Nanoparticle Catalysts Research Articles

Capacity of Aqueous Solutions of the Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate to Partially Depolymerize Lignin at Ambient Temperature and Pressure.

Lignin is a very attractive and abundant biopolymer with the potential to be a biorenewable source of a large number of value-added organic chemicals. The current state-of-the-art methods fail to provide efficient valorization of lignin in this regard without the involvement of harsh conditions and auxiliary substances that compromise the overall sustainability of the proposed processes. Making an original approach from the set of mildest temperature and pressure conditions, this work identifies and explores the capacity of an aqueous solution of the nonvolatile ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) to partially depolymerize technical lignin (Indulin AT) by means of a treatment consisting in the simple contact at ambient temperature and pressure. Among a considerable number of valuable phenolic molecules that were identified in the resulting fluid, vanillin (yield of about 3 g/kg) and guaiacol (yield of about 1 g/kg) were the monophenolic compounds obtained in a higher concentration. The properties of the post-treatment solids recovered remain similar to those of the original lignin, although with a relatively lower abundance of guaiacyl units (in agreement with the generation of guaiacyl-derived phenolic molecules, such as vanillin and guaiacol). The assistance of the treatment with UV irradiation in the presence of nanoparticle catalysts does not lead to an improvement in the yields of phenolic compounds.

Self-dispersed bimetallic NiRu nanoparticles on CeO2 for CO2 methanation

Redispersing bimetallic active nanoparticles in a heterogeneous catalyst can significantly improve metal utilization and catalytic performance, but it is very challenging. In this work, we report a feasible method to redisperse large bimetallic NiRu particles (30–40 nm) on the CeO2 support into small alloyed NiRu nanoparticles (3–5 nm) in an Ar gas atmosphere (NiRu/CeO2-Ar). During the high-temperature treatment, Ru metal in big bimetallic NiRu particles migrated to the surface of small alloyed nanoparticles because of the metal-phase separation, forming more Ni−Ru metal interfaces. As a result, NiRu/CeO2-Ar showed much better catalytic performance in CO2 methanation than the pristine catalyst (NiRu/CeO2) and the catalysts treated in air, H2, and reactant gases, respectively. Experimental and theoretical calculation results reveal that the newly generated Ni−Ru metal interfaces are conducive to the adsorption of CO2 and further direct dissociation into CO*, thus enhancing the catalytic performance. This work provides a reliable strategy to redisperse bimetallic NiRu nanoparticles into small ones with more intermetallic interfaces.

Temperature–Controlled hydrothermal hydrogenation of palmitic acid to alkanol or alkanes over Co@CN–x catalysts derived from ZIF–67

Biomass is one of the most abundant and important renewable resource. The selective hydrothermal hydrogenation of microalgae-based bio–oil to produce fine chemicals and fuels such as alkanols or alkanes has been widely studied in the past decade. However, developing a low–cost catalyst with high hydrogenation activity and hydrothermal stability remains a huge challenge. Here, we have constructed a new type of catalyst (Co@CN–900) to achieve highly selective preparation of alkanol (1-hexadecanol, 97.4 %, 220 °C, 30 min) and alkanes (composed of n-pentadecane, n-hexadecane, and cracking alkanes, 96.8 %, 280 °C, 300 min) from temperature–controlled hydrothermal hydrogenation of palmitic acid (a model compound of microalgae-based bio–oil). A large number of N–doped carbon nanotubes confined Co nanoparticles (NPs) catalysts are obtained through the simple one–step pyrolysis of ZIF–67. Catalysts with the special structures exhibit extremely high activity in the hydrothermal hydrogenation of palmitic acid, surpassing the commercial Pt/C catalyst, especially in the conversion rate of palmitic acid, the generation rate of 1-hexadecanol and n-hexadecane. More importantly, no significant deactivation was observed after 5 cycles, demonstrating relatively strong hydrothermal stability.

Assessment of Ailanthus altissima seed oil as a potential source for biodiesel production using nickel oxide nanoparticles catalyst

The identification of suitable non-edible plant feedstock is crucial not only to meet energy demands but also to be environmentally friendly. This study aimed to synthesize nickel oxide (NiO) nanoparticles and use these for synthesizing biodiesel from the non-edible feedstock Ailanthus altissima. The confirmation of NiO synthesis and its characteristics were studied using XRD and SEM. The biodiesel synthesis and its physicochemical characteristics were confirmed using GC–MS, NMR, and FT-IR spectroscopies. The fuel characteristics were examined using ASTM standard procedures. The results confirmed that the nanoparticles were crystalline, spherical to cuboidal in shape, and had an average diameter of 24 nm. The suitable set of parameters for the optimum biodiesel yield (95 %) was the oil-to-methanol ratio of 1:24, 25 mg of catalyst, 60 °C temperature, and a reaction time of 90 min. The majority of the fuel's characteristics fell within ASTM D-6751 acceptable ranges. 14 distinct kinds of FAMEs are present, according to the GC–MS results. The FT-IR spectra confirmed the successful synthesis of biodiesel, which displayed significant peaks for several functional groups. 1H NMR and 13C NMR spectrums confirm the conversion of biodiesel synthesis. The environmental friendliness of AAB (Ailanthus altissima biodiesel) and its competitiveness as a feedstock for biodiesel production on a commercial scale are confirmed by its physicochemical properties.

Synthesis of core-shell nanostructured SiO2/TiO2 photocatalysts via atomic layer deposition in a fluidized bed with central tube

Fluidized bed atomic layer deposition is an efficient technique for particle coating with precise control over the film thickness and uniformity at the sub-nanoscale. In this study, a fluidized bed with a central tube is designed, where the central tube has two roles: improve fluidization and deliver precursors separately. The synthesis of core-shell structured SiO2/TiO2 nanoparticle catalysts for photodegradation of tetracycline hydrochloride (TC) is carried out using TiCl4 and H2O as precursors at 180 °C under atmospheric pressure. Under the combination of vibration and central tube, the segregation of agglomerate size along the bed height is weakened, and the prepared SiO2/TiO2 nanoparticles show excellent photocatalytic degradation performance: the degradation efficiency on TC is 96% under 300 W xenon lamp irradiation for 60 min. The mechanism of enhanced photocatalytic activity is due to the Ti-O-Si bonds generated at the interface, which increase the ability to absorb sunlight and accelerate the separation of holes and electrons.

Single-atom and cluster catalysts for thermocatalytic ammonia synthesis at mild conditions.

Ammonia (NH3) is closely related to the fields of food and energy that humans depend on. The exploitation of advanced catalysts for NH3 synthesis has been a research hotspot for more than one hundred years. Previous studies have shown that the Ru B5 sites (step sites on the Ru (0001) surface uniquely arranged with five Ru atoms) and Fe C7 sites (iron atoms with seven nearest neighbors) over nanoparticle catalysts are highly reactive for N2-to-NH3 conversion. In recent years, single-atom and cluster catalysts, where the B5 sites and C7 sites are absent, have emerged as promising catalysts for efficient NH3 synthesis. In this review, we focus on the recent advances in single-atom and cluster catalysts, including single-atom catalysts (SACs), single-cluster catalysts (SCCs), and bimetallic-cluster catalysts (BCCs), for thermocatalytic NH3 synthesis at mild conditions. In addition, we discussed and summarized the unique structural properties and reaction performance as well as reaction mechanisms over single-atom and cluster catalysts in comparison with traditional nanoparticle catalysts. Finally, the challenges and prospects in the rational design of efficient single-atom and cluster catalysts for NH3 synthesis were provided.

Metal-support interactions in metal oxide-supported atomic, cluster, and nanoparticle catalysis.

Supported metal catalysts are essential to a plethora of processes in the chemical industry. The overall performance of these catalysts depends strongly on the interaction of adsorbates at the atomic level, which can be manipulated and controlled by the different constituents of the active material (i.e., support and active metal). The description of catalyst activity and the relationship between active constituent and the support, or metal-support interactions (MSI), in heterogeneous (thermo)catalysts is a complex phenomenon with multivariate (dependent and independent) contributions that are difficult to disentangle, both experimentally and theoretically. So-called "strong metal-support interactions" have been reported for several decades and summarized in excellent review articles. However, in recent years, there has been a proliferation of new findings related to atomically dispersed metal sites, metal oxide defects, and, for example, the generation and evolution of MSI under reaction conditions, which has led to the designation of (sub)classifications of MSI deserving to be critically and systematically evaluated. These include dynamic restructuring under alternating redox and reaction conditions, adsorbate-induced MSI, and evidence of strong interactions in oxide-supported metal oxide catalysts. Here, we review recent literature on MSI in oxide-supported metal particles to provide an up-to-date understanding of the underlying physicochemical principles that dominate the observed effects in supported metal atomic, cluster, and nanoparticle catalysts. Critical evaluation of different subclassifications of MSI is provided, along with discussions on the formation mechanisms, theoretical and characterization advances, and tuning strategies to manipulate catalytic reaction performance. We also provide a perspective on the future of the field, and we discuss the analysis of different MSI effects on catalysis quantitatively.

General synthesis of secondary imines via reductive coupling of carbonyl and nitro compounds employing a reusable cobalt catalyst

Reusable nitrogen-doped carbon-encapsulated Co nanoparticle catalysts are found robust for the synthesis of secondary imines via the reductive amination of carbonyl compounds with NH3 or directly with nitro compounds.

Purified CaO supported Pt nanoparticles for the selective hydrogenation of styrene oxide with enhanced selectivity of 1-phenylethanol

The purified CaO supported Pt nanoparticles exhibit the best selectivity toward 1-phenylethanol in the selective hydrogenation of styrene oxide.

Selective catalytic hydrogenation of 5-hydroxymethylfurfural over silica supported FeCoNiCuRu high-entropy alloy nanoparticles

A simple organic ligand chelate-assisted thermal-reduction method provides a universal strategy for generating high-entropy alloy (HEA) nanoparticles catalysts with uniformly dispersed particles for efficient catalytic hydrogenation.

Controlling Pt nanoparticle sintering by sub-monolayer MgO ALD thin films.

Metal nanoparticle (NP) sintering is a major cause of catalyst deactivation, as NP growth reduces the surface area available for reaction. A promising route to halt sintering is to deposit a protective overcoat on the catalyst surface, followed by annealing to generate overlayer porosity for gas transport to the NPs. Yet, such a combined deposition-annealing approach lacks structural control over the cracked protection layer and the number of NP surface atoms available for reaction. Herein, we exploit the tailoring capabilities of atomic layer deposition (ALD) to deposit MgO overcoats on archetypal Pt NP catalysts with thicknesses ranging from sub-monolayers to nm-range thin films. Two different ALD processes are studied for the growth of MgO overcoats on Pt NPs anchored on a SiO2 support, using Mg(EtCp)2 and H2O, and Mg(TMHD)2 and O3, respectively. Spectroscopic ellipsometry and X-ray photoelectron spectroscopy measurements reveal significant growth on both SiO2 and Pt for the former process, while the latter exhibits a drastically lower growth per cycle with an initial chemical selectivity towards Pt. These differences in MgO growth characteristics have implications for the availability of uncoated Pt surface atoms at different stages of the ALD process, as probed by low energy ion scattering, and for the sintering behavior during O2 annealing, as monitored in situ with grazing incidence small angle X-ray scattering (in situ GISAXS). The Mg(TMHD)2-O3 ALD process enables exquisite coverage control allowing a balance between physically blocking the Pt surface to prevent sintering and keeping Pt surface atoms free for reaction. This approach avoids the need for post-annealing, hence also safeguarding the structural integrity of the as-deposited overcoat.

Four-step continuous-flow total synthesis of (-)-debromoflustramine B using a chiral heterogeneous Pd NP catalyst.

Various prenylated indoline alkaloids with diverse biological activities, including (-)-debromoflustramine B with significant butyrylcholinesterase inhibitory activity, could be synthesized by dearomative prenylation reactions of tryptophan derivatives. However, previously reported dearomative prenylations were limited to batch reactions at the milligram scale, requiring multistep reactions and complex post-processing to obtain the desired natural products. The more efficient synthesis of alkaloids remains challenging, as does the recovery of expensive catalysts. Herein, we developed a chiral heterogeneous Pd nanoparticle (NP) catalyst supported on a polymer, which produces indoline alkaloids in high yields with excellent enantioselectivities. Additionally, the first gram-scale four-step continuous-flow total synthesis of (-)-debromoflustramine B was successfully achieved with this chiral Pd heterogeneous catalyst, requiring only a simple post-processing step.

Effective treatment of 2,4,6-trinitrotoluene from aqueous media using a sono-photo-Fenton-like process with a zero-valent iron nanoparticle (nZVI) catalyst.

In this study, we examine the effectiveness of using a combination of a sono-photo-Fenton-like procedure and nano zero-valent iron catalyst (nZVI) to treat 2,4,6-trinitrotoluene (TNT) in an aquatic environment. Zero-valent iron particles were generated by a chemical reduction technique. nZVI nanoparticles were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) to characterize the nanocatalyst. The resulting nZVI nanoparticles were used as an addition in a sono-photo-Fenton method to remediate an aqueous solution contaminated with TNT. Furthermore, influences of operational factors such as temperature, catalyst dosage, wavelength, ultraviolet power, ultrasonic frequency and power, pH level, H2O2/nZVI ratio, initial TNT concentration, and reaction duration on the treatment of TNT were investigated. Under the conditions of an ideal pH of 3, temperature range of 40-45 °C, concentration of 50 mg per L TNT, dose of 2 mM of nZVI, and ratio of H2O2/Fe0 of 20, a treatment efficiency of 95.2% was achieved after a duration of 30 minutes. The sono-photo-Fenton process combined with nZVI showed a higher TNT removal efficiency compared to the Fenton, sono-Fenton, and photo-Fenton processes under the same conditions. Moreover, it promises a potential solution to treat TNT at the pilot scale while allowing reuse of the nZVI catalyst and the limitation of sludge.

Structure control and evolution of atomically precise gold clusters as heterogeneous precatalysts.

Metal clusters have distinct features from single atom and nanoparticle (>1 nm) catalysts, making them effective catalysts for various heterogeneous reactions. Nevertheless, the ambiguity and complexity of the catalyst structure preclude in-depth mechanistic studies. The evolution of metal species during synthesis and reaction processes represents another challenge. One effective solution is to precisely control the structure of the metal cluster, thus offering a well-defined pre-catalyst. The well-defined chemical formula and configurations make atomically precise metal nanoclusters optimal choices. To fabricate an atomically precise metal nanocluster-based heterogeneous catalyst with enhanced performance, careful structural design of both the nanocluster and support material, an effective assembling technique, and a pre-treatment method for these hybrids need to be developed. In this review, we summarize recent advances in in the development of heterogeneous catalysts using atomically precise gold and alloy gold nanoclusters as precursors. We will begin with a brief introduction to the structural properties of atomically precise nanoclusters and structure determination of cluster/support hybrids. We will then introduce heterogeneous catalysts prepared from medium size (tens to hundreds of metal atoms) and low nuclearity nanoclusters. We will illustrate how ligand modification, support-cluster interaction, hybrid fabrication, and heteroatom (Pt, Pd Ag, Cu, Cd, Fe) introduction affect the structural properties and pretreatment/reaction-induced structural evolution of gold nanocluster pre-catalysts. Lastly, we will highlight the synthetic method of NCs@MOF hybrids and their effectiveness in circumventing the adverse cluster structural evolution. These findings are expected to shed light on the structure-activity relationship studies and future catalyst design strategies using atomically precise metal nanocluster pre-catalysts.

Hierarchical zeolite-encapsulated metal nanoparticles for heterogeneous catalysis.

Zeolites, characterized by their highly porous structure, have become integral to modern industry and environmental science due to their broad applications in adsorption, separation, and catalysis. Recent advancements in zeolite synthesis, particularly through hydrothermal methods and the incorporation of metal nanoparticles, have significantly expanded their utility. This review delves into the innovative strategies for encapsulating metal nanoparticles within zeolite matrices, enhancing catalytic reactions' efficiency, selectivity, and durability. Challenges such as nanoparticle agglomeration and catalyst deactivation are addressed through hierarchical zeolite encapsulation, which provides a novel route for the development of multifunctional materials. By examining methods ranging from in situ encapsulation to post-synthetic recrystallization, this review highlights the versatility and potential of metal@zeolite catalysts in various applications, including organic synthesis, pollutant treatment, and energy conversion. The review underscores the importance of optimizing the interaction between metal nanoparticles and the zeolite framework to achieve superior catalytic performance, offering new directions for research in catalytic science and industrial process optimization.

Synthesis of MOF-supported Pt catalyst with high electrochemical oxidation activity for methanol oxidation.

Fuel cells, one of the clean energy sources, is quite remarkable for energy production. In this context, catalysts are needed for the electrochemical reactions of DMFCs (direct methanol fuel cells) to work efficiently. In this study, Pt and Pt@Ti-MOF (Pt@MIL-125) NPs (nanoparticles) catalysts were synthesized by chemical synthesis. The Ti-MOF (MIL-125) structure was synthesized using the solvothermal method, and the effect of Ti-MOF on methanol oxidation was investigated. The results showed that Pt@Ti-MOF NPs provided 9.45 times more electrocatalytic activity for methanol oxidation compared to Pt NPs. In addition, Ti-MOF doping was shown to increase the stability and durability by long-term tests. The study provides important results on how MOF-supported structures behave electrochemically. The results show that Ti-MOF provides very high potential in MOR applications and is promising for use as an anode catalyst in DMFC systems.

Integrating single atoms with nanoparticle catalysts for efficient electrochemical energy conversion

This review summarizes the development (integrated effects, classifications, and applications) of emerging catalysts that integrate single atoms with nanoparticles (SA/NPCs). It also highlights the future challenges and opportunities in this field.

Promoting CO2 electroreduction to CO by a graphdiyne-stabilized Au nanoparticle catalyst.

The electrochemical CO2 reduction reaction (CO2RR) gives an ideal approach for producing valuable chemicals, offering dual benefits in terms of environmental preservation and carbon recycling. In this work, a strong synergistic effect is constructed by adopting electron-rich graphdiyne (GDY) as the supporting matrix, which significantly stabilizes the Au active sites and boosts the CO2RR process. The as-prepared GDY-supported Au nanoparticles (Au/GDY) exhibit excellent CO2RR performance, with an extremely high faradaic efficiency of 94.6% for CO as well as good stability with continuous electrolysis for 36 hours. The superior activity and stability of the Au/GDY catalyst can be attributed to the electronic interaction between Au nanoparticles and the GDY substrate, resulting in enhanced electron transfer rates and a stable network of catalytically active sites that ultimately promote the CO2RR.

Synthesis of an MXene supported Co nanoparticle catalyst for efficient catalytic transfer hydrogenation of nitro compounds with formic acid

The developed 2.6% Co/MXene exhibited excellent catalytic performance for the catalytic transfer hydrogenation of readily available nitroarenes employing HCOOH, leading to the specific generation of essential and versatile formamides.

Atomically dispersed cobalt catalysts for tandem synthesis of primary benzylamines from oxidized β-O-4 segments.

This work presents an innovative approach focusing on fine-tuning the coordination environment of atomically dispersed cobalt catalysts for tandem synthesis of primary benzylamines from oxidized lignin model compounds. By meticulously regulating the Co-N coordination environment, the activity of these catalysts in the hydrogenolysis and reductive amination reactions was effectively controlled. Notably, our study demonstrates that, in contrast to cobalt nanoparticle catalysts, atomically dispersed cobalt catalysts exhibit precise control of the sequence of hydrogenolysis and reductive amination reactions. Particularly, the CoN3 catalyst with a triple Co-N coordination number achieved a remarkable 94% yield in the synthesis of primary benzylamine. To our knowledge, there is no previous documentation of the synthesis of primary benzylamines from lignin dimer model compounds. Our study highlights a promising one-pot route for sustainable production of nitrogen-containing aromatic chemicals from lignin.