A. Corma’s research while affiliated with Spanish National Research Council and other places

This review explores linear cascade reactions by combining chemo-, photo- and biocatalysts for organic synthesis and strategies to overcome incompatibility issues.

Photocatalytic processes are regarded as a sustainable and environmental-friendly way to attenuate mankind’s strong dependence on fossil fuels, which is the main responsable for high pollution levels in our planet. Metal microporous chalcogenides, due to band structure, bandgap value and highly reduced charge carrier’s residence time within the crystal lattice, are probably more suitable for photocatalysis than metal oxides, the most used photocatalysts. This review, besides updating the existing literature, intends to expand on the possibilities of these materials. This review is divided into two parts. The first part will focus on materials science, more specifically on presenting the main chalcogenide clusters and materials that are made up by such clusters: structures analogous to zeolites and ultimately hybrid materials. To finish the section, three alternatives of synthesis that have been investigated recently are presented. The second part will focus on photocatalysis, in particular the application of these materials for the production of solar fuels by H2O photodecomposition and CO2 photoreduction, and the degradation of organic pollutants. This review concludes by presenting the challenges of these materials and future perspectives for their synthesis and use as photocatalysts.

Combining IR spectroscopy of NO adsorption on copper exchanged molecular sieves with the chabazite structure, i.e. Cu-SAPO-34 and Cu-SSZ-13, and theoretical calculations, different types of copper species have been identified. On one hand, [Cu–OH]⁺ species can be accurately distinguished, characterized by a νNO frequency at 1788–1798 cm⁻¹ depending on their location in the chabazite structure (6R vs. 8R) and composition (Cu-SAPO-34 vs. Cu-SSZ-13). On the other hand, dimeric copper oxo [Cu–O–Cu]²⁺ species have been properly identified by means of DFT modelling, that proposes a νNO stretching frequency of 1887 cm⁻¹, which has been confirmed experimentally in the Cu-SAPO-34 sample. Finally the location of isolated Cu²⁺ ions either in the 6R units or in the 8R positions of the chabazite cavity could be accurately defined according to DFT data, and validated in the experimental IR spectra with IR bands between 1907 and 1950 cm⁻¹. Regarding to Cu⁺ species, IR spectroscopy of CO reveals different types of Cu⁺ species as evidenced by their ability to form mono, di and try carbonyls. The unambiguous differentiation of different types of copper species is of great interest in further identification of active sites for the NH3-SCR reaction.

A biocrude was obtained via the catalytic hydrothermal treatment of lignocellulosic biomass. This was further co-hydroprocessed with Straight Run Gas Oil (SRGO) under desulphurization conditions. Amounts of biocrude of up to 20. wt% could be co-processed, while maintaining a diesel stream density within the specifications contained in the road diesel regulation EN 590. The changes in the diesel properties associated with an increasing amount of biocrude were not a simple linear function of biocrude content. Rather, some positive correlations seem to exist between biocrude and SRGO at low biocrude contents, possibly due to intramolecular hydrogen transfer, yielding a diesel stream with a better quality than would be obtained from simply mixing hydrotreated pure streams in a 80% to 20% ratio.

In this study, the immobilization of Rhizomucor miehei lipase into hybrid nanospheres containing a liposomal core was reported. Organic internal liposomal enzyme phase was protected by inorganic silica matrix, obtained with and without surfactant, that stabilizes the internal organic phase and isolates and protects the bioactive molecules. The optimized heterogeneous catalyst thus prepared was used for enantioselective esterification of (R,S)-ibuprofen. The influence of several catalytic parameters on the activity of hybrid nanospheres (type of solvent, nature of the alcohol, reaction temperature, etc.,) was investigated. The heterogeneous biocatalysts best performed at 37. °C, using isooctane as solvent and 1-propanol as alcohol (with ester yield ranging between 78 and 93%). High activity and stability (up to nine reaction cycles) of enzyme-immobilized hybrid nanospheres, with respect to the free form, were observed. R. miehei lipase, both in its free and immobilized forms, reacts only with the S(+) enantiomer of (R,S)-ibuprofen, in all the tested reaction conditions.

Zr-containing metal-organic frameworks (MOFs) formed by either terephthalate (UiO-66) or 2-aminoterephthalate ligands (UiO-66-NH2) are active and stable catalysts for the acid catalyzed esterification of levulinic acid with EtOH, n-BuOH and long-chain biomass derived alcohols, with activities comparable (in some cases superior) to other solid acid catalysts previously reported. The effect of functional group substitution at the ligand benzene ring, alcohol chain length, particle size and contents of defects on the catalytic activity of the MOFs are studied in detail. In UiO-66-NH2, a dual acid-base activation mechanism is proposed, in which levulinic acid is activated on Zr sites and the alcohol at the amino groups of the ligand. Large variations of the catalytic activity from batch to batch suggest that the active sites are located at defect positions associated to ligand deficiency of the solid. Particle size seems to have a minor impact only in UiO-66-NH2, in which diffusion of levulinic acid is somehow hindered due to the amino groups present in the linkers.

2′-Aminochalcones of pharmaceutical and commercial interest have been obtained in high yields and selectivities through a one-pot process using a bifunctional heterogeneous catalyst bearing base and metal active sites. This is a physical mixture material formed by a high-surface-area MgO and Pt on TiO2. The process involves as the first step the Claisen–Schmidt condensation between o-nitroacetophenone and benzaldehyde derivatives on the basic catalytic function. This is followed by a chemoselective hydrogenation of the nitro group in the presence of the carbonyl and double-bond carbon–carbon groups within the molecule. Using the bifunctional catalyst and the reaction system proposed here, it is possible to produce, under mild reaction conditions and short reaction times, 2′-aminochalcones with higher yields and selectivities than those obtained by conventional multistep methods.Keywords: heterogeneous catalysis; 2′-aminochalcones; fine chemicals; cascade process; bifunctional catalyst

Zr-containing metal organic frameworks (MOFs) formed by terephthalate (UiO-66) and 2-aminoterephthalate ligands (UiO-66-NH2) are active and stable catalysts for the acid catalyzed esterification of various saturated and unsaturated fatty acids with MeOH and EtOH, with activities comparable (in some cases superior) to other solid acid catalysts previously reported in literature. Besides the formation of the corresponding fatty acid alkyl esters as biodiesel compounds (FAMEs and FAEEs), esterification of biomass-derived fatty acids with other alcohols catalyzed by the Zr-MOFs allows preparing other compounds of interest, such as oleyl oleate or isopropyl palmitate, with good yields under mild conditions.

MOFs with Cu2+ centers linked to four nitrogen atoms from azaheterocyclic compounds, i.e., pyrimidine [Cu(2-pymo)2] and imidazole [Cu(im)2], are active, stable and reusable catalysts for oxidative C–O coupling reactions by direct C–H activation of formamides, aldehydes and ethers. The measured catalytic activities are clearly superior to other homogeneous cupric salts, especially for the [Cu(im)2] MOF. The previously reported activity of the Cu2+ centers for cumene oxidation allows the use of the MOF as a bifunctional catalyst for olefin epoxidation with O2. The overall catalytic process consists of a cascade reaction in which the Cu-MOF first produces cumyl hydroperoxide and then the same Cu2+ centers catalyze the oxidative C–O coupling reaction using the generated hydroperoxide as the oxidant

The enthalpies of formation of the large pore pure silica beta polymorph C (BEC) and the extra-large pore germanosilicate ITQ-33 zeolite are investigated by high temperature oxide melt solution calorimetry. The enthalpies of formation from quartz for two BECs synthesized with different organic structure directing agents, SDA1 and SDA9 differ by 4 kJ/mol. The two SDAs produce phases with different properties as well as different energetics for the same framework and composition, due to the different amount of structural defects, while the more defective BEC is energetically less stable by 4 kJ/mol. The enthalpy of formation of defect-free pure silica BEC agrees with the predicted value proposed several years ago. Moreover, the enthalpy of formation of ITQ-33 (Ge/(Ge + Si) = 0.3) supports the energetic trends seen previously, namely that the enthalpy of formation becomes more endothermic as the content of double four rings (D4R) increases. The previous trend of energetics of porous materials versus molar volume is supported by the present data, with a diminishing destabilization for very open structures.