The Earth-abundant and inexpensive manganese oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn(3+) species, a small amount of AuNPs (<5%) in α-MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α-MnO2.

The Earth‐abundant and inexpensive manganese oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn3+ species, a small amount of AuNPs (<5 %) in α‐MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α‐MnO2.

Iron oxide catalysts supported on nanostructured silica SBA-15 were synthesized with various iron loadings using two different precursors. Structural characterization of the as-prepared Fe O /SBA-15 samples was performed by nitrogen physisorption, X-ray diffraction, DR-UV-Vis spectroscopy, and Mössbauer spectroscopy. An increasing size of the resulting iron species correlated with an increasing iron loading. Significantly smaller iron species were obtained from (Fe(III), NH 4 )-citrate precursors compared to Fe(III)-nitrate precursors. Moreover, smaller iron species resulted in a smoother surface of the support material. Temperatureprogrammed reduction (TPR) of the Fe O /SBA-15 samples with H 2 revealed better reducibility of the samples originating from Fe(III)-nitrate precursors. Varying the iron loading led to a change in reduction mechanism. TPR traces were analyzed by modelindependent Kissinger method, Ozawa, Flynn, and Wall (OFW) method, and model-dependent Coats-Redfern method. JMAK kinetic analysis afforded a one-dimensional reduction process for the Fe O /SBA-15 samples. The Kissinger method yielded the lowest apparent activation energy for the lowest loaded citrate sample ( ≈ 39 kJ/mol). Conversely, the lowest loaded nitrate sample possessed the highest apparent activation energy ( ≈ 88 kJ/mol). For samples obtained from Fe(III)-nitrate precursors, decreased with increasing iron loading. Apparent activation energies from model-independent analysis methods agreed well with those from model-dependent methods. Nucleation as rate-determining step in the reduction of the iron oxide species was consistent with the Mampel solid-state reaction model.

Mixed iron and molybdenum oxide catalysts supported on nanostructured silica, SBA‐15, were synthesized with various Mo/Fe atomic ratios ranging from 0.07/1.0 to 0.57/1.0. Structural characterization of as‐prepared Mo x O y _Fe x O y /SBA‐15 samples was performed by nitrogen physisorption, X‐ray diffraction, and DR‐UV‐Vis spectroscopy. Adding molybdenum resulted in a pronounced dispersion effect on supported iron oxidic species. Increasing atomic ratio up to 0.21Mo/1.0Fe was accompanied by decreasing species sizes. Strong interactions between iron and molybdenum during the synthesis resulted in the formation of Fe−O−Mo structure units, possibly Fe 2 (MoO 4 ) 3 ‐like species. Reducibility of Mo x O y _Fe x O y /SBA‐15 catalysts was investigated by temperature‐programmed reduction experiments with hydrogen as reducing agent. The lower reducibility obtained when adding molybdenum was ascribed to both dispersion and electronic effect of molybdenum. Catalytic performance of Mo x O y _Fe x O y /SBA‐15 samples was studied in selective gas‐phase oxidation of propene with O 2 as oxidant. Adding molybdenum resulted in an increased acrolein selectivity and a decreased selectivity towards total oxidation products.

Iron oxidic species supported on silica SBA‐15 were synthesized with various iron loadings using two different FeIII precursors. The effect of varying powder layer thickness during calcination on structural and solid‐state kinetic properties of FexOy/SBA‐15 samples was investigated. Calcination was conducted in thin (0.3 cm) or thick (1.3 cm) powder layer. Structural characterization of resulting FexOy/SBA‐15 samples was performed by nitrogen physisorption, X‐ray diffraction, and DR‐UV/Vis spectroscopy. Thick powder layer during calcination induced an increased species size independent of the precursor. However, a significantly more pronounced influence of calcination mode on species size was observed for the FeIII nitrate precursor compared to the FeIII citrate precursor. Temperature‐programmed reduction (TPR) experiments revealed distinct differences in reducibility and reduction mechanism dependent on calcination mode. Thick layer calcination of the samples obtained from FeIII nitrate precursor resulted in more pronounced changes in TPR profiles compared to samples obtained from FeIII citrate precursor. TPR traces were analyzed by model‐dependent Coats‐Redfern method and model‐independent Kissinger method. Differences in solid‐state kinetic properties of FexOy/SBA‐15 samples dependent on powder layer thickness during calcination correlated with differences in iron oxidic species size.