Fabrizio Cavani

On the Chemistry of Ethanol on Basic Oxides: Revising Mechanisms and Intermediates in the Lebedev and Guerbet reactions

A common way to convert ethanol into chemicals is by upgrading it over oxide catalysts with basic features; this method makes it possible to obtain important chemicals such as 1-butanol (Guerbet reaction) and 1,3-butadiene (Lebedev reaction). Despite their long history in chemistry, the details of the close inter-relationship of these reactions have yet to be discussed properly. Our present study focuses on reactivity tests, inu2005situ diffuse reflectance infrared Fourier transform spectroscopy, MS analysis, and theoretical modeling. We used MgO as a reference catalyst with pure basic features to explore ethanol conversion from its very early stages. Based on the obtained results, we formulate a new mechanistic theory able to explain not only our results but also most of the scientific literature on Lebedev and Guerbet chemistry. This provides a rational description of the intermediates shared by the two reaction pathways as well as an innovative perspective on the catalyst requirements to direct the reaction pathway toward 1-butanol or butadiene.

Butadiene from biomass, a life cycle perspective to address sustainability in the chemical industry

In the past few decades, innovative approaches such as Green Chemistry and Green Engineering have come out in order to set the basic principles for a more sustainable chemical industry. However, researchers also need a more scientific and quantitative tool to address the sustainability behind the application of those principles. Therefore, a multi-criteria approach based on life cycle thinking was proposed to investigate the production of 1,3-butadiene. Five indicators were selected to address sustainability: the Cumulative Energy Demand, the carbon footprint, the water depletion, a midpoint-oriented analysis method and an economic index. The use of renewable feedstock was evaluated in comparison with the traditional fossil-based route from naphtha. Two alternative pathways which use bio-ethanol were considered – the Lebedev and Ostromisslensky processes – evaluating the possibility to locate the plant in three different regions (the EU, Brazil and the US). Detailed analysis reveals how the use of bio-based feedstock leads to a significantly lower consumption of fossil sources, despite the higher exploitation of renewable resources leading to larger water withdrawals. Moreover, the assessment of the global warming potential reveals how bio-routes are far from able to be considered carbon-neutral. In addition, the ReCiPe single-score was used, showing greater sustainability of the Lebedev process compared with the traditional way. On the other hand, the two-step pathways (Ostromisslensky) result in the worst scores. An economic evaluation was also applied. The index reveals how the direct conversion into 1,3-butadiene seems more suitable than the two-step method, particularly in the case of production in the US.

An analysis of the chemical, physical and reactivity features of MgO–SiO2 catalysts for butadiene synthesis with the Lebedev process

New insights into the transformation of ethanol to butadiene over MgO–SiO2 catalysts, prepared by means of the sol–gel technique, have been gained via characterization, catalytic tests, and in situ infrared diffuse reflectance spectroscopy. Catalysts with low Si-content, i.e., with a Mg/Si atomic ratio in the range between 9 and 15, gave superior butadiene yields, because of the proper combination of strong basic sites, required for ethanol activation, and a moderate number of medium-strength acid sites, needed for the dehydration of intermediately formed alkenols to butadiene. A model of the medium-strength, Lewis-type acid sites, consisting of Mg2+ cations with neighbouring Si4+ atoms, has been proposed; these sites are converted into Bronsted sites in the presence of water, a co-product of the multistep transformation of ethanol into C4 molecules.

Glycerol as feedstock in the synthesis of chemicals: a life cycle analysis for acrolein production

Glycerol is an important bio-platform molecule, potentially usable for the synthesis of various chemicals and fuel additives, the synthesis of acrolein by dehydration being one of the most studied reactions. Through the application of the life cycle assessment (LCA) methodology we investigated the production of acrolein from glycerol, by comparing two alternative scenarios in which glycerol is obtained as a co-product either in triglyceride trans-esterification to FAME or in hydrolysis to fatty acids. Our results show how the main impacts are not related to the energy involved in the two processes. In fact, the use of dedicated crops as a source of triglycerides in the biodiesel production entailed higher impacts in terms of land exploitation. On the other hand, beef tallow was assumed as a starting raw material in the production of fatty acids, and this involved some significant impacts associated with animal rearing. At the same time, however, avoiding the use of dedicated biomass ensured a lower global impact (in terms of single scores). Lastly, in order to validate the model created, a sensitivity analysis using the Monte Carlo method was performed. The two routes from glycerol were also compared with the classical chemical route where acrolein is produced by propylene oxidation.

Multielement crystalline and pseudocrystalline oxides as efficient catalysts for the direct transformation of glycerol into acrylic acid

Glycerol surplus from biodiesel synthesis still represents a major problem in the biofuel production chain. Meanwhile, those in the acrylic acid market are looking for new processes that are able to offer viable alternatives to propylene-based production. Therefore, acrylic acid synthesis from glycerol could be an effective solution to both issues. Among the viable routes, one-pot synthesis theoretically represents the most efficient process, but it is also highly challenging from the catalyst design standpoint. A new class of complex W--Mo--V mixed-oxide catalysts, which are strongly related to the hexagonal tungsten bronze structure, able to directly convert glycerol into acrylic acid with yields of up to 51u2009% are reported.

Towards an improved process for hydrogen production: the chemical-loop reforming of ethanol

M-modified ferrospinels with the formula M0.6Fe2.4Oy (M = Co, Mn or Co/Mn) were employed as ionic oxygen and electron carrier materials for an alternative sustainable route to produce hydrogen via chemical-loop reforming of ethanol. The new materials were tested in terms of both redox properties and catalytic activity to generate hydrogen by oxidation with steam, after a reductive step carried out with ethanol. In addition, the research includes in situ DRIFTS and in situ XPS studies that allowed the extraction of information at the molecular level and following surface changes within the reduction/re-oxidation processes during ethanol chemical-loop reforming. It was found that Co(II)-incorporation in spinels effectively improves decomposition/oxidation of ethanol, however a greater amount of coke is accumulated. On the other hand, addition of Mn(II) into the system helps to significantly reduce the amount of coke and hence to avoid fast deactivation of the material. Thus, the behavior of Co0.3Mn0.3Fe2.4Oy was shown to be the most promising one, as this material forms less coke during the reduction step, and consequently less COx is generated during the re-oxidation step with water, nevertheless a high hydrogen yield is maintained.

A New Process for Maleic Anhydride Synthesis from a Renewable Building Block: The Gas‐Phase Oxidehydration of Bio‐1‐butanol

We investigated the synthesis of maleic anhydride by oxidehydration of a bio-alcohol, 1-butanol, as a possible alternative to the classical process of n-butane oxidation. A vanadyl pyrophosphate catalyst was used to explore the one-pot reaction, which involved two sequential steps: 1)u20051-butanol dehydration to 1-butene, catalysed by acid sites, and 2)u2005the oxidation of butenes to maleic anhydride, catalysed by redox sites. A non-negligible amount of phthalic anhydride was also formed. The effect of different experimental parameters was investigated with chemically sourced 1-butanol, and the results were then confirmed by using genuinely bio-sourced 1-butanol. In the case of bio-1-butanol, however, the purity of the product remarkably affected the yield of maleic anhydride. It was found that the reaction mechanism includes the oxidation of butenes to crotonaldehyde and the oxidation of the latter to either furan or maleic acid, both of which are transformed to produce maleic anhydride.

A study of surface and structural changes of magnetite cycling material during chemical looping for hydrogen production from bio-ethanol

Magnetite samples were synthesized and studied as the cycling material of a chemical loop process for hydrogen production from ethanol and water used as reducing and oxidizing species, respectively. Surface and structural changes during the process were characterized by various techniques such as X-ray diffraction, X-ray photoelectron, and Mossbauer spectroscopy in order to evidence the real cycling process and understand the cause of the material deactivation so that it can be suppressed or minimized for an industrial application. We found that the complete recovery of the initial cycling material was possible, but that a slow accumulation of coke took place over time under cycling conditions. Indeed, this deposited coke corresponds to only a part of the coke formed, since water makes partial re-oxidation possible. A third step to burn the coke left over by the air will thus have to be periodically added for a sustainable industrial process, unless a cycling material and/or certain conditions capable of either totally preventing the formation of coke or leading to the formation of coke that is not oxidized by water are found.

Ethanol gas-phase ammoxidation to acetonitrile: the reactivity of supported vanadium oxide catalysts

New insights on the gas-phase ammoxidation of ethanol to acetonitrile over supported vanadia catalysts were obtained by means of reactivity experiments (in ethanol ammoxidation and oxidation) as well as in situ Raman and DRIFT spectroscopy. It was found that the rate-determining step during the redox process depends on the support type. In the case of V2O5/ZrO2, the V oxidation state under reaction conditions is closer to V5+, whereas with V2O5/TiO2, the reduction of V5+ is faster than the re-oxidation of the corresponding reduced V species by O2; thus, the V oxidation state under steady state conditions is lower than for V2O5/ZrO2. In the latter catalyst, the more oxidized V species is responsible for ammonia activation and reaction with the intermediate acetaldehyde, leading in the end to a better acetonitrile yield than with V2O5/TiO2. It was also found that V2O5/ZrO2 is more selective to acetaldehyde than V2O5/TiO2. With the former catalyst, ethanol is able to reduce V2O5 only to a limited extent. Conversely, V2O5/TiO2 is readily reduced by ethanol but this reduced V species is responsible for an unselective oxidation of the alcohol, giving more CO and CO2.

Synthesis of Terephthalic Acid by p‐Cymene Oxidation using Oxygen: Toward a More Sustainable Production of Bio‐Polyethylene Terephthalate

The synthesis of terephthalic acid from biomass remains an unsolved challenge. In this study, we conducted the selective oxidation of p-cymene (synthesized from biodegradable terpenes, limonene, or eucalyptol) into terephthalic acid over a Mn-Fe mixed-oxide heterogeneous catalyst. The impact of various process parameters (oxidant, temperature, reaction time, catalyst amount, oxygen pressure) on the selectivity to terephthalic acid was evaluated, and some mechanistic aspects were elucidated. An unprecedented synthesis of biobased terephthalic acid (51u2009% yield) in the presence of O2 is reported.