Negligible Catalytic Activity Research Articles

Breaking the Limitations of Activity and Stability in Powdered Materials for Oxygen Evolution Reaction: The Critical Role of Catalyst-Inducing Seeds

Powdered catalysts are extensively employed in industrial-scale energy conversion devices but struggle with weak powder-substrate adhesion and inherent instability in gas-evolving and highly oxidative oxygen evolution reactions (OER). This work introduces an innovative strategy in which powdered materials serve a critical role as catalyst-inducing seeds to break these limitations. Specifically, powdered Ti2CTx MXene with anchored cobalt single atoms (Co-SAs) shows negligible catalytic activity on its own but serves as catalyst-inducing seeds, significantly enhancing the catalytic activity of the conductive FeNi substrate. Mechanistic studies demonstrate that Co-SAs accelerate the oxidation rate of Ti2CTx, leading to the micro-battery corrosion behavior between oxidized Co/Ti2CTx and FeNi alloy, which generates highly OER-active corrosion products tightly bonded to FeNi alloy, thereby enhancing catalytic activity and ensuring stability. The prepared porous electrode shows a low overpotential of 303mV to deliver an ultra-high current density of 1000mAcm-2 and maintains activity for 1200hours under high current density conditions, rivaling advanced self-supporting electrodes. Moreover, replacing Co in Co/Ti2CTx with metals like Fe, Ni or Mn, yields comparable effects, suggesting the scalability of catalyst-inducing seeds. This approach breaks traditional limitations of powdered materials in OER, offering an effective pathway to engineer advanced catalytic electrodes.

The Central Role of Oxo Clusters in Zirconium‐Based Esterification Catalysis

Oxo clusters are a unique link between oxide nanocrystals and Metal‐Organic Frameworks (MOFs), representing the limit of downscaling each of the respective crystals. Herein, the superior catalytic activity of clusters, compared to zirconium MOF UiO‐66 and nanocrystals is shown. Focus is on esterification reactions given their general importance in consumer products and the challenge of converting large substrates. Oxo clusters have a higher surface‐to‐volume ratio than nanocrystals, rendering them more active. For large substrates, for example, oleic acid, MOF UiO‐66 has negligible catalytic activity while clusters provide almost quantitative conversion, a fact we ascribe to limited diffusion of large substrates through the MOF pores. Clusters do not suffer from limited mass transfer and we also obtain high conversion in solvent‐free reactions with sterically hindered alcohols (hexanol, 2‐ethyl hexanol, benzyl alcohol, and neopentyl alcohol). The cluster catalyst can be recovered and shows identical activity when reused. The structural integrity of the cluster is confirmed using X‐ray total scattering and pair distribution function analysis. Moreover, when homogeneous zirconium alkoxides are used as catalysts, the same oxo cluster is retrieved, showing that oxo clusters are the active catalytic species, even in previously assumed homogeneously catalyzed reactions.

Cu2O@PdCu synergistic catalysis for highly effective C-H arylation of azoles.

An efficient heterogeneous Pd/Cu synergistic catalysis system without a ligand was utilized for C-H arylation of azoles. The reaction exhibits excellent catalytic activity with high functional group tolerance. The synergistic effect between the Cu2O core and PdCu shell was confirmed, whereas pure PdCu nanocages and Cu2O exhibited negligible catalytic activity.

Gas flow–directed growth of aligned carbon nanotubes from nonmetallic seeds

Kite growth is a process that utilizes laminar gas flow in chemical vapor deposition to grow long, well-aligned carbon nanotubes (CNTs) for electronic application. This process uses metal nanoparticles (NPs) as catalytic seeds for CNT growth. However, these NPs remain as impurities in the grown CNT. In this study, nanodiamonds (NDs) with negligible catalytic activity were utilized as nonmetallic seeds instead of metal catalysts because they are stable at high temperatures and facilitate the growth of low-defect CNTs without residual metal impurities. Results demonstrate the successful growth of over 100-μm-long CNTs by carefully controlling the growth conditions. Importantly, we developed an analysis method that utilizes secondary electron (SE) yield to distinguish whether or not CNTs grown from metal impurities. The absence of metallic NPs at the CNT tips was revealed by the SE yield mapping, whereas the presence of some kind of NPs at the same locations was confirmed by atomic force microscopy (AFM). These results suggest that most of the aligned CNTs were grown from nonmetallic seeds, most likely ND-derived NPs, via the tip-growth mode. Structural characterizations revealed the high crystallinity of CNTs, with relatively small diameters. This study presents the first successful use of nonmetallic seeds for kite growth and provides a convincing alternative for starting materials to prepare long, aligned CNTs without metal impurities. The findings of this study pave the way for more convenient fabrication of aligned CNT-based devices, potentially simplifying the production process by avoiding the need for the removal of metal impurities.

Experimental comparison of solar methane pyrolysis in gas-phase and molten-tin bubbling tubular reactors

This study experimentally compares solar methane pyrolysis in gas phase and molten tin for hydrogen and solid carbon production. Molten media are expected to facilitate carbon separation and to enhance solar-to-gas heat transfer. Effects of temperature (1000–1400 °C), gas feed flow rate (0.5–1.0 NL/min), and methane molar fraction in the feed (0.1–0.5) on methane decomposition were investigated in a tubular solar reactor. Methane conversion in molten tin was significantly lower than in gas phase at all temperatures (e.g., 64% vs. 92% at 1300 °C). It was justified by the negligible catalytic activity of tin, the small gas-liquid surface contact (bubble diameter ∼5 mm) and the reduced bubble-tin contact time, in comparison with gas-phase pyrolysis (e.g., 0.83 s vs. 0.5 s for 0.5 NL/min gas feed at 1300 °C). For both routes, a temperature increase (1000–1400 °C) improved methane conversion (gas phase: 2–98%, molten tin: 0–91%). Increasing gas feed flow rate (0.5–1.0 NL/min) decreased conversion (gas phase: 93-85%, molten tin: 64-48% at 1300 °C) by reducing space-time in gas phase (0.83–0.42 s) or by inducing bubbles coalescence in molten tin. Increasing methane molar fraction in the feed generally decreased methane conversion but energy efficiencies were enhanced. The carbon produced in gas-phase pyrolysis was carbon black powder (50–100 nm particle size) and carbon sheets in molten tin.

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO 2 /Epoxide Copolymer

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO ₂ /Epoxide Copolymer

Biodiesel production from wastewater sludge using exchange resins as heterogeneous acid catalyst: Catalyst selection and sludge pre-treatments

Three different ion-exchange resins (Amberlyst 15, 36 and IR120) were used as heterogeneous catalysts for the transesterification of the secondary sludge lipids. Catalyst performance was evaluated based on the biodiesel yield and quality; the best biodiesel yield, with the best properties was obtained with Amberlyst IR120. Microwaves (MW) and ultrasounds (US) were studied as a pre-treatment step to increase lipid extraction. US treatment shows the highest biodiesel yield, providing a biodiesel that fulfils the current regulations. The sludge particle size effect was also studied obtaining the best results using the smallest one. However, in these conditions, ultrasound damage the lipids, decreasing the biodiesel yield. Temperature and catalyst/sludge ratio have been optimized. The maximum biodiesel yield (32.9% FAMEs/lipids) was obtained with Amberlyst IR120, catalyst/sludge ratio 1:2, MeOH/sludge ratio 33:1, 120 °C, 21 h reaction time and US as pre-treatment. The catalyst was also reused for six times under the optimal reaction conditions with negligible catalytic activity loss.

Cofactor-free organic nanozyme with assembly-induced catalysis and light-regulated activity

Organic nanozymes that mimic cofactor-free enzymes avoid the use of metal ions and other cofactors, and show great advantages in the field of biomimetic catalysis. The assembly of organics such as peptides is usually necessary for their catalysis and is also a major challenge for organic nanozymes. Here we constructed cofactor-free organic nanozyme by self-assembly of cyclodextrins modified gold nanoparticle and azobenzene modified peptide chain through host–guest interaction. At room temperature, free peptide chain has negligible catalytic activity. Organic nanozyme reduces the activation energy and increases the reaction rate of hydrolysis of 4-nitrophenyl acetate. The catalysis of organic nanozyme derives from the ordered assembly of peptide chains on the surface of support and the deprotonation of the imidazole groups of neighboring histidines that facilitates the splitting of a proton from water, and thus promotes the nucleophilic attack on the incoming substrate. Photoisomerization of azobenzene group leads to the assembly and disassembly of nanozyme, causing the change of catalytic activity. These findings may contribute to the design of advanced biomimetic catalysts and provide a model for cofactor-free nanozymes.

Iron‐Catalyzed Water Oxidation: O–O Bond Formation via Intramolecular Oxo–Oxo Interaction

AbstractHerein, we report the importance of structure regulation on the O−O bond formation process in binuclear iron catalysts. Three complexes, [Fe2(μ‐O)(OH2)2(TPA)2]4+(1), [Fe2(μ‐O)(OH2)2(6‐HPA)]4+(2) and [Fe2(μ‐O)(OH2)2(BPMAN)]4+(3), have been designed as electrocatalysts for water oxidation in 0.1 M NaHCO3solution (pH 8.4). We found that1and2are molecular catalysts and that O−O bond formation proceeds via oxo–oxo coupling rather than by the water nucleophilic attack (WNA) pathway. In contrast, complex3displays negligible catalytic activity. DFT calculations suggested that theantitosynisomerization of the two high‐valent Fe=O moieties in these catalysts takes place via the axial rotation of one Fe=O unit around the Fe‐O‐Fe center. This is followed by the O−O bond formation via an oxo–oxo coupling pathway at the FeIVFeIVstate or via oxo–oxyl coupling pathway at the FeIVFeVstate. Importantly, the rigid BPMAN ligand in complex3limits theantitosynisomerization and axial rotation of the Fe=O moiety, which accounts for the negligible catalytic activity.

Iron-Catalyzed Water Oxidation: O-O Bond Formation via Intramolecular Oxo-Oxo Interaction.

Herein, we report the importance of structure regulation on the O-O bond formation process in binuclear iron catalysts. Three complexes, [Fe2 (μ-O)(OH2 )2 (TPA)2 ]4+ (1), [Fe2 (μ-O)(OH2 )2 (6-HPA)]4+ (2) and [Fe2 (μ-O)(OH2 )2 (BPMAN)]4+ (3), have been designed as electrocatalysts for water oxidation in 0.1 M NaHCO3 solution (pH 8.4). We found that 1 and 2 are molecular catalysts and that O-O bond formation proceeds via oxo-oxo coupling rather than by the water nucleophilic attack (WNA) pathway. In contrast, complex 3 displays negligible catalytic activity. DFT calculations suggested that the anti to syn isomerization of the two high-valent Fe=O moieties in these catalysts takes place via the axial rotation of one Fe=O unit around the Fe-O-Fe center. This is followed by the O-O bond formation via an oxo-oxo coupling pathway at the FeIV FeIV state or via oxo-oxyl coupling pathway at the FeIV FeV state. Importantly, the rigid BPMAN ligand in complex 3 limits the anti to syn isomerization and axial rotation of the Fe=O moiety, which accounts for the negligible catalytic activity.

Manipulating Energy Transfer in UCNPs@SiO2@Ag Nanoparticles for Efficient Infrared Photocatalysis.

Conventional photocatalysts must be activated by ultraviolet or visible light to meet the energy requirement of populating an initial excited state, while infrared light has a high penetration depth to reaction media but does not have enough photon energy to activate conventional photocatalysts. Here, we report the activation of Ag nanoparticles by upconversion nanoparticles (UCNPs) in UCNPs@SiO2@Ag with manipulated energy transfer for infrared photocatalysis. UCNPs can efficiently convert infrared light to visible and ultraviolet light and are very ideal candidates for bridging the advantage of infrared light and the activation energy requirement of conventional photocatalysts. In the UCNPs@SiO2@Ag nanosystem, we employ the UCNPs to activate conventional Ag nanoparticles under infrared light irradiation. The evanescent field of UCNPs is confined for enhancing the near-field energy-transfer efficiency using a designed core/shell heterostructure, while a SiO2 layer is used for blocking the phonon exchange of thermal vibration between photon upconverters and Ag nanoparticles. Based on the manipulated energy transfer, UCNPs@SiO2@Ag nanoparticles exhibit efficient photocatalytic activity under the irradiation of 980 nm infrared light, while single Ag nanoparticles have negligible catalytic activity under infrared irradiation.

Ultrathin Metal–Organic Framework Nanosheets-Derived Yolk–Shell Ni 0.85 Se@NC with Rich Se-Vacancies for Enhanced Water Electrolysis

We present a controlled fabrication of selective ultrathin metal–organic framework (MOF) nanosheets as preassembling platforms, yolk–shell structured with a few-layered N-doped carbon (NC) shell-en...

Nanocatalytic Medicine of Iron-Based Nanocatalysts

Iron can be found in all mammalian cells and is of critical significance to diverse cellular activities within human bodies. Widespread applications and the underlying chemical and biological funda...

Comparative study of structure-catalytic activity relationship for Ni–Cr–Al–O and Cu–Ni–Cr–Al–O spinel oxide solid solutions

A spinel solid solution expressed by a composition formula of CuxNi1−xAl1.8Cr0.2O4 (0 ≤ x ≤ 0.2) was studied focusing on the role of Cu species in the catalytic activity toward NO reduction under a simulated three-way catalysis condition. X-ray Rietveld analysis revealed that Cu and Cr prefer to occupy the tetrahedral site and the octahedral site, respectively, whereas Ni and Al are distributed across both sites. Although NiAl1.8Cr0.2O4 (x = 0) showed negligible catalytic activity for NO reduction, the partial replacement of Ni by Cu significantly enhanced the activity, achieving the highest activity at x = 0.05 not only for NO reduction but also for CO and C3H6 oxidation. Based on the infrared spectra and pulsed reaction experiments, it was concluded that the monovalent Cu site in the tetrahedral site plays a key role in CO chemisorption, oxygen vacancy formation, and subsequent NO reduction via the Mars–van Krevelen mechanism.

Thermomagneto-Responsive Smart Biocatalysts for Malonyl-Coenzyme A Synthesis.

Smart biocatalysts, in which enzymes are conjugated to stimuli-responsive polymers, have gained considerable attention because of their catalytic switchability and recyclability. Although many systems have been developed, they require separate laboratory techniques for their recovery, making them unsuitable for many practical applications. To address these issues, we designed a thermomagneto-responsive biocatalyst by immobilizing an enzyme on the terminal of thermo-responsive polymer brushes tethered on magnetic nanoparticle (NP) clusters. The concept is demonstrated by a system consisting of iron oxide NPs, poly(N-isopropyl-acrylamide), and a malonyl-Coenzyme A synthetase (MatB). By using free malonate and coenzyme A (CoA), the designed catalyst exhibits adequate activity for the production of malonyl-CoA. Thanks to the use of a magnetic NP cluster, whose magnetic moment is high, this system is fully recoverable under the magnetic field at above 32 °C because of the collapse of the thermo-responsive polymer shell in the clusters. In addition, the recycled catalyst maintains moderate activity even after three cycles, and it also shows excellent catalytic switchability, that is, negligible catalytic activity at 25 °C because of the blockage of the active sites of the enzyme by the extended hydrophilic polymer chains but great catalytic activity at a temperatures above the lower critical solution temperature at which the enzymes are exposed to the reaction medium because of the thermo-responsive contraction of polymer chains. Because the azide functionality in our system can be easily functionalized depending upon our need, such catalytically switchable, fully recoverable, and recyclable multiresponsive catalytic systems can be of high relevance for other cell-free biosynthetic approaches.

Transition Metal-Free Alkyne Hydrogenation Catalysis with BaGa2, a Hydrogen Absorbing Layered Zintl Phase.

Inexpensive, transition metal-free intermetallic compounds have received almost no attention as heterogeneous catalysts. Here, we show that BaGa2, a Zintl-Klemm compound composed of honeycomb sheets of Ga- anions separated by Ba2+ cations and known to react with H2 under moderate conditions to form a layered polyanionic hydride BaGa2H2, effectively catalyzes the hydrogenation of phenylacetylene into styrene and ethylbenzene under modest conditions (1-50 bar H2, 40-100 °C). Remarkably, the catalytic activity of BaGa2 (surface specific activities up to 8390 h-1) is on the same order of magnitude as commercial Pd-based catalysts. In contrast, BaGa2H2 shows negligible catalytic activity, thereby indicating that the unsaturated Ga- framework is necessary for phenylacetylene and styrene adsorption. These findings open up future explorations of utilizing and optimizing the long-term stability of transition metal-free intermetallic hydrogen absorbing compounds for hydrogen-based catalysis.

Structural analysis of pathogenic mutations targeting Glu427 of ALDH7A1, the hot spot residue of pyridoxine-dependent epilepsy.

Certain loss-of-function mutations in the gene encoding the lysine catabolic enzyme aldehyde dehydrogenase 7A1 (ALDH7A1) cause pyridoxine-dependent epilepsy (PDE). Missense mutations of Glu427, especially Glu427Gln, account for ~30% of the mutated alleles in PDE patients, and thus Glu427 has been referred to as a mutation hot spot of PDE. Glu427 is invariant in the ALDH superfamily and forms ionic hydrogen bonds with the nicotinamide ribose of the NAD+ cofactor. Here we report the first crystal structures of ALDH7A1 containing pathogenic mutations targeting Glu427. The mutant enzymes E427Q, Glu427Asp, and Glu427Gly were expressed in Escherichia coli and purified. The recombinant enzymes displayed negligible catalytic activity compared to the wild-type enzyme. The crystal structures of the mutant enzymes complexed with NAD+ were determined to understand how the mutations impact NAD+ binding. In the E427Q and E427G structures, the nicotinamide mononucleotide is highly flexible and lacks a defined binding pose. In E427D, the bound NAD+ adopts a "retracted" conformation in which the nicotinamide ring is too far from the catalytic Cys residue for hydride transfer. Thus, the structures revealed a shared mechanism for loss of function: none of the variants are able to stabilise the nicotinamide of NAD+ in the pose required for catalysis. We also show that these mutations reduce the amount of active tetrameric ALDH7A1 at the concentration of NAD+ tested. Altogether, our results provide the three-dimensional molecular structural basis of the most common pathogenic variants of PDE and implicate strong (ionic) hydrogen bonds in the aetiology of a human disease.

Helicity Induction and Its Static Memory of Poly(biphenylylacetylene)s Bearing Pyridine N‐Oxide Groups and Their Use as Asymmetric Organocatalysts

ABSTRACTNovel poly(biphenylylacetylene) derivatives carrying different types of pyridine N‐oxide units with a bulky or less‐bulky substituent at a different position as the functional pendant groups (poly‐2a and poly‐2b) were synthesized by the rhodium‐catalyzed polymerization of the corresponding monomers. The influence of the steric environment around the catalytically active pyridine N‐oxide sites on the helicity induction and its static memory as well as the asymmetric catalytic activities of the resulting helical polymers with a macromolecular helicity memory was investigated. The polyacetylenes formed an excess one‐handed helical conformation upon noncovalent interactions with optically active alcohols and the induced macromolecular helicities of the polyacetylenes were efficiently memorized after the removal of the chiral inducers. Poly‐2b with the macromolecular helicity memory showed an enantioselectivity for the catalytic asymmetric allylation of benzaldehydes, producing optically active allyl alcohols, although their enantioselectivities were low. On the other hand, poly‐2a exhibited a negligible catalytic activity probably due to the bulky substituent at the o‐position of the pyridine N‐oxide residues, while poly‐2a underwent a unique helix‐inversion with the increasing concentration of chiral alcohols and the opposite helicity of poly‐2a was further successfully memorized. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2481–2490

From Molecular Understanding to Organismal Biology of N-Terminal Acetyltransferases

In this issue of Structure, Deng etal. (2019) determine the structure of the yeast N-terminal acetyltransferases Naa10 and Naa50 in complex with Naa15 and demonstrate that Naa50 has negligible catalytic activity on its own but modulates Naa10/Naa15. This study provides insights into mechanisms involving amino-terminal acetylation of proteins.

Water-assisted rapid growth of monolayer graphene films on SiO2/Si substrates

Metal-free growth of high-quality monolayer graphene films by chemical vapor deposition (CVD) on dielectric substrates is of great significance for the development of high-performance graphene-based electronic and optoelectronic devices. However, the existing CVD processes suffer from poor structural uniformity (or growth quality) and/or a slow growth rate due to the negligible catalytic activity of dielectric substrates. Here, we report a water-assisted CVD process for rapid growth of monolayer graphene film on SiO2/Si substrate without using metal catalysts or ultra-high temperature. Even trace amount of water enables the preferential formation of monolayer graphene films with significantly reduced structural defects. Particularly, this strategy enables the rapid growth of monolayer graphene by effectively lowering the growth kinetic barrier. We attribute the benefits of water on simultaneously improving the structural uniformity and growth rate to its mild oxidative effect and the role in accelerating the release of oxygen from the SiO2/Si substrate, respectively. Our work provides helpful information for efficient and controllable CVD growth of high-quality graphene on dielectric substrates.