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[Display omitted] • The optimized V-doped FeP nanoflowers are prepared for enhanced HER. • V doping lowers d-band central position and hydrogen formation energy barrier. • V-FeP shows low overpotentials of 290 mV to deliver 1000 mA cm−2 for 24 h. • Over 100-h stability at 1000 mA cm−2 for water electrolysis is obtained. Reasonable design of hydrogen evolution reaction (HER) electrocatalyst from the perspective of electronic structure is a vital way to optimize the catalytic activity. Mono-metallic iron-based phosphates have been shown to be active toward HER, but their performance remains unsatisfactory despite their abundant reserves and low preparation cost. Here, guided by the d-band center and band structure theories, V-doped FeP nanoflower grown directly on iron foam are constructed. Combining the density functional theory (DFT) simulations with physical characterizations reveal that the enhanced HER activity is mainly attributed to the lowed d-band central position, increased water dissociation capacity, decreased hydrogen formation energy barrier and reduced charge transfer impedance. As a HER catalyst in 1 M KOH, the obtained V-FeP shows low overpotentials of ∼149, ∼246 and ∼290 mV to deliver the current densities of 100, 500 and 1000 mA cm−2 with at least 24 h. When coupled with other highly active oxygen evolution reaction (OER) catalyst (NiFe-LDH/IF), the NiFe-LDH/IF(+) || V-FeP/IF(-) pair also performs a low cell voltage and over 100-h stability at high current density of 1000 mA cm−2, which endows it a large potential in the practical electrolytic water industry. Our work may provide a reference for the enhancement of inert and low-cost HER-active iron phosphide. [ABSTRACT FROM AUTHOR]

Three kinds of bulk iron phosphates were prepared via different methods and employed as model catalysts in the oxy-bromination of methane (OBM). NaFe(PO) was obtained via a fluoride route for the first time that showed even superior catalytic performance than FePO. Phase evolution from NaFe(PO) to NaFe(PO) after the OBM was confirmed both by X-ray diffraction and Fe Mössbauer spectroscopy. Temperature-programmed reduction of hydrogen and desorption of CHBr revealed that the redox capacity of iron phosphates were responsible for the generation of bromine radicals on catalyst surfaces while CHBr-involved reactions likely belonged to gas-phase reactions. Graphical Abstract: Model iron phosphate catalysts were synthesized by three different methods. It was found that the NaFe(PO) catalyst prepared by a fluoride route showed superior OBM performance than the other two catalysts both with the phase of FePO, especially for producing higher CHBr selectivity.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Currently, catalytic processing of biorenewable raw materials into valuable products attracts more and more attention. In the present work, silica-supported FePO4 and Fe-Mo-O catalysts are prepared, their phase composition, and catalytic properties are studied in the process of selective oxidation of propylene glycol into valuable mono- and bicarbonyl compounds, namely, hydroxyacetone and methylglyoxal. A comparative analysis of the main routes of propylene glycol adsorption with its subsequent oxidative conversion into carbonyl products is carried out. The DFT calculations show that in the presence of adsorbed oxygen atom, the introduction of the phosphate moiety to the Fe-containing site strengthens the alcohol adsorption on the catalyst surface with the formation of the 1,2-propanedioxy (–OCH(CH3)CH2O–) intermediate at the active site. The introduction of the molybdenum moiety to the Fe-containing site in the presence of the adsorbed oxygen atom is also energetically favorable, however, the interaction energy is found by 100 kJ/mol higher compared to the case with phosphate moiety that leads to an increase in the propylene glycol conversion while maintaining high selectivity towards C3 products. The catalytic properties of the synthesized iron-containing catalysts are experimentally compared with those of Ag/SiO2 sample. The synthesized FePO4/SiO2 and Fe-Mo-O/SiO2 catalysts are not inferior to the silver-containing catalyst and provide ~70% selectivity towards C3 products, while the main part of propylene glycol is converted into methylglyoxal in contrast to the Ag/SiO2 catalyst featuring the selective transformation of only the secondary C-OH group in the substrate molecule under the studied conditions with the formation of hydroxyacetone. Thus, supported Fe-Mo-O/SiO2 catalysts are promising for the selective oxidation of polyatomic alcohols under low-temperature conditions. [ABSTRACT FROM AUTHOR]

Abstract: Vanadium-doped iron phosphates (with 1, 3 and 5wt.% V) were prepared and characterized by XRD, FTIR, UV-DRS, TPR, TEM, Laser Raman, XPS, and potentiometric titration techniques. Both undoped and V-doped catalysts displayed predominant formation of quartz type iron phosphate. In addition, the V-doped catalysts indicated formation of two more phases: V2O5 and (VO)2P2O7. The nitrile yield of V-doped catalysts in the ammoxidation of methyl pyrazine to cyanopyrazine were found to be higher than the yield of bulk FePO4, V2O5 and (VO)2P2O7. The increase in the redox property of the catalyst, as obtained by benzyl alcohol oxidation to benzaldehyde, was found to be the reason for enhanced activity. The variation of V-content in FePO4 revealed that the catalyst reached its optimum activity at 3wt.% V. However, the acid strength of the V-doped catalysts decreased with V-content and this reflected in their cyanopyrazine selectivity. [Copyright &y& Elsevier]

Abstract: Ammoxidation of methylpyrazine (MP) to cyanopyrazine (CP) was performed at 633–693K over iron phosphate catalysts having a P/Fe ratio of 1.2, obtained by adopting different methods of catalyst preparation. The catalysts were characterized by XRD, FTIR, UV-DRS, laser-Raman spectroscopy, TPR, TEM, XPS, acidity by Potentiometric titration and TPD of NH3. XRD and Raman data suggested predominant formation of quartz phase of iron phosphate. The structure and texture of the catalysts varied with the nature of starting material as well as the preparation method. The catalytic activity depended on the extent of quartz phase formation. Precipitation in the basic medium improved quartz phase formation and enhanced the activity. However, the decreased acid strength caused reduction in nitrile selectivity. A judicious combination of the redox and acid strength properties is required for obtaining maximum yield of CP. [Copyright &y& Elsevier]

Iron-doped, ammonium/potassium salts of 12-molybdophosphoric acid (Keggin-type polyoxometalates (POMs)) were prepared, characterized and tested as catalysts for the selective oxidation of isobutane to methacrylic acid. In samples calcined at 623 K, iron was incorporated in the secondary framework of the polyoxometalate, replacing for ammonium up to a maximum amount of ≈0.35 Fe atoms per Keggin unit. Iron was present as a partly hydrolyzed species, i.e. Fe(OH)2+. Excess iron was dispersed in the form of amorphous oxide or phosphate. The calcination of the compounds at 673 K or the permanence under reaction conditions led to a partial structural decomposition of the compound; the extent of decomposition was proportional to the iron content in catalysts. [Copyright &y& Elsevier]

Iron phosphate catalysts possess a unique selectivity to oxidative dehydrogenation. Unlike ordinary catalysts consisting of molybdenum and/or vanadium, they have no double-bond oxygen species (M&z.dbnd6;O) that are considered to be responsible for the oxygen insertion function and, as a result, for the degradation by C–C bond fission. The defect of iron phosphate catalysts is a lack of oxidation activity. Addition of a very small amount of molybdenum into iron phosphate enhances markedly the oxidation activity without modifying the high selectivity originated from iron phosphate. The marked increase in the activity is ascribable to an increase in the reducibility of iron phosphate, because the reoxidizability of iron phosphate is high enough. It is proposed that the reaction over a Mo-doped iron phosphate is promoted by redox cycle of iron phosphate but not by that of molybdenum phosphate. [Copyright &y& Elsevier]

Iron phosphate supported on MCM-41 has been studied for partial oxidation of methane with both oxygen and nitrous oxide. Characterizations with XRD, Raman spectroscopy, XPS, and H2-TPR suggest that the supported iron phosphate species with loading amounts lower than 40 wt% are located and dispersed in the mesopores of MCM-41. Such iron phosphate species can be reduced more readily than the unsupported iron phosphate at lower temperatures. Methane is selectively converted to methanol, formaldehyde, and dimethyl ether over the supported and the unsupported iron phosphate with nitrous oxide at milder temperatures (300–500 °C), while formaldehyde is mainly produced along with carbon oxides with oxygen at relatively higher temperatures (400–600 °C). The supporting of iron phosphate onto MCM-41 with loading amounts of ca. 20–40 wt% increases both methane conversion and overall selectivity to useful oxygenates with either oxygen or nitrous oxide. Kinetic studies indicate that the activation of oxygen occurs rapidly, while the activation of nitrous oxide proceeds at a comparable rate with the conversion of methane by the active oxygen species over both the supported and the unsupported catalysts. The supported catalyst, however, enhances the activation of nitrous oxide and thus remarkably inhibits the carbon deposition occurring over the unsupported iron phosphate. [Copyright &y& Elsevier]

The catalytic activity of iron phosphate in the oxidative dehydrogenation of lactic acid increases markedly by doping of a small amount of palladium (Pd) on the surface. At the beginning of the reaction, the selectivity of the Pd-doped catalysts to form pyruvic acid is very low, i.e. the main products are carbon oxides. However, as the time-on-stream increases, the selectivity increases gradually. After about 8 h on stream, the selectivity reaches the level of neat iron phosphate (80 mol%). On the other hand, the activity remains almost unchanged with a large variation in the time-on-stream. For example, the iron phosphate doped with 0.8 wt.% Pd is 10 times more active than the neat iron phosphate. [Copyright &y& Elsevier]