Ion-Exchange Loading Promoted Stability of Platinum Catalysts Supported on Layered Protonated Titanate-Derived Titania Nanoarrays

Abstract

Supported metal catalysts are one of the major classes of heterogeneous catalysts, which demand good stability in both the supports and catalysts. Herein, layered protonated titanate-derived TiO2 (LPT-TiO2) nanowire arrays were synthesized to support platinum catalysts using different loading processes. The Pt ion-exchange loading on pristine LPTs followed by thermal annealing resulted in superior Pt catalysts supported on the LPT-TiO2 nanoarrays with excellent hydrothermal stability and catalytic performance toward CO and NO oxidations as compared to the Pt catalysts through wet-impregnation on the anatase TiO2 (ANT-TiO2) nanoarrays resulted from thermal annealing of LPT nanoarrays. Both loading processes resulted in highly dispersed Pt nanoparticles (NPs) with average sizes smaller than 1 nm at their pristine states. However, after hydrothermal aging at 800 °C for 50 h, highly dispersed Pt NPs were only retained on the ion-exchanged LPT-TiO2 nanoarrays with the support structure consisting of a mixture of 74% anatase and 26% rutile TiO2. For the wet-impregnation loading directly on anatase TiO2 nanoarrays derived from LPT, the Pt catalysts experienced severe agglomeration after hydrothermal aging, with the nanoarray supports consisting of 86% anatase and 14% rutile TiO2. Spectroscopy analysis suggested that Pt2+ cations intercalated into the interlayers of the titanate frameworks through ion-exchange impregnation procedure, which altered the chemical and electronic structures of the catalysts, resulting in the shifts of the electronic binding energy, Raman bands, and optical energy bandgap. The ion-exchangeable nature of LPT nanoarrays clearly provides a structural modification in Pt-doped LPT that has resulted in a strong interaction between the Pt catalysts and LPT-TiO2 nanoarray supports, leading to the enhanced hydrothermal stability of the catalysts. Considering the wide applications of the LPT and TiO2 nanomaterials as supports for catalysts, this finding provides a new pathway to design highly stable supported metal catalysts for different reactions.

Rh-induced Support Transformation and Rh Incorporation in Titanate Structures and Their Influence on Catalytic Activity

“…Protonated nanowires and nanotubes have good ionic exchange properties. The incorporation of the ionic form of the metal precursor (Rh + ) to the structure can significantly help to increase the loading of the catalysts and maintain a high catalyst dispersion during the reactions, as was nicely presented in the case of platinum supported on layered protonated titanate nanowires [63]. The metal cations resulted in a strong interaction between metal and titanate support, leading the enhanced thermal and chemical stability of the catalyst.…”

“…While the electrons accumulated typically on the co-catalyst nanoparticles (Pt, Pd, Rh) are expected to interact with unsaturated and aromatic bonds in organic moieties, the holes on the surface of TiO 2 are responsible for the initiation of oxidative processes that may result in C-C bond scission, dehydrogenation and the like [55][56][57][58][59][60][61][62]. Recently, platinum catalysts supported on layered protonated titanate-derived titania nanoarrays were found to have a high activity in CO and NO oxidation as compared to Pt catalysts through wet-impregnation on the anatase TiO 2 [63].…”

Synergistic promotion of transition metal ion-exchange in TiO2 nanoarray-based monolithic catalysts for the selective catalytic reduction of NOx with NH3

“…25 Their high surface area and abundant ionexchange positions allow an atomic-scale distribution of metal cations, thus achieving a higher metal loading and dispersion. 24,26,27 In practical applications, monolithic catalysts are widely applied in the abatement of air pollution from various sources. 28,29 In particular, nanostructured array (nanoarray) based monolithic catalysts have been successfully developed and demonstrated for various catalytic reactions in the past decades, such as automotive aftertreatment, CO 2 hydrogenation, and VOC abatement.…”

“…LPT nanoarray-based monolithic catalysts were also demonstrated for diesel oxidation catalysts (DOC). 26,33 Therefore, it would be of great value to investigate LPT-based monolithic catalysts for NO x abatement.…”

Ion Exchange of Layered Alkali Titanates (Na2Ti3O7, K2Ti4O9, and Cs2Ti5O11) with Alkali Halides by the Solid-State Reactions at Room Temperature

“…Among layered transition-metal oxides, layered alkali titanates such as A 2 Ti n O 2 n +1 and lepidocrocite (A x Ti 2– y M y O 4 : A, interlayer cation; M, metal ion or vacancy) have been studied extensively as unique nanostructured titanium oxide materials. − The cation exchange ability is one of the most important characteristics of the layered alkali titanates which connects to a wide range of applications, including the adsorbents of metal ions from aqueous environments ,− and electrodes of battery, where the mobility and the density of the ion are key parameters. − In addition, functionalization of the layered alkali titanates has been done using cation exchange reactions. − Interlayer cations of a layered alkali titanate were reported to play an important role on the molecular recognition ability in a photocatalytic reaction . The ion exchange with cationic surfactants has been done to obtain organically modified titanates, which were further functionalized to be used as a polymer additive, and an adsorbent with molecular recognition .…”