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To overcome deactivation of Pd-based catalysts at high temperatures, we herein design a novel pathway by introducing a certain amount of CoO to the supported Au-Pd alloy nanoparticles (NPs) to generate high-performance Au-Pd-xCoO/three-dimensionally ordered macroporous (3DOM) Co 3 O 4 (x is the Co/Pd molar ratio) catalysts. The doping of CoO induced the formation of PdO-CoO active sites, which was beneficial for the improvement in adsorption and activation of CH 4 and catalytic performance. The Au-Pd-0.40CoO/3DOM Co 3 O 4 sample performed the best (T 90% = 341 °C at a space velocity of 20 000 mL g -1 h -1 ). Deactivation of the 3DOM Co 3 O 4 -supported Au-Pd, Pd-CoO, and Au-Pd-xCoO nanocatalysts resulting from water vapor addition was due to the formation and accumulation of hydroxyl on the catalyst surface, whereas deactivation of the Pd-CoO/3DOM Co 3 O 4 catalyst at high temperatures (680-800 °C) might be due to decomposition of the PdO y active phase into aggregated Pd 0 NPs. The Au-Pd-xCoO/3DOM Co 3 O 4 nanocatalysts exhibited better thermal stability and water tolerance ability compared to the 3DOM Co 3 O 4 -supported Au-Pd and Pd-CoO nanocatalysts. We believe that the supported Au-Pd-xCoO nanomaterials are promising catalysts in practical applications for organic combustion.

Co(1-x)M(x)Cr(2)O(4) (M = Li, Zr; x = 0-0.2) catalysts were prepared via the citric acid method and investigated for catalytic combustion of methane. Substitution at tetrahedral (A) sites with monovalent (Li) or tetravalent (Zr) metal ions led to a decrease or increase of the catalytic activity, respectively. The Co(0.95)Zr(0.05)Cr(2)O(4) catalyst proved to be the most active and its catalytic activity reached 90% of methane conversion at 448 °C, which dropped by 66 °C compared with that of the undoped CoCr(2)O(4) catalyst. XRD and Raman results indicated that lithium or zirconium substitution could modify the spinel structure and electronic properties. For lithium-doped catalysts, oxygen deficiency and a strong surface enrichment in lithium and chromium were detected. Zirconium substitution enhanced the reducibility of zirconium-doped catalysts and decreased the strength constant of both the Co-O band and the Cr-O band, which may contribute to the catalytic activity toward methane combustion. In addition, the prevalent catalytic combustion activity of the zirconium-substituted catalysts could be explained by their higher concentration of suprafacial, weakly chemisorbed oxygen.

BACKGROUND The effect of the B cation on the surface properties and catalytic activity in the dry reforming reaction over La0. 4M0. 6Al0. 2Ni0. 8O3 (M=noble metal) perovskite-type oxides with surface area 3.26-4.14 m2 g-1 and rhombohedral structure was studied. RESULTS Among LaAlxNi1- xO3 series, LaAl0. 2Ni0. 8O3 had the highest catalytic activity, but suffered a slow deactivation with time-on-stream ( TOS). It is observed that all samples presented similar activity at low reaction temperatures (500-600°C), while at higher temperatures (600-850°C) the prepared solid was more active and perovskite phase was transformed into Ni0 or La2O2CO3. It was found that among the noble metal samples, La0. 4Rh0. 6Al0. 2Ni0. 8O3 possessed the highest surface area and surface oxygen concentration and the best low-temperature reducibility. For the Rh catalyst the CH4 and CO2 conversions were 89.1 and 86.2%, which were the most resistant against coke deposition and showed very high stability without decrease in reforming and remained constant during the 3000 min TOS. The following order of activity was observed: La0. 4Rh0. 6Al0. 2Ni0. 8O3 > La0. 4Ru0. 6Al0. 2Ni0. 8O3 > LaAl0. 2Ni0. 8O3> La0. 4Ir0. 6Al0. 2Ni0. 8O3 ≥La0. 4Pt0. 6Al0. 2Ni0. 8O3 > La0. 4Pd0. 6Al0. 2Ni0. 8O3. CONCLUSIONS It is believed that the high surface area and surface oxygen concentration and good low-temperature reducibility were responsible for the good catalytic performance of the La0. 4Rh0. 6Al0. 2Ni0. 8O3 sample. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Highlights: [•] LSCO synthesized via a novel and facile one-pot dextrose-assisted hydrothermal route. [•] High-surface-area nanowire LSCO is prepared by the DHR method. [•] Surface area, Oads content, and reducibility account for the good catalytic activity. [•] Catalytic activity is related to surface area, oxygen adspecies and reducibility. [•] l-Lysine/dextrose ratio can greatly influence on the morphology and pore structure. [ABSTRACT FROM AUTHOR]

Highly dispersed Ag nanoparticles supported on high-surface-area 3DOM La0.6Sr0.4MnO3 were successfully generated via the dimethoxytetraethylene glycol-assisted gas bubbling reduction route. The macroporous materials showed super catalytic performance for methane combustion. [ABSTRACT FROM AUTHOR]

A bimetallic RhNi/Al 2 O 3 catalyst prepared by galvanic replacement (GR) offers enhanced catalytic CO 2 hydrogenation to selectively produce methane. • Galvanic replacement offers a facile route to bimetallic Rh@Ni core–shell catalysts. • Bimetallic Ni@Rh core–shell catalysts offer significant rate enhancements for CO 2 methanation. • Operando IR identifies reactively-formed CO as the key intermediate to CH 4 production. • Surface formate is a catalytic spectator in methanation. CO 2 utilisation as a chemical feedstock could transform fuels production and help mitigate climate change. Direct CO 2 reduction for energy production requires the development of active, stable, and low-cost catalysts selective for methane. A bimetallic Ni@Rh core–shell catalyst prepared by galvanic replacement (GR) exhibits a 3.5-fold rate enhancement for CO 2 methanation relative to an analogue prepared by chemical reduction (CR) and is twice as active as monometallic Rh/Al 2 O 3. Superior performance of RhNi/Al 2 O 3 (GR) is attributed to Rh dispersion as an atomically thin RhO x shell encapsulating Ni nanoparticles, stabilised by a strong Rh-Ni interaction. Operando IR spectroscopy identifies reactively-formed CO from the dissociative chemisorption of CO 2 over Rh as the key intermediate for methane production. Surface formate from the dissociative chemisorption of CO 2 and subsequent hydrogenation (via spillover from Rh sites) over alumina is a catalytic spectator. This mechanistic insight paves the way to high activity nanostructured catalysts for CO 2 methanation. [ABSTRACT FROM AUTHOR]

Abstract: Cobalt chromium oxides with different Co/Cr ratios were prepared via co-precipitation method and their catalytic performances on methane combustion were evaluated from 300°C to 650°C at a space velocity of 36,000h−1. A significant improvement of activity was observed over the Co1Cr2 catalyst with a Co/Cr molar ratio of 1:2, and the methane conversion reached 90% at 464°C. The Co1Cr2 catalyst also showed excellent resistance to water vapor poisoning. In addition, the catalytic activity was inhibited in the presence of water vapor at the entire temperature range, while catalytic activity decreased only at low temperature in the presence of sulfur dioxide. Based on BET, TPR, XRD and XPS results, the superior performance of Co1Cr2 would origin from the higher valence and coordination number of the metal ions. Both Cr3+ and Cr6+ species were observed on the surface of cobalt chromites, and Cr6+ causes disorders in the spinel structure of cobalt chromites, which would enhance the adsorption of chemisorbed oxygen species and thus improve the catalytic performance, especially at low temperature. [Copyright &y& Elsevier]

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]

Abstract Nanocrystalline Ni/CeO 2 catalysts with various loadings of Ni (10, 15, 20, and 25%) were synthesised by a facile solvent deficient precipitation method for methane autothermal reforming process. The characterisation techniques such as XRD, BET, TPH, H 2 -TPR were carried out on fresh and spent samples to investigate the catalytic properties of the Ni/CeO 2. On the basis of characterisation results, the 20% Ni/CeO 2 performs the best activity among the catalysts with different Ni contents. The optimal reaction conditions for autothermal methane reforming has been investigated by evaluating the effect of reaction parameters including the reactivity temperature, the gas hourly space velocity (GHSV) and H 2 O/CH 4 (S/C) and O 2 /CH 4 (O/C) molar ratios. The stability of 20 wt% Ni/CeO 2 catalyst at 700 °C is examined for 20 h on-stream reaction. It reveals that the methane conversion starts a graduate decrease trend from the second 10 h, which is found to be because of the sintering of Ni nanoparticles by TPH and BET analysis. Graphical abstract Image 1 Highlights • Nanocrystalline Ni/CeO 2 catalysts were studied for autothermal reforming reaction. • 20 wt% Ni/CeO 2 with the large surface area and good reducibility exhibited the highest catalytic performance. • 20 wt% Ni/CeO 2 shown excellent thermal stability at 700 °C for 20 h on-stream reaction. • Carbon depositions were determined to occur on the surface of the samples with high Ni loading. [ABSTRACT FROM AUTHOR]

This paper describes a facile method to produce mesoporous nanostructure Ni/Al 2 O 3 , Ni/MgO, and Ni/xMgO.Al 2 O 3 (x: MgO/Al 2 O 3 molar ratio) catalysts prepared by “one-pot” evaporation-induced self-assembly (EISA) method with some modifications for investigating in the thermocatalytic decomposition of methane. Detailed characterizations of the material were performed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and N 2 adsorption/desorption, hydrogen temperature-programmed reduction (H 2 -TPR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed oxidation (TPO). The characterizations demonstrated that the synthesized catalysts with various MgO/Al 2 O 3 molar ratios possessed mesoporous structure with the high BET area in the range of 216.79 to 31.74 m 2 g −1 . The effect of different surfactants and calcination temperatures on the characterizations and catalytic activity of the catalysts were also examined in details. The experimental results showed that the catalysts exhibited high catalytic potential in this process and the 55 wt.% Ni/2 MgO·Al 2 O 3 catalyst calcined at 600 ο C possessed an acceptable methane conversion (∼60%) under the harsh reaction conditions (GHSV = 48000 (mL h −1 g cat −1 )). [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 mesoporous Co 3 O 4 ( meso -Co 3 O 4 ) and its supported Au, Pd, and Au–Pd alloy ( x Au y Pd/ meso -Co 3 O 4 ; x = 0.43–2.94 wt%; Au/Pd molar ratio ( y ) = 0.43–0.50) nanocatalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected reduction methods, respectively. It is found that the meso -Co 3 O 4 with a high surface area of 106 m 2 /g was cubic in crystal structure and the noble metal nanoparticles (NPs) with a size of 2.7–4.5 nm were uniformly dispersed on the surface of meso -Co 3 O 4 . The 2.94Au 0.50 Pd/ meso -Co 3 O 4 sample performed the best for methane combustion, showing the T 10% , T 50% , and T 90% (temperatures required for achieving methane conversions of 10%, 50%, and 90%) of 230, 280, and 324 °C at a space velocity of 20,000 mL/(g h) and the lowest apparent activation energy of 44.4 kJ/mol. Furthermore, the effects of CO 2 , SO 2 , and H 2 O addition on the catalytic stability of 2.94Au 0.50 Pd/ meso -Co 3 O 4 were also examined. It is concluded that the excellent catalytic performance of 2.94Au 0.50 Pd/ meso -Co 3 O 4 was associated with its porous structure, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd alloy NPs and meso -Co 3 O 4 . [ABSTRACT FROM AUTHOR]

Co1-xMxCr2O4 (M = Li, Zr; x = 0-0.2) catalysts were prepared via the citric acid method and investigated for catalytic combustion of methane. Substitution at tetrahedral (A) sites with monovalent (Li) or tetravalent (Zr) metal ions led to a decrease or increase of the catalytic activity, respectively. The Co0.95Zr0.05Cr2O4 catalyst proved to be the most active and its catalytic activity reached 90% of methane conversion at 448 °C, which dropped by 66 °C compared with that of the undoped CoCr2O4 catalyst. XRD and Raman results indicated that lithium or zirconium substitution could modify the spinel structure and electronic properties. For lithium-doped catalysts, oxygen deficiency and a strong surface enrichment in lithium and chromium were detected. Zirconium substitution enhanced the reducibility of zirconium-doped catalysts and decreased the strength constant of both the Co-O band and the Cr-O band, which may contribute to the catalytic activity toward methane combustion. In addition, the prevalent catalytic combustion activity of the zirconium-substituted catalysts could be explained by their higher concentration of suprafacial, weakly chemisorbed oxygen. [ABSTRACT FROM AUTHOR]