AbstractMulticomponent oxides are intriguing materials in heterogeneous catalysis, and the interface between various components often plays an essential role in oxidations. However, the underlying principles of how the hetero-interface affects the catalytic process remain largely unexplored. Here we report a unique structure design of MnCoOx catalysts by chemical reduction, specifically for ethane oxidation. Part of the Mn ions incorporates with Co oxides to form spinel MnxCo3-xO4, while the rests stay as MnO2 domains to create the MnO2-MnxCo3-xO4 interface. MnCoOx with Mn/Co ratio of 0.5 exhibits an excellent activity and stability up to 1000 h under humid conditions. The synergistic effects between MnO2 and MnxCo3-xO4 are elucidated, in which the C2H6 tends to be adsorbed on the interfacial Co sites and subsequently break the C-H bonds on the reactive lattice O of MnO2 layer. Findings from this study provide valuable insights for the rational design of efficient catalysts for alkane combustion.

Transition metal oxides are potential alternatives to noble metal catalysts for oxidation reactions. Co-based spinel oxides, in particular, have attracted significant attention. Herein, NixCo3-xO4 catalysts were synthesized to elucidate the influence of oxygen vacancies on catalyst activities and reaction mechanisms for ethane combustion. A correlation between the activity and the population and properties of O defects was developed, with an increased number of O defects typically resulting in higher activity. Also, the shape-induced facet effect is related to the amount of Ni that is incorporated into the octahedral sites of Co oxide. The substituted Ni atoms altered the redox ability of NixCo3-xO4 by changing O vacancy formation and C-H bond dissociation. The NiCo2O4-TM catalyst (6.0 mmol mL-1 h-1) exhibits the highest activity for ethane oxidation compared with NiCo2O4-PC (0.5 mmol mL-1 h-1) and NiCo2O4-OL catalysts (1.3 mmol mL-1 h-1) at 330 degrees C, and its activation energy (Ea) is 70.9 kJ mol-1. No activity decay is observed after the initial transition stage of the reaction in a long-term stability test up to 500 h on the NiCo2O4- TM-coated monolith, either with or without water addition. A vacancy-mediated pathway was proposed according to in situ diffuse reflectance infrared Fourier transform (DRIFT) and density functional theory (DFT) calculations over the NiCo2O4(311) facet. Findings from this study expand our understanding of the facet-dependent catalytic behavior and ultimately enable the rational design of high-performance catalysts.

Bio-oils are thermally unstable with high acidity, viscosity, and low heating value. Hence, crude bio-oils must be upgraded to obtain a product that meets current fuel standards while minimizing coke formation and catalyst deactivation. This study combined esterification and hydrodeoxygenation (HDO) in a two-step process to obtain an upgraded bio-oil. Mo2C-based catalysts had sufficient acidity to generate esters and stabilize the bio-oil. Among them, 2Ni-Mo2C/ABC (ABC & horbar;activated biochar) performed better because of a high hydrogenation activity. In the subsequent HDO step, the best Mo2C-based catalyst achieved 69% HDO with an overall carbon yield of 67%. The results are comparable to the one-step HDO using a Pd/C catalyst but offer the use of a lower-cost catalyst and reduced coke formation.

Well-faceted alloyed Pt nanoparticles (NPs) have been widely investigated as promising electrocatalysts with impressively high activity for oxygen reduction reaction (ORR). Reducing the size of such well-faceted NPs would be anticipated to enhance the utilization efficiency but lower the intrinsic activity of Pt. It is thus crucial to balance between the Pt utilization and its intrinsic activity. Herein, relatively small PtnNi nanotetrahedrons (4-5 nm, n refers to the Pt/Ni ratio in the metal precursors) were synthesized by one-pot solvothermal synthesis in N,N-dimethylformamide using form-aldehyde as an additive and polyvinylpyrrolidone as a stabilizer. The as-synthesized PtnNi NPs were then immobilized on carbon to make PtnNi/C catalysts for cathode ORR. Among these PtnNi/C samples, Pt3Ni/C shows up as the most active Pt catalyst, whose intrinsic (IA(Pt)) and mass-specific activity (MSA(Pt)) numbers are ca. 6.7- and 5.8-fold higher than those for commercial Pt/C (20% Pt, E-TEK), respectively. Pt1Ni/C is also distinctive, showing an EAS(Pt) as high as 82 m(2) g(Pt)(-1) and IA(Pt) and MSA(Pt) numbers of 4-5 folds higher than those for the Pt/C. The significantly enhanced Pt activity in the PtnNi tetrahedrons would arise from combined effects of their small sizes and Pt-enrichment at the surface layers after the electrochemical (dealloying) treatment.

Palladium oxide nanoparticles were loaded onto a nanostructured MnO2 aerogel by a deposition-precipitation method. The resulting nanomaterial exhibited excellent catalytic activity for low-temperature methane combustion, achieving complete methane conversion to CO2 at 330 degrees C (GHSV = 180000 mL/(g h)). The enhanced activity is attributed to excellent reducibility and exposure of active PdO facets. The hydrothermal stability of the composite catalyst was improved, and the deactivation mechanism was explored. These novel catalysts form free-standing monoliths and could be useful in natural gas vehicles and other methane scrubbing applications.

Spinel CoCr2O4 nanostructured catalysts for methane oxidation were prepared by a facile solvothermal method using benzyl alcohol as both a structure-directing agent and a reagent.

Bowtie-shaped NiCo2O4 nanostructures are prepared using a hydrothermal method. Variation of the synthesis parameters, including reaction time, additives, and calcination temperature, allows an understanding of the origin of the bowtie-shaped structure to be developed. Methane oxidation experiments performed using temperature-programed oxidation (TPO) show that the new materials, which do not contain precious metals, have excellent activity for low-temperature methane combustion, with 100% conversion at approximate to 410 degrees C (gas hourly space velocity (GHSV): 90 000 mL (STP) g(-1) h(-1)). The structure-activity relationships of the bowtie-shaped nanostructures are explored.

Novel aerogel materials with periodic structures derived from chiral nematic liquid crystalline cellulose nanocrystals (CNCs) are reported. The liquid crystalline structure of phase-separated CNCs is locked by a simple solvent exchange method or silica condensation. Both cellulose and silica/cellulose aerogel materials were obtained after critical point drying, and subsequent calcination of the silica/cellulose composite afforded a silica aerogel with periodic order. Gas adsorption and electron microscopy studies revealed that these materials have high surface areas and a unique chiral nematic structure imparted from the helicoidal CNC template. This is a new, scalable approach to aerogel materials with highly anisotropic structures. The high porosity and periodic, chiral features of these new materials may make them suitable for applications that require anisotropic properties or as hard templates for the construction of other ordered aerogels.

Nanostructured PdO/CeO2 supported on mesoporous SBA-15 silica was synthesized using a combination of incipient wetness impregnation and surface-assisted reduction. After calcination, the materials showed good activity as catalysts for the low-temperature oxidation of methane, with a sample having 5 wt % Pd loading showing 50% conversion to CO2 at ∼290 °C and complete conversion below 360 °C. The stability of catalysts in the presence of water was studied. The formation of Pd(0) during the methane oxidation reaction increases the oxygen vacancies on the surface of catalysts, improving the catalytic activity.