Deactivation Mechanism Research Articles

Progress in palladium-based bimetallic catalysts for lean methane combustion: Towards harsh industrial applications

<p>Significant volumes of lean methane (0.1–1.0 vol%) are released untreated into the atmosphere during industrial operations, contributing to the greenhouse effect and energy wastage. Catalytic methane combustion presents a promising avenue to mitigate these emissions. Depending on their active components, catalytic systems are predominantly categorized into noble metal-based and non-noble metal-based catalysts, with palladium (Pd)-based catalysts recognized for their superior low-temperature oxidation activity. Nevertheless, enhancing the thermal stability of Pd remains challenging, complicated by impurities such as H<sub>2</sub>O, SO<sub>2</sub> and H<sub>2</sub>S in the lean methane stream, which can cause catalyst poisoning and deactivation. Recent research has focused on the design of Pd-based bimetallic catalysts, offering improved stability, activity, and resistance to poisoning in harsh industrial conditions. This review examines advancements in improving the deactivation resistance of Pd-based bimetallic catalysts for lean methane combustion, covering active site characterization, dispersion and metal-support interactions, the role of auxiliary metals, and structural modulation strategies. It also investigates the impact of harsh industrial environments on Pd-based catalyst performance, focusing on deactivation mechanisms and mitigation strategies. Ultimately, this review identifies current research trends and challenges for Pd-based catalysts in demanding applications. By providing insights into the design of Pd-based catalysts with enhanced stability, activity, and resistance to poisoning, this review aims to guide the development of catalysts that meet industrial demands.</p>

Deeply revealing the deactivation and decomposition mechanism of ammonium bisulfate on the nanotube structured SCR catalyst for low-temperature NH3-SCR reaction

Sulfates formed on the catalyst surface have been the main cause of its rapid deactivation during the NH3-SCR reaction. Here, after loading ABS onto nanotube structured Ce-Mn-TNTs and nanoparticle CeMnTiOx...

Shedding new light on quadrupolar 1,4-dihydropyrrolo[3,2-b]pyrroles: impact of electron-deficient scaffolds over emission.

In this work, we disclose a series of seven quadrupolar centrosymmetric 1,4-dihydropyrrolo[3,2-b]pyrroles (DHPPs) linked to the two peripheral, strongly electron-accepting heterocycles such as benzoxadiazole, benzothiadiazole and benzoselenadiazole. This represents the first study probing the influence of electron-deficient heterocycles, rather that small electron-withdrawing substituents, on photophysics of DHPPs. These new acceptor-donor-acceptor hybrid dyes exhibit an appreciable combination of photophysical properties including absorption maxima in the range of 470-620 nm, and emission in the range of 500-720 nm with fluorescence quantum yields reaching 0.88. We discovered that the presence of two 7-nitro-benzoxadiazolyl substituents at positions 2 and 5 of DHPP core, evokes a strong fluorescence in non-polar solvents shifted to 639 nm. This is the most bathochromically shifted emission for quadrupolar, centrosymmetric chromophore bearing exclusively biaryl linkages. Interestingly, 1,2,4,5-tetraaryl-1,4-dihydropyrrolo[3,2-b]pyrrole (TAPP) possessing 4-benzothiadiazolyl groups is strongly emitting in the crystalline state (fluorescence quantum yield = 0.43). The combined photophysical and crystallographic studies point towards existence of intermolecular hydrogen bonds which modify the dihedral angles between the donor and acceptor moieties as a primary reason for this strong emission. Small structural alteration via the replacement of two 2,1,3-benzoxadiazole scaffolds with 2,1,3-benzoxadiazole-2-oxide moieties causes >103 decrease in the fluorescence intensity. Computational studies point out to strong charge transfer originating from exceptionally large dihedral angles as the pivotal reason of this phenomenon. Although internal conversion originating from the charge-transfer state is the prevailing non-radiative deactivation mechanism, intersystem crossing also plays a role. The rational design of DHPPs that enables modulation of emission will advance their applicability.

Sulfonation of IAA in Urtica eliminates its DR5 auxin activity

Key messageN-Sulfonated IAA was discovered as a novel auxin metabolite in Urtica where it is biosynthesized de novo utilizing inorganic sulfate. It showed no auxin activity in DR5::GUS assay, implying possible inactivation/storage mechanism.A novel auxin derivative, N-sulfoindole-3-acetic acid (IAA-N-SO3H, SIAA), was discovered in stinging nettle (Urtica dioica) among 116 sulfonated metabolites putatively identified by a semi-targeted UHPLC–QqTOF-MS analysis of 23 plant/algae/fungi species. These sulfometabolites were detected based on the presence of a neutral loss of sulfur trioxide, as indicated by the m/z difference of 79.9568 Da in the MS2 spectra. The structure of newly discovered SIAA was confirmed by synthesizing its standard and comparing retention time, m/z and MS2 spectrum with those of SIAA found in Urtica. To study its natural occurrence, 73 species in total were further analyzed by UHPLC–QqTOF-MS or targeted UHPLC–MS/MS method with a limit of detection of 244 fmol/g dry weight. However, SIAA was only detected in Urtica at a concentration of 13.906 ± 9.603 nmol/g dry weight. Its concentration was > 30 times higher than that of indole-3-acetic acid (IAA), and the SIAA/IAA ratio was further increased under different light conditions, especially in continuous blue light. In addition to SIAA, structurally similar metabolites, N-sulfoindole-3-lactic acid, 4-(sulfooxy)phenyllactic acid and 4-(sulfooxy)phenylacetic acid, were detected in Urtica for the first time. SIAA was biosynthesized from inorganic sulfate in seedlings, as confirmed by the incorporation of exogenous 34S-ammonium sulfate (1 mM and 10 mM). SIAA exhibited no auxin activity, as demonstrated by both the Arabidopsis DR5::GUS assay and the Arabidopsis phenotype analysis. Sulfonation of IAA may therefore be a mechanism for IAA deactivation and/or storage in Urtica, similar to sulfonation of the jasmonates in Arabidopsis.

Regulating and Stabilizing Strong Metal‐Support Interactions on Ni/TiO2 by Crystal Phase for Ultra‐Stable Ethanol Reforming

AbstractThe regulation and stabilization of strong metal‐support interactions (SMSI) in high temperature hydrogen‐rich reaction condition remains a huge challenge due to its structural sensitivity. Herein, tunable SMSI is constructed and stabilized on TiO2 supported Ni catalysts by TiO2 crystal phase engineering strategy, and then a SMSI‐degree‐depended ethanol stream reforming (ESR) performance is demonstrated. Rutile supported Ni exhibited a weakened SMSI with 48.6% coverage, exposing more metallic Ni and Ni‐TiO2 perimeter interface sites, and displayed exceptional H2 yield of 4.7 molH2/molethanol and an ultra‐long stability of 420 h without deactivation at 500 °C. The low reaction energy and high resistance to carbon deposition (0.9 mgc/gcat·h) and Ni0 sintering on Ni/r‐TiO2 catalyst explained its excellent catalytic performance. Furthermore, the effect of well‐defined SMSI structures on the reaction pathway and deactivation mechanism of the ESR is clarified. This work provides a precedent for the tailor and application of SMSI in high temperature hydrogen‐rich reaction conditions.

Theoretical Insights on the Excited State Deactivation Mechanism in Protonated Adenosine.

We present herein our computational exploration of the conformational landscape and photophysical properties of protonated adenosine (AdoH+). Several different protonated isomers and conformers have been considered and their relevant photophysical properties have been addressed. From our ab initio quantum computational results, an S1/S0 conical intersection (CI) has been located for all considered conformers, providing a significant route for the ultrafast deactivation mechanism of the S1 excited state of AdoH+. Our results are also supported by nonadiabatic dynamics (NAD) simulation results indicating the S1 excited state lifetime of 240-300 fs for the two most stable conformers of AdoH+ (i.e., the most stable syn- and anti-N3 protonated tautomers), which is comparable with protonated adenine, reported in the literature. The results confirm the ultrafast deactivation mechanism as well as photostability in nucleosides in protonated form.

Thermal Management Approach to Stabilization of Disordered Active Sites for Sabatier Reaction.

The transition metal nanocatalysts containing disordered active sites can potentially achieve efficient Sabatier reactions with high selectivity. However, it remains a challenge to maintain the stability of these active sites in such an exothermic reaction. Here, a thermal management approach is reported to address this challenge. Specifically, an efficient and stable catalytic system is developed by integrating urchin-like Ru nanoparticles with disordered active sites (d-RuNUs) and multi-walled carbon nanotubes (MWCNTs) as heat transfer framework, which achieves a CH4 yield of 3.3mol g-1 h-1 with nearly 100% selectivity in 12h. The characterizations reveal that the thermal-induced crystallization seriously weakens the adsorption of CO2, leading to significant degradation of catalytic performance. The heat transfer simulation confirms that the MWCNTs with high thermal conductivity play a key role in rapidly redistributing the reaction heat, thereby preventing the crystallization of disordered structures. This work elucidates the deactivation mechanism of disordered active sites in exothermic reactions and opens the avenue for local thermal management of non-thermal equilibrium reactions.

Deactivation Mechanism of Spent TiO2-Based Selective Catalytic Reduction (SCR) Catalysts and State-of-the-Art Recycling Technologies.

Nitrogen oxides (NOx) make up a group of gases that are mainly formed during the combustion of fossil fuels at high temperatures. NOx contributes to environmental degradation by forming acid rain and enhancing global warming. Exposure to air with a high concentration of NOx can aggravate respiratory diseases, particularly asthma. The elimination of NOx in practical applications mainly proceeds through selective catalytic reduction (SCR) of NOx with NH3 to harmless N2 and H2O. One practical issue of the SCR process is the deactivation of TiO2-based SCR catalysts. In addition, growing numbers of spent SCR catalysts present a serious waste-management challenge for recyclers at end of life. It is therefore crucial to disclose the deactivation mechanism of the spent TiO2-based NH3-SCR catalysts and propose effective recycling technologies for waste valorization. Here we outline the catalyst deactivation pathways for TiO2-based SCR catalysts and critically review methods of improving the direct sustainability of spent catalysts, in areas such as direct regeneration and recovery of spent catalysts. Through this review, the challenges, solutions, and future strategies for handling spent SCR catalysts are clarified for future studies of application on an industrial scale.

Degradation of the Antibiotic Sulfamethoxazole by Ozonation: A Comprehensive Review

ABSTRACTSulfamethoxazole (SMX) is an antibiotic widely used for the treatment of several diseases, especially respiratory and urinary. Due to its widespread use, its presence in the environment has been on the rise. This study discusses the degradation of the antibiotic SMX through the ozonation process. SMX is preferentially degraded by the direct action of O3 on the molecule, starting by breaking the double bonds in the aromatic ring. Through ozonation it is possible to obtain complete SMX degradation within 10 min, but the mineralization of the solution is not achieved, reaching total organic carbon removal efficiencies of 5%–60%, depending on the reaction time. Factors such as the presence of organic matter (OM) and the pH of the solution interfere with the degradation of SMX. The OM acts as a radical scavenger, decreasing the efficiency of degradation, while the pH interferes with the decomposition of O3 into radicals and the dissolution of the oxidant in the medium, in addition to influencing the state of ionization of the SMX making it more or less prone to reactions. In general, most other remediation processes are carried out on a laboratory scale. To increase the level of these processes to a full scale, more pilot‐scale studies are needed. In addition, it is necessary to focus on the practice of reusing materials, avoiding the generation of secondary pollution, and increasing the useful life of the material. The review also discusses the reaction mechanisms, intermediate compounds formed, mineralization of the solution, and factors that influence the process, which can help in making decisions for future studies to be carried out in the area. Prospects in the research area revolve around using metal–organic frameworks as molecular imprinting technology to modify heterogeneous catalysts, integration of external energy, bimetallic systems, and evaluation of deactivation mechanisms.

Two major deactivation mechanisms in carbon-based advanced oxidation processes (AOPs) dominated by electron-transfer pathway (ETP)

Carbon-based advanced oxidation processes through electron-transfer pathway are regarded as a green technology for efficient and selective oxidation of the emerging pollutants in complex water matrixes. Despite achievements in the superior activity and selectivity for organic degradation of carbocatalysts, their stabilities remain unsatisfactory, primarily because of the underexplored deactivation mechanisms. This study identifies two distinct deactivation mechanisms. The first is Oxidant Deactivation, due to overoxidation by the oxidant and predominantly affected by the concentration of oxidant. The other is Organic Deactivation, primarily caused by attachment of organic byproducts on catalyst surface, which reduces the overall oxidation potential of carbon/persulfate complex, instead of covering the surface “active sites”. Furthermore, the deactivation mechanisms mainly depend on intrinsic catalytic pathways: Oxidant Deactivation originates from the adjacent transfer pathway and Organic Deactivation from the electron shuttle pathway. Finally, the relationship between the deactivation mechanisms and carbon configuration (sp2/sp3) is revealed, and a catalyst with optimal activity and stability can be achieved through properly regulating the sp2/sp3 ratio. Results indicate that different protective strategies and application scenarios should be adopted for different systems to extend their lifespan in real wastewater treatment. This work sheds light on rational catalyst design toward advanced water purification systems with high efficiency and stability.

In-Situ Analysis of Reversible Deactivation and Reactivation Mechanisms of Ir Catalysts for Lifetime Extension of Proton Exchange Membrane Water Electrolysis

Building a hydrogen society to replace the current carbon energy systems is one of humanity's most pressing challenges. Green hydrogen production via proton exchange membrane water electrolysis (PEMWE) is thus a promising technology. However, the strong acid environment at high voltage leads to the corrosion of non-noble metal components, driving PEMWE demand towards expensive materials such as titanium and noble metal catalysts like Ir to drive the sluggish oxygen evolution reaction (OER) in PEMWE. Decreasing Ir loading in an effort to decrease costs while maintaining efficient and stable PEMWE is challenging due to Ir dissolution [1]. Reversible deactivation of iridium, along with irreversible degradation like agglomeration and dissolution, is of great interest [2], due to lifespan extension and reduced hydrogen production costs. Therefore, a comprehensive understanding of the mechanisms of OER deactivation and reactivation of Ir, which can be accomplished by operando studies, is crucial. However, only limited operando studies provide insight into the underlying mechanisms of OER de-/re-activation of Ir [3].In this research, we study the correlation between consumption and production of μ-oxo species in Ir catalysts to explain the de-/re-activation of Ir through specially designed electrochemical protocols coupled with operando techniques such as X-ray Absorption Spectroscopy (XAS), electrochemical Quartz Crystal Microbalance (eQCM) connected with Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), and Surface Enhanced Raman Spectroscopy (SERS), including the application of the reactivation protocol in a single cell mode of operation. Surface-terminated electrophilic μ-oxo species on Ir oxide promote intermediate formation and lower the energy barrier of OER [4-8]. Operando XAS elucidates the potential-dependent formation of a thin oxide layer, including μ-oxo species, on the Ir surface while maintaining the Ir core. However, consumption of μ-oxo species and detachment of adsorbates during OER result in a reversible mass reduction of catalysts. The relationship between dissolved Ir and replenished μ-oxo species is demonstrated by ICP-OES. Although the dissolutions of Ir catalysts increase after applying certain reactivation potentials, the average OER currents are enhanced, further indicating the presence of an additional primary factor for the activity of the catalysts, apart from the amount of present catalysts. Operando SERS further clarifies the direct correlation between the generation of μ-oxo species on the catalyst surface during catalyst reactivation and the degree of the recovered catalyst activity.Further, we implemented the reactivation protocol in a PEM single-cell and revealed the effectiveness of catalyst reactivation in PEMWE. Our findings not only contributed to an enhanced understanding of the observed phenomena on the catalyst surface during de-/re-activation but also to the development of a protocol for stable water electrolysis in a single-cell mode of operation. Reference Alia, S.M., et al., Activity and Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction. Journal of The Electrochemical Society2016. 163(11), F3105-F3112.Tan, X., et al., Decoupling structure-sensitive deactivation mechanisms of Ir/IrOx electrocatalysts toward oxygen evolution reaction. Journal of Catalysis 2019. 371, 57-70.Papakonstantinou, G., et al., Electrochemical evaluation of the de-/re-activation of oxygen evolving Ir oxide. Phys Chem Chem Phys 2022. 24(23), 14579-14591.Pfeifer, V., et al., Reactive oxygen species in iridium-based OER catalysts. Chemical Science2016. 7(11), 6791-6795.Pfeifer, V., et al., The electronic structure of iridium oxide electrodes active in water splitting. Phys Chem Chem Phys 2016. 18(4), 2292-2296.Pfeifer, V., et al., In situ observation of reactive oxygen species forming on oxygen-evolving iridium surfaces. Chemical Science2017. 8(3), 2143-2149.Frevel, L.J., et al., In Situ X-ray Spectroscopy of the Electrochemical Development of Iridium Nanoparticles in Confined Electrolyte. The Journal of Physical Chemistry C 2019. 123(14), 9146-9152.Mom, R.V., et al., Operando Structure–Activity–Stability Relationship of Iridium Oxides during the Oxygen Evolution Reaction. ACS Catalysis2022. 12(9), 5174-5184.

A Flexible Electrochemical/Thermochemical Operation to Improve Carrier Release of H2 and Counter Catalyst Instability

Formic acid is being actively pursued as a secure and potentially effective liquid organic hydrogen carrier (LOHC). Given its capability to store hydrogen through chemical bonds, it necessitates catalysis by efficient and durable catalysts for both storage and release processes. However, there remains a lack of comprehensive understanding regarding the mechanisms involved in formate dehydrogenation and catalyst deactivation.In my presentation, I delve into the exploration of the solution-phase formate dehydrogenation mechanism over Pd(111) and the significant role of operating potential in influencing both dehydrogenation activity and potential deactivation mechanisms. Notably, the operating potential plays a critical role in determining the mechanisms of both dehydrogenation and deactivation during formate dehydrogenation catalysis. Various steps involve charge-transfer processes, and their associated barriers and energies exhibit a strong dependence on the catalyst's work function or potential under reaction conditions. Through implicit solvent and constant-potential density functional theory (DFT) calculations, we observe that under the proposed conditions, formate tends to accumulate on the surface, occupying a substantial portion of it in a tightly bound oxygen-down configuration. This accumulation not only obstructs numerous surface sites but also escalates the activation energy for the process, suggesting that formate might significantly contribute to catalyst deactivation over time. Our analysis of the potential dependency of potential rate-limiting steps provides valuable insights into the prospect of adjusting this parameter, aiming at optimizing the reaction's activation energy and deepening our comprehension of the time-dependent deactivation effects observed experimentally. Additionally, I contrast these operational decisions with conventional thermal conversion pathways, serving as a benchmark for enhancing operational and conversion efficiency. The ultimate objective is to evaluate the hydrogen production rate concerning potential (U), temperature (T), and surface coverage, thereby examining the intricate interplay between thermochemical and electrochemical processes.Furthermore, I also highlight the role of the Pd phase in influencing dehydrogenation. For instance, Pd2+ tends to weaken formate binding and enhance H adsorption relative to Pd0, potentially counteracting formate-based catalyst poisoning. Illustrated in Figure 1, the thermal operation mode is represented by the vertical red line (at the PZC of Pd), whereas the room temperature electrochemical route is depicted by the horizontal blue line. The figure underscores that electrochemical conversion routes can significantly enhance dehydrogenation activity by several orders of magnitude, regardless of the maintained temperature. Moreover, activity can be further fine-tuned at these potentials by elevating the operating temperature.Hence, my research offers a qualitative description of the interplay between operating reaction conditions and operating voltage. Additionally, the dehydrogenation mechanism is slated for further investigation, taking into account the effect of support, composition, and associated phase changes as influenced by the operating potentials. Figure 1. A heatmap for the variation of dehydrogenation rate constants against the operational choices of temperature and the electrode potential. the thermal mode of operation is denoted by the vertical red line (at the PZC of Pd), while the room temperature electrochemical route is shown via the horizontal blue line. Figure 1

Fluoride Product Inhibition: New Insight into the Degradation of Nerve Agents by Zr-MOFs.

Zirconium-based metal-organic frameworks (Zr-MOFs) have shown remarkable efficacy in catalytically degrading neurotoxic agents in recent years. However, the catalytic activity of Zr-MOFs can be inhibited due to the binding of phosphate degradation products to the Zr nodes. Here, we reported the inhibition effect of a nonphosphate substance, fluoride, which can deactivate Zr-MOF nodes for the degradation of GD and VX and simulate DEPPT. The experimental and theoretical calculation results reveal that the fluoride product during GD degradation shows much more significant suppression than phosphate. The phosphate products can depart from the Zr nodes completely by adding H2O molecules on the Zr nodes to reduce the energy barrier. However, the fluoride can replace the bridged μ3-OH groups and terminal -OH groups on Zr-oxo clusters irreversibly, changing the electric density of Zr nodes and eliminating the terminal -OH. Without the terminal -OH, the five-coordinate phosphorus intermediate cannot be formed, resulting in the inactivation of Zr-O-Zr sites. This study provides new insights into Zr-MOF catalyst deactivation mechanisms and may help to develop a new strategy to design MOFs with high anti-inhibition efficiency for the degradation of nerve agents.

Excited State Dynamics of Geometrical Evolution of α-Substituted Dibenzoylmethanatoboron Difluoride Complex with Aggregation-Induced Emission Property.

Organic molecules with an aggregation-induced emission (AIE) property have been attracting much attention from the viewpoint of application to solid state emissive materials. For the AIE mechanism, quantum mechanical studies proposed the restriction of the intramolecular motion (RIM) model with the contribution of the conical intersection (CI) and deduced the importance of the restricted access to a conical intersection (RACI) in the potential energy surface (PES). Although these theoretical studies have contributed to the elucidation of AIE phenomena, direct detection of the reaction dynamics is indispensable to clarify the actual PES and the deactivation mechanism. Along this line, we investigated excited state dynamics of the AIE molecule with dibenzoylmethanatoboron difluoride complexes using time-resolved absorption spectroscopies in both visible and infrared (IR) regions. While the reference system of 1,3-bis(4-methoxyphenyl)methanatoboron difluoride (2aBF2) showed strong emission in solution, the methyl-substituted derivative at the α-position of the dioxaborine ring (2amBF2) led to the very weak fluorescence in solution but strong emission in the solid state. Time-resolved visible absorption measurements revealed a peak shift and broadening of the stimulated emission in the solution of 2amBF2, owing to the rapid change of the molecular geometry. With the temporal evolution of time-resolved IR absorption signals and density functional theory (DFT) calculation of these systems, it was deduced that 2amBF2 has two stable geometries, namely, planar and bending, in the S1 state and the bending geometry in the S1 state led to rapid conversion to the S0 state. These results support the RACI model in the aggregated states, leading to the AIE properties.

Enzyme stabilisation due to incorporation of a fluorinated non-natural amino acid at the protein surface

We have previously engineered E. coli transketolase (TK) enzyme variants that accept new substrates such as aliphatic or aromatic aldehydes, and also with improved thermal stability. Irreversible aggregation is the primary mechanism of deactivation for TK in the buffers used for biocatalysis, and so we were interested in determining the extent to which this remains true in more complex media, crude cell lysates or even in vivo. Such understanding would better guide future protein engineering efforts. NMR offers a potential approach to probe protein structure changes, aggregation, and diffusion, and19F-labelled amino acids are a useful NMR probe for complex systems with little or no background signal from the rest of the protein or their environment. Here we labelled E. coli TK with two different19F probes, trifluoromethyl-L-phenylalanine (tfm-Phe), and 4-fluoro phenylalanine (4 F-Phe), through site specific non-natural amino acid incorporation. We targeted them to residue K316, a highly solvent exposed site located at the furthest point from the enzyme active sites. Characterisation of the19F-labelled TK variants revealed surprising effects of these mutations on stability, and to some extent on activity. While variant TK-tfm-Phe led to a 7.5 °C increase in the thermal transition midpoint (Tm) for denaturation, the TK-4 F-Phe variant largely abolished the aggregation of the enzyme when incubated at 50 °C19. F-NMR revealed different behaviours in response to temperature increases for the two TK variants, displaying opposite temperature gradient chemical shifts, and diverging motion regimes, suggesting that the mutations affected differently both the local environment at this site, and its temperature-induced dynamics. A similar incubation of TK at 40–55 °C is also known to induce higher cofactor-binding affinities, leading to an apparent heat activation under low cofactor concentration conditions. We have hypothesised previously that a heat-inducible conformational change in TK leads to this effect1. H-NMR revealed a temperature-dependent re-structuring of methyl groups, also at 30–50 °C, which may be linked to the heat activation. While our kinetic studies were not expected to observe the heat activation event due to the high cofactor concentrations used, this was not the case for TK-4 F-Phe, which did appear to heat activate slightly at 45 °C. This implied that the mutations at K316 could influence cofactor-binding, despite their location at 47 Å from either active site. Such long-distance effects of mutations are not unprecedented, and indeed we have previously shown how distant mutations can influence active-site loop stability and function in TK, mediated via dynamically coupled networks of residues. Molecular dynamics simulations of the two19F containing variants similarly revealed networks of residues that could couple the changes in dynamics at residue K316, through to changes in active site dynamics. These results independently highlight the sensitivity of active-site function to distant mutations coupled through correlated dynamic networks of residues. They also highlight the potential influence of surface-incorporated probes on protein stability and function, and the need to characterise them well prior to further studies.

Influence of activation/deactivation process on surface-initiated atom transfer radical polymerization: An in silico investigation

We propose a simulation approach to explore surface-initiated atom transfer radical polymerization (SI-ATRP), in which how the chain growth is affected by activation/deactivation process could be considered explicitly. Our findings indicate that these activation and deactivation mechanisms provide all polymer chains with equal growth opportunities. This process leads to a significant increase of grafting density while concurrently reducing the dispersity of the grafted chains. The ratio of activated and dormant chains is theoretically proved to eventually reach equilibrated within the activation/deactivation process. The shorter lifetime of activation/deactivation cycle leads to an even equal opportunity and a faster “stop-continue” pace for the growth of all chains. Our study is helpful for better understanding the role of activation/deactivation process in SI-ATRP from a microscopic perspective.

High-Temperature Behavior of Pd/MgO Catalysts Prepared via Various Sol-Gel Approaches.

A series of Pd/MgO catalysts based on nanocrystalline MgO were prepared via different sol-gel approaches. In the first two cases, palladium was introduced during the gel preparation, followed by drying it in supercritical or ambient conditions. In the third case, aerogel-prepared MgO was impregnated with an ethanol solution of Pd(NO3)2. The prepared catalysts differ in particle size and oxidation state of palladium. The catalytic performance and thermal stability of the samples were examined in a model reaction of CO oxidation at prompt thermal aging conditions. The as-prepared and aged materials were characterized by low-temperature nitrogen adsorption, UV-vis spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and ethane hydrogenolysis testing reaction. The highest initial activity (T50 = 103 °C) was demonstrated by the impregnated sample, containing Pd0 particles of 3 nm in size. The lowest T50 value (215 °C) after aging at 1000 °C was demonstrated by the impregnated Pd/MgO-WI sample. The high-temperature behavior of the catalysts was found to be affected by the initial oxidation state and dispersion of Pd. Two deactivation mechanisms, such as the agglomeration of Pd particles and migration of small Pd species into the bulk of the MgO support with the formation of Pd-MgO solid solutions, were discussed.

Failure Mechanism Analysis and Emerging Strategies for Enhancing the Photoelectrochemical Stability of Photoanodes.

The development of efficient and stable photoanode materials is essential for driving the possible practical application of photoelectrochemical water splitting. This article begins with a basic understanding of the fundamentals of photoelectrochemical devices and photoanodes. State-of-the-art strategies for designing photoanodes with long-term stability are highlighted, including insertion of hole transport layers, construction of protective/passivation layers, loading of co-catalysts, construction of heterojunctions, and modification of the electrolyte. Based on the insights gained from these effective strategies, we present an outlook for addressing key aspects of the challenges of stabilizing photoanodes development in the future work. Widespread adoption of stability assessment criteria will facilitate reliable comparisons of results from different laboratories. In addition, deactivation of photoanode is defined as a 50 % reduction in productivity. An in-depth understanding of the deactivation mechanism is essential for the design and development of efficient and stable photoanodes. This work will provide insights into the stability assessment of photoanode and facilitate the production of practical solar fuels.

Identification of Deactivation Mechanisms by the Periodic Transient Kinetic Method

AbstractThe understanding of deactivation processes in heterogeneous catalysis is key for the development of new materials and exploration of new operation windows. In this contribution, the periodic transient kinetic method (PTK) is used to identify and separate catalyst deactivation processes for the first time. The PTK method is applied for a standard Ni/Al2O3 catalyst in CO and CO2 methanation for 24 h and compared to steady‐state experiments. For the example reactions, the study exhibits different deactivation behavior for CO and CO2 methanation. The results demonstrate that the PTK method delivers an insight into the deactivation process and furthermore gives evidence for the underlying mechanism.

Diving into the influence of phosphorus on ceria-supported copper manganese bimetallic oxides for catalytic removal of carbon monoxide

The application of ceria-supported catalysts as promising catalysts for air pollutant abatement via heterogeneous catalytic processes is still a challenge. Phosphorus (P) is a potential threat to catalyst deactivation but has not been sufficiently explored. Herein, a systematic study reveals the poisoning behaviors of P on Cu-Mn bimetallic oxides supported by ceria (Cu-Mn/CeO2) as a typical case in CO oxidation and provides new insights into the deactivation mechanism. The P impregnation decreases the surface area of Cu-Mn/CeO2 and leads to the emergence of a new sheet morphology. The interactions between P and catalyst components (support and active species) result in the generation of dominant P species of PO43− and PO3−. The P addition also weakens the oxygen storage capacity of ceria and decreases the proportions of low-valent Cu and Mn, hindering electron transfers among metals. Furthermore, the reducibility and the adsorption and activation of O2 are limited in P-loaded Cu-Mn/CeO2 catalysts as found in H2-TPR and O2-TPD when increasing the P concentration. In situ DRIFTS experiments demonstrate that the inhibition of the formation and transformation of active intermediates, namely carbonyls and carbonates, is responsible for the poisoning behaviors of P in the pathway of CO oxidation over Cu-Mn/CeO2 catalyst.