Functional Acid and Base Hybrid Catalysts Organized by Associated (Organo)aluminosilicate Layers for C–C Bond Forming Reactions and Tandem Processes

Novel bifunctional acid–base monolayered hybrid catalysts (MLHMs), based on associated individual (organo)­aluminosilicate sheets with amino and sulfonic pending groups located in the interlayer space, have been successfully prepared by direct alkaline hydrothermal synthesis and evaluated in consecutive catalytic transformations. Different characterization techniques such as chemical and thermogravimetrical analyses, X-ray diffraction, TEM microscopy, nuclear magnetic resonance (NMR), temperature-programmed desorption of CO₂ and NH₃ (TPD), and textural measurements were used to show the physicochemical and structural nature of the materials, evidencing their effectiveness as functional acid, base, and acid–base catalysts for different one-pot two-step tandem reactions, which were performed in the presence of only one active and recoverable lamellar-type hybrid solid catalyst

Rigid/Flexible Organic Structure Directing Agents for Directing the Synthesis of Multipore Zeolites: A Computational Approach

The preferential crystallization of pure silica ITQ-39 and MFI zeolites using SDAEt and SDAPr, respectively, as organic structure directing agents (SDAs) is investigated here by theoretical methods using a periodic DFT-D model. For this purpose, the templating roles of SDAEt and SDAPr have been analyzed following a systematic study of the interaction of these two SDAs with the previously described zeolites through SDA stabilization energies (balance of intermolecular SDA dispersive interactions and SDA strain). From theoretical studies, it has been found that SDAEt located inside ITQ-39 zeolite and SDAPr placed within MFI show the largest stabilizations. These theoretical results agree with previous experimental observations for the preferential crystallization of pure silica ITQ-39 and MFI using SDAEt and SDAPr molecules, respectively

Nanolayered Cobalt–Molybdenum Sulfides as Highly Chemo- and Regioselective Catalysts for the Hydrogenation of Quinoline Derivatives

Herein, a general protocol for the preparation of a broad range of valuable <i>N</i>-heterocyclic products by hydrogenation of quinolines and related <i>N</i>-heteroarenes is described. Interestingly, the catalytic hydrogenation of the <i>N</i>-heteroarene ring is chemoselectively performed when other facile reducible functional groups, including alkenes, ketones, cyanides, carboxylic acids, esters, and amides, are present. The key to successful catalysis relies on the use of a nanolayered cobalt–molybdenum sulfide catalyst hydrothermally synthesized from earth-abundant metal precursors. This heterogeneous system displays a tunable composition of phases that allows for catalyst regeneration. Its catalytic activity depends on the composition of the mixed phase of cobalt sulfides, being higher with the presence of Co₃S₄, and could also be associated with the presence of transient Co-Mo-S structures that mainly vanish after the first catalytic run

Two-Dimensional ITQ‑2 Zeolite for Biomass Transformation: Synthesis of Alkyl 5‑Benzyl-2-furoates as Intermediates for Fine Chemicals

A new catalytic process to produce alkyl 5-benzyl-2-furoates has been performed through a two-step process that involves (a) selective oxidative esterification of 5-hydroxymethylfurfural (HMF) to 5-hydroxymethyl furoic acid methyl ester (HMFE) using Au/TiO₂ as catalyst and oxygen as oxidant and (b) alkylation of benzene derivatives with HMFE using zeolites as acid catalysts. The alkylation process has been carried out using large pore tridimensional zeolites such as Beta and USY, a mesoporous aluminosilicate (MCM-41), and a two-dimensional delaminated ITQ-2 zeolite. The results showed that ITQ-2 zeolite, which combines easy product diffusion and adequate acitidy, was the most active and selective catalyst to produce alkyl 5-benzyl-2-furoates. Finally, we have presented a simple protocol to prepare 5-(4-fluorobenzyl)-2-furyl methyl ketone, a key intermediate in the synthesis of S-1360, an antiviral for the treatment of AIDS, in good yield through a more sustainable method than the existing ones, starting from biomass platform molecules

Synthesis and Structure Determination of a New Microporous Zeolite with Large Cavities Connected by Small Pores

A new small-pore germanosilicate zeolite, named as ITQ-49, has been synthesized using a new ditetraalkylphosphonium dication as an organic structure-directing agent, and its structure has been solved by direct methods applied to the powder X-ray diffraction pattern of the calcined solid. This new zeolite crystallizes in the space group <i>Immm</i> with cell parameters <i>a</i> = 19.6007(8) Å, <i>b</i> = 18.3274(7) Å, and <i>c</i> = 16.5335(6) Å. The pore topology of ITQ-49 consists of large, nonspherical cavities that are connected to each other through small eight-membered-ring windows, resulting in a unidirectional small-pore zeolite that has a relatively large adsorption capacity. Also, ITQ-49 contains double four-membered-ring units where Ge is preferentially located, and fluoride anions are placed inside these units

Synthesis and Structure Determination of a New Microporous Zeolite with Large Cavities Connected by Small Pores

A new small-pore germanosilicate zeolite, named as ITQ-49, has been synthesized using a new ditetraalkylphosphonium dication as an organic structure-directing agent, and its structure has been solved by direct methods applied to the powder X-ray diffraction pattern of the calcined solid. This new zeolite crystallizes in the space group <i>Immm</i> with cell parameters <i>a</i> = 19.6007(8) Å, <i>b</i> = 18.3274(7) Å, and <i>c</i> = 16.5335(6) Å. The pore topology of ITQ-49 consists of large, nonspherical cavities that are connected to each other through small eight-membered-ring windows, resulting in a unidirectional small-pore zeolite that has a relatively large adsorption capacity. Also, ITQ-49 contains double four-membered-ring units where Ge is preferentially located, and fluoride anions are placed inside these units

Heterogeneous Catalysis for Tandem Reactions

Heterogeneous Catalysis for Tandem Reaction

Nanocrystalline CeO₂ as a Highly Active and Selective Catalyst for the Dehydration of Aldoximes to Nitriles and One-Pot Synthesis of Amides and Esters

The dehydration of aldoximes into nitriles has been performed in the presence of various metal oxides with different acid–base properties (Al₂O₃, TiO₂, CeO_2, MgO). The results showed that a nanocrystalline CeO₂ was the most active catalyst. An in situ IR spectroscopy study supports a polar elimination mechanism in the dehydration of aldoxime on metal oxide catalysts, in which Lewis acid sites and basic sites are involved. The Lewis acid sites intervene in the adsorption of the oxime on the catalyst surface while surface base sites are responsible for the C1–H bond cleavage. Thus, the acid–base properties of nanocrystalline CeO₂ are responsible for the high catalytic activity and selectivity. A variety of aldoximes including alkyl and cycloalkyl aldoximes have been dehydrated into the corresponding nitriles in good yields (80–97%) using nanosized ceria which moreover resulted in a stable and reusable catalyst. Additionally, it has been showed that a variety of pharmacologically important products such as picolinamide and picolinic acid alkyl ester derivatives can be obtained in good yields from 2-pyridinaldoxime in a one-pot process using the nanoceria as catalyst