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A thorough investigation of two novel hybrid materials, namely, (2,2'-Hbpy)

Understanding the origin and mechanism of the formation of methane from CO2 is important because its formation would be related also to the origin of life on Earth. Both processes seem indissociable. To form methane, CO2 is reduced to CO by hydrogen. The reduction of CO2 might also correspond to the first step allowing the transition from CO2 to organic molecules and then to the first block of life on Earth. In our experiments, we used a natural rock (chromitite) collected from an open mine. The major mineral phase naturally occurring in this sample is magnesiochromite (85–95%) with subordinate serpentine and chlorite (including Cr-bearing chlorite). For the first time, we provide an indisputable experimental proof of the (abiotic) formation of methane on a natural chromitite rock, without any previous pretreatment, in the presence of gaseous CO2 and H2 under low temperature and atmospheric pressure, which are the expected atmospheric environmental conditions that existed on Earth’s crust when methane was formed in Nature. Methane is formed by a heterogeneous catalytic hydrogenation process at low temperature and atmospheric pressure. These results suggest that this transformation also goes on in other natural rocks existing on the surface of Earth, probably with higher efficacity. This means that natural rocks on Earth may contain catalytic sites and play the role of catalysts. The catalytic activity can be assigned to the presence of crystallographic phases and their surface composition, which promote the surface adsorption and transformation of gaseous reactants. The results demonstrate that a natural rock can activate, via heterogeneous catalysis, a very stable molecule such as CO2. The literature demonstrates that N2 can be also activated by the same process suggesting a coherent pathway to explain the formation of organic molecules and amino acids in Nature. In situ catalytic CO2 hydrogenation in natural cavities should be considered as a realistic alternative method for CO2 mitigation. It is supported that catalysis would play an important role in the formation of the first block of life on Earth.

Imparting hydrophobicity to solid acid catalysts is critical to regulating their performances by allowing the creation of a less polar environment and improved partitioning of the reactants. Here we present different approaches for the preparation of silica-based catalysts comprising sulfonic acid (-SO3H) sites and hydrophobic decyl (-C10) chains by either simultaneous or sequential postfunctionalization of an azide-functionalized mesoporous silica platform. This set of hybrid bifunctional catalysts is compared in the model esterification of octanol with acetic acid, and the influence of the preparation methods together with the resulting site spatial distribution is discussed. In parallel, we show that pairing the two functional groups affords a maximum synergistic effect compared to more traditional mixed catalysts with random distributions of acid and hydrophobic functions.

Intermetallic compounds (IMCs) have diverse electronic and geometrical properties to offer. However, the synthesis of intermetallic nanoparticles is not always easy; developing new methodologies th...

We investigated how secondary additives for tableting vanadium-aluminummixed-oxides affect the mechanical resistance, surface chemistry, and catalytic performance inpropane oxidation of tablets based on this material. The secondary additives were magnesium oxide, silica, boron nitride, sepiolite, and zinc oxide while graphite was used as the primaryshaping agent. Our results showed that the changes in mechanical strength and porosity weredirectly related to the softness and ductility of the secondary additive. Overall, we learned thatwhen manufacturing catalyst tablets, there is a compromise between mechanical strength andloss in mesoporosity and surface area. On the other hand, the components of the formulatedtablets did not show signs of establishing a chemical interaction with the vanadium-aluminummixed oxide. Therefore, the effects of the additives that we found on the catalytic performancewere ascribed to the fact that the selected secondary additives may act as co-catalysts duringpropane oxidation. In this sense, boron nitride and sepiolite were best for promoting both thereactivity of the catalytic formulations while showing a better productivity of propene. The datawas interpreted suggesting that the promotion effect may be due to the combination of a redoxmechanism over the vanadium-aluminum mixed oxide phase and to a surface radical mechanismoccurring over the active moieties of these secondary additives.

Heteropolyacids (HPAs) are metal–oxygen clusters that are nowadays widely used in acid catalysis. Indeed, as they possess a very strong Bronsted acidity, approaching the superacid region, they generally allow performing reactions at lower temperatures than conventional catalysts. In the present paper, we use in situ/operando Raman spectroscopy to optimize the catalytic performance of H3PW12O40—the strongest Keggin-type HPA—in the low temperature (150 °C) gas phase dehydration of methanol to dimethyl ether (DME), which is one of the most promising renewable fuels for the future. Precisely, we demonstrate that the ability of methanol to displace the HPA’s crystallization water located in-between the Keggin units—and thus to reach the acidic protons—decreases with increasing temperature. Actually, we show that one and the same flow of methanol scarcely displaces the crystallization water at reaction temperature 150 °C, whereas, at a temperature as low as 25 °C, it succeeds to completely dehydrate the HPA. By...

Integrating enzymatic and heterogeneous catalysis can pave the way to new and performing cascade chemical processes. In this perspective, the preparation of bifunctional structures combining both an active inorganic catalyst and an enzyme is a key. However, such combinations are not straightforward, for example in the case of zeolite catalysts for which enzyme immobilization would be restricted to the external surface. We overcame this challenge by developing a new kind of hybrid catalysts based on hollow zeolite microspheres. The method leverages on the aerosol-assisted assembly of TS-1 nanocrystals to form hollow zeolite microspheres with tailored hierarchical texture and high epoxidation activity in water. The latter spheres were subsequently loaded with glucose oxidase enzymes which were then cross-linked to secure their entrapment. This controlled design allows to combine all the decisive features of the zeolite with a high enzyme loading. A chemo-enzymatic reaction is demonstrated, where the structured zeolite microsphere is used both as a nest for the enzyme and as an efficient inorganic heterogeneous catalyst. The enzyme ensures the in situ production of H2O2 subsequently utilized by the zeolite for the epoxidation of allylic alcohol. We anticipate our method will open up new perspectives in the field of hybrid catalysis. Starting from various catalytic nano-building blocks, hollow microspheres with open entry ways could be prepared using the aerosol process and could be used as vessels for enzymes or even multi-enzymatic systems, thereby giving access to a multitude of new heterogeneous chemo-biocatalysts.

© 2016 American Chemical Society. Amino acids have huge potential as platform chemicals in the biobased industry. Pd-catalyzed decarboxylation is a very promising route for the valorization of these natural compounds derived from protein waste or fermentation. We report that the highly abundant and nonessential amino acid L-proline is very reactive in the Pd-catalyzed decarboxylation. Full conversions are obtained with Pd/C and different Pd/MeOx catalysts; this allowed the identification of the different side reactions and the mapping of the reaction network. Due to the high reactivity of pyrrolidine, the selectivity for pyrrolidine was initially low. By carefully modifying Pd/ZrO2 with Pb in a controlled mannervia two incipient wetness impregnation stepsthe selectivity increased remarkably. Finally, a thorough investigation of the reaction parameters resulted in an increased activity of this modified catalyst and an even further enhanced selectivity under a low H2 pressure of 4 bar at 235 °C in water. This results in a very selective and sustainable production route for the highly interesting pyrrolidine. ispartof: ACS Catalysis vol:6 issue:11 pages:7303-7310 status: published

Hybridization of polyoxometalates (POMs) via the formation of an organic-inorganic association constitutes a new route to develop a heterogeneous POM catalyst with tunable functionality imparted through supramolecular assembly. Herein, we report on strategies to obtain tunable well-defined supramolecular architectures of an organic-inorganic heterogeneous hybrid catalyst formed by the association of a hydrophobically substituted polyampholyte copolymer (poly N, N-diallyl-N-hexylamine-alt-maleic acid) and phosphotungstic acid (H3PW12O40) POMs. The self-assembling property of the initial polyampholyte copolymer matrix is modulated by controlling the pH of the hybridization solution. When deposited on a mica surface, isolated, long and extended polymer chains are formed under basic conditions (pH 7.9), while globular or coiled structures are formed under acidic conditions (pH 2). The supramolecular assembly of the POM-polymer hybrid is found to be directed by the type and quantities of charges present on the polyampholyte copolymer, which themselves depend on the pH conditions. The hypothesis is that the Keggin type [PW12O40](3-) anions, which have a size of ~1 nm, electrostatically bind to the positive charge sites of the polymer backbone. The hybrid material stabilized at pH 5.3 consists of POM-decorated polymer chains. Statistical analysis of distances between pairs of POM entities show narrow density distributions, suggesting that POM entities are attached to the polymer chains with a high level of order. Conversely, under acidic conditions (pH 2), the hybrid shows the formation of a core-shell type of structure. The strategies reported here, to tune the supramolecular assembly of organic-inorganic hybrid materials, are highly valuable for the design and a more rational utilization of POM heterogeneous catalysts in several chemical transformations.

The influence of using graphite (G) as a shaping agent for bismuth molybdate (BiMo) catalysts was analyzed. Shaping was done by tableting, with addition of different loadings of graphite (0, 0.5, 1, 3, 5, 7, and 10 wt %). The use of graphite during the pressing of bismuth molybdate powders eases tableting because of the lubricating properties of the former. Furthermore, the compressive strength of BiMo-G tablets is higher than that of pure BiMo. Concerning the physicochemical properties of BiMo-G, XRD and XPS showed that graphite changes neither the relative distribution of the crystallographic phases of bismuth molybdate nor the oxidation state of bismuth and molybdenum in the tableted powders. Consequently, the shaped BiMo-G catalysts displayed similar, or slightly better, performances in the selective oxidation of propylene to acrolein. TGA analysis of samples of BiMo-G confirmed the thermal stability of the catalysts under oxidative conditions. Graphite was observed to experience crystallization into the hexagonal 2H phase during the catalytic tests. The results reported herein demonstrate that graphite is an effective shaping agent for bismuth molybdate powders.

Supported palladium nanoparticles with different diameters were synthesized by the water-in-oil microemulsion method using TiO2 as support. The materials were characterized by different physicochemical methods such as X-ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and H2 chemisorption. The results confirmed that the microemulsion method permits well-dispersed palladium nanoparticles to be obtained. The size of the nanoparticles was estimated by XPS intensity ratios using models proposed by Davis and by Kerkhof and Moulijn and compared with XRD, TEM, and H2 chemisorption analysis. Good accordance of the two models was found for very small Pd particles (smaller than 3 nm). The Kerkhof−Moulijn model seemed to be very sensitive to the small variation in the particle size distribution. The Davis model seemed to be more adequate to determine the size of small and biggest particles as compared with ...

The combination of X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) allowed a clear identification and quantification of nitrogenous species incorporated upon nitridation in three different zeolites one Y zeolite (Si/Al ratio of 2.6) and two ultrastable Y zeolites (Si/Al ratios of 13 and 37). Both the amount and the chemical nature of incorporated nitrogen species were controlled by the nitridation temperature. Namely, an increase of the temperature induces an increase of the nitrogen content and the appearance of nitrogenous species in the following order of increasing temperature: NH4+, adsorbed NH3, −NH2, >NH, and >N−. Based on these spectroscopic results, a mechanism of nitridation in function of temperature was proposed, this mechanism being independent of the properties of the parent zeolite. We evidenced here that the replacement of hydroxyls groups located in the microposity of the zeolite by nitrogen species was effective which can be...

MoO3-based heterogeneous catalysts prepared by dispersion of Mo-oxide species on preformed supports are highly regarded candidates for industrial light olefin metathesis. An original approach for the elaboration of Mo-based catalysts is presented here. Mesoporous ternary Si/Al/Mo mixed oxides are prepared in one step by a nonhydrolytic sol−gel route in nonaqueous medium. Taking advantage of the migration of Mo species during the calcination, effective catalysts with very good textures and highly dispersed surface Mo species are obtained, as shown by XRD, XPS, and TOF-SIMS characterization. The presence of isolated Mo species is evidenced and these species are proposed to be the precursors to the active species in the metathesis of propene. These new materials compare well with catalysts prepared by classical wet impregnation of silica−alumina supports with ammonium heptamolybdate, eventually outperforming them at high Mo loading.

The catalytic behavior of “Mo8O23”, a sample composed mainly of Mo8O23, was investigated in the oxidation of isobutene to methacrolein and compared to that of fully oxidized MoO3. “Mo8O23” was initially more active and selective than MoO3 but exhibited a deactivation with time-on-stream. Conversely, when used in a physical mixture with α-Sb2O4, the catalytic performance of “Mo8O23” progressively increased. In both cases, the bulk of “Mo8O23” was reoxidized to MoO3 after the catalytic reaction. However, after being catalytically tested alone, the surface of “Mo8O23” was more reduced compared to that of the fresh material, whereas it was more oxidized, with a stoichiometry likely corresponding to Mo18O52, when reacted in the presence of α-Sb2O4. The results indicate that the shear structures in the bulk of the molybdenum suboxides are not necessarily the origin of the high levels of catalytic performance observed for molybdenum oxide-containing oxidation catalysts. The results also show that the key to main...

The catalytic behavior of three well-defined Re−Sb−O compounds, SbOReO4·2H2O, Sb4Re2O13, and SbRe2O6, was investigated in the selective oxidation of isobutylene to methacrolein at 673 K. We have directed our attention to the correlation between the catalytic performance of the compounds and their structural and superficial changes undergone under the reaction conditions. For the purpose, the effects of the pretreatment conditions for the catalysts and of the isobutylene/oxygen ratio in the reaction atmosphere on the performance of the catalysts were explored. Each Re−Sb−O compound was characterized before and after the pretreatments and the catalytic reactions by X-ray diffraction, X-ray photoelectron spectrocopy, scanning electron microscopy, and in situ laser Raman microscopy. Among the three Re−Sb−O compounds, a novel SbRe2O6 compound exhibited the highest catalytic performance for selective oxidation. The compound underwent a progressive decomposition to Sb4Re2O13 and Re2O7 when pretreated or reacted at 673 K in the presence of oxygen. The decomposition was favored under more oxidative conditions, and a close parallelism between the catalytic performance and the quantity of Re2O7 stabilized at the surface of the catalyst was observed. On the other hand, the activities of pure Re2O7 and a new Sb4Re2O13 compound were very low when each of them was used as a catalyst independently. The results indicate that the reactivity of SbRe2O6 is likely due to the presence of Re2O7 at the surface, benefitting from a cooperation with Sb4Re2O13. The model also accounts for the performance of SbOReO4·2H2O. SbOReO4·2H2O decomposed to Sb4Re2O13 and Re2O7 regardless of the reaction atmosphere, which explains a higher activity of SbOReO4·2H2O than Sb4Re2O13. However, the amount of Re2O7 stabilized at the surface was smaller than that for the case of SbRe2O6, which leads to lower performances of SbOReO4·2H2O than those of SbRe2O6.

We investigated the possible role of binary oxides associating Sb and Mo in the synergetic effects between physically mixed MoO and alpha-Sb2O4 in the selective oxidation of isobutene to methacrolein. The catalytic behavior of three Sb-Mo-O phases-Sb2MoO6 on one hand, a mixture of Sb2Mo10O31 and Sb4Mo10O31 on the other hand-was investigated. The samples were characterized using X-ray diffraction (XRD), confocal laser Raman microscopy, specific area measurements, and scanning electron microscopy. Additional in situ high-temperature XRD was also performed. At similar conversions of isobutene, the selectivities to methacrolein for the Sb-Mo-O phases were always lower than those of mixtures of MoO3 with alpha-Sb2O4 with the same atomic compositions. A second result was that the three Sb-Mo-O phases were unstable in the conditions of reaction and tended to decompose to simple molybdenum and antimony oxides. An improvement of the catalytic performances of the Sb-Mo-O catalysts occurred in parallel to their decomposition. Some apparent cooperation effects were observed for mechanical mixtures of the Sb-Mo-O phases with MoO3 or alpha-Sb2O4. These effects are actually related to the decomposition of the Sb-Mo-O phases and are due to the cooperation between MoO3 and alpha-Sb2O4 formed at their surface. The spontaneous decomposition of the Sb-Mo-O phases shows that these phases cannot form in operandi (during the catalytic reaction) starting from the simple oxides. Consequently, this shows that they cannot be the real most performant phases in the mixtures of MoO3 with alpha-Sb2O4 and hence that they cannot be at the origin of the synergism between the simple oxides.