Ammonia is the second most widely produced chemical in the world. It is essential for fertilizer manufacturing and has recently emerged as an energy carrier. Ammonia has been produced for over 100 years using the Haber-Bosch process, which is highly energy-intensive and accounts for nearly 3 % of annual COQ emissions. Efforts to improve the energy efficiency of this process, particularly the development of more efficient catalysts, are therefore of major interest. This study investigates how the chemical composition and basicity of hydroxyapatite (HAp) supports influence the catalytic performance of supported Ru metal nanoparticles in ammonia synthesis under mild conditions. Particular attention was paid to synthesizing catalysts with HAp supports of different chemical compositions, comparable specific surface areas, and with supported Ru metal nanoparticles of similar sizes (2.2 +/- 0.2 nm) to allow for a reliable comparison. The HAp-supported Ru (2 wt%) catalysts exhibited optimal NH3 performance with HAp supports precipitated at a pH ranging from 7.4 to 7.8. These catalysts exhibited an NH3 TOF of 0.40 +/- 0.01 min-1 at 400 degrees C and 1 bar, which is approximately 50 % higher than that of a Ru/MgO reference catalyst. The superior NH3 synthesis performance of these catalysts is attributed to the minimization of defects incorporated in the HAp crystalline structure and the higher basicity of the corresponding HAps. NH3 TOF was remarkably correlated with the electron density of the Ru metal nanoparticles, as monitored by N2 adsorption at low temperatures followed by FTIR, making this finding of great interest in the field of ammonia synthesis.

Accurate assessment of the metal dispersion is known to be important in the field of catalysis as these data are used to calculate the turnover frequency of a given reaction on a given metal. This study shows that N2 can be used as a Fourier transform infrared spectroscopy (FTIR) probe molecule not only qualitatively but also quantitatively. For the first time, it is found that the integrated molar absorption coefficient of N2 adsorbed on the hydroxyapatite (HAp) supports (epsilon N2-HAp = 0.092 +/- 0.008 cm/mu mol) does not depend on the chemical composition of HAp, while that of N2 adsorbed on the HAp-supported Ru0 nanoparticles of about 2.2 nm (epsilon N2-Ru 0: 0.5-1.03 cm/mu mol) is sensitive to the chemical composition of HAp. This study also shows, for the first time, that epsilon N2-Ru 0 increases with increasing electron density of the Ru0 nanoparticles, as monitored by the position of the maximum of the absorption band of the N2 stretching vibration at about 2200 cm-1 (nu N2-Ru 0), with a remarkable correlation between epsilon N2-Ru 0 and nu N2-Ru 0. The epsilon N2-Ru 0 values are 2 orders of magnitude smaller than the previously reported integrated molar absorption coefficients of CO (epsilon CO-Ru 0). Finally, epsilon N2-HAp and epsilon N2-Ru 0 allow us to estimate the Ru dispersion, which is in remarkable agreement with that determined by transmission electron microscopy (TEM).

Hydroxyapatite (HAp)-supported cobalt catalysts have been evaluated in the oxidative dehydrogenation of propane to propene (ODHP). The morphology of the HAp supports and the cobalt immobilization mechanisms strongly influence the surface accessibility of cobalt species and their dispersion. A calibration curve obtained from NO-TPD experiments for the cobalt-exchanged materials allowed us to derive their cobalt surface densities. These values were used to better compare the evolution of propane conversion and propene selectivity, as well as to analyze the parameters governing these performances. Co3O4 nanoparticles formed by the strong electrostatic adsorption process are poorly selective in propene compared to isolated Co2+ cations immobilized by the cationic exchange mechanism. The isolated Co species exhibit a turnover frequency per Co atom that is two orders of magnitude higher than that reported for Co-based systems in previous studies. This much better performance is attributed to (i) the promotion of HAp basicity by cobalt incorporation as shown by the model MBOH conversion, (ii) the complete surface accessibility of the isolated Co2+ cations, and (iii) the close proximity between the Co2+ redox centers and the basic sites, as investigated by DFT.

Cobalt deposition in an excess of solution was used to design Co-modified hydroxyapatite materials with various Co loadings and controlled dispersion. It is rationalized how the properties of hydroxyapatite supports (more or less stoichiometric compositions, nanorod or platelet morphologies and crystalline (100) zig-zag termination or non-apatitic hydrated external layer), influence the immobilization processes of Co by operating either with slightly acidic (natural) or basic pH of the suspension media. Four cobalt immobilization mechanisms impacting the final dispersion of Co on hydroxyapatites were identified by combining structural (XRD, 1H and 31P solid-state NMR, UV-Vis, Raman and X-ray fluorescence spectroscopies), surface (XPS) characterizations of Co-modified hydroxyapatites after drying and thermal treatment at 500 °C, and monitoring of the pH and the composition of the supernatant solutions during the Co deposition step. On dried Co-modified crystalline stoichiometric hydroxyapatite nanorods, cobalt is highly dispersed through cationic exchange or strong electrostatic adsorption (SEA) at slightly acidic or basic pH, respectively. After thermal treatment at 500 °C, only cation exchange preserved atomic dispersion of Co(II) ions since Co3O4 nanoparticles were observed on samples for which Co deposition occurred via SEA. On defective hydroxyapatite platelets, cobalt deposited at acidic natural pH could diffuse in an external non-apatitic layer, whereas under basic pH media, this surface layer was hydrolysed, resulting in the formation of a cobalt-substituted hydroxyapatite layer in which only a limited fraction of the surface cobalt species could be probed by XPS.

Hydroxyapatite (Ca-10(PO4)(6)(OH)(2) or HAp)-the main mineral component of bones and teeth-is a material of great interest not only in biomedical applications but also in heterogeneous catalysis. Its framework Ca2+ cations can be substituted by a wide variety of catalytically active metals (Cu2+, Ni2+, Ag+, etc.). In the present work, for the first time, to our knowledge, we demonstrate that highly valuable HAp-based catalysts can be obtained through a novel advantageous bottom-up approach. Unlike classical surface cation deposition in the excess of solution, this approach is one-pot. It consists in preparing the bulk-metal-substituted HAp by coprecipitation and then submitting it to a finely adjusted thermal treatment under a H-2-containing gas flow. For a Cu(similar to 1.5 wt %)-HAp, we show that such a treatment at 450 degrees C leads to the exsolution of the whole Cu contained in the material, leading to highly dispersed Cu species at the HAp surface. After appropriate activation, these Cu species are active in the selective catalytic reduction of NOx by NH3. The phenomenon of exsolution has been reported so far mainly for perovskites but to lead to metal nanoparticles and not to highly dispersed species as achieved here.

Lean exhausts aftertreatment has been the subject of numerous investigations due to ever stringent regulations on pollutants emissions such as that of NOx. Among aftertreatment technologies, the selective catalytic reduction of NOx by the hydrocarbons (HC-SCR) has been studied intensively, in particular by using Ag/Al2O3 materials. The present work highlights that pretreatment of pristine Al2O3 in warm water prior to Ag deposition allows to prepare catalysts of significantly higher (H2-)C3H6-SCR performance compared to conventional Ag/Al2O3 catalysts. In addition, NOx-TPD-C3H6-SCR structure-activity correlations indicate that optimum composition of the Ag/Al2O3 catalysts can be improved by about 50% in terms of Ag content for the first time. Unprecedented indepth NMR investigations allow for the identification of the alumina sites of importance in the anchoring of Ag. These sites are mu 1-OH groups located near the (100)/(110)l edge and then near the (110)b/(100) edge of Al2O3 crystallites and bonded to octahedrally coordinated Al species.

The present work aims at investigating the oxidative dehydrogenation of propane (ODHP) catalytic properties of Co species supported on a Si ss zeolitic support. The Co2+ species incorporated in the silanol nests created by dealumination of a HAlSi ss pristine support (Co-Si ss) appeared to be about 4 times more active (3.1 x 10(-3) s(-1)) compared with that in exchange position of HAlSi ss (0.9 x 10(-3) s(-1)) for the formation of propene at 400 degrees C. The turn over frequency of the Co-Si ss samples are found to be greater than or equal to those reported in most of the earlier studies performed with Co-containing materials to date and to be about 7 times greater than that of V-Si ss materials (0.4 x 10(-3) s(-1)) from an earlier study, which illustrates the superiority of Co-Si ss over V-Si ss for the ODHP reaction. Maximum incorporable content of Co as Co-Si ss is dictated by the amount of removable Al.

Bone is created by osteoblasts that secrete osteoid after which an ordered texture emerges, followed by mineralization. Plywood geometries are a hallmark of many trabecular and cortical bones, yet the origin of this texturing in vivo has never been shown. Nevertheless, extensive in vitro work revealed how plywood textures of fibrils can emerge from acidic molecular cholesteric collagen mesophases. This study demonstrates in sheep, which is the preferred model for skeletal orthopaedic research, that the deeper non-fibrillar osteoid is organized in a liquid-crystal cholesteric geometry. This basophilic domain, rich in acidic glycosaminoglycans, exhibits low pH which presumably fosters mesoscale collagen molecule ordering in vivo. The results suggest that the collagen fibril motif of twisted plywood matures slowly through self-assembly thermodynamically driven processes as proposed by the Bouligand theory of biological analogues of liquid crystals. Understanding the steps of collagen patterning in osteoid-maturation processes may shed new light on bone pathologies that emerge from collagen physico-chemical maturation imbalances.

The present study combines experimental and theoretical approaches to investigate the competitive precipitation of calcium phosphates (CaPs) in aqueous solution in order to understand and control both the structural and textural properties of the synthesized hydroxyapatites (HAps). Some of the precipitation reactions were followed by in situ Raman spectroscopy or achieved under kinetically controlled conditions. The CaP precursors of HAps were identified as a function of the precipitation pH of the medium and the order of introduction of the precursor ions in the synthesis reactor. Their formation was rationalized by calculations based on a homogeneous nucleation model. Depending on the synthesis conditions, precipitation reaction pathways of HAps are proposed by bringing together the kinetic model developed in the present study and our previous thermodynamic model. HAps are complex materials due to the ease with which large amounts of crystallographic defects, such as carbonates and hydrogen phosphates, can be incorporated in their structure. As these defects play a key role in material sciences (bone substitute, heterogeneous acid-base catalysis, etc.), the present work also includes the analysis of the formation of these crystallographic defects in the apatitic framework, allowing a better control of their incorporation through careful selection of operating parameters.

Surface reactive oxygen species play a fundamental role in selective oxidation and combustion reactions catalyzed by metal oxides. Unravelling the nature of these transient species, and understanding the details of both their electronic structure and reactivity has been for decades one of the prime research areas of surface and catalytic chemistry. The longstanding activity of Michel Che in this area has been a source of inspiration for generation of researchers, and constitute his outstanding and enduring scien-tific legacy. Present review provides a survey of the surface oxygen species on oxide materials, which moving on from the Che's pioneering works includes noteworthy results obtained during the years by other researchers. In particular, applications of two powerful techniques such as electron paramagnetic resonance (EPR) and photoluminescence (PL) for detailed characterization of paramagnetic (O-, O-2, O-3) and diamagnetic surface oxygen varieties (O-surf(2)), respectively, are addressed here. Classification and insights into the formation pathways of these species on various oxide surfaces, as well as their involvement in model and real gas/solid and liquid/solid reactions of catalytic and photocatalytic relevance is also con-sidered. Finally, the relationship between the thermodynamic and kinetic Bronsted basicity of low coordi-nated O-2(Lc) anions is discussed, on the basis of Che's fundamental studies and on recent developments. (C) 2020 Elsevier Inc. All rights reserved.

Bone models set for studying apatite mineralization tend to use excess of organic additives and a very low concentration of collagen in light of those described in the biological tissue. However, the activity of soluble additives during mineral deposition is highly dependent on their concentration and confinement state, among others. Here, we investigate the role of concentration of organic additives described as key components in bone mineralization, i.e., the bioinspired synthetic polyaspartate mimicking noncollagenous protein (NCP), citrate, and collagen on apatite formation. The precipitation setup tends to mimic the acidic mineralization front in bone and is monitored by in situ Raman and ex situ solid-state nuclear magnetic resonance. This model helps to identify specific effects of organic additives on mineral formation. In particular, we show that the sequence of apatite precursors often described in vitro, i.e., amorphous calcium phosphate and subsequent octacalciumphosphate formation, is noticeably modified by varying the concentration of the additives. NCP and citrate are identified as either inhibitors or activators in the formation of calcium phosphate. In addition, collagen acts either as additives or as organic scaffold below and above the liquid-crystal threshold, respectively. This result highlights that confinement drives thermodynamically apatite formation by slowing down the kinetic formation of precursors, even at alkaline pH.

Thermodynamics of the precipitation of calcium phosphates shows the importance of the pH and the order of introduction of the precursor ions on the textural (morphology, surface area) and structural (defects) properties of hydroxyapatites.

The present work reports on a new type of V-based catalysts, namely V-substituted hydroxyapatites, and the influence of the synthesis conditions on their catalytic performance in the oxidative dehydrogenation of propane (ODHP) reaction. V-x-substituted hydroxyapatite materials prepared with the periodic addition of ammonia during the maturation step (V-x-HAp-pH-per) were shown to exhibit a Ca4V4O14 phase in addition to the V-substituted hydroxyapatite phase for x greater than or equal to 3.5. TEM characterization of the biphasic samples allowed us to demonstrate that the Ca4V4O14 phase was grown epitaxially on the V-x-HAp nanorods. The close intimacy between the two phases was confirmed by NMR suggesting the involvement of V4+ species. Consistently EPR data of the fresh and spent samples showed that V4+ species may be stabilized at the boundaries of these two phases. The strong promotion of the oxidative dehydrogenation reaction to propene observed from 723 K for the V-4-HAp-pH-per composition is attributed to a synergistic effect between the V-x-HAp nanorods that enable the activation of propane and the Ca4V4O14 phase that helps the redox exchanges. This synergy may be attributed to an easier electron delocalization on the V4O14 units located at the phases' boundaries.

Monitoring apatite formation throughin situRAMAN andex situssNMR spectroscopy.

ADVERTISEMENT RETURN TO ISSUEPREVCorrespondenceNEXTORIGINAL ARTICLEThis notice is a correctionComment on "Direct Decomposition of NOx over TiO2 Supported Transition Metal Oxides at Low Temperatures"Josefine Schnee*Josefine SchneeSorbonne Université, CNRS, Laboratoire de Réactivité de Surface (LRS), Tour 43, Case 178, 4, Place Jussieu, F-75252 Paris Cedex 05, France*E-mail: [email protected] (J. Schnee).More by Josefine Schneehttp://orcid.org/0000-0001-8521-9922, Laurent DelannoyLaurent DelannoySorbonne Université, CNRS, Laboratoire de Réactivité de Surface (LRS), Tour 43, Case 178, 4, Place Jussieu, F-75252 Paris Cedex 05, FranceMore by Laurent Delannoy, Guylène CostentinGuylène CostentinSorbonne Université, CNRS, Laboratoire de Réactivité de Surface (LRS), Tour 43, Case 178, 4, Place Jussieu, F-75252 Paris Cedex 05, FranceMore by Guylène Costentinhttp://orcid.org/0000-0003-1559-6890, Frédéric MeunierFrédéric MeunierUniv Lyon, Université Claude Bernard Lyon 1, CNRS, Institut de Recherches sur la Catalyse et l'Environnement de Lyon, IRCELYON, 2, Av. Albert Einstein, F-69626 Villeurbanne, FranceMore by Frédéric Meunierhttp://orcid.org/0000-0001-7953-2883, and Cyril Thomas*Cyril ThomasSorbonne Université, CNRS, Laboratoire de Réactivité de Surface (LRS), Tour 43, Case 178, 4, Place Jussieu, F-75252 Paris Cedex 05, France*E-mail: [email protected] (C. Thomas).More by Cyril Thomashttp://orcid.org/0000-0003-4224-6095Cite this: Ind. Eng. Chem. Res. 2020, 59, 10, 4835–4837Publication Date (Web):February 21, 2020Publication History Published online21 February 2020Published inissue 11 March 2020https://pubs.acs.org/doi/10.1021/acs.iecr.0c00412https://doi.org/10.1021/acs.iecr.0c00412correctionACS PublicationsCopyright © 2020 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views1059Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (1 MB) Get e-AlertscloseSUBJECTS:Animal feed,Catalysts,Organic reactions,Oxides,Transition metals Get e-Alerts

Keggin heteropolyacids (HPAs) have been known to be efficient NOx absorbers for many years, and to decompose a significant fraction of the NOx species pre-absorbed at 100-150 °C into harmless N2 an...

Alkaline-earth phosphates efficient in the dehydration of lactic acid to acrylic acid were previously shown to contain a surface mono/dihydrogen phosphate amorphous layer composed of M2+ cations and both P=O and POH groups. In this work, acidic properties of such a layer were determined combining Fourier transform infrared (FTIR) spectra achieved at the dehydrated state and under water vapor and density functional theory (DFT) simulations of nondefective and defective MPOH structure. The FTIR spectra of adsorbed pyridine and lutidine revealed the presence of moderate Lewis acid sites (LAS) and of POH groups interacting by H-bonding without significant protonation. DFT calculations were key to interpret FTIR spectra after adsorption of NH3: when solely adsorbed, NH3 interacts with the LAS on both the nondefective surface and the defective surface, whereas the POH for which H points up toward the gas phase are reoriented downward. Bronsted acid sites (BAS) were shown to form under water vapor. This phenomenon was shown by DFT to arise from a more acidic character of H2PO4- species for the nondefective surface and casual formation of nondefective surface leading to higher amount of H2PO4- species, which are more acidic BAS.

Ultrapure ZnO nanopowders were synthesized via vapor-phase-based methods under oxygen-deficient conditions. The type and relative proportions of intrinsic point defects were studied by photoluminescence (PL) and EPR spectroscopies performed under strictly controlled conditions. Besides coupled PL/EPR signals recently assigned to Zn-i(+) (2.80 eV, g = 1.96), two green emissions were systematically detected at 2.50 and 2.22 eV without EPR counterparts, whereas their contributions were observed to depend on the synthesis oxygen partial pressure (P-O2). Among diamagnetic defects likely to be formed in O-2-poor conditions, Zn-i(0) and Zn-i(2+) were discarded based on their energy levels that were reported to rather correspond to the transitions associated to match the violet light. Conversely, the involvement of oxygen vacancies (V-O(0) and V-O(2+)) as recombination centers for the green emission in ZnO was supported by Raman and XPS data. In line with the expected trends based on formation energies, the always dominant green luminescence (2.50 eV) was assigned to V-O(2+) and the weaker one (2.22 eV) to V-O(0). The involvement of an electron-containing defect (V-O(0)) was confirmed by visible light absorption observed in DR UV-vis spectra. We also showed that the Zn-i(+)/V-O(2+) ratio can be tuned by P-O2 or by the choice of static or flow synthesis conditions. Overall, this study demonstrates that by controlling the conditions during synthesis, processing, and spectroscopic investigations, the ultrapure ZnO nanopowders represent reliable models for the identification of photoluminescent crystal defects-an approach that can be widely applied on other systems.