Catalytic Hydrogenation of Acetic Acid to Acetaldehyde: Synergistic Effect of Bifunctional Co/Ce‐Fe Oxide Solid Solution Catalysts

The large‐scale industrial production of acetic acid (HAc) from carbonylation of methanol has enabled intense research interest from direct hydrogenation of HAc to acetaldehyde (AA). Herein, a series of cerium‐iron oxide solid solution supported metallic cobalt catalysts were prepared by modified sol‐gel method and were applied in gas‐phase hydrogenation of HAc to AA. A synergistic effect between the hydrogenation metal cobalt and Ce‐Fe oxide solid solution is revealed. Specifically, oxygen vacancies provide the active sites for adsorption of HAc, while highly uniformly dispersed metallic Co adsorbs H₂ and activates the reduction of HAc into AA. Moreover, the metallic Co can also assist the cyclical conversion between Fe³⁺/Fe²⁺ and Ce³⁺/Ce⁴⁺ on the surface of Ce_1‐xFe_xO_2‐δ supports. The unique effect substantially enhances the ability of the support material to rapidly capture oxygen atoms from HAc. It is found that the catalyst of 5% Co/Ce_0.8Fe_0.2O_2‐δ with the highest concentration of oxygen vacancy presents the best catalytic performance (i.e. acetaldehyde yield reaches 49.9%) under the optimal reaction conditions (i.e. 623 K and H₂ flow rate = 10 mL/min). This work indicates that the Co/Ce‐Fe oxide solid solution catalyst can be potentially used for the selective hydrogenation from HAc to AA. The synergy between the metallic Co and Ce_1‐xFe_xO_2‐δ revealed can be extended to the design of other composite catalysts.     

Chemoselective Hydrogenation of Nitroaromatics at the Nanoscale Iron(III)–OH–Platinum Interface

Catalytic hydrogenation of nitroaromatics is an environment‐benign strategy to produce industrially important aniline intermediates. Herein, we report that Fe(OH)_x deposition on Pt nanocrystals to give Fe(OH)_x/Pt, enables the selective hydrogenation of nitro groups into amino groups without hydrogenating other functional groups on the aromatic ring. The unique catalytic behavior is identified to be associated with the Fe^III‐OH‐Pt interfaces. While H₂ activation occurs on exposed Pt atoms to ensure the high activity, the high selectivity towards the production of substituted aniline originates from the Fe^III‐OH‐Pt interfaces. In situ IR, X‐ray photoelectron spectroscopy (XPS), and isotope effect studies reveal that the Fe³⁺/Fe²⁺ redox couple facilitates the hydrodeoxygenation of the ‐NO₂ group during hydrogenation catalysis. Benefitting from Fe^III‐OH‐Pt interfaces, the Fe(OH)_x/Pt catalysts exhibit high catalytic performance towards a broad range of substituted nitroarenes.     

Easy synthesis of three‐dimensionally ordered macroporous CuO–CeO2 mixed oxide catalysts and their high activities for the catalytic combustion of soot

Three‐dimensionally ordered macroporous (3DOM) Cu_xCe‐M (x denote the mole ratio of Cu/[Ce + Cu]) oxide catalysts with large pore sizes and interconnected macroporous frameworks were successfully synthesized using a polymethyl methacrylate template method. The 3DOM structure improves the contact efficiency between catalyst and soot, which benefits soot elimination in the low temperature range. The low redox barriers of the 3DOM Cu–Ce solid solution also facilitate the elimination of the soot. The 3DOM Cu_0.1Ce catalysts exhibit the highest catalytic activity with maximum soot oxidation rate temperatures at 375 and 351 °C in the air and NO _x atmosphere, respectively. The NO _x‐TPD results demonstrate that the NO₂ produced in the Ce_0.1Cu‐M sample plays a curial role in improving the soot oxidation performance. Meanwhile, the NO‐DRIFTs reveal that the nitrates stored in the Cu_0.1Ce‐M sample also had a promotional effect on the soot elimination.     

Catalytic Properties of Nanoscale Iron‐Doped Zirconia Solid‐Solution Aerogels

Nanoscale iron‐doped zirconia solid‐solution aerogels are prepared via a simple ethanol thermal route using zirconyl nitrate and iron nitrate as starting materials, followed by a supercritical fluid drying process. Structural characteristics are investigated by means of powder X‐ray diffraction (XRD), thermal analyses (TG/DTA), N₂ adsorption measurements and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the resulting iron‐doped solid solutions are metastable tetragonal zirconia which exhibit excellent dispersibility and high solubility of iron oxide. Further, when the Fe:(Fe+Zr) ratio x is lower than 0.10, all of the Fe³⁺ ions can be incorporated into ZrO₂ by substituting Zr⁴⁺ to form Zr_1?xFe_xO_y solid solutions. Moreover, for the first time, an additional hydroxyl group band that is not present in pure ZrO₂ is observed by DRIFTS for the Zr(Fe)O₂ solid solution. This is direct evidence of Fe³⁺ ions incorporated into ZrO₂. These Zr_1?xFe_xO_y solid solutions are excellent catalysts for the solvent‐free aerobic oxidation of n‐hexadecane using air as the oxidant under ambient conditions. The Zr_0.8Fe_0.2O_y solid‐solution catalyst demonstrates the best catalytic properties, with the conversion of n‐hexadecane reaching 36.2 % with 48 % selectivity for ketones and 24 % selectivity for alcohols and it can be recycled five times without significant loss of activity.     

Effectively promoted catalytic activity by adjusting calcination temperature of Ce-Fe-Ox catalyst for NH3-SCR

A series of Ce-Fe-O_x catalysts prepared by the different calcination temperatures (marked as CF-X, where X represented calcination temperature) were used to the selectivity catalytic reduction of NO_x by NH₃. The results explained the relationship between calcination temperature and the sulfate species over Ce-Fe-O_x, and then investigated the surface acidity and catalytic performance. The large amounts of sulfate species were formed over CF-450 and CF-550 while it was decomposed with further the increasing of calcination temperature, which resulted in the loss of surface acidity, causing a decrease in the catalytic activity over Ce-Fe-O_x. Thereby, the CF-450 catalyst showed the best catalytic activity and over 90% NO_x conversion was obtained at 244–450 °C. Besides, the favored pore structure, more Fe³⁺ active species, higher Ce³⁺ concentration and the abundance of chemical adsorbed oxygen species, as well as the surface acid sites, would together contribute to the excellent catalytic activity of CF-450 catalyst.     

Ordered mesoporous SBA‐15 functionalized with yttrium(III) and cerium(III) complexes: Towards active heterogeneous catalysts for oxidation of sulfides and preparation of 5‐substituted 1H‐tetrazoles

Mesoporous SBA‐15 was synthesized and modified with 3‐chloropropyltrimethoxysilane and then used in immobilization of creatinine groups, which were employed to introduce Y³⁺ and Ce³⁺ to give rise to two novel yttrium and cerium catalysts: SBA‐15@Creatinine@M (M = Y and Ce). The structures of the SBA‐15@Creatinine@M catalysts were determined using various techniques. These catalysts offered outstanding catalytic performances in the oxidation of sulfides to sulfoxides and in the preparation of 5‐substituted 1H‐tetrazoles. An important characteristic of the SBA‐15@Creatinine@M catalysts is that they are very stable without a considerable decrease in their catalytic performance lasting seven cycles.     

Encapsulating Perovskite Quantum Dots in Iron‐Based Metal–Organic Frameworks (MOFs) for Efficient Photocatalytic CO2 Reduction

Improving the stability of lead halide perovskite quantum dots (QDs) in a system containing water is the key for their practical application in artificial photosynthesis. Herein, we encapsulate low‐cost CH₃NH₃PbI₃ (MAPbI₃) perovskite QDs in the pores of earth‐abundant Fe‐porphyrin based metal organic framework (MOF) PCN‐221(Fe_x) by a sequential deposition route, to construct a series of composite photocatalysts of MAPbI₃@PCN‐221(Fe_x) (x=0–1). Protected by the MOF the composite photocatalysts exhibit much improved stability in reaction systems containing water. The close contact of QDs to the Fe catalytic site in the MOF, allows the photogenerated electrons in the QDs to transfer rapidly the Fe catalytic sites to enhance the photocatalytic activity for CO₂ reduction. Using water as an electron source, MAPbI₃@PCN‐221(Fe_0.2) exhibits a record‐high total yield of 1559 μmol g^?1 for photocatalytic CO₂ reduction to CO (34 %) and CH₄ (66 %), 38 times higher than that of PCN‐221(Fe_0.2) in the absence of perovskite QDs.     

On‐surface Fenton and Fenton‐like reactions appraised by paper spray ionization mass spectrometry

On‐surface degradation of sildenafil (an adequate substrate as it contains assorted functional groups in its structure) promoted by the Fenton (Fe²⁺/H₂O₂) and Fenton‐like (Mⁿ⁺/H₂O₂; Mⁿ⁺ = Fe³⁺, Co²⁺, Cu²⁺, Mn²⁺) systems was investigated by using paper spray ionization mass spectrometry (PS‐MS). The performance of each system was compared by measuring the ratio between the relative intensities of the ions of m/z 475 (protonated sildenafil) and m/z 235 (protonated lidocaine, used as a convenient internal standard and added to the paper just before the PS‐MS analyzes). The results indicated the following order in the rates of such reactions: Fe²⁺/H₂O₂ ≫ H₂O₂ ≫ Cu²⁺/H₂O₂ > Mⁿ⁺/H₂O₂ (Mⁿ⁺ = Fe³⁺, Co²⁺, Mn²⁺) ~ Mⁿ⁺ (Mⁿ⁺ = Fe²⁺, Fe³⁺, Co²⁺, Cu²⁺, Mn²). The superior capability of Fe²⁺/H₂O₂ in causing the degradation of sildenafil indicates that Fe²⁺ efficiently decomposes H₂O₂ to yield hydroxyl radicals, quite reactive species that cause the substrate oxidation. The results also indicate that H₂O₂ can spontaneously decompose likely to yield hydroxyl radicals, although in a much smaller extension than the Fenton system. This effect, however, is strongly inhibited by the presence of the other cations, ie, Fe³⁺, Co²⁺, Cu²⁺, and Mn²⁺. A unique oxidation by‐product was detected in the reaction between Fe²⁺/H₂O₂ with sildenafil, and a possible structure for it was proposed based on the MS/MS data. The on‐surface reaction of other substrates (trimethoprim and tamoxifen) with the Fenton system was also investigated. In conclusion, PS‐MS shows to be a convenient platform to promptly monitor on‐surface oxidation reactions.     

Oxidation‐State Analysis of Ceria by X‐ray Photoelectron Spectroscopy

Three different methods to determine the oxide‐phase concentration in mixed cerium oxide by hard X‐ray photoelectron spectroscopy are applied and quantitatively compared. Synchrotron‐based characterization of the O 1s region was used as a benchmark to introduce a method based on the weighted superposition of the Ce 3d spectra of the pure Ce³⁺ and Ce⁴⁺ phases, which was shown to lead to reliable and highly accurate determination of the mean oxidation state in mixed cerium oxides. The results obtained reveal a linear relation between the third distinct final state (u′′′) satellite peak intensity of the Ce⁴⁺ phase and the Ce⁴⁺ concentration by proper inclusion of Ce³⁺‐related plasmon satellite peaks, which contradicts previous claims of nonlinear behavior. In contrast, quantitative conventional peak‐fitting procedures were shown to be well suited for the Ce 2p region due to its relatively simple structure. Additional satellite features observed in the Ce 3d spectrum of CeO₂ were proposed to originate from plasmon contributions.     

Real‐time Probing the Formation of [M(2,2‐bipyridine)2(NO3)3] (M = Ce,La, Tb) Complexes and Influence of Synthesis Parameters

Despite the strong technological importance of lanthanide complexes, their formation processes are rarely investigated. This work is dedicated to determining the influence of synthesis parameters on the formation of [Ce(bipy)₂(NO₃)₃] as well as Ce³⁺‐ and Tb³⁺‐substituted [La(bipy)₂(NO₃)₃] (bipy = 2,2′‐bipyridine) complexes. To this end, we performed in situ luminescence measurements, synchrotron‐based X‐ray diffraction (XRD) analysis, infrared spectroscopy (IR), and measured pH value and/or ion conductivity during their synthesis process under real reaction conditions. For the [Ce(bipy)₂(NO₃)₃] complex, the in situ luminescence measurements initially presented a broad emission band at 490 nm, assigned to the 5d→4f Ce³⁺ ions within the ethanolic solvation shell. Upon the addition of bipy, a red shift to 700 nm was observed. This shift was attributed to the changes in the environment of the Ce³⁺ ions, indicating their desolvation and incorporation into the [Ce(bipy)₂(NO₃)₃] complex. The induction time was reduced from 8 to 3.5 min, by increasing the reactant concentration by threefold. In contrast, [La(bipy)₂(NO₃)₃] crystallized within days instead of minutes, unless influenced by high Ce³⁺ and Tb³⁺ concentrations. Monitoring and controlling the influence of the reaction parameters on the structure of emissive complexes is important for the development of rational synthesis approaches and optimization of their structure‐related properties like luminescence.     

Coordination Polymer Nanobamboos of {FexIn1−x}‐MIL‐88B: Induced Formation of a Virtual In‐MIL‐88B

A precise fabrication of nanobamboo structures made from hybrid coordination polymers of the type {Fe_xIn_1?x}‐MIL‐88B is demonstrated. The compositions of the hybrid coordination polymer nanobamboos of {Fe_xIn_1?x}‐MIL‐88B (x=0.06, 0.19, or 0.75) are regulated by altering the amount of metal ions used in the reactions. Interestingly, the formation of a virtual In‐MIL‐88B (precise structure, {Fe_0.06In_0.94}‐MIL‐88B), which cannot be created in a typical reaction, is induced by the assistance of a Fe‐MIL‐88B structure. The a and c cell parameters of {Fe_0.06In_0.94}‐MIL‐88B are calculated at 10.95 and 19.86 Å, respectively. These values of {Fe_0.06In_0.94}‐MIL‐88B are larger than those of pure Fe‐MIL‐88B owing to the large ionic size of In³⁺ within the framework.     

Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III)

Ceric ammonium nitrate (CAN) or Ce^IV(NH₄)₂(NO₃)₆ is often used in artificial water oxidation and generally considered to be an outer‐sphere oxidant. Herein we report the spectroscopic and crystallographic characterization of [(N4Py)Fe^III‐O‐Ce^IV(OH₂)(NO₃)₄]⁺ ( 3 ), a complex obtained from the reaction of [(N4Py)Fe^II(NCMe)]²⁺ with 2 equiv CAN or [(N4Py)Fe^IV=O]²⁺ ( 2 ) with Ce^III(NO₃)₃ in MeCN. Surprisingly, the formation of 3 is reversible, the position of the equilibrium being dependent on the MeCN/water ratio of the solvent. These results suggest that the Fe^IV and Ce^IV centers have comparable reduction potentials. Moreover, the equilibrium entails a change in iron spin state, from S =1 Fe^IV in 2 to S =5/2 in 3 , which is found to be facile despite the formal spin‐forbidden nature of this process. This observation suggests that Fe^IV=O complexes may avail of reaction pathways involving multiple spin states having little or no barrier.     

Cerium‐Complex‐Catalyzed Oxidation of Arylmethanols under Atmospheric Pressure of Dioxygen and Its Mechanism through a Side‐On μ‐Peroxo Dicerium(IV) Complex

A new Ce^IV complex [Ce{NH(CH₂CH₂N=CHC₆H₂‐3,5‐(tBu)₂‐2‐O)₂}(NO₃)₂] ( 1 ), bearing a dianionic pentadentate ligand with an N₃O₂ donor set, has been prepared by treating (NH₄)₂Ce(NO₃)₆ with the sodium salt of ligand L1 . Complex 1 in the presence of TEMPO and 4 Å molecular sieves (MS4 A) has been found to serve as a catalyst for the oxidation of arylmethanols using dioxygen as an oxidant. We propose an oxidation mechanism based on the isolation and reactivity study of a trivalent cerium complex [Ce{NH(CH₂CH₂N=CHC₆H₂‐3,5‐(tBu)₂‐2‐O)₂}(NO₃)(THF)] ( 2 ), its side‐on μ‐O₂ adduct [Ce{NH(CH₂CH₂N=CHC₆H₂‐3,5‐(tBu)₂‐2‐O)₂}(NO₃)]₂(μ‐η²:η²‐O₂) ( 3 ), and the hydroxo‐bridged Ce^IV complex [Ce{NH(CH₂CH₂N=CHC₆H₂‐3,5‐(tBu)₂‐2‐O)₂}(NO₃)]₂(μ‐OH)₂ ( 4 ) as key intermediates during the catalytic cycle. Complex 2 was synthesized by reduction of 1 with 2,5‐dimethyl‐1,4‐bis(trimethylsilyl)‐1,4‐diazacyclohexadiene. Bubbling O₂ into a solution of 2 resulted in formation of the peroxo complex 3 . This provides the first direct evidence for cerium‐catalyzed oxidation of alcohols under an O₂ atmosphere.     

General and facile synthesis of ceria-based solid solution nanocrystals and their catalytic properties

Uniform Ce_1−xZr_xO₂ (x=0.2–0.8) nanocrystals with ultra-small size were synthesized through a thermolysis process, facilitated by the initial formation of precursor (hydrated (Ce,Zr)-hydroxides) at low temperature. TEM, XRD, EDAX, and Raman spectra were employed to study the formation of the solid solutions with various Ce/Zr ratios. Ultraviolet–visible (UV–vis) spectra showed that the ratios of Ce³⁺ to Ce⁴⁺ in both surface and bulk for the as-prepared Ce_1−xZr_xO₂ nanocrystals increased with the zirconium content x. The well-distributed Zr and Ce in the hydrated (Ce,Zr)-hydroxides before their thermolysis became the crucial factor for the structural homogeneity of the products. In addition, this strategy was extended to the synthesis of Ce_1−xGd_xO_1−x/2, Ce_1−xSm_xO_1−x/2, and Ce_1−xSn_xO₂ solid solutions. Catalytic measurements indicated that the ceria-based catalysts were active for CO oxidation at temperatures beyond 250 °C and the sequence of catalytic activity was Ce_0.5Zr_0.5O₂>Ce_0.8Zr_0.2O₂>Ce_0.2Zr_0.8O₂>Ce_0.5Sm_0.5O_1.75.     

Trinitratobis{N′‐[1‐(2‐pyridyl)ethylidene]isonicotinohydrazide}cerium(III): a three‐dimensional cerium–organic supramolecular structure

The Ce^III ion in the title complex, [Ce(NO₃)₃(C₁₃H₁₂N₄O)₂], is 12‐coordinated by six chelating nitrate O atoms and six donors (2 O and 4 N atoms) of two N′‐[1‐(2‐pyridyl)ethylidene]isonicotinohydrazide ligands, exhibiting a bicapped pentagonal‐antiprism‐type coordination geometry. The title complex possesses C₂ point symmetry and is located on a twofold crystallographic axis. Each molecule is linked with four surrounding molecules by four N—H...N hydrogen bonds, resulting in an extended two‐dimensional layer parallel to the ab plane, while π–π interactions between pyridine rings from neighboring complex molecules connect the two‐dimensional layers into a three‐dimensional cerium–organic supramolecular structure.     

Cerium iron sulfide,Ce3Fe1.94S7

Tricerium(III) diiron(II,III) hepta­sulfide, Ce₃Fe_1.94S₇, crystallizes in the polar hexagonal space group P6₃ and adopts the Ce₆Al_3.33S₁₄ structure type. The Fe atoms occupy both tetrahedral and octahedral sites. Isolated FeS₄ tetrahedra, all pointing in the same direction, are stacked along the threefold rotation axes. Chains of face‐sharing FeS₆ octahedra propagate along the 6₃ axis. Vacancies resulting from the partial oxidation of Fe²⁺ to Fe³⁺ occur exclusively in the octahedral Fe sites. The Ce atoms are coordinated by [7+1] S atoms, which form bicapped trigonal prisms.     

Perylene diimide‐modified magnetic γ‐Fe2O3/CeO2 nanoparticles as peroxidase mimics for highly sensitive colorimetric detection of Vitamin C

Perylene diimide‐modified magnetic γ‐Fe₂O₃/CeO₂ nanoparticles (γ‐Fe₂O₃/CeO₂‐PDI) were prepared and exhibited excellent peroxidase‐like activity. The samples were characterized by HR‐TEM, XRD, Raman, N₂ adsorption, magnetic strength and XPS. The obtained γ‐Fe₂O₃/CeO₂‐PDI had size of 10~20 nm with high specific surface area of 77 m²/g, and could be easily separated from the aqueous solution by using a magnet, which are in favor of its practical application. Due to the decoration of PDI, the γ‐Fe₂O₃/CeO₂‐PDI possessed more surface defects (Ce³⁺) and active oxygen species than that of γ‐Fe₂O₃/CeO₂, resulting in the outstanding catalytic performance. And the composite catalyst also showed highly sensitive and selectivity toward VC with a limit of detection of 0.45 μM. Based on the fluorescent results, a possible hydroxyl radical (?OH) catalytic mechanism was proposed. It is believed that the as‐prepared γ‐Fe₂O₃/CeO₂‐PDI nanoparticles are promising biosensors applied for biomedical and food analysis.     

Role of yttrium loading in the physico-chemical properties and soot combustion activity of ceria and ceria–zirconia catalysts

Ce_1−xY_xO₂ and Ce_0.85−xZr_0.15Y_xO₂ mixed oxides have been prepared by 1000 °C-nitrates calcination to ensure thermally stable catalysts. The physico-chemical properties of the mixed oxides have been studied by N₂ adsorption at −196 °C, XPS, XRD, Raman spectroscopy and H₂-TPR, and the catalytic activity for soot oxidation in air has been studied by TG in the loose and tight contact modes. Yttrium is accumulated at the surface of Ce_1−xY_xO₂ and Ce_0.85−xZr_0.15Y_xO₂, and this accumulation is more pronounced for the former formulation than for the latter, because the deformation of the lattice due to zirconium doping favours yttrium incorporation. Yttrium and zirconium exhibit opposite effects on the surface concentration of cerium; while zirconium promotes the formation of cerium-rich surfaces, yttrium hinders the accumulation of cerium on the surface. For experiments in tight contact between soot and catalyst, all the Ce_1−xY_xO₂ catalysts are more active than bare CeO₂, and Ce_0.99Y_0.01O₂ is the most active catalyst. The benefit of yttrium doping in catalytic activity of ceria can be related to two facts: (i) the Y³⁺ surface enrichment hinders crystallite growth; (ii) the surface segregation of Y³⁺ promotes oxygen vacancies creation. High yttrium loading (x = 0.12) is less effective than low dosage (x = 0.01) because yttrium is mainly accumulated at the surface of the particles and hinders the participation of cerium in the soot oxidation reaction, which is the active component. For the mixed oxides with formulation Ce_0.85−xZr_0.15Y_xO₂ (operating in tight contact) the effect of zirconium on the catalytic activity prevails with respect to that of yttrium. For experiments in loose contact between soot and catalyst, the catalytic activity depends on their BET surface area, and the catalysts Ce_0.85−xZr_0.15Y_xO₂ (BET = 10–13 m²/g) are more active than the catalysts Ce_1−xY_xO₂ (BET = 2–3 m²/g). In the loose contact mode, the yttrium doping and loading have a minor or null affect on the activity, and the stabilising effect of the BET area due to zirconium doping prevails.     

Controllable construction of Ce-Mn-Ox with tunable oxygen vacancies and active species for toluene catalytic combustion

A series of Ce-Mn-O_x catalysts synthesized under different hydrothermal conditions were evaluated by catalytic removal of toluene. The results of characterization showed that the contents of oxygen vacancies and active species in catalysts were crucial for the catalytic oxidation process. The concentration of Ce³⁺, Mn³⁺, and adsorbed oxygen associated with structural defects in Ce-Mn-O_x catalysts could be controlled by hydrothermal conditions, which were considered to promote redox capacity and improve catalytic oxidation performance. In addition, suitable synthetic conditions could increase the S_BET and V_p of catalysts. Among the prepared catalysts, CM-100 showed the best catalytic performance due to the generation of more defective oxygen and active species (Ce³⁺, Mn³⁺, and surface-adsorbed oxygen). In addition, the CM-100 catalyst showed satisfactory water resistance and stability.     

Structural Properties,Mössbauer Spectra,and Magnetism of Perovskite‐Type Oxides SrFe1–xTixO3–y

Perovskite‐type phases SrFe_1–xTi_xO_3–y with 0.1 ≤ x ≤ 0.7 have been prepared from the oxides, and, in order to reach high oxygen contents and Fe^IV fractions, annealed at oxygen pressures of 60 MPa. The materials were characterised by powder x‐ray and neutron diffraction, ⁵⁷Fe Mössbauer spectroscopy, and magnetic susceptibility measurements. All samples of the series crystallise in a cubic perovskite structure and reveal considerable oxygen deficiency. The Mössbauer parameters suggest that for x = 0.1, where the Fe^IV fraction is about 90%, the itinerant electronic state of SrFeO₃ is essentially retained. In materials with larger x increasing amounts of Ti^IV and Fe^III ions lead to a stronger localisation of the σ* (Fe 3 d – O 2 p) electrons. There is no evidence for a charge disproportionation of Fe^IV in any of the materials. Magnetic susceptibility measurements show a divergence of zero‐field cooled and field‐cooled data below a temperature T_m and deviations from Curie‐Weiss behaviour above T_m. The data are indicative of spin‐glass behaviour due to disorder and competing exchange interactions.