Better performance for gas-phase epoxidation of propylene using H2 and O2 at lower temperature over Au/TS-1 catalyst

Precisely Engineered Supported Gold Clusters as a Stable Catalyst for Propylene Epoxidation

Designing a stable and selective catalyst with high H₂ utilisation is of pivotal importance for the direct gas-phase epoxidation of propylene. This work describes a facile one-pot methodology to synthesise ligand-stabilised sub-nanometre gold clusters immobilised onto a zeolitic support (TS-1) to engineer a stable Au/TS-1 catalyst. A non-thermal O₂ plasma technique is used for the quick removal of ligands with limited increase in particle size. Compared to untreated Au/TS-1 catalysts prepared using the deposition precipitation method, the synthesised catalyst exhibits improved catalytic performance, including 10 times longer lifetime (>20 days), increased PO selectivity and hydrogen efficiency in direct gas phase epoxidation. The structure-stability relationship of the catalyst is illustrated using multiple characterisation techniques, such as XPS, ³¹ P MAS NMR, DR-UV/VIS, HRTEM and TGA. It is hypothesised that the ligands play a guardian role in stabilising the Au particle size, which is vital in this reaction. This strategy is a promising approach towards designing a more stable heterogeneous catalyst.

Reversing Titanium Oligomer Formation towards High-Efficiency and Green Synthesis of Titanium-Containing Molecular Sieves

Green and efficient synthesis of titanium-containing molecular sieves is limited by the quantity of environmentally unfriendly additives and complicated synthesis procedures required. Oligomerization of Ti monomers into anatase TiO₂ is the typical outcome of such procedures because of a mismatch between hydrolysis rates of Si and Ti precursors. We report a simple and generic additive-free route for the synthesis of Ti-containing molecular sieves (MFI, MEL, and BEA). This approach successfully reverses the formation of Ti oligomers to match hydrolysis rates of Ti and Si species with the assistance of hydroxyl free radicals generated in situ from ultraviolet irradiation. Moreover, fantastic catalytic performance for propene epoxidation with H₂ and O₂ was observed. Compared with the conventional hydrothermal method, this approach opens up new opportunities for high-efficiency, environmentally benign, and facile production of pure titanium-containing molecular sieves.

Direct Gas-Phase Oxidation of Propylene to Acetone in the Presence of H2 and O2 over Au/TS-1 Catalyst

A novel process for the preparation of acetone is reported by gas-phase oxidation of propylene in the presence of H2 and O2 with Au supported TS-1 catalyst (Au/TS-1). By elevating the reaction temperature to 280°C, Au/TS-1 catalyzes 11.6% propylene generating acetone with 70.6% selectivity, and 8.2% acetone in onepass yield. Acetone is originated from propylene oxide isomerization, which is mainly attributed to the surface of the Lewis base and high reaction temperature. Furthermore, small Au nanoparticle size promotes the reaction.

Advances in Designing Au Nanoparticles for Catalytic Epoxidation of Propylene with H2 and O2

Au nanoparticles, which can be used in various industrial and environmental applications, have drawn substantial research interest. In this review, a comprehensive background and some insights are provided regarding recent studies concerning the use of Au nanoparticles for catalytic propylene epoxidation with H2 and O2. Over the last two decades, substantial progress has been made toward the efficient production of propylene oxide (PO); this includes the design of highly dispersed Au catalysts on Ti-modified mesoporous silica supports, the optimization of catalytic epoxidation, and the determination of the mechanisms and reaction pathways of epoxidation. Particularly, the critical roles of catalyst synthesis, the types of material support, Au nanoparticle sizes, and the dispersion amounts of Au nanoparticles are emphasized in this review. In future studies, novel, practical, robust, and highly PO-selective Au nanoparticle catalyst systems are expected to be continually designed for the enhanced catalytic epoxidation of propylene.

Hierarchical AuNPs-Loaded Fe₃O₄/Polymers Nanocomposites Constructed by Electrospinning with Enhanced and Magnetically Recyclable Catalytic Capacities

Gold nanoparticles (AuNPs) have attracted widespread attention for their excellent catalytic activity, as well as their unusual physical and chemical properties. The main challenges come from the agglomeration and time-consuming separation of gold nanoparticles, which have greatly baffled the development and application in liquid phase selective reduction. To solve these problems, we propose the preparation of polyvinyl alcohol(PVA)/poly(acrylic acid)(PAA)/Fe₃O₄ nanocomposites with loaded AuNPs. The obtained PVA/PAA/Fe₃O₄ composite membrane by electrospinning demonstrated high structural stability, a large specific surface area, and more active sites, which is conducive to promoting good dispersion of AuNPs on membrane surfaces. The subsequently prepared PVA/PAA/Fe₃O₄@AuNPs nanocomposites exhibited satisfactory nanostructures, robust thermal stability, and a favorable magnetic response for recycling. In addition, the PVA/PAA/Fe₃O₄@AuNPs nanocomposites showed a remarkable catalytic capacity in the catalytic reduction of p-nitrophenol and 2-nitroaniline solutions. In addition, the regeneration studies toward p-nitrophenol for different consecutive cycles demonstrate that the as-prepared PVA/PAA/Fe₃O₄@AuNPs nanocomposites have outstanding stability and recycling in catalytic reduction.