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The oxidative dehydrogenation of propane into propene could be a way to produce propylene as an alternative to steam cracking or fluid catalytic cracking, if efficient catalysts were discovered and...

In this paper, two biosystems based on filamentous fungi and Pd nanoparticles (NPs) were synthesized and structurally characterized. In the first case, results concerning the integration and distribution of Pd-NPs on Phialomyces macrosporus revealed that nanoparticles are accumulated on the cell wall, keeping the cytoplasm isolated from abiotic particles. However, the Penicillium sp. species showed an unexpected internalization of Pd-NPs in the fungal cytosol, becoming a promising biosystem to further studies of in vivo catalytic reactions. Next, we report a new solution-based strategy to prepare palladized biohybrids through sequential reduction of Pd2+ ions over previously harvested fungus/Au-NP composites. The chemical composition and the morphology of the biohybrid surface were characterized using a combination of scanning electron microscopy, transmission electron microscopy, and photoelectron spectroscopy. The deposition of Pd0 over the fungal surface produced biohybrids with a combination of Au and Pd in the NPs. Interestingly, other chemical species such as Au+ and Pd2+ are also observed on the outermost wall of microorganisms. Finally, the application of A. niger/AuPd-NP biohybrids in the 3-methyl-2-buten-1-ol hydrogenation reaction is presented for the first time. Biohybrids with a high fraction of Pd0 are active for this catalytic reaction.

Low-temperature solution phase synthesis of nanomaterials using designed molecular precursors enjoys tremendous advantages over traditional high-temperature solid-state synthesis. These include atomic-level control over stoichiometry, homogeneous elemental dispersion and uniformly distributed nanoparticles. For exploiting these advantages, however, rationally designed molecular complexes having certain properties are usually required. We report here the synthesis and complete characterization of new molecular precursors containing direct Sn-E bonds (E = S or Se), which undergo facile decomposition under different conditions (solid/solution phase, thermal/microwave heating, single/mixed solvents, varying temperatures, etc.) to afford phase-pure or mixed-phase tin chalcogenide nanoflakes with defined ratios.

The development of efficient, stable, and non-precious metal water oxidation catalysts (WOCs) is a matter of importance for sustainable energy research. In this work, iron cobaltite (FeCo2O4) nanoparticles were prepared by the coprecipitation method, and we present the effect of heat treatment (250, 350, 450, 650 and 900 °C) on the catalytic properties. Catalytic activity tests of FeCo2O4 nanocatalysts were performed in the presence of ammonium cerium(IV) nitrate (CAN), and the formation of oxygen was followed using a Clark-type oxygen electrode. The samples were characterized by infrared (IR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their surface areas were determined by the Brunauer, Emmett, and Teller (BET) method. Fourier transform infrared (FTIR) data confirm a metal-oxygen bond at the octahedral and tetrahedral sites. XRDs data were characteristic of spinel-like cubic materials. The XPS results confirmed the presence of trivalent and divalent cobalt and iron ions in the samples and showed that the non-heated sample has a greater amount of cobalt on the nanoparticles’ surface than those heated to 900 °C. The surface area decreased from 92.00 m2 g-1 for the material that was unannealed to 2.00 m2 g-1 for the sample annealed at 900 °C. The unannealed nanomaterials showed an oxygen production of 790 mmol s−1 g−1. This was 790 times greater than the oxygen production from nanomaterials heated to 900 °C. Although the surface structure of nanomaterials is unclear, the amount of surface cobalt appears to have implications for catalytic activity. Optimization of superficial cobalt content may be key to improving catalytic activity.

Chemical state analysis of a sample surface through fitting bell-shaped curves to x-ray photoelectron spectroscopic polymer data is reviewed using nylon to introduce and discuss aspects of data analysis. Different strategies for modeling chemistry in nylon spectra are presented and in so doing, a case is made to include in published science the design logic and implementation in terms of line shapes and optimization parameter constraints between components in a peak model. Imperfections in line shape relative to the true shape for photoemission lines, when compensated for using constraints to optimization parameters, are shown to provide chemical state information about a sample that justify, for peak models constructed with these limitations, metrics for goodness-of-fit different from those expected for pulse-counted data.

Chemometrics/informatics, and data analysis in general, are increasingly important in x-ray photoelectron spectroscopy (XPS) because of the large amount of information (spectra/data) that is often collected in degradation, depth profiling, operando, and imaging studies. In this guide, we present chemometrics/informatics analyses of XPS data using a summary statistic (pattern recognition entropy), principal component analysis, multivariate curve resolution (MCR), and cluster analysis. These analyses were performed on C 1s, O 1s, and concatenated (combined) C 1s and O 1s narrow scans obtained by repeatedly analyzing samples of cellulose and tartaric acid, which led to their degradation. We discuss the following steps, principles, and methods in these analyses: gathering/using all of the information about samples, performing an initial evaluation of the raw data, including plotting it, knowing which chemometrics/informatics analyses to choose, data preprocessing, knowing where to start the chemometrics/informatics analysis, including the initial identification of outliers and unexpected features in data sets, returning to the original data after an informatics analysis to confirm findings, determining the number of abstract factors to keep in a model, MCR, including peak fitting MCR factors, more complicated MCR factors, and the presence of intermediates revealed through MCR, and cluster analysis. Some of the findings of this work are as follows. The various chemometrics/informatics methods showed a break/abrupt change in the cellulose data set (and in some cases an outlier). For the first time, MCR components were peak fit. Peak fitting of MCR components revealed the presence of intermediates in the decomposition of tartaric acid. Cluster analysis grouped the data in the order in which they were collected, leading to a series of average spectra that represent the changes in the spectra. This paper is a companion to a guide that focuses on the more theoretical aspects of the themes touched on here.

Chemometrics/informatics and data analysis, in general, are increasingly important topics in x-ray photoelectron spectroscopy (XPS) because of the large amount of information (data/spectra) that are often collected in degradation, depth profiling, operando, and imaging studies. In this guide, we discuss vital, theoretical aspects and considerations for chemometrics/informatics analyses of XPS data with a focus on exploratory data analysis tools that can be used to probe XPS datasets. These tools include a summary statistic [pattern recognition entropy (PRE)], principal component analysis (PCA), multivariate curve resolution (MCR), and cluster analysis. The use of these tools is explained through the following steps: (A) Gather/use all the available information about one's samples, (B) examine (plot) the raw data, (C) developing a general strategy for the chemometrics/informatics analysis, (D) preprocess the data, (E) where to start a chemometrics/informatics analysis, including identifying outliers or unexpected features in datasets, (F) determine the number of abstract factors to keep in a model, (G) return to the original data after a chemometrics/informatics analysis to confirm findings, (H) perform MCR, (I) peak fit the MCR factors, (J) identify intermediates in MCR analyses, (K) perform cluster analysis, and (L) how to start doing chemometrics/informatics in one's work. This guide has Paper II [Avval et al., J. Vac. Sci. Technol. A 40, 063205 (2022)] that illustrates these steps/principles by applying them to two fairly large XPS datasets. In these papers, special emphasis is placed on MCR. Indeed, in this paper and Paper II, we believe that, for the first time, it is suggested and shown that (1) MCR components/factors can be peak fit as though they were XPS narrow scans and (2) MCR can reveal intermediates in the degradation of a material. The other chemometrics/informatics methods are also useful in demonstrating the presence of outliers, a break (irregularity) in one of the datasets, and the general trajectory/evolution of the datasets. Cluster analysis generated a series of average spectra that describe the evolution of one of the datasets.

In this manuscript, we prepared gold nanorods (Au-NRs) through “silver-assisted seeded methodology” and studied their outermost layer using XPS spectroscopy and ab initio calculations to compare the chemical states of the constituents of the metallic core. Supporting first-principles calculations employing a relativistic, full-potential and all-electron method, with augmented plane waves plus local orbitals as a basis set, ensure proper treatment of the core electron states. Three significant findings can be reported. First, we found that besides Au (0), there are two chemical states for silver, namely Ag (0) and Ag(I), on the Au surface. Our results corroborate with recent results reported in the literature, indicating that Ag monolayer can be oxidized to Ag(I) during the steps of centrifugation and washing with diluted CTAB solution. Second, ab initio simulations showed that Ag atoms have different binding energies, depending on their configuration in Au-NRs (whether silver atoms are found on the surface or if they are spread in bulk as interstitial or substitutional defects). Third, theoretical studies showed that silver atoms located at interstitial sites could distort the crystalline structure, and, therefore, we do not expect interstitial Ag to occur in Au-NRs.

International audience; Golden grass is a vegetal fiber used in arts and crafts for its peculiar optical properties, namely, its shiny golden-like reflectivity. Since vegetal fiber structure is usually heterogeneous, complementary techniques have been used to understand the electronic properties of the external and core regions of golden grass fibers. The composition and dielectric function of the few nanometer-thick external surfaces has been investigated using X-ray photoelectron spectroscopy and energy loss spectroscopy (XPS-PEELS), while a comparison of vibrational and optical properties of the few-micron-thick external and fiber core regions was derived from Raman, optical, photoluminescence (PL) and photoacoustic (PAS) spectroscopies. Raman signature and valence-band distribution indicate that the internal and external parts of the fibers are made of some oxygen-depleted lignin-like carbonaceous material. Besides a plasmon peak at 21 eV, two main absorption bands at 3.7 eV and 8.2 eV have been identified as π−π* and σ−σ* electronic transitions at aromatic moieties. PL excitation and emission behavior confirm heterogeneous molecular structures at the core and external regions. Specular reflectance spectra calculated from the complex refractive index (derived from XPS-PEELS) do not explain the shiny golden-like aspect of golden grass, which may arise from diffuse reflectance within a collection of heterogeneous hollow fibers.

Perovskites with formula LaNi 1-x Co x O 3 (x = 0.0, 0.2, 0.5 and 1.0) were investigated in the Partial Oxidation of Methane (POM) reaction. In situ XRD results suggest that the reduction of the perovskites under H 2 lead to the formation of La 2 B 2 O 5 (B = Ni and Co) which is further transformed to Ni 1-x Co x /La 2 O 3 . The phase structure evolution when increasing the temperature of LaNi 0.8 Co 0.2 O 3 without pre-reduction with H 2 but submitted to a mixture CH 4 + O 2 allows the formation of a spinel phase La 2 BO 4 (B = Ni and Co) before obtaining Ni and Co over La 2 O 3 . On the other hand LaNi 0.8 Co 0.2 O 3 presented a different behavior after previous reduction with H 2 and the spinel phase is not detected. The H 2 pre-reduction favored lower mean crystallite size of Ni on La 2 O 3 . The catalytic tests suggest that H 2 pretreatment promotes the production of the syngas with a H 2 /CO = 2 close to the stoichiometry. Without pretreatment, the H 2 /CO ratio is lower (1.6) indicating the occurrence of parallel reactions such as RWGS. The sample Ni 0.8 Co 0.2 /La 2 O 3 pretreated with H 2 presented a higher molar rate H 2 /CO = 2.2. Deactivation was not observed after 24 h run test but graphitic carbon was detected on all samples. In the case of Ni 0.8 Co 0.2 /La 2 O 3 less carbon formation was detected.

This study reports the application of immobilized Ag/TiO2 onto coconut and sisal fibers to anthracene degradation via the UV–vis radiation. The fibers were previously treated with hot water and CTAB to clean their impurities surfaces. Immobilizations of Ag/TiO2 to the fibers were performed by anchorage of the catalysts via the post-synthesis method. The materials were characterized using AAS, TGA, XRD, UV–vis DRS, FTIR, STEM, EDS, and XPS analysis. FTIR and XPS results indicated the presence of hydroxyl groups and different silver species (Ago, Ag+, and Ag2+) on the catalyst surface. Immobilized Ag/TiO2 exhibited higher activity as compared to suspended Ag/TiO2 and TiO2. Ag/TiO2 immobilized on fibers treated with CTAB promoted the full anthracene photodegradation within 2 h at 40 °C. The results demonstrated that sisal and coconut fibers could be used as a support for Ag/TiO2.

The low stability of Pt-based catalysts due to severe corrosion of carbon support is one of the most critical technical issues hindering the widespread application of proton exchange membrane fuel cells. Here, we report the successful deposition of Pt nanoparticles on both pure titanium dioxide (TiO2) and Fe-doped TiO2 powder by chemical reduction using formic acid and their performance toward ethanol oxidation in acid media. First, the supported TiO2 was synthesized by the sol–gel method, and its physical-chemical properties were modified by the incorporation of iron (5.0 and 10.0 wt% Fe) into the structure of TiO2. The supports and catalysts were characterized by photoacoustic spectroscopy (PAS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The PAS data show that the doping of TiO2 with iron ions (III) decreases the band gap from 2.95 eV (undoped TiO2) to lower values depending on the iron content in the support (1.97 eV and 1.90 eV for 5Fe–TiO2 and 10Fe–TiO2, respectively). The XRD and TEM results indicate the presence of small-sized (around 3.5 nm) Pt nanostructures deposited onto the supports. The XPS analyses reveal surfaces rich in metallic Pt and oxygen species (O2− species, OH− and O atoms) in the vicinity of oxygen vacancies, as well as strong interactions between Pt nanoparticles and the Fe–TiO2 support. The Pt/Fe–TiO2 electrocatalyst exhibits higher catalytic activity toward ethanol oxidation than Pt/TiO2 and commercial Pt/C electrocatalysts (used as reference). The efficiency of Pt utilization increases with the Fe content. The sample with 10 wt% (mol/mol) of iron is then the most active catalyst. The enhanced activity and stability of the Pt/Fe–TiO2 catalyst can be attributed to the synergic and electronic effect of the compounds, Pt, and Fe–TiO2.

Nanosized BiTaO4 and BiNbO4 were prepared by the citrate method. The electronic and optical properties of BiTaO4 and BiNbO4 have been investigated by means of photo-acoustic spectroscopy (PAS), X-r ...

The structural, optical, and electronic properties of nitrogen doped TiO 2 have been investigated experimentally and theoretically. The electronic and optical properties are investigated by using the first principles calculations in the framework of density functional theory and based on the full-potential linearized augmented plane wave method. The local density approximation plus on site Coulomb interaction was used for the exchange and correlation potential. The absorption and dielectric functions experimental data of as-grown sample show very good agreement with the theory.

Catalytic performance of binary nanostructured oxides has been evaluated in the gas-phase dehydration of glycerol, an environmental friendly reaction. SnO2–Mn2O3, SnO2–ZrO2, SnO2–TiO2, ZrO2–Mn2O3 nanocasted oxides, and a reference, NiO–Co3O4, were characterised by XRD, Raman spectroscopy, acid–base measurements, SEM–EDX, TPR, HTEM and XPS. Correlations among the catalyst's activity and the surface, textural, and acid–base properties of the nanocasted oxides were tentatively conducted in attempts to justify the catalytic results. Influences of nanoparticle or nanostructure structural properties on the catalytic activity have been investigated. The better activity of SnO2–TiO2 at 250 °C and a glycerol/water molar ratio of 0.25 was due to cooperativity of Sn4+ and Ti4+. The most important finding was that nanostructure features of the solid enhanced nanoparticle stability through the redox ability of the binary solid compared to conventional binary catalysts.

A series of nanocasted oxides were synthesised, and an analysis using basicity measurements provided evidence that low strength basic sites with high accessibility favoured the production of 1-hydroxyacetone from glycerol dehydration. Among the oxides studied (e.g., CeO2, ZrO2, and TiO2), the best results were obtained for a CeO2–ZrO2 binary oxide (activity = 3 × 10−6 mmol g−1 h−1), which revealed that a moderate basicity allowed acid–base cooperativity in the Ce0.8Zr0.2O2 phase to produce 1-hydroxyacetone. Indeed, TEM, Raman, XPS and SEM-EDX analyses and textural properties showed that these features influenced the activity of the catalyst towards glycerol conversion by preventing coking.

The optical properties of zinc oxide (ZnO) nanorods (NRs) synthesized by the low-temperature aqueous chemical method on top of silicon (Si) substrate have been investigated by means of photoelectron energy loss spectroscopy (PEELS). The ZnO NRs were obtained by the low temperature aqueous chemical synthesis on top of Si substrate. The measured valence band, the dynamical dielectric functions and optical absorption of the material show a reasonable agreement when the trending and shape of the theoretical calculations are considered. A first-principle calculation based on density functional theory (DFT) was performed using the partially self-consistent GW approximation (scGW0) and compared to the experimental results. The application of these two techniques brings a new analysis of the electronic properties of this material. The experimental results regarding the density of states (DOS) obtained for the valence band using x-ray photoelectron spectroscopy (XPS) was found to be consistent with the theoretical calculated value. Due to this consistency, the same wavefunctions was then employed to calculate the dielectric function of the ZnO NRs. The experimentally extracted dielectric function was also consistent with the calculated values. Funding agencies: National Research Council of Scientific and Technological Development (CNP); Bahia Research Foundation (FAPESB)/PRONEX; CAPES Foundation within the Ministry of Education, Research Council of Norway [243642]

1D nanostructured sodium trititanate was synthesized by alkali hydrothermal treatment of TiO 2 anatase, coexisting with incompletely converted precursors like nanosheets and poorly crystalline aggregates. This product easily exchanged with Fe 3+ at room temperature to saturation at approximately 8 wt% Fe, following the Langmuir adsorption model. Iron exchange caused changes on the structural (interlayer shrinkage) and optical properties of the nanomaterial without affecting significantly its original morphology and mesoporous structure. According to consistent XRD and TEM/EDS data, iron was saturated within the interlayers of the 1D nanostructured particles at a lower content as compared to the coexisting poorly crystalline aggregates. Based on XPS results iron was found to be also in a lower oxidation state Fe 2+ , likely on the layered surface of the 1D nanostructured particles, through a mechanism tentatively explained by formation of structural iron defects promoted by the acidic medium. The iron modified trititanate nanostructure (Fe/TTNS) is stable up to 400 °C and at high temperatures it is eventually transformed into rutile (TiO 2 ) and pseudobrookite (Fe 2 TiO 5 ), whereas some freudenbergite phase (Na 2 Fe 2 Ti 6 O 16 ) is generated due to residual sodium.

Hydrogen production from the dry reforming of methane has been studied over MAl2O4 (M = Cu2+, Ni2+ or both) with respect to the structure, surface properties and coke deposition of the spinel oxides. The catalysts were characterized by Raman, XPS, TEM, and N2 adsorption isotherms methods. The Nio/NiAl2O4 system was significantly more active due to the intimated contact between Nio specie and the NiAl2O4. This system is found to give carbon filaments which easily react with CO2, in comparison with the Cu-based spinel oxides.

Water–gas shift reaction has found new purpose and challenges due to its application in clean power generation systems based on fuel cells. It has been shown that the catalysts performance is dependent on both the metal phase and the nature of the support. In this contribution the modification of Pt/CeO 2 catalyst with vanadium was exploited. Spectroscopic techniques revealed that distinct dispersed VOx species were generated onto the catalysts by using different vanadium loadings. The reduction of the catalysts and CO adsorption were monitored by infrared spectroscopy. It was found that the formation/decomposition of surface carbonates is affected by vanadium. Generation of multicoordinated carbonates is inhibited due to the decrease of the exposed cerium surface cations. The catalytic activity increased up to a vanadium surface density of 6 V atoms/nm 2. Improvement in water–gas shift reaction kinetics is associated with the V O Ce bonds.

Due to stringent environmental regulations, the reduction of aromatic compounds present in diesel fuel, precursors of particulate matter, is becoming one of the most important technologies in petroleum refining industries. However, the high quantity of nitrogen and sulfur compounds limits the use of catalytic processes. In this work Pt and Pd catalysts supported on alumina modified with rare earth oxides (Ce and Pr) were prepared, characterized by XRF, XRD, UV–vis-DRS and XPS, and tested in the hydrogenation of tetralin reaction, in the presence of different concentrations of thiophene. The results showed that the use of a Pr-modified alumina support enhanced the tolerance of the Pt/Al2O3 catalyst to thiophene. The addition of a second metal, Pd, despite a loss in activity, increased tolerance to this poison. The combination of both promoters exhibited a synergic effect, as the bimetallic catalyst supported in the Pr-modified alumina showed a very low sensitivity to thiophene, up to 2600 ppm, explained by the electron-deficiency of the metallic Pt.

Si-MCM-41 molecular sieves, which are largely used in a number of acid and redox catalyzed reactions, as reported by the literature, were used as basic catalyst for the Knoevenagel condensation. This reaction involves the condensation of carbonyl compounds with active methylene compounds to generate unsaturated products. The catalyst, which pores were occluded by the organic template, provided high activity in mild conditions, even under 10 °C. The high activity is due to the presence of siloxy anions, of high basicity, located in the pore cavity of the hexagonally ordered mesopores. Ion exchange procedures evidenced the presence of these high basic sites as a consequence of the high pH increase of the solution containing tetramethylammonium chloride, or the high H + consumption, added to a the medium as HCl, to keep constant pH. O 1s XPS and 29 Si CP/MAS NMR measurements confirmed the existence of only ≡SiO − CTA + ionic pair, which is the basic site itself.

A porous solid iminobis(N-2-aminoethylacetamide) polysiloxane ligand system of the general formula P–(CH2)3–N(CH2CONHCH2CH2NH2)2, (where P represents [Si–O]n siloxane network) has been prepared by modification of immobilized diethyliminidiacetate P–(CH2)3N(CH2CO2Et)2 with ethylenediamine in toluene. The new modified polysiloxane system exhibits high potential for the uptake of metal ions (Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+). This ligand system shows higher capacity toward the metal ions than its parent iminiodiacetate precursor. Complexation of ligand system for the metal ions at the optimum conditions was found in the order: Cu2+ > Fe3+ > Ni2+ > Co2+ > Mn2+ > Zn2+. Stability studies of the immobilized ligand system show that a degradation of the siloxane network and leaching of some species occurred upon treatment with acid or basic aqueous solutions in addition to metal ion solution.