Growth of Nanocrystalline Platinum in a Zeolite Host ‐ An in Situ X‐Ray Powder Diffraction Study

Abstract

The growth of nanocrystalline platinum particles in zeolite [Pt(NH,),]NAX was investigated by in situ X-ray diffraction in combination with Rietveld refinement at T = 509, 519, 530 and 562K. The reaction was directly followed by the gradual decrease of the Pt2+ -occupation and the simultaneous increase of the metallic platinum particles, which grow up to an average size of 4 nm. An increase of the zeolite lattice constant and a gradual decomposition of the framework up to 20% were simultaneously observed.The process of crystal growth can be influenced by the preparation conditions of the zeolite. After dehydration up to 383 K at bar more than 90% of the platinum cations are located near the centre of the 12-ring-window. Dehydration in the temperature range from 403 to 443 K under vacuo results in a partial shift of the platinum cations to a second position and to an increase of the reactivity.E 9033 heim 1988.

A First Principles Study of Palladium Clusters in Gmelinite and Their Interaction with CO

“…While there are some experimental data for these kinds of systems, the degree of precision is limited by the lack of long range order of the adsorbed metal within the materials. Spectroscopy, − diffraction, microscopy, and a combination ,− of the aforementioned techniques can yield some information about the cluster size of metal particles, the coordination numbers of the constituent atoms, and sometimes, the oxidation state or magnetic properties of the species under study. Nevertheless, a precise picture of the actual interactions taking place between the metal atoms and the zeolite framework is seldom obtained. , Since it is difficult to determine an accurate picture of the catalyst itself, it is clearly even harder to follow their catalytic processes mechanistically.…”

Effect of using polyimide capillaries during thermal experiments on the particle size distribution of supported Pt nanoparticles

“…Critical synthesis parameters for this catalyst have been studied using extended X-ray absorption fine structure (de Graaf et al, 2001;Akdogan et al, 2008;Ji et al, 2005), annular dark field scanning transmission electron microscopy (ADF-STEM) (Liu & Cowley, 1990), high-angle ADF-STEM (HAADF-STEM) (Rice et al, 1990), transmission electron microscopy (Tonscheidt et al, 1993), X-ray photoeletron spectroscopy (Nová ková et al, 1996) and X-ray diffraction (Schnell & Fuess, 1996). It has been determined that to obtain small (< 20 Å ) Pt particles that are occluded in the zeolite pores the sample must first be calcined to dry the zeolite and remove the ligand of the metal precursor and then reduced with hydrogen at moderate temperatures.…”