Heat distribution and good adhesion of the washcoat on monolith catalysts are critical to improving catalytic activity and long-term stability. Compared with cordierite, metal foam presents a high thermal conductivity coefficient. Also, the availability of “washcoat” in situ grown on metal substrates opens the door to eliminating the problem of coating peeling. Generally, hydrothermal or thermal methods are used for the fabrication of in situ grown washcoat on metal substrates. In this research, the aluminum foam monolith vertically aligned Al2O3 nanowire array is successfully prepared at ambient temperature in an alkaline solution for the first time. Furthermore, the Pt-loaded Al2O3 nanowire array (0.5 gPt/L monolith) is applied to C2H4 degradation. The catalyst converts 90% C2H4 at 147 °C with a gas hourly space velocity (GHSV) of 20,000 h–1. And a little decrease (1%) is observed in catalytic activity, even in 15 vol % water vapors. The catalysts show good thermal stability and water resistance property over 36 h at 300 °C. Above all, this study presents a simple way of in situ growth of washcoat on metal-substrate monolith with potentially scaled manufacturing. And the monolith catalyst shows good catalytic performance on C2H4, which can be applied for volatile organic compound treatment.

Up to now, a great number of catalysts have been reported that are active in the oxidation of volatile organic compounds (VOCs). However, supported noble-metal catalysts (especially Pt-based catalysts) are still the most excellent ones for this reaction. In this study, Pt species supported on γ-Al2O3 and ranging from single-atom sites to clusters (less than 1 nm) and 1–2 nm nanoparticles were prepared and investigated for oxidizing C2H4. The Pt-loaded γ-Al2O3 nanoflakes (PtAl-NF) and Pt-loaded γ-Al2O3 nanowires (PtAl-NW) were successfully prepared. The samples were characterized using XRD, TEM, XPS, HAADF-STEM, and in situ DRIFTS. Based on in situ DRIFTS, a simple surface reaction mechanism was developed. The stable intermediates CO on single-atom Pt, subnanometer Pt particles, and fully exposed Pt clusters could be explained by the strong binding of CO molecule poisoning Pt sites. Moreover, the oxidation of C2H4 was best achieved by Pt particles that were 1–2 nm in size and the catalytic activity of PtAl-NF was better when it had less Pt. Lastly, the most exposed (110) facets of γ-Al2O3 nanoflakes were more resistant to water than the majorly exposed (100) facets of γ-Al2O3 nanowires.

Pd/Al2O3 catalysts modified by different chemical elements (Mg, Si, Ce, and Zr) were tested for methane (CH4) catalytic combustion, and PdO nanoparticles loaded on modified Al2O3 were systematically studied. These conditions assess the carrier effects of Pd/Al2O3 and acid strength influences on CH4 combustion. We observed carrier effects on activation energy through tuning Pd 3d binding energies (BEs) and on pre-exponential factors (A) through Pd dispersion and acidity on supports. When the BE of Pd 3d5/2 is 337.3 eV, PdO nanoparticles loaded on modified Al2O3 have excellent activity in cracking the C−H bond of CH4, which leads to the lowest activation energy (Ea), regardless of the size effect of the PdO nanoparticle. Furthermore, a theoretical construction that acid sites on catalysts promote the reversible elementary step (2Pd−OH ↔ Pd−O* + Pd* + H2O) right shifts improving the A dependency on the quantity of exposed Pd* and Pd−O*. As a result, Al2O3, as the carrier, not only modifies the electronic characteristics and size of supported PdO nanoparticles but also participates in the reaction process via acid sites on the surface of Al2O3.

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