Bulk Characterization Research Articles

A review on processing and characterization of bulk functionally graded polymer materials

Functionally Graded Polymer Materials (FGPMs) have received much interest in replacing conventional composites due to their multifunctional properties and microstructural variation of desired materials to enhance performance for specific applications. In addition, these are recognized for their build with varying compositions in a smooth gradient throughout its structure and the possibility of stress reduction due to the absence of sharp interfaces compared to conventional homogenous structures. Recently, the contribution of FGPMs with multiple material combinations for various applications in materials science and engineering has attracted many researchers, and its awareness has led to significant advancements in processing techniques. This study reviews recent developments in processing techniques and conventional attempts made to prepare bulk FGPMs. Further, the mechanical, thermal, electrical, and other characterizations of prepared FGPM structures and their related properties are addressed. Also, their applications in exciting fields include dielectrics, radiation shielding, vibration damping, and bio-medical fields, are highlighted.

Fabrication and characterization of bulk conducting bamboo

Fabrication and characterization of bulk conducting bamboo

Expanding the Analytical Window for Biochar Speciation: Molecular Comparison of Solvent Extraction and Water-Soluble Fractions of Biochar by FT-ICR Mass Spectrometry.

Biochar, a low-density yet carbon-rich material derived from different organic materials pyrolyzed under low or no oxygen conditions, has been widely studied as a soil amendment, for greenhouse gas mitigation and in remediation of trace element-contaminated soils. Molecular speciation of biochar compounds has been challenging due to low solubility, aggregation, and immense compositional polydispersity that challenges nearly all mass spectrometry methods routinely applied to carbon-based organic materials. Through a combined technique approach that applies advanced analytical strategies, we provide bulk and molecular characterization of Kentucky bluegrass biochar that can be applied to any biomass or biochar sample. First, we characterize Kentucky bluegrass biochar chemical functional groups by solid-state magic-angle spinning dynamic nuclear polarization NMR (MAS-DNP NMR) and resolve aromatic and aliphatic signals from the pyrogenic material and intact plant material. Next, we isolate water-soluble biochar species by solid-phase extraction followed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and identify highly polar, oxygen species across a wide carbon number range. Solvent fractionation of biochar further expands the compositional range and identifies condensed polycyclic aromatic species across nonpolar and polar classes detected by two ionization modes (-ESI and +APPI) by FT-ICR MS. Plotting biochar species with DBE versus carbon number highlights the pericondensed molecular structural motif that persists across numerous heteroatom classes and ionization modes. To the best of our knowledge, this is the first molecular level identification of nonfunctionalized PAHs in biochar extracts by APPI FT-ICR MS. Thus, we identify biochar species that span the same compositional space as coal, heavy oil asphaltenes, and coal tar and correspond to condensed ring PAHs.

The Study of C3H6 Impact on Selective Catalytic Reduction by Ammonia (NH3-SCR) Performance over Cu-SAPO-34 Catalysts

In present work, the catalytic performance of Cu-SAPO-34 catalysts with or without propylene during the NH3-SCR process was conducted, and it was found that the de-NOx activity decreased during low temperature ranges (<350 °C), but obviously improved within the range of high temperatures (>350 °C) in the presence of propylene. The XRD, BET, TG, NH3-TPD, NOx-TPD, in situ DRIFTS and gas-switch experiments were performed to explore the propylene effect on the structure and performance of Cu-SAPO-34 catalysts. The bulk characterization and TG results revealed that neither coke deposition nor the variation of structure and physical properties of catalysts were observed after C3H6 treatment. Generally speaking, at the low temperatures (<350 °C), active Cu2+ species could be occupied by propylene, which inhibited the adsorption and oxidation of NOx species, confining the SCR reaction rate and causing the deactivation of Cu-SAPO-34 catalysts. However, with the increase of reaction temperatures, the occupied Cu2+ sites would be recovered and sequentially participate into the NH3-SCR reaction. Additionally, C3H6-SCR reaction also showed the synergetic contribution to the improvement of NOx conversion at high temperature (>350 °C).

Operando bulk and interfacial characterization for electrochemical energy storage: Case study employing isothermal microcalorimetry and X-ray absorption spectroscopy

The global shift to electricity as the main energy carrier will require innovation in electrochemical energy storage (EES). EES systems are the key to the “electron energy economy,” minimizing losses and increasing reliability between energy supply and demand. However, steep challenges such as cost, cycle/calendar life, energy density, material availability, and safety limit widespread adoption of batteries for large-scale grid and vehicle applications. Battery innovation that meets today’s challenges will require new chemistries, which can originate from understanding charge transport phenomena at multiple time and length scales. The advancement of operando characterization can expedite this progress as changes can be observed during battery function. This article highlights progress in bulk and interfacial operando characterization of batteries. Specifically, a case study involving Fe3O4 is provided demonstrating that combining X-ray absorption spectroscopy and isothermal microcalorimetry can provide real-time characterization of productive faradaic redox processes and parasitic interfacial reactions during (de)lithiation.Graphic abstract

Investigating the Cold Plasma Surface Modification of Kaolin- and Attapulgite-Bound Zeolite A

Hydrophilic zeolites with low catalytic activity are considered as suitable adsorbents for drying gas streams containing olefinic compounds. In this contribution, the surface treatment of kaolin and attapulgite/zeolite A extrudates is investigated using argon glow discharge plasma. The zeolite is synthesized from kaolin using the hydrothermal method. Surface and bulk characterization is performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 physisorption, Fourier-transform infrared (FT-IR) spectroscopy, temperature-programmed-desorption (TPD) of NH3 and X-ray photoelectron spectroscopy (XPS) techniques. Plasma treatment increases surface area and pore volume, but it decreases the weak acidic site density of the extrudates. The obtained results show that attapulgite/zeolite extrudates are more affected by plasma treatment than kaolin/zeolite extrudates. The catalytic activity of untreated and plasma-treated extrudates are compared with respect to coke formation resulting from 1-butene and 1,3-butadiene. The plasma-treated sample is more resistant to coke formation (∼35% decrease compared to untreated one). The potassium contents of extrudates decreased as a result of sputtering loosely bound potassium cations on the crystal surface by argon ions, which led to a decrease in water sorption capacity (by ∼15% of the initial sorption capacity).

Isostructural M 2pt (M = Al, Ga, In, Sn) As OER Anode Materials

Looking for the future energy infrastructure, hydrogen will play an important role as energy carrier molecule. Among different physical and chemical methods of hydrogen production, water electrolysis has numerous advantages. However, the sluggish kinetics of anodic oxygen evolution reaction (OER) hinders its large-scale implementation. The intensive search for new OER electrocatalytic materials is limited by harsh oxidative conditions and instability/ changes of electrocatalyst under reaction conditions. Platinum is characterized by pronounced stability against dissolution compared to other noble metals. However, the OER activity of Pt is one of the lowest one. Combining the platinum with main group elements in form of M 2Pt intermetallic compound will lead to the different electronic state of Pt and, correspondingly, different OER activity.The compounds M2 Pt (M = Al, Ga, In, Sn) crystallize with cubic anti-CaF2 type of crystal structure [1]. Due to the pronounced charge transfer from M to Pt, Pt atoms are negatively charged in these compounds. There is only one type of strongly polar covalent interactions between M and Pt atoms. The OER activity decreases in the following sequence In2Pt > Ga2Pt > Al2Pt. This trend is governed by the chemical nature of the counterpart elements M (M = Al, Ga, In) and their leaching rates under OER conditions. The leaching of M into the electrolyte leads to formation of composite material of intermetallic M2 Pt and Pt-rich phase in the near-surface region. The inactivity of Sn2Pt is due to the formation of passivating SnO2 layer with poor electrical conductivity.The study of OER activity of M 2Pt materials under different electrochemical treatments was combined with surface- and bulk characterization of electrodes after electrochemical experiments, elemental analysis of electrolyte and quantum chemical calculations. This allows to investigate the influence of chemical nature of counterpart element M onto the OER performance of isostructural M 2Pt electrode materials [2].[1]. Antonyshyn, I., Barrios Jiménez, A.M., Sichevych, O., Burkhardt, U., Veremchuk, I., Schmidt, M., Ormeci, A., Spanos, I., Tarasov, A., Teschner, D., Algara-Siller, G., Schlögl, R., Grin, Yu. // Angew. Chem. Int. Ed. 59, 16770–16776 (2020).[2]. Barrios Jiménez, A.M., Burkhardt, U., Altendorf, S.G., Kaiser, F., Veremchuk, I., Ormeci, A., Auffermann, G., Antonyshyn, I., Grin, Yu., submitted.

Design and Testing of a New Cooling System using Solid Nitrogen for Pulsed Field Magnetization and Characterization of HTS Bulks

Solid Nitrogen (SN2) can provide a uniform and stable cryogenic environment for High Temperature Superconducting (HTS) systems such as bulk samples during their magnetization and/or characterization. In this paper, a SN2 cooling system consisting of a cryocooler Sumitomo CH-110 and an exchanger in a Liquid Nitrogen (LN2) bath is studied. In order to design this cooling system, an analytical model based on a nodal method coupled to a formulation of the thermal capacity was realized. The model considers the thermal parameters variation as well as the phase change of the Nitrogen. In order to compare our results, we performed a 3D simulation on COMSOL Multiphysics. The performance of the cooling system was evaluated by measurements and we estimate that 10 L of LN2 can be cooled down to 25 K in 45 hours.

Coupling Long‐Range Raman with X‐Ray Photoelectron Spectroscopy for Complementary Bulk and Surface Characterization of Battery Materials

AbstractFor the combined surface and bulk characterization of functional powder materials, we report on the direct coupling of Raman spectroscopy with X‐ray photoelectron spectroscopy (XPS) within one setup, avoiding the influence of different sample states and measurement environments. Our approach is based on the Raman integration into the XPS analysis chamber, employing a long‐range camera objective connected to a portable 532 nm Raman spectrometer. For optimization of the measurement geometry, a (400) single crystal (SC), chemical vaper deposition (CVD)‐grown diamond was employed. The applicability of the combined XPS‐Raman spectroscopy approach was first validated by measurements on powder V2O5, used as a commercial standard, and then demonstrated on lithium ion battery materials, that is, LixV2O5 lithium pentoxides. The transferability to other XPS systems is strongly facilitated by the long‐range Raman‐spectroscopic approach, which allowed for Raman analysis over a distance of 320 mm for the CVD‐grown (400) single crystal diamond and 285 mm for LixV2O5. Our results demonstrate the inexpensive and straightforward implementation of coupled XPS‐Raman spectroscopy for combined surface/bulk analysis.

Hard X-Ray Nanotomography for 3D Analysis of Coking in Nickel-Based Catalysts.

Understanding catalyst deactivation by coking is crucial for knowledge‐based catalyst and process design in reactions with carbonaceous species. Post‐mortem analysis of catalyst coking is often performed by bulk characterization methods. Here, hard X‐ray ptychographic computed tomography (PXCT) was used to study Ni/Al2O3 catalysts for CO2 methanation and CH4 dry reforming after artificial coking treatment. PXCT generated quantitative 3D maps of local electron density at ca. 80 nm resolution, allowing to visualize and evaluate the severity of coking in entire catalyst particles of ca. 40 μm diameter. Coking was primarily revealed in the nanoporous solid, which was not detectable in resolved macropores. Coke formation was independently confirmed by operando Raman spectroscopy. PXCT is highlighted as an emerging characterization tool for nanoscale identification, co‐localization, and potentially quantification of deactivation phenomena in 3D space within entire catalyst particles.

Diffusional and Partitionless Ferrite‐to‐Austenite Phase Transformations during Intercritical Annealing of Medium‐Mn Steels

Experimental research on intercritical annealing of a cold‐rolled Fe–7Mn steel with ultralow carbon concentration is presented, providing insight into the efficacy of generating Mn‐enriched austenite during relatively short (≈1000 s) heat treatments compared with batch annealing, as well as the phase transformation mechanisms that can occur during intercritical annealing. It is shown through both bulk characterization and electron microscopy in conjunction with energy‐dispersive X‐ray spectroscopy that Mn partitioning to austenite occurs via diffusional, partitioning growth of austenite during these shorter treatments and that the intercritical temperature influences the level of Mn enrichment in austenite. Evidence of massive (partitionless) and diffusional (partitioning) transformations of ferrite to austenite occurring simultaneously in a single sample are also shown along with a thermodynamic rationale for this occurrence, which is suggested to be related to residual Mn‐banding that develops during solidification.

Absence of moment fragmentation in the mixed B -site pyrochlore Nd2GaSbO7

Nd-based pyrochlore oxides of the form Nd$_{2}B_{2}$O$_{7}$ have garnered a significant amount of interest owing to the moment fragmentation physics observed in Nd$_{2}$Zr$_{2}$O$_{7}$ and speculated in Nd$_{2}$Hf$_{2}$O$_{7}$. Notably this phenomenon is not ubiquitous in this family, as it is absent in Nd$_{2}$Sn$_{2}$O$_{7}$, which features a smaller ionic radius on the $B$-site. Here, we explore the necessary conditions for moment fragmentation in the Nd pyrochlore family through a detailed study of the mixed $B$-site pyrochlore Nd$_{2}$GaSbO$_{7}$. The $B$-site of this system is characterized by significant disorder and an extremely small average ionic radius. Similarly to Nd$_{2}$Sn$_{2}$O$_{7}$, we find no evidence for moment fragmentation through our bulk characterization and neutron scattering experiments, indicating that chemical pressure (and not necessarily the $B$-site disorder) plays a key role in the presence or absence of this phenomenon in this material family. Surprisingly, the presence of significant $B$-site disorder in Nd$_{2}$GaSbO$_{7}$ does not generate a spin glass ground state and instead the same all-in-all-out magnetic order identified in other Nd pyrochlores is found here.

Fabrication and characterization of a bulk micromachined polysilicon piezoresistive accelerometer

This paper presents the fabrication and characterization of a MEMS bulk micromachined piezoresistive accelerometer. For transduction of acceleration into output voltage, polysilicon piezoresistors are used. Due to cost effectiveness, polysilicon piezoresistors are preferred over SOI-based silicon piezoresistors. The accelerometer is designed using FEM-based MEMSCAD tool CoventorWare®. The accelerometer sensor is realized using a hybrid approach, consisting of wet and dry bulk micromachining techniques. The developed sensor is characterized for static and dynamic performance using nano-indenter and electrodynamic shaker, respectively. From static characterization, stiffness and natural frequency are found to be 7.25 kN/m and 6.78 kHz, respectively. From dynamic characterization, bandwidth and sensitivity are found to be 475 Hz and 10 mV/V/g, respectively.

Dielectric Barrier Discharge (DBD) Plasma Coating of Sulfur for Mitigation of Capacity Fade in Lithium-Sulfur Batteries.

Sulfur particles with a conductive polymer coating of poly(3,4-ethylene dioxythiophene) "PEDOT" were prepared by dielectric barrier discharge (DBD) plasma technology under atmospheric conditions (low temperature, ambient pressure). We report a solvent-free, low-cost, low-energy-consumption, safe, and low-risk process to make the material development and production compatible for sustainable technologies. Different coating protocols were developed to produce PEDOT-coated sulfur powders with electrical conductivity in the range of 10-8-10-5 S/cm. The raw sulfur powder (used as the reference) and (low-, optimum-, high-) PEDOT-coated sulfur powders were used to assemble lithium-sulfur (Li-S) cells with a high sulfur loading of ∼4.5 mg/cm2. Long-term galvanostatic cycling at C/10 for 100 cycles showed that the capacity fade was mitigated by ∼30% for the cells containing the optimum-PEDOT-coated sulfur in comparison to the reference Li-S cells with raw sulfur. Rate capability, cyclic voltammetry, and electrochemical impedance analyzes confirmed the improved behavior of the PEDOT-coated sulfur as an active material for lithium-sulfur batteries. The Li-S cells containing optimum-PEDOT-coated sulfur showed the highest reproducibility of their electrochemical properties. A wide variety of bulk and surface characterization methods including conductivity analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and NMR spectroscopy were used to explain the chemical features and the superior behavior of Li-S cells using the optimum-PEDOT-coated sulfur material. Moreover, postmortem [SEM and Brunauer-Emmett-Teller (BET)] analyzes of uncoated and coated samples allowed us to exclude any significant effect at the electrode scale even after 70 cycles.

(Invited) Interplay between Surface/Porosimetric, Chemical and Electrochemical Characterization of “Core-Shell” High-Pt ORR Electrocatalysts

A critical bottleneck of PEMFC operation is the performance of the cathode electrode, where the oxygen reduction reaction (ORR) takes place. Two of the most important phenomena that conspire to curtail the cathode performance are: (i) the sluggish kinetics of the oxygen reduction reaction (ORR) [1]; and (ii) the mass transport issues. In particular, the latter become progressively more evident as the current density of the PEMFC is increased upon approaching operating conditions that are relevant for practical applications [2].Both of these shortcomings are addressed by developing new ORR electrocatalysts (ECs). The ECs described here exhibit a “core-shell” morphology: a hierarchical graphene-based support (H-GR) “core” is covered by a carbon nitride “shell” stabilizing the active sites in “coordination nests” [3]. The “core” comprises highly defected graphene nanoplatelets [4] and carbon black nanoparticles; the latter act as spacers and facilitate the charge and mass transport phenomena occurring during the EC operation. The ECs proposed here are characterized by a significant loading of platinum (on the order of ca. 20-40 wt%), that is the “active metal”. Ni and Cu are introduced as the “co-catalysts” to further boost the ORR kinetics of the ECs [3]. The high loading of “active metal” and “co-catalyst” in the ECs is meant to minimize the bulk of the support, facilitating mass transport phenomena.The innovative support of the proposed ECs is very different from that typically adopted in the state of the art in terms of morphology and especially porosity. Thus, this latter feature is to be studied in detail to fully exploit the potential of such support and guide the synthesis of new ECs beyond today’s state of the art. This information is achieved by a comprehensive characterization of the proposed ECs by a variety of porosimetric methods involving the adsorption of suitable probe molecules.Physisorption of N2 is carried out to evaluate the specific surface area of the ECs, together with their micro- and mesoporosity. Water adsorption is executed as well, being a crucial tool to elucidate the hydrophobicity of the ECs. Indeed, the latter feature is critical to prevent electrode flooding during PEMFC operation. Furthermore, through the study of the real ECs’ density a new parameter is proposed, namely the surface area per volume “Σ” (expressed as m2/cc). This latter is of paramount importance to design efficient membrane electrode assemblies (MEAs).As a final step, the results of morphologic/porosimetric studies are correlated with: (i) the outcome of both bulk and surface chemical characterizations carried out by CHNS microanalysis, energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS); and (ii) the “ex-situ” intrinsic ORR performance and selectivity in the 4-electron mechanism determined by cyclic voltammetry with the thin-film rotating ring-disk method (CV-TF-RRDE). Acknowledgements The research leading to the results reported in this work has received funding from: (a) the European Union’s Horizon 2020 research and innovation programme under grant agreement 881603; (b) the project “Advanced Low-Platinum hierarchical Electrocatalysts for low-T fuel cells” funded by EIT Raw Materials; and (c) the project “Hierarchical electrocatalysts with a low platinum loading for low-temperature fuel cells e HELPER” funded by the University of Padova.

Investigating the Cycling Stability of Fe2WO6 Pseudocapacitive Electrode Materials.

The stability upon cycling of Fe2WO6 used as a negative electrode material for electrochemical capacitors was investigated. The material was synthesized using low temperature conditions for the first time (220 °C). The electrochemical study of Fe2WO6 in a 5 M LiNO3 aqueous electrolyte led to a specific and volumetric capacitance of 38 F g−1 and 240 F cm−3 when cycled at 2 mV·s−1, respectively, associated with a minor capacitance loss after 10,000 cycles. In order to investigate this very good cycling stability, both surface and bulk characterization techniques (such as Transmission Electron Microscopy, Mössbauer spectroscopy, and magnetization measurements) were used. Only a slight disordering of the Fe3+ cations was observed in the structure, explaining the good stability of the Fe2WO6 upon cycling. This study adds another pseudocapacitive material to the short list of compounds that exhibit such a behavior up to now.

Multi-Technique Investigation of a Biomimetic Insect Tarsal Adhesive Fluid

There is substantial motivation to develop novel adhesives which take advantage of the superior adhesive strength and adaptability of many natural animal adhesives; however, the tools typically used to study these mechanisms are incapable of determining the precise interactions of molecules at an adhesive interface. In this study, a surface specific, order sensitive vibrational spectroscopy called sum frequency generation (SFG) is, for the first time, combined with multiple bulk characterization techniques to examine a novel, simple biomimetic adhesive fluid inspired by tarsal fluid of insects. Insects perform complex adhesive demands, including sticking, climbing vertically and running upside-down with little difficulty. Thus, we hypothesize that both bulk and surface specific properties of the fluid contribute to the success of this wet adhesive mechanism. SFG spectra of biomimetic emulsion exhibited similar hydrocarbon organization on hydrophobic and hydrophilic substrates to natural beetle fluid previously studied with the same method. Bulk characterization techniques indicated that the emulsion had a shear-thinning profile with the ability to enhance traction forces during climbing and low surface tension ideal for surface wetting on the majority of natural surfaces. Multi-technique comparisons between emulsion and pure squalane revealed that a hydrocarbon only based fluid could not replicate the traction promoting properties of the emulsion. We conclude that the insect tarsal fluid adhesive mechanism relies upon contributions from both surface-specific properties optimizing traction force and bulk properties promoting rapid surface wetting and maintaining pull-off force for fast detachment.

Highly selective production of syngas (>99%) in the partial oxidation of methane at 480 °C over Pd/CeO2 catalyst promoted by HCl

The partial oxidation of methane (POM) is an attractive catalytic route for producing syngas (CO/H2), although there are problems to overcome such as high reaction temperature (>650 °C) and the deactivation of the catalyst due to the coke formation. We addressed the problem by including HCl in the POM over a Pd/CeO2 catalyst. Pd/CeO2 produces CO, CO2, and coke with low CO selectivity in the absence of HCl, while it converts methane to chlorinated products at below 450 °C in the presence of HCl. At above 480 °C, however, highly selective CO (>99%) is produced over Pd/CeO2 via the POM. Moreover, it is found that coke is not formed during the reaction, leading to the stable partial oxidation activity and selectivity up to 40 h. Both surface and bulk characterization results strongly propose that HCl plays an essential role in transforming Pd/CeO2 into (PdClx + Pd0)/CeOCl (0 < x ≤ 2), which provides the ideal environment for the catalytic route of the POM.

Raman Fingerprint of Extracellular Vesicles and Conditioned Media for the Reproducibility Assessment of Cell-Free Therapeutics.

Extracellular Vesicles (EVs) and Conditioned Medium (CM) are promising cell-free approaches to repair damaged and diseased tissues for regenerative rehabilitation purposes. They both entail several advantages, mostly in terms of safety and handling, compared to the cell-based treatment. Despite the growing interest in both EVs and CM preparations, in the light of a clinical translation, a number of aspects still need to be addressed mainly because of limits in the reproducibility and reliability of the proposed protocols. Raman spectroscopy (RS) is a non-destructive vibrational investigation method that provides detailed information about the biochemical composition of a sample, with reported ability in bulk characterization of clusters of EVs from different cell types. In the present brief report, we acquired and compared the Raman spectra of the two most promising cell-free therapeutics, i.e., EVs and CM, derived from two cytotypes with a history in the field of regenerative medicine, adipose-derived mesenchymal stem/stromal cells (ASCs) and dermal fibroblasts (DFs). Our results show how RS can verify the reproducibility not only of EV isolation, but also of the whole CM, thus accounting for both the soluble and the vesicular components of cell secretion. RS can provide hints for the identification of the soluble factors that synergistically cooperate with EVs in the regenerative effect of CM. Still, we believe that the application of RS in the pipeline of cell-free products preparation for therapeutic purposes could help in accelerating translation to clinics and regulatory approval.

Impact of dual calcium and manganese substitution of La-deficient perovskites on structural and related catalytic properties: Future opportunities in next three-way-catalyst generation?

The impact of La-deficiency and substitution by calcium and manganese in LaFeO3 has been investigated in Three-Way-Catalysis. Despite significant structural distortions, predominantly induced by calcium substitution, no significant phase segregation occurs. On the other hand, bulk and surface characterization revealed the stabilization of Mn4+ and Fe4+ in different extent. Kinetic analysis of CO and propene oxidation reactions and the NO reduction reaction showed that La0.7Fe0.8Mn0.2O3 exhibits the best performance. By contrast, a detrimental effect of calcium more pronounced for propene oxidation is observed. It was found that catalytic properties are neither related to bulk properties nor to the extent of specific surface area but are mostly governed by the redox couple Mn4+/Mn3+. The formation of Fe4+ improving with partial substitution of La by Ca in A-site was not found as a determining criterion.