Hydrogenation of biofuels with formic acid over a palladium-based ternary catalyst with two types of active sites

Hydrogen-transfer strategy in lignin refinery: Towards sustainable and versatile value-added biochemicals

Lignin, the most prevalent natural source of polyphenols on Earth, offers substantial possibilities for the conversion into aromatic compounds, which is critical for attaining sustainability and carbon neutrality. The hydrogen-transfer method has garnered significant interest owing to its environmental compatibility and economic viability. The efficacy of this approach is contingent upon the careful selection of catalytic and hydrogen-donating systems that decisively affect the yield and selectivity of the monomeric products resulting from lignin degradation. This paper highlights the hydrogen-transfer technique in lignin refinery, with a specific focus on the influence of hydrogen donors on the depolymerization pathways of lignin. It delineates the correlation between the structure and activity of catalytic hydrogen-transfer arrangements and the gamut of lignin-derived biochemicals, utilizing data from lignin model compounds, separated lignin, and lignocellulosic biomass. Additionally, the paper delves into the advantages and future directions of employing the hydrogen-transfer approach for lignin conversion. In essence, this concept investigation illuminates the efficacy of the hydrogen-transfer paradigm in lignin valorization, offering key insights and strategic directives to maximize lignin's value sustainably.

Elucidating the Reaction Pathways of Veratrylglycero-β-Guaiacyl Ether Degradation over Metal-Free Solid Acid Catalyst with Hydrogen

Efficient cleavage of β-O-4 bonds in lignin to high-yield aromatic compounds for the potential production of fuels and chemicals is vital for the economics of the modern biorefinery industry. This work is distinct in that a detailed mechanistic analysis of the reaction pathways of veratrylglycero-β-guaiacyl ether (VGE) catalyzed by transition-metal-free solid acid zeolite in aqueous conditions at high hydrogen pressure has been performed. VGE degradation produced high monomers yields (≈87 %), including guaiacol (48.2 %), 1-(3,4-dimethoxyphenyl)ethanol (10.3 %), 1-(3,4-dimethoxyphenyl)-2-propanol (6.1 %), 3,4-dimethoxyphenylpropanol (4.7 %), 3,4-dimethoxycinnamyl alcohol (4.1 %), and 1,2-dimethoxy-4-propylbenzene (2 %). The products were identified and confirmed by the in situ solid-state magic angle spinning (MAS) ¹³ C NMR spectroscopy in real-time conditions and the two-dimensional gas chromatography (GC×GC). A variety of products reveal the crucial role of hydrogen, water, and acid sites for heterolytic cleavage of the β-O-4 bond in VGE. Decarbonylation, hydrogenolysis, hydrogenation, and dehydration reaction pathways are proposed and further validated using first-principles calculations.

TiO2-Modified Montmorillonite-Supported Porous Carbon-Immobilized Pd Species Nanocomposite as an Efficient Catalyst for Sonogashira Reactions

In this study, a combination of the porous carbon (PCN), montmorillonite (MMT), and TiO₂ was synthesized into a composite immobilized Pd metal catalyst (TiO₂-MMT/PCN@Pd) with effective synergism improvements in catalytic performance. The successful TiO₂-pillaring modification for MMT, derivation of carbon from the biopolymer of chitosan, and immobilization of Pd species for the prepared TiO₂-MMT/PCN@Pd⁰ nanocomposites were confirmed using a combined characterization with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption-desorption isotherms, high-resolution transition electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was shown that the combination of PCN, MMT, and TiO₂ as a composite support for the stabilization of the Pd catalysts could synergistically improve the adsorption and catalytic properties. The resultant TiO₂-MMT₈₀/PCN₂₀@Pd⁰ showed a high surface area of 108.9 m²/g. Furthermore, it exhibited moderate to excellent activity (59-99% yield) and high stability (recyclable 19 times) in the liquid-solid catalytic reactions, such as the Sonogashira reactions of aryl halides (I, Br) with terminal alkynes in organic solutions. The positron annihilation lifetime spectroscopy (PALS) characterization sensitively detected the development of sub-nanoscale microdefects in the catalyst after long-term recycling service. This study provided direct evidence for the formation of some larger-sized microdefects during sequential recycling, which would act as leaching channels for loaded molecules, including active Pd species.

Base-free catalytic aerobic oxidation of mercaptans over MOF-derived Co/CN catalyst with controllable composition and structure

The oxidation of mercaptans under mild and base-free conditions is of vital importance in terms of economy and environment for petroleum processing industry. Here, we developed a series of MOF-derived cobalt-based nitrogen-doped (N-doped) carbon (Co/CN-x) catalysts for the base-free catalytic oxidation of mercaptans. The optimal Co/CN-900 showed excellent catalytic activity for the oxidation of mercaptans under base-free conditions, yielding complete conversion of various mercaptans and > 99.0% selectivity of disulfides. The high performance can be contributed to the advantages of hierarchical pore structure for the diffusion and migration of substrates, self-carrying alkalinity for the formation of mercaptide anion, abundant active Co sites for catalytic oxidation of mercaptans as well as the synergistic effects between the Co nanoparticles (NPs) and N-doped carbon supports. Furthermore, a possible mechanism for base-free catalytic oxidation of mercaptans over Co/CN-x catalysts is proposed based on a set of control experiments and density functional theory (DFT) calculations.

In situ hydrodeoxygenation of vanillin over Ni-Co-P/HAP with formic acid as a hydrogen source

A new noble metal-free Ni-Co-P/HAP (hydroxyapatite) amorphous alloy catalyst was synthesized by an impregnation-chemical reduction method; the structure and properties of the catalysts were characterized by XRD, SEM, BET, XPS and DSC. Based on the model of the hydrodeoxygenation (HDO) of vanillin to 2-methoxy-4-methylphenol (MMP) with formic acid as a hydrogen source, the catalytic performance of the catalyst was studied. The results found that the Ni-Co-P/HAP catalyst exhibited excellent catalytic activity for the in situ HDO reaction of vanillin compared with Ni-P and Ni-Co-P. The conversion of vanillin could be high to 97.86% with MMP selectivity of 93.97% under optimized reaction conditions. In addition, mechanism studies have shown that the side reaction of carbocation and vanillyl alcohol (HMP) condensation can be effectively reduced with increasing the hydrogenation rate, thereby the selectivity of MMP was effectively increased.

Bio-waste chitosan-derived N-doped CNT-supported Ni nanoparticles for selective hydrogenation of nitroarenes

In this study, a facile method for the synthesis of leach proof and earth-abundant non-noble Ni nanoparticles on N-doped carbon nanotubes is reported.

Cobalt Nanoparticles Supported on Nitrogen-Doped Carbon: An Effective Non-Noble Metal Catalyst for the Upgrade of Biofuels

A new method has been developed for the deoxygenation of vanillin to produce 2-methoxy-4-methylphenol (MMP) as a promising liquid fuel over a heterogeneous non-noble metal catalyst. Cobalt nanoparticles supported on nitrogen-doped carbon (Co/N-C-600) exhibit high activity and stability for the deoxygenation of vanillin into MMP under mild conditions (150 °C, 10 bar H₂ ). Nearly quantitative MMP yield is obtained in isopropanol after 8 h at 150 °C and 10 bar H₂ pressure. According to the distribution of products with time, the deoxygenation of vanillin into MMP mainly proceeds through the hydrogenation of vanillin into vanillyl alcohol and the subsequent hydrogenolysis of vanillyl alcohol into MMP, of which the latter is the rate-determining step, owing to a much higher activation energy. Moreover, after being recycled several times, the loss of catalytic activity is negligible, which demonstrates that the Co/N-C-600 catalyst shows good resistance to deactivation.

Greatly changed performance of a metal Pd catalyst by a rather easily formed and removed species–PdHx

Some Pd atoms in metal Pd catalyst can adsorb hydrogen element to form PdH_x species under normal conditions during catalyst preparation and catalytic reaction, which boosts HCOOH dehydrogenation (FAD) to produce H₂, but greatly poisons the chemical reduction by FAD.

High performance of a cobalt-nitrogen complex for the reduction and reductive coupling of nitro compounds into amines and their derivatives

Replacement of precious noble metal catalysts with low-cost, non-noble heterogeneous catalysts for chemoselective reduction and reductive coupling of nitro compounds holds tremendous promise for the clean synthesis of nitrogen-containing chemicals. We report a robust cobalt-nitrogen/carbon (Co-N _x /C-800-AT) catalyst for the reduction and reductive coupling of nitro compounds into amines and their derivates. The Co-N _x /C-800-AT catalyst was prepared by the pyrolysis of cobalt phthalocyanine-silica colloid composites and the subsequent removal of silica template and cobalt nanoparticles. The Co-N _x /C-800-AT catalyst showed extremely high activity, chemoselectivity, and stability toward the reduction of nitro compounds with H₂, affording full conversion and >97% selectivity in water after 1.5 hours at 110°C and under a H₂ pressure of 3.5 bar for all cases. The hydrogenation of nitrobenzene over the Co-N _x /C-800-AT catalyst can even be smoothly performed under very mild conditions (40°C and a H₂ pressure of 1 bar) with an aniline yield of 98.7%. Moreover, the Co-N _x /C-800-AT catalyst has high activity toward the transfer hydrogenation of nitrobenzene into aniline and the reductive coupling of nitrobenzene into other derivates with high yields. These processes were carried out in an environmentally friendly manner without base and ligands.

Transfer hydrogenation of bio-fuel with formic acid over biomass-derived N-doped carbon supported acid-resistant Pd catalyst

The strong Pd–N interaction on biomass-derived N-doped highly mesoporous carbons (NMCs) generates co-existence of electron-deficient Pd (Pd^δ+) and metallic Pd (Pd⁰), leading to Pd/NMC as novel bifunctional catalyst for both FA dehydrogenation and vanillin hydrogenation.

Selective hydrogenolysis of carbon–oxygen bonds with formic acid over a Au–Pt alloy catalyst

A CeO₂-supported Au–Pt alloy catalyst is highly efficient for selective hydrogenolysis of carbon–oxygen species using formic acid as the hydrogen source.

Efficient aqueous hydrodeoxygenation of vanillin over a mesoporous carbon nitride-modified Pd nanocatalyst

CN is prepared via polymerization between EDA and CF, which renders coordinated Pd with high activity for selective HDO of vanillin at low H₂ pressure and temperature. This Pd/CN is reusable and the best TOF reaches 295.4 h⁻¹.

Nitrogen-doped porous carbon materials: promising catalysts or catalyst supports for heterogeneous hydrogenation and oxidation

Developing novel and efficient catalysts is a critical step in common heterogeneous hydrogenation and oxidation reactions.

Nitrogen-doped carbon supported iron oxide as efficient catalysts for chemoselective hydrogenation of nitroarenes

Chemoselective hydrogenation has been widely used in the production of fine chemicals, and developing heterogeneous catalysts with high activity and chemoselectivity is always a challenging topic.