Metal–Support Interactions within a Dual-Site Pd/YMn₂O₅ Catalyst during CH₄ Combustion

Abstract

Catalytic combustion is a promising technology for removing unburnt CH4 from natural gas vehicle exhaust gas under lean-burn conditions. Supported Pd catalysts are widely applied and studied for use in CH4 oxidation at <500–550 °C, with their activities significantly affected by the interactions between Pd and the support, depending on the dispersion, Pd valence state, and properties of the support. However, whether metal–support interactions are favorable in catalytic CH4 oxidation is unclear. We therefore used YMn2O5 as a catalytically active support to prepare a dual-site catalyst, Pd/YMn2O5, which shows high CH4 catalytic activities in dry and wet atmospheres. Experimental and density functional theory studies reveal that the CH4 adsorption and lattice oxygen activity of the support are significantly enhanced due to the interactions between PdO x and YMn2O5. In situ X-ray photoelectron spectroscopy shows that Pd x+ (x = 2 and 4) and Mn x+ (x = 3 and 4) species undergo changes during CH4 oxidation. The PdO x sites are the main active sites, as the CH4 activation barrier is much lower than those at other sites. YMn2O5 and PdO x participate in CH4 activation and oxidation via active oxygen transfer.

Advancement of modification engineering in lean methane combustion catalysts based on defect chemistry

“…In addition, surface defect sites can also anchor single atoms, atomic clusters, or groups to form active sites. 102,103 In heterogeneous catalysis, the Strong Metals–Support Interaction (SMSI) can significantly enhance the adsorption of CH 4 and the activity of lattice oxygen of the supports, 104–106 and strongly modify the dispersion and morphology of the metal particles. 107–109 For example, Wu et al 110 prepared a highly dispersed palladium catalyst supported on defective Al 2 O 3 –CeO 2 (RAl 2 O 3 –CeO 2 : ceria was immobilized on the coordinatively unsaturated Al 3+ penta sites of γ-alumina activated by pre-reduction to fabricate hybrid-oxide support) for methane combustion.…”

Size-Controlled Palladium Nanoparticles Encapsulated in Silicalite-1 for Methane Catalytic Combustion

“…In order to further obtain insight into the reaction pathway of methane catalytic oxidation over Pd/S-1-in, in situ DRIFTS experiments were performed, and the results are shown in Figure 5. The characteristic bands at 3016 and 1305 cm −1 were assigned to the C−H stretching vibration and the C−H deformation vibration of methane, 45,46 while the bands at 3200−3800 cm −1 were attributed to hydroxyl groups (OH − ) adsorbed on the surface that originated from methane combustion. 47,48 In a 1% CH 4 /Ar atmosphere (Figure 5a,b), the bands that appeared at 2374 cm −1 were assigned to CO 2 species, and the bands associated with hydroxyl groups (OH − ) were shown at 1738 cm −1 .…”

Novel Insights on the Metal–Support Interactions of Pd/ZrO2 Catalysts on CH4 Oxidation

“…15 Our previous work proposed the electron transfer (Pd ↔ e − Mn) in Pd/YMn 2 O 5 during the CH 4 oxidation process, which enhances its ability to dissociate the C−H bonds in CH 4 . 16 Willis et al found that the redox and acid−base properties of supports exert a limited influence on the Pd/support activity. 17 Murata et al demonstrated that Pd particles on the supports with moderate oxide (such as Al 2 O 3 and ZrO 2 ) formation enthalpy (Δ f H M−O °) adopted a Pd 0 -core−PdO-shell structure, which exhibited higher CH 4 combustion activities than those with lower or higher…”

“…Campbell proposed the term electronic metal support interaction to describe the phenomena of electron transfer between the nanoparticles and its support based on the research finding that Pt clusters contacted with CeO 2 experience huge electronic perturbations, improving the dissociation ability of O–H bonds . Our previous work proposed the electron transfer (Pd ↔ e – Mn) in Pd/YMn 2 O 5 during the CH 4 oxidation process, which enhances its ability to dissociate the C–H bonds in CH 4 . Willis et al found that the redox and acid–base properties of supports exert a limited influence on the Pd/support activity .…”