Weakening Mn-O Bond Strength in Mn-Based Perovskite Catalysts to Enhance Propane Catalytic Combustion.

Exploring highly efficient and robust non-noble metal catalysts for VOC abatement is crucial but challenging. Mn-based perovskites are a class of redox catalysts with good thermal stability, but their activity in the catalytic combustion of light alkanes is insufficient. In this work, we modulated the Mn-O bond strength in a Mn-based perovskite via defect engineering, over which the catalytic activity of propane combustion was significantly enhanced. It demonstrates that the oxygen vacancy concentration and the Mn-O bond strength can be efficiently modulated by finely tuning the Ni content in SmNixMn1-xO3 perovskite catalysts (SNxM1-x), which in turn can enhance the redox ability and generate more active oxygen species. The SN0.10M0.90 catalyst with the lowest Mn-O bond strength exhibits the lowest apparent activation energy, over which the propane conversion rate increases by 3.6 times compared to that on the SmMnO3 perovskite catalyst (SM). In addition, a SN0.10M0.90/cordierite monolithic catalyst can also exhibit a remarkable catalytic performance and deliver excellent long-term durability (1000 h), indicating broad prospects in industrial applications. Moreover, the promotional effect of Ni substitution was further unveiled by density functional theory (DFT) calculations. This work brings a favorable guidance for the exploration of highly efficient perovskite catalysts for light alkane elimination.

Constructing an oxygen vacancy- and hydroxyl-rich TiO2-supported Pd catalyst with improved Pd dispersion and catalytic stability.

Surface property modification of catalyst support is a straightforward approach to optimize the performance of supported noble metal catalysts. In particular, oxygen vacancies and hydroxyl groups play significant roles in promoting noble metal dispersion on catalysts as well as catalytic stability. In this study, we developed a nanoflower-like TiO2-supported Pd catalyst that has a higher concentration of oxygen vacancies and surface hydroxyl groups compared to that of commercial anatase and P25 support. Notably, due to the distinctive structure of the nanoflower-like TiO2, our catalyst exhibited improved dispersion and stabilization of Pd species and the formation of abundant reactive oxygen species, thereby facilitating the activation of CO and O2 molecules. As a result, the catalyst showed remarkable efficiency in catalyzing the low-temperature CO oxidation reaction with a complete CO conversion at 80 °C and stability for over 100 h.

Measuring the route topography impact on real driving emissions based on neural network models.

Route topography is an important test boundary of real driving emission (RDE) tests. However, the RDE test boundaries, such as atmospheric environment, driver behavior, route topography, and traffic congestion, are random, uncertain, and completely coupled. It is difficult to know to what extent route topography can determine on-road emissions, especially in a region with hilly topography. In this regard, the neural network predictor importance algorithms were proposed to measure the importance of the route topography test boundary. Based on tens of thousands of data window samples from the RDE tests in Chongqing, factor analysis was performed to reduce the data dimensionality and eliminate information overlap, and neural network models were established to predict pollutant emissions and calculate the relative importance of input variables. The results show that route topography is comparable to trip dynamics for on-road emissions but the importance of the route topography test boundary is not fully appreciated in the existing RDE regulation, making mountain cities suffer from severe vehicle emissions that are not effectively controlled.

Fabricating Uniform TiO2-CeO2 Solid Solution Supported Pd Catalysts by an In Situ Capture Strategy for Low-Temperature CO Oxidation.

Support properties regulation has been a feasible method for the improvement of noble metal catalytic performance. For Pd-based catalysts, TiO2-CeO2 material has been widely used as an important support. However, due to the considerable discrepancy in the solubility product constant between titanium and cerium hydroxides, it is still challenging to synthesize a uniform TiO2-CeO2 solid solution in the catalysts. Herein, an in situ capture strategy was constructed to fabricate a uniform TiO2-CeO2 solid solution as supports for an enhanced Pd-based catalyst. The obtained Pd/TiO2-CeO2-iC catalyst possessed enriched reactive oxygen species and optimized CO adsorption capability, manifesting a superior CO oxidation activity (T100 = 70 °C) and stability (over 170 h). We believe this work provides a viable strategy for precise characteristic modulation of composite oxide supports during the fabrication of advanced noble metal-based catalysts.

Modeling Interfacial Interaction between Gas Molecules and Semiconductor Metal Oxides: A New View Angle on Gas Sensing.

With the development of internet of things and artificial intelligence electronics, metal oxide semiconductor (MOS)-based sensing materials have attracted increasing attention from both fundamental research and practical applications. MOS materials possess intrinsic physicochemical properties, tunable compositions, and electronic structure, and are particularly suitable for integration and miniaturization in developing chemiresistive gas sensors. During sensing processes, the dynamic gas-solid interface interactions play crucial roles in improving sensors' performance, and most studies emphasize the gas-MOS chemical reactions. Herein, from a new view angle focusing more on physical gas-solid interactions during gas sensing, basic theory overview and latest progress for the dynamic process of gas molecules including adsorption, desorption, and diffusion, are systematically summarized and elucidated. The unique electronic sensing mechanisms are also discussed from various aspects including molecular interaction models, gas diffusion mechanism, and interfacial reaction behaviors, where structure-activity relationship and diffusion behavior are overviewed in detail. Especially, the surface adsorption-desorption dynamics are discussed and evaluated, and their potential effects on sensing performance are elucidated from the gas-solid interfacial regulation perspective. Finally, the prospect for further research directions in improving gas dynamic processes in MOS gas sensors is discussed, aiming to supplement the approaches for the development of high-performance MOS gas sensors.

Investigating the impact of route topography on real driving emission tests based on large data sample at data window level.

Route topography is an important boundary condition for the regulated real driving emission (RDE) test. However, accurately and comprehensively evaluating the influence of route topography on the RDE test is difficult, because the effect cannot be easily separated from those of other test boundaries. We selected two light-duty gasoline vehicles to complete two rounds of RDE tests on four different test routes, and conducted the correlation analysis between pollutant emissions and route topography quantified by the cumulative positive altitude gains of the test routes based on the moving averaging window method. Since the small number of sample data at the total trip and road section level were not sufficiently representative of the population, we proposed to use the pollutant emission data of the data windows to analyze the complex coupling effect of the cumulative positive altitude gains and trip dynamic parameters of v·apos[95] on the RDE tests. At data window level, thousands of data windows were treated as the road section subsets of the RDE test, and the sample space of road section emission data was expanded by several orders of magnitude. With the help of the large data sample space, the influence mechanism of the random test boundaries on the RDE tests was demonstrated.

1D Electromagnetic-Gradient Hierarchical Carbon Microtube via Coaxial Electrospinning Design for Enhanced Microwave Absorption.

1D structures have been gaining traction in the microwave absorption (MA) field benefiting from their electromagnetic (EM) anisotropy. However, there remain considerable challenges in adjusting EM properties by structural design. Herein, using the coaxial electrospinning and solvothermal method, the EM gradient has been achieved in TiO2@Co/C@Co/Ni multilayered microtubes. From the outer layer to the inner one, the impedance matching is gradually worsened, while the EM loss capacity is continuously enhanced, facilitating both the incidence and attenuation of microwave. Besides, 1D structural anisotropy simultaneously realizes multilevel magnetic interaction and 3D conductive double network. Therefore, the 1D EM-gradient hierarchical TiO2@Co/C@Co/Ni carbon microtube composite exhibits excellent MA performance. Its maximum reflection loss (RL) value reaches -53.99 dB at 2.0 mm and effective absorption bandwidth (EAB, RL ≤ -10 dB) is as wide as 6.0 GHz, covering most of the Ku band with only 15% filling. The unique design of 1D EM-gradient hierarchical composites promises great potential in the construction of advanced MA materials.

An Imine-Linked Metal-Organic Framework as a Reactive Oxygen Species Generator.

A new metal-organic framework (MOF) with both coordination linkages and covalent linkages is prepared by coordinating CuI with pyrazolate for an aldehyde-functionalized trinuclear complex, and subsequent imine condensation with p-phenylenediamine, a reaction typical for covalent organic framework (COF) synthesis. This MOF×COF collaboration yields FDM-71 with honeycomb layers stacked in eclipsed fashion. After dissociating the CuI -pyrazolate coordination in FDM-71, the obtained organic components carry the information of structural defects, and thus vacancy identity (aldehyde-based unit vacancy and amine-based unit vacancy) and concentration are definitely resolved. Further to the redox catalytic activity inherited from the complex, FDM-71 features effective photosensitizing activity. The two functions integrated in one well-defined structure is demonstrated by its high efficiency in decomposing H2 O2 and consequent excitation of O2 to reactive oxygen species.

Evolution of a Metal-Organic Framework into a Brønsted Acid Catalyst for Glycerol Dehydration to Acrolein.

Metal-organic frameworks (MOFs) as solid acid catalysts provide active sites with definite structures. Here, Zr6 -based MOF-808 and its derivatives were studied as catalysts for glycerol dehydration, the products of which (acrolein vs. acetol) are very sensitive to the nature of the catalytic acid sites. Evolving MOF-808 into MOF-808-S with a 120 % increase in the number of Brønsted OH- /H2 O coordinated to ZrIV and a vanished Lewis acidity by steam treatment, the post-synthetically modified catalyst presented 100 % conversion of glycerol, 91 % selectivity to acrolein, and 0 % selectivity to acetol within the active window. Real-time analysis of the product composition indicated the in situ MOF structural evolution. Overall, the specific MOF-substrate interaction characterized by the probe reaction provides more understandings on the structural evolution of the MOFs and their impact on the performance as solid acid catalysts.

Fabrication of Functionalized Porous Silica Nanocapsules with a Hollow Structure for High Performance of Toluene Adsorption-Desorption.

Functionalized mesoporous silicas are an emerging kind of adsorbents for the removal of volatile organic compounds (VOCs). Breaking the limitations of traditional mesoporous silica, in this study, porous silica nanocapsules (PSNs) functionalized with phenyl and n-octyl groups (named as p-PSN and n-PSN, respectively) were developed for the first time. Under dry conditions, the PSNs exhibited highest dynamic adsorption capacity and desorption efficiency among the ever-reported typical adsorbents (i.e., SBA-15, KIT-6, silicalite-1, and activated carbon). Under wet conditions, the functionalized PSNs made up the defects of pure PSNs, displaying excellent hydrophobicity. The Q WET for n-PSN and p-PSN increased by 44 and 76%, respectively, as compared with that of pure PSNs in 50% relative humidity. The Henry constant of static adsorption demonstrated that p-PSN had a better capture ability for toluene, which was owing to the π-interaction between the phenyl groups and the toluene molecules. In addition, p-PSN showed considerable stability after six consecutive dynamic adsorption-desorption cycles in 50% relative humidity.

Facile Synthesis of Uniform Metal Carbide Nanoparticles from Metal-Organic Frameworks by Laser Metallurgy.

We report the fast and efficient conversion of metal-organic frameworks (MOFs) to phase pure transition-metal carbide (TMC) nanoparticles with uniform size using laser as the energy source, consuming only 6 W power. Nanoparticles of HfC, ZrC, TiC, V8C7, α-MoC, Cr3C2, and FeCx with homogeneous sizes (varied between 6 and 20 nm) were successfully produced, among which HfC and ZrC nanoparticles were obtained, for the first time, with sizes less than 10 nm and in the pure phase. This method was operated directly in air, in stark contrast to traditional furnace heating and laser spray methods, where a protective atmosphere is required. The use of MOFs allowed us to precisely tune the composition of TMC nanoparticles by dialing in the right type and desirable amounts of organic linkers. FeCx nanoparticles doped with various percentages of nitrogen atoms were synthesized for the Fischer-Tropsch reaction without any pretreatment or activation. Extremely high iron time of yield (FTY) values were observed, 415 and 550 µmol gFe-1 s-1 (with addition of K), in a 40 h test without any decay in performance. A high olefin to paraffin ratio was achieved for C2 to C11 products, where the ratio for C3 was higher than 10.

Porous Graphene-Confined Fe-K as Highly Efficient Catalyst for CO2 Direct Hydrogenation to Light Olefins.

We devised iron-based catalysts with honeycomb-structured graphene (HSG) as the support and potassium as the promoter for CO2 direct hydrogenation to light olefins (CO2-FTO). Over the optimal FeK1.5/HSG catalyst, the iron time yield of light olefins amounted to 73 µmolCO2 gFe-1 s-1 with high selectivity of 59%. No obvious deactivation occurred within 120 h on stream. The excellent catalytic performance is attributed to the confinement effect of the porous HSG on the sintering of the active sites and the promotion effect of potassium on the activation of inert CO2 and the formation of iron carbide active for CO2-FTO.

Facile Synthesis of a Novel Hierarchical ZSM-5 Zeolite: A Stable Acid Catalyst for Dehydrating Glycerol to Acrolein.

Catalytic biomass conversion is often hindered by coking. Carbon compounds cover active surface and plug pores, causing catalyst deactivation. Material design at the nanoscale allows tailoring of the catalytic activity and stability. Here, we report a simple synthesis of nanosized ZSM-5 materials by using a silicalite-1 seeding suspension. ZSM-5 crystals were grown from a deionized silica source in the presence of ammonia. By using silicalite-1 seeds, crystalline ZSM-5 is synthesized without any structure-directing agent. This method allows parallel preparation of a range of ZSM-5 samples, eliminating time-consuming ion-exchange steps. Mesoporosity is introduced by formation of intercrystallite voids, owing to nanocrystal agglomeration. The effects of crystal sizes and morphologies are then evaluated in the catalytic dehydration of glycerol to acrolein, with results compared against commercial ZSM-5. The most active nanosized ZSM-5 catalysts were five times more stable compared with commercial ZSM-5, giving quantitative conversion and twice the acrolein yield compared with the commercial catalyst. The influence of the catalyst structure on the chemical diffusion and the resistance to coking are discussed.

Plasma-Assisted Synthesis of Monodispersed and Robust Ruthenium Ultrafine Nanocatalysts for Organosilane Oxidation and Oxygen Evolution Reactions.

We report a facile and general approach for preparing ultrafine ruthenium nanocatalysts by using a plasma-assisted synthesis at <100 °C. The resulting Ru nanoparticles are monodispersed (typical size 2 nm) and remain that way upon loading onto carbon and TiO2 supports. This gives robust catalysts with excellent activities in both organosilane oxidation and the oxygen evolution reaction.

Simultaneous Ni Doping at Atom Scale in Ceria and Assembling into Well-Defined Lotuslike Structure for Enhanced Catalytic Performance.

Oxide materials with redox capability have attracted worldwide attentions in many applications. Introducing defects into crystal lattice is an effective method to modify and optimize redox capability of oxides as well as their catalytic performance. However, the relationship between intrinsic characteristics of defects and properties of oxides has been rarely reported. Herein, we report a facile strategy to introduce defects by doping a small amount of Ni atoms (∼1.8 at. %) into ceria lattice at atomic level through the effect of microstructure of crystal on the redox property of ceria. Amazingly, a small amount of single Ni atom-doped ceria has formed a homogeneous solid solution with uniform lotuslike morphology. It performs an outstanding catalytic performance of a reduced T50 of CO oxidation at 230 °C, which is 135 °C lower than that of pure CeO2 (365 °C). This is largely attributed to defects such as lattice distortion, crystal defects and elastic strain induced by Ni dopants. The DFT calculation has revealed that the electron density distribution of oxygen ions near Ni dopant, the reduced formation energy of oxygen vacancy originated from local chemical effect caused by local distortion after Ni doping. These differences have a great effect on increasing the concentration of oxygen vacancies and enhancing the migration of lattice oxygen from bulk to a surface which is closely related to optimized redox properties. As a result, oxygen storage capacity and the associated catalytic reactivity has been largely increased. We have clearly demonstrated the change of crystal lattice and the charge distribution effectively modify its chemical and physical properties at the atomic scale.

Generation of photocurrent by visible-light irradiation of conjugated dawson polyoxophosphovanadotungstate-porphyrin copolymers.

Four hybrid polyoxometalate-porphyrin copolymer films were obtained by the electrooxidation of zinc octaethylporphyrin in the presence of four different Dawson-type polyoxometalates bearing two pyridyl groups (POM(py)2) with various spacers. The POM monomers were designed around 1,3,5-trisubstituted benzene rings. Two of the substituents of the benzene ring are linked to the pyridyl groups, and the third is connected to the POM subunit. The four monomers vary in the relative positions of the nitrogen atoms of the pyridine rings or in the distance from the carbonyl group. The monomers were fully characterized by (1)H, (31)P, and (13)C NMR spectroscopy, electrospray mass spectrometry, IR and UV/Vis spectroscopy, and electrochemistry. The copolymers were characterized by UV/Vis spectroscopy, X-ray photoelectron spectroscopy, electrochemistry, and AFM. Their photovoltaic performance under visible light irradiation was investigated by photocurrent transient measurements under visible illumination.

Bridging silicon nanoparticles and thermoelectrics: phenylacetylene functionalization.

Silicon is a promising alternative to current thermoelectric materials (Bi(2)Te(3)). Silicon nanoparticle based materials show especially low thermal conductivities due to their high number of interfaces, which increases the observed phonon scattering. The major obstacle with these materials is maintaining high electrical conductivity. Surface functionalization with phenylacetylene shows an electrical conductivity of 18.1 S m(-1) and Seebeck coefficient of 3228.8 µV K(-1) as well as maintaining a thermal conductivity of 0.1 W K(-1) m(-1). This gives a ZT of 0.6 at 300 K which is significant for a bulk silicon based material and is similar to that of other thermoelectric materials such as Mg(2)Si, PbTe and SiGe alloys.

Nafion-resin-modified mesocellular silica foam catalyst for 5-hydroxymethylfurfural production from D-fructose.

Catalytic dehydration of D-fructose to 5-hydroxymethylfurfural (HMF) was investigated over a series of Nafion-modified mesocellular silica foam (MCF) materials. By using an impregnation method, Nafion resin was highly dispersed in the ultra-large pores of the MCFs. Highly efficient and selective dehydration of D-fructose to HMF was achieved in dimethyl sulfoxide solvent; an 89.3% HMF yield with 95.0% selectivity was obtained in the presence of the Nafion(15)/MCF catalyst. The effects of reaction temperature, reaction time, and solvent on the dehydration of D-fructose were systematically investigated. The catalyst could be regenerated through an ion-exchange method and a high yield was retained after being used five times. As a heterogeneous catalytic process, a possible reaction mechanism for the dehydration of D-fructose over Nafion-modified MCF catalysts was proposed.

Synthesis and characterization of conjugated Dawson-type polyoxometalate-porphyrin copolymers.

Hybrid polyoxometalate-porphyrin copolymeric films were obtained by the electro-oxidation of zinc octaethylporphyrin (ZnOEP) in the presence of a Dawson type polyoxophosphovanadotungstate bearing two pyridyl groups (POM(py)2). The synthesis of a series of POM(py)2 consisting of [P2W15V3O62](9-) functionalized with diol-amide or triol moieties, as well as the characterization of the copolymers are presented.

Synthesis of disulfides and diselenides by copper-catalyzed coupling reactions in water.

A simple and efficient protocol for copper-catalyzed coupling reactions between aryl halides and elemental sulfur or selenium has been developed. A variety of disulfides and diselenides can be obtained in moderate to excellent yields up to 96%.