Advanced Insight into the Size Effect of PtPd Nanoparticles on NO Oxidation by in Situ FTIR Spectra

Abstract

It is a recognized view that particle size could play a significant role in catalytic performance. To obtain the nanoparticles with the different size, a series of bimetallic PtPd/SiO 2 −Al 2 O 3 catalysts subjected to hydrothermal treatment in different time were prepared and applied for NO oxidation under diesel exhaust. The experimental results confirmed that the average noble particle size was gradually increased at a different variation rate, along with aging time. An increasing of average particle size resulted in the reduction of the corresponding NO turnover frequencies (TOFs) by different degrees. Thus, a new sight on the relationship between particle size and NO catalytic activity is obtained. In the aging process, the overall trend of noble metal particles got larger along with receding NO catalytic performance, yet in a period, a few small particles presented more bridged/chelating nitrate and ionic nitrate species, further retarding its rate of loss activity.

Stability and Electronic Properties of PtPd Nanoparticles via MD and DFT Calculations

“…These results correspond well with previous finding of charge transfer in core−shell Pd@Pt NPs is directed from Pd to Pt. 18,58 While the explanation of enhanced catalytic activity of the Pt atoms in NPs, for example, in oxygen adsorption reaction is related to the ability of Pt to donate electrons to oxygen, 16 the localization of excess electronic density on the surface of NPs can lead to enhancement of its catalytic activity. 66,67 The opposite situation is observed when Pt NPs are coated with a monoatomic layer of Pd.…”

“…There are four possible structures bimetallic platinum–palladium NPs can form: core–shell Pt@Pd and Pd@Pt (Figure a,b), Janus Pt|Pd (Figure c), and homogeneous bimetallic alloy Pt–Pd (Figure d) NPs. Up to date, only core–shell (Pt@Pd and Pd@Pt) and bimetallic alloy Pt–Pd NPs have been synthesized experimentally. − The evidence of Janus-type Pt|Pd NPs has not been reported yet.…”

Anomalous metal vaporization from Pt/Pd/Al2O3under redox conditions

“…11,12 Furthermore, it is known that Pd improves the stability of the Pt catalyst by increasing the barrier to sintering and lowering the PtO 2 vapor pressure through the presence of a PdO phase. 13,14 Supported Pt/Pd catalysts have been studied extensively using electron microscopy, [15][16][17][18][19][20] x-ray absorption fine structure, [21][22][23][24] infrared spectroscopy, 25,26 and temperature-programmed reduction or desorption measurements. 27,28 Pt sintering at low pressures has also been studied using environmental transmission electron microscopy (ETEM).…”

“…29 There are also numerous in-situ x-ray studies of supported Pt/Pd catalysts that describe the transformation of the metal particles under reaction environments. 19,21,23,25,26 However, there are many remaining questions about the real-time structural, morphological, and compositional changes of the metal particles under realistic redox conditions. Much of what is understood about catalyst structural changes are implied from a combination of ex-situ TEM and in-situ X-ray studies.…”

Anomalous Metal Vaporization from Pt/Pd/Al2O3 Under Redox Conditions

“…11,12 Furthermore, it is known that Pd improves the stability of the Pt catalyst by increasing the barrier to sintering and lowering the PtO 2 vapor pressure through the presence of a PdO phase. 13,14 Supported Pt/Pd catalysts have been studied extensively using electron microscopy, [15][16][17][18][19][20] x-ray absorption fine structure, [21][22][23][24] infrared spectroscopy, 25,26 and temperature-programmed reduction or desorption measurements. 27,28 Pt sintering at low pressures has also been studied using environmental transmission electron microscopy (ETEM).…”