Base-free direct oxidation of 1-octanol to octanoic acid and its octyl ester over supported gold catalysts

One-Step Hydrothermal/Solvothermal Preparation of Pt/TiO2: An Efficient Catalyst for Biobutanol Oxidation at Room Temperature

The selective oxidation of biobutanol to prepare butyric acid is an important conversion process, but the preparation of low-temperature and efficient catalysts for butanol oxidation is currently a bottleneck problem. In this work, we prepared Pt-TiO2 catalysts with different Pt particle sizes using a simple one-step hydrothermal/solvothermal method. Transmission electron microscopy and X-ray diffraction results showed that the average size of the Pt particles ranged from 1.1 nm to 8.7 nm. Among them, Pt-TiO2 with an average particle size of 3.6 nm exhibited the best catalytic performance for biobutanol. It was capable of almost completely converting butanol, even at room temperature (30 °C), with a 98.9% biobutanol conversion, 98.4% butyric acid selectivity, and a turnover frequency (TOF) of 36 h-1. Increasing the reaction temperature to 80 and 90 °C, the corresponding TOFs increased rapidly to 355 and 619 h-1. The relationship between the electronic structure of Pt and its oxidative performance suggests that the synergistic effect of the dual sites, Pt0 and Pt2+, could be the primary factor contributing to its elevated reactivity.

Potentials of bio-butanol conversion to valuable products

In the last decade, there was observed a growing demand for both n-butanol as a potential fuel or fuel additive, and propylene as the only raw material for production of alcohol and other more bulky propylene chemical derivatives with faster growing outputs (polymers, propylene oxide, and acrylic acid). The predictable oilfield depletion and the European Green Deal adoption stimulated interest in alternative processes for n-butanol production, especially those involving bio-based materials. Their commercialization will promote additional market penetration of n-butanol for its application as a basic chemical. We analyze briefly the current status of two most advanced bio-based processes, i.e. ethanol–to-n-butanol and acetone–butanol–ethanol (ABE) fermentation. In the second part of the review, studies of n-butanol and ABE conversion to valuable products are considered with an emphasis on the most perspective catalytic systems and variants of the future processes realization.

Phytosterols and Novel Triterpenes Recovered from Industrial Fermentation Coproducts Exert In Vitro Anti-Inflammatory Activity in Macrophages

The unstoppable growth of human population that occurs in parallel with all manufacturing activities leads to a relentless increase in the demand for resources, cultivation land, and energy. In response, currently, there is significant interest in developing strategies to optimize any available resources and their biowaste. While solutions initially focused on recovering biomolecules with applications in food, energy, or materials, the feasibility of synthetic biology in this field has been demonstrated in recent years. For instance, it is possible to genetically modify Saccharomyces cerevisiae to produce terpenes for commercial applications (i.e., against malaria or as biodiesel). But the production process, similar to any industrial activity, generates biowastes containing promising biomolecules (from fermentation) that if recovered may have applications in different areas. To test this hypothesis, in the present study, the lipid composition of by-products from the industrial production of β-farnesene by genetically modified Saccharomyces cerevisiae are studied to identify potentially bioactive compounds, their recovery, and finally, their stability and in vitro bioactivity. The assayed biowaste showed the presence of triterpenes, phytosterols, and 1-octacosanol which were recovered through molecular distillation into a single fraction. During the assayed stability test, compositional modifications were observed, mainly for the phytosterols and 1-octacosanol, probably due to oxidative reactions. However, such changes did not affect the in vitro bioactivity in macrophages, where it was found that the obtained fraction decreased the production of TNF-α and IL-6 in lipopolysaccharide (LPS)-induced inflammation.

Catalytic Enhancement of Inductively Heated Fe3 O4 Nanoparticles by Removal of Surface Ligands

Heat management in catalysis is limited by each material's heat transfer efficiencies, resulting in energy losses despite current thermal engineering strategies. In contrast, induction heating of magnetic nanoparticles (NPs) generates heat at the surface of the catalyst where the reaction occurs, reducing waste heat via dissipation. However, the synthesis of magnetic NPs with optimal heat generation requires interfacial ligands, such as oleic acid, which act as heat sinks. Surface treatments using tetramethylammonium hydroxide (TMAOH) or pyridine are used to remove these ligands before applications in hydrophilic media. In this study, Fe₃ O₄ NPs are surface treated to study the effect of induction heating on the catalytic oxidation of 1-octanol. Whereas TMAOH was unsuccessful in removing oleic acid, pyridine treatment resulted in a roughly 2.5-fold increase in heat generation and product yield. Therefore, efficient surfactant removal has profound implications in induction heating catalysis by increasing the heat transfer and available surface sites.

Coordinately unsaturated O2c–Ti5c–O2c sites promote the reactivity of Pt/TiO2 catalysts in the solvent-free oxidation of n-octanol

Coordination unsaturated O_2c–Ti_5c–O_2c of TiO₂ (001) facets promote the formation of low-coordinate Pt metal clusters, which enhances catalytic performance in aerobic 1-octanol oxidation.

Effect of Gold Electronic State on the Catalytic Performance of Nano Gold Catalysts in n-Octanol Oxidation

This study aims to identify the role of the various electronic states of gold in the catalytic behavior of Au/M_xO_y/TiO₂ (where M_xO_y are Fe₂O₃ or MgO) for the liquid phase oxidation of n-octanol, under mild conditions. For this purpose, Au/M_xO_y/TiO₂ catalysts were prepared by deposition-precipitation with urea, varying the gold content (0.5 or 4 wt.%) and pretreatment conditions (H₂ or O₂), and characterized by low temperature nitrogen adsorption-desorption, X-ray powder diffraction (XRD), energy dispersive spectroscopy (EDX), scanning transmission electron microscopy-high angle annular dark field (STEM HAADF), diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy of CO adsorption, temperature-programmable desorption (TPD) of ammonia and carbon dioxide, and X-ray photoelectron spectroscopy (XPS). Three states of gold were identified on the surface of the catalysts, Au⁰, Au¹⁺ and Au³⁺, and their ratio determined the catalysts performance. Based on a comparison of catalytic and spectroscopic results, it may be concluded that Au⁺ was the active site state, while Au⁰ had negative effect, due to a partial blocking of Au⁰ by solvent. Au³⁺ also inhibited the oxidation process, due to the strong adsorption of the solvent and/or water formed during the reaction. Density functional theory (DFT) simulations confirmed these suggestions. The dependence of selectivity on the ratio of Brønsted acid centers to Brønsted basic centers was revealed.

Fabrication of Integrated Cu2O@HKUST-1@Au Nanocatalysts via Galvanic Replacements toward Alcohols Oxidation Application

Metastable Cu₂O is an attractive material for the architectural design of integrated nanomaterials. In this context, the in situ growth of microporous metal-organic frameworks (MOFs) on Cu₂O nanocrystals with well-defined shapes (such as octahedron, truncated octahedron, and corner-truncated cube) was conducted under ambient conditions by using sacrificial Cu₂O nanocrystals as a copper ion source for the construction of HKUST-1. It was found that the growth rate of HKUST-1 on the (111) facet of octahedral Cu₂O was much faster than that on the (100) facet of cubic Cu₂O. A subsequent etching process on the core-shell-structured Cu₂O@HKUST-1 to remove Cu₂O results in hollow HKUST-1 with hierarchical pores, where the shapes of cavities are tailored depending on the original Cu₂O crystals. Importantly, it was found that the integrated Cu₂O@HKUST-1@Au nanocatalysts could be fabricated by galvanic replacement reaction between Cu₂O and AuCl₄^-, wherein the copper(I) ions from Cu₂O etching diffuse through the microporous MOF shell and reach to the external surface to reduce AuCl₄^- ions, thereby forming Au nanoparticles exclusively on the MOF external surface. Furthermore, the catalytic applications of Cu₂O@HKUST-1@Au toward liquid-phase oxidation of both aromatic and aliphatic alcohols were studied. Notably, 100% selectivities of aldehyde products were achieved without any further oxidation byproducts such as acid and ester.

Oxidation of Aliphatic Alcohols by Using Precious Metals Supported on Hydrotalcite under Solvent- and Base-Free Conditions

Precious metal nanoparticles supported on magnesium-aluminum hydrotalcite (HT), TiO2 , and MgO were prepared by sol immobilization and assessed for the catalytic oxidation of octanol, which is a relatively unreactive aliphatic alcohol, with molecular oxygen as the oxidant under solvent- and base-free conditions. Compared with the TiO2 - and MgO-supported catalysts, platinum HT gave the highest activity and selectivity towards the aldehyde. The turnover number achieved for the platinum HT catalyst was >3700 after 180 min under mild reaction conditions. Moreover, the results for the oxidation of different substrates indicate that a specific interaction of octanal with the platinum HT catalyst could lead to deactivation of the catalyst.

Direct C-H arene homocoupling over gold nanoparticles supported on metal oxides

The direct CH/CH bond coupling of dimethyl phthalate was performed successfully over supported gold nanoparticle catalysts. Gold on reducible metal oxides, such as Co3 O4 , and on inert oxides that have an oxygen-releasing capacity, such as ZrO2 , showed the highest catalytic activity for the production of biphenyl tetracarboxylate using O2 as the sole oxidant. Supported Pd(OH)2 also catalyzed the reaction, but the catalytic activity was inferior to that of gold. Moreover, the gold catalysts exhibited excellent regioselectivity for the synthesis of valuable 3,3',4,4'-tetrasubstituted biphenyls by coupling with each other at the 4-position without the need for additional ligands. Gold catalysts also promoted the oxidative homocoupling of arenes including o-xylene to give symmetrical biaryls with high regioselectivity. X-ray absorption fine structure measurements revealed that the catalytically active species was Au(0) and that the lattice oxygen of Co3 O4 played an important role in the gold-catalyzed oxidative coupling. The results of the kinetic studies were consistent with an electrophilic aromatic substitution pathway. Regioselectivity is not controlled by directing groups or the electronic character of the substituents but by steric hindrance, which suggests that gold nanoparticles not only catalyze the oxidative coupling but also act as bulky ligands to control the regioselectivity.

Conversion of a metal–organic framework to N-doped porous carbon incorporating Co and CoO nanoparticles: direct oxidation of alcohols to esters

A Co-based metal–organic framework undergoes pyrolysis to afford Co–CoO@N-doped porous carbon, which exhibits excellent catalytic performance toward the direct oxidation of alcohols to esters.