At 60–150 °C and 15–35 bar H2, two model reactions of levulinic acid (LA), hydrogenation and reductive amination with cyclohexylamine, were explored in a multiphase system composed of an aqueous ...solution of reactants, a hydrocarbon, and commercial 5 % Ru/C as a heterogeneous catalyst. By tuning the relative volume of the immiscible water/hydrocarbon phases and the concentration of the aqueous solution, a quantitative conversion of LA was achieved with formation of γ‐valerolactone or N‐(cyclohexylmethyl)pyrrolidone in >95 and 88 % selectivity, respectively. Additionally, the catalyst could be segregated in the hydrocarbon phase and recycled in an effective semi‐continuous protocol. Under such conditions, formic acid additive affected the reactivity of LA through a competitive adsorption on the catalyst surface. This effect was crucial to improve selectivity for the reductive amination process. The comparison of 5 % Ru/C with a series of carbon supports demonstrated that the segregation phenomenon in the hydrocarbon phase, never previously reported, was pH‐dependent and effective for samples displaying a moderate surface acidity.
It's a phase: Two reactions of levulinic acid (LA), hydrogenation and reductive amination with cyclohexylamine, are explored in a multiphase system. By tuning the relative volume of the immiscible water/hydrocarbon phases and the concentration of the aqueous solution, quantitative conversion of LA can be achieved with formation of γ‐valerolactone (GVL) or N‐(cyclohexylmethyl)pyrrolidone in >95 and 88 % selectivity, respectively.
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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.
The transformation of 1-butanol into either butenes or maleic anhydride was carried out both with and without oxygen, using V/P/O catalysts. With vanadyl pyrophosphate prepared by coprecipitation, at ...temperature lower than 240 °C and without oxygen, selectivity to butenes was higher than 90%, but a slow deactivation took place. At temperature higher than 300 °C and in the presence of air, maleic and phthalic anhydrides were the prevailing products, with selectivity of 60% and 14%, respectively. Catalytic performance was affected by crystallinity and acidity. αI-VOPO4 showed a poor performance in the absence of air, with a quick deactivation due to coke accumulation; but it displayed an excellent selectivity to butenes (close to 98%) at temperatures lower than 320 °C in the presence of air, with stable performance. At temperature higher than 360 °C, α I-VOPO4 was reduced to vanadyl pyrophosphate and catalyzed the direct oxidation of 1-butanol into maleic anhydride, but with 35% selectivity.
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•(VO)2P2O7 catalyses 1-butanol oxidation to maleic anhydride with 60% yield.•The maximum yield to maleic anhydride decreases on increasing 1-butanol inlet concentration.•Both (VO)2P2O7 and αI-VOPO4 catalyse 1-butanol dehydration to butenes but deactivate.•In the presence of O2, αI-VOPO4 catalyses 1-butanol dehydration with 98% yield to butenes.•The catalytic performance of αI-VOPO4 in the presence of O2 is also very stable, with no deactivation.
In the search for a more sustainable future, the biorefinery approach can help by replacing fossil feedstocks with renewable sources. When biorefineries meet circular economy, the production of new ...platform chemicals from residual lignocellulosic biomasses becomes the joint goal. In this frame, the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) has gained increasing interest, with the aim of producing intermediates for the chemical industry. Enabling technologies, particularly microwaves, have proven to be an efficient tool for process intensification, as they can reduce the reaction time and the formation of byproducts. In this work, MW-assisted processes with heterogeneous Ru-based catalysts were exploited for the reduction of LA both with H2 and 2-PrOH as reductants. Different metal loadings and supports were considered, such as a commercial active carbon (Ru/AC) and titania (Ru/TiO2). Among the different hydrogen sources, molecular hydrogen led to milder reaction conditions, enabling the complete flash conversion of LA in only 2 min without any solvent. In terms of catalytic activity, AC showed slightly better performances as support. In addition, flow MW-assisted processes were tested using a multiphase reactor, reaching complete conversion in only 8 min in an open loop system for both the tested catalysts. Performance enhancement and material reuse support the suitability of flow approach, paving the way for a sustainable and scalable process.
In this study, alkali metal-doped sepiolite based catalysts were developed for the up-grading of ethanol through the Guerbet reaction mechanism. The catalysts were prepared by wetness impregnation ...with aqueous solution containing alkali metal precursors salts over calcined sepiolite, and finally activated at 500ºC in air. The catalysts have been characterized by XRD, SEM-EDS, TGA-DSC, N2-adsorption. In addition, TPD-CO2 and TPD-NH3 were used to determine the acid and basic characteristics of catalysts. The catalysts were tested into a quartz continuous gas-flow reaction system working at atmospheric pressure to investigate the effects of metal loading (wt%), the nature of the alkali metals and of the main reaction parameters (e.g., reaction temperature, weight hourly space velocity), on the production of n-butanol starting from ethanol. The highest yield (18%) was obtained at 400 ºC with the catalyst consisting in sepiolite, calcined at 500ºC, impregnated with 7 wt% of Cs. This study proves that ad hoc modified natural sepiolites with alkali metals are effective catalysts for the Guerbet upgrading of ethanol.
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•Alkali-metal modified sepiolite was used as catalyst for the Guerbet conversion of ethanol.•Alkaline metals modified sepiolite acid-base properties changing products distribution.•The catalysts containing ca0.06 mmolMe/gsep of alkali metals were the more selective to n-butanol.•The Cs-doped sepiolite containing 7 wt% of metal led to the highest yield of n-butanol.
Authors must supply a graphical abstract at the time the paper is first submitted. The abstract should summarize the contents of the paper in a concise, pictorial form designed to capture the ...attention of a wide readership and for compilation of databases. Authors must provide images that clearly represent the work described in the paper. The content of the graphical abstract will be typeset and should be kept within an area of 5 cm by 17 cm. Authors must supply the graphic separately as an electronic file.
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•Salicylic alcohol easily converts into o-cresol when feed with methanol onto MgO.•Salicylic alcohol can also disproportionate into o-cresol and salicylic aldehyde.•Both transformations involve the metastable o-methide intermediate.•A à la Mannich Meerwein-Ponndorf-Verley reaction transforms o-methide into o-cresol.•DFT calculations indicate a low barrier for all steps in the cascade.
The gas-phase alkylation of phenol with methanol, a reaction triggered for the production of o-cresol and 2,6-xylenol, is catalysed by MgO-based catalysts. Despite the industrial use of this process, the mechanism of the reaction – which is commonly believed to be based on a classical electrophilic attack of activated methanol onto the aromatic ring – is far from being fully understood. In some previous studies we reported that the reaction intermediate is salicylic alcohol, which is formed by the reaction between the adsorbed phenolate and formaldehyde, the latter being formed in-situ by methanol dehydrogenation. Here we elucidate the following steps of the reaction mechanism, by combining reactivity experiments and DFT calculation, with MgO as a model catalyst. It was found that salicylic alcohol dehydrates into quinone methide, which is then reduced via H-transfer by methanol to o-cresol. Moreover, a dehydrogenation/hydrogenation equilibrium is established between salicylic alcohol and salicylic aldehyde. The methide can also react with methanol to form 2-methoxymethylphenol, which may decompose into o-cresol, thus providing an alternative pathway for the formation of the alkylated compound.
This work reports a 1 mol scale catalytic process to synthesize adipic acid directly from cyclohexane in solvent‐free conditions using air as oxidant. Catalysts based on vanadium phosphorus oxides ...were prepared, characterized and tested. They showed good activity and remarkably high selectivity to adipic acid in comparison to other already known heterogeneous catalysts. The use of solvent‐free conditions permits the easy separation of the product from the reactant mixture, which is very important from the industrial point of view. The process can be used at industrial scale for sustainable adipic acid synthesis.
Getting greener with a new one‐pot sustainable and scalable synthesis of adipic acid via solvent‐free air oxidation of cyclohexane.
Bi-functional VPP catalyst for both ethanol ammoxidation to acetonitrile and β-picoline oxidation to nicotinic acid: investigation of reaction mechanisms and the role of acidic and redox sites for ...the optimization of the selectivity to target products.
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•Vanadyl pyrophosphate VPP is a bi-functional catalyst used in oxidation reactions.•Selective oxidations may require a multifunctional approach.•Acetonitrile is synthesized by ethanol ammoxidation.•Nicotinic acid is synthesized by β-picoline oxidation.•VPP features may be either favourable or detrimental depending on reaction mechanism.
This study investigates the catalytic activity of vanadyl pyrophosphate (VPP) for both gas-phase ethanol ammoxidation to acetonitrile and β-picoline oxidation to nicotinic acid. Both reactions may be alternative processes to the industrial technologies used to produce these two chemicals. The reaction networks were investigated, also by feeding possible intermediates; in-situ DRIFT spectroscopy was used to monitor the interaction of ethanol and ammonia with the catalyst. VPP bi-functionality features played an important role in the two reactions; specifically, acidity was detrimental either because it catalyzed undesired reactions, such as ethanol dehydration to ethylene during ethanol ammoxidation, or because it caused a strong interaction with reactants – especially those containing N atoms, ammonia and β-picoline – thus giving rise to some surface saturation phenomena which inhibited the consecutive reactions leading to the final desired compounds, acetonitrile and nicotinic acid. The co-feeding of steam helped product desorption, thus enhancing selectivity in β-picoline oxidation.
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