In response to the global imperative for sustainable resources, gamma-valerolactone (GVL), derived from levulinic acid found in biomass and food waste, holds particular interest to yield bio-monomers for polymer synthesis. This study investigates the catalytic potential of magnesium silicates in gas-phase GVL ring-opening via transesterification reaction with methanol (methanolysis), producing methyl 2-pentenoate, methyl 3-pentenoate, methyl 4-pentenoate, and butene. The aim of the study is to selectively produce the 3 and 4 isomers due to their utility as nylon precursors. Through systematic adjustments of the catalyst synthesis conditions, including the nature and/or ratios of the precursors as well as the pH levels, the acid-base properties of co-precipitated magnesium silicates are modulated. The materials are prepared in micromixer equipment, and their structural and textural properties are characterized by X-ray diffraction (XRD) and N2 physisorption, respectively. An in-depth exploration of the products and of the spent catalysts leads to identifying strongly adsorbed carboxylates as responsible for a non-negligible carbon balance gap. Moreover, the surface acid-base characteristics are determined by means of a model reaction of 2-methyl-3-butyn-2-ol (MBOH) conversion and correlated to the selectivity to methyl pentenoates and butene in the methanolysis of GVL. The findings underscore that the least acidic catalyst yields the highest selectivity to the desired products, while the most acidic catalyst favours the production of butene.

Research results about the structure, acid-base, redox, and adsorption characteristics of zinc(yttrium)-containing dealuminated BEA zeolites (Si/Al=1000), Zn(Y)SiBEA and their catalytic properties in the propane dehydrogenation with CO2 (CO2-PDH) are presented. The catalysts were prepared through a two-step procedure involving complete dealumination of the BEA zeolite followed by the introduction of Zn2+ and Y3+ cations into vacant T-atom sites, by impregnation. The samples obtained were characterized using XRD, XPS, 29Si DP MAS NMR, low-temperature N2 ad/desorption, TPR-H2, C3H8/C3H6 (CO2, NH3)-TPD, and FTIR-Py techniques. The influence of zinc content and yttrium on the functional properties of Zn(Y)SiBEA surface and activity/selectivity of the catalysts (Zn1.0-, Zn2.0-, and Zn2.0Y2.0SiBEA) in the CO2-PDH process are analyzed. The balanced acid-base characteristics of the Zn(Y)SiBEA catalysts determine their activity/selectivity in the CO2-mediated propane dehydrogenation to propene. Propane conversion and propene selectivity/yield over Zn(Y)SiBEA catalysts are higher in the CO2-PDH process compared to direct propane dehydrogenation (without CO2).

We present a straightforward one-pot hydrothermal method for the synthesis of zirconia nanodispersions, leading to the formation of stable sols. By simply varying the nature of the stabilizer used, one can obtain a large variety of objects with different sizes, shapes and crystallinities. Our results demonstrate the crucial role played by aliphatic amino acids both during the formation of the objects and after, since their interaction with the surface of the inorganic crystals influences strongly the optical properties and colloidal stability of the latter. Importantly, the versatility of this method allows for the introduction of different dopants, increasing substantially the scope of applications that can be achieved with such nanoscale oxides. The high transparencies and the easy dispersibility of nanoparticles in different liquid matrixes ensure the formation of zirconia-based nanocomposites and ceramics with outstanding optical features for the orthopedic, dental, photonics and chemical sectors. This method can be easily scaled up, being already available for the production of high-quality zirconia nanodispersions at the industrial level. We present a simple, scalable and versatile hydrothermal method for the formation of zirconia-based nanodispersions with an outstanding control of the morphology, composition and crystalline structure of the objects obtained. Given their optical features, these dispersions can be used as starting materials for the formation of organic-inorganic nanocomposites in a large number of applications. image

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.

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.

Straw is a substantial agricultural by-product for biogas production. Hydrolysis of straw is found to be a rate-limiting step during its anaerobic digestion and could be enhanced by pretreatment. In this paper, the effect of various combinations of particle size reduction, autoclaving, and low-level Fenton reaction was studied on straw for biogas production. Grinding of straw contributed to the maximum increase in the biomethane potential. Only Fenton or only the autoclave process improves the kinetics slightly but does not considerably improve the biomethane potential. Combining autoclaving and low-concentration Fenton pretreatment considerably improves the BMP values. Lignin content, CHNSO elemental analysis, Scanning Electronic Microscopy (SEM), Simon’s staining, infrared spectroscopy (DRIFT and ATR), Nuclear magnetic resonance spectroscopy, and wide-angle X-ray diffraction analysis (WAXD) were used to characterize the physical and chemical changes of straw due to pretreatment. Results show a poor correlation between biogas production and the different physical and chemical biomass characteristics. It makes it difficult to explain the outcome of various pretreatment methods applied to biomass. Without further improvement and development of analytical techniques, the prediction of the biomethane potential of a feedstock with the aid of pretreatment can only be considered in case-by-case studies.

Silica surface functionalization is often done through the condensation of functional silanes on silanols, silica surfaces' terminal groups. APTES, aminopropyltriethoxysilane, is widely used due to its assumed high reactivity with silanols, kinetically promoted by the catalytic action of the terminal amine function. Here, we revisit, based on a quantitative analysis by solid-state 29Si NMR, the assembly of this silane on silica surfaces to investigate whether its presence results from grafting, i.e., hetero-condensation with silanol groups or from homo-condensation of silane molecules in solution leading to polycondensates physisorbed on silica. We investigate the interaction of APTES with a crystalline layered silicate, ilerite, and with amorphous nonporous silica. We also studied a second silane, cyanopropyltrichlorosilane (CPTCS), terminated with a nitrile group. Our results undoubtedly prove that while CPTCS is grafted on the silica surface, the presence of APTES on silica and silicate materials is only marginally associated with silanol consumption. The analysis of the signal related to silicon atoms from silanes (Tn species) and those from silica (Qn species) allowed for the accurate estimation of the extent of homo-condensation vs grafting based on the ratio of T-O-T/Q-O-T siloxane bridges. These findings deeply question the well-established certainties on APTES assembly on silica that should no longer be seen as grafting of alkoxysilane by hetero-condensation with silanol groups but more accurately as a homo-condensed network of silanes, predominantly physisorbed on the surface but including some sparse anchoring points to the surface involving less than 6% of the overall silanol groups.

Magnesium silicates combining acidic and basic surface properties are known to be interesting as heterogeneous catalysts. Nevertheless, their catalytic performances are highly dependent on the synthesis method used. In this study, a series of magnesium silicates was synthesized for the first time using a coprecipitation method with a micromixer. It is first shown that changes in synthesis/precipitation pH led to magnesium silicates with different Mg/Si ratios: the higher the synthesis pH, the higher the Mg/Si ratio. Moreover, prepared silicates with a final Mg/Si ratio greater than 0.7, thus prepared at high pH, exhibit negligible specific surface area, whereas relatively high values (>180 m2/g) have been obtained for lower Mg/Si ratios. A set of experimental characterization data obtained by N2 physisorption, SEM, XRD, TGA-DTA as well as Raman and 29Si NMR spectroscopies are presented and discussed. They show the existence of two distinct families with a similar Magnesium Silicate Hydrate (MSH) phase, but they reveal different aggregation states and textural properties. Finally, the surface acid–base reactivity of the co-precipitated magnesium silicates was determined using the model reaction of 2-methylbut-3-yn-2-ol (MBOH) conversion. The results obtained suggest that it is possible to prepare silicates with a wide range of surface acid–base properties, from purely basic solids to those with both acidic and basic properties, by adjusting the final Mg/Si ratio via the control of the synthesis parameters.

Research results about the influence of BEA zeolite preliminary dealumination on the acid–base characteristics and catalytic performance of 1% Zn-BEA compositions in propane dehydrogenation with CO2 are presented. The catalyst samples, prepared through a two-step post-synthesis procedure involving partial or complete dealumination of the BEA specimen followed by the introduction of Zn2+ cations into the T-positions of the zeolite framework, were characterized using XRD, XPS, MAS NMR, SEM/EDS, low-temperature N2 ad/desorption, C3H8/C3H6 (CO2, NH3)-TPD, TPO-O2, and FTIR-Py techniques. Full dealumination resulted in the development of a mesoporous structure and specific surface area (BET) with a twofold decrease in the total acidity and basicity of Zn-BEA, and the formation of Lewis acid sites and basic sites of predominantly medium strength, as well as the removal of Brønsted acid sites from the surface. In the presence of the ZnSiBEA catalyst, which had the lowest total acidity and basicity, the obtained selectivity of 86–94% and yield of 30–33% for propene (at 923 K) exceeded the values for ZnAlSiBEA and ZnAlBEA. The results of propane dehydrogenation with/without carbon dioxide showed the advantages of producing the target olefin in the presence of CO2 using Zn-BEA catalysts.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Synergistic Effect Between Ca 4 V 4 O 14 and Vanadium-Substituted Hydroxyapatite in the Oxidative Dehydrogenation of Propane Sarah Petit, Cyril Thomas, Yannick Millot, Frederic Averseng, Dalil Brouri, Jean-marc Krafft, Stanislaw Dzwigaj, Gwenaelle Rousse, Christel Laberty-robert, Guylène Costentin

Three series of zeolite catalysts Co all-silica and Co Al-containing zeolites beta were prepared for use in the selective oxidative dehydrogenation of propane to propylene. Two series of zeolite catalysts Co all-silica were prepared by a two-step postsynthesis method at pH = 2.5 and pH = 3.0–9.0, respectively, which allows the incorporation of cobalt into SiBEA zeolite in the form of isolated framework pseudo-tetrahedral Co(II) species. The incorporation of Co ions into vacant T-atom sites and their reaction with silanol groups were demonstrated by NMR and FTIR methods. The generation of Lewis acid sites without the formation of Brønsted sites was proved by FTIR using pyridine and CO as probe molecules. The state of cobalt in three series of prepared and calcined zeolite catalysts was characterized by DR UV-vis. This technique allowed to show that for low Co content (<2 wt.%) cobalt is present in the form of framework pseudo-tetrahedral Co(II) species. For higher Co content (>2 wt.%), both framework pseudo-tetrahedral and extra-framework octahedral Co(II) species are present. The Co Al-containing zeolite beta series prepared on non-dealuminated support shows the presence of extra-framework octahedral Co(II) only.

TixSiBEA zeolites prepared by a two-step post-synthesis method are applied in the liquid-phase Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone in the oxygen-aldehyde system. Such method of ε-caprolactone synthesis offers the application of milder reaction conditions with the catalytic system which transforms cyclic ketones into lactones in the presence of molecular oxygen and aldehyde. They are the source of in situ peracid formation. The Ti incorporation into SiBEA involves the formation of Ti(IV) (OSi)4 as main species and small numbers of Ti(III) (OSi)3–O(H)–Si sites having Brønsted and Lewis acid properties. The acidity is a key factor for efficient transformation of cyclohexanone to ε-caprolactone in the BV oxidation depending on the titanium oxidation state and environment. Among all of the studied catalysts, the highest catalytic activity is observed for Ti2.0SiBEA zeolite. The active catalyst of the studied BV oxidation reaction is bi-functional, possessing both the acidic and redox properties, catalyzing different reaction stages.

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.

The speciation of vanadium in initial aqueous NH4VO3 solutions as a function of pH and concentration, in supernatant and in wet solids were investigated by V-51 static and MAS NMR. Two series of VSiBeta zeolite catalysts were prepared by a two-step postsynthesis procedure at pH= 2.5 and 6. V-51 static and MAS NMR, V-51 3Q MAS NMR, DR UV-vis, XPS and EPR allowed determining the state of vanadium in both series of catalysts. The catalytic activity of VSiBeta catalysts in SCR of NO strongly depended on the state of the vanadium present. The V-single site V(1.0)SiBeta(I) and V(1.4)SiBeta(I) catalysts with isolated pseudo-tetrahedral V(V) were active in SCR of NO with NH3 process, with maximum NO conversion about 75 % at 773 K for V(1.4)SiBeta(I). In contrast, V(1.0)SiBeta(II) and V(7.5)SiBeta(I) catalysts containing pseudo-octahedral V(V) were much less active in SCR of NO and high amount of undesired N2O was produced.

The combination of spectroscopically characterized bulk- and surface-active zirconium sites makes Zr-MOF crystals efficient catalysts for alcohol dehydrogenation under mild conditions.

The influence of dealumination of two commercial amorphous silica-aluminas (ASAs) with acetylacetone on their textural properties, acidity and catalytic activity was studied by N-2-sorption, NH3-TPD, FTIR of adsorbed pyridine as well as H-1 and Al-27 MAS NMR. Acetylacetone treatment increases the pore volume and surface area (+20 ->+30%) of commercial ASA without changing the pore size. More than half of the Al species are extracted from ASA but the total acidity is preserved or even slightly increased (for the ASA with higher Al content). The percentage of acidic Al is increased by a factor 2. Dealumination results in a better access to acid sites and an increase of medium Bronsted acid sites (BAS), leading to a 1.5 higher catalytic activity for 3,3-Dimethyl-1-butene (33DMB1) isomerization.

The morphology, surface speciation, NMR, and IR spectroscopic properties of nanosized layered magnesium silicate isostructural to talc at equilibrium in an aqueous environment were computed from first principles. The theoretical predictions were successfully compared with experimental results obtained on a commercial magnesium silicate hydrate, revealing insights relevant for understanding the catalytic and other surface properties of such materials of promising industrial applications.

Insights into the catalytic transformation of propane to propene on V-apatite catalysts are provided based on structure-reactivity relationships. Substitution of phosphates by vanadates in the hydroxyapatite structure leads to the formation of Ca-10(PO4)(6-x)(VO4)(x)(OH)(2-y)O-y V-oxy-hydroxy-apatite solid solutions (x=0 -> 6). Bulk vanadium incorporation promotes (i) calcium rich terminations (XPS, CO adsorption), (ii) proton deficiency inside the OH- channels (H-1 NMR) giving rise to O2- native species, (iii) the thermally-activated formation of additional O2- species along the OH- channels resulting in H-bonding interaction (in situ DRIFT) and (iv) the proton conduction process that eventually results in the surface exposure of O2- species (in situ impedance spectroscopy). The exposure of Ca2+-O2- surface acid-base pairs allows the dissociation of hydrogen, emphasizing the strong basicity of the related O2- species. Whereas an increasing vanadium content is beneficial to propene selectivity, it scarcely impacts propane conversion. The reaction proceeds mainly upon oxidative dehydrogenation, even if the minor dehydrogenation route is also observed. Surface O2- generated thanks to proton mobility are involved in the C-H bond activation, as shown by the synergistic effect between the oxidative dehydrogenation of propane reaction and the bulk proton conduction measured under operando conditions. This puts emphasis on the key role of strong basic sites for propane activation.