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The surface atomic arrangement and defective structures of electrocatalysts play a crucial role in determining their catalytic activity and selectivity. Hematite (α-Fe2O3) nanostructures with oxygen vacancies are promising electrocatalysts for the oxygen reduction reaction (ORR) due to their low-cost and environmental friendliness. However, a systematic study of their ORR performance, especially selectivity at high oxygen vacancy concentrations, is still lacking. In this study, we synthesized α-Fe2O3 nanosheets with surface oxygen vacancies using a simple solvothermal reaction followed by a liquid phase NaBH4 reduction method. The oxygen vacancy amount was adjusted by varying the concentrations of NaBH4 solution, and it was found that increasing the oxygen vacancy concentration from 11.4% to 43.4% improved the ORR activity, but further increasing it to 77.3% deteriorated the crystalline quality and thus affected the ORR performance. The optimized sample (α-Fe2O3-1 M), treated with a 1 M NaBH4 solution, showed a high limiting current density of 5.75 mA cm−2 at 0.4 V vs. the reversible hydrogen electrode (RHE). The observed enhancement in ORR activity can be attributed to the optimal surface oxygen vacancies, which improve catalytic kinetics and increase the exposure of active sites. [ABSTRACT FROM AUTHOR]

This study aims to investigate the catalytic activity of spinel-type oxides (NixCoyO4) for the oxidation of toluene and carbon monoxide at low temperatures. A series of Ni/Co catalysts with different mole ratios were synthesized via citric acid assisted sol-gel method and the influence of the nickel to cobalt ratios on the properties and catalytic performance of NixCoyO4 were investigated by characterization such as XRD, SEM-EDX, BET, H2–TPR. The results indicate that the catalyst with the Ni/Co atomic ratio of 1.5/1.5 exhibits the highest complete toluene oxidation activity, with 85% toluene conversion rate at 100 – 250 °C and complete toluene oxidation at 300 °C. However, for the complete oxidation of CO, the Ni/Co atomic ratio of 1/2 exhibits higher activity, converting 100% CO at 150 °C. The results show that NiO and CoOx are proved to be more active than the other for the oxidation of toluene and CO, respectively. The characteristic results show that high surface area, small particle size, good temperature reducibility, and oxygen species with high mobility in low-temperature regions are responsible for the catalytic performance of nickel cobalt spinel-type catalyst for toluene and carbon monoxide oxidation. The good stability of the Ni-Co oxide catalysts for the oxidation reactions originates from the strong Ni-Co interaction. [ABSTRACT FROM AUTHOR]

Using [Ni{(POEt)3}4] as catalyst precursor for the catalytic isomerization of allylbenzene to beta‐methylstyrene, time‐course studies suggest a mechanism that is consistent with an autocatalytic reaction. The sigmoidal curve observed when plotting conversion vs. time fits exceptionally well to a kinetic model of an autocatalytic process (R2 = 0.998). We show that the uncoordinated phosphite, generated during the catalyst activation, reduces the acid concentration and, consequently, has a detrimental effect on the formation of the protonated active nickel catalyst. The nickel complex protonation is seen as a key step in forming the active catalytic species. The novel use of a mercury salt as a phosphite scavenger leads to inhibition of the free phosphite's capability to lower acid concentration, improving the catalytic performance of the system, consistent with the mechanism proposed. [ABSTRACT FROM AUTHOR]

Nano‐sized perovskites were synthesized in a spray flame from nitrate precursors dissolved in ethanol and in ethanol/2‐ethylhexanoic acid (2‐EHA) mixtures. Experiments with ethanol led to a broad particle‐size distribution and to the formation of undesired phases such as La2CoO4, La2O3, and Co3O4. The addition of 2‐EHA can initiate micro explosions of the burning droplets and has been systematically investigated toward the formation of single‐phase, high‐surface‐area LaCoO3 and LaFeO3 with a narrow size distribution. To investigate the effect of 2‐EHA, temperature‐dependent changes of the chemical composition of the precursor solutions were analyzed with ATR‐FTIR between 23 and 70°C. In all cases, the formation of esters was identified while in the solutions containing iron, additional formation of carboxylates was observed. The synthesized materials were characterized by BET SSA, XRD, SAED and EDX‐TEM and their catalytic activity was analyzed, reaching 50% CO conversion at temperatures below 160 and 300°C for LaCoO3 and LaFeO3, respectively. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) ordered mesoporous Ag/MnO2 catalyst was prepared by impregnation method based on 3D-MnO2 and used for catalytic oxidation of HCHO. Ag nanoparticles are uniformly distributed on the polycrystalline wall of 3D-MnO2. The addition of Ag does not change the 3D ordered mesoporous structure of the Ag/MnOx, but does reduce the pore size and surface area. Ag nanopartides provide suffident active site for the oxidation reaction of HCHO, and Ag (i l l) crystal facets in the Ag/MnO2 are active faces. The 8.9% Ag/MnO2 catalyst shows a higher normalized rate (10.1 nmol-s-1 m-2 at 110 °C) and TOF (0.007 s-1 at 110 °C) under 1300 ppm of HCHO and 150 000 h-1 of GHSV, and its apparent activation energy of the reaction is the lowest (39.1 kj/mol). More Ag active sites, higher low-temperature redudbility, more abundant surface lattice oxygen spedes, oxygen vacancies, and lattice defects generated from interaction Ag with MnO, are responsible for the excellent catalytic performance of HCHO oxidation on the 8.9% A g/MnO2 catalyst. The 8.9% A g/MnO2 catalyst remained highly active and stable under space velodty increasing from 60 000 to 150 000 h-1, under initial HCHO concentration increasing from 500 to 1300 ppm, and under the presence of humidity, respectively. [ABSTRACT FROM AUTHOR]

Ethanol steam reforming is a promising reaction which produces hydrogen from bio and synthetic ethanol. In this study, the nano-structured Ni-based bimetallic supported catalysts containing Cu, Co and Mg were synthesized through impregnation method and characterized by XRD, BET, SEM, TPR and TPD analysis. The prepared catalysts were tested in steam reforming of ethanol in the S/C = 6, GHSV of 20,000 mL/(g cat h) at the temperature range of 450–600 °C. Among the xNi/CeO 2 (x = 10, 13, 15 wt%) catalyst, the sample containing 13 wt% Ni with surface area of 64 m2/g showed the best performance with 89% ethanol conversion and 71% H 2 selectivity as well as low CO selectivity of 8% at 600 °C and The addition of Cu, Mg, and Co to catalyst structure were evaluated and it was found that the nature of second metal has a strong influence on the catalyst selectivity for H 2 production. Considering to results of TPR analysis, the 13Ni–4Cu/CeO 2 catalyst showed proper reduction which caused in better activity. On the other side based on TPD analysis, the more basic property of 13Ni–4Mg/CeO 2 bimetallic catalyst provided a better condition to methane steam reforming, leading to lower CH 4 selectivity and consequently more H 2 production. The 13Ni–4Cu/CeO 2 exhibited the highest activity and lowest selectivity towards ethanol conversion and CO production about 99% and 4%, while the 13Ni–4Mg/CeO 2 catalyst possessed the highest H 2 selectivity and lowest CH 4 selectivity about 74% and 1% respectively at 600 °C. The Ni–Cu and Ni–Mg bimetallic catalysts shows good stability with time on stream. Image 1 • 13 wt% Ni/CeO 2 catalyst with proper activity and sufficiently hydrogen selectivity at 600 °C. • Increasing the catalytic activity towards ESR reaction by using the promoter of Cu, Mg and Co. • Obtaining almost full conversion over 13Ni–4Cu/CeO 2 catalyst at 600 °C. • Increasing the water-gas shift reaction by using 4 wt% Cu to formulation of 13Ni/CeO 2 catalyst. • High improvement of the methane steam reforming by addition of 4 wt% Mg as promoter. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • One-pot synthesis allows generation of Ni catalysts supported on MgO. • Effect of group VIB metal addition to Ni/MgO on catalytic activity is examined. • The Ni−Cr/MgO catalysts exhibit high catalytic activity and stability. Abstract Mesoporous 55 wt.% Ni/MgO and group VIB metal (Cr, Mo or W)-doped catalysts were prepared using the facile "one-pot" evaporation-induced self-assembly in ethanol and wetness impregnation methods, respectively. Physicochemical properties of the as-prepared catalysts were characterized by means of the BET, XRD, SEM, TEM, HAADF, XPS, H 2 -TPR, TPO, and Raman techniques. The doping of Cr to 55 wt% Ni/MgO improved catalytic activity and stability for the decomposition of methane under harsh reaction conditions. The maximal initial methane conversions of 80, 87, and 75% were achieved over the 55 wt.% Ni− x Cr/MgO (denoted as 55Ni− x Cr/MgO; x = 5, 10, and 15 wt.%) at 675 oC and GHSV = 48,000 mL/(g h), respectively. It is concluded that the high catalytic efficiency of the Cr-doped sample in methane decomposition was associated with its high surface area, high oxygen adspecies concentration, and good low-temperature reducibility. In addition, multi-walled carbon filaments with metal-encapsulated carbon particles were deposited on the Cr-doped catalysts, and the ordered carbon filaments with different diameters and good crystallinity were produced on the surface of the 55Ni−10Cr/MgO catalyst. [ABSTRACT FROM AUTHOR]

Abstract The concurrent production of CO x -free hydrogen and multi-walled carbon filaments by thermocatalytic decomposition of methane is advantageous in the environmental and energy catalysis. In the present work, a facile "one-pot" evaporation-induced self-assembly strategy was effectively adopted to fabricate the nickel catalysts supported on mesoporous Al 2 O 3 , SiO 2 , TiO 2 , and MgO, and their catalytic activities for methane decomposition were evaluated for the first time. The structural, textural, and redox properties of the as-obtained materials were characterized using a number of analytical techniques. The nitrogen sorption analysis indicated the presence of a mesoporous structure due to homogeneous aggregation of the catalyst particles with a high specific surface area of 32–236 m2/g. Among all of the catalysts, Ni/MgO exhibited the best catalytic activity for methane decomposition (65% methane conversion at 600 °C and GHSV of 48,000 mL/(g h)). The activity increased when Ni loading increased from 25 to 55 wt%. The investigation on the correlation between catalytic performance and promoter doping effect suggests that incorporating copper into the MgO support considerably enhanced the catalytic activity and stability at high temperatures. The XPS results reveal that doping of Cu to Ni/MgO enhanced the adsorption and activation of oxygen molecules. In addition, the disordered crystalline carbon filaments with different diameters and good crystallinity were generated on the surface of the Cu-doped Ni/MgO catalysts. Graphical abstract Unlabelled Image Highlights • The work is focused on pure hydrogen production via catalytic CH 4 decomposition. • One-pot synthesis allows to prepare Ni catalysts supported on various metal oxide. • The catalysts were characterized for their physicochemical properties and activity. • The Ni supported on MgO shows a higher activity than that supported on other metal oxides. • Effect of Ni content and Cu addition in Ni/MgO were investigated in detail. [ABSTRACT FROM AUTHOR]

In this article, the synthesis, characterization and catalytic performance of the Pd and Pt promoted Ni-Cu/MgO·Al 2 O 3 catalysts were investigated in the thermocatalytic dehydrogenation of methane to highly pure hydrogen. The physicochemical properties of the prepared catalysts were investigated using different characterization methods such as XRD, BET, SEM, TEM, XPS, H 2 -TPR and TPO techniques. The Ni–Cu/MgO·Al 2 O 3 catalyst possessing mesoporous structure and large BET surface area (126.28 m 2  g −1 ) was successfully synthesized by facile simultaneous sol-gel method (SSGM) in the absence of surfactants. The results showed that the addition of Pd significantly improved the catalytic activity and stability. The effect of different nominal loadings of palladium (2, 4 and 6 wt%) on the catalytic performance was also studied. Among the prepared samples, the promoted sample with 4 wt% of palladium showed optimal catalytic performance and stability at higher temperatures towards methane thermocatalytic decomposition. [ABSTRACT FROM AUTHOR]

Three-dimensionally ordered macroporous (3DOM) CoFe 2 O 4 , z MnO x /3DOM CoFe 2 O 4 ( z = 4.99–12.30 wt%), and y Pd–Pt/6.70 wt% MnO x /3DOM CoFe 2 O 4 ( y = 0.44–1.81 wt%; Pd/Pt molar ratio = 2.1–2.2) have been prepared using the polymethyl methacrylate microspheres-templating, incipient wetness impregnation, and bubble-assisted polyvinyl alcohol-protected reduction strategies, respectively. All of the samples were characterized by means of various techniques. Catalytic performance of the samples was measured for methane combustion. It is shown that the as-prepared samples exhibited a high-quality 3DOM structure (103 ± 20 nm in pore size) and a surface area of 19–28 m 2 /g, and the noble metal or alloy nanoparticles (NPs) with a size of 2.2–3.0 nm were uniformly dispersed on the macropore wall surface of 3DOM CoFe 2 O 4 . The loading of MnO x on CoFe 2 O 4 gave rise to a slight increase in activity, however, the dispersion of Pd–Pt NPs on 6.70MnO x /3DOM CoFe 2 O 4 significantly enhanced the catalytic performance, with the 1.81Pd 2.1 Pt/6.70MnO x /3DOM CoFe 2 O 4 sample showing the highest activity ( T 10% = 255 °C, T 50% = 301 °C, and T 90% = 372 °C at a space velocity of 20,000 mL/(g h)). We believe that the excellent catalytic activity of 1.81Pd 2.1 Pt/6.70MnO x /3DOM CoFe 2 O 4 was related to its well-dispersed Pd–Pt alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between MnO x or Pd–Pt NPs and 3DOM CoFe 2 O 4 . [ABSTRACT FROM AUTHOR]

Three-dimensionally ordered macroporous (3DOM) Mn 2 O 3 -supported AuPd y alloy ( x AuPd y /3DOM Mn 2 O 3 ; x = 1.0–3.8 wt%; Pd/Au molar ratio : y = 1.85, 1.92) catalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous techniques, and their catalytic activities were evaluated for toluene oxidation. It is found that the AuPd y alloy nanoparticles (NPs) with an particle size of 2–4 nm were uniformly dispersed on the surface of 3DOM Mn 2 O 3 , and the 3.8AuPd 1.92 /3DOM Mn 2 O 3 sample performed the best: the temperature at 90% toluene conversion was 162 °C at 40,000 mL/(g h). Furthermore, the 3.8AuPd 1.92 /3DOM Mn 2 O 3 sample was highly active even after calcination at 700 °C. The introduction of water vapor to the feedstock induced a positive effect on toluene oxidation over 3.8AuPd 1.92 /3DOM Mn 2 O 3 , but a negative effect over 1.9Au/3DOM Mn 2 O 3 or 1.9Pd/3DOM Mn 2 O 3 . The excellent catalytic activity, thermal stability, and water resistance of 3.8AuPd 1.92 /3DOM Mn 2 O 3 were associated with its good activation adsorption of oxygen on AuPd 1.92 NPs and strong interaction between noble metal NPs and 3DOM Mn 2 O 3 . The 3DOM Mn 2 O 3 -supported AuPd y alloy NPs are promising industrial catalysts for efficient removal of volatile organic compounds. [ABSTRACT FROM AUTHOR]

The synthesis of mesoporous organosilicas (MOs) using co-condensation for a high ratio of a long and flexible chained organosiloxane bridge with silica precursor (e.g. tetraethylorthosilicate (TEOS)) is a complex and challenging task. By complementing the experimental characterisations with density functional calculations, The critical ratio of the urea-based organosiloxane bridge (BTPU) to tetraethyl orthosilicate of 1:8 was identified to delivers reliably stable urea bridged MO (MO-urea) with relatively large surface area and mesoporosity. Moreover, the Pd nanoparticles supported on the pore channels of MO-urea achieve a narrow distribution size averaging at a diameter of ~2 nm. This fine distribution is driven by the Pd nanoparticles nucleating only on the exposed SiO 2 section of MO-urea while the BTPU bridges punctuate the growth of the Pd nanoparticles limiting their size. As a result, the obtained Pd@MO-urea exhibits excellent multifunctional catalytic activity for hydrogen production from formic acid and p-nitrophenol (PN) reduction in aqueous media with four folds increase in yield compared to the non-punctuated Pd nanoparticles. Image 1 • Urea-based bridges in mesoporous organosilica punctuate the growth of Pd nanoparticles. • Pd nanoparticles on urea-bridged mesoporous organosilica grow uniformly at ~2 nm. • Leading to a multifunctional catalyst, e.g. H 2 production from formic acid and nitroaromatic reduction. [ABSTRACT FROM AUTHOR]