Adsorption Of Species Research Articles

Operando X-Ray Absorption Spectroscopic Study on Influence of Specific Adsorption of Sulfo Group in Perfluorosulfonic Acid Ionomer Towards ORR Activity of Pt/C Catalyst

Polymer electrolyte fuel cells (PEFCs) are clean energy devices with polymer electrolytes and are expected to play an important role in the development of a global renewable energy system and a pure hydrogen energy society in the future. PEFCs have already been applied for small-scale energy systems such as fuel cell vehicles (FCVs). Pt-based catalysts are basically used due to the relatively inefficient reaction kinetics and catalyst degradation under strong acidic conditions during the oxygen reduction reaction (ORR). However, there are still many difficulties in realizing acceptable cost-effective FCVs. It is known that the ORR activity of Pt-based catalysts is reduced by specific adsorption of anionic species. Perfluorosulfonic acid ionomers such as Nafion® are commonly included in the catalyst layers of PEFCs to provide protonic pathways for promoting the ORR1. However, direct observation of anion adsorption on practical Pt nanoparticle/C catalysts for perfluorosulfonic acid ionomers using X-ray absorption spectroscopy (XAS) still has less report. In this study, to achieve specific adsorption over a higher potential range that is at least equal to the ORR active potential (around 0.90 V vs. RHE), operando XAS measurements were performed; the electronic status and local structural change of Pt atoms induced by the specific adsorption of anions at any potential were observed2.Pt/C (29.1 wt.%; TEC10V30E) catalyst supported was purchased from TKK. Nafion® solution was employed to prepare Pt/C catalyst ink with I/C ranging from 0.0 to 1.0. And the amount of Pt/C was adjusted to form a 20 µgcarbon cm-2 catalyst layer after dropping 10 μL on a glassy carbon RDE. The electrochemical cell was constructed using a model electrode fabricated in the working electrode, a Pt mesh for the counter electrode, a reversible hydrogen electrode for the reference electrode, and 0.1 M HClO4 aq for the electrolyte. operando XAS measurement of Pt L-edge was carried out in SPring-8 (Japan).The specific activity decreased as the I/C ratio increased from 0.0 to 0.20. We utilized many methods to evaluate the adsorption species separately, including the measurements of ECSA and oxygen coverage, CO stripping voltammetry, operando X-ray absorption fine structure, and analysis of 5d orbital vacancy. The ECSA and oxygen coverage did not change with increasing ionomer content, indicating that the Pt/C catalyst activity was affected by other adsorption species. A comparison of the CO displacement charge and 5d orbital vacancies of the Pt/C catalysts with I/C = 0.0 and 1.0 suggests that the ionomer-specific adsorption increases when the I/C ratio of the Pt/C catalyst is 1.0; active sites on the surface of the Pt/C catalyst are occupied, resulting in lower catalyst activity. Acknowledgment This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Efficient synthesis of PdIr nanocatalysts with controllable surface composition for electrochemical oxidation of methanol

Pure iridium (Ir) is easy to produce OH adsorbent species and has a wide range of applications in electrocatalysis. The structure–activity relationship between controlled synthesis and surface regulation of Ir-based alloys and their properties needs further study.When P123(poly (ethylene oxide)-poly (ethylene oxide)-poly (ethylene oxide)(PEO20-PPO70-PEO20) is used as reducing agent and protective agent, the ir-rich core–shell structure PdIr@Ir catalyst can be obtained by the solution thermal method without adding KI, and the PdIr alloy can be obtained after the addition of KI. The complexation ability of KI can change the reduction rate of the precursor and regulate the surface composition of the catalyst.After optimizing the dose of KI, the PdIr-4 shows the highest methanol oxidation reaction (MOR) activity and anti-CO toxicity.The PdIr-2 catalysts with rich Ir on the surface showed high stability, possibly due to the gradual activation of Ir on the surface by PdIr inside. The results of experimental characterization and theoretical calculations show that the main reasons for the performance improvement of PdIr series catalysts are the special three-dimensional structure of PdIr, the bifunctional mechanism between Pd and Ir, especially the synergistic catalytic action of Ir and the effect of regulating the electron structure.The experimental results of this paper are expected to provide some ideas and guidance for Ir-based catalysts with high activity and high stability.

Adsorption behavior of molecules on Zn2SnO4(1 1 1) crystal plane and its effect on electrical conductivity

• O 2 molecules bond with Sn atoms on the crystal plane and H 2 O molecules bond with Zn atoms to form characteristic adsorbed species. • As the characteristic adsorbed species, H 2 O molecules further promoted the natural adsorption of O 2 molecules in the form of hydrogen bond. • The crystal conductivity changes with the adsorption and desorption. • High temperature facilitates the adsorption of O 2 molecules. The molecular adsorption behavior of Zn 2 SnO 4 (1 1 1) crystal plane was studied. DFT theoretical simulation result shows that O 2 and H 2 O molecules are adsorbed on the crystal plane by bonding with Zn atom and Sn atom respectively and forming characteristic adsorption species. H 2 O molecules as characteristic adsorbed species promote the natural adsorption of O 2 molecules in the form of hydrogen bonds, N 2 molecules adsorb naturally in the form of physical adsorption. Meanwhile, the crystal surface conductivity varies with the adsorption and desorption of different gases. When the adsorbent is only O 2 molecule, the crystal surface conductivity decreases, the DOS of Fermi is from 8.00 to 4.01 electrons/eV. The conductivity of crystal surface increases when H 2 O molecule acts as a characteristic adsorbent and further adsorbs O 2 molecule, the DOS of Fermi is from 5.74 to 8.51 electrons/eV. When oxygen molecules are directly adsorbed on Zn 2 SnO 4 (1 1 1) crystal plane, the adsorption energy is +0.79 eV, while when oxygen molecules are further adsorbed on Zn 2 SnO 4 (1 1 1) crystal plane through water molecule, the adsorption energy is +2.71 eV. This conclusion was confirmed by EIS. In situ Raman spectroscopy detection of acetone molecule gas sensitive experiment showed that the adsorption of O 2 molecules is slow at room temperature and fast at high temperature, which is consistent with the calculation result that O 2 molecule belongs to endothermic adsorption. The results show that, through the method of combining experiment and theory, the influencing mechanism is analyzed, which effects of different gases on adsorption properties of crystal surfaces. This work provides guidance for optimizing catalytic and gas sensitive properties of materials and realizing controllable optimization of surface properties of materials.

Microkinetic Barriers of the Oxygen Evolution on the Oxides of Iridium, Ruthenium and their Binary Mixtures

AbstractThe performance of electrocatalytic water splitting in polymer electrolyte membrane electrolysis is substantially determined by the microkinetic processes of the oxygen evolution reaction (OER). Even highly active catalysts such as the nanoparticulated transition metal oxides IrO2, RuO2 and their mixtures, IrxRu1−xO2, exhibit overpotentials up to several hundreds of millivolts. The surface of the oxide mixtures IrxRu1−xO2 is found to consist of actives sites of both Ir and Ru on which the OER mechanism is processed independently and at different overpotentials. By applying microkinetic modelling and parameterization via cyclic voltammograms we show that there is a correlation between performance and the relative Ir content, that can be explained by two different deprotonation steps. These are in particular the formation of the adsorbate species *OOH on rutile RuO2 and *OO on IrO2. The respective free reaction energies are quantified to 1.44 eV and 1.58 eV, which are the highest values of the process and thus determining the overpotential. The additional finding of adsorbed oxygen *O covering >40 % of the active sites during the OER suggests that subsequent water adsorption is the major performance limiting step. Finally, a synergetic effect between both active sites on the binary transition metal oxides is identified: the respective other metal lowers the potential determining reaction energy on the Ru or Ir active site. This insight into the surface processes on Ir and Ru binary oxides forms the basis for deeper understanding of the active sites for further OER catalyst development.

Molecular adsorption behavior and photoelectric properties of SnO2 (221) crystal plane

In this paper, the molecular adsorption behavior of the SnO2 (221) crystal plane is simulated by density functional theory, and the photoelectric properties of the crystal plane are studied. Through theoretical simulation, H2O, O2, and N2 molecules are located on three different adsorption active sites of the crystal plane. The individual adsorption of the three molecules reduces the conductivity of the crystal plane. The conductivity increases when the molecules are co-adsorbed. The characteristic adsorption species (CAS) of the crystal plane are H2O and O2 molecules. This is consistent with the experimental results of electrochemical impedance spectroscopy (EIS). The O2 molecule shifts the response peak of the photocurrent spectrum to a low wavelength. Understanding the CAS of the crystal plane and its influence on the optical and electrical properties of materials has enlightening significance for further analysis of the photoelectric behavior of materials, and is helpful to provide the theoretical and experimental basis for the controllable design and synthesis of gas-sensitive materials.

The Steady State Characteristics of Multicomponent Diffusion in Micro- and Mesoporous Media for Adsorbable and Nonadsorbable Species.

The study addresses one of the fundamental issues in the mathematical modeling and quantitative process analysis of complex multicomponent diffusion in meso- and microporous materials. The model presented here incorporates combined molecular diffusion, Knudsen diffusion, viscous flow, and surface diffusion. A methodology and algorithm for the determination of steady states of such complex diffusive processes are proposed. The adopted form of the surface diffusion model does not require the calculation of the thermodynamic factor matrix. The method was verified by comparing the profiles of the state variables with those obtained from the dynamic model for sufficiently long diffusion times. The application of the method is illustrated for two diffusion processes involving three components. In the first one, all components are subject to adsorption. In the other, one gaseous component is an inert and is therefore not adsorbed and does not participate in surface diffusion. It is shown that the presence of inerts as well as their number does not impede the application of the proposed algorithm for the determination of steady states.

Copper biosorption over green silver nanocomposite using artificial intelligence and statistical physics formalism

The metal uptake capacity of green synthesized silver nanoparticles (AgNPs) and activated carbon (AC) are widespread. The AgNPs loaded AC for the copper ions (Cu2+) biosorption via an artificial neural network (ANN) and statistical physics formalism (SPF) applied at a pressure range of 0.03–0.3 bar and temperatures of 310, 340, and 370 K were studied. For ANN modeling, a multi-layer perceptron was used with five input nodes to obtain biosorption data. The percentage of Cu2+ uptake efficiency was used as an output variable. The transfer function was applied using the Tanh transference function. SPF through grand canonical ensemble provides models for monolayer and multilayer layers of biosorption. These models explain the sorption by calculating the layers involved, adsorbed species, and energy levels. The results demonstrated that the ANN modeling could be quite helpful in predicting biosorption parameters. The effective covariables were dose, pH, and concentration. The ANN models were consistent with experimental values albeit with minor differences. The error values were between −6.5 + 2.0%. Results showed that adsorbate species remain perpendicular to the adsorbent surfaces while macro- and micropore volumes seem critical. These adsorbents carry single or multiple layers of biosorption and tend to fluctuate with variations in temperature. Exothermic and endothermic processes are represented by negative and positive biosorption energies. Energy distributions in sophisticated SPF models confirm surface characteristics and interactions with adsorbates.

Practical issues concerning two-component equilibria of strongly adsorbing species in porous solids

The study addresses one of the fundamental issues in the area of mathematical modeling and quantitative analysis of the process of multicomponent diffusion in microporous materials. One of the elements of mathematical models of such processes is the thermodynamic equilibrium between the bulk phase and the solid. This results from the fact that surface diffusion takes place in the adsorbed phase. It is illustrated what kind of change occur in the isotherms of pure strongly adsorbable species in comparison with isotherms of these species in binary mixtures. The reason of these changes are explained by analyzing isotherms with different values of affinity coefficients. The RAS (Real Adsorption Solution) method was used to compute sorption isotherms for selected binary mixtures of strongly adsorbable organic compounds on activated carbon. The methods of approximate determination of isotherms of components in mixture for weakly and strongly adsorbable species obtained according to IAS (Ideal Adsorption Solution) and RAS methods are proposed. The results are illustrated by several examples of mixtures of some common hydrocarbons and for two kinds of porous material. Thermodynamic calculations were performed for mixtures of two components subject to adsorption and at high excess of inerts.

Insight into the dynamic behaviors of reactants with temperature over a TiOx-based catalyst for NOx removal via NH3-SCR

NH3-SCR has been an efficient technology for purifying NOx from industrial facilities. However, it is still a huge challenge to clearly understand the intrinsic mechanisms. Here, in situ DRIFTS was employed for elucidating the adsorption behaviors, active sites and reaction routes over the model catalyst of CuNbTiOx. The oxygen played a vital role in the reactant adsorption and reaction process, especially for NOx adsorbing, in which oxygen could promote monodentate and bidentate nitrates forming and bridged nitrate increasing. Then the correlation between DRIFTS peak locations and active sites for NH3 adsorption was further defined, thereinto, the bands at ca. 1604 cm−1 represented the coordinated NH3 species at Cu2+. Similar with most SCR catalysts, CuNbTiOx exhibited various catalytic activities among different temperature ranges. It was found that NH3-SCR reaction occurred mainly via Langmuir-Hinshelwood pathway at 200 °C, in which the relatively inert nitrates and NH3 adsorption species restricted the low temperature activity. Afterwards, the reaction mechanism transformed into Eley-Rideal when the temperature was elevating to a high temperature of 400 °C due to the weak adsorption of NOx. These new findings provide an innovative view for understanding the surface reaction on catalysts, further facilitate the development of NH3-SCR catalysts.

Two-dimensional NiO nanosheets for efficient Congo red adsorption removal

Strategies for developing new adsorbents are necessary for more efficient processes to remove contaminants from wastewater. Thus, it is essential to adjust the synthesis parameters of the adsorbent nanomaterial to control the surface area and morphology and, therefore, enhance the adsorption performance. Herein, α-Ni(OH)2 nanosheets were synthesized via a simple and fast microwave-assisted solvothermal method and converted to NiO nanostructures by calcination in air. The effect of different calcination temperatures (range of 300–600 °C) on the morphology, crystal structure, and adsorption performance of Congo red (CR) was evaluated. The calcination of α-Ni(OH)2 at 300 °C resulted in 2D NiO nanosheets, which showed the best performance to remove CR dye due to the increased surface area and porosity provided by the 2D morphology. The nanosheet-like structure is lost with increasing the calcination temperature and the nanoparticles become bigger, consequently, the CR adsorption capacities are significantly reduced. The 2D NiO nanosheets can adsorb a significant amount of CR quickly, reaching equilibrium after only 120 min, indicating a high affinity between the adsorbate species and the surface of the adsorbent. Additionally, the adsorption isotherm was compatible with the Langmuir model, which provides a maximum calculated adsorption capacity of 259.74 mg g−1. Thus, our findings showed how to adequate the synthesis parameters to obtain NiO nanosheets and improve the adsorption parameters to CR, which can be extended to the fabrication of new materials to promote advances in sustainable technologies.

Examining the photoelectric properties of hexagonal prism-shaped ZnO based on density functional theory

In this study, hexagonal prism-shaped ZnO with exposed (002) and (200) planes is synthesized by using the hydrothermal method, and XRD and SEM images are used to confirm the results. Density functional theory (DFT) was used to simulate the characteristic adsorption species (CAS) of the hexagonal prism-shaped ZnO, and this revealed the mechanism of the CAS on the crystal surface. The results of simulations showed that O2 and H2O molecules were chemically adsorbed on the (002) and (200) planes, respectively. As the rate of coverage of the (002) plane by oxygen molecules increased, its photocurrent and conductivity significantly increased, while the photocurrent spectrum moved to the direction of the long wave and appeared to have two peaks. The photocurrent and conductivity on the (200) plane did not change significantly with the increase in the rate of coverage by H2O molecules. The results of the theoretical simulations were consistent with the experimental results for the photocurrent spectrum. Therefore, the hexagonal prism-shaped ZnO can be used to detect reduced gas molecules by consuming adsorbed oxygen or using the photocurrent spectrum in gas-sensitive detection through a redox reaction.

Fabricating Z-scheme C-doped TiO2/rGO nanocomposites for enhanced photocatalytic NO removal

It is attractive to explore practical approaches to optimize the photodegraded NO property of TiO2. Herein, a typical Z-shaped heterojunction C-TiO2/rGO composed of carbon-doped TiO2 and reductive graphene oxide (rGO) was constructed to optimize the NO removal efficiency through an in situ one-pot hydrothermal process with glucose as reductant and dopant. The C-TiO2/rGO (0.11%) composite displays a remarkable NO removal performance of 40.6% under visible light illumination. It was found that the C-TiO2 nanoparticles were tightly attached to the rGO sheets and had strong interactions with rGO, which induced a positive impact on not only the light absorption and photo-generated charge separation but also the NO adsorption and reactive oxygen species formation, resulting in boosted photodegrade NO activity. As to the photodegrade NO process over the C-TiO2/rGO, the HO• and O2 •− were the dominant radicals, of which the O2 •− radical originated from the interactions between C-TiO2 and rGO. We proposed a Z-scheme mechanism to illuminate the advanced photocatalytic activity of C-TiO2/rGO. This work affords an approach to developing effective photocatalysts in the NO purification field.

Metal-free catalysis for organic micropollutant degradation in waste activated sludge via poly(3-hydroxybutyrate) biopolymers using Cupriavidus sp. L7L coupled with peroxymonosulfate

This study employed a novel and environment-friendly biopolymer/oxidant catalytic system, viz., poly(3-hydroxybutyrate)/peroxymonosulfate (PHB/PMS), for pretreating wastewater sludge for the first time. Under optimal conditions, i.e., 3.1 × 10−4 M of PMS and 3.3 g/L of PHB at pH = 6.0, the PAHs in the sludge matrix was decreased by 79 % in 12 h. Increase in salinity (75 % synthetic seawater) achieved 83 % of PAHs degradation. Functional groups (CO) of the biopolymer matrix were active centers for biopolymer-mediated electron transfer that produced reactive oxygen species (SO4−, HO, and 1O2) for adsorption and catalytic oxidation of PAHs in the sludge. Functional metagenomic analysis revealed the main genus, Conexibacter (phylum, Actinobacteria) exhibited PAH-degrading function with high efficiency in the biodegradation of PAHs from sludge pretreated with PHB/PMS. Coupling chemical oxidation and biostimulation using bacterial polymer-based biomaterials is effective and beneficial for pretreating wastewater sludge toward circular bioeconomy.

The Microkinetic Performance Barriers of Ruthenium and Iridium Oxides during the Electrocatalytic Oxygen Evolution Reaction

Electrocatalytic water splitting is currently one of the most promising reactions to produce green hydrogen in a de-fossilized energy system.[1] The performance of PEM electrolyzers is substantially determined by the sluggish reaction kinetics of the oxygen evolution reaction (OER). Even highly active catalysts such as nanoparticulated transition metal oxides IrO2, RuO2 and their mixtures IrxRu1-xO2 exhibit overpotentials up to several hundreds of millivolts.[2] Dynamic microkinetic modeling is a powerful tool to analyze the single reactions and their interplay during OER at the electrode surface.[3] Quantitative insight into process-limiting steps on different active sites on the material surface can be used to suggest ways to improve dynamic OER operation.In this work, we present the analysis of an experimentally validated microkinetic model. It allows to study the electrocatalytic reaction mechanism including the coverage of emerging surface species (e.g. *OH, *O, *OOH and *OO) for a wide potential range including OER. We show that there is a correlation between performance and the Ir:Ru ratio, that can be explained by two different potential determining deprotonation steps. In particular, the highest equilibrium potentials of 1.44 V and 1.58 V are quantified for the production of the adsorbate species *OOH on rutile RuO2 and *OO on IrO2, respectively. During OER at a potential of >1.5 V, adsorbed oxygen *O covers >40 % of the active sites, suggesting that subsequent water adsorption is the major process limitation. The surface of the oxide mixtures IrxRu1-xO2, is found to consist of actives sites of both Ir and Ru on which the OER mechanism is processed independently and at different overpotentials. Compared to the pure oxides, the mixtures reveal reduced reaction energies of the potential determining deprotonation processes. One can conclude that incorporating Ru into IrO2 provides higher overall performance while stability is remained. Dynamic microkinetic modelling is therefore a viable method to study catalytic surface processes as well as their limitations and to make suggestions for improving the performance of electrocatalytic systems.[1] K. Kalz et al., ChemCatChem, 2017, 9, 17.[2] D. Escalera-López et al., ACS Catalysis, 2021, 11, 15, 9300.[3] J. Geppert et al., Electrochimica Acta, 2021, 380, 137902.

CeO2 nanosheets with anion-induced oxygen vacancies for promoting photocatalytic toluene mineralization: Toluene adsorption and reactive oxygen species

The deep oxidation of toluene is recognized as a major challenge for photocatalytic oxidation of toluene. Herein, we introduced oxygen vacancies into CeO2 nanosheets through novel anion-removal of Ce-LDH, with the calcining temperatures of 750, 850, 950 °C. The photocatalytic toluene performance was ordered by CeMO-850 > CeMO-750 > CeMO-950, and CeMO-850 had better activity than P25, common CeO2, and CeO2-H2. Different reaction pathways were founded on CeMO photocatalysts, i.e., on CeMO-950 and CeMO-750, the cresol and hydroquinone intermediates were observed, which hindered toluene adsorption/activation and were hard to deep-mineralization. Whereas, more benzoic acid, open-loop oxygen-containing intermediates were observed on CeMO-850, which were resulted from its oxygen vacancies (Ov), i.e., surface Ov and Ce3+ were beneficial for toluene adsorption, B acid sites and active radicals’ generation, respectively, and bulk Ov were helpful for oxygen mobility and efficient deep-mineralization. The mechanism of Ov generation and toluene degradation were proposed.

Adsorption equilibrium modelling for different temperature conditions and its influence on adsorption mass transfer

The paper deals with numerical modelling of adsorption kinetics in a narrow channel of a honeycomb type adsorber. The mass transfer model consists of solving the diffusion-convection transport equation for adsorbate species in the fluid phase. The adsorbate flux to the wall is computed implicitly by using the Boundary Element Method for the solution of the transport equation. Scalable boundary condition for the adsorbate concentration on the adsorbent walls is used, defined on basis of the ratio of the accumulated adsorbate mass and the equilibrium adsorbate mass for a given system temperature. As the state of equilibrium is dependent also on the system temperature, a sensitivity study of the adsorption process under different system temperatures is performed. Among the studied adsorption equilibria models, including the Freundlich model, Simplified local density (SLD) model and the Dubinin-Radushkevich model, the latter is proved as the best compromise between accuracy and computational cost and applied in mass transfer kinetics computations. The results of computations show, that the increase in system temperature results in a decrease of breakthrough times, as the equilibrium amounts of adsorbate at the adsorbent walls decrease with increasing temperature, therefore making the derived numerical model suitable for further use in detailed mass transfer kinetics computations.

Improving NH3-SCR denitrification performance over WaCo0.4TiOx catalysts: Effect of surface acidity due to W addition on low-temperature and high-temperature activity

A serial of WaCo0.4TiOx catalysts (a = 0.04, 0.06, 0.08, 0.10) was synthesized by sol-gel method, which exhibited high NH3-SCR denitrification performance in a wide activity temperature window. W0.08Co0.4TiOx achieve best SCR activity (over 90% NO conversion) at 190–430 °C and good resistance to H2O/SO2. Various characterizations were used to investigate the influence of W doping on physicochemical property of these catalysts. Especially, in-situ DRIFTS were used to evaluate the type of acid sites, NOx adsorption, the reactivity of surface adsorption species, and the influences of H2O/SO2 on adsorption of NOx and NH3. The doping of W enhanced the acidity and weakened the oxidation capacity of WaCo0.4TiOx, but higher surface acidity, especial more Brønsted acid sites, can compensate for the effect of the decrease in the oxidation capacity on low-temperature activity. The optimal activity over W0.08Co0.4TiOx can be derived from the synergistic effect of surface acidity and oxidation performance.

In-situ DRIFTS study on the k-poisoning resistance mechanism of titanium bearing blast furnace slag catalyst by Sm/La doping

Benefiting from the construction of lamellar framework Sm-CeZrTiAl amorphous mixed oxides synthesized by the hydrothermal method, enhanced NH3-SCR performance over a wide temperature window for K poisoning resistance was observed. The Sm-CeZrTiAl catalyst preserved higher catalytic performance after K was introduced than the catalysts without added Sm, as it maintained > 90% NO conversion between 300 and 420 °C. The outstanding K poisoning-resistance of the Sm-CeZrTiAl catalyst could benefit from its good nano-Al2O3 flake skeleton structure, high specific surface area, and rich pore channels. In addition, Sm doping can effectively increase the number of surface acid sites, especially strong acid sites, which promote the formation of NOx adsorption species such as nitrite, bidentate nitrate and bridging nitrate intermediates and facilitate the conversion of NO to N2 by following the Langmuir-Hinshelwood mechanism. In addition, the synergy between Sm/La and Ce leads to more Ce3+ and Brønsted acid sites. Through the redox cycle of Ce4++Sm2+→Ce3++Sm3+ or Ce4++La2+→Ce3++La3+, catalytic reduction can be realized with good performance. Moreover, a significant portion of K on the catalyst surface preferentially interacted with strong acidic sites provided by Sm/La doping, thereby preventing Ce species from poisoning and leaving them available for the catalytic cycle.

Emerging multifunctional iron-based nanomaterials as polysulfides adsorbent and sulfur species catalyst for lithium-sulfur batteries—A mini-review

Lithium-sulfur (Li-S) battery has been considered as one of the most promising next generation energy storage technologies for its overwhelming merits of high theoretical specific capacity (1673 mAh/g), high energy density (2500 Wh/kg), low cost, and environmentally friendliness of sulfur. However, critical drawbacks, including inherent low conductivity of sulfur and Li2S, large volume changes of sulfur cathodes, undesirable shuttling and sluggish redox kinetics of polysulfides, seriously deteriorate the energy density, cycle life and rate capability of Li-S battery, and thus limit its practical applications. Herein, we reviewed the recent developments addressing these problems through iron-based nanomaterials for effective synergistic immobilization as well as conversion reaction kinetics acceleration for polysulfides. The mechanist configurations between different iron-based nanomaterials and polysulfides for entrapment and conversion acceleration were summarized at first. Then we concluded the recent progresses on utilizing various iron-based nanomaterials in Li-S battery as sulfur hosts, separators and cathode interlayers. Finally, we discussed the challenges and perspectives for designing high sulfur loading cathode architectures along with outstanding chemisorption capability and catalytic activity.

LIFE-CLIVUT, ecosystem benefits of urban green areas: a pilot case study in Perugia (Italy)

Trees have a great value in terms of ecosystem services in urban areas. LIFE CLIVUT is an “Information and Governance” European project developed in 4 Mediterranean Cities, with the goal of increasing the knowledge and awareness of citizens, especially young people, on the importance of the presence and good management of urban trees to mitigate the “Heat Island” effects. The data collected on the value of tree heritage and their future potential are used to design a green asset management strategy that will help urban planners adopt better practices for the mitigation of the effects of climate change in urban environments. This paper illustrates the results of tree census activity in four urban green areas of Perugia, Central Italy, that will be compared with those recorded in others cities involved in the project. Dendrometric parameters (diameter at breast height, tree height, first branch height, max and min crown width, crown shape and density) were recorded in situ using a dedicated software operating through a web app (“Clivut-Treedb”). The following ecosystem services were estimated: CO2 sequestration, particulate matter (PM) absorption, shadow effect, biodiversity indexes. Several tree species characterized by important wood structures during their adult phase, such as Pinus pinea, Quercus ilex, Q. pubescens, Ulmus carpinifolia, Populus alba and Aesculus hippocastanum showed the highest estimates of CO2 stored. Q. ilex was the most efficient species in particulate adsorption, showing similar estimates (about 60 g PM10 tree-1 year-1) in the 3 oldest green areas established in the 1980s, while the youngest plantations (dating back to 2005) absorbed about 10 g tree-1 of PM10 per year. In terms of the potential cooling effect of trees, preliminary estimates of the shaded areas highlighted the difference between the older green areas (about 50% of shading) compared to the younger ones (about 15% and 8%).