2O3 lattice resulted in an improved catalytic activity for N2O decomposition, due to the enhanced redox properties and increased amount of active sites. Among the prepared catalysts, (Yb0.90Co0.10)2O3−δ exhibited the highest activity for the decomposition of N2O, which was completely converted to N2 and O2 at 500 °C. Moreover, (Yb0.90Co0.10)2O3−δ also showed high durability in the presence of H2O, O2, or CO2.

A Sensitive Pyrimethanil Sensor Based on Electrospun TiC/C Film.

Titanium carbide (TiC) is a very significant transition metal carbide that displays excellent stability and electrical conductivity. The electrocatalytic activity of TiC is similar to noble metals but is much less expensive. Herein, carbon nanofibers (CNFs)-supported TiC nanoparticles (NPs) film (TiC/C) is prepared by electrospinning and carbothermal processes. Well-dispersed TiC NPs are embedded tightly into the CNFs frameworks. The electrochemical oxidation of pyrimethanil (PMT) at the TiC/C-modified electrode displays enhanced redox properties, and the electrode surface is controlled simultaneously both by diffusion and adsorption processes. When TiC/C is applied for PMT determination, the as-fabricated sensor shows good sensing performance, displaying a wide linear range (0.1–600 μM, R2 = 0.998), low detection limit (33 nM, S/N = 3), and good reproducibility with satisfied anti-interference ability. In addition, TiC/C shows long-term stability and good application in natural samples. The facile synthetic method with good sensing performance makes TiC/C promising as novel electrode materials to fabricate efficient sensors.

Heterostructured simple perovskite nanorod-decorated double perovskite cathode for solid oxide fuel cells: Highly catalytic activity, stability and CO2-durability for oxygen reduction reaction

Apart from conventional composite materials, in situ exsolution for constructing the heterostructure is one of the most effective strategies to design the high-performance electro-catalysts. Herein we report a novel heterostructured simple perovskite nanorod-decorated A site-deficient double perovskite PrBa0.94Co2O5+δ (SPN-A-PBC) cathode, synthesized by an in situ exsolving process from A site-deficient double perovskite PrBa0.94Co2O5+δ (A-PBC). The results demonstrate a highly electro-catalytic activity of the SPN-A-PBC cathode toward oxygen reduction reaction (ORR) for intermediate-temperature solid oxide fuel cells (IT-SOFCs), achieving a very low and stable polarization resistance of ˜0.025 Ω cm2 at 700 °C in air. The anode-supported single cell with this heterostructured cathode delivers a maximum power density of 1.1 W cm−2 at 700 °C and a superior steady operation over 120 h at a loading voltage of 0.6 V. Furthermore, the SPN-A-PBC electrode exhibits a good tolerance to CO2. When tested in air with 6 vol% CO2 at 700 °C, the SPN-A-PBC electrode still maintains a stable polarization resistance of ˜0.078 Ω cm2. The unique catalytic activity of the SPN-A-PBC cathode for ORR may be attributed to extended active sites, abundant interface defects, enhanced redox property and oxygen mobility. The fast ORR kinetics and excellent durability in air with CO2 highlight the potential of SPN-A-PBC as a potential functional material in the energy conversion devices.

Engineering Rhynchostylis retusa-like heterostructured α-nickel molybdate with enhanced redox properties for high-performance rechargeable asymmetric supercapacitors

Rhynchostylis retusa-like α-NiMoO4 was synthesized using a simple, single-step, and cost-effective wet-chemistry approach, and it exhibited the superior electrochemical properties.

Oxidative reactivity enhancement for soot combustion catalysts by co-doping silver and manganese in ceria

Co-doping of silver and manganese ions in ceria was found to be an effective method for enhancing the oxidative reactivity of soot combustion. Several Ag-MnxCe1-xOy catalysts were prepared through the facile co-precipitation method, which exhibited a Tm in the range of 321–370 °C in loose contact conditions, much lower than the generally required ∼600 °C. Characterizations of XRD, XPS, Raman, H2/O2 pulse reaction, H2-TPR and O2-TPD revealed increased oxygen defects and improved catalytic performance of Ag-MnxCe1-xOy for soot combustion due to incorporation of Ag+ and Mnδ+ in the solid solutions. The effective co-doping of silver and manganese in ceria was achieved at an optimal ratio of x = 0.1, which facilitates the formation of Ag+ with a new structure that delivers extra oxygen vacancies with enhanced oxygen mobility. The Ag-Mn0.1Ce0.9Oy showed a minimum Tm of 321 °C with superior stability in repeated soot oxidation tests among all the Ag-MnxCe1-xOy catalysts prepared. It was hypothesized that the enhanced redox property of ceria by the co-doping of Ag and Mn is responsible for the excellent performance of the Ag-MnxCe1-xOy type catalysts.

Enhanced Redox properties of amorphous Fe63.3-83.3Co0-20Si4B8P4Cu0.7 alloys via long-term CV cycling

Effect of partial substitution of Fe by Co on the Redox properties and cyclicity of amorphous Fe83.3Si4B8P4Cu0.7 alloy has been investigated in 0.5 M KOH solution by short-term and long-term cyclic voltammetry (CV). Redox performance of amorphous Fe83.3-xCoxSi4B8P4Cu0.7 (x = 0, 1, 4, 10 and 20 at.%) alloys is enhanced by the partial substitution of Fe by Co of 1–20 at.%, and the best chemical composition is considered to be Fe79.3Co4Si4B8P4Cu0.7 on the basis of the highest Redox peak current density after short-term CV cycling. The flake-shaped FeOOH, CoOOH and/or Fe-oxides and Co-oxides form and become more and more with an increasing of the cycle numbers. After 3000 cycles of the long-term CVs, amorphous Fe79.3Co4Si4B8P4Cu0.7 alloy also exhibits the superior and stable Redox properties with two times higher oxidation peak current densities than amorphous Fe83.3Si4B8P4Cu0.7 alloy. Redox peak current densities after long-term CV cycling are enhanced more than 200 times due to the octahedral crystalline Fe3O4, Co3O4 and CoO with a large surface area in comparison to those after the short-term CVs. The substitution of Fe by 4 at.% Co is considered to be the optimal chemical composition for the enhancement of Redox properties and high stability during the long-term CV cycling.