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A stable and repeatable protocol has been developed to convert bio-sourced unsaturated diesters into mercaptans diesters using a thio-Michael catalysed reaction showing strong different reactivities when comparing monounsaturated dicarboxylic acids with conjugated diunsaturated counterparts. Additionally, new approach based on thiourea addition was developed showing complete conversion into MSA when using maleic acid. With cis,cis-muconic acid, thiourea works as an efficient catalyst for the isomerization into trans,trans-muconic acid opening a green alternative way to produce PET polymers.

TiO2 nanotubes (NTs), even if better photocatalysts than classical 3D particles, still suffer from recombination of electron-hole pairs. In a previous study, we found that adding graphene oxide (GO) to NTs help to improve the separation of photogenerated charges. However, the driving force for the transfer of electrons from TiO2 to GO was also found to come from the reduction of functional oxygen groups on graphene layers leading to instability under irradiation. Herein, an alternative is proposed through the addition of Cu NPs onto GO without contact with TiO2 NTs leading to a physical separation of charges with GO acting here only as a 2D support shuttle without inactivation. Comparison was performed between Cu/TiO2 NTs and Cu/(R)GO/NTs systems. On Cu/TiO2 NTs, results show a stabilization of Cu NPs at a +I oxidation state due to a strong interaction with TiO2 NTs leading to photocatalytic activity under visible light for the formic acid (FA) photodegradation. On Cu/(R)GO/TiO2 systems, strong activity was observed using non-reduced GO due to a physical separation of Cu NPs and TiO2 nanotubes confirming our assumption while reducing GO leads to a relocation of Cu NPs onto TiO2 NTs and loss of any beneficial effect due to GO. Application for H2 production will also be presented.

The influence of adding strontium to Cu-doped TiO2 nanotubes (TNT) on the photocatalytic performance of the resulting materials was herein studied considering changes in structural, textural, optical and morphological properties. Results emphasize that up to a Sr loading of 0.8 wt%, the addition of Sr results in in situ formation of Sr-O-Ti entities on the surface of Cu-doped TNT. A direct correlation was observed between the optimized formation of surface Sr-O-Ti entities and an enhanced photocatalytic response due to improved stabilization of photogenerated charges on 0.5Cu-TiNT resulting from the ferroelectric interference of neighbouring SrTiO3 entities. Finally, ferroelectric enhancement of the photocatalytic response induced by Sr was confirmed on similar systems containing graphene oxide.

The following study opens the way for the comprehension of the link between the nanoscale structure of Ni-containing POWs and their final HDS activity by showing that two parameters influence the propensity to form a promoted phase in NiW/Al2O3 catalysts: 1) the openness of Ni localization allowing to form a highly intrinsic active NiWS promoted phase and 2) the initial degree of contact between Ni and W influencing the sulfidation ability. A rationalized approach correlating localized configuration of Ni inside POW precursor and final HDS properties can be achieved offering new possibilities to use POMs for a variety of catalytic applications.

Addition of 2D conductive materials like graphene oxide (GO) or MXene sheets was herein demonstrated as an efficient way to separate physically electrons and holes in a composite photocatalytic system comprising TiO2 nanotubes on one side and Cu2O nanoparticles on the other side. Contrary to GO/TiO2 for which the GO overreduction under photocatalytic conditions leads to a complete loss of beneficial effect from GO, the use of two semiconductors Cu2O and TiO2 nanotubes separated physically by GO acting here as an electron-conductive 2D “shuttle” for electrons helps both to achieve a higher stability under photocatalytic conditions and a better separation of electrons and holes resulting in highly active photocatalytic systems.

The interest of ZrO2 as semiconductor for photocatalytic applications has increased because of its non-toxicity, chemical stability, low cost and environmental friendliness. Zirconia is a wide band-gap oxide with an Eg value of about 5 eV. Therefore, controlling its defect profile in order to induce energy states in the band gap is the only possibility to make it a photocatalyst active.In our work, ZrO2 photocatalysts were prepared using a ‘one-pot’ sol-gel method followed by drying under supercritical conditions of solvent and calcination at temperatures varying between 400°C and 800°C. Samples were characterized by means of nitrogen adsorption-desorption isotherms at 77K, X-Ray Diffraction (XRD), Thermal analysis (TG), Raman spectroscopy, (High Resolution) Transmission Electron Microscopy (HR)TEM, Diffuse Reflectance Spectroscopy (DRS), Photoluminescence spectroscopy (PL) and X-ray photoelectron spectroscopy (XPS). Results emphasize that the aerogel preparation allows the creation of lower band gap states making it active under UV irradiation. The photoactivity of ZrO2 samples for the formic acid degradation follow the order; ZrO2 400 > ZrO2 800 > ZrO2 700 > ZrO2 500 > ZrO2 600. This activity order depends on the surface area, the nature of the ZrO2 phase (tetragonal or monoclinic) and the tendency to lattice distortion for high temperature treated samples. In this respect, ZrO2 800, even if calcined at high temperature, presents the highest surface density of structural defects compensating the low surface area (21 m2/g). This aerogel method of preparation therefore allows obtaining highly active zirconia photocatalytic samples in a wide range of thermal post-treatment.

SSCI-VIDE+ECI2D+GBE; International audience; Sulfide NiMo/Al2O3 catalysts have been herein modified by adding different amounts of manganese as dopant (0.1-5.0 mol % as MnO) at several pHs of impregnation of the Ni and Mo precursors (5, 7 or 9) using a sol-gel approach to form directly Mn-Al2O3 supports. The resulting different sulfide solids were then evaluated in the HDS of dibenzothiophene and in the HDO of waste cooking oil. A direct influence of the oxidation state of Mn on the nature of the Mo oxide species is observed showing particularly that formation of Mn3+ should be avoided since forming NiMnO spinel. Optimum activity is reached at a loading of 1.0 mol % as MnO with Mn leading to weaker support interaction, higher sulfidation rate and higher active NiMo phase. Adding Mn in optimized conditions leads to turnover frequencies twice higher for NiMo catalysts and to a strong direct synergetic effect of Mn towards the NiMoS phase. Results were also acquired during the HDO of a waste cooking oil showing again a strong beneficial effect of Mn on the NiMo phase at a manganese content of 1.0 mol % with an activity 50% higher than using Mn-free catalysts. However, the pH of impregnation used also influence the final HDO mechanism. While if impregnation occurs at pH=9, the C-O bond rupture of free fatty acids in alkanes is favored, impregnation at pH=5 leads to a more favored transformation of triglycerides into free fatty acids. In terms of selectivity, if impregnation is performed at pH=9, decarboxylation processes can be completely suppressed. A strong synergetic effect of manganese on the HDS and HDO properties of NiMo/Al2O3 catalysts has then been observed showing that Mn is a very interesting dopant improving the hydrotreating properties of MoS2-based catalysts making these solids highly suitable for converting O-containing molecules into useful biofuels.

SSCI-VIDE+CARE:ECI2D+MHM:CGU:GBE; International audience; Reduced graphene oxide(RGO)/ TiO2 nanotubes composites were herein studied considering the effect of the GO reduction treatment and of its loading on textural, structural, electronic and optical properties of TiO2 nanotubes (NT). The resulting GO-NT composites were then evaluated for the photocatalytic degradation of formic acid in aquous solution and compared to their GO-free NT conterpart and to P25 used as references. Results emphasize a strong increase of the electron affinity and conductivity of the GO-NT composites particularly at low loading (1wt% GO) and if GO in only partially reduced (XPS). A remarkable gain in photocatalytic activity is then observed with a photocatalytic efficiency 3 and 1.9 times higher than for P25 and NT respectively.

SSCI-VIDE+ECI2D+GBE; National audience; Different options are generally envisaged to improve the HDS activity of nickel- or cobalt-promoted Mo(W)S2 catalysts including: 1) new methods for preparing promoted MoS2 or WS2 catalysts, 2) replacing the traditional -Al2O3 by new supports (ZrO2, TiO2, SBA-16, ..) or 3) modifying -Al2O3 by additives (P, F, B) or other oxides (TiO2-Al2O3 for ex.). Among the different oxides to be added to alumina, manganese oxide has been rarely considered since forming readily spinels when supported on Al2O3 or ZrO2. Chianelli et al. [1] have reported the periodic evolution in the HDS of DBT of different transition metal sulfides (TMS) showing that manganese sulfide has the lowest activity of the first TMS series. However, Ho et al. [2] emphasized in an industrial report that supported NiMnMo catalysts show high activity for the HDS of 4,6-DMDBT. Therefore, Mn seems to appear as poorly active if forming separate MnS phase but as an active promoter of NiMo catalysts. Interestingly, Mn also presents different oxidation degrees (mainly +2, +3, +4) and therefore it can markedly influence the Al2O3 support effect when preparing nickel-promoted catalysts. In the present study, NiMo/Al2O3 catalysts have been modified by adding different amounts of Mn (01-5.0 mol % as MnO) at several pHs of impregnation of the Ni and Mo precursors (5, 7, or 9) using either an impregnation technique for adding Mn to an existing Al2O3 support [3] or a sol-gel approach to form directly Mn-Al2O3 supports [4]. As-formed catalysts are characterized at each step of the preparation: after drying, after calcination and finally after sulfidation.Initial work was done by considering first the impregnation of a Mn precursor, manganese acetate on existing Al2O3 support. Both the pH of impregnation of the nickel nitrate and ammonium heptamolybdate precursors and the amount of Mn (1 or 5 mol%) strongly influence the dispersion of Mo and the final sulfide state. At a Mn content of 1.0 mol%, impregnation at pH 7 leads to well-dispersed molybdate species easily sulfided into a Ni-promoted MoS2 phase while impregnation at pH 9 favors more polymerized molybdate species and loss of Ni into NiMnO spinel. Increasing the Mn content to 5.0 mol% leads to the formation of MoO3 clusters and a severe loss of Ni into NiMnO spinels whatever the pH of impregnation. Optimized preparation of NiMo/Mn-Al2O3 leads to an HDS activity twice higher than without Mn. In a second step, manganese was added to the Al2O3 support using a sol-gel approach in a 0.1-5.0 mol% range. Impregnation of Ni and Mo precursors were carried out at pH 9 since leading to better final dispersion in this case. Results show a direct influence of the oxidation state of Mn on the nature of the Mo oxide species and their interaction with the Al2O3 support. A high proportion of Mn2+ (observed at low % of Mn:  0.5 mol %) leads to a weaker interaction with the support and to a very intrinsically active NiMo phase but in a lower proportion than without Mn. At too high amount in Mn ( 2.0 mol%), Mn3+ is mainly formed and reacts with Ni to form the NiMnO spinel phase leading to depleted HDS activity. Optimum activity is therefore reached at an intermediate loading of 1.0 mol % with weaker support interaction, higher sulfidation rate and highly active NiMo phase.Interestingly, whatever the method of preparation, adding Mn in optimized conditions leads to turnover frequencies twice higher for NiMo catalysts. Moreover, migration of Mn oxides to the surface of the support was observed during calcination of sol-gel prepared Mn-Al2O3 while sulfidation conditions leads to the formation of MnS showing a strong direct synergetic effect of Mn towards the NiMoS phase. Finally, results were also acquired during the HDO of a waste cooking oil showing once again a strong beneficial effect of Mn on the NiMo phase at a manganese content of 1.0 mol %. In conclusion, the present work shows undoubtedly for the first time a strong beneficial effect of manganese on the HDS and HDO properties of NiMo/Al2O3 catalysts confirming the presence of synergetic effects observed previously by Ho et al. [2] on NiMnMo systems.

SSCI-VIDE+ECI2D+GBE:DLA; International audience; In this work, 2 different carbon materials (carbon nanotubes – CNT; mesoporous carbon – MC) were used as the support of Ni2P and the obtained Ni2P/C catalysts were employed in guaiacol HDO reaction (300 °C and 30 bar (H2) in batch reactor). Samples were prepared in such a way to present the same number of Ni atoms per surface area of support (9.3% wt. for CNT and 29.3% wt. for MC) and were characterized by TPR, ICP-OES, DRX, HR-TEM, and CO chemisorption and desorption (CO TPD). Catalysts characterization data showed that each support has a different interaction force with the supported material and if affectsboth the reduction and the hydrotreating nature of Ni2P. 9.3Ni2P/CNT presented a lower reduction temperature and a more hydrogenating nature while 29.3Ni2P/MC had a higher reduction temperature and a more hydrotreating nature. Moreover, the addition of 1% Pd to each Ni2P/C precursor led to a lowering in Ni2P synthesis temperature and a suppression in guaiacol direct hydrogenation

SSCI-VIDE+ECI2D+LPI:GBE:PAF; National audience; Heterogeneous catalysis is ubiquitous in refining and chemical industries as it enables the formation of desirable products with minimal energy consumption. Since catalysis is a surface process, (metal) nanoparticles (NPs) often constitute the catalyst active phase, which is stabilized by a high-surface-area support and possibly promoted by a second metal.In this work, we have designed AuRh NPs supported on rutile TiO2 nanorods as model catalysts for several reactions involving hydrogen. A simple colloidal co-reduction method using NaBH4 and polyvinyl alcohol (PVA) generates 3 nm-sized bimetallic NPs.[1] However, unlike their Au and Rh counterparts, the AuRh colloids are instable in solution, as monitored in situ by dynamic light scattering and liquid-phase TEM.[2] Thus, once formed the NPs must be readily immobilized on the support in order to avoid their further growth. The AuRh/TiO2 catalysts present synergistic nanoalloying effects in all the investigated processes: stronger oxidation resistance of Rh in air,[1] stronger sulfidation resistance of Rh during tetralin hydrogenation in the presence of H2S,[1] higher selectivity to oxygen-free products in the hydrodeoxygenation of guaiacol,[3] and higher performance in the selective hydrogenation of cinnamaldehyde.[2] The structures of the colloids and their evolutions after immobilization and thermal treatments in a hydrogen atmosphere relevant to the catalytic reactions have been investigated by aberration-corrected STEM, EDX, UV-Vis, CO-FTIR, XPS and XRD. Heating the catalysts to 350 °C eliminates the PVA and leads to the segregation of Au and Rh within the particles: the NPs adopt a Janus configuration with the Rh side in contact with the titania support.[1,4] Further heating to 700 °C leads to NP coalescence and formation of “Au ball-Rh cup” ~10 nm-sized particles.[4] DFT calculations on unsupported and supported clusters show that the observed restructuring is driven by the strong Au-Rh segregation tendency, the lower surface energy of Au with respect to Rh, and the stronger Rh-TiO2 bonding with respect to Au-TiO2.[4–6]References[1]Z. Konuspayeva, P. Afanasiev, T.-S. Nguyen, L. Di Felice, F. Morfin, N.-T. Nguyen, J. Nelayah, C. Ricolleau, Z. Y. Li, J. Yuan, G. Berhault, L. Piccolo, Phys. Chem. Chem. Phys. 2015, 17, 28112–28120.[2]Z. Konuspayeva, G. Berhault, P. Afanasiev, T.-S. Nguyen, S. Giorgio, L. Piccolo, Submitted.[3]T.-S. Nguyen, D. Laurenti, P. Afanasiev, Z. Konuspayeva, L. Piccolo, J. Catal. 2016, 344, 136–140.[4]L. Piccolo, Z. Y. Li, I. Demiroglu, F. Moyon, Z. Konuspayeva, G. Berhault, P. Afanasiev, W. Lefebvre, J. Yuan, R. L. Johnston, Sci. Rep. 2016, 6, 35226.[5]I. Demiroglu, Z. Y. Li, L. Piccolo, R. L. Johnston, Catal. Sci. Technol. 2016, 6, 6916–6931.[6]I. Demiroglu, Z. Y. Li, L. Piccolo, R. L. Johnston, Comput. Theor. Chem. 2017, 1107, 142–151.

SSCI-VIDE+CARE:ECI2D+CGU:GBE; International audience; Due to its high electron mobility and conductivity, good transparency, large specific surface area and high chemical stability, graphene is regarded as a promising candidate to obtain graphene–TiO2 nanocomposites with lower electron-hole recombination and enhanced oxidative reactivity. During the past few years, graphene-based photocatalysts have been extensively studied and numerous research investigations have already been published. In 2015 more than 850 publications have been issued and there are already 500 publications this year. Graphene oxide was first synthesized using a modified Hummers’ method. TiO2 nanotubes were obtained through 1) an alkaline hydrothermal reaction with commercial P25 as starting material using concentrated NaOH (11.25M) at 130°C for 20 h followed by 2) a calcination step at 400 °C for 2 h in air. Graphene/TiO2 nanocomposites were then elaborated by wet impregnation of graphene oxide (GO) on TiO2 nanotubes. The H2 reduction of the resulting GO-TiO2 nanotubes at two different temperatures (200 and 300°C) leads to reduced graphene oxide (RGO)-TiO2 composites. Structure and morphology of RGO/TiO2 composites were determined by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM).The photocatalytic properties of these nanocomposites were then evaluated by comparison to P25 and pure TiO2 nanotubes under visible light and under UV/A light irradiation using formic acid as model pollutant. The impact of the RGO content and of the degree of reduction of RGO were particularly investigated. If properly prepared by reduction at 200°C, RGO/TiO2 composites can exhibit higher photocatalytic activity than pure TiO2 thanks to a better separation of photogenerated charges. However, a fully reduced RGO at 300°C has surprisingly no effect in photocatalysis. The role of surface properties of reduced graphene oxide arising from different reduction degrees and its interaction with titanium dioxide will be discussed to explain this behavior.