Homogeneous Catalyzed Valorization of Furanics: A Sustainable Bridge to Fuels and Chemicals

Homogeneous Catalyzed Direct Conversion of Furfural to Gamma-Valerolactone

Herein, we report the direct conversion of biomass-derived furfural to γ-valerolactone (GVL) in a one-pot system, using the combination of Ru-MACHO-BH and a Brønsted acid (H3 PO4 ). A GVL yield of 84 % is achieved under mild reaction conditions using 1 mol% of Ru-MACHO-BH and 3.8 M H3 PO4 (aq) at 100 °C for 7 hours.

Biofuels and Nanocatalysts: Python Boosting Visualization of Similarities

Among the most relevant themes of modernity, using renewable resources to produce biofuels attracts several countries' attention, constituting a vital part of the global geopolitical chessboard since humanity's energy needs will grow faster and faster. Fortunately, advances in personal computing associated with free and open-source software production facilitate this work of prospecting and understanding complex scenarios. Thus, for the development of this work, the keywords "biofuel" and "nanocatalyst" were delivered to the Scopus database, which returned 1071 scientific articles. The titles and abstracts of these papers were saved in Research Information Systems (RIS) format and submitted to automatic analysis via the Visualization of Similarities Method implemented in VOSviewer 1.6.18 software. Then, the data extracted from the VOSviewer were processed by software written in Python, which allowed the use of the network data generated by the Visualization of Similarities Method. Thus, it was possible to establish the relationships for the pair between the nodes of all clusters classified by Link Strength Between Items or Terms (LSBI) or by year. Indeed, other associations should arouse particular interest in the readers. However, here, the option was for a numerical criterion. However, all data are freely available, and stakeholders can infer other specific connections directly. Therefore, this innovative approach allowed inferring that the most recent pairs of terms associate the need to produce biofuels from microorganisms' oils besides cerium oxide nanoparticles to improve the performance of fuel mixtures by reducing the emission of hydrocarbons (HC) and oxides of nitrogen (NOx).

Oxidation of Organic Compounds Using Water as the Oxidant with H2 Liberation Catalyzed by Molecular Metal Complexes

Oxidation reactions of organic compounds play a central role in both industrial chemical and material synthesis as well as in fine chemical and pharmaceutical synthesis. While traditional laboratory-scale oxidative syntheses have relied on the use of strong oxidizers, modern large-scale oxidation processes preferentially utilize air or pure O₂ as an oxidant, with other oxidants such as hydrogen peroxide, nitric acid, and aqueous chlorine solution also being used in some processes. The use of molecular oxygen or air as an oxidant has been very attractive in recent decades because of the abundance of air and the lack of wasteful byproduct generation. Nevertheless, the use of high-pressure air or, in particular, pure oxygen can lead to serious safety concerns with improper handling and also necessitates the use of sophisticated high-pressure reactors for the processes.Several research groups, including ours, have investigated in recent times the possibility of carrying out catalytic oxidation reactions using water as the formal oxidant, with no added conventional oxidants. Along with the abundant availability of water, these processes also generate dihydrogen gas as the reaction coproduct, which is a highly valuable fuel. Several well-defined molecular metal complexes have been reported in recent years to catalyze these unusual oxidative reactions with water. A ruthenium bipyridine-based PNN pincer complex was reported by us to catalyze the oxidation of primary alcohols to carboxylate salts with alkaline water along with H₂ liberation, followed by reports by other groups using other complexes as catalysts. At the same time, ruthenium-, iridium-, and rhodium-based complexes have been reported to catalyze aldehyde oxidation to carboxylic acids using water. Our group has combined the catalytic aqueous alcohol and aldehyde oxidation activity of a ruthenium complex to achieve the oxidation of biomass-derived renewable aldehydes such as furfural and 5-hydroxymethylfurfural (HMF) to furoic acid and furandicarboxylic acid (FDCA), respectively, using alkaline water as the oxidant, liberating H₂. Ruthenium complexes with an acridine-based PNP ligand have also been employed by our group for the catalytic oxidation of amines to the corresponding lactams, or to carboxylic acids via a deaminative route, using water. Similarly, we also reported molecular complexes for the catalytic Markovnikov oxidation of alkenes to ketones using water, similar to Wacker-type oxidation, which, however, does not require any terminal oxidant and produces H₂ as the coproduct. At the same time, the oxidation of enol ethers to the corresponding esters with water has also been reported. This account will highlight these recent advances where water was used as an oxidant to carry out selective oxidation reactions of organic compounds, catalyzed by well-defined molecular complexes, with H₂ liberation. The oxidation of alcohols, aldehydes, amines, alkenes, and enol ethers will be discussed to provide an outlook toward other functional groups' oxidation. We hope that this will aid researchers in devising other oxidative dehydrogenative catalytic systems using water, complementing traditional oxidative processes involving strong oxidants and molecular oxygen.

Sustainable catalysis with fluxional acridine-based PNP pincer complexes

Because of the widespread use of fossil fuels and the resulting global warming, development of sustainable catalytic transformations is now more important than ever to obtain our desired fuels and building materials with the least carbon footprint and waste production. Many sustainable (de)hydrogenation reactions, including CO2 reduction, H2 carrier systems, and others, have been reported using molecular pincer complexes. A specific subset of pincer complexes containing a central acridine donor with flanking CH2PR2 ligands, known as acridine-based PNP pincer complexes, exhibit special reactivities that are not imitable by other PNP pincer complexes such as pyridine-based or (R2PCH2CH2)2NH type ligands. The goal of this article is to highlight the unique reactivities of acridine-based complexes and then investigate how these reactivities allow these complexes to catalyse many sustainable reactions that traditional pincer complexes cannot catalyse. To that end, we will initially go over the synthesis and structural features of acridine complexes, such as the labile coordination of the central N donor and the observed fac-mer fluxionality. Following that, distinct reactivity patterns of acridine-based complexes including their reactivity with acids and water will be discussed. Finally, we will discuss the reaction systems that have been developed with acridine complexes thus far, including the notable selective transformations of primary alcohols to primary amines using ammonia, N-heteroaromatic synthesis from alcohols and ammonia, oxidation reactions with water with H2 liberation, development of H2 carrier systems, and others, and conclude the article with future possible directions. We hope that the systemic study presented here will aid researchers in developing further sustainable reactions based on the unique acridine-based pincer complexes.

Catalytic Furfural/5-Hydroxymethyl Furfural Oxidation to Furoic Acid/Furan-2,5-dicarboxylic Acid with H2 Production Using Alkaline Water as the Formal Oxidant

Furfural and 5-hydroxymethyl furfural (HMF) are abundantly available biomass-derived renewable chemical feedstocks, and their oxidation to furoic acid and furan-2,5-dicarboxylic acid (FDCA), respectively, is a research area with huge prospective applications in food, cosmetics, optics, and renewable polymer industries. Water-based oxidation of furfural/HMF is a lucrative approach for simultaneous generation of H2 and furoic acid/FDCA. However, this process is currently limited to (photo)electrochemical methods that can be challenging to control, improve, and scale up. Herein, we report well-defined ruthenium pincer catalysts for direct homogeneous oxidation of furfural/HMF to furoic acid/FDCA, using alkaline water as the formal oxidant while producing pure H2 as the reaction byproduct. Mechanistic studies indicate that the ruthenium complex not only catalyzes the aqueous oxidation but also actively suppresses background decomposition by facilitating initial Tishchenko coupling of substrates, which is crucial for reaction selectivity. With further improvement, this process can be used in scaled-up facilities for a simultaneous renewable building block and fuel production.