Gas-solid Reaction Research Articles

Fabrication of TiO2 with Ru-induced lattice strain for enhancing photocatalytic nitrogen fixation in gas–solid reaction system

Fabrication of TiO2 with Ru-induced lattice strain for enhancing photocatalytic nitrogen fixation in gas–solid reaction system

Exploring the kinetics and thermodynamics of TiFe0.8CrxMn0.2-x hydrogen storage alloys

The influence of Fe substitution by Cr and/or Mn on the hydrogenation properties of TiFe0.8CrxMn0.2-x hydrogen storage alloys was explored for several substitution amounts (x = 0, 0.05, 0.1, 0.15 and 0.2). The synthesized alloys consisted of a dominant TiFe (cubic, CsCl-type) and a secondary C14 Laves phase (hexagonal, MgZn2-type). The increase in Cr content, and consequently in C14 Laves phase fraction, improved the first hydrogenation kinetics and the hydrogen intake after activation (1.60–1.70 wt% H2 at 30 °C within 3 min), while substantially stabilizing the monohydride phase. The reaction enthalpy obtained from pressure-composition-temperature (PCT) curves hence increased along Cr substitution, ranging 24.35 ± 0.34 to 35.39 ± 1.00 kJmol-1 for the absorption, and 31.08 ± 1.39 to36.34 ± 1.99 kJmol−1for the desorption (absolute values). These experimental findings were in good agreement with density functional theory (DFT) predictions performed across the explored composition space. The estimated entropy values on the other hand remained nearly constant, fluctuating between 84.28 ± 4.76 and 102.64 ± 3.12 J mol−1 H2 K−1 for the absorption, and 100.46 ± 9.71 up to 105.45 ± 4.31 J mol−1 H2 K−1 for the desorption. Solid-gas reaction modeling showed that, under practical service conditions, the hydrogenation of activated alloys was interface-controlled followed by diffusion-controlled mechanisms as the reaction proceeded.

Thermochemical energy storage with the solid-gas reaction of SrCO3 improved with CaCO3

Abstract In the context of thermochemical energy storage (TCES) for concentrating solar power (CSP) applications, metal carbonates’ reversible calcination and carbonation are gaining prominence, particularly in the SrCO3/SrO system. This system is notable for its high theoretical energy density of 10.61 GJ/m³ and operational temperatures up to 1,200 °C. However, like the CaCO3/CaO system, SrO experiences a significant drop in reactivity during cycling due to sintering and agglomeration of particles. In this work is proposed that the conversion effective will be improved by mixing the strontium carbonate with calcium carbonate. The best mix found was 80/20 SrCO3/CaCO3 with the operating parameters of calcination-carbonation temperatures of 1,200 °C and 900 °C, respectively. This reaction has a notably better stable conversion rate than pure strontium carbonate. The study was carried out using thermogravimetry analysis. The mixture was subjected to 9 cycles, and for the ninth cycle, there was an effective conversion of 33.14 %, which, compared to pure SrCO3, was 2.33 %; that was improved noticeably during the carbonation process. There was an increase in the percentage effective conversion of 30.81 %. Volumetric energy density was reduced from 6.93 to 2.81 GJ/m3 in the first and after nine cycles. The XRD analysis of the unprocessed mixture after 4 and 9 cycles showed no formation of new or secondary compounds, only the expected compounds: SrO, SrCO3, CaO, and CaCO3. This important change is explained during the carbonation looping because the CaO remains encapsulated in the SrCO3 and does not react completely at 900 °C. As a hypothesis, this encapsulation delays the sintering of the SrCO3. Using a T carb = 850 °C promotes the carbonation of CaO. By promoting CaO to react, the CaO encapsulated is released rapidly, and the material was sintering faster than the T carb = 900 °C. Comparing the seventh cycle at a T carb = 900 and 850 °C, it is observed that the effective conversion decreases from 0.4431 to 0.4202 and, in the same proportion, the volumetric energy density.

D-Electrons of Platinum Alloy Steering CO Pathway for Low-Charge Potential Li-CO2 Batteries.

Aprotic Li-CO2 batteries suffer from sluggish solid-solid co-oxidation kinetics of C and Li2CO3, requiring extremely high charging potentials and leading to serious side reactions and poor energy efficiency. Herein, we introduce a novel approach to address these challenges by modulating the reaction pathway with tailored Pt d-electrons and develop an aprotic Li-CO2 battery with CO and Li2CO3 as the main discharge products. Note that the gas-solid co-oxidation reaction between CO and Li2CO3 is both kinetically and thermodynamically more favorable. Consequently, the Li-CO2 batteries with CoPt alloy-supported on nitrogen-doped carbon nanofiber (CoPt@NCNF) cathode exhibit a charging potential of 2.89 V at 50 μA cm-2, which is the lowest charging potential to date. Moreover, the CoPt@NCNF cathode also shows exceptional cycling stability (218 cycles at 50 μA cm-2) and high energy efficiency up to 74.6 %. Comprehensive experiments and theoretical calculations reveal that the lowered d-band center of CoPt alloy effectively promotes CO desorption and inhibits further CO reduction to C. This work provides promising insights into developing efficient and CO-selective Li-CO2 batteries.

Vitalizing Perovskite Oxide-Based Acetone Sensors with Metal-Organic Framework-Derived Heterogeneous Oxide Catalysts.

Perovskite oxides are promising candidates for chemiresistive-type gas sensors owing to their exceptional thermal and chemical stability during solid-gas reactions. However, perovskites suffer from critical issues such as low surface area and poor surface activity, which negatively influence the sensing characteristics. While metal nanoparticles can be incorporated in perovskites to improve their reactivity, the fundamental incompatibility between catalytic metals and perovskite oxides often leads to substantial structural degradation as well as phase instability. Herein, we overcome this challenge through the introduction of an intermediary phase that forms coherent interfaces with both the perovskite phase and catalyst metals. Specifically, we present the case study of p-type La0.8Ca0.2Fe0.98Pt0.02O3 perovskite, whose hole accumulation layer was modulated by the incorporation of metal-organic framework (MOF)-derived n-type α-Fe2O3 nanoparticles decorated with highly dispersed Pt catalysts. The resulting composite exhibited significantly improved surface activity over the nonmodified La0.8Ca0.2FeO3 perovskite, leading to exceptional chemiresistive sensing performance toward acetone gas (Rg/Ra = 39.8 toward 10 ppm of acetone at 250 °C) with high cross-sensitivity against interfering gases. Importantly, our findings reaffirm the critical influence of interfacial engineering in facilitating surface chemical reactions on perovskite oxides and, by doing so, effectively provide a general synthetic guideline to the design of perovskite-based chemiresistors.

A general rate equation theory for non– and catalytic coupling gas–solid reactions and its application to sorption-enhanced water gas shift

Sorption-enhanced water gas shift (SEWGS) involves the catalytic WGS reaction of CO with H2O and the non-catalytic gas–solid carbonation reaction of CO2 with CaO. This work proposes a first-principal rate equation theory for non– and catalytic coupling gas–solid reactions. The theory starts from quantum chemistry calculation and extends to larger scales to predict SEWGS experiments conducted in the reactor result without any empirical hypothesis. The coupling mechanism of non– and catalytic reactions is illustrated in a mesoscopic way, based on which the kinetic transition behavior and morphology change on the catalyst surface for WGS can be obtained. The hierarchical framework bridges the scale gap between elementary reactions and pilot plants and the prediction results of and gas profile at the exit of the bubbling bed and carbonation conversion are validated by experiments. The multiscale kinetics is promising to apply to non– and catalytic coupling gas–solid reaction kinetics studies.

Coupled heat transfer and chemical kinetics in a calcium oxide/hydroxide fixed bed thermochemical energy storage reactor

Among energy storage technologies, thermochemical heat storage despite its unique advantages, remains at a nascent state due to varied technical challenges. One of the key unknowns in the otherwise well-studied calcium oxide/hydroxide chemistry, is a lack of understanding of the possible output power profiles. Here, we investigate the theoretical power output from a fixed-bed, modular, honeycomb-geometry thermochemical energy storage (TCS) reactor based on a calcium oxide/hydroxide, using finite element modeling of heat transfer coupled with reaction kinetics. We calculate the extent of reaction and temperature profiles in a lattice of honeycomb cells that make up the bed, while varying heat transfer related parameters. We find that the size of the unit cell can limit energy discharge, for example, increasing the time to completion for the reaction to ∼7 hours as the cell size increases to 6 cm, even though the reaction kinetics is fast at ∼2 mins. The time constant of the transient power profile increases by a factor of ∼4 as the cell size increases by a factor of ∼3, when considering cells in the nominal size range 2–6 cm. Besides cell size, we investigate how the power profile is affected by the following parameters: the thermal conductivity of the bed, the initial temperature, the material of the cell wall and the heat transfer coefficient of external flows. In particular, we identify the combination of parameters that can vary the power profile on demand to operate the same reactor as either a thermal capacitor or alternately, a thermal battery. This work informs future design possibilities with oxide-hydroxide, solid–gas reaction TCS and provides insight into critical heat transfer parameters.

Rational design of Z-scheme configured polymeric carbon nitride-decorated ZnWO4 nanofibers for enhanced visible-light-driven photodegradation of antibiotics

In this study, a Z-scheme heterostructure was meticulously engineered between zinc tungstate (ZnWO4) nanofibers and polymeric carbon nitride (PCN) nanosheets to augment the photocatalytic degradation of tetracycline (TC) under visible light irradiation. A cohesively integrated PCN/ZnWO4 photocatalyst structure was synthesized through an in-situ gas-solid reaction. The quantity and spatial distribution of PCN nanosheets were modulated by fine-tuning the gas precursor and reaction parameters. Relative to pristine ZnWO4 nanofibers and PCN photocatalysts, the distinct three-dimensional PCN/ZnWO4 heterostructure manifests a notable enhancement in photocatalytic performance, attributed to its plethora of active sites and a Z-scheme configuration that bolsters charge separation efficiency, achieving a tetracycline degradation rate of 95.4% upon exposure to simulated sunlight for 160 minutes. The employment of gas-solid reaction as a design paradigm pioneers a fresh paradigm in the strategic assembly of Z-scheme heterostructured photocatalysts, thereby illuminating a promising pathway for advancements in environmental remediation technologies.

In-Situ Construction of Functional Multi-Dimensional MXene-based Composites Directly from MAX Phases through Gas-Solid Reactions.

The weak bonding of A atoms with MX layers in MAX phases not only enables the selective etching of A layers for MXene preparation but brings about the chance to construct A derivatives/MXene composites via in situ conversion. Here, a facile and general gas-solid reaction systems are elegantly devised to construct multi-dimensional MXene based composites including AlF3 nanorods/MXene, AlF3 nanocrystals/MXene, amorphous AlF3/MXene, A filled carbon nanotubes/MXene, layered metal chalcogenides/MXene, MOF/MXene, and so on. The intrinsic effect mechanism of interlayer confinement towards crystal growth, catalytic behavior, van der Waals-heterostructure construction and coordination reaction are rationally put forward. The tight interface combination and synergistic effect from distinct components make them promising active materials for electrochemical applications. More particularly, the AlF3 nanorods/Nb2C MXene demonstrate bi-directional catalytic activity toward the conversion between Li2S and lithium polysulfides, which alleviates the shuttle effect in lithium-sulfur batteries.

Achieving superior hydrogen sorption kinetics of MgH2 by addition of Ni-doped TiO2 catalysts

MgH2 is a high-density hydrogen storage material but requires an efficient catalyst to improve its poor kinetics and reduce high operating temperature. TiO2 is a widely used photocatalyst for water splitting and hydrogen production, and has also demonstrated catalytic ability in the gas-solid reaction of MgH2. In this study, we synthesize the Ni-doped TiO2 nanoparticles, which significantly reduce the hydrogen absorption temperature down to subzero temperatures. The milled composite of MgH2 with 10 wt% Ti(5Ni)O2 can absorb 5.25 wt% H2 within 30 s at 25 °C, 4.30 wt% H2 within 50 s at 0 °C, and 3.94 wt% H2 within 50 s even at a low temperature of −30 °C. This composite can release 6.04 wt% of hydrogen in 3 min at 250 °C, and the dehydrogenation activation energy is reduced to 74.57±1.36 kJ/mol, a notable reduction in comparison to that observed in pure MgH2. This study demonstrates the potential of the modified TiO2 as an important kind of catalyst for solid-state hydrogen storage materials.

State of the art on solid–gas sorption based long-term thermochemical energy storage

Solid-gas sorption thermochemical heat storage technology is an innovative and promising solution for storing heat over long periods. The review focuses on the construction of composite sorption thermochemical heat storage materials and binary mixed salt materials with porous matrix as the supporting materials, which can further improve the hydration rate and cycle stability of single hydrated salt. Furthermore, the heat storage capabilities of the metal halide/ammonia working pair make it suitable for extreme environments, surpassing the limitations of water-based working pairs in terms of low-temperature adaptability. It is worth noting that common solid–gas reactors and measures to enhance heat and mass transfer are also reviewed. Meanwhile, the efficient open and closed heat storage systems and their optimization schemes are introduced, and the feasibility of the practical operation of the heat storage systems is evaluated comprehensively from the technical and economic perspectives, and the future research challenges are prospected.

Direct fabrication of polycrystalline γ-alumina nanochains-supported Pt nanoparticles on macroscopic ceramic substrates

We report the direct fabrication of polycrystalline γ-Al2O3 nanochains-supported Pt nanoparticles on macroscopic substrates, such as monolithic honeycombs and porous disc-typed ceramics, via chemical vapor deposition. We also investigate solid-gas reactions between the γ-Al2O3 nanochains@Pt nanoparticles and CO using in-situ transmission electron microscopy (TEM). The SEM, TEM, STEM, and XRD patterns reveal that γ-Al2O3 nanochains, 80 nm in diameter, were uniformly formed on the surfaces of macroscopic ceramic substrates. High-resolution TEM (HTEM) images confirm the polycrystalline and kinking structures connecting the nanochains. The coating thickness of γ-Al2O3 nanochains layer is approximately 100㎛. The EDX images and XPS graphs indicate that Pt nanoparticles, 3.5 nm in diameter, are well-coated on the surfaces of the γ-Al2O3 nanochains. The uniform distribution of Pt nanoparticles is precisely controlled utilizing autogenic pressure reaction. Additionally, in-situ observation significantly highlights the physicochemical phenomena of the γ-Al2O3 nanochains@Pt nanoparticles over time under CO supply at 300 °C. Coke formation was accelerated on the surface of catalysts as increase of CO partial pressure increase, while Pt nanoparticles is very stable without the migration and aggregation.

CO2 sequestration by indirect mineral carbonation of serpentine with (NH4)2SO4 as a recyclable extractant

Mineral carbonation with serpentine can offer a sustainable and safe process option for simultaneous CO2 emission reduction and utilization of nature mineral. In this study, a sustainable process for CO2 mineral sequestration was proposed by using serpentine and ammonium sulfate as feedstocks. The mixture of feedstocks was subjected to roasting with temperature ranging from 390°C to 480°C, converting magnesium into the corresponding sulfate. Then, water leaching was employed to dissolve the magnesium sulfate from the roasted samples. Finally, through a mineralization reaction, the corresponding magnesium bicarbonate was generated after sequestrating CO2. Under the optimal roasting-leaching conditions, i.e. roasting temperature of 420ºC, roasting time of 2 hours, and mass ratio of ammonium sulfate/serpentine of 3; leaching temperature of 80ºC, leaching time of 1 hour, and a liquid-to-solid ratio of 1, the magnesium extraction efficiency reached 76 %. Thermodynamics and experimental results demonstrated that during the sulfation roasting process, the products generated during roasting, magnesium sulfate and silicon dioxide, adhered to the surface of the serpentine, thus inhibiting the mass transfer process and impeding the progress of the reaction. However, the liquid-solid reaction facilitated by molten ammonium sulfate and the gas-solid reaction provided by the decomposition of ammonium salts into SO2 played a promoting role in the sulfation roasting reaction. The carbonation of sulfated serpentine results indicated that the optimal CO2 storage capacity can reach 204 kg/t serpentine.

A monolithic self-supporting ZnFe2O4/ZnO/ZnNi foam photocatalyst and application in the decomposition of gaseous benzene

Volatile organic compounds (VOCs) are major air pollutants which seriously affect ecological environment and pose threats to human health. In this investigation, a monolithic self-supporting ZnFe2O4/ZnO/ZNF(ZFO/ZnO/ZNF) photocatalyst was developed by in-situ growing ZnFe2O4 and ZnO on ZnNi foam (ZNF). Using benzene as a representative of the target gaseous contaminants, the optimal 5ZFO/ZnO/ZNF achieved a 99.8 % removal efficiency and 99.7 % mineralization efficiency within 20 min at an initial benzene concentration of 600 ppm under simulated sunlight irradiation. Moreover, this catalyst presents the lower ullage during gas–solid reaction, and thus enables durable recycling reuse of the photocatalyst, which still retains a 95.8 % benzene decomposition after 30th consecutive run. The mechanism studies reveal that the metal-mediated Z-type heterostructure of ZFO/ZnO/ZNF enhances rapid transportation of the photo-generated electrons and promotes redox potential, leading to the excellent photocatalytic oxidation activity and mineralization efficiency. This study highlights the potential of self-supporting monolithic metal-mediated catalysts and provides a key strategy for effective VOCs degradation.

Simulation analysis of gas-solid two-phase flow and reaction in a novel catalytic cracking reactor

A gas-solid two-phase flow reaction model was developed to evaluate the performance of a novel catalytic cracking reactor in the residue-to-chemicals (RTC) process. Coupled TFM, EMMS drag, and 12-lump kinetic models were employed to simulate the flow reaction process. The reaction temperature and product yields at the reactor exit aligned well with real industrial RTC reactor test results, indicating the reliability and effectiveness of the coupling model. Catalyst particles formed an internal circulation structure in the reactor, increasing the instantaneous catalyst-to-oil ratio. The reactor exhibited low axial and radial temperature gradients with higher reaction temperatures, accelerating the catalytic cracking rate and enhancing the selectivity for high-value products. The effects of the catalyst-to-oil ratio, catalyst inlet temperature, and feedstock mass flow rate on the flow reaction process were optimized. Results showed that both the catalyst-to-oil ratio and catalyst inlet temperature influenced the overall catalyst velocity distribution. Within the limit range, increasing the catalyst-to-oil ratio increased feedstock conversion, gasoline, LPG, dry gas, and coke yields, but decreased diesel yield. Conversely, increasing the feedstock mass flow rate showed opposite trends. Different trends in product yields were observed with varying inlet catalyst temperatures, with optimal product distribution at 973.15 K.

Solvent Vapor/Gas-Induced Guest Transport and Exchange of a Nonporous Organic Crystal to Construct Smart Host-Guest Energetic Materials.

Supramolecular materials with advanced properties constructed by intermolecular interactions have attracted extensive attention in many fields, such as sensing, catalysis, and biomedicine. However, in the field of energetic materials, limited by the tight-packed crystal structure of explosives and the strong intermolecular interaction forces, most supramolecular explosives can only be obtained in organic solution or under extreme external loading (high temperature/high pressure). Given the practical issues such as safety risks, operational difficulties, serious environmental pollution, and large-scale production of the existing technology, a new method of constructing host-guest explosives by solvent vapor/gas induction is proposed. This gas-solid reaction method takes advantage of the metastable properties from the explosives solvate (HNIW/ACN), and cleverly opens a fast channel for gas molecules to enter the explosives cell cavities, which results in the highly efficient preparation of the host-guest explosives (HNIW/CO2 and HNIW/N2O). The embedding of functional gas molecules greatly improves the structural stability and comprehensive performance of the explosive skeleton, and the detonation velocity of HNIW/N2O even reaches 9802 m·s-1, which is higher than that of ε-HNIW (9455 m·s-1). In addition, compared with ε-HNIW, HNIW/CO2 and HNIW/N2O exhibit high energy but low sensitivity, enhanced thermal stability, and combustion properties, which present a potential prospect in the field of energetic materials. The new method effectively overcomes the high-energy barrier of nonporous organic explosives, offering the advantages of simplicity, safety, efficiency, and environmental friendliness. This study provides a valuable pathway for constructing advanced supramolecular energetic materials, which contributes to the enrichment of supramolecular engineering systems.

A kinetic comparison between in situ hybrid microwave and conventional magnetising roasting of low-grade iron ore composite pellet

This article aims to comprehensively summarise the essential aspects of reduction kinetics in magnetising roasting of low-grade iron ore–coal composite pellets in the hybrid microwave and conventional furnace. The influence of crucial process parameters like temperature, time, and heating methods, including traditional and hybrid microwave heating, is explored. Investigating the impact of low-grade iron ore and coal quality on reduction kinetics is conducted to identify optimal heating methods for upgrading low-grade iron ore to blast furnace grade through magnetising roasting. The study uses diverse gas–solid reaction models to assess the reduction mechanism (Fe2O3 to Fe3O4). Results indicate the success of the contracting volume model for microwave heating, while conventional heating transitions from phase-boundary chemical control to diffusion control. XRD confirms magnetite dominance post-reduction, while scanning electron microscopy analysis establishes microwave crack-assisted efficiency over conventional heating for ease of reduction. A comparative study of apparent activation energy reveals the hybrid microwave method's four-fold lower (36.71 kJ/mol) than conventional resistance heating (156.19 kJ/mol). This underscores the potential of microwave heating for enhanced reduction kinetics and low-grade iron ore material processing applications.

Enhanced properties of hard metal WC-Ni processed from nanostructured powders

In this study, we investigated the effects of nanostructured composite powders (WC-Ni), nickel binder content, and sintering techniques on the morphology and mechanical properties of tungsten carbide. An alternative low-temperature gas-solid reaction route with a short reaction time was employed to produce nanostructured composite powders with 5 and 15 wt% Ni. The powders were consolidated using spark plasma sintering (SPS) and conventional vacuum furnace sintering at temperatures of 1350 °C and 1450 °C. The composite powders were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and particle size measurements. The expansion/contraction of the compacted nanocomposite powders was studied through dilatometric analysis. The composite powders exhibited a uniform distribution of Ni, in both compositions. For the WC-5 wt% Ni nanocomposite powders, the average crystallite sizes for WC and Ni were 41.6 nm and 46.2 nm, respectively. While, for the WC-15 wt% Ni nanocomposite, the crystallite sizes for WC and Ni were 45.6 and 38.4 nm. The sintered composites were evaluated through XRD, SEM, measurements of density and Vickers hardness. The enhanced sinterability of the nanostructured powders enabled their consolidation into (WC-Ni) hard metal with densities approaching the theoretical relative density of 96.07 %, even with low binder content (5 wt% Ni). This is attributed to the uniform distribution of Ni and an extensive Ni-WC interface present prior to sintering. The SPS process at 1350 °C produced sintered bodies (WC-5 wt% Ni and WC-15 wt% Ni) with higher Vickers hardness (2322 HV and 1512 HV, respectively) and superior microstructural quality compared to samples produced by conventional vacuum furnace techniques. These results demonstrated that the mechanical properties of the system WC-Ni processed by SPS are superior to those obtained by vacuum furnace. Therefore, WC-Ni hard metals processed by this approach is a promising alternative to conventional hard metals (WC-Co) for a wide range of applications.

The process optimization and exergy efficiency analysis for biogas to renewable hydrogen by chemical looping technology

The study on biogas-Chemical Looping Hydrogen Production (biogas-CLHP) highlights its potential to produce high-purity hydrogen with recycling waste bioenergy. It delves into the gas-solid reaction characteristics and optimizes crucial process parameters for the fixed-bed CLHP system. Movement rate equations for the reaction fronts of Fe2O3-Fe3O4 (Rf1), Fe3O4-FeO (Rf2), and FeO-Fe (Rf3) are formulated, aiding in clarifying CO breakthrough curves. The identified convergence temperatures (Tm) under CO and H2 atmospheres are 916 °C and 907 °C, respectively. Rf1 and Rf2 converged above Tm, which leads to the disappearance of the Fe3O4 region in oxygen carrier (OC) beds. A theoretical model for calculating the reduction solid conversion (Xaver) is established, accurately characterizing Xaver under varying reaction times, H2/CO ratios, and temperatures. By using the Particle Swarm Optimization (PSO) algorithm and thermodynamic analysis, the study determines the optimal length-radius ratio (L/r), reduction temperature (T), and H2/CO ratio (α) for the OC bed as 12.5, 916 °C, and 0.72, respectively, at which a maximum conversion ratio of 43.55 % is achieved. Based on optimal parameters, the results of Aspen simulation reveal energy and exergy efficiencies of 74.9 % and 70.8 %. Generally, this research comprehensively outlines the process dynamics, optimizes key parameters, and evaluates exergy efficiency of the biogas-CLHP system.

Ce(III) formate-derived hierarchical cerium oxide particles with icosahedral symmetry-based architectures: Effect of third level of structural hierarchy in soot and propane oxidation

The article investigates the role of architecture of complex hierarchically structured ceria and gadolinium doped ceria particles in soot combustion (solid-solid reaction) and propane oxidation (gas-solid reaction). Synthesis of hierarchical ceria mesostructures showing icosahedral symmetry-based architecture has been presented for the first time. Carefully choosing synthetic conditions allows to obtain particles with intended morphology of dodecahedron, rhombic hexecontahedron, great stellated dodecahedron, fractal-like branched great stellated dodecahedron and great dodecahemicosacron polyhedra. Twinning-based multiple branching of Ce(III) formate crystals by {101} twin orientation relation was proposed as a driving mechanism for the formation of macroparticles architecture that has been confirmed by the construction of macroparticle models using the identified twinning law. In the catalytic studies, the third level of the material organizational structure referring to shape of hierarchical macroparticles was chosen as a tested variable, while other architecture-related properties were controlled to be alike. In result, the shape of hierarchical particles plays a vital role in the catalytic soot oxidation, and architecture modulation allows the catalytic properties of the material to be enhanced through increasing the geometrical fit between ceria and soot particles. The best sample lowers temperature of half oxidation by 143 °C as compared to non-hierarchically organized ceria nanocrystals. The shape of hierarchical particles does not play leading role in gas-solid propane oxidation, but introduction of Gd dopant diversifies catalytic activity. The architecture of the particles may serve as a modifier of the catalytic activity through grain boundary engineering of gadolinium doped ceria.