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The improved performance of the multi-component Cu–Ce–Mn/TNA catalysts over the mono-metallic catalysts demonstrated the synergistic promotion of multi-transition-metal-doped nanoarray catalysts for efficient NO abatement.

Constructing robust catalysts by growing nanostructure arrays directly onto honeycomb monoliths is a promising technology for fabricating highly active reactors with low materials usage and cost-effectiveness. In this study, catalytically active NiO nanosheet arrays were uniformly grown onto the channel surfaces of cordierite honeycombs to form monolithic catalysts with ultra-low loading. Ce doping was found to significantly enhance the catalytic propane oxidation performance of pristine NiO nanosheet arrays. With a Ce doping of ∼4 wt.% in NiO, a conversion of 90 % propane oxidation into CO2 was achieved at 440 °C, a ∼40 °C decrease compared to the pristine NiO under a space velocity of 24,000 h−1. With the promoting effect of Ce, the Ce-doped NiO nanosheet arrays exhibited a much better thermal stability, with only 1.1 % loss of conversion after a 48 h operation at 425 °C, in comparison with a 21.5 % loss over the pristine NiO catalyst.

One-dimensional titanium dioxide (TiO2) nanostructure arrays (nanoarrays) are important metal oxide nanomaterials that can be synthesized via facile solvothermal methods. The properties of the organic solvents can impose significant effects on the microstructures and properties of the final products. However, the discussions were limited to the homogeneously nucleated TiO2 nanomaterials in free-standing powder form, while the solvent effects are less understood during the heterogeneous growth of TiO2 nanoarrays on a substrate surface. In this work, six organic compounds, namely 2-butanone, n-decane, n-hexane, toluene, ethylene glycol and ethanol, were selected as the solvents for the solvothermal synthesis of TiO2 nanoarrays on the cordierite monolithic substrates. Special attentions are paid to the morphology, crystallinity, specific surface area, and porosity of the samples. The heterogeneous growth of TiO2 nanoarrays on substrate surfaces is found to favor the solvents with moderate dielectric constants, which can be partially dissolved in the aqueous solution and modulate the reaction rate during the solvothermal synthesis. Organic solvents with low dielectric constants may result in a complete separation between the precursors and aqueous solution, and therefore slow down the overall reaction, causing the insufficient growth of the nanoarrays. The TiO2 nanoarrays are obtained with optimum morphology from the combination of 2-butanone and titanium (IV) butoxide as solvent and precusor, respectively, with a high specific surface area up to 56 m2/g including cordierite substrate given a micron thickness. When loaded with Pt catalyst, the TiO2 nanoarray-based monolithic catalysts show excellent low-temperature catalytic activity and hydrothermal stability for the CO and hydrocarbon oxidation under the simulated exhausted conditions. This work shall shed light on a better understanding of the growth mechanism and rational design of TiO2 nanoarrays for high-performance catalytic converters.

Nanoarray-based monolithic catalysts have been developed for various applications, including CO oxidation, hydrocarbon combustion, lean NOx trapping, and low-pressure CO2 hydrogenation. In this work, SO2 adsorption properties have been explored and evaluated on the cordierite honeycomb monoliths grown with zinc oxide nanoarray (ZnO), zinc oxide nanoarray washcoated by BaCO3 nanoparticles (ZnO/BaCO3), and manganese oxide nanowire array with cryptomelane structure (MnOx) at a temperature range from 50 to 425 °C. All samples show temperature-dependent SO2 adsorption behaviors. The adsorption results reveal the performance order: MnOx > ZnO/BaCO3 > ZnO, with ~ 90% SO2 adsorbed in MnOx at 425 °C. Washcoated BaCO3 contributes to the improvement of SO2 adsorption in ZnO nanoarray, and the best performance displayed in MnOx may be attributed to their high specific surface area. After regeneration, nanoarrays all exhibit good thermal stability during test-regeneration cycles. No additional phase is formed in regenerated ZnO nanoarrays (ZnO-R), while BaCO3 is converted to BaSO4 in the regenerated ZnO/BaCO3 nanoarrays (ZnO/BaCO3-R), and the sulfur species (possibly MnSO4) and Mn2O3 are found in regenerated MnOx nanoarrays (MnOx-R). It is noted that a small amount of sulfur species (possibly MnSO4) may promote the SO2 adsorption of MnOx-R at a lower temperature, while the formed Mn2O3 contributes to the deactivation of MnOx-R.

Supported metal single atom catalysts (SACs) present an emerging class of low-temperature catalysts with high reactivity and selectivity, which, however, face challenges on both durability and practicality. Herein, we report a single-atom Pt catalyst that is strongly anchored on a robust nanowire forest of mesoporous rutile titania grown on the channeled walls of full-size cordierite honeycombs. This Pt SAC exhibits remarkable activity for oxidation of CO and hydrocarbons with 90% conversion at temperatures as low as ~160 oC under simulated diesel exhaust conditions while using 5 times less Pt-group metals than a commercial oxidation catalyst. Such an excellent low-temperature performance is sustained over hydrothermal aging and sulfation as a result of highly dispersed and isolated active single Pt ions bonded at the Ti vacancy sites with 5 or 6 oxygen ions on titania nanowire surfaces., Supported metal single-atom catalysts face challenges on both durability and practicality. Here, the authors demonstrate that a sustained 90% diesel oxidation conversion at ~160 oC is achieved by single-atom Pt on TiO2 nanowire-array integrated catalytic converter.

Stabilized Cu+ species have been widely considered as catalytic active sites in composite copper catalysts for catalytic reactions with industrial importance. However, few examples comprehensively ...

Amongst various gaseous pollutants, NO2 is one of the major exhausts originating from fossil fuel and gas combustions in vehicle engines and power plants at high temperature. Under such a scenario, in situ and real-time gas detection and monitoring solutions are largely limited, which hinders the energy-efficient and resource-saving operations of these advanced energy systems. In this report, a new type of perovskite-sensitized β-Ga2O3 nanorod-array has been successfully fabricated to detect NOx at high temperature selectively and sensitively. The demonstrated gas sensors are highly sensitive to NO2 at 800 °C, with excellent reversible and reproducible response characteristics. Through the surface decoration of perovskite-type La0.8Sr0.2CoO3 (LSCO) nanoparticles, the sensitivity of β-Ga2O3 nanorod array gas sensors is enhanced by nearly an order of magnitude, along with much faster response dynamics. A remarkable selectivity toward oxidative gases was also demonstrated with the robust differentiation of NO2.

Quantitative measurement of the nitrogen oxide mixture (NO

Photoabsorption, charge separation efficiency and surface reactive catalytic sites are three critical factors in semiconductor photocatalytic process, which determine the photocatalytic activity. For bulk g-C3N4 derived from direct pyrolysis of C/N rich precursors, reactive sites distributed on the lateral edges are very scarce. In this work, we report the template-free preparation of three novel structured g-C3N4, namely, porous tubular (PT) g-C3N4, porous tubular yolk-shell (PTYS) g-C3N4, and porous split yolk-shell (PSYS) g-C3N4, by an unprecedented precursor microstructure regulation of melamine crystals in a gas-pressure mediated re-crystallization process. Enhanced photoabsorption, increased surface area, largely improved separation and migration efficiencies of photoinduced charge carriers are simultaneously realized in these g-C3N4 structures. Noticeably, selective photo-deposition test uncovers that the porous outer-walls and inner-rods of PTYS g-C3N4 are enriched by abundant reductive reactive sites, which consumedly boost the photo-reduction activity. Collectively promoted by these advantages, PTYS g-C3N4 shows not only an efficient H2 production activity with a high apparent quantum efficiency (AQE) of 11.8% at λ = 420 ± 15 nm, but also a superior CO2 reduction for CO production than bulk g-C3N4 by a factor 5.6, which is verified by the 13C isotopic labeling. This work develops precursor microstructure engineering as a promising strategy for rational design of unordinary g-C3N4 structure for renewable energy production.

Diesel soot combustion suffers from ignition temperatures (T10) as high as > 450 °C in the absence of catalysts, which are unavailable in diesel exhaust during normal driving cycles (normally 200–400 °C). A catalytic diesel particulate filter (CDPF) could decrease T10 greatly, but it is often inadequate due to the poor contact associated with the solid (catalyst)-solid (soot) interactions. Herein, a highly significant T10, as low as ˜200 °C, was achieved on noble metal-free ultrathin MnO2-x nanosheet array fabricated by in situ etching of a La layer from LaMnO3 under loose contact conditions in a NO-containing atmosphere. A number of advantages were found with such a system including the improved reducibility. Then, the nanosheet array ensures high dispersion of soot on the catalyst. Finally, high NO-to-NO2 oxidation activity further facilitates contact between catalyst and soot via NO2, a stronger oxidant than O2.

Supported metal catalysts are one of the major classes of heterogeneous catalysts, which demand good stability in both the supports and catalysts. Herein, layered protonated titanate-derived TiO2 (LPT-TiO2) nanowire arrays were synthesized to support platinum catalysts using different loading processes. The Pt ion-exchange loading on pristine LPTs followed by thermal annealing resulted in superior Pt catalysts supported on the LPT-TiO2 nanoarrays with excellent hydrothermal stability and catalytic performance toward CO and NO oxidations as compared to the Pt catalysts through wet-impregnation on the anatase TiO2 (ANT-TiO2) nanoarrays resulted from thermal annealing of LPT nanoarrays. Both loading processes resulted in highly dispersed Pt nanoparticles (NPs) with average sizes smaller than 1 nm at their pristine states. However, after hydrothermal aging at 800 °C for 50 h, highly dispersed Pt NPs were only retained on the ion-exchanged LPT-TiO2 nanoarrays with the support structure consisting of a mixture of 74% anatase and 26% rutile TiO2. For the wet-impregnation loading directly on anatase TiO2 nanoarrays derived from LPT, the Pt catalysts experienced severe agglomeration after hydrothermal aging, with the nanoarray supports consisting of 86% anatase and 14% rutile TiO2. Spectroscopy analysis suggested that Pt2+ cations intercalated into the interlayers of the titanate frameworks through ion-exchange impregnation procedure, which altered the chemical and electronic structures of the catalysts, resulting in the shifts of the electronic binding energy, Raman bands, and optical energy bandgap. The ion-exchangeable nature of LPT nanoarrays clearly provides a structural modification in Pt-doped LPT that has resulted in a strong interaction between the Pt catalysts and LPT-TiO2 nanoarray supports, leading to the enhanced hydrothermal stability of the catalysts. Considering the wide applications of the LPT and TiO2 nanomaterials as supports for catalysts, this finding provides a new pathway to design highly stable supported metal catalysts for different reactions.

A new, surfactant-free hydrothermal method has been developed for the growth of CeO2-based nanoflake arrays onto three-dimensional-channeled cordierite honeycomb substrates. Herein, a leaching-crystallization mechanism was proposed where the hydrothermal reaction, only involving cerium nitrate and water, leached the cordierite surface slightly and induced the formation of CeO2 nanoparticles subsequently. Further continued reaction reincorporated Al and Si atoms leached from cordierite into CeO2, finally recrystallizing Ce-Al-Si composite nanoflake structures. By using atomic layer deposition process, well-dispersed, size-controlled Pt nanoparticles were uniformly decorated on the CeO2-based nanoflakes to form the Pt/ CeO2 nano-array-based monolithic catalyst. Despite 5-50 times reduction in the active material usage compared with the traditional wash-coated catalyst, the Pt/CeO2 nano-array monolithic catalyst exhibited good catalytic oxidation activities over various individual gases, such as propylene, propane, CO, and NO oxidation, with 90% conversion efficiencies at temperatures below 200 °C. Under the simulated exhaust condition of low-temperature diesel combustion (LTC-D) developed by US DRIVE, the monolithic catalyst with low Pt loading (˜1 g/l) exhibits 90% conversion of catalytic oxidation over CO and hydrocarbonsat temperatures as low as ˜180 °C, much superior to the performance of traditional washcoated catalysts.

High performance of an ultra-low Pt loading diesel oxidation catalyst can be achieved by using a combination of novel nano-array structured support, precise control of ultrafine active Pt particles, and an addition of H2 as a promoter into the exhausts. Highly stable mesoporous rutile TiO2 nano-array was uniformly grown on three-dimensional (3-D) cordierite honeycomb monoliths using a solvothermal synthesis. Atomic layer deposition was employed for precise dispersion of ultrafine Pt particles (0.95 ± 0.24 nm) on TiO2 nano-array with a Pt loading of 1.1 g/ft3. Despite low Pt loading, the Pt/TiO2 nano-array catalyst shows impressive low-temperature oxidation reactivity, with the conversion of CO and total hydrocarbon (THC) reaching 50% at 224 and 285 °C, respectively, in the clean diesel combustion (CDC) simulated exhaust conditions. The excellent activity is attributed to the unique nano-array structure that promotes gas-solid interaction and ultra-small Pt particle dispersion that increase surface Pt atoms. We also demonstrate that addition of more H2 into the exhaust can lower light-off temperature for CO and THC by up to ∼60 °C and ∼30 °C, respectively.

Channel surfaces of 3-D cordierite honeycomb were readily etched with basic solution and became rougher with formation of a uniform layer of silicate nanosheet array structures. The reaction between KMnO4 and Co(NO3)2 was applied for integrating Mn-Co-O nanosheet array on both blank and modified cordierite honeycombs. The etched cordierite channels can induce the Mn-Co-O arrays with larger unit size, higher density and thickness. Compared to the blank cordierite, the Mn-Co-O array on etched cordierite has much better catalytic performance in oxidation of hydrocarbons, which can be due to its varied features such as more abundant porosity, higher surface area, more Mn4+, Co3+ and adsorbed oxygen species. This study provides an efficient way for tuning the nanostructures of Mn-Co composite oxide nano-array based monolith, further boosting their catalytic activities in combustion of hydrocarbons.

The catalytic total oxidation of short-chain alkanes released from automobile exhausts is still a big challenge in volatile organic compound (VOC) elimination. The significant degradation of catalytic activity after hydrothermal aging is a widely existing issue. Herein, we report a facile one-pot hydrothermal method to successfully grow TiO2–Al2O3 binary nanoarrays on the 3D channel surfaces of ceramic honeycombs. Such a binary nanoarray was heterogeneously integrated on the cordierite honeycomb channel surface with closely separated nanowire arrays of anatase-TiO2 and mesoporous γ-Al2O3, which exhibited excellent robustness under mechanical vibration and thermal and hydrothermal aging. Moreover, propane conversion with the Pt/TiO2–Al2O3 binary nanoarray catalyst rapidly reached 80% at a temperature as low as 224 °C, suggesting that the binary nanoarray catalyst is a promising candidate for practical applications.

Heterojunctions are an important strategy for designing high performance electrical sensor materials and related devices. Herein, a new type of metal-semiconductor hybrid nanoparticle has been successfully used to remarkably sensitize the surface of ZnO nanowires for detecting NO

In this study, a new type of lean NOx traps (LNT) based on Pt:La0.8Sr0.2MnO3 (LSMO) nanoparticles decorated on ZnO nanorod array integrated monoliths have been successfully designed and demonstrated. Compared to the commercial catalyst, the nanorod array based catalyst demonstrates competitive NO oxidation activity, and exceptional hydrothermal stability and recoverability after sulfur poisoning. With uniform distribution of perovskite and Pt nanoparticles, the ZnO nanorod array retains its structure after long-time exposure to the reducing gaseous atmosphere. The H2 treatment induces the surface Mn4+ reduction to Mn3+ and subsequently to Mn2+, affecting oxygen mobility, and decreasing the amount of surface lattice oxygen on the LSMO perovskite, thus leading to the catalyst performance decay according to a Mars-Van Krevelen reaction mechanism. Such surface state change was found to be reversible, with the catalytic performance fully recovered after O2 re-treatment, making it suitable for NOx storage and reduction (NSR). The complete lean NOx traps are formulated with rationally-designed sequential BaCO3 and Pt loading, improving NOx storage capacity. The ZnO nanorod array supported LNT shows good water compatibility under simulated exhaust. The nanorod array catalysts may be potentially suitable for vehicular NOx emission control.

Rational modification of interfacial structure and chemistry can help effectively tailor the reactivity and stability of heterogeneous catalysts regardless of their elemental or compound natures. Herein, a diluted acidic treatment was designed and utilized to modify the surface structure and chemistry of spinel Co3O4 nanoparticles. Such a chemical leaching strategy has significantly promoted the propane oxidation activity of the PGM-free Co3O4 nanocrystal aggregates. With a much higher activity than the commercial Al2O3 supported Pt and Pd catalysts, these leached nanoparticle aggregates exhibited much more abundant defects, surface Co2+ and chemisorbed oxygen species. Such surface-modified Co3O4 nanocatalysts have displayed excellent and stable propane oxidation efficiency independent of both O2 and C3H8 concentrations, where the activities of both commercial Pt (or Pd)/Al2O3 and self-made Pt (or Pd)/CeO2 catalysts were greatly affected by different O2 and C3H8 concentrations. Meanwhile, the Co3O4 nanocrystal aggregates catalyst exhibited good performance in presence of water or sulfur dioxide. This facile chemical leaching based technique provides a potential means to make highly active and stable oxide catalysts.

Copper manganese oxide (CuMn2O4) was introduced into the nanoarray-based monolithic catalysts system for advanced exhaust after-treatment. Through scalable and cost-effective hydrothermal reactions, nanosheet layers of copper manganese oxide were uniformly coated onto the manganese oxide nanoarrays (HM-PCR), which were grown on the cordierite honeycomb monoliths. The core nanoarray support, HM-PCR, a well-defined array architecture for active material deposition, contributed to an increase of open surface area and thus enhanced catalytic oxidation performance. The CuMn2O4 coated nanoarray-based catalyst, NA-CuMn2O4, shows efficient 90% propane (C3H8) conversion at around 400 °C, which is 50 °C and 75 °C lower than CuMn2O4 wash-coated catalyst (WC-CuMn2O4) and Pd loaded catalyst (WC-Pd), respectively. Compared to monolithic catalysts with a traditional alumina support, the benefit of nanoarray morphology was demonstrated by correlating the variation of surface area to the reactivity. The incorporation of cobalt ions was found to increase the specific surface area and thus enhance C3H8 conversion of CuMn2O4. The CuMn2O4/MnO2 nanoarray-based monoliths are promising types of emission control devices.

Stranded Natural Gas (SNG) flaring has increased over the last decade resulting in additional Green House Gas (GHG) emissions and underutilization of our finite fossil fuel resources. However, utilization of SNG is difficult due to its low volume, inconsistent composition, and intermittent flow. In this paper, intensified Chemical looping for Ammonia Synthesis (CLAS) is explored as a process suitable for remote deployment at SNG sites. CLAS mediate ammonia synthesis by using compounds that carry nitrogen and hydrogen in stepwise reactions, allowing ammonia synthesis under milder conditions and smaller, more flexible processes. The challenge in CLAS is to find a feasible combination of materials and process conditions that yield ammonia at economically acceptable rates. We propose a framework that systematically evaluates CLAS to determine their suitability for SNG deployment. CLAS reaction schemes are reviewed and organized based on the mediating compounds used to synthesize ammonia. Different compounds are evaluated for each CLAS in search of a thermodynamically spontaneous pair. Spontaneous CLAS flowsheets are, then, optimized to maximize ammonia output at equilibrium. The results are ranked against performance metrics of energy intensity, efficiency, and cost. Chemical loops with Ca3N2/CaH2, SrH2/Sr3N2, MnO2/Mn5N2 and MoO2/Mo2N are found to have favorable performance, along with literature-reported evidence and are recommended for further evaluation toward a distributed ammonia synthesis solution.

The redox reaction between KMnO4 and Co(NO3)2 was designed and readily utilized for the scalable integration of spinel MnxCo3−xO4 nanosheet arrays in three-dimensional ceramic honeycombs by controlling the reaction temperature. The Co2+ can reduce MnO4− to form Mn–Co spinel oxide nanosheet arrays uniformly on the channel surface of cordierite honeycomb. The novel platinum group metal free oxide nanosheet array integrated ceramic honeycomb monolith shows good low-temperature catalytic activity for propane oxidation, with the 50 % conversion temperature achieved at 310 °C, which is a much lower temperature than that over the wash-coated commercial Pt/Al2O3. These integrated Mn–Co composite oxide nanoarrays may hold great promise for the construction of advanced monolithic catalyst for high-performance and low-cost emission control.

Scalable and cost-effective synthesis and assembly of technologically important nanostructures in three-dimensional (3D) substrates hold keys to bridge the demonstrated nanotechnologies in academia with industrially relevant scalable manufacturing. In this work, using ZnO nanorod arrays as an example, a hydrothermal-based continuous flow synthesis (CFS) method is successfully used to integrate the nano-arrays in multi-channeled monolithic cordierite. Compared to the batch process, CFS enhances the average growth rate of nano-arrays by 125%, with the average length increasing from 2 μm to 4.5 μm within the same growth time of 4 hours. The precursor utilization efficiency of CFS is enhanced by 9 times compared to that of batch process by preserving the majority of precursors in recyclable solution. Computational fluid dynamic simulation suggests a steady-state solution flow and mass transport inside the channels of honeycomb substrates, giving rise to steady and consecutive growth of ZnO nano-arrays with an average length of 10 μm in 12 h. The monolithic ZnO nano-array-integrated cordierite obtained through CFS shows enhanced low-temperature (200 °C) desulfurization capacity and recyclability in comparison to ZnO powder wash-coated cordierite. This can be attributed to exposed ZnO {100} planes, better dispersion and stronger interactions between sorbent and reactant in the ZnO nanorod arrays, as well as the sintering-resistance of nano-array configurations during sulfidation–regeneration cycles. With the demonstrated scalable synthesis and desulfurization performance of ZnO nano-arrays, a promising, industrially relevant integration strategy is provided to fabricate metal oxide nano-array-based monolithic devices for various environmental and energy applications.

Significant reduction of noble metal catalyst loading and simplification of electrode fabrication are urgently needed in order to lower the cost of proton exchange membrane electrolyzer cells (PEMECs) for large-scale hydrogen production. Herein, we report an integrated electrode design comprising in-situ grown platinum nanowires (PtNW) on ultrathin titanium liquid/gas diffusion layers (LGDLs) via a cost-effective and green chemical synthesis approach. The ultrathin integrated PtNW electrodes showed a low cell voltage of 1.643 V and high efficiency of 90.08% at 1000 mA cm−2 using about 15 times lower catalyst loadings than a conventional catalyst-coated membrane in PEMEC tests. Ex-situ electrochemical characterizations and microscale visualizations further reveal that PtNW electrodes display highly efficient hydrogen evolution reactions and excellent electrode durability due to high active surface area, favorable bubble detachment, and structural stability. This work provides new insights into catalyst layer design and facile ultrathin electrode fabrication for more compact and low-cost PEM electrolyzers, fuel cells and other systems.

Mesoporous manganese doped cerium oxide catalysts were prepared by an inverse micelle method with different manganese loadings. These materials exhibited superior activity for epoxidation of alkenes with molecular oxygen. Highest active 10MnCe material showed an activity of 80 % conversion and >99 % selectivity for cyclooctene epoxidation. The fluorite crystal structure which facilitates the high oxygen mobility, low temperature reducibility, homogeneous distribution of manganese on ceria, nanoparticle nature, higher number of oxygen vacancies, low valent states of manganese and cerium, and the ability to generate reactive oxygen species of the manganese doped cerium oxide could be correlated to the high catalytic activity. The reaction followed first order kinetics with a rate constant of 0.31 h−1 at 100 °C, and the activation energy turned out to be 10.5 kJ/mol. The mechanistic study revealed that the reaction proceeds via a unique mechanism which involves in situ generated superoxide and singlet oxygen species.

Reducing the mass transfer resistance globally of a catalyst is a key to enhancing the catalytic reaction kinetics and fully utilizing the catalyst activity. Despite the success in tailoring the external mass transfer in the widely studied washcoat monoliths, the internal mass transfer resistance is difficult to be reduced due to the requirement of increasing macroporosity while maintaining high specific surface area and mechanical stability. Therefore, nanostructured array-based monolithic catalysts (nanoarray catalysts) have been developed in the past decade as a promising class of structured catalysts that may complement or substitute washcoat catalysts. This work fundamentally elucidates the enhanced mass transport properties of the nanoarray monolithic catalysts by a combination of experimental measurements and theoretical modeling. Using a low-dimensional model, the relative contributions of resistances were quantified in terms of chemical kinetics, internal and external mass transfers based on a probe model of C2H4 oxidation over the TiO2 supported Pt-based monolithic catalysts. The nanoarray catalysts displayed a lower internal mass transfer resistance than the washcoat counterparts as a result of the high macroporosity and small thickness of nanoarray layers. The nanoarray configuration provides a new pathway towards designing high-performance monolithic reactors and catalysts with low internal diffusion limitations for various gas phase reactions.

Monolithic catalysts have been widely used in automotive, chemical, and energy relevant industries. Nanoarray-based monolithic catalysts have been developed, demonstrating high catalyst utilization efficiency and good thermal/mechanical robustness. Compared with the conventional washcoat-based monolithic catalysts, they have shown advances in precise and optimum microstructure control and feasibility in correlating materials structure with properties. Recently, the nanoarray-based monolithic catalysts have been studied for low temperature oxidation of automotive engine exhaust and exhibited interesting and promising catalytic activities. This review focuses on discussing the key structural parameters of nanoarray catalyst that affect the catalytic performance from the following aspects: (1) geometric shape and crystal planes, (2) guest atom doping and defects, (3) array size and size-assisted active species loading, and (4) the synergy effect of metal oxide in composite nanoarrays. Prior to the discussion, an overview of the current status of synthesis and development of the nanoarray-based monolithic catalysts is introduced. The performance of these materials in low temperature simulated engine exhaust oxidation is also demonstrated. We hope this review will elucidate the science and chemistry behind the good oxidation performance of the nanoarray-based monolithic catalysts and serve as a timely and useful research guide for rational design and further improvement of the nanoarray-based monolithic catalysts for automobile emission control.

Nanostructured cerium oxide (CeO2) with outstanding physical and chemical properties has attracted extensive interests over the past few decades in environment and energy-related applications. With controllable synthesis of nanostructured CeO2, much more features were technologically brought out from defect chemistry to structure-derived effects. This review highlights recent progress on the synthesis and characterization of nanostructured ceria-based materials as well as the traditional and new applications. Specifically, several typical applications based on the desired ceria nanostructures are focused to showcase the importance of nanostructure-derived effects. Moreover, some challenges and perspectives on the nanostructured ceria are presented, such as defects controlling and retainment, scale-up fabrication, and monolithic devices. Hopefully, this review can provide an improved understanding of nanostructured CeO2 and offer new opportunities to promote the further research and applications in the future.

High-performance photodetectors are costly due to either the expensive nature of active materials or sophistication in the fabrication process required to meet performance targets. In this work, low-cost metal stannate based nanostructures are demonstrated as active materials for high-performance UV photodetectors. A robust, inexpensive, and scalable drop-casting process was successfully developed to fabricate thin film devices composed of amorphous ZnSnO3 nanocubes and/or polycrystalline Zn2SnO4–SnO2 nanoparticles with different optical and electronic structures. Moreover, the Zn2SnO4–SnO2 heterojunction nanoparticles were directly obtained by thermal treatment of amorphous ZnSnO3 nanocubes. Large-area, uniform, and continuous film photodetectors were achieved with pronounced and fast response upon exposure to UV illumination (λ 102 and ∼103 was achieved for ZnSnO3 and Zn2SnO4–SnO2 photodetectors, respectively) and excellent responsivity (as high as 0.5 A W−1 at 5.0 V bias from the Zn2SnO4–SnO2 photosensors) under low light intensity. This work provides a simple, cost-effective and tunable processing strategy to synthesize and apply earth-abundant metal stannate based nanomaterials for high performance UV photodetectors and other optoelectronic devices.

The scalable three-dimensional (3-D) integration of functional nanostructures into applicable platforms represents a promising technology for meeting the ever-increasing demands of fabricating high performance devices featuring cost-effectiveness, structural sophistication and multi-functional enabling. Such an integration process generally involves a diverse array of nanostructural entities (nano-entities) consisting of dissimilar nanoscale building blocks such as nanoparticles, nanowires, and nanofilms made of metals, ceramics, or polymers. Various synthetic strategies and integration methods have enabled the successful assembly of both structurally and functionally tailored nano-arrays into a unique class of monolithic devices. The performance of nano-array based monolithic devices is dictated by a few important factors such as materials substrate selection, nanostructure composition and nano-architecture geometry. Therefore, the rational material selection and nano-entity manipulation during the nano-array integration process, aiming to exploit the advantageous characteristics of nanostructures and their ensembles, are critical steps towards bridging the design of nanostructure integrated monolithic devices with various practical applications. In this article, we highlight the latest research progress of the two-dimensional (2-D) and 3-D metal and metal oxide-based nanostructural integrations into prototype devices applicable with ultrahigh efficiency, good robustness and improved functionality. Select examples of nano-array integration, scalable nanomanufacturing and representative monolithic devices such as catalytic converters, sensors and batteries will be utilized as the connecting dots to display a roadmap from hierarchical nanostructural assembly to practical nanotechnology implications ranging from energy, environmental, to chemical and biotechnology areas.

Low temperature propane oxidation has been achieved by Co3O4-based nano-array catalysts featuring low catalytic materials loading (15 mg under flow rate of 150 mL/min). The increased Ni doping into the Co3O4 lattice has led to 100% propane conversion at low temperature (

Atomically-thin two-dimensional (2D) nanostructure, an emerging class of nanomaterials, has achieved tremendous progress in the past decade and will remain a significant research topic in the near future Apart from the discoveries of various 2D nanomaterials, remarkable attentions have been paid to the rational design and alteration of architectures based on pristine 2D materials to meet demands of next-generation functional applications in the near term Herein, this review intends to provide an instant survey over the recent key advances on the structural engineering strategies of 2D nanomaterial-based architectures for new sensing capabilities and opportunities Through intrinsic or extrinsic alterations, the pristine 2D nanostructures of some unique intrinsic properties could be modified and functionalized in a predictable pattern to overcome existing drawbacks and obtain synergistic abilities, demonstrating a great potential in promoting sensing device performance In parallel with the review of latest development of structural engineering strategies and related highly functionalized sensor devices including sensing capabilities towards Covid-19 antigens, the underlying mechanisms of these designs are revealed to offer a unique insight in understandings of architecture design and property tailoring for boosting new sensing capabilities and performances

Heterojunctions are an important strategy for designing high performance electrical sensor materials and related devices. Herein, a new type of metal-semiconductor hybrid nanoparticle has been successfully used to remarkably sensitize the surface of ZnO nanowires for detecting NO2 with high responses over a broad temperature window ranging from room temperature to 600 °C. These hybrid nanoparticles are comprised of iron oxide nanowires with well dispersed single crystalline Au nanoparticles. The hybrid nanoparticle decorated ZnO nanowires have achieved a giant response, as high as 74 500 toward NO2 gas, about 42 times that of Au decorated ZnO nanowire sensors. This dramatic enhancement may be attributed to the efficient charge transfer across the Au-Fe2O3 Schottky and Fe2O3-ZnO semiconductor heterojunction interfaces. Due to the incorporation of thermally-stable Fe2O3 nanoparticles as the support of Au nanoparticles, the working temperature of nanowire sensors was successfully extended to higher temperatures, with an increase of 200 °C, from 400 °C to 600 °C. Such a combination of semiconductor heterojunction and semiconductor-metal Schottky contact presents a new strategy for designing high performance electrical sensors with high sensitivity, stability, selectivity, and wide operation temperature window, which are potentially suitable for advanced energy systems such as automotive engines and power plants.