Catalytic Micro Research Articles

Multifunctional glucose-powered nanomotors with robust dual enzyme mimic activities

Catalytic micro-/nanomotors (MNMs) that use H2O2 as fuel to generate O2 bubbles for propulsion hold great promise for exciting applications in the biological and environmental fields. However, it is still a challenge to alleviate or avoid the negative impact of H2O2 on the ecological environment of water body. Herein, a novel glucose-driven nanomotor with robust dual enzyme-like activities was prepared by precisely controlling the phase composition and enzyme immobilization to construct a 3D hierarchical structure integrating Fe-MOF, MnO2 and glucose oxidase (GOx) on halloysite nanotube (HNTs) support. Embedding GOx into the framework of Fe-MOF by a simple one-step coprecipitation process allowed the in-situ generation of H2O2 in the presence of glucose. Such H2O2 could be further decomposed to O2 bubbles to drive nanomotors. Meanwhile, O2 bubbles and residual H2O2 could convert to active species superoxide radical (O2•−) and hydroxyl radical (•OH) due to the high peroxidase/oxidase-like activities of Fe-MOF/MnO2 in nanomotors. As a proof of concept, the as-synthesized nanomotors could realize sensitively colorimetric detection of glutathione (GSH) with a detection limit of 9.3 × 10−8 M. In particular, the nanomotors could also rapidly degrade tetracycline hydrochloride (TCH) under neutral conditions without additional H2O2. It is envisioned that the new strategy that combines strong enzyme-like activity with enhanced autonomous motion can promote the nanomotors efficiency for biomolecular sensing and environmental remediation.

Effect of inserted baffles on hydrogen heterogeneous reaction in planar catalytic micro combustor

Heterogeneous reaction characteristics of premixed H2/Air mixture are numerically investigated in micro combustor with coating platinum (Pt) catalyst on the inner wall. The well-designed combustor with the inserted baffle is committed to improving the transport of bulk species on the catalytic surface, therefore enhancing the fuel conversion ratio. A two-dimensional numerical model with detailed heterogeneous reaction mechanism is developed and verified. In this work, the numerical results reveal that the heterogeneous reaction rate and fuel conversion ratio are significantly improved in the combustor with inserted baffle. The velocity of gaseous mixture swiftly increases between the baffle and catalytic surface, resulting in the increasing adsorption-desorption of bulk species on the catalytic surface. The main influencing factors of inserted baffle body comprise of slit width between two ribs in the same row (W), rib length (L), distance between adjacent baffles row (D), number of baffle row (n) which are studied to obtain a set of optimized parameters of baffle in the well-designed combustor. The optimized parameters of the baffle are W = 0 mm, L = 0.4 mm, D = 4 mm and n = 4, which are employed in the combustor to obtain a high hydrogen conversion ratio. Moreover, the effect of different inlet velocities and equivalent ratios of the mixture on the heterogeneous reaction characteristics are carried out in the designed combustor. As the designed combustor performs well, and the improvement effect of the optimized baffle gradually increases together with the inlet velocity, particularly for high inlet velocity (7 m/s). The promotion effects of baffle in the designed combustor are presented when the rich and lean fuel are adopted at inlet velocity of 7 m/s. Finally, the relative parameters of this work can serve as a reference and guidance for the design of micro scale combustor.

Nanogel Catalysts for the Hydrolysis of Underivatized Disaccharides Identified by a Fast Screening Assay

Applying high-throughput synthetic and screening methods for the development of catalytic micro- and nanogels remains challenging due to the nature of the workflow. Typical procedures require the preparation of stable miniemulsions, followed by radical polymerization, purification of the obtained gels by extensive extraction or dialysis, and subsequent characterization of physical properties and examination of desired functions. To streamline the process, we altered the gel synthesis procedure and developed a screening protocol to identify gel compositions with the desired catalytic function. The assays identify five out of 50 synthesized gels from eight different cross-linkers with high potential to hydrolyze carbohydrates. A catalytic proficiency (kcat/KM × knon) of up to 1.4 × 106 and gel activity of 0.8 μmol h–1 mg–1 were observed placing the synthesized gels among the most proficient catalysts known for the hydrolysis of nonactivated glycosidic bonds.

Motion Analysis and Real‐Time Trajectory Prediction of Magnetically Steerable Catalytic Janus Micromotors

Chemically driven micromotors display unpredictable trajectories due to the rotational Brownian motion interacting with the surrounding fluid molecules. This hampers the practical applications of these tiny robots, particularly where precise control is a requisite. To overcome the rotational Brownian motion and increase motion directionality, robots are often decorated with a magnetic composition and guided by an external magnetic field. However, despite the straightforward method, explicit analysis and modeling of their motion have been limited. Here, catalytic Janus micromotors are fabricated with distinct magnetizations and a controlled self‐propelled motion with magnetic steering is shown. To analyze their dynamic behavior, a dynamic model that can successfully predict the trajectory of micromotors in uniform viscous flows in real time by incorporating a form of state‐dependent‐coefficient with a robust two‐stage Kalman filter is theoretically developed. A good agreement is observed between the theoretically predicted dynamics and experimental observations over a wide range of model parameter variations. The developed model can be universally adopted to various designs of catalytic micro‐/nanomotors with different sizes, geometries, and materials, even in diverse fuel solutions. Finally, the proposed model can be used as a platform for biosensing, detecting fuel concentration, or determining small‐scale motors’ propulsion mechanisms in an unknown environment.

Numerical investigation on the self-ignition and combustion characteristics of H2/air in catalytic micro channel

The self-ignition of hydrogen/air is an important process in the micro thermophotovoltaic system. The transient numerical models of gas-phase reaction and catalytic reaction in the various catalytic micro combustors were built and verified. The self-ignition process of gas-phase reaction caused by catalytic reaction in the catalytic micro channel with conventional heat dissipation was studied. The self-ignition process could be divided into four stages, fuel diffusion stage - pure catalytic reaction stage - flame front moving stage - stable combustion stage. The ignition time and temperature limit at different inlet temperatures, inlet velocities and channel heights were analyzed. The results showed that the wall quenching effect, thermal effect and flame propagation effect are dominant at low temperature, medium temperature and high temperature respectively. The catalyst length and the mixture internal energy were the main factor at low inlet velocity and high inlet velocity respectively. The steady-state time was also studied in the various operation conditions. Finally, the catalytic combustion characteristics in the stable combustion stage were analyzed. The influence of inert section length, inlet temperature and inlet velocity on the maximum temperature and fuel conversion ratio were investigated.

Parametric study of methane catalytic combustion in a micro-channel reactor: Effects of porous washcoat properties

A washcoat resolved numerical model of catalytic micro combustor fueled by methane is developed. Detailed gas phase mechanism and alumina dioxide supported Pt-based surface mechanism are adopted. This model proves to capture flow, temperature and species fields precisely including impermeable flow and products accumulation in porous washcoat layer. The novelty and superiority of this research compared to traditional modeling method in which instantaneous diffusion onto catalytic wall is assumed lies in that: it is possible to investigate effects of porous washcoat properties with this full-scale numerical model. Computational results show that homogeneous reactions (HR) are impaired and heterogeneous reactions (HTR) are strengthened as channel confinement increases. Da number analysis reveals that the micro combustor works under a mixed controlled mode in which catalytic reaction rate and internal mass diffusion rate are comparable. When washcoat layer thickness increases from 15 μm to 75 μm, overall catalyst usage roughly decreases from 0.34 to 0.05. It is concluded washcoat thickness can’t be too thin in order to maintain HTR intensity and too thick since catalyst usage is extremely low. Porous washcoat properties impact combustion characteristics in a similar mechanism: modifying effective mass diffusion coefficient. In general, increasing porosity, average pore diameter and decreasing tortuosity will enhance HTR and impair HR. In real application, these parameters can be utilized to modify combustion temperature, emission performance and stability operation map.

Kinetic Modelling of Methanol to Propylene Process on Cerium-hierarchical SAPO-34 Catalyst

In this paper, conventional SAPO-34 and Cerium Hierarchical SAPO-34 zeolites are synthesized using a hydrothermal method for methanol-to-propylene (MTP) reaction. The Ce-H-SAPO-34 catalyst shows a slightly larger crystal size, bimodal pore size distribution (microporous and mesoporous) and lower surface acidity compared to conventional SAPO-34 catalysts. According to these physicochemical properties and the previously suggested reaction mechanisms on the conventional SAPO-34 catalyst, a new reaction network is introduced for Ce-H-SAPO-34 catalyst. This was based on the data collected from a catalytic micro reactor in the temperature range of 390-450°C and at atmospheric pressure. The lumped kinetic model and the reaction rate expression have been introduced by considering the reaction network. The parameters were then estimated based on the experimental data using genetic algorithms. Comparing the experiments with the predicted data suggests a good correlation between the experimental data and the model.

Mathematical Modeling of Heat, Mass and Moisture Transfer in Catalytic Porous Media

The discovery of ordered mesoporous materials has opened great opportunities for new applications in heterogeneous catalysis e.g. in soil purification processes. The focus of this study is the development of a mathematical model to simulate heat, mass and moisture transfer in soil arrays tacking into account catalytic micro- or nanoparticles. The nonlinear mathematical model of contaminant distribution in unsaturated catalytic porous media to the filter-trap in non-isothermal conditions is presented. The finite differences method was used to find the numerical solution of the corresponding boundary value problem and the analytical solution for mass transfer in catalytic micro- or nanoparticles was presented as well. Numerical experiments and their analysis were conducted using NanoSurface software complex.

Catalytic fast co-pyrolysis of organosolv lignin and polypropylene over in-situ red mud and ex-situ HZSM-5 in two-step catalytic micro reactor

The additional use of red mud (RM) on the catalytic fast co-pyrolysis (CFCP) of organosolv lignin (OL) and polypropylene (PP) over ex-situ HZSM-5 was investigated using a tandem micro reactor system. Non-catalytic fast co-pyrolysis of OL and PP increased their decomposition efficiency owing to the effective interactions. The in-situ catalytic fast pyrolysis (CFP) of OL over RM led to the enhanced conversion of large molecular OL pyrolyzates with the additional production of aromatic hydrocarbons. The in-situ CFCP of OL/PP over RM resulted in a further increase in the cracking efficiency of OL/PP pyrolyzates as well as an increase in the aromatics formation efficiency owing to the effective interactions between their CFP intermediates. Furthermore, the application of RM in 1st in-situ catalytic reactor was found to be the optimal catalyst system because the in-situ CFCP of OL/PP over RM can enhance the formation of the proper hydrocarbons precursors for the production of aromatics over ex-situ HZSM-5 in 2nd reactor. Compared to the one-step CFCP of OL/PP over ex-situ HZSM-5, two-step CFCP of OL/PP over in-situ RM and ex-situ ZSM-5 maintained the higher aromatics formation during the 7 times sequential reaction due to the slow deactivation of ex-situ HZSM-5.

Comparison of the effect of heat release and products from heterogeneous reaction on homogeneous combustion of H2/O2 mixture in the catalytic micro combustor

Numerical simulation was carried out to investigate the hetero-/homogeneous combustion of stoichiometric H2/O2 premixed flames in a platinum-coated planar micro channel. Three-dimensional Computational Fluid Dynamics (CFD) models with detailed reaction mechanisms for homogeneous (gas phase, G) and heterogeneous (catalytic, C) reactions were adopted. The effects of the heat released and products from heterogeneous reaction (CR) on the homogeneous reaction (GR) were analyzed and compared systematically. In the presence of additional released heat, the flame temperature, intermediate concentrations and product yield increased, especially near the inner wall. The promotion effect of heat released from the CR on the GR was indicated, and it mainly reflected in the increase of chemical reaction rate and fuel consumption. When the heat released and the products from the CR were added simultaneously, the flame temperature and species (OH) concentration were still low as compared with the model without addition. The inhibition effect of the product on the GR was larger than the promotion effect of the additional heat on the GR. The increase in the chemical reaction rate and fuel conversion rate demonstrated that, the heat released from the CR could improve the combustion efficiency of the micro combustor.

A 3D CFD study of homogeneous-catalytic combustion of hydrogen in a spiral microreactor

A spiral microreactor is analyzed for combustion of hydrogen on Pt catalyst using 3D computational fluid dynamics (CFD) simulations with detailed mechanisms for both catalytic and gas phase reactions. A spiral microreactor comprises of a single channel that is curled-up in a spiral, starting at the center and spiraling outwards. A comparison of the spiral with a conventional straight-channel reactor is presented. Maximum temperature attained in the spiral microreactor, investigated for equivalence ratios within the range of 0.3 to 0.65 under non-adiabatic conditions (with heat losses by convection and radiation), is found to be greater than the adiabatic flame temperatures. Comparison with a straight-channel reactor of equivalent dimensions shows higher temperature and higher contribution of homogeneous chemistry in the spiral microreactor. The nature of homogeneous reactions in the presence of catalytic micro reactor is presented. Combustion characteristics presented herein indicate that the preheating of reactants and protection of reaction zone in the spiral reactor make it superior to the straight channel reactor. The effect of inlet velocity is presented and the effect of heat recirculation on homo-catalytic interactions is analyzed.

Numerical study on stability and influencing factors of heterogeneous reaction for hydrogen/oxygen mixture in planar catalytic micro combustor

The combustion and flow characteristics of H2/O2 mixture were numerically studied in a platinum-coated planar channel with a length of 20 mm and a height of 1 mm. Two-dimensional numerical models were built and verified by experimental data. The fundamental of generating unstable combustion and flow and its influencing factors were studied via changing the parameters (equivalent ratio, initial position of reaction, with or without homogeneous reaction). It was found that pure heterogeneous reaction could affect the flow state in the planar micro combustor because of the intense convective heat transfer on the inner wall. The critical Reynolds number in micro combustor calculated by pure heterogeneous reaction model was in the range of 650–1100. The reaction heat of catalyst surface and the thickness of boundary layer at the initial position of heterogeneous reaction are two main factors which influenced the stability of combustion and flow. Finally, the pure heterogeneous reaction had higher complete combustion efficiency than coupling reaction. Based on these conclusions, the applicable conditions for achieving stable flow and combustion in the microchannel were obtained, which could provide a theoretical basis for the application in micro-combustion.

The effect of embedded high thermal conductivity material on combustion performance of catalytic micro combustor

A novel micro combustor embedded with high thermal conductivity material has been proposed for micro-thermophotovoltaic system application. The effect of the materials, which is graphite and nickel with widths 1 mm and 3 mm on the thermal and radiant performance of the new micro combustor, was experimentally and numerically investigated. It was found that high and uniform temperature distribution along the walls of the combustor was obtained by embedding graphite with width of 1 mm because of the enhanced heat transfer, which is desirable for the micro-thermophotovoltaic system. The available radiation energy increased from 4.6 W for the conventional combustor to 5.2 W for the novel combustor when the inlet velocity was 1.0 m/s and the hydrogen/oxygen equivalence ratio was 0.5 under the experimental conditions. The available radiation efficiency increased from 8.9% to 9.8% and the effect of the embedded material could be enhanced by increasing the chemical energy input. Based on the combustor and fuel in this study, the conditions for good thermal performance are graphite with width of 1 mm, inlet velocity of 1.0 m/s and 0.5 equivalence ratio of hydrogen/oxygen by considering the reliability and durability of the combustor.

Kink and Delta Self-Actuating Platinum Micro-Robot

Catalytic micro- and nanorobots exhibit self-propulsion in the presence of chemical fuels such as glucose, hydrogen peroxide. Generally, swimmers incorporate a catalyst as a part of their structure for the decomposition of a chemical fuel. Several applications such as active drug delivery, minimally invasive surgery, and water remediation, have been envisaged. In this letter, we investigated the influence of geometric variable of catalytic microrobot to their swimming behaviors in hydrogen peroxide (H2O2) solutions. V-shaped microrobots with various opening angles (45°, 90°, and 135°), and triangle-shaped microrobots that have similar dimensions with V-shaped microrobots, have been fabricated by focused-ion-beam etching on commercial platinum microwires. Swimming tests were performed in 15% and 30% H2O2 solutions. We have found that V-shaped microrobot with 45° opening angle showed a superior swimming speed of 4.3 μm/s in 15% H2O 2 solution, while 90° microrobot exhibits a speed of 1.52 μm/s. The 135° V-shaped microrobot and all triangle-shaped microrobots have not shown any obvious motions in 30% H2O2 solution. Our observation that the swimming performances of various shaped microrobots change in tandem proves the necessity of structural asymmetry in designing catalytic micro- and nanorobots.

Progress toward Catalytic Micro- and Nanomotors for Biomedical and Environmental Applications.

Synthetic micro- and nanomotors (MNMs) are tiny objects that can autonomously move under the influence of an appropriate source of energy, such as a chemical fuel, magnetic field, ultrasound, or light. Chemically driven MNMs are composed of or contain certain reactive material(s) that convert chemical energy of a fuel into kinetic energy (motion) of the particles. Several different materials have been explored over the last decade for the preparation of a wide variety of MNMs. Here, the discovery of materials and approaches to enhance the efficiency of chemically driven MNMs are reviewed. Several prominent applications of the MNMs, especially in the fields of biomedicine and environmental science, are also discussed, as well as the limitations of existing materials and future research directions.

Self-propelled supramolecular nanomotors with temperature-responsive speed regulation.

Self-propelled catalytic micro- and nanomotors have been the subject of intense study over the past few years, but it remains a continuing challenge to build in an effective speed-regulation mechanism. Movement of these motors is generally fully dependent on the concentration of accessible fuel, with propulsive movement only ceasing when the fuel consumption is complete. Here we report a demonstration of control over the movement of self-assembled stomatocyte nanomotors via a molecularly built, stimulus-responsive regulatory mechanism. A temperature-sensitive polymer brush is chemically grown onto the nanomotor, whereby the opening of the stomatocytes is enlarged or narrowed on temperature change, which thus controls the access of hydrogen peroxide fuel and, in turn, regulates movement. To the best of our knowledge, this represents the first nanosized chemically driven motor for which motion can be reversibly controlled by a thermally responsive valve/brake. We envision that such artificial responsive nanosystems could have potential applications in controllable cargo transportation.

Design of catalytic micro trickle bed reactors

Design of catalytic micro trickle bed reactors

Particle Advances

While the journal Particle & Particle Systems Characterization is entering its 33rd volume, the relaunched and restructured Particle is just about to enter its 4th year of publication. This is a point that provided much confusion for our authors in the initial years after the relaunch at the start of 2013. However, in the intervening period, the journal has evolved into an increasingly attractive option in which to publish cutting-edge, particle-related research across the broad field of materials science. With no shortage of journals, both well-established and new, for authors to choose from in which to disseminate their original research results to their peers, we are grateful that they entrust their work to us. Earlier this year we highlighted a number of original articles that have been highly accessed and a number of overview, review-type articles that have caught the attention of the community. These articles are free for you to read, please follow the links provided on our news portal Materials Views http://www.materialsviews.com/best-of-particle-enjoy-free-access/. Particle belongs to the Advanced Materials journal family (see Figure 1). Selected articles from all journals in the portfolio can be accessed here http://www.emagcloud.com/wiley/AdvancedFamilyBooklet2/index.html. I often feel rather privileged as an editor, as we are among the first people that get to read exciting research discoveries before the articles make it to press and in doing so to a larger readership. However, I have to acknowledge at this stage the excellent work that our expert reviewers do, which enables a stringent evaluation process, ensuring that only the highest quality articles make it into a published issue. I am also indebted to our most active Editorial Advisory Board members who, through their involvement and enthusiastic engagement, have provided enormous support to Particle since the board was established at the start of 2013. The impact factor of a journal is a metric that is well known to our authors and readers. Without wanting to dwell on this number, or the interpretation of it, I can mention that Particle received its first partial impact factor in 2015. To clarify, the partial impact factor is calculated by counting the number of times articles published in 2012 and 2013 were cited in Thompson Reuters ISI Web of Science indexed journals in 2014. The impact factor of 3.081 shows strong growth in the first year since the relaunch, an increase of 474% on the journal prior to relaunch. It has to be acknowledged that this is in part due to the change in focus pre and post relaunch; while the prior focus was on the fields of industrial chemistry and engineering, the new focus of the journal is on materials science. However, this new impact factor also shows that the articles we have published since the start of 2013 are widely read and are of relevance to researchers working in many areas of materials science. Particle will receive its first impact factor (based on two years of post-relaunch citation) in June 2016, which will report further strong growth. In the editorial office our main focus going forward is to keep the quality of published work at a high level. In planning for 2016 are a number of topical special issues on catalytic micro- and nanoparticles, energy materials, advanced particle characterization techniques, and on nanocrystals and their emerging applications, among others. We welcome suggestions for further projects and are contactable on the address [email protected] Also, I invite you to connect with me on LinkedIn, should you use this professional network, where I regularly provide access to selected articles from the most recently published journal issues.

Selectively catalytic micro- and nanocrystals of metal–organic framework [Co(4-bpdh)(HIA)

Metal–organic framework micro-crystals [Co(4-bpdh)(HIA)]∝ (1Co), crystallized in the monoclinic system (space group P12/n1, a=10.0009(16)Å, b=15.472(3)Å, c=18.563(3)Å, β=91.81(0)°, and Z=4), were controllably synthesized through the adjustment of the solvent system. The Co2+ ion center located in a six-coordinated environment combined with 5-hydroxyisophthalic acid (HIA) to produce ladder-like structures, which again linked with 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hxadiene (4-bpdh) to yield a double-layer network. Micro-crystals 1Co exhibited selectively oxidation-catalytic properties for the degradation of methyl orange (conversion 90%) owing to ligand to metal charge transfer. Our work determined that the synthesized catalyst is not only highly selective for degradation of organic dyes, but also very efficient.

Functionalized Clay Microparticles as Catalysts for Chemical Oscillators

Catalytic micro- and nanoparticles are widely employed to study the global behavior of large networks of coupled chemical oscillators. In this paper, we present a new class of catalysts for the BZ oscillating reaction, based on the functionalization of natural inorganic materials (1:1 and 2:1 clays) through the sorption of the iron-complex ferroin on their surface. The small size of the clay basic units (diameter < 2 μm) and their colloidal nature make these particles interesting for studying systems having dimensions at the border between the nano- and the mesoscale. In the first part of this paper, we present the synthesis and the characterization of the ferroin-functionalized clay. We then show an extensive study on the oscillatory dynamics of the BZ reaction catalyzed by the clay. Through a direct comparison with a classical ferroin-catalyzed BZ system, we describe the modifications of the oscillation mechanisms induced by the new catalyst. Finally, we illustrate an application of the microparticles a...