Selective Hydrodeoxygenation of Esters to Unsymmetrical Ethers over a Zirconium Oxide-Supported Pt-Mo Catalyst

Building lactams by highly selective hydrodeoxygenation of cyclic imides using an alumina-supported AgRe bimetallic nanocatalyst

The rational design of robust nanocatalysts containing the suitable active sites for building relevant organic compounds, such as lactams, is a desired approximation towards the development of a sustainable fine chemistry field. In that sense, the design of a proper nanomaterial able to mediate the selective hydrodeoxygenation of cyclic imides to lactams with high tolerance to the preservation of aromatic rings remains rather unexplored. Here, we show the design of a bimetallic AgRe nanomaterial with notable activity and selectivity to mediate this transformation affording more than 60 lactams from the corresponding imides. Interestingly, in this work we disclose that the optimal AgRe nanocatalyst is constituted by AgReO4 nanoaggregates that undergo an in situ hydrogenative dispersion to form the active centers composed by Ag0 nanoparticles and ReOx species. Deep characterization, together with kinetic and mechanistic studies, have revealed that the intimate Ag-Re contact intrinsic to AgReO4 species is key for the formation of the most active catalytic sites and the proper bimetallic cooperation required for mediating the desired process.

Selective Asymmetric Hydrogenation of Waste Polyethylene Terephthalate via Controlled Sorption through Precisely Tuned Moderate Acid Sites

The partial hydrogenation of waste polyethylene terephthalate (PET) offers a great opportunity to produce valuable chemicals, yet achieving precise catalytic control remains challenging. Herein, for the first time, we realized one-pot selective hydrogenation of waste PET to p-toluic acid (p-TA) with a record-high yield of 53.4%, alongside a 36.4% yield of p-xylene (PX), using a specially designed PtW/MCM-48 catalyst. Mechanistic investigations revealed that the exceptional catalytic performance arises from synergistic interaction between Pt nanoparticles and WOx species. Low-valent WOx enhances Pt dispersion, while Pt stabilizes WOx as low-polymerized polytungstates. The moderate acidity of PtW1.5/MCM-48 ensures controlled desorption of p-TA, preventing overhydrogenation to PX. The catalyst demonstrated robust performance with real-world PET waste. Life cycle assessment and technical and economic evaluation further highlight its practical feasibility. This study establishes a sustainable pathway for PET chemical upcycling and provides a framework for designing advanced catalysts for selective hydrogenation reactions, addressing critical challenges in circular chemistry and plastic waste management.

Reductive amination of triglycerides to fatty amines over a titanium oxide-supported Pt-Mo catalyst

The reductive amination of naturally abundant triglycerides is a promising approach for the synthesis of fatty amines. However, existing catalytic systems for this transformation typically require harsh reaction conditions. Herein, we present a titanium oxide-supported platinum-molybdenum (Pt-Mo/TiO2) catalyst that promotes the reductive amination of triglycerides to fatty amines. The Pt-Mo/TiO2 catalyst exhibits a high activity under milder conditions, specifically at 1 MPa of H2, surpassing the performance of previously reported catalysts. A wide range of triglycerides, including cooking oils, are successfully converted into the corresponding fatty amines in high yields. The Pt-Mo/TiO2 catalyst is reusable and applicable to gram-scale reactions, demonstrating the high potential of Pt-Mo/TiO2 for green and sustainable fatty amine production.

Turning on Low-Temperature Catalytic Conversion of Biomass Derivatives through Teaming Pd1 and Mo1 Single-Atom Sites

On-purpose atomic scale design of catalytic sites, specifically active and selective at low temperature for a target reaction, is a key challenge. Here, we report teamed Pd1 and Mo1 single-atom sites that exhibit high activity and selectivity for anisole hydrodeoxygenation to benzene at low temperatures, 100-150 °C, where a Pd metal nanoparticle catalyst or a MoO3 nanoparticle catalyst is individually inactive. The catalysts built from Pd1 or Mo1 single-atom sites alone are much less effective, although the catalyst with Pd1 sites shows some activity but low selectivity. Similarly, less dispersed nanoparticle catalysts are much less effective. Computational studies show that the Pd1 and Mo1 single-atom sites activate H2 and anisole, respectively, and their combination triggers the hydrodeoxygenation of anisole in this low-temperature range. The Co3O4 support is inactive for anisole hydrodeoxygenation by itself but participates in the chemistry by transferring H atoms from Pd1 to the Mo1 site. This finding opens an avenue for designing catalysts active for a target reaction channel such as conversion of biomass derivatives at a low temperature where neither metal nor oxide nanoparticles are.

Catalyst- and Stoichiometry-Dependent Deoxygenative Reduction of Esters to Ethers or Alcohols with Borane-Ammonia

A facile and selective room temperature deoxygenation of both aromatic and aliphatic carboxylic esters to ethers has been achieved by regulating the stoichiometry of the reductant, BH3-NH3, and the catalyst, TiCl4. This first, practical borane-mediated process is compatible with various potentially sensitive functional groups and is applicable to the deoxygenative ether formation from typically challenging aromatic acid esters. Substituting BF3-Et2O as the catalyst alters the reaction pathway, reducing the esters to alcohols. Mechanistic insights are provided by NMR spectroscopy, deuterium labeling, and kinetic isotope studies.

Ester Reduction with H2 on Bifunctional Metal-Acid Catalysts: Implications of Metal Identity on Rates and Selectivities

Esters reduce to form ethers and alcohols on contact with metal nanoparticles supported on Brønsted acidic faujasite (M-FAU) that cleave C-O bonds by hydrogenation and hydrogenolysis pathways. Rates and selectivities for each pathway depend on the metal identity (M=Co, Ni, Cu, Ru, Rh, Pd, and Pt). Pt-FAU gives propyl acetate consumption rates up to 100 times greater than other M-FAU catalysts and provides an ethyl propyl ether selectivity of 34 %. Measured formation rates, kinetic isotope effects, and site titrations suggest that ester reduction involves a bifunctional mechanism that implicates the stepwise addition of H* atoms to the carbonyl to form hemiacetals on the metal sites, followed by hemiacetal diffusion to a nearby Brønsted acid site to dehydrate to ethers or decompose to alcohol and aldehyde. The rates of reduction of propyl acetate appear to be determined by the H* addition to the carbonyl and by the C-O cleavage of hemiacetal.

Multifunctional WO3-ZrO2-Supported Platinum Catalyst for Remarkably Efficient Hydrogenolysis of Esters to Alkanes

The hydrogenolysis of esters to alkanes is a key protocol for the synthesis of high-quality hydrocarbon fuels from renewable plant oils or fats. However, performing this process under mild energy-efficient conditions is challenging. Herein, we report a robust tungsten- and zirconium-oxide-supported platinum catalyst (Pt/WO₃-ZrO₂) for the hydrogenolysis of esters to alkanes at low temperatures (as low as 70 °C) and under ambient pressure (1 atm) of H₂. For example, tristearin undergoes a complete conversion at 130 °C with more than 95% selectivity for the corresponding alkanes without carbon loss. In addition, the heterogeneous nature of the catalyst system reported herein permits multiple reuse of the catalyst without any significant loss of its high activity and selectivity. Mechanistic studies suggest that the multifunctional nature (acid and redox properties) of the WO₃-ZrO₂ support plays an important role in the high activity of the catalyst.

Hydrogenation of Carboxylic Acids, Esters, and Related Compounds over Heterogeneous Catalysts: A Step toward Sustainable and Carbon-Neutral Processes

The catalytic hydrogenation of esters and carboxylic acids represents a fundamental and important class of organic transformations, which is widely applied in energy, environmental, agricultural, and pharmaceutical industries. Due to the low reactivity of the carbonyl group in carboxylic acids and esters, this type of reaction is, however, rather challenging. Hence, specifically active catalysts are required to achieve a satisfactory yield. Nevertheless, in recent years, remarkable progress has been made on the development of catalysts for this type of reaction, especially heterogeneous catalysts, which are generally dominating in industry. Here in this review, we discuss the recent breakthroughs as well as milestone achievements for the hydrogenation of industrially important carboxylic acids and esters utilizing heterogeneous catalysts. In addition, related catalytic hydrogenations that are considered of importance for the development of cleaner energy technologies and a circular chemical industry will be discussed in detail. Special attention is paid to the insights into the structure-activity relationship, which will help the readers to develop rational design strategies for the synthesis of more efficient heterogeneous catalysts.