Selective oxidation of primary carbon-hydrogen bonds with oxygen is of crucial importance for the sustainable exploitation of available feedstocks. To date, heterogeneous catalysts have either shown low activity and/or selectivity or have required activated oxygen donors. We report here that supported gold-palladium (Au-Pd) nanoparticles on carbon or TiO2 are active for the oxidation of the primary carbon-hydrogen bonds in toluene and related molecules, giving high selectivities to benzyl benzoate under mild solvent-free conditions. Differences between the catalytic activity of the Au-Pd nanoparticles on carbon and TiO2 supports are rationalized in terms of the particle/support wetting behavior and the availability of exposed corner/edge sites.

https://science.sciencemag.org/content/sci/331/6014/195.full.pdf

Solvent-Free Oxidation of Primary Carbon-Hydrogen Bonds in Toluene Using Au-Pd Alloy Nanoparticles

Continuous-flow liquid phase oxidation chemistry in microreactors receives a lot of attention as the reactor provides enhanced heat and mass transfer characteristics, safe use of hazardous oxidants, high interfacial areas, and scale-up potential. In this review, an up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given. A description of mass and heat transfer phenomena is provided and fundamental principles are deduced which can be used to make a judicious choice for a suitable reactor. In addition, the safety aspects of continuous-flow technology are discussed. Next, oxidation chemistry in flow is discussed, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow. Finally, the scale-up potential for continuous-flow reactors is described.

/pdf/liquid-phase-oxidation-chemistry-in-continuous-flow-q8s21u2ge1.pdf

Liquid phase oxidation chemistry in continuous-flow microreactors

Oxidation of hydrocarbons with clean oxidants is a crucial process for the development of products ranging from commodity chemicals to speciality pharmaceuticals. While selective oxidation is commonplace in nature and mainly occurs through a broad variety of cytochrome P450 enzymes, the synthetic catalysts that have been identified so far are relatively inactive with aliphatic C–H bonds. We present here a promising strategy for modifying polymeric graphitic carbon nitride by replacing the carbon atoms in the “melon” network using boron. 11B solid-state MAS NMR and XPS spectral studies confirmed the incorporation of the boron atoms in the polymeric g-C3N4 as well as the degree of doping, while X-ray diffraction and IR indicated that the characteristic structural properties of polymeric g-C3N4, such as the original graphitic structure, and the C–N heterocycle units were essentially retained. The boron-doped polymeric carbon nitride shows promising catalytic activity and high selectivity (≥87%) in the oxidation of benzylic aromatics. The use of this metal-free, organic, semiconducting polymer as an oxidation catalyst and H2O2 or O2 as oxidants makes the reactions interesting from both an economic and environmental point of view. It is also hoped that our findings will stimulate further investigation and will open new possibilities to form hybrid carbon nitride materials with new and probably exciting applications.

Synthesis of boron doped polymeric carbon nitride solids and their use as metal-free catalysts for aliphatic C–H bond oxidation

This critical review aims to update the recent development in the selective oxidation of organic compounds by gold catalysis, highlighting the progress in the last three years. Following the impressive developments in the last decades, several protocols for catalytic oxidation are today available, which are based on the extraordinary properties of gold in terms of catalytic activity, selectivity, reusability and resistance to poisons. Beside many other applications, gold can be recommended for green processes dedicated to fine chemicals, pharmaceuticals and the food industry owing to its recognized bio-compatibility. The collected literature is focused on experiments concerning the oxidation of different chemical groups and could be of interest, in the wide area of organic chemistry, for improving previous processes or for exploring new catalytic pathways (174 references).

Update on selective oxidation using gold

Graphitic carbon nitride polymers: promising catalysts or catalyst supports for heterogeneous oxidation and hydrogenation

We conducted the liquid phase oxidation of toluene with molecular oxygen over heterogeneous catalysts of copper-based binary metal oxides. Among the copper-based binary metaloxides, iron-copper bi- nary oxide (Fe/Cu ¼ 0.3 atomic ratio) was found to be the best catalyst. In the presence of pyridine, overox- idation of benzaldehyde to benzoic acid was partially prevented. As a result, highly selective formation of benzaldehyde (86% selectivity) was observed after 2 h of reaction (7% conversion of toluene) at 463 K and 1.0 MPa of oxygen atmosphere in the presence of pyridine. These catalytic performances were similar or better than those in the gas phase oxidation of tol- uene at reaction temperatures higher than 473 K and under 0.5 - 2.5 MPa. It was suggested from competi- tive adsorption measurements that pyridine could re- duce the adsorption of benzaldehyde. At a long reac- tion time of 4 h, the conversion increased to 25% and benzoic acid became the predominant reaction prod- uct (72% selectivity) in the absence of pyridine. The yield of benzoic acid was higher than that in the Snia-Viscosa process, which requires corrosive halo- gen ions and acidic solvents in the homogeneous reac- tion media. The catalyst was easily recycled by simple filtration and reusable after washing and drying.

Liquid Phase Oxidation of Toluene to Benzaldehyde with Molecular Oxygen over Copper-Based Heterogeneous Catalysts

The invention provides is a combinational zeolite catalyst making alcohol and aether kinds compounds and the preparation method. The zeolites of the invention are the zeolite Y with 2.420-2.462nm parameter and ZSM-5 zeolite through burning and with the organic module agent removed. Mix the two kinds of zeolites and use the mixing agent containing H+ and NH4+ for the treatment and then implement drying treatment. The combinational zeolites are the acid components, and are matched with one or some of P, B and Zn and use Al2O3, SiO2-Al2O3 or the clay to form. The catalyst of the invention has high activity, fine selection and flexible operation.

Jin Gao

Papers

Liquid Phase Oxidation of Toluene to Benzaldehyde with Molecular Oxygen over Copper-Based Heterogeneous Catalysts

Composite zeolite catalyst for preparing alcohol and ether compounds and preparation thereof

A composite zeolite catalyst for preparing alcohol and ether compounds and a preparation method thereof