Maria J. Climent

Conversion of biomass platform molecules into fuel additives and liquid hydrocarbon fuels

In this work some relevant processes for the preparation of liquid hydrocarbon fuels and fuel additives from cellulose, hemicellulose and triglycerides derived platform molecules are discussed. Thus, it is shown that a series of platform molecules such as levulinic acid, furans, fatty acids and polyols can be converted into a variety of fuel additives through catalytic transformations that include reduction, esterification, etherification, and acetalization reactions. Moreover, we will show that liquid hydrocarbon fuels can be obtained by combining oxygen removal processes (e.g. dehydration, hydrogenolysis, hydrogenation, decarbonylation/descarboxylation etc.) with the adjustment of the molecular weight via C–C coupling reactions (e.g. aldol condensation, hydroxyalkylation, oligomerization, ketonization) of the reactive platform molecules.

Converting carbohydrates to bulk chemicals and fine chemicals over heterogeneous catalysts

In this Critical Review, we discuss how carbohydrates can be transformed into a variety of chemicals through heterogeneous catalysis. We focus particularly on oxidation, reduction and dehydration of hexoses, as well as one-pot reactions of di- and polysaccharides. Most of the reactions involve heterogeneous catalysts, although some interesting homogeneously catalyzed processes are also included.

Homogeneous and heterogeneous catalysts for multicomponent reactions

Organic synthesis performed through multicomponent reactions is an attractive area of research in organic chemistry. Multicomponent reactions involve more than two starting reagents that couple in an exclusive ordered mode under the same reaction conditions to form a single product which contains the essential parts of the starting materials. Multicomponent reactions are powerful tools in modern drug discovery processes, because they are an important source of molecular diversity, allowing rapid, automated and high throughput generation of organic compounds. This review aims to illustrate progress in a large variety of catalyzed multicomponent reactions performed with acid, base and metal heterogeneous and homogeneous catalysts. Within each type of multicomponent approach, relevant products that can be obtained and their interest for industrial applications are presented.

Designing the adequate base solid catalyst with Lewis or Bronsted basic sites or with acid-base pairs

Abstract A series of heterogeneous catalysts with Lewis and Bronsted basic sites, and acid–base bifunctional pairs has been used in order to perform organic reactions. By changing the chemical composition and activation conditions it is possible to have predominantly Lewis or Bronsted base catalysts within a large range of well defined basicities. This allows to select the most appropriate catalyst for a specific reaction. Thus, MgO, calcined hydrotalcites, rehydrated hydrotalcites and grafted quaternary organic ammonium hydroxides on MCM-41, have been used as catalysts in Knoevenagel condensation, aldolization and Michael additions. Catalysts containing mild acid–base pairs such as those existing in amorphous aluminophosphates (ALPOs) allow to achieve high selectivities with still very reasonable activities.

Aldol Condensations on Solid Catalysts: A Cooperative Effect between Weak Acid and Base Sites

An amorphous aluminophosphate (ALPO) catalyst containing weak acid and base centers can carry out the aldol condensation of heptanal with benzaldehyde at much higher rates and selectivities than conventional solid acid (amorphous or crystalline aluminosilicates) or base catalysts (MgO, hydrotalcites, KF/Al2O3, nitrurated ALPO). With the weak acid-base catalyst, the reaction occurs through a bifunctional acid-base mechanism that involves the activation of benzaldehyde, by protonation-polarization of the carbonyl group on the acid sites, and the attack of the enolate heptanal intermediate generated on the basic sites. With this type of bifunctional acid-base catalyst, compounds with weak basicities are already able to undergo the reaction with a much higher selectivity than those obtained on stronger acid or base catalysts.

Design of a solid catalyst for the synthesis of a molecule with blossom orange scent

The synthesis of 2-methyl-2-naphthyl-4-methyl-1,3-dioxolane, a compound with blossom orange scent, has been successfully carried out by acetalization reaction between methyl naphthyl ketone and propylene glycol using different acid solid catalysts. The size and polarity of reactants, intermediates and product determine the strong influence of the textural properties of the catalyst (crystal size, acidity and adsorption properties) with the large pore tridirectional zeolites (Y and Beta) being the most active. It has been found that the hydrophobicity of the catalyst can be more determinant than the number of active sites present in the catalyst. The results show an optimum in activity for Si/Al ratios in Y and Beta zeolites that correspond to 35 and 100, respectively.

Synthesis of pseudoionones by acid and base solid catalysts

The preparation of pseudoionones by aldol condensation reaction between citral and acetone have been carried out in the presence of acid (HY and beta zeolites), an acid–base (amorphous aluminophosphate) and basic catalysts such as an aluminophosphate oxynitride, MgO and different activated hydrotalcites. The results showed that acid or acid–base catalysts were not successful for performing in one pot the preparation of ionones. MgO and calcined hydrotalcites showed excellent activity and selectivity to pseudoionones, with calcined hydrotalcite more selective than MgO. Moreover, the rate of reaction can be improved by activating the hydrotalcite through rehydration. This activation can be successfully done by simply adding the optimum amount of water to the calcined hydrotalcite before reaction. The inhibiting effect of the concentration citral on the catalytic activity of rehydrated hydrotalcites that has been reported to occur at 273 K can be avoided by working at a reaction temperature of 333 K.

Formation and hydrolysis of acetals catalysed by acid Faujasites

Abstract Dimethyl and cyclic ethylene acetals can be obtained in the presence of HY zeolites by treatment of the corresponding carbonyl compound with trimethyl orthoformate at room temperature or with ethylene glycol using a Dean-Stark system, respectively. The relationship between the percentage of Na + exchange of the zeolite and the initial reaction rates shows that only strong acid sites are active in the dimethyl acetal formation. Similarly, regeneration of the parent carbonyl compound was accomplished by simply heating suspensions of the appropriate acetal in carbon tetrachloride with HY catalysts. Evidence supporting the implication in the hydrolysis of the adsorbed water remaining on the zeolite after thermal activation was drawn from the results obtained using a dried solvent and a highly dealuminated zeolite. The possibility of using hydrolytic cleavage of acetals as a chemical activation procedure for zeolites was tested.

Mono‐ and Multisite Solid Catalysts in Cascade Reactions for Chemical Process Intensification

Catscade reactions: Heterogeneous catalysis can enable sustainability by carrying out multistep reactions in one step. It is shown that single- and multisite solid catalysts can be designed to carry out cascade reactions for the synthesis of fine chemicals.

From Biomass to Chemicals: Synthesis of Precursors of Biodegradable Surfactants from 5‐Hydroxymethylfurfural

The selective acetalization of 5-hydroxymethylfurfural (HMF) with long-chain alkyl alcohols has been performed to obtain precursors of molecules with surfactant properties. If direct acetalization of HMF with n-octanol is performed in the presence of strong acids (homogeneous and heterogeneous catalysts), an increase in etherification versus acetalization occurs. Beta zeolite catalyzes both reactions. However, if the acidity of a zeolite (Beta) was controlled by partial exchange of H(+) with Na(+), the dioctyl acetal of HMF can be achieved in 95% yield by transacetalization. It is possible to achieve a high yield in a very short reaction time through a two-step one-pot process, which includes the synthesis of the dimethyl acetal of HMF followed by transacetalization with n-octanol. The one-pot process could be extended to other alcohols that contain 6-12 carbon atoms to afford 87-98% yield of the corresponding dialkyl acetal with a selectivity higher than 96%. The optimized catalyst with an adequate Na content (1.5NaBeta) could be recycled without loss of activity or selectivity.