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x AuPd z / y Co 3 O 4 /3DOM MnCo 2 O 4 (x = 0.56–1.98 wt%, z = 1.9–2.1, and y = 4.80–24.36 wt%) samples are prepared using PMMA-templating, incipient wetness impregnation, and PVA-protected reduction methods. The good performance for methane combustion of 1.98AuPd 2.1 /18.20Co 3 O 4 /3DOM MnCo 2 O 4 is related to its high O ads species concentration, good low-temperature reducibility, and strong interaction between Co 3 O 4 or AuPd 2.1 NPs and 3DOM MnCo 2 O 4. [Display omitted] • 3DOM MnCo 2 O 4 is fabricated using the PMMA-templating method. • 18.20Co 3 O 4 /3DOM MnCo 2 O 4 is obtained by the incipient wetness impregnation method. • 1.98AuPd 2.1 /18.20Co 3 O 4 /3DOM MnCo 2 O 4 is prepared via the PVA-protected reduction route. • 1.98AuPd 2.1 /18.20Co 3 O 4 /3DOM MnCo 2 O 4 perform the best for methane combustion. • O ads concentration, reducibility, and AuPd 2.1 or Co 3 O 4 and MnCo 2 O 4 interaction govern activity. Three-dimensionally ordered macroporous (3DOM) MnCo 2 O 4 -supported Co 3 O 4 and AuPd (x AuPd z / y Co 3 O 4 /3DOM MnCo 2 O 4 ; x = 0.56–1.98 wt%, z = 1.9–2.1, and y = 4.80–24.36 wt%) catalysts were prepared using polymethyl methacrylate (PMMA) microsphere-templating, incipient wetness impregnation, and polyvinyl alcohol (PVA)-protected reduction methods. Physicochemical properties of the materials were characterized by means of numerous techniques, and their catalytic activities were evaluated for methane combustion. It is found that the x AuPd z / y Co 3 O 4 /3DOM MnCo 2 O 4 samples with a surface area of 26.5–53.1 m2/g possessed a high-quality 3DOM architecture, in which the AuPd nanoparticles (NPs) with a size of 4.6–5.8 nm were highly dispersed on the surface of the macropore framework. Among all of the samples, 1.98AuPd 2.1 /18.20Co 3 O 4 /3DOM MnCo 2 O 4 exhibited the highest catalytic activity: the T 10% , T 50% , and T 90% (temperatures required for achieving methane conversions of 10, 50, and 90 %, respectively) were 262, 340, and 408 °C at a space velocity of 40,000 mL/(g h). Partial deactivation of the 1.98AuPd 2.1 /18.20Co 3 O 4 /3DOM MnCo 2 O 4 sample due to introduction of water vapor or carbon dioxide was reversible. It is concluded that the good catalytic performance of 1.98AuPd 2.1 /18.20Co 3 O 4 /3DOM MnCo 2 O 4 was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Co 3 O 4 or AuPd 2.1 NPs and 3DOM MnCo 2 O 4. [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]

[Display omitted] • The change in A-site element influences the r A / r B ratio of A 2 B 2 O 7 (A = Ln; B = Ti). • Ln 2 Ti 2 O 7 alters from monoclinic layered perovskite to pyrochlore with a rise in r A / r B. • Pyrochlore has a stronger interaction with Ni species than monoclinic layered perovskite. • Ni dispersion and surface oxygen determine catalytic performance of Ni/Ln 2 Ti 2 O 7. • Ni/Y 2 Ti 2 O 7 shows the best catalytic performance and coke-resistant ability. Ln 2 Ti 2 O 7 (Ln = La, Pr, Sm, and Y) and Ni/Ln 2 Ti 2 O 7 catalysts were prepared using the co-precipitation and incipient wetness impregnation methods, respectively. XRD and Raman results reveal that with the decrease in r A / r B ratio of A 2 B 2 O 7 (A = La, Pr, Sm, and Y; B = Ti), the crystal structure transformed from the monoclinic layered perovskite (La 2 Ti 2 O 7 and Pr 2 Ti 2 O 7) to the ordered pyrochlore (Sm 2 Ti 2 O 7 and Y 2 Ti 2 O 7). H 2 -TPR results demonstrate that the active Ni species had a stronger interaction with Sm 2 Ti 2 O 7 or Y 2 Ti 2 O 7 than with La 2 Ti 2 O 7 or Pr 2 Ti 2 O 7. Therefore, smaller Ni crystallites with larger active metallic surface areas could be formed in the Ni/Sm 2 Ti 2 O 7 and Ni/Y 2 Ti 2 O 7 catalysts. XPS results indicate that the oxygen vacancies and oxygen mobility were also gradually enhanced with the decrease in r A / r B ratio. As a consequence, the Ni/Y 2 Ti 2 O 7 sample exhibited the highest catalytic activity and the best coke-resistant ability in the steam reforming of methane for hydrogen production among all of the catalysts. It is concluded that the change in A-site element influenced the structures of Ln 2 Ti 2 O 7 significantly, which ultimately affected catalytic performance of Ni/Ln 2 Ti 2 O 7 for the steam reforming of methane. [ABSTRACT FROM AUTHOR]

Palladium-based catalysts are highly active for eliminating volatile organic compounds. Reducing the use of noble metals and enhancing performance of a catalyst are always desirable. The three-dimensionally ordered macroporous (3DOM) Mn 2 O 3 -supported transition metal M ( M = Mn, Cr, Fe, and Co)-doped Au–Pd nanoparticles (NPs) with an Au–Pd– xM loading of 1.86–1.97 wt% were prepared using the modified polyvinyl alcohol-protected reduction method. It is found that the Au–Pd– xM NPs with a size of 3.6–4.4 nm were highly dispersed on the surface of 3DOM Mn 2 O 3 . The 1.94 wt% Au–Pd–0.21Co/3DOM Mn 2 O 3 and 1.94 wt% Au–Pd–0.22Fe/3DOM Mn 2 O 3 samples performed the best for the oxidation of methane and o -xylene, respectively. The methane oxidation rate at 340 °C (339.0 × 10 −6 mol/(g Pd s)) over 1.94 wt% Au–Pd–0.21Co/3DOM Mn 2 O 3 was three times higher than that (93.8 × 10 −6 mol/(g Pd s)) over 1.97 wt% Au–Pd/3DOM Mn 2 O 3 , and the o -xylene reaction rate at 140 °C (2.59 μmol/(g N s) over 1.94 wt% Au–Pd–0.22Fe/3DOM Mn 2 O 3 was two times higher than that (0.93 μmol/(g N s) over 1.97 wt% Au–Pd/3DOM Mn 2 O 3 . It is concluded that doping a certain amount of the transition metal to Au–Pd/3DOM Mn 2 O 3 could modify the microstructure of the alloy NPs, thus improving the oxygen activation and methane adsorption ability. We are sure that the M -doped Au–Pd/3DOM Mn 2 O 3 materials are promising catalysts for the efficient removal of volatile organic compounds. [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 CeO 2 (3DOM CeO 2 ) and its supported Pd@Co (Co x Pd/3DOM CeO 2 , x (Co/Pd molar ratio) = 2.4–13.6) nanocatalysts were prepared using the polymethyl methacrylate-templating and modified polyvinyl alcohol-protected reduction methods, respectively. The Pd@Co particles displayed a core-shell (core: Pd; shell: Co) structure with an average size of 3.5–4.5 nm and were well dispersed on the surface of 3DOM CeO 2 . The Co x Pd/3DOM CeO 2 samples exhibited high catalytic performance and super stability for methane oxidation, with the Co 3.5 Pd/3DOM CeO 2 sample showing the highest activity ( T 90% = 480 °C at space velocity of 40,000 mL/(g h) and excellent stability in the temperature range 400–800 °C. The apparent activation energies (58–73 kJ/mol) obtained over Co x Pd/3DOM CeO 2 were much lower than those (104–112 kJ/mol) over Co/3DOM CeO 2 and 3DOM CeO 2 for methane oxidation, with the Co 3.5 Pd/3DOM CeO 2 sample possessing the lowest apparent activation energy (58 kJ/mol). It is concluded that the excellent catalytic performance of Co 3.5 Pd/3DOM CeO 2 was associated with its good abilities to adsorb oxygen and methane as well as the unique core-shell structure of CoPd nanoparticles. [ABSTRACT FROM AUTHOR]