Nanocatalysis on Supported Oxides for CO Oxidation

Recent advances and progress in biotemplate catalysts for electrochemical energy storage and conversion

Complex structures and morphologies in nature endow materials with unexpected properties and extraordinary functions. Biotemplating is an emerging strategy for replicating nature structures to obtain materials with unique morphologies and improved properties. Recently, efforts have been made to use bio-inspired species as a template for producing morphology-controllable catalysts. Fundamental information, along with recent advances in biotemplate metal-based catalysts are presented in this review through discussions of various structures and biotemplates employed for catalyst preparation. This review also outlines the recent progress on preparation routes of biotemplate catalysts and discusses how the properties and structures of these templates play a crucial role in the final performance of metal-based catalysts. Additionally, the application of bio-based metal and metal oxide catalysts is highlighted for various key energy and environmental technologies, including photocatalysis, fuel cells, and lithium batteries. Biotemplate metal-based catalysts display high efficiency in several energy and environmental systems. Note that this review provides guidance for further research in this direction.

Conformal Noble Metal High-Entropy Alloy Nanofilms by Atomic Layer Deposition for an Enhanced Hydrogen Evolution Reaction

The current synthesis methods of high-entropy alloy (HEA) thin-film coatings face huge challenges in facile preparation, precise thickness control, conformal integration, and affordability. These challenges are more specific and noteworthy for noble metal-based HEA thin films where the conventional sputtering methods encounter thickness control and high-cost issues (high-purity noble metal targets required). Herein, for the first time, we report a facile and controllable synthesis process of quinary HEA coatings consisting of noble metals (Rh, Ru, Pt, Pd, and Ir), by sequential atomic layer deposition (ALD) coupled with electrical Joule heating for post-alloying. Furthermore, the resulting quinary HEA thin film with a thickness of ∼50 nm and an atomic ratio of 20:15:21:18:27 shows promising potential as a platform for catalysis, exhibiting enhanced electrocatalytic hydrogen evolution reaction (HER) performances with lower overpotentials (e.g., from 85 to 58 mV in 0.5 M H₂SO₄) and higher stability (by retaining more than 92% of the initial current after 20 h with a current density of 10 mA/cm² in 0.5 M H₂SO₄) than other noble metal-based structure counterparts in this work. The enhanced material properties and device performances are attributed to the efficient electron transfer of HEA with the increased number of active sites. This work not only presents RhRuPtPdIr HEA thin films as promising HER catalysts but also sheds light on controllable fabrication of conformal HEA-coated complex structures toward a broad range of applications.

New horizons of MBenes: highly active catalysts for the CO oxidation reaction

The search for materials with high intrinsic carbon monoxide oxidation reaction (COOR) catalytic activity is critical for enhancing the efficiency of reducing CO contamination. COOR catalysts, however, have long relied heavily on noble metals and CeO₂. Herein, in order to search for non-noble COOR catalysts that are more active than CeO₂, 18 oxygen-functionalized MBenes with orthorhombic and hexagonal crystal structures, denoted as orth-M₂B₂O₂ and hex-M₂B₂O₂ (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W), were investigated in terms of their COOR catalytic activity by high-throughput first-principles calculations. Hex-Mo₂B₂O₂, orth-Mo₂B₂O₂, hex-V₂B₂O₂ and hex-Cr₂B₂O₂ were found to be more active than CeO₂ and possess structural stability below 1000 K, showing the potential to replace CeO₂ as the substrates of COOR catalysts. Moreover, orth-Mo₂B₂O₂, hex-V₂B₂O₂ and hex-Cr₂B₂O₂ exhibit even higher COOR catalytic activity than Pt-CeO₂ and Au-CeO₂, and are expected to be applied as COOR catalysts directly. Further investigations showed that the formation energy of oxygen vacancies could be used as the descriptor of COOR catalytic activity, which would help to reduce the amount of calculations significantly during the catalyst screening process. This work not only reports a series of 2D materials with high COOR catalytic activity and opens up a new application area for MBenes, but also provides a reliable strategy for highly efficient screening for COOR catalysts.

Prospects and Applications of Palladium Nanoparticles in the Cross-coupling of (hetero)aryl Halides and Related Analogues

Discovering efficient methods for the formation of carbon-carbon bonds is a central ongoing theme in organic synthesis. Cross-coupling reactions catalysed by metal nanoparticles are attractive alternatives to the traditional use of metal counterparts due to the catalytic tunability, selectivity, recyclability and reusability of the nanoparticles. The ongoing search for sustainable processes demands that reusable and environmentally benign catalysts are used. While the advantages of nanoparticles catalysts over bulk catalysts cannot be overemphasised, the problem of sintering, agglomeration and leaching are drawbacks to their full industrial applications. Hence, efforts are being made towards advancing the efficiency of the catalytic nanoparticle systems over the years. This review presents the progress, the challenges and the prospects of palladium nanoparticle with focus on Heck, Suzuki, Hiyama and Sonogashira cross-coupling reactions involving (hetero) aryl halides and the analogues.

Ligand-Protected Ultrasmall Pd Nanoclusters Supported on Metal Oxide Surfaces for CO Oxidation: Does the Ligand Activate or Passivate the Pd Nanocatalyst?

Herein, we report on the synthesis of ultrasmall Pd nanoclusters (∼2 nm) protected by L-cysteine [HOCOCH(NH₂ )CH₂ SH] ligands (Pd_n (L-Cys)_m ) and supported on the surfaces of CeO₂ , TiO₂ , Fe₃ O₄ , and ZnO nanoparticles for CO catalytic oxidation. The Pd_n (L-Cys)_m nanoclusters supported on the reducible metal oxides CeO₂ , TiO₂ and Fe₃ O₄ exhibit a remarkable catalytic activity towards CO oxidation, significantly higher than the reported Pd nanoparticle catalysts. The high catalytic activity of the ligand-protected clusters Pd_n (L-Cys)_m is observed on the three reducible oxides where 100 % CO conversion occurs at 93-110 °C. The high activity is attributed to the ligand-protected Pd nanoclusters where the L-cysteine ligands aid in achieving monodispersity of the Pd clusters by limiting the cluster size to the active sub-2-nm region and decreasing the tendency of the clusters for agglomeration. In the case of the ceria support, a complete removal of the L-cysteine ligands results in connected agglomerated Pd clusters which are less reactive than the ligand-protected clusters. However, for the TiO₂ and Fe₃ O₄ supports, complete removal of the ligands from the Pd_n (L-Cys)_m clusters leads to a slight decrease in activity where the T_100% CO conversion occurs at 99 °C and 107 °C, respectively. The high porosity of the TiO₂ and Fe₃ O₄ supports appears to aid in efficient encapsulation of the bare Pd_n nanoclusters within the mesoporous pores of the support.

Enhancing the feasibility of Pd/C-catalyzed formic acid decomposition for hydrogen generation – catalyst pretreatment, deactivation, and regeneration

Formic acid decomposition (FAD) generates H₂ at low temperatures. CO poisoning inhibits FAD but is lifted under oxidative treatment.

Green Synthesized ZnO Nanoparticles Mediated by Mentha Spicata Extract Induce Plant Systemic Resistance against Tobacco Mosaic Virus

Globally, plant viral infection is one of the most difficult challenges of food security, where considerable losses in crop production occur. Nanoparticles are an effective control agent against numerous plant pathogens. However, there is limited knowledge concerning their effects against viral infection. In the present study, the green synthesis of zinc oxide nanoparticles (ZnO NPs) using aqueous leaf extract of Mentha spicata was achieved. X-ray diffraction patterns confirmed the crystalline nature of the prepared ZnO NPs. Dynamic light scattering and scanning electron microscopy analyses revealed that the resultant ZnO NPs were spherical in shape with a particle size ranged from 11 to 88 nm. Fourier transmission infrared spectroscopy detected different functional groups, capping and stability agents, and showed Zn-O bond within wavenumber of 487 cm−1. Under greenhouse conditions, the antiviral activity of biological synthesized ZnO NPs (100 µg/mL) against Tobacco mosaic virus (TMV) was evaluated. The double foliar application of the prepared ZnO NPs, 24 h before and 24 h after TMV-inoculation, was the most effective treatment that showed a 90.21% reduction of viral accumulation level and disease severity. Additionally, the transcriptional levels of PAL, PR-1 (salicylic acid marker gene), CHS, and POD genes were induced and up-regulated in all ZnO NPs treated plants. Notably, the results exhibited that aqueous extract of Mentha spicata was an effective reducing agent for the green synthesis of ZnO NPs, which showed significant antiviral activity. Finally, the detected protective and curative activity of ZnO NPs against TMV can encourage us to recommend its application for plant viral disease management. To our knowledge, this is the first study describing the antiviral activity of the green synthesized ZnO NPs.

Hollow Au@TiO2 porous electrospun nanofibers for catalytic applications

Catalytically active porous and hollow titania nanofibers encapsulating gold nanoparticles were fabricated using a combination of sol–gel chemistry and coaxial electrospinning technique. We report the fabrication of catalytically active porous and hollow titania nanofibers encapsulating gold nanoparticles (AuNPs) using a combination of sol–gel chemistry and coaxial electrospinning technique. The coaxial electrospinning involved the use of a mixture of poly(vinyl pyrrolidone) (PVP) and titania sol as the shell forming component, whereas a mixture of poly(4-vinyl pyridine) (P4VP) and pre-synthesized AuNPs constituted the core forming component. The core–shell nanofibers were calcined stepwise up to 600 °C which resulted in decomposition and removal of the organic constituents of the nanofibers. This led to the formation of porous and hollow titania nanofibers, where the catalytic AuNPs were embedded in the inner wall of the titania shell. The catalytic activity of the prepared Au@TiO₂ porous nanofibers was investigated using a model reaction of catalytic reduction of 4-nitrophenol and Congo red dye in the presence of NaBH₄. The Au@TiO₂ porous and hollow nanofibers exhibited excellent catalytic activity and recyclability, and the morphology of the nanofibers remained intact after repeated usage. The presented approach could be a promising route for immobilizing various nanosized catalysts in hollow titania supports for the design of stable catalytic systems where the added photocatalytic activity of titania could further be of significance.

Catalytically active porous and hollow titania nanofibers encapsulating gold nanoparticles were fabricated using a combination of sol–gel chemistry and coaxial electrospinning technique.

Lemon-Fruit-Based Green Synthesis of Zinc Oxide Nanoparticles and Titanium Dioxide Nanoparticles against Soft Rot Bacterial Pathogen Dickeya dadantii

Edible plant fruits are safe raw materials free of toxicants and rich in biomolecules for reducing metal ions and stabilizing nanoparticles. Zinc oxide nanoparticles (ZnONPs) and titanium dioxide nanoparticles (TiO₂NPs) are the most produced consumer nanomaterials and have known antibacterial activities but have rarely been used against phytopathogenic bacteria. Here, we synthesized ZnONPs and TiO₂NPs simply by mixing ZnO or TiO₂ solution with a lemon fruit extract at room temperature and showed their antibacterial activities against Dickeya dadantii, which causes sweet potato stem and root rot disease occurring in major sweet potato planting areas in China. Ultraviolet–visible spectrometry and energy dispersive spectroscopy determined their physiochemical characteristics. Transmission electron microscopy, scanning electron microscopy, and X-ray diffraction spectroscopy revealed the nanoscale size and polymorphic crystalline structures of the ZnONPs and TiO₂NPs. Fourier-transform infrared spectroscopy revealed their surface stabilization groups from the lemon fruit extract. In contrast to ZnO and TiO₂, which had no antibacterial activity against D. dadantii, ZnONPs and TiO₂NPs showed inhibitions on D. dadantii growth, swimming motility, biofilm formation, and maceration of sweet potato tuber slices. ZnONPs and TiO₂NPs showed similar extents of antibacterial activities, which increased with the increase of nanoparticle concentrations, and inhibited about 60% of D. dadantii activities at the concentration of 50 µg∙mL⁻¹. The green synthetic ZnONPs and TiO₂NPs can be used to control the sweet potato soft rot disease by control of pathogen contamination of seed tubers.

Hollow Micro/Nanostructured Ceria-Based Materials: Synthetic Strategies and Versatile Applications

Hollow micro/nanostructured CeO₂ -based materials (HMNCMs) have triggered intensive attention as a result of their unique structural traits, which arise from their hollowness and the fascinating physicochemical properties of CeO₂ . This attention has led to widespread applications with improved performance. Herein, a comprehensive overview of methodologies applied for the synthesis of various hollow structures, such as hollow spheres, nanotubes, nanoboxes, and multishelled hollow spheres, is provided. The synthetic strategies toward CeO₂ hollow structures are classified into three major categories: 1) well-established template-assisted (hard-, soft-, and in situ template) methods; 2) newly emerging self-template approaches, including selective etching, Ostwald ripening, the Kirkendall effect, galvanic replacement, etc.; 3) bottom-up self-organized formation synthesis (namely, oriented attachment and self-deformation). Their underlying mechanisms are concisely described and discussed in detail, the differences and similarities of which are compared transversely and longitudinally. Niche applications of HMNCMs in a wide range of fields including catalysis, energy conversion and storage, sensors, absorbents, photoluminescence, and biomedicines are reviewed. Finally, an outlook of future opportunities and challenges in the synthesis and application of CeO₂ -based hollow structures is also presented.

Fast Synthesis of Pt Nanocrystals and Pt/Microporous La2O3 Materials Using Acoustic Levitation

Usually, we must use an appropriate support material to keep the metal species stable and finely dispersed as supported metal nanoparticles for industry application. Therefore, the choice of support material is a key factor in determining the dispersion and particle size of the noble metal species. Here, we report the synthesis of a single-atom Pt material in the solution and supported Pt nanoclusters on microporous La₂O₃ by a one-step acoustic levitation method without any pretreatment/modification of raw oxide. We have strongly contributed to the synthetic methodology of the surface/interfacial heterogeneous catalysts in this study, and this finding could open another door for synthesis of supported metal nanoparticles on porous materials for environmental catalysis.

Palladium Nanoparticles Supported on Ce-Metal-Organic Framework for Efficient CO Oxidation and Low-Temperature CO2 Capture

In this article, we report the lowest-temperature CO oxidation catalyst supported on metal-organic frameworks (MOFs). We have developed a facile, general, and effective approach based on microwave irradiation for the incorporation of Pd nanoparticle catalyst within Ce-MOF. The resulting Pd/Ce-MOF material is a unique catalyst that is capable of CO oxidation at modest temperatures and also of efficient uptake of the product CO₂ gas at low temperatures. The observed catalytic activity of this material toward CO oxidation is significantly higher than those of other reported metal nanoparticles supported on MOFs. The high activity of the Pd/Ce-MOF catalyst is due to the presence of Ce(III) and Ce(IV) ions within the metal-organic framework support. The Pd nanoparticles supported on the Ce-MOF store oxygen in the form of a thin palladium oxide layer at the particle-support interface, in addition to the oxygen stored on the Ce(III)/Ce(IV) centers. Oxygen from these reservoirs can be released during CO oxidation at 373 K. At lower temperatures (273 K), the Pd/Ce-MOF has a significant CO₂ uptake of 3.5 mmol/g.

Selective oxidation of alcohols by supported gold nanoparticles: recent advances

The review presents a commercially important field of alcohol oxidation using gold nanoparticles. It systematically discusses scope and limitation of various supports on the activity and selectivity of catalyst.

Nanocatalysis: Academic Discipline and Industrial Realities

Nanotechnology plays a central role in both academic research and industrial applications. Nanoenabled products are not only found in consumer markets, but also importantly in business to business markets (B2B). One of the oldest application areas of nanotechnology is nanocatalysis—an excellent example for such a B2B market. Several existing reviews illustrate the scientific developments in the field of nanocatalysis. The goal of the present review is to provide an up-to-date picture of academic research and to extend this picture by an industrial and economic perspective. We therefore conducted an extensive search on several scientific databases and we further analyzed more than 1,500 nanocatalysis-related patents and numerous market studies. We found that scientists today are able to prepare nanocatalysts with superior characteristics regarding activity, selectivity, durability, and recoverability, which will contribute to solve current environmental, social, and industrial problems. In industry, the potential of nanocatalysis is recognized, clearly reflected by the increasing number of nanocatalysis-related patents and products on the market. The current nanocatalysis research in academic and industrial laboratories will therefore enable a wealth of future applications in the industry.

The local structure of PdxCe1−xO2−x−δsolid solutions

In this paper, physical methods in combination with quantum chemistry calculations are used to study the local structure of Pd_xCe_1−xO_2−δsolid solutions.

Novel CeO2 yolk-shell structures loaded with tiny Au nanoparticles for superior catalytic reduction of p-nitrophenol

Direct fabrication of core-shell or yolk-shell functional nanomaterials via a facile template-free method remains a challenge. In this work, we present a novel approach that involves straightforward chemical transformation and thermal treatment of the infinite coordination polymer particles to obtain composition-tunable CeO(2) yolk-shell structures. Uniform CeO(2) yolk-shell hollow spheres with a high surface area are promising support materials for tiny gold nanoparticles (ca. 4 nm), forming Au-CeO(2) nanocomposites which exhibit a remarkable catalytic activity and high stability for the reduction of p-nitrophenol. A possible mechanism for the formation of CeO(2) yolk-shell microspheres is also proposed.

Nanocatalysis and prospects of green chemistry

Designing and developing ideal catalyst paves the way to green chemistry. The fields of catalysis and nanoscience have been inextricably linked to each other for a long time. Thanks to the recent advances in characterization techniques, the old technology has been revisited with a new scope. The last decade has witnessed a flood of research activity in the field of nanocatalysis, with most of the studies focusing on the effect of size on catalytic properties. This led to the development of much greener catalysts with higher activity, selectivity and greater ease of separation from the reaction medium. This Minireview describes the emerging trends in the field of nanocatalysis with implications towards green chemistry and sustainability.

Gold nanoparticles supported on magnesium oxide for CO oxidation

Au was loaded (1 wt%) on a commercial MgO support by three different methods: double impregnation, liquid-phase reductive deposition and ultrasonication. Samples were characterised by adsorption of N2 at -96°C, temperature-programmed reduction, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. Upon loading with Au, MgO changed into Mg(OH)2 (the hydroxide was most likely formed by reaction with water, in which the gold precursor was dissolved). The size range for gold nanoparticles was 2-12 nm for the DIM method and 3-15 nm for LPRD and US. The average size of gold particles was 5.4 nm for DIM and larger than 6.5 for the other methods. CO oxidation was used as a test reaction to compare the catalytic activity. The best results were obtained with the DIM method, followed by LPRD and US. This can be explained in terms of the nanoparticle size, well known to determine the catalytic activity of gold catalysts.

Biopreparation of Highly Dispersed Pd Nanoparticles on Bacterial Cell and Their Catalytic Activity for Polymer Electrolyte Fuel Cell

Rapid development in the area of low-temperature fuel cells has led to increased attention on catalyst synthesis with cost effective and environmentally-benign technology (green chemistry). In this study, a highly dispersed palladium nanoparticle catalyst was successfully prepared on a bacterial cell support by a single-step, room-temperature microbial method without dispersing agents. The metal ion reducing bacterium Shewanella oneidensis were able to reduce palladium ions into insoluble palladium at room temperature when formate was provided as the electron donor. The prepared biomass-supported palladium nanoparticles were characterized for their catalytic activity as anodes in polymer electric membrane fuel cell for power production. The maximum power generation of the biomass-supported palladium catalyst was up to 90% of that of a commercial palladium catalyst.