Fine chemicals are highly pure substances that are commercially produced by chemical reactions for highly specialized applications. In most cases, however, these reactions involve stoichiometric and ...highly polluting steps. A possible solution is the development of processes using enzymatic, homogeneous or heterogeneous catalysts. In this review, selected examples of clean heterogeneously-catalyzed reactions applied to the synthesis of fine chemicals are reported for the purpose of highlighting the growing need for more sustainable industrial processes, i.e., processes that produce minimal waste and avoid as much as possible the use of toxic and/or hazardous reagents and solvents. A thorough knowledge of catalyst properties, reaction conditions and interactions with the reacting substrate are essential for optimizing the synthesis, thus making it possible to move on from laboratory to industrial production.
Clean biogas, produced by anaerobic digestion of biomasses or organic wastes, is one of the most promising substitutes for natural gas. After its purification, it can be valorized through different ...reforming processes that convert CH4 and CO2 into synthesis gas (a mixture of CO and H2). However, these processes have many issues related to the harsh conditions of reaction used, the high carbon formation rate and the remarkable endothermicity of the reforming reactions. In this context, the use of the appropriate catalyst is of paramount importance to avoid deactivation, to deal with heat issues and mild reaction conditions and to attain an exploitable syngas composition. The development of a catalyst with high activity and stability can be achieved using different active phases, catalytic supports, promoters, preparation methods and catalyst configurations. In this paper, a review of the recent findings in biogas reforming is presented. The different elements that compose the catalytic system are systematically reviewed with particular attention on the new findings that allow to obtain catalysts with high activity, stability, and resistance towards carbon formation.
The combined steam/dry reforming of clean biogas (CH4/CO2 = 50/50 v/v) represents an innovative way to produce synthesis gas (CO + H2) using renewable feeds, avoiding to deplete the fossil resources ...and increase CO2 pollution. The reaction was carried out to optimize the reaction conditions for the production of a syngas with a H2/CO ratio suitable for the production of methanol or fuels without any further upgrading. Ni-Rh/Mg/Al/O catalysts obtained from hydrotalcite-type precursors showed high performances in terms of clean biogas conversion due to the formation of very active and resistant Ni-Rh bimetallic nanoparticles. Through the utilization of a {Ni10Rh(CO)19}{(CH3CH2)4N}3 cluster as a precursor of the active particles, it was possible to promote the Ni-Rh interaction and thus obtain low metal loading catalysts composed by highly dispersed bimetallic nanoparticles supported on the MgO, MgAl2O4 matrix. The optimization of the catalytic formulation improved the size and the distribution of the active sites, leading to a better catalyst activity and stability, with low carbon deposition with time-on-stream.
The hydrodeoxygenation of furfural (FU) was investigated over Fe-containing MgO catalysts, on a continuous gas flow reactor, using methanol as a hydrogen donor. Catalysts were prepared either by ...coprecipitation or impregnation methods, with different Fe/Mg atomic ratios. The main product was 2-methylfuran (MFU), an important highly added value chemical, up to 92% selectivity. The catalyst design helped our understanding of the impact of acid/base properties and the nature of iron species in terms of catalytic performance. In particular, the addition of iron on the surface of the basic oxide led to (i) the increase of Lewis acid sites, (ii) the increase of the dehydrogenation capacity of the presented catalytic system, and (iii) to the significant enhancement of the FU conversion to MFU. FTIR studies, using methanol as the chosen probe molecule, indicated that, at the low temperature regime, the process follows the typical hydrogen transfer reduction, but at the high temperature regime, methanol dehydrogenation and methanol disproportionation were both presented, whereas iron oxide promoted methanol transfer. FTIR studies were performed using furfural and furfuryl alcohol as probe molecules. These studies indicated that furfuryl alcohol activation is the rate-determining step for methyl furan formation. Our experimental results clearly demonstrate that the nature of iron oxide is critical in the efficient hydrodeoxygenation of furfural to methyl furan and provides insights toward the rational design of catalysts toward C–O bonds’ hydrodeoxygenation in the production of fuel components.
In recent years, the upgrading of lignocellulose bio-oils from fast-pyrolysis by means of ketonization has emerged as a frontier research domain to produce a new generation of biofuels. Propionic ...acid (PA) ketonization is extensively investigated as a model reaction over metal oxides, but the activity of other materials, such as metal phosphates, is mostly unknown. Therefore, PA ketonization was preliminarily investigated in the gas phase over both phosphates and oxides of Al, Zr, and La. Their catalytic activity was correlated to the physicochemical properties of the materials characterized by means of XRD, XRF, BET N2 porosimetry, and CO2- and NH3-TPD. Noteworthy, monoclinic ZrO2 proved to be the most promising candidate for the target reaction, leading to a 3-pentanone productivity as high as 5.6 h−1 in the optimized conditions. This value is higher than most of those reported for the same reaction in both the academic and patent literature.
•Pd–Au composition in alloys is crucial for FDCA formation.•Au and Pd–Au alloys are able to oxidize HMFCA to FDCA.•Cannizzaro reaction is involved in FDCA synthesis with some of the studied systems.
...This work deals with the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in water using supported Pd–Au nanoparticles. The active phase composition was shown to be crucial for FDCA formation. Indeed, both Au and Pd monometallic nanoparticles formed 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) under the studied conditions; however, with Pd nanoparticles HMFCA was not further transformed, while Au and bimetallic Pd–Au systems both catalysed its oxidation to FDCA.
The thermal treatment of Pd–Au catalysts considerably modified their catalytic activity, because Pd atoms migrated and concentrated onto the outer part of bimetallic nanoparticles. The resulting active phase morphology showed a different reaction path for FDCA formation compared to the untreated catalyst, with an important contribution of the Cannizzaro reaction. PVP-protected Pd–Au nanoparticles with different structures (either alloy or core-shell morphology) were synthesized and their reactivity tested in order to confirm the presence of different mechanisms for HMF oxidation, depending on whether the active phase preferentially exposes either Pd or Au atoms.
Ammonia borane-based transfer hydrogenation mechanisms on copper nanoparticles (CuNPs) are identified and assessed by isotope labeling and Kohn–Sham density functional methods, using the ...hydrogenation of styrene to ethylbenzene under ambient conditions as the model reaction. The key role of protonic solvents in permitting ammonia borane decomposition is confirmed. Different dehydrogenation pathways are evidenced for the N–H and B–H bonds: while the metal surface always acts as an intermediary in the hydrogen transfer from the B–H bond to the organic substrate, the N–H bond can directly hydrogenate the most negatively charged carbon atom of the unsaturated bond. The styrene to ethylbenzene reaction is here proved to have a >99% conversion with 100% selectivity at ambient conditions, using methanol and pure water as the solvents. The CuNPs are obtained in situ by reduction of the copper source, SION-X (Cu2(BO)(OH)2(OH)3), by ammonia borane. The catalytic properties of these CuNPs are stable for at least 5 cycles without the need for reduction steps and upon their exposure to air in between subsequent cycles. This is due to ammonia borane’s ability to act simultaneously as the hydrogen source for the reaction and as the reducing agent of copper. Ammonia borane shows then a significant advantage over other hydrogen sources for transfer hydrogenation in combination with CuNPs, eliminating both the catalyst preparation and activation steps and reducing the complexity and operational cost of the process.
The reaction of NaCo(CO)4 with M(IPr)Cl (M = Cu, Ag, and Au; IPr = C3N2H2(C6H3 iPr2)2) affords the neutral heterometallic complexes Co(CO)4{M(IPr)} (M = Cu, 1; Ag, 2; and Au, 3). Formation of 2 ...is accompanied by traces of Ag(IPr)2Ag{Co(CO)4}2 (4). The reaction of NaCo(CO)4 with M(IMes)Cl (IMes = C3N2H2(C6H2Me3)2) results in mixtures of Co(CO)4{M(IMes)} (M = Cu, 5; Ag, 6; and Au, 7) and M(IMes)2M{Co(CO)4}2 (M = Cu, 8; Ag, 9; and Au, 10). In the cases of Cu and Ag, ionic complexes 8 and 9 are the major products, whereas neutral species 7 is the major product for Au. All species 1–10 have been spectroscopically characterized by IR and 1H and 13C{1H} NMR spectroscopy. Moreover, the molecular structures of 2, 3, and 8 have been determined by single-crystal X-ray diffraction (SC-XRD). Bimetallic Co–M–NHC complexes 1–3 and 7–9 have been tested as catalysts for the dehydrogenation of ammonia–borane (AB) in THF as solvent, and their performances compared to Fe(CO)4{M(NHC)}2, M(NHC)Cl, and NaCo(CO)4. DFT computations have been performed to provide information on the structure, IR spectroscopy, and the thermodynamics of Co–M carbonyl clusters.
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