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The glycerol partial oxidation reaction over Pt/Al2O3 catalysts was studied under basic (NaOH/GLY molar ratio 4) and base‐free conditions (NaOH/GLY molar ratio 0). Catalysts with small (2.95 nm) and large particle sizes (260.83 nm) were synthesized according to the use of different reducing agents, formaldehyde or sodium borohydride, and hydrazine, respectively. These different Pt particle sizes lead to a dramatic change in terms of activity, irrespective of the applied conditions. The biggest particles (i.e., 260 nm) seem to generate overoxidation products leading to a decrease in the carbon balance (to ~80%) while the smallest particles exhibit the highest initial glycerol transformation rate (i.e., ~10,000 mol h−1 molPt−1 under basic conditions at 60°C and ~2000 mol h−1 molPt−1 in the absence of a base at 100°C). In terms of selectivities, the main products are different as a function of the initial reaction conditions. For base‐free conditions, the two main products are glyceraldehyde and glyceric acid with a sum of selectivities always larger than 80%. Under basic conditions, the major product is glyceric acid while no trace of glyceraldehyde is detected. [ABSTRACT FROM AUTHOR]

This review paper presents the current state of the art on maleic acid synthesis from biomass-derived chemicals over homogeneous or heterogeneous catalysts. It is based on the most recent publications on the topic, which are discussed in details with respect to the observed catalytic performances. The recent developments and the technical drawbacks in the gas and the liquid phases are also reported. In addition, recent results on the mechanistic aspect are discussed giving insights into the probable reaction mechanisms depending on the starting molecule (furan, furfural and 5-hydroxymethylfurfural). [ABSTRACT FROM AUTHOR]

In this paper, we report for the first time a one-pot reaction enabling total transformation of lactic acid to acetic acid over a Mo-V-Nb mixed oxide catalyst having an optimal atomic ratio 19:5:1. The mechanism of the reaction consists in two parallel ways leading to acetic acid: (i) oxi-dehydrogenation of lactic acid to pyruvic acid followed by decarboxylation and (ii) decarbonylation of lactic acid to acetaldehyde followed by oxidation. In the operating conditions we used, the catalyst is very active (total conversion of lactic acid) and selective towards acetic acid (100% selectivity). A 100% yield into acetic acid is hence obtained. [ABSTRACT FROM AUTHOR]

When using heteropolycompounds in the selective oxidation of isobutane to methacrolein and methacrylic acid, both the keeping of the primary structure (Keggin units) and the presence of acidic sites are necessary to obtain the desired products. The structural evolution of supported (NH4)3HPMo11VO40 (APMV) catalysts under preliminary thermal oxidizing and reducing treatments was investigated. Various techniques, such as TGA/DTG (Thermo-Gravimetric Analysis/Derivative Thermo-Gravimetry), H2-TPR (Temperature Programed Reduction), in situ XRD (X-Ray Diffraction) and XPS (X-ray Photoelectron Spectroscopy), were applied. It was clearly evidenced that the thermal stability and the reducibility of the Keggin units are improved by supporting 40% APMV active phase on Cs3PMo12O40 (CPM). The partial degradation of APMV takes place depending on temperature and reaction conditions. The decomposition of ammonium cations (releasing NH3) leads to the formation of vacancies favoring cationic exchanges between vanadium coming from the active phase and cesium coming from the support. In addition, the vanadium expelled from the Keggin structure is further reduced to V4+, species, which contributes (with Mo5+) to activate isobutane. The increase in reducibility of the supported catalyst is assumed to improve the catalytic performance in comparison with those of unsupported APMV. [ABSTRACT FROM AUTHOR]

Due to its three hydroxyl groups, glycerol is a potential starting material for various high value fine chemicals such as dihydroxyacetone, tartronic acid and mesoxalic acid. The corresponding oxidation reactions are catalysed by various metals such as palladium, platinum, bismuth or gold. Nevertheless, the selectivity not only depends on the type of the active phase, but is also influenced by numerous parameters such as the metal particles size, the pore size of the support and the pH of the reaction medium. This review not only describes the recent developments in the field of research for new catalysts but also spotlights the role of the reaction conditions as well as the possible transport limitations in this tri-phasic system. Furthermore, an economical analysis of some processes is given, which shows that this is realistic to envision sustainable production of, e.g., dihydroxyacetone. [ABSTRACT FROM AUTHOR]

We report here the highest productivity ever observed in the direct conversion of methanol into 1,1-dimethoxymethane (ca.4.6 kgDMMh−1kgcat−1at 553 K), this result being obtained over an FeMo catalyst. This catalyst is industrially used to selectively convert methanol into formaldehyde but has never before been applied to the present reaction. Placing this FeMo catalyst under unusual reaction conditions, i.e., using a feed rich in methanol, completely changed its behaviour in terms of selectivity: the massive production of 1,1-dimethoxymethane, instead of formaldehyde, was observed. [ABSTRACT FROM AUTHOR]

The first part of this paper is a short review of the [sup 35]S radioactive tracer methods developed in recent years. Then, the experimental results obtained so far on Mo/Al[sub 2]O[sub 3] catalysts are compared with computer simulation results recently claimed in order to elucidate the coordinatively unsaturated site (CUS) creation/replenishment/ regeneration mechanism over MoS[sub 2] crystallites. The computer simulations allowed us to pre-select thermodynamically acceptable mechanisms among a set of suggested ones. Then, by comparison of the calculated activation energies with the [sup 35]S experiments results we could further validate the most probable mechanism. This mechanism involved the dissociative adsorption of an H[sub 2] molecule on the metallic edge of a MoS[sub 2] crystallite surface with further creation of a CUS by release of one H[sub 2]S molecule in the gas phase. Both laboratory and computer simulated experiments permitted to calculate the activation energy for the H2S liberation reaction. In both cases, this energy was about 10- 12 kcal/mol, confirming the accuracy of the proposed mechanism. Moreover, the calculated activation energy of the rate-limiting step for the creation of one CUS by the proposed mechanism was about 23 kcal/mol, which was also in good agreement with the experimental activation energy of the dibenzothiophene (DBT) hydrodesulphurisation (HDS) reaction (typically about 20- 22 kcal/mol). This correlation indicated that the DBT HDS reaction rate might be intrinsically governed by the CUS formation/replenishment process, i.e. that the vacancy formation process is a crucial parameter in the global HDS reaction mechanism. Nevertheless, in the case of the 4,6-dimethyl DBT (4,6-DMDBT) HDS reaction, the experimental activation energy is higher (approx. 30 kcal/mol), confirming that external parameters induced by the 4,6-DMDBT-specific properties themselves are likely to play an important role in the reaction process, in addition to the ones intrinsic to the catalytic phase. [ABSTRACT FROM AUTHOR]

[Display omitted] • The active phase of calcium-based catalysts for glycerol polymerization was investigated. • Ca-glycerolate was identified as being the in situ formed solid active phase. • A mechanism is proposed to explain the in situ formation of calcium glycerolate. • A mechanism is proposed for the polymerization of glycerol catalyzed by Ca-glycerolate. Ca-based catalysts are of strong interest for glycerol polymerization reaction due to their high catalytic performances, their wide availability and the absence of any toxicity. In the present study, we investigated the active phase of CaO, Ca(OH) 2 , CaCO 3 and calcium diglyceroxide used as catalysts for this reaction. The solids were analyzed by XRD, solid-state 13C-NMR and TGA-DSC. XRD evidenced the presence of calcium glycerolate in the spent catalysts when CaO, Ca(OH) 2 and calcium diglyceroxide were used as starting materials. This was corroborated by the TGA-DSC results. Further, the SS NMR results showed that the as-formed calcium glycerolate is a mixture of linear Ca(C 3 H 7 O 3) and cyclic-branched Ca(C 3 H 6 O 3). Moreover, the recycled catalyst issued, e.g. , from CaO was more efficient that the initial catalyst with a glycerol conversion of 47 % (vs. 22 % initially for CaO) and a 70 % (vs. 55 %) selectivity to polyglycerols higher than tetraglycerol at 245 °C after 4 h in the presence of 3.5 mol.% of catalyst. As the main outcome, we have shown that Ca-glycerolate is the actual solid active phase, which is formed in situ from CaO and Ca(OH) 2 playing the role of catalyst precursors. A mechanism involving the dissolution of CaO and Ca(OH) 2 , the formation of Ca-glycerolate and its precipitation followed by crystallization, supported by characterization studies, is proposed. [ABSTRACT FROM AUTHOR]

Hydrotalcite-type Mg 6− x Cu x Al 2 (OH) 16 CO 3 ·4H 2 O solids (with x = 0, 1, 3, 5) were synthesized as precursors of mixed oxides obtained by subsequent calcination. Two families of samples (synthesized by coprecipitation with and without sonication) were thoroughly characterized by XRD, TG–TDA, H 2 -TPR, NMR, SEM and N 2 -physisorption. Their reactivity towards ethanol was further assessed. Sonication enabled considerably reducing the preparation duration. MgO and Al 2 O 3 were formed upon calcination of the hydrotalcites under air at 400 °C, while copper-enriched phases ( e.g. CuO, spinel like structure…) were formed from the solids with higher Cu contents. Magnesium atoms substitution by copper atoms in the hydrotalcite structure was evidenced for the first time in this kind of materials using high-resolution solid state NMR. Indeed, a very unusual but remarkable “Fermi contact effect” was responsible for specific features observed on the NMR spectra. Further, partial substitution of magnesium by copper led to an increase in specific surface area, with the formation of particles of a smaller size. Copper addition considerably enhanced the dehydrogenation properties of the solids at low temperature (∼250 °C), with a higher reactivity towards ethanol, and higher selectivities to acetaldehyde. [ABSTRACT FROM AUTHOR]

Highlights: [•] Linear relationship for reducibility and Ni/Nb atomic ratio. [•] Specific productivity correlates to Ni/Nb ratio. [•] Low reaction temperature inhibits decarboxylation to acetaldehyde. [ABSTRACT FROM AUTHOR]