Identification of the Au/ZnO interface as the specific active site for the selective oxidation of the secondary alcohol group in glycerol

Enhanced Glycerol Oxidation Toward Dihydroxyacetone Over Gold/Palladium Binary Nanocatalysts by Structure Control

Gold/palladium binary catalysts have been widely used to the selective oxidation of glycerol to produce value-added chemicals. However, the essential effect of the structure of Au/Pd binary catalysts on the catalytic performance has not been elucidated yet. In this work, Au, Pd, AuPd alloy, Au@Pd core-shell, and Au-Pd Janus nanoparticle catalysts prepared by sol-immobilization and photochemical deposition methods were employed to the selective oxidation of glycerol toward dihydroxyacetone (DHA). The results showed that the activation of glycerol and oxygen molecule was significantly promoted with the appropriate interaction between Au and Pd atoms. That was, the turnover frequency of glycerol and DHA generation rate over the alloyed AuPd nanoparticles were remarkably higher than those of Au@Pd core-shell and Au-Pd Janus nanoparticle catalysts. It was due to the synergistic effect of Pd and Au atoms remarkably promoted the electron transfer from Pd to Au, resulting in increasing the activity of the exposed Au sites, and moderately inhibiting the activity of the exposed Pd sites, which benefited to generate DHA rapidly. After optimizing, up to 61 % yield of DHA was achieved at 87 % glycerol conversion over the alloyed AuPd catalyst.

Manipulating the interfacial integration mode of a bio-templated porous ZSM-5 platform with an Au/CuZnOx catalyst for enhanced efficiency and recycling stability in glycerol conversion to 1,3-dihydroxyacetone

Despite the potential to significantly enhance the economic viability of biomass-based platforms through the selective conversion of glycerol to 1,3-dihydroxyacetone (DHA), a formidable challenge persists in simultaneously achieving high catalytic activity and stability along this reaction pathway. Herein, we have devised a strategic approach to manipulate the interfacial integration within composite catalysts to address the performance trade-off. Through the modulation of the composite process involving a bio-templated porous ZSM-5 zeolite platform (bZ) and an Au/CuZnOx catalyst, three distinct interfacial bonding modes were achieved: physical milling, encapsulation by zeolite, and in situ growth on zeolite. The catalyst prepared via the physical milling mode (denoted as Au/CuZnOx@bZ) demonstrated remarkable catalytic efficiency with a glycerol conversion rate of 93% and a DHA selectivity of 86%. In particular, Au/CuZnOx@bZ maintained over 72% of glycerol conversion and DHA selectivity even after five cycles, exhibiting superior stability that surpasses the majority of current catalysts. The differences in interfacial integration modes play a crucial role in regulating the surface Au+ content and the reduction temperatures of the catalysts and minimizing Au nanoparticle agglomeration during cycling, as confirmed by comprehensive characterization and experimental analyses.

Selective oxidation of glycerol mediated by surface plasmon of gold nanoparticles deposited on titanium dioxide nanowires

This paper describes an alternative method for the in situ synthesis of gold nanoparticles (AuNPs) with a particle size of less than 3 nm, using nanoreactors formed by reverse micelles of 1,4-bis-(2-ethylhexyl) sulfosuccinate sodium (AOT) and nanoparticle stabilization with l-cysteine, which favor the preparation of nanoparticles with size and shape control, which are homogeneously dispersed (1% by weight) on the support of titanium dioxide nanowires (TNWs). To study the activity and selectivity of the prepared catalyst (AuNPs@TNWs), an aqueous solution of 40 mM glycerol was irradiated with a green laser (λ = 530 nm, power = 100 mW) in the presence of the catalyst and O2 as an oxidant at 22 °C for 6 h, obtaining a glycerol conversion of 86% with a selectivity towards hydroxypyruvic acid (HA) of more than 90%. From the control and reactions, we concluded that the Ti-OH groups promote the glycerol adsorption on the nanowires surface and the surface plasmon of the gold nanoparticles favors the selectivity of the reaction towards the hydroxypyruvic acid.

Dihydroxyacetone production by glycerol oxidation under moderate condition using Pt loaded on La1-xBixOF solids

Pt/La_1-xBi_xOF/SBA-16 (SBA-16: Santa Barbara Amorphous no. 16) catalysts were prepared to produce dihydroxyacetone (DHA) from glycerol under moderate conditions. By using 7 wt% Pt/16 wt% La_0.95Bi_0.05OF/SBA-16, the DHA yield reached up to 78.4% (glycerol conversion: 100%) after reacting for 6 h at 30 °C in an atmospheric open-air system.

Dihydroxyacetone: A User Guide for a Challenging Bio-Based Synthon

1,3-dihydroxyacetone (DHA) is an underrated bio-based synthon, with a broad range of reactivities. It is produced for the revalorization of glycerol, a major side-product of the growing biodiesel industry. The overwhelming majority of DHA produced worldwide is intended for application as a self-tanning agent in cosmetic formulations. This review provides an overview of the discovery, physical and chemical properties of DHA, and of its industrial production routes from glycerol. Microbial fermentation is the only industrial-scaled route but advances in electrooxidation and aerobic oxidation are also reported. This review focuses on the plurality of reactivities of DHA to help chemists interested in bio-based building blocks see the potential of DHA for this application. The handling of DHA is delicate as it can undergo dimerization as well as isomerization reactions in aqueous solutions at room temperature. DHA can also be involved in further side-reactions, yielding original side-products, as well as compounds of interest. If this peculiar reactivity was harnessed, DHA could help address current sustainability challenges encountered in the synthesis of speciality polymers, ranging from biocompatible polymers to innovative polymers with cutting-edge properties and improved biodegradability.

A Carbon-Negative Hydrogen Production Strategy: CO2 Selective Capture with H2 Production

We reported a strategy of carbon-negative H₂ production in which CO₂ capture was coupled with H₂ evolution at ambient temperature and pressure. For this purpose, carbonate-type Cu_x Mg_y Fe_z layered double hydroxide (LDH) was preciously constructed, and then a photocatalysis reaction of interlayer CO₃ ^2- reduction with glycerol oxidation was performed as driving force to induce the electron storage on LDH layers. With the participation of pre-stored electrons, CO₂ was captured to recover interlayer CO₃ ^2- in presence of H₂ O, accompanied with equivalent H₂ production. During photocatalysis reaction, Cu_0.6 Mg_1.4 Fe₁ exhibited a decent CO evolution amount of 1.63 mmol g^-1 and dihydroxyacetone yield of 3.81 mmol g^-1 . In carbon-negative H₂ production process, it showed an exciting CO₂ capture quantity of 1.61 mmol g^-1 and H₂ yield of 1.44 mmol g^-1 . Besides, this system possessed stable operation capability under simulated flu gas condition with negligible performance loss, exhibiting application prospect.

Pt1 enhanced C-H activation synergistic with Ptn catalysis for glycerol cascade oxidation to glyceric acid

The selective oxidation of glycerol to glyceric acid, an important value-added reaction from polyols, is a typical cascade catalytic process. It is still of great challenge to simultaneously achieve high glycerol activity and glyceric acid selectivity, suffering from either deep oxidation and C-C cleavage or poor oxidation efficiency from glyceraldehyde to glyceric acid. Herein, this work, inspired by nature, proposes a cascade synergistic catalysis strategy by atomic and low-coordinated cluster Pt on well-defined Cu-CuZrO_x, which involves enhanced C-H activation on atomic Pt₁ and O-H activation on cluster Pt_n in the oxidation of glycerol to glyceraldehyde, and cluster Pt_n for C=O activation followed by O-H insertion and atomic Pt₁ for C-H activation in the tandem oxidation of glyceraldehyde to glyceric acid. The enhanced C-H activation in the cascade process by atomic Pt₁ is revealed to be essential for the high glycerol activity (90.0±0.1%) and the glyceric acid selectivity (80.2±0.2%).

The selective oxidation of glycerol to glyceric acid is an important value-added cascade catalytic process. Here the authors report a cascade synergistic catalysis strategy by atomic and low-coordinated cluster Pt on well-defined Cu-CuZrOx to simultaneously achieve high activity and selectivity.

Leveraging Pt/Ce1-xLaxO2-δ To Elucidate Interfacial Oxygen Vacancy Active Sites for Aerobic Oxidation of 5-Hydroxymethylfurfural

The interfacial oxygen-defective sites of oxide-supported metal catalysts are generally regarded as active centers in diverse redox reactions. Identification of their structure-property relationship at the atomic scale is of great importance but challenging. Herein, a series of La³⁺-doped three-dimensionally ordered macroporous CeO₂ (3D-Ce_1-xLa_xO_2-δ) were synthesized and applied as supports for Pt nanoparticles. The pieces of evidence from a suite of in-situ/ex-situ characterizations and theoretical calculations revealed that the La³⁺-mono-substituted La-□(-Ce)₂ sites (where □ represents an oxygen vacancy) exhibited superior charge transfer ability, behaving as trapping centers for Pt nanoparticles. The resulting interfacial Pt^δ+/La-□(-Ce)₂ sites served as the reversible active species in the aerobic oxidation of 5-hydroxymethylfurfural to boost catalytic performance by simultaneously promoting oxygen activated capacity and the cleavage of O-H/C-H bonds of adsorbed hydroxymethyl groups. Consequently, the Pt/3D-Ce_0.9La_0.1O_2-δ catalyst possessing the highest number of Pt^δ+/La-□(-Ce)₂ sites showed the best catalytic performance with 99.6% yield to 2,5-furandicarboxylic acid in 10 h. These results offer more insights into the promoting mechanism of interfacial oxygen-defective sites for the liquid-phase aerobic oxidation of aldehydes and alcohols.

Boosting the catalytic behavior and stability of a gold catalyst with structure regulated by ceria

In this work, a series of colloidal gold nanoparticles with controllable sizes were anchored on carbon nanotubes (CNT) for the aerobic oxidation of benzyl alcohol. The intrinsic influence of Au particles on the catalytic behavior was unraveled based on different nanoscale-gold systems. The Au/CNT-A sample with smaller Au sizes deserved a faster reaction rate, mainly resulting from the higher dispersion degree (23.5%) of Au with the available exposed sites contributed by small gold particles. However, monometallic Au/CNT samples lacked long-term stability. CeO2 was herein decorated to regulate the chemical and surface structure of the Au/CNT. An appropriate CeO2 content tuned the sizes and chemical states of Au by electron delivery with better metal dispersion. Small CeO2 crystals that were preferentially neighboring the Au particles facilitated the generation of Au-CeO2 interfaces, and benefited the continuous supplementation of oxygen species. The collaborative functions between the size effect and surface chemistry accounted for the higher benzaldehyde yield and sustainably stepped-up reaction rates by Au-Ce5/CNT with 5 wt% CeO2.

One-pot synthesis of finely-dispersed Au nanoparticles on ZnO hexagonal sheets for base-free aerobic oxidation of vanillyl alcohol

Highly-dispersed and small-sized Au (2.2 nm)/ZnO catalyst was prepared using metal ions and 2-methylimidazole by one-pot coordination–calcination method, and showed superior performances for vanillin synthesis via base-free oxidation.

Oxidative esterification of renewable furfural on cobalt dispersed on ordered porous nitrogen-doped carbon

A series of highly dispersed cobalt-based catalysts on N-doped ordered porous carbon (Co-NOPC) were synthesized using the sacrificial-template method. MCM-41, ZSM-5 and SBA-15 were employed as hard templates with 2,2'-bipyridine as the ligand. The physical and chemical properties of the Co-NOPC catalyst were characterized by Raman, XRD, SEM, TEM, EDX, ICP, BET, XPS. Co-NOPC had been proven to be a highly efficient catalyst for oxidative esterification of furfural (FUR) to methyl 2-furoate without alkaline additives. Catalytic performance was correlated to the dispersed cobalt, porous structure and specific surface area. The relationship between oxygen activation and the strong interaction of cobalt and pyridine nitrogen were confirmed by XPS. Catalytic performance enhancement mechanisms were correlated with the redistribution of electrons at the interface between carbon material and cobalt atoms through the molecular dynamics method and a reaction mechanism was also proposed. The optimized catalysts showed outstanding catalytic activity and stability and no obvious decrease in activity was found after 6 cycles with 99.6% FUR conversion and 96% methyl 2-furoate selectivity.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts

In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO₂ hydrogenation, C–C coupling, and methane oxidation. Only studies where the role of support has been explicitly studied in detail have been selected for discussion. However, the role of support is also examined using examples of reactions involving unsupported metal nanoparticles (i.e., colloidal nanoparticles). It is clear that the support functionality can play a crucial role in tuning the catalytic activity that is observed and that advanced theory and characterization add greatly to our understanding of these fascinating catalysts.

Nanoscale Au-ZnO Heterostructure Developed by Atomic Layer Deposition Towards Amperometric H2O2 Detection

Nanoscale Au-ZnO heterostructures were fabricated on 4-in. SiO2/Si wafers by the atomic layer deposition (ALD) technique. Developed Au-ZnO heterostructures after post-deposition annealing at 250 °C were tested for amperometric hydrogen peroxide (H2O2) detection. The surface morphology and nanostructure of Au-ZnO heterostructures were examined by field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), etc. Additionally, the electrochemical behavior of Au-ZnO heterostructures towards H2O2 sensing under various conditions is assessed by chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that ALD-fabricated Au-ZnO heterostructures exhibited one of the highest sensitivities of 0.53 μA μM-1 cm-2, the widest linear H2O2 detection range of 1.0 μM-120 mM, a low limit of detection (LOD) of 0.78 μM, excellent selectivity under the normal operation conditions, and great long-term stability. Utilization of the ALD deposition method opens up a unique opportunity for the improvement of the various capabilities of the devices based on Au-ZnO heterostructures for amperometric detection of different chemicals.

Preparation of AuPd/ZnO–CuO for the directional oxidation of glycerol to DHA

Under alkali-free conditions, 86% DHA selectivity and 65% DHA yield were achieved in the selective oxidation of glycerol.

Cu–Al composite oxides: a highly efficient support for the selective oxidation of glycerol to 1,3-dihydroxyacetone

A series of Au catalysts supported on Cu–Al composite oxides were prepared and applied for the selective catalytic oxidation of glycerol to 1,3-dihydroxyacetone (DHA) in base-free conditions.

Selective Oxidation of Glycerol to Dihydroxyacetone over Au/CuxZr1-xOy Catalysts in Base-Free Conditions

In this paper, a series of Cu-Zr mixed metal oxide-supported Au catalysts were prepared by deposition-precipitation and evaluated for selective oxidation of glycerol to dihydroxyacetone (DHA) in base-free conditions. The best catalytic performance was obtained with DHA selectivity of up to 95% and yield of 70% in 4 h, 50 °C and P_O2 = 0.2 MPa over the Au/Cu_0.95Zr_0.05 and Au/Cu_0.9Zr_0.1 catalysts. Combined with the characterization results of Brunauer-Emmett-Teller, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and CO₂ temperature programmed desorption, it was proposed that the content of Au⁰, the size of Au, and the basicity of the catalyst affected the glycerol conversion and DHA selectivity. After the catalyst was recycled four times, the glycerol conversion decreased by about 14% which might result from the carbon deposition or the byproduct adsorption and the agglomeration of Au particle.