Palladium Nanoparticles Encapsulated in Surface-Defected SBA-15 for Lean Methane Oxidation

Abstract

Mesoporous silica-supported palladium nanoparticles represent promising catalyst materials for lean methane oxidation. However, as only secondary palladium–silica interactions could be generally established in such compounds, active phases would inevitably agglomerate during the long-term reaction and finally result in performance deterioration and poor recyclability. Via the ammonia evaporation (AE) method, we successfully prepared highly active, stable, and recyclable Pd/Santa Barbara amorphous-15 (SBA-15) catalysts for lean methane oxidation. Our Pd/SBA-15-AE catalyst, which not only exhibited excellent catalytic performance for lean methane oxidation (T 90 = 335 °C in the first reaction cycle) but also achieved complete methane oxidation at 400 °C in the fifth reaction cycle of the designed test, presented more application potential than its impregnated and ion-exchanged counterparts. Combined with systematic characterizations, the enhanced palladium–silica interaction in AE-prepared catalysts was confirmed and proved to be critical for their excellent catalytic properties. DFT calculations revealed that the binding strength of palladium atoms on the surface-defected silica surface was enhanced when comparing with that on the perfect ones, finally rationalizing the obtained conclusion at the molecular level. The approach proposed in this work to create enhanced metal–support interactions may provide some inspiration for the design of application-oriented palladium catalysts.

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.…”

“…In addition, surface defect sites can also anchor single atoms, atomic clusters, or groups to form active sites. 102,103…”

Cu and Zn Bimetallic Co-Modified H-MOR Catalyst for Direct Oxidation of Low-Concentration Methane to Methanol

“…Solid-state 27 Al MAS NMR spectroscopy was one of the main characterization techniques for aluminosilicate molecular sieves, which provided a method to study the coordination of aluminum sites. The 27 Al MAS NMR spectra are displayed in Figure 5.…”

“…Inspired by the results of 27 Al MAS NMR spectroscopy and H 2 -TPR, XPS studies of the CuZn−MOR catalysts were carried out to obtain more direct information on the oxidation and surface chemical states of copper and zinc. The XPS corelevel spectra of O 1s, Cu 2p, and Zn 2p are presented in Figure 7a,b separately, while the results of fitting the photoelectric emission peaks of the Cu 2p 3/2 and Zn 2p 3/2 catalysts were summarized in Table 3.…”

“…21,22 Nevertheless, the direct conversion of methane, In this work, we synthesized a novel bimetallic CuZn−MOR catalyst via the impregnation method for the oxidation of lowconcentration methane to methanol. X-ray diffraction (XRD), inductively coupled plasma (ICP), N 2 -physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive system (EDS)-mapping, hydrogen temperature program reduction (H 2 -TPR), 27 Al MAS nuclearmagnetic-resonance (NMR), X-ray photoelectron spectroscopy (XPS), diffuse reflectance ultraviolet−visible (DR UV−Vis) spectroscopy, and CH 4 -temperature program desorption (CH 4 -TPD) were conducted to analyze the relevant physicochemical properties of catalysts. The results of these analyses suggested that in the CuZn−MOR catalyst, the good dispersion of Zn and Cu in the zeolite framework promoted the generation of active sites, thus enhancing the reactivity. )…”