The in situ formation of ammonia decomposition catalysts derived from perovskites ABO₃ (A=La,Ca,Sr, and B=Fe,Co,Ni) was examined via operando X-ray diffraction experiments. The reduction behavior of the perovskites, the intermediate phases during activation, the catalysts’ crystallite size distribution, their morphology, and their catalytic activity were analyzed.

Abstract

This work addresses the formation of ammonia (NH₃) decomposition catalysts derived from perovskites ABO₃ (A=La, Ca, Sr, and B=Fe, Co, Ni) precursors via operando synchrotron X-ray diffraction experiments. During the reaction in NH₃, the perovskite precursors are decomposed and the transition metals are reduced. Depending on their reduction properties, active metallic catalysts are formed in situ on La₂O₃ as support. The reduction behavior of the perovskites, formation of intermediate phases during activation, and catalytic performance was studied in detail. In addition, microstructure properties such as crystallite sizes and particle morphology were analyzed. Co-/Ni-based perovskites decomposed completely during activation to Co⁰/Ni⁰ supported on La₂O₃ while Fe-based perovskites were fully stable but inactive in catalysis. This difference is due to varying electronic properties of the transition metals, e. g., decreasing electronegativity from Ni to Fe. With decreasing reducibility, the intermediate phases during activation formed more distinct. La³⁺ was partially substituted by Ca²⁺/Sr²⁺ in LaCoO₃ to test for advantageous effects in NH₃ decomposition. The best performance was observed using the precatalyst La_0.8Sr_0.2CoO₃ with a conversion of 86 % (100 % NH₃, 15000 mL g⁻¹ h⁻¹) at 550 °C.

Nanometric metal overlayer on the Fe−Cr−Al metal foil prepared by pulsed arc plasma deposition enables easy fabrication of metal honeycomb catalysts, and the Rh overlayer shows excellent catalytic performance for CO−NO reaction and three-way catalytic reaction. The two-dimensional structure has an advantage in NO reduction with extremely high turnover frequency.

Abstract

Although most of the currently used solid catalysts possess a three-dimensional structure of nanoparticles dispersed on a porous support, the nanoparticle structure should not be considered the optimal structure for all catalytic reactions due to some disadvantages such as thermal instability and catalyst poisoning. Herein, we present the unique catalytic performance of a two-dimensional metal foil-supported nanometric Rh thin film, referred to as the “Rh overlayer”, for a catalytic CO−NO reaction and a stoichiometric three-way catalytic reaction under practical conditions. The extremely high turnover frequency for NO reduction using two-dimensional Rh is a key to understanding this phenomenon, the detailed mechanism of which can be explained by theoretical calculations.

This work demonstrates the facile and cost-effective synthesis of magnetic crosslinked laccase aggregates (m-CLEAS) on CuFe₂O₄. m-CLEAS showed high enzyme loading, improved catalytic performance and thermal stability with exceptional storage stability than free enzyme and CLEAS. The results highlight the promise of m-CLEAS for green industrial processes.

Abstract

Highly stable and reusable magnetic crosslinked enzyme aggregates (m-CLEAS) of laccase are synthesized with simultaneous improved enzymatic activity. Magnetic copper ferrite nanoparticles (CFNPs) were synthesized by solvothermal procedure with an average size of ~8 nm. The nanometric m-CLEAS were formed by co-aggregation of enzyme with CFNPs and crosslinked using glutaraldehyde. Different mass ratios of CFNPs:Laccase were assayed (1 : 2, 1 : 3, and 1 : 6), where 1 : 6 resulted in the highest activity recovery (97 %). The m-CLEAS showed an average size of ~239 nm, ~24 % enzyme immobilization efficiency, and loading as high as 1.75 g of protein per g of support. As expected, m-CLEAS oxidized the substrate with a higher transformation rate (k _cat) and catalytic efficiency (k _cat/K_m) than the free enzyme. m-CLEAS showed superior storage and thermostability compared to free enzyme and non-magnetic CLEAS. In particular, the m-CLEAS showed ~150 % and ~100 % residual activity after 30 days of storage at 4 °C and room temperature, respectively. Furthermore, m-CLEAS showed good recyclability, retaining ~78 % and ~54 % laccase activity after 5 and 10 cycles of reuse, respectively. This work highlights the facile and cost-effective synthesis of nanometric m-CLEAS with exceptional storage stability and simultaneously improved laccase activity, making them suitable for a range of green industrial processes.

Carbon monoxide (CO) oxidation is crucial in fuel cell anodes. Recent research has focused on electrocatalysts that synergistically enhance CO oxidation alongside alcohol/hydrogen oxidation. High sensitivity and selectivity for CO oxidation at lower onset potentials are the key objectives. Molybdenum (Mo) has emerged as a promising non-noble transition metal co-catalyst for CO oxidation. Mo versatility arises from its ability to alloy with Pt and mix with other non-noble transition metals in various forms (MoOx, MoS2, MoC). Carbon-supported Mo nanoparticles have shown potential in reducing Pt loading and improving CO tolerance due to Mo oxyphilic properties, effectively oxidizing weakly adsorbed CO and lowering onset and peak potentials. However, challenges persist, such as a limited potential window for CO oxidation and decreased CO adsorption affinity at higher potentials. Addressing these issues requires understanding factors affecting Mo-based electrocatalysts (Mo-ECs) activity, including PtMo alloy composition, Mo's chemical state, cell temperature, and the role of carbon support. This article provides a comprehensive review of Mo-ECs role in CO electrooxidation in direct alcohol fuel cells (DAFCs) over the past two decades.

Beyond the scope of classical Tsuji-Trost reaction, an alkene bearing a remote leaving group is not considered as a potential substrate for allylation. The concept of migratory Tsuji-Trost reaction focuses on the transformations with this type of substrates. Two pathways including olefin migration and leaving group migration to form typical allyl intermediate for following substitution have been explored to demonstrate the feasibility of this new concept.

The photocatalytic selective reduction of 3-nitrophenol to 3-aminophenol was studied in the presence of titanium dioxide in the form of various anatase and rutile compositions. The reaction progress is altered by various parameters, which can be classified as intrinsic (depending on the chemical, structural, and electronic features) and extrinsic (depending on the reaction and conditions). The goal of the studies was to understand the influence of intrinsic factors and to compare the performance of anatase and rutile materials. The (photo)electrochemical analysis revealed unequivocally the differences in interfacial electron transfer, charge recombination, reduction driving force, and methanol photooxidation efficiency for titania polymorphs. It appeared that all mentioned processes were phase-dependent, and they contributed unequally to overall photocatalytic activity. In particular, methanol oxidation was the most efficient at the rutile phase, which overcame the critical limitation of the oxidation pathway and facilitated the reduction of 3-nitrophenol. On the other hand, the dark electron transfer efficiency was highest at the anatase phase, despite the lower driving force in this case. The presented thorough and systematic analysis of the discussed photocatalytic system (the photocatalyst and the reaction) should allow the rational design of efficient and selective photocatalysts.

This paper constructed internal and surface defects to modulate the crystal structure of CdS, and investigated the synergistic impact of 0D (0-dimensional) internal and surface defects regulation coupled with pyroelectric effects for optimizing the photoelectrocatalytic properties.

Abstract

Rational defect regulation is an effective way to enhance the performance of photoelectrocatalytic (PEC) water splitting. In this paper, we firstly constructed internal and surface defects to modulate the crystal structure of CdS, and investigated the synergistic impact of 0D (0-dimensional) internal and surface defects regulation coupled with pyroelectric effects for optimizing the photoelectrocatalytic properties of CdS. It was found that the synergistic impact had a significant enhancement effect on the carrier separation and transfer, and the current density reached 3.93 mA/cm² at 1.23 V vs. RHE increased by 16.38 times, meanwhile, the stability of the photoelectrodes was greatly promoted. The advantages and intrinsic relationships are also described: the formation of 0D dual-type of defects alters the atomic arrangement in the crystal, optimizes the energy band structure, reduces carrier recombination, and increases carrier density. What's more, the introduction of defects induces electron redistribution and changes the state of dipoles inside the crystal, thus increasing built-in electric field and generating more thermally generated carriers to optimize the pyroelectric effect. This work demonstrates the feasibility of defect modulation for optimizing pyroelectric performance and photocatalytic performance and bringing new light to PEC water splitting.

N-doped TiO₂ with layered structure was obtained by solvothermal method using ethylene glycol as the sheet-structure linking agent, and pyridine as N source. N-doped TiO₂ showed good catalytic performance for photocatalytic degradation of Cr(VI) to Cr(III) owing to its high surface area, high Ti³⁺ ratio and abundant N in the layered structure.

Abstract

Layered TiO₂ sheets with high Cr(VI) photoreduction ability were prepared by template free solvothermal method using ethylene glycol (EG) as structure directing agent. EG linking function in the layered TiO₂ structure were confirmed by SEM, TEM, FTIR, XPS and so on. Moreover, the obtained large sized TiO₂ (20~50 μm in length, about 5~10 μm in width) were assembled by N-doped TiO₂ thin sheets with about 1.2 nm gap in between, resulting in very high surface area (327.5 m²/g) and abundant Ti³⁺ sites for Cr(VI) adsorption and reduction. This structure can not only have good performance during Cr(VI) photocatalysis reduction application (Cr(VI) removal rate: 0.84 mg*g⁻¹*min⁻¹), but also endow the material with good cycle ability.

Herein, we report a cascade process that is initiated by radical Brook rearrangement and promoted by 1,5-hydrogen atom transfer. A series of α-fluoroalkyl alkyl secondary alcohols were synthesized with unactivated terminal olefins and α-fluoroalkyl-α-silyl methanols. The strategy features mild reaction conditions and broad substrate scope. The diversified down-stream transformations demonstrated the synthetic potential of the reaction.

While polypropylene (PP) is one of the most widely used polyolefin materials, its post-functionalization has been a continuously researched topic in the polymer field since it could significantly improve physical and chemical properties by introducing polar groups, beneficial for development of the next generation of polyolefin materials. In this work, we describe the development of a visible-light promoted, environmentally friendly iron-catalyzed strategy and establishing of the reaction scope for C−H alkylated modification of polypropylene. Under our conditions, various polypropylenes could be functionalized with diverse polar alkenes with good levels of functionalization (LOF). The properties of the resulting polymers were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tensile testing. Polypropylene wastes could also be upcycled. While the incorporation of the polyglycol groups enhanced hydrophilicity, the installation of the ester groups increased the miscibility with other polymers by acting as a compatibilizer for polystyrene and polyethylene.