Three-dimensionally ordered macroporous LaMnAl 11 O 19 -supported Pd nanocatalysts highly active for methane combustion

Pd/δ-MnO2 nanoflower arrays cordierite monolithic catalyst toward toluene and o-xylene combustion

Exploring high-efficiency and stable monolithic structured catalysts is vital for catalytic combustion of volatile organic compounds. Herein, we prepared a series of Pd/δ-MnO₂ nanoflower arrays monolithic integrated catalysts (0.01–0.07 wt% theoretical Pd loading) via the hydrothermal growth of δ-MnO₂ nanoflowers onto the honeycomb cordierite, which subsequently served as the carrier for loading the Pd nanoparticles (NPs) through the electroless plating route. Moreover, we characterized the resulting monolithic integrated catalysts in detail and evaluated their catalytic activities for toluene combustion, in comparison to the controlled samples including only Pd NPs loading and the δ-MnO₂ nanoflower arrays. Amongst all the monolithic samples, the Pd/δ-MnO₂ nanoflower arrays monolithic catalyst with 0.05 wt% theoretical Pd loading delivered the best catalytic performance, reaching 90% toluene conversion at 221°C at a gas hourly space velocity (GHSV) of 10,000 h⁻¹. Moreover, this sample displayed superior catalytic activity for o-xylene combustion under a GHSV of 10,000 h⁻¹. The monolithic sample with optimal catalytic activity also displayed excellent catalytic stability after 30 h constant reaction at 210 and 221°C.

The unique Pd@Pt/C core-shell nanoparticles as methanol-tolerant catalysts using sonochemical synthesis

Over the past decades, there were a few reports on the use of sonochemical method to prepare noble metals catalysts for fuel cells. However, the synthetic processes were conducted under high frequency (200 kHz)/long reaction time in most cases. In this work, Pd and PdxPt nanoparticles were prepared by sonochemical method under low frequency (20 kHz) in a shorter time (20-40 mins). In the first time, a sequentialsonochemical synthesis was explored to achieve a core/shell structure of PdxPt nanoparticles. Consequently, the unique core-shell structure was formed with two shells surrounding the Pd core. The Pd core was firstly grown. In the second step, the Pd²⁺ ion existing in the Pd core reduced simultaneously with Pt⁴⁺ ion in the solution as the first layer of PdPt alloy. Further, the Pt layer was formed subsequently. The Pd-based catalysts exhibited a superior ORR selective activity and exceptional methanol-tolerance property compared with the commercial Pt/C catalyst. In 0.5 M CH₃OH + 0.5MH₂SO₄ solution, the best performance was achieved on Pd₃Pt/C catalyst with increased overpotential of 24 mV. However, overpotentials was increased 174 mV on commercial Pt/C catalyst. The excellent performance of the Pd₃Pt/C catalyst is ascribed to its combination of preferable growth of the Pd (1 1 1) plane, small particle size (∼4 nm), unique core/shell structure as well as the electronic effects between Pd and Pt. These results have demonstrated that the sequential ultrasonic synthesis is an effective method for the synthesis of binary/trinary catalysts in a green approach.

Improved durability of Co3O4 particles supported on SmMn2O5 for methane combustion

To eliminate the aggregation of Co₃O₄ in the methane combustion process at high temperature, a thermally stable mullite structure, SmMn₂O₅ (SMO), was utilized as a support to improve the catalytic durability of Co₃O₄ particles.