Surface Catalytic Properties Research Articles

Enhancement of anodic oxidation of formic acid on Pd–Fe bimetallic nanoparticles by thermal treatment

The surface composition and catalytic properties of Pd–Fe bimetallic catalysts with identical bulk composition can be continuously tuned by treatment at different temperatures. The activity of these catalysts in formic acid oxidation was related to the treatment temperature. The thermal treatment temperatures ranged from 400 to 600 °C. The Pd–Fe nanoparticles are characterized by an array of analytical techniques including TEM (transmission electron microscopy), XRD (X-ray diffraction), ICP (inductively coupled plasma) and HS-LEIS (low energy ion scattering spectroscopy). The electrocatalytic activity is examined using cyclic voltammetric and chronoamperometric measurements. The Pd–Fe/C catalyst with 500 °C shows the highest electrocatalytic activity for formic acid oxidation, with a current activity 3 times higher than that of before treated Pd–Fe/C catalyst, 5.6 times higher than that of commercial Pt/C catalyst. The migration of Pd to the surface on the nanoparticle catalysts as well as the electrochemical active surface area of the PdFe–H catalysts was shown to play a major role in enhancing the electrocatalytic activity for catalyst. These findings provided important insights into the correlation between the electrocatalytic activity and the treatment temperature of the nanoengineered bimetallic catalysts.

Role of oxygen vacancy in metal oxide based photoelectrochemical water splitting

AbstractPhotoelectrochemial (PEC) water splitting relies on the optoelectric property of the photoelectrodes. Oxygen vacancy (VO) has attracted increasing attention in tailoring photoelectrodes in the following three aspects: light harvest, charge separation and transfer, and surface reaction kinetics. Even though the VO may increase the recombination as a kind of defects in metal oxide based photoelectrode, a number of recent researches have revealed the beneficial feature of VO in PEC, which is controversial to the former understanding. Thus, a comprehensive analysis about the oxygen vacancy in the metal oxide photoelectrodes will be important for applying VO in achieving high PEC performance. Herein, we contribute a critical review on the role of oxygen vacancy including its formation mechanism, characterization methods, and the influence on the semiconductor and surface catalytic properties. The knowledge will help to clarify the effect of VO in terms of the structure‐performance relationship in the PEC process.image

Dip-coating of MXene and transition metal dichalcogenides on 3D-printed nanocarbon electrodes for the hydrogen evolution reaction

3D-printing technology is widely accepted as a scalable and advanced manufacturing procedure for the fabrication of electrodes for electrochemical applications. 3D-printed carbon-based electrodes can be used for electrochemical analysis, replacing conventional carbon electrodes. However, a bare 3D-printed carbon electrode exhibits poor electrochemical performance. Herein, a post-treatment of 3D-printed electrodes was carried out using catalytically active materials to improve their electrochemical performance. We used a dip-coating technique which is a more universal, facile, and cost-effective approach compared with other conventionally used techniques such as atomic layer deposition or electrodeposition. The 3D-printed nanocarbon electrodes were dip-coated with MXene (Ti3C2Tx) and different transition metal dichalcogenides such as MoS2, MoSe2, WS2, and WSe2 to study their catalytic activity towards the hydrogen evolution reaction (HER). This study demonstrates a simple method of improving the catalytic surface properties of 3D-printed nanocarbon electrodes for energy conversion applications.

Single-Crystalline Co3O4 Nanocubes for Highly Sensitive Acetone Gas Sensors

Semiconductor metal oxide (SMO) based gas sensors have been considered a promising candidate for gas detection over the past few years due to their simplicity of use, low cost, and flexibility in production. Semiconductor metal oxide gas sensors have various application field such as non-invasive diagnosis of diseases as well as monitoring flammable and toxic gases in domestic and industrial environments. Nowadays, with the increase in interest in health care, gas sensor for early diagnosis of disease and monitoring health status are becoming the next generation of medical technology. However, it is still difficult to selective and accurate analyze only a small amount of target gas in a respiratory gas with a humidity of 95% or more. According to many studies, important detection parameters including sensitivity and selectivity of resistive SMO sensors can be improved through the synthesis of high-efficiency nanostructures.Various metal oxides are suitable for detecting oxidizing or reducing gases by measuring conductivity. Most p-type oxide semiconductors such as NiO, CuO, Cr2O3 and Co3O4 have been widely studied as excellent catalysts for promoting the selective oxidation of various volatile organic compounds (VOCs). The inherent oxygen adsorption of p-type oxide semiconductors can be used to design high-performance gas sensors with low humidity dependence and high recovery rates. Moreover, by introducing a p-type oxide semiconductor as a complex to the n-type oxide semiconductor, it can be used to change the electrical properties near the hetero interface and to change the gas sensing properties.According to the gas sensing mechanism, the operating characteristics of solid-state gas sensors are determined by the receptor and transducer functions. Therefore, it is very important to synthesize metal oxides with optimal morphology and crystal structure. The sensitivity of the sensor can be improved by using nanoparticles with a size of 1 – 100 nm as a sensing material, which is in good agreement with previously reported studies. However, since it is difficult to sufficiently increase the gas sensitivity by simply adjusting the size, it is required to form high sensitivity and selectivity to the target gas by using various types of nanostructures.Among the various p-type SMO, Co3O4 has been studied as a potential material in many applications, including catalysts, magnetism, supercapacitors, batteries, and gas sensors, with indirect band gaps in the region of 1.6-2.2 eV. In most cases, Co3O4 play an important role in strong catalytic activity for specific reactions based on their surface catalytic properties. In particular, the microstructure of Co3O4 in gas sensors is known to be an important factor in determining sensing characteristics. The shape and size of the sensing material greatly influences the sensing performance due to the exposed surface. The selectivity also can be improved by the inherent surface characteristics of p-type oxide semiconductors, and thus the synthesis and characterization of shape-related structure with controlled crystal facet exposure is very interesting research area. Recently, a lot of research has been studied on the gas sensing properties according to the crystal plane of sensing materials.For example, Zhou et al reported that the {111} plane of Co3O4 has a significant effect on ethanol gas detection performance and reacts more sensitively. Liu et al demonstrated that both p-type and n-type sensing responses are facet dependent and sensitivity increases as the exposed {001} facet of TiO2 increases.Therefore, exposing a crystal surface rich in unsaturated metal cations has been identified as the most promising approach to achieving excellent gas sensing performance.In this paper, we report facile preparation of Co3O4 nanostructures for highly active gas-sensing properties for acetone at sub-ppm levels controlling size and shape of nanoparticles. Co3O4 nanocubes shows high reactivity for 1 ppm acetone compared to Co3O4 nanospheres. These results show the potential of Co3O4 as a promising gas sensing material having a different gas response, selectivity, and response kinetics.

Polymer photocatalysts for solar-to-chemical energy conversion

Solar-to-chemical energy conversion for the generation of high-energy chemicals is one of the most viable solutions to the quest for sustainable energy resources. Although long dominated by inorganic semiconductors, organic polymeric photocatalysts offer the advantage of a broad, molecular-level design space of their optoelectronic and surface catalytic properties, owing to their molecularly precise backbone. In this Review, we discuss the fundamental concepts of polymeric photocatalysis and examine different polymeric photocatalysts, including carbon nitrides, conjugated polymers, covalent triazine frameworks and covalent organic frameworks. We analyse the photophysical and physico-chemical concepts that govern the photocatalytic performance of these materials, and derive design principles and possible future research directions in this emerging field of ‘soft photocatalysis’. In this Review, the authors analyse the fundamental concepts that govern the photocatalytic performance of organic polymer photocatalysts and discuss the challenges and future of the field of ‘soft photocatalysis’.

Increasing Complexity Approach to the Fundamental Surface and Interface Chemistry on SOFC Anode Materials.

ConspectusIn this Account, we demonstrate an increasing complexity approach to gain insight into the principal aspects of the surface and interface chemistry and catalysis of solid oxide fuel cell (SOFC) anode and electrolyte materials based on selected oxide, intermetallic, and metal–oxide systems at different levels of material complexity, as well as into the fundamental microkinetic reaction steps and intermediates at catalytically active surface and interface sites. To dismantle the complexity, we highlight our deconstructing step-by-step approach, which allows one to deduce synergistic properties of complex composite materials from the individual surface catalytic properties of the single constituents, representing the lowest complexity level: pure oxides and pure metallic materials. Upon mixing and doping the latter, directly leading to formation of intermetallic compounds/alloys in the case of metals and oxygen ion conductors/mixed ionic and electronic conductors for oxides, a second complexity level is reached. Finally, the introduction of an (inter)metall(ic)–(mixed) oxide interface leads to the third complexity level. A shell-like model featuring three levels of complexity with the unveiled surface and interface chemistry at its core evolves. As the shift to increased complexity decreases the number of different materials, the interconnections between the studied materials become more convoluted, but the resulting picture of surface chemistry becomes clearer. The materials featured in our investigations are all either already used technologically important or prospective components of SOFCs (such as yttria-stabilized zirconia, perovskites, or Ni–Cu alloys) or their basic constituents (e.g., ZrO2), or they are formed by reactions of other compounds (for instance, pyrochlores are thought to be formed at the YSZ/perovskite phase boundary). We elaborate three representative case studies based on ZrO2, Y2O3, and Y-doped ZrO2 in detail from all three complexity levels. By interconnection of results, we are able to derive common principles of the influence of surface and interface chemistry on the catalytic operation of SOFC anode materials. In situ measurements of the reactivity of water and carbon surface species on ZrO2- and Y2O3-based materials represent levels 1 and 2. The highest degree of complexity at level 3 is exemplified by combined surface science and catalytic studies of metal–oxide systems, oxidatively derived from intermetallic Cu–Zr and Pd–Zr compounds and featuring a large number of phases and interfaces. We show that only by appreciating insight into the basic building blocks of the catalyst materials at lower levels, a full understanding of the catalytic operation of the most complex materials at the highest level is possible.

On the surface-dependent oxidation of Cu2O during CO oxidation: Cu2+ is more active than Cu+

Solid materials can exhibit very different surface catalytic properties depending on the exposed surface. Different from the previous finding by Bao et al. (Angew. Chem. Int. Ed. 50 (2011) 12294–12298) that Cu2O octahedra are more active than Cu2O cubes in CO oxidation, we found that Cu2O cubes exposing {100} surface showed significantly higher activity than Cu2O octahedra exposing {111} surface in the reaction. The Cu2O(100) surface was found to be oxidized during CO oxidation, leading to the formation of a CuO surface layer. On the other hand, Cu2O(111) strongly resisted such surface oxidation under CO oxidation conditions. Density functional theory calculations demonstrate that CO oxidation follows a Mars-Van Krevelen mechanism on Cu2O(111) with a high activation barrier of 1.36 eV. In contrast, the overall activation barrier is only 0.58 eV for CuO(111). These differences explain well the higher activity of oxidized Cu2O cubes.

Facet-dependent electrocatalysis in the HCOOH synthesis from CO2 reduction on Cu catalyst: a density functional theory study

Copper (Cu) has unique hydrogenation properties in the CO2 reduction reaction (CO2RR) for the synthesis of valuable hydrocarbons and alcohols such as methane, ethylene, ethanol and formic acid. Among the C1 products, formic acid (HCOOH) is chemically stable in the liquid phase at room temperature and is the simplest energy source that can be synthesized from CO2. The electrochemical CO2RR on Cu has been widely studied due to its very high selectivity toward target products and mild reaction conditions. However, electrochemistry activity can be impacted by many catalytic surface properties, including the morphology, crystallinity and surface index. Cu has a face-centered cubic (FCC) structure, and the Cu(1 1 1) surface index tends to be naturally exposed. Since the number of dangling bonds on the surface of the catalyst is different for each exposed surface, each surface activity is different, and the reaction pathway may also be different. The surface indexes of Cu(1 0 0) and (2 1 1) can be observed as a supported catalyst, and Cu(1 1 0) can be observed in a rod shape nanoparticle. Herein, we performed CO2RR over each surface and proposed an energy diagram of HCOOH formation via the COOH and HCOO intermediates using spin-polarized density functional theory. We elucidate the determining factor of catalytic activity and discuss the relationship between the coordination number/surface roughness (caused by the different surface facet) and the activity through electronic analysis of the d orbitals.

(Invited) Discovery and Design of Alloy Catalysts and Lithium-Ion Battery Materials through Machine Learning

Drawing on examples from alloy catalysis and lithium-ion batteries, I will demonstrate how machine learning can be used to significantly accelerate the design and discovery of new materials. In the first example, I will present a way to create complete maps of the surface structures and catalytic properties of an alloy catalyst at every point in its phase diagram. The key to this approach is the generation of surface cluster expansions that depend on the lattice parameter of the bulk material and are trained using a Bayesian method. I will discuss how these maps reveal insights into the catalytic properties of intermetallic phases and demonstrate how the maps can be used to rapidly identify the target synthesis conditions for stable and active catalysts. In the second example, I will demonstrate how training an interatomic potential model using on-the-fly machine learning can accelerate the calculation of activation energies for lithium diffusion by seven orders of magnitude, resulting in significantly improved agreement with experiment compared to pure density functional theory. Using the machine-learned interatomic potential models, we have identified new candidate coating materials designed to improve interfacial stability in solid state lithium-ion batteries.

Rational Design of Copper Alloy Catalysts for Electrochemical CO2 Reduction

Electrochemical conversion of CO2 is a potentially exciting route towards production of sustainable drop-in fuels and chemicals using renewable electricity. A key obstacle in the commercial scale-up and deployment of CO2 utilization and conversion is the lack of active and selective catalysts. Across all monometallic candidates, Cu exhibits distinctive ability to electrochemically reduce CO2 to several products including methane and ethylene, albeit its multifunctional nature makes selectivity control challenging [1]. Alloying offers a means to break scaling relationships and uniquely manipulate the reactivity and selectivity in ways that would be hard to achieve using monometallic compositions alone. Here, we employ a coupled quantum mechanics/molecular mechanics (QM/MM) scheme [2] to screen various copper alloys for their reactivity and selectivity towards key rate-limiting and selectivity-determining steps in CO2 conversion. The activity-selectivity screening is carried out under reducing conditions to thoroughly probe the influence of the electrolytic ions under the applied potential on the alloy stability and reactivity. The results of these studies show how alloying in conjunction with electrolyte tuning can non-intuitively alter the surface electronic and catalytic properties of the catalyst leading to changes in activity-selectivity towards CO2 conversion. This serves to provide a rationale for improved composition and environment driven design and screening, and allows the use of chemical computation using nuanced, dynamical models of the electrochemical double layer[i].[1] Y. Hori, in Handbook of Fuel Cells: Fundamentals, Technology and Application (VHC Wiley, Chichester, 2003), Vol. 2, 720-733.[2] J. Haruyama, T. Ikeshoji and M. Otani, Electrode potential from density functional theory calculations combined with implicit solvation theory. Physical Review Materials (2018), 2(9), p.095801. [i] This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

Detailed insight into electrochemical reaction mechanisms and rate limiting steps is crucial for targeted optimization of solid oxide fuel cell (SOFC) electrodes, especially for new materials and processing techniques, such as Ni/Gd-doped ceria (GDC) cermet anodes in metal-supported cells. Here, we present a comprehensive model that describes the impedance of porous cermet electrodes according to a transmission line circuit. We exemplify the validity of the model on electrolyte-supported symmetrical model cells with two equal Ni/Ce0.9Gd0.1O1.95-δ anodes. These anodes exhibit a remarkably low polarization resistance of less than 0.1 Ωcm2 at 750 °C and OCV, and metal-supported cells with equally prepared anodes achieve excellent power density of >2 W/cm2 at 700 °C. With the transmission line impedance model, it is possible to separate and quantify the individual contributions to the polarization resistance, such as oxygen ion transport across the YSZ-GDC interface, ionic conductivity within the porous anode, oxygen exchange at the GDC surface and gas phase diffusion. Furthermore, we show that the fitted parameters consistently scale with variation of electrode geometry, temperature and atmosphere. Since the fitted parameters are representative for materials properties, we can also relate our results to model studies on the ion conductivity, oxygen stoichiometry and surface catalytic properties of Gd-doped ceria and obtain very good quantitative agreement. With this detailed insight into reaction mechanisms, we can explain the excellent performance of the anode as a combination of materials properties of GDC and the unusual microstructure that is a consequence of the reductive sintering procedure, which is required for anodes in metal-supported cells.

Critical effect of carbon vacancies on the reverse water gas shift reaction over vanadium carbide catalysts

Experimental and theoretical evidences show that carbon vacancies determine the catalytic behavior of vanadium carbides in the CO2 conversion to CO via the Reverse Water Gas Shift (RWGS) reaction. Two VCx samples, one mostly containing stoichiometric VC and the other being C deficient, mainly V8C7, were synthesized, characterized, and studied. The samples show different CO2 adsorption heats, which correlate with those calculated using Density Functional Theory (DFT) on suitable models. The sample containing more V8C7 shows a higher CO2 conversion and CO selectivity and a lower apparent activation energy, being a stable catalyst over long-time tests. DFT calculations confirm that C vacancies in V8C7 are responsible for the observed catalytic behavior, allowing reactants to adsorb more strongly and lowering the energy barrier for both H2 and CO2 dissociation steps. The present work highlights the importance of such native point defects in the transition metal carbides surface chemistry and catalytic properties.

Room temperature blooming of CeO2 3D nanoflowers under sonication and catalytic efficacy towards CO conversion.

Carbon monoxide (CO), being a highly toxic gas, bears hazardous effects on human health and contributes majorly to environmental pollution. It is mostly produced by automobile exhausts and incomplete combustion of carbon-containing substances. Thus, the development of catalysts for CO conversion is highly imperative and has always gained interest for real field applications. Besides the high oxygen storage capacity and facile transitions between oxidation states, the huge abundance of cerium on earth makes CeO2 a low-cost and highly effective alternative to noble metal catalysts for CO oxidation. The present work delineates the room temperature synthesis of flower-shaped 3D CeO2 nanostructures using a sonication-assisted simple synthesis method within 2 hours under the pivotal importance of a structure-directing agent, polyvinylpyrrolidone (PVP). The bifunctional contributions of PVP as a surfactant and as a capping agent are discussed with a plausible mechanism. The method leading to the formation of hierarchical CeO2 nanoflowers provides an appreciable surface area of 132.69 cm2 g−1. The morphological and structural characterizations of the catalyst were thoroughly investigated using FESEM, TEM, XRD, UV-visible spectroscopy, photoluminescence spectroscopy, FTIR spectroscopy and X-ray photoelectron spectroscopy. The structural efficacies of flower-like CeO2 nanostructures have also been correlated to the narrowing of the band gap and the generation of the corresponding oxygen vacancies, resulting in surface catalytic properties towards 80% conversion of CO.

Rational strain engineering in delafossite oxides for highly efficient hydrogen evolution catalysis in acidic media

The rational design of hydrogen evolution reaction (HER) electrocatalysts which are competitive with platinum is an outstanding challenge to make power-to-gas technologies economically viable. Here, we introduce the delafossites PdCrO$_2$, PdCoO$_2$ and PtCoO$_2$ as a new family of electrocatalysts for the HER in acidic media. We show that in PdCoO$_2$ the inherently strained Pd metal sublattice acts as a pseudomorphic template for the growth of a strained (by +2.3%) Pd rich capping layer under reductive conditions. The surface modification continuously improves the electrocatalytic activity by simultaneously increasing the exchange current density j$_0$ from 2 to 5 mA/cm$^2_{geo}$ and by reducing the Tafel slope down to 38 mV/decade, leading to overpotentials $\eta_{10}$ < 15 mV for 10 mA/cm$^2_{geo}$, superior to bulk platinum. The greatly improved activity is attributed to the in-situ stabilization of a $\beta$-palladium hydride phase with drastically enhanced surface catalytic properties with respect to pure or nanostructured palladium. These findings illustrate how operando induced electrodissolution can be used as a top-down design concept for rational surface and property engineering through the strain-stabilized formation of catalytically active phases.

Surface plasmon resonance excited electron induction greatly extends H2 evolution and pollutant degradation activity of g‐C3N4 under visible light irradiation

AbstractEnergy crises and environmental pollution have sparked tremendous research work to handle their impacts. Herein, we fabricated Au/g‐C3N4 nanocomposites to produce H2 and degrade 2,4‐dichlorophenol (2,4‐DCP) under visible light and at different wavelengths. Interestingly, the optimized photocatalyst generated 114 μmol H2 and degraded 25% 2,4‐DCP in 1 hr as compared with 10 μmol H2 generation and 8% 2,4‐DCP degradation by pure g‐C3N4. This improvement is credited to the extended light absorption and improved charge induction from gold to g‐C3N4 even at 590 nm as confirmed from photoluminescence, surface photovoltage, and photoelectrochemical study of the samples. Moreover, the surface catalytic property of g‐C3N4 was much improved after loading a proper amount of gold nanoparticles. We hope that this technique to photosensitize semiconductors with noble metal nanoparticles may provide a feasible way to construct surface plasmon resonance‐assisted photocatalysts to cope with energy crises and environmental pollution simultaneously.

Excess Electrons on Reduced AnO2 (111) Surfaces (An = Th, U, Pu) and Their Impacts on Catalytic Water Splitting

Excess electrons from intrinsic oxygen vacancies play a key role in the surface chemistry and catalytic properties of metal oxides. This effect is particularly critical in actinide dioxides (AnO2),...

Modified Ceria for “Low‐Temperature” CO2Utilization: A Chemical Looping Route to Exploit Industrial Waste Heat

AbstractEfficient CO2utilization is key to limit global climate change. Carbon monoxide, which is a crucial feedstock for chemical synthesis, can be produced by splitting CO2. However, existing thermochemical routes are energy intensive requiring high operating temperatures. A hybrid redox process (HRP) involving CO2‐to‐CO conversion using a lattice oxygen‐deprived redox catalyst at relatively low temperatures (&lt;700 °C) is reported. The lattice oxygen of the redox catalyst, restored during CO2‐splitting, is subsequently used to convert methane to syngas. Operated at temperatures significantly lower than a number of industrial waste heat sources, this cyclic redox process allows for efficient waste heat‐utilization to convert CO2. To enable the low temperature operation, lanthanum modified ceria (1:1 Ce:La) promoted by rhodium (0.5 wt%) is reported as an effective redox catalyst. Near‐complete CO2conversion with a syngas yield of up to 83% at low temperatures is achieved using Rh‐promoted LaCeO4−x. While La improves low‐temperature bulk redox properties of ceria, Rh considerably enhances the surface catalytic properties for methane activation. Density functional theory calculations further illustrate the underlying functions of La‐substitution. The highly effective redox catalyst and HRP scheme provide a potentially attractive route for chemical production using CO2, industrial waste heat, and methane, with appreciably lowered CO2emissions.

Highly Active Mn3–xFexO4 Spinel with Defects for Toluene Mineralization: Insights into Regulation of the Oxygen Vacancy and Active Metals

A series of highly defected Mn3-xFexO4 spinels with different amounts of oxygen vacancies and active metals were successfully synthesized by regulating the insertion of Fe ions into the crystal structure of Mn3O4 via self-polymerizable monomer adjustment of the molten Mn-Fe salt dispersion. The characterization of X-ray diffraction, Raman, scanning electron microscopy, X-ray photoelectron spectroscopy, and N2 adsorption-desorption showed that the doping of Fe increased the lattice defects, oxygen vacancy concentration, specific surface area, mesoporosity, and catalytic properties compared to Cu ions doping. Temperature-programmed reduction with hydrogen and oxygen pulse chemisorption tests determined that the doping level of Fe ions had an important influence on the oxygen vacancy content and the dispersion of active metals on the catalysts' surfaces. For the best Mn-dispersed and most active Mn2.4Fe0.6O4 catalyst, a long-term toluene oxidation measurement running for 120 h of uninterrupted reaction, at the low temperature of 240 °C, high humidity (relative humidity = 100%), and high weight hourly space velocity of 60000 mL·g-1·h-1, was also carried out, which indicated that the catalyst possessed high stability and endurability. Moreover, the continuous oxidation route and internal principle for toluene oxidation were also revealed by the in situ diffuse-reflectance infrared Fourier transform spectroscopy and gas chromatography-mass spectrometry techniques and deep dynamics study.

Manipulation of electrospun mesoporous zirconia nanofiber with enhanced surface area and catalytic property

Mesoporous zirconia nanofiber is a promising material in various fields, such as energy storage devices, catalyst supports, separation membranes and so on. How to enhance the surface area of mesoporous zirconia nanofiber is still an urgent problem for the pore collapse with high temperature treatment. In the present work, mesoporous zirconia nanofiber with a high surface area of 332 m 2 g −1 was obtained with the addition of SiO 2 and water vapor preheat treatment. The crystallinity and the change in microstructure of the mesoporous zirconia nanofiber, heat-treated at different temperatures in different atmospheres (air and water vapor), were compared and analyzed. The mesoporous structure formation mechanism and the validate addition of SiO 2 were presented. Furthermore, with zirconia nanofiber possessing high surface area as the supporting material, tungstate supported zirconia catalyst showed a high specific activity of bromination of phenol red up to 2.13 mmol h −1 g −1 . We anticipated that water vapor pretreatment was a promising way to enhance the surface area of mesoporous oxide nanofiber with soft template method.

LaNixFe1-xO3 (0 ≤ x ≤1) as photothermal catalysts for hydrocarbon fuels production from CO2 and H2O

LaNixFe1-xO3 perovskite compounds (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were successfully synthesized by a sol-gel combustion method. The crystal structure, morphology, BET surface area, oxygen vacancies, band gap and catalytic properties of the catalyst were characterized in detail. The results showed that LaNi0.4Fe0.6O3 compound exhibits the best photothermal catalytic performance. Under the same catalytic conditions (350 ℃ + Vis-light), CH4 and CH3OH yields are about 3.5 and 4.0 times, 1.8 and 2.1 times of that of LaFeO3 and LaNiO3. It was found that all the solid solutions possesses better catalytic properties than the pure end compounds. The doping of Ni lead to a significant modification with the quantity of oxygen vacancies and band gaps. These findings may further broaden the materials scope for photothermal conversion of CO2 and H2O.