Silver-Nanoparticle-Catalyzed Dearomatization of Indoles toward 3‑Spiroindolenines via a 5-<i>exo</i>-dig Spirocyclization

We present a supported silver-nanoparticle-catalyzed dearomatization of 3-substituted indoles toward 3-spiroindolenines. Two scaffolds were investigated for this transformation. The yields range from moderate to high. In the case of chiral reactants (Ugi four-component reaction adducts), the process is diastereoselective with a diastereomeric excess between 75% and 92%. The catalyst was characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Metal leaching was investigated using hot-filtration and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) experiments. An apparent turnover frequency (TOF) was determined

Titania-Silica Catalysts for Lactide Production from Renewable Alkyl Lactates: Structure–Activity Relations

Different Ti-Si catalysts, viz. TiO₂ supported on amorphous SiO₂ or Si-MCM-41, TiO₂-SiO₂ xerogels, and Ti zeolites (TS-1 and Ti-beta), were compared in terms of activity and selectivity for the direct conversion of methyl lactate to lactide in the gas phase. Except for Ti-beta, all catalysts exhibit a high lactide selectivity of 88–92% at conversions below 50%. From DR UV–vis spectroscopy, it is evidenced that the catalytic activity of tetrahedral TiO₄ sites is higher than those of polymerized TiO₅ or the octahedral TiO₆ counterparts, irrespective of the catalyst structure, an analysis supported by ToF-SIMS measurements. A kinetic analysis shows that the catalytic activity is proportional to the number of vacant sites on the catalyst surface. Thus, the activity increase observed for tetrahedral TiO₄ sites may be attributed to an increased number of vacant sites (e.g., two for TiO₄, zero for TiO₆). Lactide productivity thus highly benefits from an increased dispersion of Ti sites on the catalyst surface and could be increased by a factor of 2.5 (up to 10 g_LD g_cat^–1 h^–1) when TiO₂ is dispersed on a Si-MCM-41 support, with higher surface areas in comparison to amorphous SiO₂ gels

Solvent-free Preparation of Ru/Al₂O₃ Catalysts for CO₂ Methanation: An Example of Frugal Innovation

To reduce the environmental impact of supported catalyst production in compliance with the recommendations of the UN’s 12th objective, which encourages more sustainable consumption and production patterns, we propose to revisit sol–gel chemistry in a more frugal mode. The principle of frugal innovation is to simplify products and processes, eliminate complexities to make solutions easier to understand and use, and reduce production costs. By this way, the synthesis of ruthenium-based catalysts supported on γ-AlOOH and γ-Al2O3 is revised via solvent-free sol–gel chemistry. Such catalysts are successfully prepared in one-pot preparation of the active phase and the support using Ru(acac)3/Al alkoxide that requires no sacrificial organic pore-generating agent, no washing, and no filtration and produces no liquid waste. The mixed Ru/Al precursor is hydrolyzed with a stoichiometric amount of water without any solvent. The obtained materials containing 1 and 3% Ru/Al molar ratios have high specific surface areas, from 300 to 690 m2·g–1 and exhibit well dispersed NPs of 1–4 nm on γ-AlOOH with interesting CO2 methanation activity and 100% CH4 selectivity. This proves that a frugal synthesis approach can do as well as traditional synthesis methods while having a much lower environmental impact (cE-factor, water consumption, and energy consumption are 24, 69, and 24 to 42 times lower, respectively) than the standard multistep protocol.

Solvent-free Preparation of Ru/Al₂O₃ Catalysts for CO₂ Methanation: An Example of Frugal Innovation

To reduce the environmental impact of supported catalyst production in compliance with the recommendations of the UN’s 12th objective, which encourages more sustainable consumption and production patterns, we propose to revisit sol–gel chemistry in a more frugal mode. The principle of frugal innovation is to simplify products and processes, eliminate complexities to make solutions easier to understand and use, and reduce production costs. By this way, the synthesis of ruthenium-based catalysts supported on γ-AlOOH and γ-Al2O3 is revised via solvent-free sol–gel chemistry. Such catalysts are successfully prepared in one-pot preparation of the active phase and the support using Ru(acac)3/Al alkoxide that requires no sacrificial organic pore-generating agent, no washing, and no filtration and produces no liquid waste. The mixed Ru/Al precursor is hydrolyzed with a stoichiometric amount of water without any solvent. The obtained materials containing 1 and 3% Ru/Al molar ratios have high specific surface areas, from 300 to 690 m2·g–1 and exhibit well dispersed NPs of 1–4 nm on γ-AlOOH with interesting CO2 methanation activity and 100% CH4 selectivity. This proves that a frugal synthesis approach can do as well as traditional synthesis methods while having a much lower environmental impact (cE-factor, water consumption, and energy consumption are 24, 69, and 24 to 42 times lower, respectively) than the standard multistep protocol.