Investigation of Thermal Stability and Reactivity of Rh Nanoclusters on an Ultrathin Alumina Film

Abstract

We studied the structural and morphological evolution of Rh clusters on an ordered ultrathin alumina film grown on NiAl(100) in annealing processes, under ultrahigh vacuum conditions and with various surface probe techniques. The Rh clusters, prepared on vapor deposition of Rh onto the alumina film at 300 K, had an fcc phase and grew in the (100) orientation; the annealing altered the cluster structure little—the lattice parameter decreased by a factor <2%—but the cluster morphology significantly. With elevated temperature, small clusters (diameter ≤1.5 nm) decreased little in size; in contrast, large clusters (diameter ≥2.0 nm) varied in a complex manner—their mean diameter decreased to about 1.5 nm on annealing to 450 K, despite their similar height, while it increased to above 2.0 nm at temperature ≥570 K. This atypical decrease in size was governed predominantly by energetics. Such a reduced size enhanced the total surface area as well as the reactivity of the clusters toward methanol decomposition, so increased the production of D2 (H2) and CO from decomposed methanol-d4 (or methanol). The result implies a higher temperature tolerance for Rh clusters on the alumina film and a practical approach to prepare small Rh clusters with high reactivity.

Decomposition of methanol-d4 on Rh nanoclusters supported by thin-film Al2O3/NiAl(100) under near-ambient-pressure conditions

“…While increasing the coverage to 4.0 ML (not shown), the diameter grew to 3.5 nm; as the lower parts of the clusters had already merged, the measured height of 0.8 nm indicated only the upper parts of the clusters. 17,50 The number and morphology of the clusters were altered only by annealing above 570 K; 53,54 therefore, as our NAP experiments were performed at 400 K, the morphological alteration induced by the temperature was limited. Our RHEED measurements shown below warranted also that the reactions under NAP conditions little altered the atomic structure of the Rh clusters.…”

Promoted activity of annealed Rh nanoclusters on thin films of Al2O3/NiAl(100) in the dehydrogenation of Methanol-d4

“…The annealing temperature 700 K was employed as the sample annealed to such temperature exhibited limited sintering but evident promotion of reactivity; a lower annealing temperature, such as 450 and 570 K, failed to promote the reactivity equally whereas a higher one, such as 800 K, induced evident sintering. 64 The Rh clusters as prepared had a mean diameter from 1.0 to 3.5 nm and a height from 0.4 to 0.8 nm evolving with the coverage; 44 with the annealing to 700 K, the morphology of neither large nor small clusters altered a lot but the cluster density decreased signicantly. Our previous work had demonstrated the structural and morphological evolution of the Rh clusters with the annealing (450-800 K).…”

“…Our previous work had demonstrated the structural and morphological evolution of the Rh clusters with the annealing (450-800 K). 64 Fig. 1a and b exemplify the annealinginduced alteration of Rh clusters on Al 2 O 3 /NiAl(100).…”

Synthesis of Stilbene and Chalcone Inhibitors of Influenza A Virus by SBA-15 Supported Hoveyda-Grubbs Metathesis

“…SBA-15 is characterized by uniform pore size (4.6-30 nm), well-defined pore structure and size-distribution, high surface area, high thermal stability and capability to support a large panel of active species [38,39]. The preparation, structural characterization and application of mesoporous molecular sieves as advanced support for olephin metathesis catalyst is reviewed [40,41]. Different examples of Hoveyda-Grubbs catalysts supported on SBA-15 have been reported, even if they have been scarcely applied in the synthesis bioactive compounds [42,43].…”