Unlocking the Potential of MXene in Catalysis: Decorated Mo2CTx Catalyst for Ammonia Synthesis under Mild Conditions.

Ammonia, which is one of the most important chemicals for the synthesis of dyes, pharmaceuticals, and fertilizers, is produced by the reaction of molecular hydrogen with nitrogen, over an iron-based catalyst at 400-500 °C under pressure of over 100 bar. Decreasing the operating temperature and pressure of this highly energy-intensive process, developed by Haber and Bosch over 100 years ago, would decrease energy consumption in the world. In this work, we used two-dimensional Mo2CTx MXene as a support for a cobalt-based catalyst. The MXene functionalized by Co showed catalytic activity for ammonia synthesis from H2 and N2 at temperatures as low as 250 °C, without any pretreatment. The developed catalyst was highly active for ammonia synthesis, demonstrating a high rate of up to 9500 µmol g-1active phase h-1 at 400 °C under ambient pressure in steady-state conditions, and did not suffer from any deactivation after 15 days of reaction. The apparent activation energy (Ea) was found to be in the range of 68-74 kJ mol-1, which is in line with values reported for highly active catalysts. This improved catalyst may decrease the energy consumption in the synthesis of ammonia and its derivatives, as well as facilitate the use of ammonia as a hydrogen carrier for renewable energy storage.

Switching on/off molybdenum nitride catalytic activity in ammonia synthesis through modulating metal-support interaction.

Modulating the interaction between Mo nanoparticles and their support is an elegant approach to finely tune the structural, physico-chemical, redox and electronic properties of the active site. In this work, a series of molybdenum nitride catalysts supported on TiO2, and SBA-15 has been prepared and fully characterized. The results of characterization confirmed the high dispersion of Mo and the formation of small molybdenum nanoparticles in both the 10-Mo-N/SBA-15 and 10-Mo-N/TiO2 catalysts. In this context, we have shown that the catalytic activity of Mo species was strongly impacted by the nature of the catalytic support. Amongst the studied supports, SBA-15 was found to be the most appropriate for Mo dispersion. In comparison, when supported on a reducible oxide (TiO2), Mo species showed poor catalytic activity in both ammonia synthesis and decomposition and were prone to quick deactivation in the ammonia synthesis reaction. Evidence of charge transfer from the reducible support to the active phase, indicative of possible SMSI behaviour, has been observed by XPS and EPR. Differences in the oxidation states, redox behaviours, and electronic properties have been further studied by means of EPR, H2-TPR and H2-TPD.

Unique orientation of 1D and 2D nanoparticle assemblies confined in smectic topological defects.

New collective optical properties have emerged recently from organized and oriented arrays of closely packed semiconducting and metallic nanoparticles (NPs). However, it is still challenging to obtain NP assemblies which are similar everywhere on a given sample and, most importantly, share a unique common orientation that would guarantee a unique behavior everywhere on the sample. In this context, by combining optical microscopy, fluorescence microscopy and synchrotron-based grazing incidence X-ray scattering (GISAXS) of assemblies of gold nanospheres and of fluorescent nanorods, we study the interactions between NPs and liquid crystal smectic topological defects that can ultimately lead to unique NP orientations. We demonstrate that arrays of one-dimensional - 1D (dislocations) and two-dimensional - 2D (grain boundaries) topological defects oriented along one single direction confine and organize NPs in closely packed networks but also orient both single nanorods and NP networks along the same direction. Through the comparison between smectic films associated with different kinds of topological defects, we highlight that the coupling between the NP ligands and the smectic layers below the grain boundaries may be necessary to allow for fixed NP orientation. This is in contrast with 1D defects, where the induced orientation of the NPs is intrinsically induced by the confinement independently of the ligand nature. We thus succeeded in achieving the fixed polarization of assemblies of single photon emitters in defects. For gold nanospheres confined in grain boundaries, a strict orientation of hexagonal networks has been obtained with the 〈10〉 direction strictly parallel to the defects. With such closely packed and oriented NPs, new collective properties are now foreseen.

From Chains to Monolayers: Nanoparticle Assembly Driven by Smectic Topological Defects.

In this Letter, we show how advanced hierarchical structures of topological defects in the so-called smectic oily streaks can be used to sequentially transfer their geometrical features to gold nanospheres. We use two kinds of topological defects, 1D dislocations and 2D ribbon-like topological defects. The large trapping efficiency of the smectic dislocation cores not only surpasses that of the elastically distorted zones around the cores but also surpasses the one of the 2D ribbon-like topological defect. This enables the formation of a large number of aligned NP chains within the dislocation cores that can be quasi-fully filled without any significant aggregation outside of the cores. When the NP concentration is large enough to entirely fill the dislocation cores, the LC confinement varies from 1D to 2D. We demonstrate that the 2D topological defect cores induce a confinement that leads to planar hexagonal networks of NPs. We then draw the phase diagram driven by NP concentration, associated with the sequential confinements induced by these two kinds of topological defects. Owing to the excellent large-scale order of these defect cores, not only the NP chains but also the NP hexagonal networks can be oriented along the desired direction, suggesting a possible new route for the creation of either 1D or 2D highly anisotropic NP networks. In addition, these results open rich perspectives based on the possible creation of coexisting NP assemblies of different kinds, localized in different confining areas of a same smectic film that would thus interact thanks to their proximity but also would interact via the surrounding soft matter matrix.

Emulsions Stabilized with Alumina-Functionalized Mesoporous Silica Particles.

Alumina-functionalized ordered mesoporous silica SBA-15 particles have been proposed to stabilize Pickering emulsions. Functionalization of SBA-15 particles have been performed by depositing alumina using a two-step synthesis (first, silica condensation, followed by alumina precipitation). Three different Al to Si ratios have been prepared. The calcined materials have been characterized by TEM, SEM, XRD, N2 physisorption, and zeta potential, in order to determine key physicochemical properties, and the alumina localization. The emulsifying and stabilizing properties of the calcined particles have been evaluated for water/toluene-based Pickering emulsions.

How Catalysts and Experimental Conditions Determine the Selective Hydroconversion of Furfural and 5-Hydroxymethylfurfural.

Furfural and 5-hydroxymethylfurfural stand out as bridges connecting biomass raw materials to the biorefinery industry. Their reductive transformations by hydroconversion are key routes toward a wide variety of chemicals and biofuels, and heterogeneous catalysis plays a central role in these reactions. The catalyst efficiency highly depends on the nature of metals, supports, and additives, on the catalyst preparation procedure, and obviously on reaction conditions to which catalyst and reactants are exposed: solvent, pressure, and temperature. The present review focuses on the roles played by the catalyst at the molecular level in the hydroconversion of furfural and 5-hydroxymethylfurfural in the gas or liquid phases, including catalytic hydrogen transfer routes and electro/photoreduction, into oxygenates or hydrocarbons (e.g., furfuryl alcohol, 2,5-bis(hydroxymethyl)furan, cyclopentanone, 1,5-pentanediol, 2-methylfuran, 2,5-dimethylfuran, furan, furfuryl ethers, etc.). The mechanism of adsorption of the reactant and the mechanism of the reaction of hydroconversion are correlated to the specificities of each active metal, both noble (Pt, Pd, Ru, Au, Rh, and Ir) and non-noble (Ni, Cu, Co, Mo, and Fe), with an emphasis on the role of the support and of additives on catalytic performances (conversion, yield, and stability). The reusability of catalytic systems (deactivation mechanism, protection, and regeneration methods) is also discussed.

Manipulating the physical states of confined ibuprofen in SBA-15 based drug delivery systems obtained by solid-state loading: Impact of the loading degree.

Using the Milling-Assisted Loading (MAL) solid-state method for loading a poorly water-soluble drug (ibuprofen, IBP) within the SBA-15 matrix has given the opportunity to manipulate the physical state of drugs for optimizing bioavailability. The MAL method makes it easy to control and analyze the influence of the degree of loading on the physical state of IBP inside the SBA-15 matrix with an average pore diameter of 9.4 nm. It was found that the density of IBP molecules in an average pore size has a direct influence on both the glass transition and the mechanism of crystallization. Detailed analyzes of the crystallite distribution and melting by Raman mapping, x-ray diffraction, and differential scanning calorimetry have shown that the crystals are localized in the core of the channel and surrounded by a liquid monolayer. The results of these complementary investigations have been used for determining the relevant parameters (related to the SBA-15 matrix and to the IBP molecule) and the nature of the physical state of the confined matter.

Differential Representation of Landmark and Self-Motion Information along the CA1 Radial Axis: Self-Motion Generated Place Fields Shift toward Landmarks during Septal Inactivation.

Spatial location in the environment can be defined in relation to specific landmarks or in relation to the global context, and is estimated from both the sensing of landmarks and the inner sense of cumulated locomotion referred to as path-integration. The respective contribution of landmark and path-integration to place-cell activity in the hippocampus is still unclear and complicated by the fact that the two mechanisms usually overlap. To bias spatial mechanisms toward landmark or path-integration, we use a treadmill equipped with a long belt on which male mice run sequentially through a zone enriched and a zone impoverished in visual-tactile cues. We show that inactivation of the medial septum (MS), which is known to disrupt the periodic activity of grid cells, impairs mice ability to anticipate the delivery of a reward in the cue-impoverished zone and transiently alter the spatial configuration of place fields in the cue-impoverished zone selectively: following MS inactivation, place fields in the cue-impoverished zone progressively shift backward and stabilize near the cues, resulting in the contraction of the spatial representation around cues; following MS recovery, the initial spatial representation is progressively restored. Furthermore, we found that place fields in the cue-rich and cue-impoverished zones are preferentially generated by cells from the deep and superficial sublayers of CA1, respectively. These findings demonstrate with mechanistic insights the contribution of MS to the spread of spatial representations in cue-impoverished zones, and indicate a segregation of landmark-based and path-integration-assisted spatial mechanisms into deep and superficial CA1, respectively.SIGNIFICANCE STATEMENT Cells encoding a cue-impoverished zone and the vicinity of landmarks responded differentially to septal inactivation and resided in distinct sublayers of CA1. These findings provide new insights on place field mechanisms: septal activity is critical for maintaining the spread of place fields in cue-impoverished areas, but not for the generation of place fields; Following MS inactivation, trial-by-trial network modifications by activity-dependent mechanisms are responsible for the gradual collapse of spatial representations. Furthermore, the findings suggest parallel coding streams for landmark and self-motion information. Superficial CA1 cells are better suited for encoding global position via the assist of path-integration, whereas deep CA1 cells can support spatial memory processes on an object-specific basis.

Wave-Function Engineering in HgSe/HgTe Colloidal Heterostructures To Enhance Mid-infrared Photoconductive Properties.

The use of intraband transition is an interesting alternative path for the design of optically active complex colloidal materials in the mid-infrared range. However, so far, the performance obtained for photodetection based on intraband transition remains much smaller than the one relying on interband transition in narrow-band-gap materials operating at the same wavelength. New strategies have to be developed to make intraband materials more effective. Here, we propose growing a heterostructure of HgSe/HgTe as a means of achieving enhanced intraband-based photoconduction. We first tackle the synthetic challenge of growing a heterostructure on soft (Hg-based) material. The electronic spectrum of the grown heterostructure is then investigated using a combination of numerical simulation, infrared spectroscopy, transport measurement, and photoemission. We report a type-II band alignment with reduced doping compared with a core-only object and boosted hole conduction. Finally, we probe the photoconductive properties of the heterostructure while resonantly exciting the intraband transition by using a high-power-density quantum cascade laser. Compared to the previous generation of material based on core-only HgSe, the heterostructures have a lower dark current, stronger temperature dependence, faster photoresponse (with a time response below 50 µs), and detectivity increased by a factor of 30.

Topological organization of CA3-to-CA1 excitation.

The CA1-projecting axons of CA3 pyramidal cells, called Schaffer collaterals, constitute one of the major information flow routes in the hippocampal formation. Recent anatomical studies have revealed the non-random structural connectivity between CA3 and CA1, but little is known regarding the functional connectivity (i.e. how CA3 network activity is functionally transmitted downstream to the CA1 network). Using functional multi-neuron calcium imaging of rat hippocampal slices, we monitored the spatiotemporal patterns of spontaneous CA3 and CA1 burst activity under pharmacological GABAergic blockade. We found that spatially clustered CA3 activity patterns were transformed into layered CA1 activity sequences. Specifically, synchronized bursts initiated from multiple hot spots in CA3 ensembles, and CA1 neurons located deeper in the pyramidal cell layer were recruited during earlier phases of the burst events. The order of these sequential activations was maintained across the bursts, but the sequence velocity varied depending on the inter-burst intervals. Thus, CA3 axons innervate CA1 neurons in a highly topographical fashion.

Clear microstructure-performance relationships in Mn-containing perovskite and hexaaluminate compounds prepared by activated reactive synthesis.

Microstructural properties of mixed oxides play essential roles in their oxygen mobility and consequently in their catalytic performances. Two families of mixed oxides (perovskite and hexaaluminate) with different microstructural features, such as crystal size and specific surface area, were prepared using the activated reactive synthesis (ARS) method. It was shown that ARS is a flexible route to synthesize both mixed oxides with nano-scale crystal size and high specific surface area. Redox properties and oxygen mobility were found to be strongly affected by the material microstructure. Catalytic activities of hexaaluminate and perovskite materials for methane oxidation were discussed in the light of structural, redox and oxygen mobility properties.

Ultrasound-assisted removal of tetracycline from aqueous solution by mesoporous alumina.

This work describes the removal of tetracycline (TC) from aqueous solution using a mesoporous alumina (meso-Al2O3) as adsorbent in the presence of ultrasonic irradiation. Adsorption of TC was investigated under various operating conditions, including pH, adsorbent dosage, ultrasound power, and initial TC concentration. The results showed that the rate of TC sorption was enhanced with the assistance of ultrasound. The TC removal increased with the increase in sorbent dosage, pH and ultrasound power, but decreased with the increase in initial TC concentration. The adsorption isotherm data were fitted properly with the Freundlich model under ultrasonic irradiation, and the adsorption process followed a pseudo-second-order kinetic model.

Stochastic characterization of navigation strategies in an automated variant of the Barnes maze.

Animals can use a repertoire of strategies to navigate in an environment, and it remains an intriguing question how these strategies are selected based on the nature and familiarity of environments. To investigate this question, we developed a fully automated variant of the Barnes maze, characterized by 24 vestibules distributed along the periphery of a circular arena, and monitored the trajectories of mice over 15 days as they learned to navigate towards a goal vestibule from a random start vestibule. We show that the patterns of vestibule visits can be reproduced by the combination of three stochastic processes reminiscent of random, serial, and spatial strategies. The processes randomly selected vestibules based on either uniform (random) or biased (serial and spatial) probability distributions. They closely matched experimental data across a range of statistical distributions characterizing the length, distribution, step size, direction, and stereotypy of vestibule sequences, revealing a shift from random to spatial and serial strategies over time, with a strategy switch occurring approximately every six vestibule visits. Our study provides a novel apparatus and analysis toolset for tracking the repertoire of navigation strategies and demonstrates that a set of stochastic processes can largely account for exploration patterns in the Barnes maze.

Carbon-Supported Ru-Ni and Ru-W Catalysts for the Transformation of Hydroxyacetone and Saccharides into Glycol-Derived Primary Amines.

Nitrogen-containing molecules are used for the synthesis of polymers, surfactants, agrochemicals, and dyes. In the context of green chemistry, it is important to form such compounds from bioresource. Short-chain primary amines are of interest for the polymer industry, like 2-aminopropanol, 1-aminopropan-2-ol, and 1,2-diaminopropane. These amines can be formed through the amination of oxygenated substrates, preferably in aqueous phase. This is possible with heterogeneous catalysts, however, effective systems that allow reactions under mild conditions are lacking. We report an efficient catalyst Ru-Ni/AC for the reductive amination of hydroxyacetone into 2-aminopropanol. The catalyst has been reused during 3 cycles demonstrating a good stability. As a prospective study, extension to the reactivity of (poly)carbohydrates has been realized. Despite a lesser efficiency, 2-aminopropanol (9 % yield of amines) has been formed from fructose, the first example from a carbohydrate. This was possible using a 7.5 %Ru-36 %WxC/AC catalyst, composition allowing a one-pot retro-aldol cleavage into hydroxyacetone and reductive amination. The transformation of cellulose through sequential reactions with a combination of 30 %W2C/AC and 7.5 %Ru-36 %WxC/AC system gave 2 % of 2-aminopropanol, corresponding to the first example of the formation of this amine from cellulose with heterogeneous catalysts.

Chemical shaping of CPO-27-M (M = Co, Ni) through an in situ crystallization within chitosan hydrogels.

The preparation of MOF composites is considered as an effective method to address the challenges of shaping MOFs and to create porous solids with enhanced properties and broader applications. In this study, CPO-27-Co was crystallized via a simple strategy within porous chitosan beads. The resulting CS@CPO-27-Co composites were tested for CO2 sorption and they demonstrated promising performances by exceeding 3 mmol(CO2) g-1. The versatility of this strategy was further demonstrated by replacing cobalt(II) ions with nickel(II), also leading to the isostructural CPO-27 framework.

Borophene: a piezocatalyst for water remediation.

Borophene is an emerging two-dimensional material exhibiting exceptional piezocatalytic activity under the influence of ultrasonic vibrations, as exemplified herein by the decomposition of highly stable organic dyes in water. After 6 minutes of exposure, borophene sheets converted up to 92 percent of a mixture of dye molecules at room temperature.

SBA-15 supported Ni-Cu catalysts for hydrodeoxygenation of m-cresol to toluene.

Amidst concerns over fossil fuel dependency and environmental sustainability, the utilization of biomass-derived aromatic compounds emerges as a viable solution across diverse industries. In this scheme, the conversion of biomass involves pyrolysis, followed by a hydrodeoxygenation (HDO) step to reduce the oxygen content of pyrolysis oils and stabilize the end products including aromatics. In this study, we explored the properties of size controlled NiCu bimetallic catalysts supported on ordered mesoporous silica (SBA-15) for the catalytic gas-phase HDO of m-cresol, a lignin model compound. We compared their performances with monometallic Ni and Cu catalysts. The prepared catalysts contained varying Ni to Cu ratios and featured an average particle size of approximately 2 nm. The catalytic tests revealed that the introduction of Cu alongside Ni enhanced the selectivity for the direct deoxygenation (DDO) pathway, yielding toluene as the primary product. Optimal performance was observed with a catalyst composition comprising 5 wt.% Ni and 5 wr.% Cu, achieving 85 % selectivity to toluene. Further increasing the Cu content improved turnover frequency (TOF) values, but reduced DDO selectivity. These findings underscore the importance of catalyst design in facilitating biomass-derived compound transformations and offer insights into optimizing catalyst composition for more selective HDO reactions.

Ultrathin, large area ß-Ni(OH)2 crystalline nanosheet as bifunctional electrode material for charge storage and oxygen evolution reaction.

Bifunctional electrode materials are highly desirable for meeting increasing global energy demands and mitigating environmental impact. However, improving the atom-efficiency, scalability, and cost-effectiveness of storage systems, as well as optimizing conversion processes to enhance overall energy utilization and sustainability, remains a significant challenge for their application. Herein, we devised an optimized, facile, economic, and scalable synthesis of large area (cm2), ultrathin (∼2.9 ± 0.3 nm) electroactive nanosheet of ß-Ni(OH)2, which acted as bifunctional electrode material for charge storage and oxygen evolution reaction (OER). The ß-Ni(OH)2 nanosheet electrode shows the volumetric capacity of 2.82 Ah.cm-3(0.82 µAh.cm-2) at the current density of 0.2 mA.cm-2. The device shows a high capacity of 820 mAh.cm-3 with an ultrahigh volumetric energy density of 0.33 Wh.cm-3 at 275.86 W.cm-3 along with promising stability (30,000 cycles). Furthermore, the OER activity of ultrathin ß-Ni(OH)2 exhibits an overpotential (η10) of 308 mV and a Tafel value of 42 mV dec-1 suggesting fast reaction kinetics. The mechanistic studies are enlightened through density functional theory (DFT), which reveals that additional electronic states near the Fermi level enhance activity for both capacitance and OER.

Green synthesis of MOF-based textile composites for the degradation of a chemical warfare agent simulant.

A green synthesis of UiO-66-NH2 embedded in chitosan and deposited on textiles has been investigated for the degradation of chemical warfare agents. This method requires no heating or use of toxic solvents. The composite synthesized presents an interesting efficiency in detoxifying common simulants of chemical warfare agents, such as DMNP. In parallel, resistance and permeability tests were also realized in order to confirm the suitability of the composites for further applications.

Temporal delays among place cells determine the frequency of population theta oscillations in the hippocampus.

Driven either by external landmarks or by internal dynamics, hippocampal neurons form sequences of cell assemblies. The coordinated firing of these active cells is organized by the prominent "theta" oscillations in the local field potential (LFP): place cells discharge at progressively earlier theta phases as the rat crosses the respective place field ("phase precession"). The faster oscillation frequency of active neurons and the slower theta LFP, underlying phase precession, creates a paradox. How can faster oscillating neurons comprise a slower population oscillation, as reflected by the LFP? We built a mathematical model that allowed us to calculate the population activity analytically from experimentally derived parameters of the single neuron oscillation frequency, firing field size (duration), and the relationship between within-theta delays of place cell pairs and their distance representations ("compression"). The appropriate combination of these parameters generated a constant frequency population rhythm along the septo-temporal axis of the hippocampus, while allowing individual neurons to vary their oscillation frequency and field size. Our results suggest that the faster-than-theta oscillations of pyramidal cells are inherent and that phase precession is a result of the coordinated activity of temporally shifted cell assemblies, relative to the population activity, reflected by the LFP.