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•The MPV reduction of aromatic aldehydes with methanol was catalyzed by MgO.•The mechanism of the reaction was elucidated by means of DFT calculations.•The mechanism was fully ...consistent with results of catalytic experiments.•The reaction was of general validity for the reduction of aromatic aldehydes.•Furfural was reduced to furfuryl alcohol with 100% yield.
The previously unexplored use of methanol as a H-transfer agent for the Meerwein–Ponndorf–Verley reduction of aromatic aldehydes and aryl ketones is described. Furfural, 5-hydroxymethylfurfural, benzaldehyde, and acetophenone were selectively reduced to the corresponding alcohols in mild conditions. The reaction mechanism was elucidated by means of reactivity tests and DFT calculations. It was found to include the highly efficient H-transfer with the formation of formaldehyde, which further reacted with excess methanol to generate the adsorbed hemiacetal. In turn, the latter reduced carbonyl, with the formation of methylformate, which further decomposed into CO, CH4, and CO2. Compared to the alcohols typically used for carbonyl reductions, methanol showed the advantage of producing gaseous components as the only co-products, which are easily separated from the reaction medium. In the case of furfural, a 100% yield to furfuryl alcohol was obtained, using the high-surface area MgO as the easily recoverable and reusable catalyst.
Au-Based catalysts supported on nanosized NiO (nNiO) were synthesized and were investigated in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) under base-free ...conditions using molecular oxygen as the oxidant, at 90 °C. By choosing the optimal composition of Au-Pd nanoparticles (6 : 4 Au/Pd atomic ratio), we report an efficient and stable nNiO-supported Au-Pd alloy catalyst. The presence of nNiO and Au-Pd nanoparticles on the surface was essential to achieve high conversion (95%) and high activity, high yield of FDCA (70%) and good level of stability. Significant synergistic effects were observed between Au and Pd in the alloy as well as on NiO. The present work provides mechanistic insights into the alloying effect and support-metal interaction in terms of understanding better the role of the alloy and support in affecting specific reaction pathways. Finally, the outcome of this knowledge can help develop efficient catalysts for the aerobic oxidation of biomass-derived molecules under base-free conditions in water and under mild reaction conditions.
AuPd nanoparticles supported on NiO exhibit high activity and stability in the base free oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA).
In this study, 5-hydroxymethylfurfural (HMF) oxidation was carried out via both the catalytic and the photocatalytic approach. Special attention was devoted to the preparation of the TiO₂-based ...catalysts, since this oxide has been widely used for catalytic and photocatalytic application in alcohol oxidation reactions. Thus, in the catalytic process, the colloidal heterocoagulation of very stable sols, followed by the spray-freeze-drying (SFD) approach, was successfully applied for the preparation of nanostructured porous TiO₂-SiO₂ mixed-oxides with high surface areas. The versatility of the process made it possible to encapsulate Pt particles and use this material in the liquid-phase oxidation of HMF. The photocatalytic activity of a commercial titania and a homemade oxide prepared with the microemulsion technique was then compared. The influence of gold, base addition, and oxygen content on product distribution in the photocatalytic process was evaluated.
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•Pt-based carbonyl clusters are suitable precursor for small Pt NPs.•Cluster derived materials are effective in base-free HMF oxidation.•Sn addition enhances catalyst activity and ...stability.
In the present work, Pt and Pt/Sn nanoparticles (NPs), synthesized from carbonyl cluster precursors were deposited on TiO2 and the resulting materials were tested as catalysts in selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). The work was mainly focused on the study of the formation of bimetallic or mixed oxide-metal nanoparticles on TiO2 starting with Pt/Sn carbonyl clusters and on the structure-activity relationship in the reaction of HMF oxidation in base-free conditions. The developed synthesis procedure allowed to obtain very small mono and bimetallic particles characterized by a narrow particle size distribution. Promising results in base-free FDCA production have been achieved using the prepared samples. In particular, the introduction of Sn in an equimolar amount with Pt improved the catalyst activity as well as its time stability upon operation, demonstrating that the modification of Pt electronic configuration by Sn is a key factor for the mastering of functional performances.
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► Preparation of Au and Au–Cu TiO2 supported catalysts from pre-formed nanoparticles. ► Cu presence allowed a remarkable increase of the catalytic behavior. ► Stability of Au–Cu ...catalysts was much higher than that shown by the Au material.
5-Hydroxymethyl-2-furfural (HMF) oxidation to furandicarboxylic acid (FDCA) was performed under mild reaction conditions using TiO2-supported Au and Au–Cu catalysts synthesized from pre-formed nanoparticles of different composition. Catalysts were characterized by BET, XRD and XPS. The Au3Cu1/TiO2 catalyst exhibited the best catalytic performance for FDCA yield. Moreover, after reaction, bimetallic Au–Cu catalysts with high gold content can be recovered by filtration and reused without significant loss of activity and selectivity; whereas, the monometallic gold materials are not stable.
This work deals with the development of a green and versatile synthesis of stable mono- and bi-metallic colloids by means of microwave heating and exploiting ecofriendly reagents: water as the ...solvent, glucose as a mild and non-toxic reducer and polyvinylpirrolidone (PVP) as the chelating agent. Particle size-control, total reaction yield and long-term stability of colloids were achieved with this method of preparation. All of the materials were tested as effective catalysts in the reduction of p-nitrophenol in the presence of NaBH₄ as the probe reaction. A synergistic positive effect of the bimetallic phase was assessed for Au/Cu and Pd/Au alloy nanoparticles, the latter showing the highest catalytic performance. Moreover, monoand bi-metallic colloids were used to prepare TiO₂- and CeO₂-supported catalysts for the liquid phase oxidation of 5-hydroxymethylfufural (HMF) to 2,5-furandicarboxylic acid (FDCA). The use of Au/Cu and Au/Pd bimetallic catalysts led to an increase in FDCA selectivity. Finally, preformed Pd/Cu nanoparticles were incorporated into the structure of MCM-41-silica. The resulting Pd/Cu MCM-41 catalysts were tested in the hydrodechlorination of CF₃OCFClCF₂Cl to CF₃OCF=CF₂. The effect of Cu on the hydrogenating properties of Pd was demonstrated.
A series of gold catalysts supported on pure CeO
2
, ZrO
2
, and two different Ce-Zr mixed oxides have been prepared and tested in the 5-hydroxymethyl-2-furfural oxidation reaction. All catalysts ...show high catalytic activity (100% conversion) and important selectivity (27–41%) to the desired product i.e., 2,5-furandicarboxylic acid at low base concentration. Products selectivity changes with the support nature as expected, however, the observed trend cannot be related neither to gold particle size, nor to catalyst reducibility and oxygen mobility. An important relation between the FDCA selectivity and the support textural properties is observed, conducing to the general requirement for optimal pore size for this reaction.
•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.
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•Furfural can be reduced to furfuryl alcohol using methanol as H-transfer and alkaline earth metal oxides catalysts.•The reduction occurs in the liquid-phase under mild conditions ...with high yield.•The specific activity of catalysts follows the rank SrO > CaO > MgO.•The activity rank is parallel to the basic strength rank of catalysts.•The stronger basicity leads to different mechanisms for methanol activation.
DRIFT characterization and DFT calculation were carried out to clarify the previously unexplored use of methanol as a H-transfer agent for the liquid-phase Meerwein-Ponndorf-Verley reduction of biomass-derived furfural using alkaline earth oxide catalysts (MgO, CaO, SrO). Methanol adsorption mechanism has been studied in detail and the energy correlated to the process has been theoretically calculated for each of the prepared catalyst to investigate the relative performances of the three basic oxides. Although, the higher-surface-area MgO displayed an exceptionally high activity for the H-transfer process at low temperatures, CaO and SrO were found to be the catalysts with the highest specific productivity per unit surface area and unit basic site. The different specific productivities of the three catalysts was explained by DRIFT with different adsorption mode selectivities (3 different modes for MgO versus only 1 for CaO and SrO, with the production of only the active methoxide), which may indicate a different methanol activation with regard to the H-transfer toward the carbonyl moiety of FAL. Furthermore, higher SrO than CaO productivity can be explained by the different basicity, which in turn leads to differences in the main methanol activation pathways. DFT calculations make it possible to gain further insight into the role of the basic strength on methanol activation and H-transfer reaction suggesting the increased ability of activating the alcohol via formation of the methoxide ion being the key factor in modulating the catalyst activity rather than the polarization of the aldehydic carbonyl group due to the coordination onto the M3C site.
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