Dependence on Size of Supported Rh Nanoclusters in the Decomposition of Methanol

Abstract

The decomposition of methanol catalyzed with Rh nanoclusters supported on an ordered thin film of Al2O3/NiAl­(100) became enhanced on decreasing the size of the clusters. The decomposition of methanol (and methanol-d 4) proceeded through dehydrogenation; the formation thereby of CO became evident above 200 K, depending little on the cluster size. In contrast, the production of CO and hydrogen (deuterium) from the reaction varied notably with the cluster size. The quantity of either CO or hydrogen produced per Rh surface site was unaltered on clusters of diameter >1.5 nm and height >0.6 nm, corresponding to about 65% of methanol undergoing decomposition on adsorption in a monolayer on the clusters. For clusters of diameter <1.5 nm and height <0.6 nm, the production per Rh surface site increased with decreasing size, up to 4 times that on the large clusters or Rh(100) single-crystal surface. The reactivity was enhanced largely because, with decreasing cluster size, the activation energy for the scission of the O–H bond in the initial dehydrogenation became smaller than the activation energy for the competing desorption. The property was associated with the edge Rh atoms at the surface of small clusters.

The interaction of CO molecules on Au–Rh bimetallic nanoclusters supported on a thin film of Al2O3/NiAl(100)

“…The details of the models can be found in our previous studies. 7,8 Additionally, four atoms at the surfaces of Au(100) and Rh(100) were substituted by Rh and Au atoms, respectively to model Rh/Au(100) and Au/Rh(100) to exam the electronic effect on the Au-Rh bimetallic clusters.…”

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

“…The objective of the present work is to study the effect of elevated temperature on the structure and morphology of oxide-supported rhodium (Rh) clusters and examine the effect with catalyzed decomposition of methanol (methanol-d 4 ), which is the principal reaction applied in direct methanol fuel cells (DMFC) [21][22][23][24][25] and also serving as a source of hydrogen. Rh-based catalysts have been extensively used; Rh is alloyed with platinum (Pt, the primary catalyst for methanol reactions) catalysts to improve catalytic properties; adsorption and decomposition of methanol on Rh single crystal surfaces [26][27][28][29] have hence been extensively studied but the methanol 2 of 17 reactions on oxide-supported Rh clusters [30,31], a realistic model system and how they are affected by thermally-induced structural changes are little investigated. The present work aims to remedy this lack and to acquire insight into the effect.…”

“…Although the morphological evolution is governed by both kinetics and energetics, this atypically decreased size is predominated by the latter [10,32]. The reduced size increased the total surface area and also promoted the reactivity of the clusters toward methanol decomposition [31]. The size-dependent reactivity has been found for varied transition metal catalysts and reactions, such as Au clusters toward various reactions (oxidation of CO, oxidation and hydrochlorination of hydrocarbons, water-gas shift and NO reduction) [33][34][35][36], Rh toward CO dissociation [37,38], Ni toward ethane hydrogenolysis [39,40] and Cu toward N 2 formation from NO [5,41].…”

Adsorption of an Au atom and dimer on a thin θ-Al2O3/NiAl(100) film: dependence on the thickness of the θ-Al2O3 film

“…[1][2][3][4][5][6] Such studies exhibit some common catalytic features as observed in realworld catalysts, and allow detailed investigation of the structure-reactivity correlation. [1][2][3][4][5][6][7][8][9][10] The results indicate that the catalytic properties depend on not only the size of the metal clusters [8][9][10][11][12][13][14][15] but also the thickness of the oxide lm. 16 For instance, both experiments and theoretical simulations show that Au atoms or clusters on MgO/Ag(001) are negatively charged, through an electron transfer from the Ag substrate to the Au atoms, when the MgO lm amounts to three monolayers; in contrast, Au adsorbates become neutral on a thick MgO lm.…”

“…Al 2 O 3 is a popular support for catalysts; a thin Al 2 O 3 /NiAl(100) lm has been studied and used as a model system. 15,[32][33][34][35][36][37][38][39][40][41] We have performed simulations with alumina slabs of 1-5 atomic layers atop a NiAl(100) slab of 11 or 12 atomic layers. The alumina slabs have the structure of q-Al 2 O 3 and a surface termination of the (001) facet to match previous experimental results.…”