Sintering Resistance Research Articles

In-situ reconstruction of LaCoO3-Co3O4 hetero-interface over lanthanum modified Co3O4 nanocatalyst for improved catalytic activity and sintering resistance in methane combustion

Nanoparticles-based catalysts still suffer from deactivation due to sintering and structural collapse through long-time running at high reaction temperature. Developing simple strategy for improving the sintering resistance of nanoparticles is of great importance for fabrication of durable heterogeneous catalysts. In this work, lanthanum was used to prevent Co3O4 nanoparticles from sintering with restricting growth of nanocrystals by in-situ generation of LaCoO3 perovskite phase during thermal ageing process, further building LaCoO3-Co3O4 hetero-interface with strong interfacial effect. Specifically, the Co3O4 nanocatalyst was loaded with different amount of La by traditional impregnation method and a series of characterizations were carried out to explore the physical and chemical properties of the as-prepared catalysts, including XRD, Raman, BET, SEM, HRTEM, XPS, H2-TPR and O2-TPD. It was found that 5 wt% La-Co3O4 has the highest catalytic activity in CH4 combustion and the value of T90 (temperature of 90% methane conversion) between fresh and aged was only 9 ºC, while this value was 108 ºC over pure Co3O4 sample. The Raman, XPS, H2-TPR and O2-TPD results exhibited that the synergistic effect between Co3O4 and LaCoO3 could not only induce lattice distortion in Co3O4 with more defects and adsorbed oxygen species, enhanced oxygen mobility and reducibility, but also significantly suppress the growth of Co3O4 nanocrystals during thermal ageing treatment.

In Situ Reconstruction of Active Heterointerface for Hydrocarbon Combustion through Thermal Aging over Strontium-Modified Co3O4 Nanocatalyst with Good Sintering Resistance.

The issue of catalyst deactivation due to sintering has gained significant attention alongside the rapid advancement of thermal catalysts. In this work, a simple Sr modification strategy was applied to achieve highly active Co3O4-based nanocatalyst for catalytic combustion of hydrocarbons with excellent antisintering feature. With the Co1Sr0.3 catalyst achieving a 90% propane conversion temperature (T90) of only 289 °C at a w8 hly space velocity of 60,000 mL·g-1·h-1, 24 °C lower than that of pure Co3O4. Moreover, the sintering resistance of Co3O4 catalysts was greatly improved by SrCO3 modification, and the T90 over Co1Sr0.3 just increased from 289 to 337 °C after thermal aging at 750 °C for 100 h, while that over pure Co3O4 catalysts increased from 313 to 412 °C. Through strontium modification, a certain amount of SrCO3 was introduced on the Co3O4 catalyst, which can serve as a physical barrier during the thermal aging process and further formation of Sr-Co perovskite nanocrystals, thus preventing the aggregation growth of Co3O4 nanocrystals and generating new active SrCoO2.52-Co3O4 heterointerface. In addition, propane durability tests of the Co1Sr0.3 catalysts showed strong water vapor resistance and stability, as well as excellent low-temperature activity and resistance to sintering in the oxidation reactions of other typical hydrocarbons such as toluene and propylene. This study provides a general strategy for achieving thermal catalysts by perfectly combining both highly low-temperature activity and sintering resistance, which will have great significance in practical applications for replacing precious materials with comparative features.

The Overlooked Potential of Sulfated Zirconia: Reexamining Solid Superacidity Toward the Controlled Depolymerization of Polyolefins.

Closed-loop recycling via an efficient chemical process can help alleviate the global plastic waste crisis. However, conventional depolymerization methods for polyolefins, which compose more than 50% of plastics, demand high temperatures and pressures, employ precious noble metals, and/or yield complex mixtures of products limited to single-use fuels or oils. Superacidic forms of sulfated zirconia (SZrO) with Hammet Acidity Functions (H0) ≤ - 12 (i.e., stronger than 100% H2SO4) are industrially deployed heterogeneous catalysts capable of activating hydrocarbons under mild conditions and are shown to decompose polyolefins at temperatures near 200 °C and ambient pressure. Additionally, confinement of active sites in porous supports is known to radically increase selectivity, coking and sintering resistance, and acid site activity, presenting a possible approach to low-energy polyolefin depolymerization. However, a critical examination of the literature on SZrO led us to a surprising conclusion: despite 40 years of catalytic study, engineering, and industrial use, the surface chemistry of SZrO is poorly understood. Ostensibly spurred by SZrO's impressive catalytic activity, the application-driven study of SZrO has resulted in deleterious ambiguity in requisite synthetic conditions for superacidity and insufficient characterization of acidity, porosity, and active site structure. This ambiguity has produced significant knowledge gaps surrounding the synthesis, structure, and mechanisms of hydrocarbon activation for optimized SZrO, stunting the potential of this catalyst in olefin cracking and other industrially relevant reactions, such as isomerization, esterification, and alkylation. Toward mitigating these long extant issues, we herein identify and highlight these current shortcomings and knowledge gaps, propose explicit guidelines for characterization of and reporting on characterization of solid acidity, and discuss the potential of pore-confined superacids in the efficient and selective depolymerization of polyolefins.

Oxygen Vacancy‐Rich Defects Porous Cu2MgO3/Mg0.78Cu0.22O Composite with Sinter‐Resistant and Highly Reactive for Long‐Duration High‐Temperature Thermochemical Energy Storage

AbstractHigh‐temperature thermochemical energy storage based on metal oxides is the key technology to reducing the levelized costs of electricity of the next‐generation concentrated solar power plants. CuO/Cu2O has wide availability and high energy density, but severe sintering leads to low reactivity. In this study, an innovative approach to modulate the oxygen vacancy content to change the surface properties and crystal structure to enhance the sintering resistance and redox reversibility is proposed. The re‐oxidation degree is increased from 46% to 99%, and the energy release rate is increased by 3.5 times. It remains 99.9% reduction and 97.1% oxidation activity after 3000 cycles, which is very valuable for engineering applications. Cu2MgO3 and Mg0.78Cu0.22O are prone to form oxygen vacancies, which promotes the formation of porous structures. Mg0.78Cu0.22O helps Cu2MgO3/CuO/Cu2O deliver more O through the surface. Mg0.78Cu0.22O is firmly and uniformly dispersed on the CuO/Cu2O surface after long cycling. They have a large binding energy, more charge transfer and enhanced bond energy at the interface. The mechanism of composite in increasing the sintering temperature and long‐term reaction stability is revealed from experimental and theoretical calculations, which provides a new idea for the rational design of thermochemical energy storage materials.

TiO2/MnFe2O4 co-modified alkaline papermaking waste for CaO-CaCO3 thermochemical energy storage

CaO-CaCO3 thermochemical energy storage is a promising technology for solar energy utilization and storage. Alkaline papermaking waste (APW) from paper mills, which is mainly composed of CaCO3. Herein, TiO2/MnFe2O4 co-modified APW was synthesized. The energy storage capacity of TiO2/MnFe2O4 co-modified APW was studied during CaO-CaCO3 thermochemical energy storage cycles in a duel fixed bed reactor. TiO2/MnFe2O4 co-modified APW mainly consists of CaO, MgO, CaTiO3, CaMnO3, and Ca2Fe2O5. The introductions of TiO2 and MnFe2O4 significantly improve the cyclic stability and optical absorption property of APW in 30 cycles. The co-modified APW (the mass ratio for CaO:TiO2:MnFe2O4 = 100:5:5) possesses high sintering resistance, energy storage, and optical absorption capacities in 30 cycles. The energy storage conversion and capacity of the co-modified APW are 0.72 and 2288.57 kJ/kg after 30 cycles, respectively. The optical absorptance of the co-modified APW reaches 49%, which is 9.25 times as high as that of APW. CaTiO3 and CaMnO3 effectively mitigate the sintering of CaO grains. CaMnO3 and Ca2Fe2O5 significantly increase the optical absorptance of APW. The co-modified APW possesses stronger basicity and more oxygen vacancies, which is favourable for the carbonation reaction. Thus, TiO2/MnFe2O4 co-modified APW is a good energy storage material.

Deposition characteristics, sintering and CMAS corrosion resistance, and mechanical properties of thermal barrier coatings by atmospheric plasma spraying

Atmospheric plasma spraying (APS) was used to fabricate 4.5 mol% Y2O3 stabilized ZrO2 (YSZ) and 4.0 mol% Yb2O3 and 0.5 mol% Y2O3 co-stabilized ZrO2 (YbYSZ) series coatings with different spraying parameters. This study presents the effects of particle size of feed powder and substrate temperature on the microstructure and performance of thermal barrier coatings. Single-pass and multi-pass experiments were conducted to explore the relationship between the splat and the coatings. The experimental results indicate that adjusting particle size of feed powders and deposition temperature can alter the splat behaviour and microstructure, improve anti-corrosion and anti-sintering abilities, and enhance the hardness and elastic modulus. Changes in parameters can cause changes in the microstructure of as-sprayed coatings. Lower substrate temperatures can lead to vertical cracks, finer powders can introduce more microdefects, and conventional sized powders can form larger pores. A coating deposited using a conventional feed powder at a substrate temperature of 800 °C shows excellent sintering resistance. A coating deposited using a fine feed powder on 800 °C substrate exhibits the best calcium‑magnesium-alumina-silicate (CMAS) corrosion resistance.

Synthesis of uniform Fe2O3@Y2O3 yolk−shell nanoreactors as chemical looping oxygen carriers

Iron-based materials are extensively employed as oxygen carriers in chemical looping processes, but their long-term performance is often inhibited by sintering and agglomeration. Here, we developed a yolk–shell structured Fe2O3@Y2O3 oxygen carrier, with each unit consisting of a Y2O3 shell encapsulating a nano-sized Fe2O3 core. The Y2O3 shell could protect the redox-active cores from sintering, and the void between the yolk and the shell is capable of tolerating cyclic volume and phase changes. During the simulated chemical looping cycles at 600 °C, the Fe2O3@Y2O3 oxygen carriers exhibit a consistent oxygen carrying capacity of 3 wt% over 50 cycles, without any distinguishable structural deterioration. With rational structure optimization, the Fe2O3@Y2O3 oxygen carriers with porous shell could enhance the mass transfer across the shell and enable higher reaction rates. The satisfactory sintering resistance of the Fe2O3@Y2O3 nanostructure demonstrates the feasibility of employing well defined yolk–shell structured oxygen carriers for chemical looping applications.

Enhanced thermal shock resistance of gradient high-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Ce2O7/YSZ thermal barrier coatings

High-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Ce2O7 (LECO) has been verified as a potential candidate for thermal barrier coatings (TBCs). In this work, two different structured LECO coatings were constructed and the thermal shock behavior was systematically investigated. In the classical double-layered LECO coating (D-LECO), the cracks initially originated from the edge and completely exfoliated from substrate after failure. To strengthen the thermal stress resistance of the coating, a gradient multilayered LECO/YSZ coating (M-LECO) was designed with five ceramic sub-layers. The thermal shock life of M-LECO was greatly enhanced by approximately 4 times. Unlike the typical TBCs, the delamination first appeared at an annular region on the surface, located away from the center and edge. Besides, the spalling only occurred in the topmost LECO layer with a thickness loss of less than 5%. After failure, the underneath coating could still provide efficient thermal protection to substrate. The better thermal shock resistance of M-LECO was mainly attributed to the fine gradient structure of the coating and the intrinsic property of high-entropy LECO. The microhardness and fracture toughness in M-LECO were strengthened layer by layer along the thickness direction, alleviating the thermal stress accumulation in the coating and greatly improving the cracking resistance of the interface. Moreover, the high-entropy effect and sluggish diffusion effect of LECO improved its sintering resistance, thereby enhancing the thermal shock resistance of M-LECO. Such design not only fully utilizes the unique thermo-physical properties of high-entropy ceramics, but also effectively solves the problem of weak adhesion between the LECO and the substrate during thermal shock.

Challenging thermodynamics: combining immiscible elements in a single-phase nano-ceramic

The Hume-Rothery rules governing solid-state miscibility limit the compositional space for new inorganic material discovery. Here, we report a non-equilibrium, one-step, and scalable flame synthesis method to overcome thermodynamic limits and incorporate immiscible elements into single phase ceramic nanoshells. Starting from prototype examples including (NiMg)O, (NiAl)Ox, and (NiZr)Ox, we then extend this method to a broad range of Ni-containing ceramic solid solutions, and finally to general binary combinations of elements. Furthermore, we report an “encapsulated exsolution” phenomenon observed upon reducing the metastable porous (Ni0.07Al0.93)Ox to create ultra-stable Ni nanoparticles embedded within the walls of porous Al2O3 nanoshells. This nanoconfined structure demonstrated high sintering resistance during 640 h of catalysis of CO2 reforming of methane, maintaining constant 96% CH4 and CO2 conversion at 800 °C and dramatically outperforming conventional catalysts. Our findings could greatly expand opportunities to develop novel inorganic energy, structural, and functional materials.

Effect of feedstock powder size on the microstructure and thermal conductivity of quasi-eutectic LaYbZr2O7 TBCs

The effect of average feedstock powder size on the evolution of microstructure and thermal conductivity are comprehensively analyzed. It was found that the porosity and thermal conductivity of the LaYbZr2O7 coatings were positively correlated with the average powder size. The conventional notion that higher porosity results in lower thermal conductivity is challenged by the above results. The abnormal porosity and thermal conductivity relationship can be ascribed to the density of horizontal cracks which dominates the thermal conductivity reduction. Reducing the average powder size leads to a greater concentration of horizontal cracks and hence reduced thermal conductivity. Moreover, the LaYbZr2O7 coatings not only show significantly lower initial thermal conductivity of under 0.70 W m−1 K−1, but also exhibit stronger sintering resistance in terms of porosity stability and thermal insulation ability compared to the conventional YSZ coatings. The present work affords a new insight in developing advanced thermal barrier coatings with ultralow thermal conductivity.

Extraordinary Thermal Stability and Sinter Resistance of Sub-2 nm Platinum Nanoparticles Anchored to a Carbon Support by Selenium.

Nanoparticle sintering has long been a major challenge in developing catalytic systems for use at elevated temperatures. Here we report an in situ electron microscopy study of the extraordinary sinter resistance of a catalytic system comprised of sub-2 nm Pt nanoparticles on a Se-decorated carbon support. When heated to 700 °C, the average size of the Pt nanoparticles only increased from 1.6 to 2.2 nm, while the crystal structure, together with the {111} and {100} facets, of the Pt nanoparticles was well retained. Our electron microscopy analyses suggested that the superior resistance against sintering originated from the Pt-Se interaction. Confirmed by energy-dispersive X-ray elemental mapping and electron energy loss spectra, the Se atoms surrounding the Pt nanoparticles could survive the heating. This work not only offers an understanding of the physics behind the thermal behavior of this catalytic material but also sheds light on the future development of sinter-resistant catalytic systems.

Structural reconfiguration of Al/CaO adsorbent by Ni doping to improve sintering resistance and arsenic removal performance

CaO-based adsorbents have poor adsorption performance due to high temperature sintering. In this study, a trace amount of Ni was added to an Al/CaO adsorbent using the Pechini hydrothermal method and anhydrous grinding method. The modified adsorbent was then used to remove As2O3, and both experimental and theoretical approaches were employed. The experimental results showed that the addition of Ni transformed the surface of the adsorbent from a two-dimensional network structure to a three-dimensional cluster structure, significantly increasing its specific surface area and improving its adsorption capacity for As2O3. The adsorption capacity reached 933.1 mg/kg at 900 °C, which was 3.79 times higher than that of pure CaO and 8.2 times higher than that of Al2O3. Additionally, the presence of nano-scale NiO particles prevented the sintering of CaO grains, allowing the adsorbent to maintain its pore structure even after the reaction. Density functional theory (DFT) calculations showed that NiO was the most active site for As2O3 adsorption on the surface of Al/Ni-CaO. Ni acted as an electron transport bridge, enhancing electron transfer on the material's surface and increasing adsorption energy. These findings are important for future research on high-temperature removal of As2O3 with doped CaO-based adsorbents.

Recent advances in promoting dry reforming of methane using nickel-based catalysts

The achievements of dry reforming of methane over Ni-based catalysts are presented with focus on the modification factors to enhance sintering and coking resistance, elaborated in the context of support, promoter, and preparation.

Simultaneous achievement of high performance and low sintering temperature in ultra-high Curie temperature La2Ti2O7 ceramics by V2O5 additive

This study uses V2O5 as a sintering aid for La2Ti2O7 ceramics, lowering the sintering temperature, increasing density and resistivity, enhancing piezoelectric performance and maintaining thermal stability.

Incomplete charge transfer bestows significant sintering resistance for metal nanoparticles on two-dimensional graphyne

The significant sintering resistance of supported nanoparticles on hydrogen-substituted graphyne (HsGY) originates from the Ostwald ripening (OR) mechanism due to strong incomplete charge transfer interaction (ICTI).

Fracture resistance of binderless tungsten carbide consolidated by spark plasma sintering and flash sintering

Binderless tungsten carbide (WC) consolidated by spark plasma sintering (SPS) and electrical resistance flash sintering (ERFS) has emerged as a promising alternative to materials obtained by traditional sintering methods. In this study, we investigated the influence of SPS and ERFS techniques on the mechanical properties of binderless WC. Hardness, indentation fracture resistance and elastic modulus were compared and analysed with respect to the microstructure of the resulting material. The results show that SPS tungsten carbide is harder, stiffer and denser when compared to the material produced by ERFS. Nevertheless, the fracture resistance of SPS ceramics was limited due to the lack of macroscopic toughening mechanisms. Conversely, flash-sintered tungsten carbide, consolidated by ERFS, possesses unique biphasic WC/W2C microstructures that promote crack deflection and bridging toughening mechanisms. Additionally, flash-sintered materials exhibit a more ductile character and are characterised by a lower effect of the strain gradient on the material plasticity upon indentation. This study provides valuable insights into the mechanical properties of ultra-hard monolithic ceramics, such as WC, influenced by ultrafast/flash sintering techniques.

Enhancing cyclic durability in CaO-based thermochemical energy storage by Zr–Y co-doping: Mechanistic insights

The CaCO3/CaO materials are promising materials for thermochemical energy storage. However, they suffer from rapidly decreasing energy storage density over multiple calcination/carbonation cycles. This paper aims to select suitable inert supports with cyclic stability enhancement for the calcium looping (CaL) process at high carbonation reaction temperatures (＞800 °C). Firstly, four metallic elements (Zr, Mn, Y and Ce) were selected, and a single-doping strategy was used to screen out single-doping inert supports. By comparison, the 20Ca–Zr had the best energy storage performance, with an energy storage density (Eg,N=30) of 1744.72 kJ/kg after 30 cycles. Subsequently, the co-doping method was applied to further screen out co-doped combinations with long-term cyclic stability potential. The Zr was co-doped with Mn, Y and Ce, respectively. Among them, the 20Ca-0.5Zr-0.5Y displayed the best cyclic stability with an average energy storage density (Eg,av) of 1950.69 kJ/kg in 30 cycles. Based on the chosen Zr–Y co-doped CaO-based composite, the doping concentration optimization and multiple cycles tests were carried out. The effective conversion (Xeff) of 10Ca-0.5Zr-0.5Y decreased by only 4.9 % after 60 cycles. Therefore, the Zr–Y co-doped CaO-based composite, possessing robust sintering resistance effects, is promising for long-term TCES technology.

Modulation of Rh species in Rh/Al2O3/FeCrAl-foam structured catalysts for steam reforming of toluene

Steam reforming of tar is an appealing way for tar elimination during biomass gasification. In this work, structured Rh/Al2O3 supported on FeCrAl-foam catalysts with different Rh species contents (Rh0, RhiOx and Rh(AlO2)y) were modulated through calcination and/or reduction at different temperatures for toluene steam reforming. Among all the structured catalysts and conventional supported catalysts, the structured Rh/Al2O3/FeCrAl-foam catalyst, calcined in air at 300 °C followed by reduction with hydrogen at 600 °C, showed superior activity as well as excellent resistance to sintering and coke deposition. Such high performance can be attributed to the suitable Rh0/RhiOx ratio as well as the enhanced mass transfer capability. The integrated studies of controlled catalytic tests, catalyst characterizations, TPSR, H2O-TPD and in-situ DRIFTS revealed that metallic Rh0 site was responsible for the cleavage of the C-C/C-H bonds in toluene. The activate ability of H2O was governed by the Rh0/RhiOx ratio, while the RhiOx specie played a significant role, which further promotes the reaction activity and eliminate coke deposition. Furthermore, the RhiOx specie enable the catalyst with high sintering resistance, due to the strong affinity to the Al2O3 surface. However, the Rh(AlO2)y specie was inactive. The catalytic performance was controlled by balancing the toluene activation and H2O dissociation. Consequently, rational tuning of these species is crucial for obtaining high-performance Rh/Al2O3 catalysts for steam reforming of toluene.

Effect of multi-component at the A site on the thermophysical properties of high entropy niobates

A series of high entropy niobates with cation at A-site varying in size disorder and mass disorder is designed. High entropy niobates are all monoclinic structures with uniform rare-earth element distribution, but different space groups, which are closely related to the average radius at A-site. High entropy niobates possess excellent sintering resistance and ultra-low thermal conductivity due to stronger phonon-point defect scattering and shorter phonon lifetime. The effect of high entropy on average grain size and thermal conductivity is inversely proportional to size disorder. Moreover, the radiative heat transfer of (Dy0.2Ho0.2Er0.2Y0.2Yb0.2)NbO4 is substantially reduced due to the co-doping of active multi-component Dy3+, Er3+, and Yb3+, which broadens the range of intrinsic absorption band and improves lattice absorption derived from lattice distortion. Besides, the (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4 exhibits an ultra-high thermal expansion coefficient (12.34 ×10−6 K−1, 673 °C). The excellent thermophysical properties imply that high entropy niobates are more promising thermal barrier coating materials.

Amorphous CeOx Islands on Dealuminated Zeolite Beta to Stabilize Pt Nanoparticles as Efficient and Antisintering Catalysts for Propane Dehydrogenation.

Pt-based catalysts have been widely used in propane dehydrogenation due to their superior activation of C-H bonds and weak scission of C-C bonds. However, in the process of repeated calcination to remove deposited coke, the active Pt species tend to sinter, resulting in a significant decline in catalytic activity. In this study, amorphous CeOx islands loaded on dealuminated Beta zeolite were prepared via simple wetness impregnation. Then, partially embedded Pt nanoparticles in CeOx islands were obtained after reduction owing to the affinity of CeOx for Pt. In the propane dehydrogenation reaction, Pt/Ce5-SiBeta with a Ce loading of 4.55 wt % and Pt loading of 0.72 wt % exhibited the highest activity and the lowest inactivation constant at 550 °C. More importantly, due to the anchoring effect of CeOx on Pt, the catalytic activity of Pt could be recovered after a simple calcination-reduction regeneration process, avoiding the chlorination treatment for the redispersion of Pt species used in industry. In addition, to improve the selectivity of the Pt/Ce5-SiBeta catalyst, a PtSn/Ce5-SiBeta catalyst with excellent activity, selectivity, and recycling stability has been prepared by introducing Sn into Pt/Ce5-SiBeta. The use of amorphous CeOx islands to improve the sintering resistance of Pt opens up new prospects for the design of stable industrial dehydrogenation catalysts.