Al-Doped Core-Shell-Structured Ni@Mesoporous Silica for Highly Selective Hydrodeoxygenation of Lignin-Derived Aldehydes

Selective deoxygenation of chemicals using non-noble metal-based catalysts poses a significant challenge toward upgrading biomass-derived oxygenates into advanced fuels and fine chemicals. Herein, we report a bifunctional core-shell catalyst (Ni@Al₃-mSiO₂) consisting of Ni nanoparticles closely encapsulated by the Al-doped mesoporous silica shell that achieves 100% vanillin conversion and >99% yield of 2-methoxy-4-methylphenol under 1 MPa H₂ at 130 °C in water. Due to the unique mesoporous core-shell structure, no significant decrease in catalytic activity was observed after 10 recycles. Furthermore, incorporating Al atoms into the silica shell significantly increased the number of acidic sites. Density functional theory calculations reveal the reaction pathway of the vanillin hydrodeoxygenation process and uncover the intrinsic influence of the Al sites. This work not only provides an efficient and cost-effective bifunctional hydrodeoxygenation catalyst but also offers a new synthetic protocol to rationally design promising non-noble metal catalysts for biomass valorization or other widespread applications.

Current Progress on Methods and Technologies for Catalytic Methane Activation at Low Temperatures

Methane (CH4 ) is an attractive energy source and important greenhouse gas. Therefore, from the economic and environmental point of view, scientists are working hard to activate and convert CH4 into various products or less harmful gas at low-temperature. Although the inert nature of CH bonds requires high dissociation energy at high temperatures, the efforts of researchers have demonstrated the feasibility of catalysts to activate CH4 at low temperatures. In this review, the efficient catalysts designed to reduce the CH4 oxidation temperature and improve conversion efficiencies are described. First, noble metals and transition metal-based catalysts are summarized for activating CH4 in temperatures ranging from 50 to 500 °C. After that, the partial oxidation of CH4 at relatively low temperatures, including thermocatalysis in the liquid phase, photocatalysis, electrocatalysis, and nonthermal plasma technologies, is briefly discussed. Finally, the challenges and perspectives are presented to provide a systematic guideline for designing and synthesizing the highly efficient catalysts in the complete/partial oxidation of CH4 at low temperatures.

Palladium encapsulated mesoporous silica nanoparticles for the rapid detection of analytes

We designed a simple, inexpensive, and user-friendly assay using mesoporous silica nanoparticles to detect analytes.

Synthesis of Noble Metal M@YSiO2 Yolk-Shell Nanoparticles with Thin Organic/Inorganic Hybrid Outer Shells via an Aqueous Medium Phase

A simple method is proposed for the synthesis of noble metal M@YSiO₂ (M = Au, Pd, Ag) yolk-shell nanoparticles. The effects of synthesis conditions on the preparation of yolk-shell nanoparticles were discussed in detail. According to the different corrosion resistances between inorganic silica and organosilicone in a selective etching solution, yolk-shell nanoparticles with large cavity and thin shell were prepared using the same aqueous medium in a step-by-step synthesis process. Different from traditional methods, this method is facile and efficient because the main synthesis process is carried out in an aqueous phase. This extended method may benefit the synthesis and application of other nanomaterials with a similar yolk-shell structure.

Pomegranate-like Core-Shell Ni-NSs@MSNSs as a High Activity, Good Stability, Rapid Magnetic Separation, and Multiple Recyclability Nanocatalyst for DCPD Hydrogenation

A novel pomegranate-like Ni-NSs@MSNSs nanocatalyst was successfully synthesized via a modified Stöber method, and its application in the hydrogenation of dicyclopentadiene (DCPD) was firstly reported. The Ni-NSs@MSNSs possessed a high specific area (658 m²/g) and mesoporous structure (1.7-3.3 nm). The reaction of hydrogenation of DCPD to endo-tetrahydrodicyclopentadiene (endo-THDCPD) was used to evaluate the catalytic performance of the prepared materials. The distinctive pomegranate-like Ni-NSs@MSNSs core-shell nanocomposite exhibited superior catalytic activity (TOF = 106.0 h^-1 and STY = 112.7 g·L^-1·h^-1) and selectivity (98.9%) than conventional Ni-based catalysts (experimental conditions: Ni/DCPD/cyclohexane = 1/100/1000 (w/w), 150 °C, and 2.5 MPa). Moreover, the Ni-NSs@MSNSs nanocatalyst could be rapidly and conveniently recycled by magnetic separation without appreciable loss. The Ni-NSs@MSNSs also exhibited excellent thermal stability (≥750 °C) and good recycling performance (without an activity and selectivity decrease in four runs). The superior application performance of the Ni-NSs@MSNSs nanocatalyst was mainly owing to its unique pomegranate-like structure and core-shell synergistic confinement effect.

Three-Dimensional Network Pd-Ni/γ-Al2O3 Catalysts for Highly Active Catalytic Hydrogenation of Nitrobenzene to Aniline under Mild Conditions

In view of the current situation of high cost and low catalytic efficiency of the commercial Pd-based catalysts, adding transition metals (Ni, Co, etc.) to form the Pd-M bimetallic catalyst not only reduces the consumption of Pd but also greatly improves the catalytic activity and stability, which has attracted increasing attention. In this work, the three-dimensional network Pd-Ni bimetallic catalysts were prepared successfully by a liquid-phase in situ reduction method with the hydroxylated γ-Al₂O₃ as the support. Through investigating the effects of the precursor salt amount, reducing agent concentration, stabilizer concentration, and reducing stirring time on the synthesis of the Pd-Ni nanocatalyst, the three-dimensional network Pd-Ni bimetallic nanostructures with four different atomic ratios were prepared under an optimal condition. The obtained wire-like Pd-Ni catalysts have a uniform diameter size of about 5 nm and length up to several microns. After closely combining with the hydroxylated γ-Al₂O₃, the supported Pd-Ni/γ-Al₂O₃ catalysts exhibit nearly 100% conversion rate and selectivity for the hydrogenation of nitrobenzene to aniline at low temperature and normal pressure. The stability testing of the supported Pd-Ni/γ-Al₂O₃ catalysts shows that the conversion rate still remained above 99% after 10 cycles. There is no doubt that the supported catalysts show significant catalytic efficiency and recyclability, which provides important theoretical basis and technical support for the preparation of low-cost, highly efficient catalysts for the hydrogenation of nitrobenzene to aniline.

Au@mSiO2 core-shell nanoparticles loaded with fluorescent dyes: synthesis and application for imaging performance

Here, Au@mSiO2 core-shell nanoparticles were easily synthesized by a one-pot method. Positively charged alkyl chains with different lengths were modified on the surface of the particles. Thus composite nanoparticles with different potentials and hydrophilic interface properties were prepared. Based on the charge properties of the shell surface, the process of loading dyes was simplified by the strong electrostatic adsorption between the particle surface and the heterogeneous negatively charged dyes. The fluorescence intensity and fluorescence lifetime of the loaded fluorescent dyes showed that the dyes could not produce effective tunneling in the mesoporous materials, which was limited to the surface of the particles, which is beneficial for the subsequent research on the loading or release of nanoparticles. After loading, the nanoparticles still exhibit a high fluorescence intensity, enabling dual-mode microscopic imaging (TEM and fluorescence).

One-pot synthesis of highly active and hydrothermally stable Pd@mHSiO2 yolk-shell-structured nanoparticles for high-temperature reactions in hydrothermal environments

The facile synthesis of yolk-shell-structured nanoparticles (YSNPs) with mobile active metal cores and mesoporous inorganic-organic hybrid silica shells (mHSiO2) is important for their applications. In this work, Pd@mHSiO2 YSNPs have been synthesized in aqueous solution at 95 °C by a one-pot method without the need for extensive purification and separation steps. The method is simple and facile, and ingeniously combines the controlled synthesis of Pd nanocubes, coating of mesoporous silica, and transition from core-shell-structured nanoparticles (CSNPs) to YSNPs. 29Si NMR spectroscopy, FTIR spectroscopy, and detailed control experiments have demonstrated that the incorporation of 1,2-bis(trimethoxysilyl)ethane (BTME) modifies the degree of condensation between the outer hybrid silica layer and the inner pure silica section, and that high temperature water is really responsible for dissolving the inner pure silica layer leading to a transition from the CSNPs to the YSNPs. The obtained Pd@mHSiO2 YSNPs have a controllable diameter, tunable shell thickness, a high specific surface area, and uniform mesoporosity. Thermal stability tests have indicated that the Pd@mHSiO2 YSNPs are remarkably stable at high temperatures up to 650 °C. Importantly, the Pd@mHSiO2 YSNPs exhibit a much higher catalytic activity and hydrothermal stability than Pd@mSiO2 CSNPs or Pd/mHSiO2 NSs in the conversion of levulinic acid (LA) into γ-valerolactone (GVL), because the hollow voids provide low mass-transfer resistance and improve the accessibility of the catalytic sites, and the incorporation of organic groups enhances the hydrothermal stability of the outer shell.