Influence of Crystal Facet and Phase of Titanium Dioxide on Ostwald Ripening of Supported Pt Nanoparticles from First-Principles Kinetics

Abstract

Metal oxide plays an important role on stability and catalytic performance of supported metal nanoparticles, but mechanistic understanding of structure sensitivity and optimization of the oxide supports remains elusive in heterogeneous catalysis. Taking Ostwald ripening of platinum nanoparticles supported on titanium dioxide (TiO2) as an example, we reveal here a great structure sensitivity of oxide facets and crystal phases on sintering of supported metal nanoparticles through first-principles kinetic simulation. Total activation energies of the Pt ripening on various pristine TiO2 surfaces of both anatase and rutile phases are calculated by density functional theory, and Ostwald ripening under isothermal condition and temperature programmed condition are simulated numerically. Calculated total activation energies are found inversely proportional to the corresponding oxide surface energies, and vary considerably from 1.76 to 3.56 eV. The Pt ripening rate on the pristine TiO2 surfaces follows the order of r(001) ≈ a(001) ≫ a(100) ≈ r(101) > r(100) > a(101) ≈ r(110). For TiO2 support exposing different facets, not only their intrinsic ripening rate but also their relative surface area determines the overall ripening kinetics and formation of transit bimodal particle size distribution. For pristine anatase TiO2 exposing a(001) and a(101) facets, ripening starts on a(101) facets only after ripening on a(001) facets finishes due to their order of magnitude difference in ripening rate, resulting a step-wise increase of average particle size with ripening time. For pristine rutile TiO2 exposing r(101) and r(110) facets, ripening could proceed simultaneously on both facets due to their modest difference in ripening rate, and the average particle size increases monotonically with ripening time. Compared to rutile TiO2, anatase TiO2 supports are less resistant to the metal nanoparticles ripening since a(001) facets with high ripening rate is likely to be exposed. The present work is compared to available experiments and the theoretical framework established could be expanded to various metal and oxide systems.

Sinter Resistance and Activity Enhancement via a Facet-Dependent Metal–Support Interaction of Pd/ZnO Catalysts in CO Oxidation

“…Metal–support interaction (MSI) plays a crucial role for supported catalysts, which not only affects the catalytic performance but also determines the stability of nanoparticles (NPs). − The stability and sinter resistance of supported metal catalysts can be improved by designing the interface between NPs and the supports. − In addition, the heterogeneous catalytic reaction is mainly carried out on the surface of the catalyst, and the surface atomic arrangement of the support directly relates to the local environment of the metal NPs. It causes the different dynamic behaviors under the reaction gas and temperature, thereby affecting its catalytic reactivity. − And the surface atomic arrangement of the support is determined by the exposed crystal planes. , It is reported that the MSI can be regulated by tailoring the support morphology to exposed different crystal planes, exhibiting different crystal plane effects. , For instance, in situ sintering experiments of Au/TiO 2 found that the Au NPs are more stable on the anatase TiO 2 {001} surface than the {101} surface, on which Au NPs sinter into large particles through both the Ostwald ripening (OR) and particle migration coalescence (PMC) mechanisms . For the CO oxidation over an α-Fe 2 O 3 -supported Au catalyst, Fe 2 O 3 nanorods could stabilize the highly dispersed Au NPs and avoid the sintering behavior during the reaction compared with Fe 2 O 3 nanospheres, which contributes to the higher activity and stability in CO oxidation .…”

Catalytic CO Oxidation and H2O2 Direct Synthesis over Pd and Pt-Impregnated Titania Nanotubes

“…Instead, it is the dynamics of the Pt nanoparticles at the respective temperature which is strongly influenced by the initial particle size and interaction with the TiO 2 support. For TiO 2 , the mobility of the noble metal on surface has been controversially discussed with respect to differently exposed TiO 2 facets [37]. For a weak interaction with the support [38], certain sintering of the small Pt particles on the short Pt/TNT catalyst (average size 2.1 ± 0.5 nm) could occur during heating up to 500 • C in the reaction mixture.…”

Achieving anti-sintering of supported platinum nanoparticles using a thermal management strategy

“…In this paper, we proposed an efficient strategy to antisintering Pt NPs by introducing h-BN, a material with high thermal conductivity, into γ-Al 2 O 3 . Our strategy for anti-sintering metal NPs by means of thermal management is different from previous approaches, namely, by strengthening the metal-support interaction effect [4][5][6][7][8][9][10][11][12], which enhances OR sintering and hinders PMC sintering. The integration of h-BN to the support not only enhances heat transfer in the system but also changes the electrical and chemical environments of the active centers.…”

“…Numerous important industrial catalytic reactions, including the production of chemicals, pharmaceuticals, clean fuels, and exhaust treatments for automobiles and stationary power plants, undergo a large loss of catalytic reactivity due to the sintering of supported metal nanoparticles (NPs) [3]. To minimize sintering, the strengthening of metalsupport interactions has allowed various methods and technologies to be established [4][5][6][7][8][9][10][11][12]. For example, TM sintering can also be decelerated by the strong steric hindrance effect, such as by encapsulating metal particles into core-shell or yolk-shell structures [13][14][15][16][17][18][19], anchoring metal particles into pores of the large surface area of catalytic supports [20][21][22], controlling the uniformity of the metal NPs [23][24][25], and synthesizing multi-element alloys [26][27][28].…”