Enhancing the Catalytic Activity of Palladium Nanoparticles via Sandwich-Like Confinement by Thin Titanate Nanosheets

Abstract

As atomically thin oxide layers deposited on flat (noble) metal surfaces have been proven to have a significant influence on the electronic structure and thus the catalytic activity of the metal, we sought to mimic this architecture at the bulk scale. This could be achieved by intercalating small positively charged Pd nanoparticles of size 3.8 nm into a nematic liquid crystalline phase of lepidocrocite-type layered titanate. Upon intercalation the galleries collapsed and Pd nanoparticles were captured in a sandwichlike mesoporous architecture showing good accessibility to Pd nanoparticles. On the basis of X-ray photoelectron spectroscopy (XPS) and CO diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) Pd was found to be in a partially oxidized state, while a reduced Ti species indicated an electronic interaction between nanoparticles and nanosheets. The close contact of titanate sandwiching Pd nanoparticles, moreover, allows for the donation of a lattice oxygen to the noble metal (inverse spillover). Due to the metal–support interactions of this peculiar support, the catalyst exhibited the oxidation of CO with a turnover frequency as high as 0.17 s–1 at a temperature of 100 °C.

Nanowire Networks of Metal–Organosilicates as Reversible Pd(II) Reservoirs for Suzuki Coupling Reactions

“…A peak separation of Δ = 5.26 eV between the Pd 3d 3/2 and 3d 5/2 spin−orbit coupling peaks was assumed for the peak deconvolution. 49 In fresh Pd−OS catalysts (Figure 7b,c), a dominant Pd(II) oxidation state at ∼337.7 eV is observed, whereas peaks corresponding to Pd(0) species at ∼335.6 eV is recognized for Pd−OS with higher Pd loading. 50,51 As mentioned earlier, this can be explained by the observed large Pd particles occasionally formed due to uneven precursor concentration (Figure 6c) as well as minor Pd(0) species not detectable with TEM.…”

Lepidocrocite-Type Layered Titanate Nanoparticles as Photocatalysts for H2 Production

“…Layered transition metal oxides (e.g., layered titanates and niobates) consisting of transition metal oxide nanolayers and interlayer exchangeable cations have been widely used for designing green materials/devices such as adsorbents, − solid acid catalysts, − lithium (sodium)-ion batteries − electrocatalysts, photocatalysts, ,,− and dye-sensitized solar cells. − The compositional variations, combined with the ability to accommodate various guest species in the interlayer space, make layered transition metal oxides more attractive. Transition metal oxide nanosheets obtained by exfoliation of the parent layered compounds have attracted attention from both scientific and practical viewpoints owing to their unique physicochemical properties based on the highly anisotropic shape associated with the large accessible surface area. − Aggregation of 2D nanosheets and positively charged species obtained by electrostatic interactions have been used to obtain porous hybrids, − which are useful due to their easily accessible pores for reactants and functional units such as dye sensitizers when compared with well-ordered (densely packed) intercalation compounds.…”

Interaction Mechanism for Simultaneous Elimination of Nitrogen Oxides and Toluene over the Bifunctional CeO2–TiO2 Mixed Oxide Catalyst

“…Meanwhile, the Ce 3d XPS peak did not shift during the whole process. As shown in Figure d, after PhCH 3 oxidation at 200 °C for 1 h, the signal of Ti changes slightly compared with step 1, and the peak area at high binding energy decreases (Figure d illustration), which indicates that the content of Ti 4+ decreases . The XPS curves of Ti in step 3 and step 2 are the same.…”

“…As shown in Figure 5d, after PhCH 3 oxidation at 200 °C for 1 h, the signal of Ti changes slightly compared with step 1, and the peak area at high binding energy decreases (Figure 5d illustration), which indicates that the content of Ti 4+ decreases. 36 The XPS curves of Ti in step 3 and step 2 are the same. When the temperature rises to 275 °C (step 4), the whole peak position moves to higher binding energy by 0.2 eV.…”