Highly Active and Dispersed Pd Nanoparticles Stabilized by Lacunary Phosphomolybdate: Synthesis, Characterization, and Liquid Phase Hydrogenation of Levulinic Acid to γ-Valerolactone

In the current scenario, one of the crucial reaction conversions is the synthesis of renewable biofuels and value-added chemicals from the hydrogenation of biomass. Therefore, in the present work, we are proposing aqueous phase conversion of levulinic acid to γ-valerolactone via hydrogenation using formic acid as a sustainable green hydrogen source over a sustainable heterogeneous catalyst. The catalyst based on Pd nanoparticles stabilized by lacunary phosphomolybdate (PMo₁₁Pd) was designed for the same and characterized by EDX, FT-IR, ³¹P NMR, powder XRD, XPS, TEM, HRTEM, and HAADF-STEM analyses. A detailed optimization study was done to achieve maximum conversion (95% conversion), using a very small amount of Pd (1.879 × 10^-3 mmol) with notable TON (2585) at 200 °C in 6 h. The regenerated catalyst was found to be workable (reusable) up to three cycles without any change in activity. Also, a plausible reaction mechanism was proposed. The catalyst exhibits superior activity against reported catalysts.

Review on supported metal catalysts with partial/porous overlayers for stabilization

Heterogeneous catalysts of supported metals are important for both liquid-phase and gas-phase chemical transformations which underpin the petrochemical sector and manufacture of bulk or fine chemicals and pharmaceuticals. Conventional supported metal catalysts (SMC) suffer from deactivation resulting from sintering, leaching, coking and so on. Besides the choice of active species (e.g. atoms, clusters, nanoparticles) to maximize catalytic performances, strategies to stabilize active species are imperative for rational design of catalysts, particularly for those catalysts that work under heated and corrosive reaction conditions. The complete encapsulation of metal active species within a matrix (e.g. zeolites, MOFs, carbon, etc.) or core-shell arrangements is popular. However, the use of partial/porous overlayers (PO) to preserve metals, which simultaneously ensures the accessibility of active sites through controlling the size/shape of diffusing reactants and products, has not been systematically reviewed. The present review identifies the key design principles for fabricating supported metal catalysts with partial/porous overlayers (SMCPO) and demonstrates their advantages versus conventional supported metals in catalytic reactions.

Systematic Investigation on Supported Gold Catalysts Prepared by Fluorine-Free Basic Etching Ti3AlC2 in Selective Oxidation of Aromatic Alcohols to Aldehydes

Conventional methods to prepare supported metal catalysts are chemical reduction and wet impregnation. This study developed and systematically investigated a novel reduction method based on simultaneous Ti₃AlC₂ fluorine-free etching and metal deposition to prepare gold catalysts. The new series of Au_pre/Ti₃Al_xC₂Ty catalysts were characterized by XRD, XPS, TEM, and SEM and were tested in the selective oxidation of representative aromatic alcohols to aldehydes. The catalytic results demonstrate the effectiveness of the preparation method and better catalytic performances of Au_pre/Ti₃Al_xC₂T_y, compared with those of catalysts prepared by traditional methods. Moreover, this work presents a comprehensive study on the influence of calcination in air, H₂, and Ar, and we found that the catalyst of Au_pre/Ti₃Al_xC₂T_y-Air600 obtained by calcination in air at 600 °C performed the best, owing to the synergistic effect between tiny surface TiO₂ species and Au NPs. The tests of reusability and hot filtration confirmed the catalyst stability.

Efficient synergism of NiO-NiSe2 nanosheet-based heterostructures shelled titanium nitride array for robust overall water splitting

Water splitting via the use of an efficient catalyst is a clean and cost-effective approach to produce green hydrogen. In this study, we successfully developed a novel hybrid coming from thin NiO-NiSe₂ nanosheet-based heterostructure shelled high-conductive titanium nitride nanoarrays (TiN@NiO-NiSe₂) supported on carbon cloth (CC) via an optimized in-situ synthesis strategy. The hybrid possesses unique physicochemical properties due to the combination of merits from individual components and their synergistic effects, thereby boosting number and type of electroactive sites, reasonably adjusting Gibbs free adsorption energy, and promoting charge/mass transfers. As a potential bifunctional electrocatalyst, the hybrid requires low overpotentials of 115 and 240 mV to reach a current response of 10 mA cm^-2 towards hydrogen evolution reaction and oxygen evolution reaction in 1.0 M KOH, respectively. Therefore, an electrolyzer of the TiN@NiO-NiSe₂ on CC exhibits a low operation voltage of 1.57 V at 10 mA cm^-2 together with a prospective durability, which exceed behaviors of Pt/C//RuO₂ as well as recently reported bifunctional electrocatalysts. The results suggest a promising approach for developing cost-effective catalyst towards green hydrogen production via water splitting.

A universal synthesis strategy for stable CsPbX3@oxide core-shell nanoparticles through bridging ligands

CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) have shown great potential in various optoelectronic devices due to their excellent photophysical properties. However, the poor stability has severely impeded their practical applications. Much effort has been devoted to the preparation of monodisperse core-shell NCs to improve the stability of CsPbX3 NCs. However, it is still challenging to develop a general method to coat CsPbX3 NCs with oxides at the single-particle level. In this work, we report a simple way to prepare monodisperse CsPbX3@SiO2/Ta2O5/ZrO2 core-shell structure NCs using 3-aminopropyl triethoxysilane (APTES) as a bridging ligand. It has been found that careful control of the hydrolysis and condensation process of oxide precursors is critical for the successful preparation of CsPbX3@oxide core-shell NCs. The stability of CsPbI3 NCs upon attack of water, UV-light irradiation, and heating before and after the oxide shell growth has been investigated, demonstrating the efficient protective effect of oxide shells. This work not only provides a novel and universal approach for coating the individual CsPbX3 nanocrystal with various oxide shells but also paves the way for potential practical applications of CsPbX3 NCs because of the enhanced stability.

Engineering of Yolk/Core-Shell Structured Nanoreactors for Thermal Hydrogenations

Heterogeneous hydrogenation reactions are of great importance for chemical upgrading and synthesis, but still face the challenges of controlling selectivity and long-term stability. To improve the catalytic performance, many hydrogenation reactions utilize special yolk/core-shell nanoreactors (YCSNs) with unique architectures and advantageous properties. This work presents the developmental and technological challenges in the preparation of YCSNs that are potentially useful for hydrogenation reactions, and provides a summary of the properties of these materials. The work also addresses the scientific challenges in applications of these YCSNs in various gas and liquid-phase hydrogenation reactions. The catalyst structures, catalytic performance, structure-performance relationships, reaction mechanisms, and unsolved problems are discussed too. Also, a brief outlook and opportunities for future research in this field are presented. This work on the advancements in YCSNs might inspire the creation of new materials with desired structures for achieving maximal hydrogenation performances.

Novel mesoporous Ag@SiO2 nanospheres as a heterogeneous catalyst with superior catalytic performance for hydrogenation of aromatic nitro compounds

Mesoporous core–shell structure Ag@SiO₂ nanospheres are constructed to prevent Ag nanoparticles from aggregation during the hydrogenation reaction. The prepared catalyst shows superior catalytic performance for hydrogenation of nitro compounds with 100% conversion and selectivity without any by-products, which also indicates good recycling performance for several times use.

Mesoporous core–shell structure Ag@SiO₂ nanospheres are constructed to prevent Ag nanoparticles from aggregation during the hydrogenation reaction.

Heterogeneous Catalytic Hydrogenation of Levulinic Acid to γ-Valerolactone with Formic Acid as Internal Hydrogen Source

As one of the most promising biomass-based platform molecules, γ-valerolactone (GVL) can be synthesized from a variety of lignocellulosic feedstocks through different hydrogen supply pathways. Among these transformation routes, the hydrogenation of levulinic acid (LA) to GVL by using formic acid (FA) as the internal hydrogen source is regarded as a critical path for the sustainable development of renewable energy systems. Although a large number of studies on the synthesis of GVL have been reported, the FA/LA catalytic system has not been interpreted as thoroughly as it should be. In this Minireview, core concerns are focused on key issues and their effects in this FA/LA catalytic system. The catalytic mechanism, together with competitive adsorption behavior between FA and LA on heterogeneous catalysts, is presented. The effects of active metal species and catalyst supports on the overall catalytic performance are summarized, and the influences of key condition parameters, including the time, temperature, FA/LA molar ratios, and aqueous solvent, are discussed. In particular, impacts and improvements of coke deposition and metal leaching, which could greatly affect the catalyst stability, are analyzed in detail. Additionally, several feasible suggestions for the enhancement of the catalytic efficiency and stability are also proposed.

Hierarchical Porous Organometallic Polymers Fabricated by Direct Knitting: Recyclable Single-Site Catalysts with Enhanced Activity

Porous organometallic polymers (POMPs) with hierarchical pore structures, high specific surface areas, and atomically dispersed metal (Ir, Pd, Ru) centers are successfully fabricated by a facile one-pot method through direct knitting of diverse N-heterocyclic carbene metal (NHC-M) complexes. These polymers can function as recyclable solid single-site catalysts and exhibit excellent catalytic activity and selectivity in both dehydrogenation and hydrogenation reactions even at ppm-level catalyst loadings. Remarkably, a record turnover number (TON) of 1.01 × 10⁶ is achieved in the hydrogenation of levulinic acid to γ-valerolactone, which is 750 times higher than that attained with corresponding bis-NHC-Ir complex.

Rhodium porphyrin molecule-based catalysts for the hydrogenation of biomass derived levulinic acid to biofuel additive γ-valerolactone

RhTPP and RhTCPP were prepared and utilized for the conversion of levulinic acid to γ-valerolactone and the reaction mechanism was proposed.

Transformation of γ-valerolactone into 1,4-pentanediol and 2-methyltetrahydrofuran over Zn-promoted Cu/Al2O3 catalysts

The presence of Zn can promote the activity and stability as well as adjust the product selectivity due to the formation of ZnCu alloy and the reduction of acidic sites, which prevents the deactivation of the catalyst and dehydration of 1,4-PDO.

Catalytic performance of a phosphorus-modified H-IM-5@meso-SiO2 composite in the alkylation of toluene with methanol

A phosphorus-modified H-IM-5@meso-SiO₂ was synthesized, and its acidity and pore channels were modified to enhance the selectivity of the target product.

Nanostructured Metal Catalysts for Selective Hydrogenation and Oxidation of Cellulosic Biomass to Chemicals

Conversion of biomass to chemicals provides essential products to human society from renewable resources. In this context, achieving atom-economical and energy-efficient conversion with high selectivity towards target products remains a key challenge. Recent developments in nanostructured catalysts address this challenge reporting remarkable performances in shape and morphology dependent catalysis by metals on nano scale in energy and environmental applications. In this review, most recent advances in synthesis of heterogeneous nanomaterials, surface characterization and catalytic performances for hydrogenation and oxidation for biorenewables with plausible mechanism have been discussed. The perspectives obtained from this review paper will provide insights into rational design of active, selective and stable catalytic materials for sustainable production of value-added chemicals from biomass resources.

Synthesis and Application of Dendritic Fibrous Nanosilica/Gold Hybrid Nanomaterials

Morphologically unique silica nanoparticles can be used as effective templates to prepare silica-metal hybrid nanomaterials, which are highly applicable in a variety of areas. Mesoporous silica nanoparticles, which have high surface areas and an abundance of pores, can be used to synthesize mesoporous silica core-metal shell nanostructures with catalytically active sites. In this work, dendritic fibrous nanosilica (DFNS) with a high surface area is successfully employed as a template to synthesize DFNS/Au hybrid nanomaterials. Au nanodots are initially synthesized through the selective reduction of Au ions on the surface of the DFNS after surface modification to form DFNS/Au dots. A seed-mediated growth method is used to controllably grow Au nanoparticles on the DFNS/Au dots to generate DFNS core-Au nanoparticles shell nanohybrids (DFNS/Au NPs) and DFNS core-Au layer shell nanohybrids (DFNS/Au layers). The catalytic activities of DFNS/Au NPs and DFNS/Au layers in the 4-nitrophenol reduction reaction are compared.

Carbon-embedded Ni nanocatalysts derived from MOFs by a sacrificial template method for efficient hydrogenation of furfural to tetrahydrofurfuryl alcohol

A Ni/C catalyst prepared by the pyrolysis of Ni-MOFs, synthesized by a facile oil-bath method, showed high activity of hydrogenation of FAL.

Effective conversion of biomass-derived ethyl levulinate into γ-valerolactone over commercial zeolite supported Pt catalysts

Selective hydrogenation of biomass-derived ethyl levulinate into γ-valerolactone over commercial zeolite supported catalysts was performed, and high yield was obtained.