Decomposition of the Precursor [Pt(NH3)4](OH)2, Genesis and Structure of the Metal-Support Interface of Alumina Supported Platinum Particles: A Structural Study Using TPR, MS, and XAFS Spectroscopy

Abstract

During the preparation of alumina supported platinum catalysts, the precursor [Pt(NH3)4](OH)2 decomposes to a neutral Pt(NH3)zO species during the drying process at 120 "C. Treatment in flowing hydrogen at 180 "C leads to partial reduction of the platinum ammine complex and formation of platinum metal particles. A large increase in metal particle size is observed after a treatment under flowing H2 at 200 "C. The final reduction at 350 "C causes the total disappearance of the platinum precursor with a further increase in platinum particle size. The direct reduction at 350 "C yields the biggest metal particles (35 A) while calcination before reduction produces a much higher dispersion (metal particle diameter 10 A). The beneficial effect of calcination, already observed by many authxs when using [Pt(NH3)4](OH)2 as a precursor for the preparation of highly dispersed WyA1203, can now be explained because this treatment avoids the formation of the mobile neutral Pt(NH3)zO complex. The metal particles produced by treatment in flowing hydrogen at 180 "C present a metal-oxygen contribution at 2.7 A formed at the metal-support interface. This long distance is assumed to be caused by the presence of hydrogen in the metal-support interface based upon our results in combination with other TPD and EXAFS studies. A second metal-oxygen contribution with similar coordination number is detected at 3.86 A. This is a consequence of the presence of the first shell metal-oxygen at 2.7 8, and implies a [ 11 11 epitaxy in the metal-support interface.

Understanding the Influence of the Pretreatment Procedure on Platinum Particle Size and Particle-Size Distribution for SiO2 Impregnated with [Pt2+(NH3)4](NO3−)2: A Combination of HRTEM, Mass Spectrometry, and Quick EXAFS

“…• C is in agreement with observations made earlier (23,24). Muñoz-Páez and Koningsberger (24) • C and cooling it down again to liquid nitrogen temperature to perform EXAFS measurements.…”

Metal Particle Size and Structure of the Metal−Support Interface of Carbon-Supported Platinum Catalysts as Determined with EXAFS Spectroscopy

“…This indicates that the EXAFS coordination parameters are in agreement with the proposed model for the structure of the metal-support interface. The results obtained in an earlier EXAFS study of our group 42 are consistent with a structural model in which small Pt particles grow with a (111) epitaxy on the (111) surface plane of the high surface area γ-Al 2 O 3 support. Also, in this case, two metal-support oxygen distances have been detected at 2.70 and 3.84 Å.…”

A Single‐Site Platinum CO Oxidation Catalyst in Zeolite KLTL: Microscopic and Spectroscopic Determination of the Locations of the Platinum Atoms

“…The former value is greater than that characterizing bulk platinum (11 564 eV) and similar to those characterizing Pt II complexes, [14] including those supported on Al 2 O 3 . [15] The white line intensity and XANES features of the as-prepared sample at approximately 11 580 eV nearly match those of Pt II tetraamine complexes. [15] The white line intensity increased during oxidation (Supporting Information, Figure S3), indicating an increase in the number of oxygen donor atoms without a change in the platinum oxidation state, [16,17] corresponding to the unchanged edge energy [18] and the increase from 2 to 3 of the PtÀO coordination number representing oxygen atoms bonded to Pt after the oxidation (Table 1).…”